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06b8529f50de00705de57a93f537c8ab | 100 287 | 4 What is new about Level 2.5 Teletext | All current Teletext display pages use Level 1 or 1.5 presentation features. In the present document these pages are termed "the basic page" and consist of packets (rows) 0 to 23 and, optionally, packets 24 and 27 for Fastext (FLOF) and 26 for extended characters (Level 1.5) and PDC. Display enhancement at Level 2.5 is achieved by overlaying additional information at selected points on the basic page. This procedure guarantees compatibility between the different Levels. Level 2.5 Teletext is fully backward compatible with the basic page. A Level 2.5 page can be displayed by existing decoders as a page without enhancement. Within the Teletext Level 2.5 specification there are several possibilities for display enhancement which will contribute to a better presentation of Teletext pages. In particular, a greater number of colours, enhanced character sets, more display attributes, improved graphics, redefinable character sets (DRCS), side-panels and objects. In addition to the presentation features, EN 300 706 [1] includes navigation-related enhancements such as information which a TV set may use to aid the acquisition and storage of pages. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 4.1 Colours | The eight colours of the basic page are extended to 32. These 32 colours are organized into two palettes of 16 colours each. Whilst the first palette consists of fixed colours (the 8 basic colours and the 8 basic colours in half-intensity), the second palette is pre-set with 16 pastel shades which can be redefined by the editor. The colours may be used within the text area as foreground (i.e. for characters) and background colours. Background colouring is not restricted to the text area, but can also be used in the area around the text window, filling the whole screen. A full screen colour is selected for the area above and below the text window. Similarly the area to the left and right of the text window can be filled with a full row colour, with a different colour on each row if required, or the full screen colour can be used as a default. Full screen colour can be overwritten by full row colour, which can be overwritten in the text area by background and foreground colours. It is relatively easy to map the colours used on the basic page to a different set of 8 colours. Recommendations: For reasons of transmission efficiency it is recommended to prefer the half-intensity colours of the first palette and the default pastel colours. If you define a new colour palette, ensure that you can use this new palette on most of your pages. When using a new palette, be aware of the remapping function which offers an easy and efficient way of replacing the colours of the basic page. First set the full screen colour and consider it for use as the default row colour for all rows. If necessary, re-colour separate rows afterwards. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 9 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 4.2 Character sets | The G0 and G1 character sets (primary alphabet and block mosaic graphics respectively) for basic pages are extended with two more sets: G2 = supplementary character set and G3 = smoothed mosaic graphics and line drawing character set. In addition, diacritic marks can be added to any G0 character to support all Latin-based European languages. Recommendation: For reasons of transmission efficiency when improved graphics are required, prefer to use symbols from the G3 set instead of DRCS. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 4.3 Attributes | The basic attributes like flashing, double height, etc, are extended by some more functions. The flashing function is enhanced with several new modes, and all could appear on a page at the same time. The sizing function is upgraded by two modes: double size and double width. There is also an underline function. Recommendations: For Level 1 compatibility be aware that each character covers two screen locations horizontally in double size and double width modes. The use of attributes is different to Level 1. Level 2.5 supports both serial attributes (like Level 1) and parallel attributes. The following example illustrates the improvement: At Level 1 a word is shown in a colour which is selected by a serial attribute in front of the word: αBlue TELETEXT This setting causes that the word TELETEXT to be shown in blue throughout. Any change of colour within the word is not possible without using a space for a new colour attribute. Level 2.5 enlarges the editorial possibilities by offering parallel attributes: αBlue TELE TEXT α R e d This combination causes the letters TEXT to be shown in red, whilst the letters TELE remain in blue. In Level 2.5 the attributes can be placed at virtually any character position and have influence from that point on for the rest of the row unless otherwise reset. More than one enhancement can be applied at any character position. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 4.4 Dynamically Re-definable Character Sets (DRCS) | If the G3 set does not fit to your enhancement ideas there is a new way to improve graphics. Up to 24 new characters with a resolution of 12 dots horizontally by 10 dots vertically can be defined for one page. The foreground and background colours are defined by the page. Recommendation: Be aware that the definition of DRCS can cost a lot of transmission capacity. Check the possibility of using G3 characters instead of DRCS, or use the defined DRCS symbols in several pages. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 10 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 4.5 Objects | 4. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 5 Objects | Level 2.5 Teletext includes the possibility to combine any collection of characters, symbols or attributes in a single entity called an object. Such an object may be transmitted once and used many times on different pages thus saving transmission capacity. Recommendation: The use of objects is beneficial, but quite complex. Please read clause 6 in the present document and clause 13 in EN 300 706 [1] very carefully. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 4.6 Side panels | Level 2.5 extends the normal Teletext format of 24 rows by 40 characters with an additional 16 characters per row. These may be placed one side or the other of the basic page, or divided either side, in areas known as side-panels. They are likely to be used for additional navigational information, logos (e.g. sports logos) or graphics. Pages with side-panels may be compressed when displayed on a TV set with an aspect ratio of 4:3 so that all 56 characters fit on the screen. Depending on the division of the characters between one or two side-panels, the position of the basic page may be shifted. Recommendations: Information in side-panels should be additional and not integral to the page. Be aware that the information given in a side-panel is not seen at Level 1, nor is it mandatory for a Level 2.5 decoder to display it. In normal use a side-panel should be the whole 16 characters positioned either to the left or the right of the basic page. The presence of side-panels and the division of side-panel characters between subsequent pages should not change very often (i.e. it should be consistent throughout a magazine or sub-section of a database). Otherwise the basic page may be seen to jump horizontally from page to page as the viewer navigates his way through a series of linked pages. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 4.7 Level 3.5 | Teletext can be developed further. Level 2.5 is not the end of the developments to enhance Teletext. The specification also includes Level 3.5. It will offer more graphical display improvements, 96 DRCSs with greater colour resolution and bold, italic and proportional fonts. 5 Objects Objects are one of the most powerful features of Level 2.5. An object can be understood as an accumulation of different enhancements put together into one entity. The "invention" of objects is a result of the intention to re-use enhancements on a number of pages and to save transmission capacity. Objects satisfy a number of different requirements, for instance the "styling" of Level 2.5 pages, the repeated use of smoothed graphic maps and logos, etc. They are also the mechanism by which side-panels are transmitted. Editorially, objects will be available at the editing workstations, but their creation and transmission requires very careful management by the origination system. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 5.1 Types of objects | There are three different types of objects: active, passive and adaptive objects (see EN 300 706 [1], clauses 13.3 and 13.5). At first sight, the differences between the three types are not easy to understand. However, an example of each kind of object will explain its function and the consequences of its use. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 11 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 5.1.1 Passive objects | In very simple terms a passive object could be a logo, or similar, "stamped" over the basic page. A passive object does not import any attributes from the basic page and does not affect the page outside of its boundaries. On starting the object the attributes are reset to the default conditions implied at the beginning of a row on the basic page. The set of attributes defined by the object is only applied to the column positions where the object explicitly defines a character. Basic page attributes Positions addressed by the passive object. All attributes defined by the object Passive object boundary Figure 1: Passive object |
06b8529f50de00705de57a93f537c8ab | 100 287 | 5.1.2 Active objects | One function of an active object is to place style-setting attributes into the page. Examples are banner headlines or principle templates for pages. On entering the area affected by the object, the set of attributes defined by the basic page remains unaltered. They have effect within the object's boundaries unless superseded by attributes defined by the object itself. The set of attributes in place at the right-hand boundary of the object affects the rest of the row unless superseded by attributes defined by the basic page. Attribute settings exported from object area into basic page Attributes defined by the basic page only Attribute settings imported into object area from basic page Attributes affected by the basic page and the active object Attributes affected by the basic page. Initial settings defined on exiting from the object Active object boundary Figure 2: Active object |
06b8529f50de00705de57a93f537c8ab | 100 287 | 5.1.3 Adaptive objects | An adaptive object allows an area of the page to be replaced while maintaining some or all of the existing attribute settings, for example substituting Level 1 graphics with DRCS. On entering the area affected by the object, the set of attributes defined by the basic page remains unaltered. They have effect within the object's boundaries unless superseded by attributes defined by the object itself. At the right-hand boundary of the object, the attribute settings revert to those of the basic page at that position. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 12 Attributes defined by the basic page only Attribute settings imported into object area from basic page Attributes affected by the basic page and the adaptive object Adaptive object boundary. Attribute settings within object do not have effect outside the object’s boundary Figure 3: Adaptive object |
06b8529f50de00705de57a93f537c8ab | 100 287 | 5.2 The use of objects | The usefulness of objects is extended by the fact that one object can call up another object according to the following simple rules: • an active object can invoke adaptive or passive objects; • an adaptive object can invoke passive objects; • a passive object cannot invoke any other object. The following is an example of the use of objects and these rules: An active object is called which sets up the style for the page and then invokes a logo as a passive object, then smoothes the graphics using an adaptive object. The adaptive object may then call another passive object which could be a mini-logo. Recommendations: A few objects can enhance the appearance of pages without causing problems with their management. Be aware that the number of objects open (i.e. overlapping) on one single page is restricted. Objects can be global, public or local. Local objects are defined within packets 26 appended to a basic page and can be used on that page alone. For global and public objects the necessary information is to be found in special object definition pages. Global objects are more likely to be stored by a decoder (i.e. they are treated with higher priority) and can accessed by any page. Public objects are treated with lower priority and, in general, their use may be restricted to fewer pages. Recommendations: Prefer the use of global objects to local objects. The use of local objects needs careful thought. It removes all need for object management, but it is not an efficient method if the same object is required by more than one page. Also, they can have a negative effect on Level 1.5 decoders as they fill the memory space with useless data. In turn, this can lead to an increase in the time taken to process a page. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 13 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 6 Saving capacity | All the information which is overlaid on a basic page to turn it into a Level 2.5 page is transmitted as additional data. The details of how the information is transmitted are of little interest to the editor, but a general awareness of the efficient transmission of additional data is very useful. The supplementary data for enhancement is transmitted in extra packets, both appended to basic pages or standalone, and in additional enhancement definition pages. The actual order of transmission of enhancement data can be complicated as it depends on how the supplementary information is used and organized. In turn this, in combination with the depth of enhancement to the basic pages, determines the number of extra packets. The key principle is that enhancement data should be used several times by several pages and not only once by one page. This can be achieved by the use of objects, packets 28 (on a page-by-page basis) and packets 29 (on a magazine basis) for colouring and side-panel control, EN 300 706 [1]. Recommendations: Create enhancement data that you will use more than once. When organizing your service for Level 2.5 start by creating enhancement data for the complete service, then for single magazines (global use) and then for single pages (local use). Taking this advice ("prefer global use to local use") into account will save capacity. The transmission of enhanced data can be partially done in packet slots which are currently unusable due to the need to obey the 20 ms rule of the original Teletext specification. Dummy headers are sometimes inserted in these filler packet slots. Therefore, do NOT assume that the reduction or addition of one enhancement packet to a page will directly affect the cycle time. If care is taken in the amount and type of enhancement data, there will be a minimal effect on cycle time. However, some apparently minor changes will have serious effects on the service as received. When using more than six VBI lines per field in serial mode there will be almost no effect on cycle time as there are many filler packets. In parallel mode there will be a greater effect, as the basic transmission is more efficient. Further recommendations designed to save transmission capacity are given elsewhere in the present document. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 7 How to work with Level 2.5 | The world of Level 2.5, which offers lots of possibilities for graphically more attractive Teletext services, has consequences on the work of the editors. As mentioned previously, this Code of Practice is a general introduction to Level 2.5 written without practical experience of any editing software. In this clause we wish to summarize hints which should be taken in account before planning the editorial work with Level 2.5. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 7.1 Working on two Levels | It is not without reason that the picture of overlaid acetate is often used to describe the relationship between Teletext Levels 1 and 2.5. In spite of all the enthusiasm about the enlargement of editing possibilities we have to keep several things in mind - above all the fundamental principle of compatibility with Level 1. Although this problem is solved technically by the specification, editors should be aware that they are editing for two different Levels. The work with two Levels will be reflected by the editing software. It is necessary to review your page output on both Levels. There are important reasons to check your editing output not only on your PC monitor but also on a TV set. Several Level 2.5 features like the flash modes or the complete colour palette might not be shown sufficiently accurately on every PC monitor. Recommendation: Check both versions of the page, preferably on a TV set, while editing. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 14 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 7.2 Enhancing Level 1 - the overlaying principle | In simple terms, the enhanced data to overlay the basic page should not transport elementary information. For the next few years Level 1 decoders will still form the majority and, by definition, cannot display enhancement data. This should consist only of supplementary information for the near future. The main work - editing news as fast as possible - will probably still be done in Level 1, while Level 2.5 features will be applied to enhance this information in an effective and graphically attractive manner. The overlaid enhancement can define the general layout of a whole magazine (e.g. a standardized background colour), the layout of a single page or simply an area of a page. You should remember that the overlaid area has to be congruent to the respective area of the basic page. As one example you might have a table on the basic page consisting of election results. With Level 2.5 this table can be turned into an attractive graph. But remember not to go beyond the margins of the original table! Another typical enhancement application in Level 2.5 might be the smoothing of banner headlines by using the G3 smoothed mosaics character set, as well as applying logos and supplementary background colouring. First of all, you should enhance the introductory page of your service (usually page 100). A page which should benefit from enhancement is the weather forecast. Some simple graphical improvements will revitalise this page. Another example might be the "TV Guide" pages which can be easily upgraded with broadcaster logos. And, for all these examples, define your own colour scheme! |
06b8529f50de00705de57a93f537c8ab | 100 287 | 7.3 More about colours, attributes, objects and side-panels | The overlaying principle of the enhancement of Teletext pages does not only include the more technical aspect of how to do it, it is also a question of planning the Teletext service. Level 2.5 offers a considerably wider palette of colours for display. Your Teletext pages can be enhanced by new back- and foreground colours from the set of 32 colours, half of which are definable by the editor. Mathematically, you have a vast number of colour combinations. In reality, the number of these combinations is much smaller. It is up to the editor to find the best combination for his service. Remember that some people are colour blind and may not appreciate certain background/foreground colour combinations. If you use the chance to create your own colours for your service, use them on as many pages (or magazines) as possible. Otherwise you risk problems with the allocation of colours and pages. The handling of several different colour palettes for different pages or magazines may lead to other problems. If you use global or public objects you should be aware that they may appear in different colours on different pages - depending on the colour palette in use for the respective page or magazine. As already mentioned, in the side-panel you should either send supplementary data in addition to the basic page or a kind of navigational information for your Teletext service. Never use the side-panel for elementary information because it will not appear on Level 1 decoders. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 7.4 The organization of enhancement | The features given in Level 2.5 will encourage your creativity as an editor and will enable you to produce more attractive pages. For instance, there are rules to be made for the creation of new colour palettes or default objects. For an efficient management of objects you should organize a "library" of DRCS and objects. All colour palettes, DRCS and objects should be available on all editing terminals. With more features there is a greater need for system management to organize your Teletext service efficiently. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 15 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 8 Transmission management | This clause covers aspects of the management of the enhancement data which the editing and transmission system should take care of automatically. Because of the limitation (laid down in the Level 2.5 specification) that the total enhancement data should not take more than 500 packets and should be transmitted once every 20 s, there is a "new" process in the origination systems concerning the transmission management for the whole service. The new enhancement data pages required are: • Magazine Organization Tables (MOT); • Object definition pages (GPOP and POP); • DRCS definition pages (GDRCS and DRCS); • Magazine Inventory Pages (MIP). The starting point for an efficient Level 2.5 operation is the Magazine Organization Table (MOT). The MOT contains an entry for each page of a magazine. It contains pointers to the page numbers of the object and DRCS definition pages required to achieve the display of the Level 2.5 version of that page. It can also invoke the display of an object (a default object) without the need to append packets 26 to the basic page. Objects are described in (Global) Public Object Pages (GPOPs or POPs). In these the objects are stored like subroutines which will be invoked through the data in the MOT (as default objects) or from the data in packets 26. DRCS pages transport the redefined characters or graphic shapes. The Magazine Inventory Page (MIP) is a system page which contains information for the decoder to help it decide whether to store a page or not. The creation of the MIP is likely to be done by the transmission system with some guidance from the editorial system manager. The MIP has an entry for every page in the magazine placing it in one of seven main categories: Normal page, Subtitle page, Current TV programme related page, TV schedule page, Data broadcasting page, Editorial system page (e.g. MOT, TOP, POP or DRCS page) and Engineering extra function pages. A TOP page contains already some of the information in the MIP. Also, some of the information in the MIP is useful to multi-page decoders which are not capable of a Level 2.5 display. Recommendations: It is recommended to use hexadecimal pages for the transmission of enhancement data. The new generation of Level 2.5 decoders do not need the 20 ms memory erase time which is necessary for the Level 1 decoders. Thus the enhancement data pages can be transmitted in the filler packet space. The one exception is the MIP because of its usefulness to a wider range of decoders. In annex A it is shown that sufficient filler packet capacity is likely to be found in serial mode transmissions using 6 or more VBI lines per field to transport the 500 enhancement packets in 20 s. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 9 Minimum service | In order to establish a Level 2.5 service which will not increase cycle time to an observable extent a minimum service is proposed. Such a service could have the following features: • full screen colour for all pages in each magazine; • a (broadcaster) logo on each index page (or any other important pages which you want to be highlighted). The number of invocations of this logo is not important if the logo is always implemented at the same position as it could then be invoked as a default object via the MOT. These enhancements will increase the cycle by two extra pages per magazine and one standalone packet. A MOT and a GPOP are needed for the logo, and packet 29 for the full screen colour and the colour palette. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 16 There is an added benefit in that the packets 29, in conjunction with page header control bits, will define unambiguously the character set requirements (i.e. alphabet(s) and national option sub-set) of each page, see clause 11.3. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10 Technical epilogue | This clause deals with a number of Teletext issues not directly related to Level 2.5 that were identified by the EBU/EACEM group during their discussions. Further topics are dealt with in the normative and informative annexes of EN 300 706 [1]. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.1 Allocation of page numbers and page sub-codes | Any page address up to including hexadecimal FE with a sub-code up to and including 3F7E, can be used for a page carrying data and can be specified as a linked page in a packet 27. However, normal decoders allow the user to enter page numbers in the range 100 to 899 only. Access to other pages in the hexadecimal range is possible via packet 27 links in the FLOF code of practice. Pages used for enhancement data (objects and DRCS definition pages) should have page numbers which include a hexadecimal digit to prevent these pages being captured as normal display pages. Page numbers with the tens or units value set to F are often used for engineering or system control purposes and thus they may not be available for editorial purposes. The page number FF in all magazines is reserved for use as a null page address. The full-page address of FF with a sub-code of 3F7F is reserved for use as a null link in packets 27. To enable multi-page decoders to handle rotating pages (otherwise known as rolling pages or multi-page sets) in an intelligent manner, the sub-codes of these pages should be set according to the following: 1) Single, non-rotating pages should use the sub-code value 0000. 2) The following applies to rotating page sets where the editorial content is significantly different from one page to the next, for example "news-reel" sequences or today/tonight/tomorrow weather details. Rotating page sets of up to 79 separate pages should use sequential sub-codes. The first 9 pages should be numbered 0001 to 0009, the next 10 pages numbered 0010 to 0019 and so on up to 0079. An intelligent decoder may choose to store these pages individually, allowing the user to step through the sequence at this own rate. If the editorial content of a certain page is not different from the preceding page, the current page may be transmitted with the same sub-code as the preceding page. Rotating page sets comprising more than 79 sub-pages should use unique sub-codes greater than 0079 on all the pages. It should not be assumed that intelligent decoders will attempt to store these pages individually. Many decoders store the last received sub-page that is greater than 0079 overwriting this on the next reception of a page with sub-code greater than 0079. 3) The following applies to a rotating page set where the editorial content is not significantly different from one page to the next to the extent that an intelligent decoder need not store each page individually. In other words, it is intended that the user sees a new version of the page with minor updates as soon as it is transmitted. A typical example is an index page which rotates to highlight a different topic. Sub-codes values greater than 0079 should be used on each page. To ensure older decoders update their displays each time a new version is transmitted, a unique sub-code should be allocated to each page in the set. Some decoders store pages with sub-codes S2, S1 identical in the same location even though they have been transmitted with a different S4 value. This overwriting can be useful in transmitting pages which have very slight editorial differences - for instance an animating advertisement on each different S2, S1 sub-page, so that they are seen to be changing by the viewer. 4) The sub-code may be used to transmit time-related information, for example an alarm clock page. Separate rules apply to the allocation of sub-code values to enhancement data pages. These should be implemented automatically by the transmission management system. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 17 It should also be noted that it is allowed to use different FLOF links on different pages within a sequence of rotating pages. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.2 Use of the Update bit (C8) | The Update bit (C8) is used by the editor specifically to indicate that an update has occurred. The expected effect in the decoder is that, where a page display has been cancelled by an appropriate user key ("cancel page", "picture", etc.), the setting of the Update bit will cause a prompt, which may involve automatic redisplay of the page. An application where this is standard practice is for newsflash pages. The unnecessary or inappropriate setting of the Update bit can cause annoying redisplay of a page or newsflash that a user wishes to cancel. The setting of the Update bit is thus an editorial decision. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.3 Language definition and the preferred use of packets 29/0 | Existing Level 1 and Level 1.5 decoders have, in general, a limited language capability and determine the language of a page from the C12, C13 and C14 control bits in the page header. The decoder is often designed to meet the needs of the local market only. Many existing decoders do not decode correctly all possible combinations of these bits but, by chance, default to the correct language if a non-supported combination occurs. By definition, Level 2.5 decoders have a much wider language capability, including the ability to display more than one alphabet. They will be more likely to display the wrong language, or even the wrong alphabet, under these circumstances. Therefore it is recommended that the correct settings for these bits are always transmitted. The C12, C13 and C14 control bits on their own provide insufficient information to identify uniquely the language of a page. For example, the combination 000 is used for both English and Polish. Thus Level 2.5 decoders require supplementary information to resolve this ambiguity. The relevant information can be transmitted on a page-by-page basis via packets 28/0, or more efficiently, on a magazine basis by packets 29/0. However, packets 29/0 also allow the simple but effective Level 2.5 enhancements of full screen/row colours and colour re-mapping. Thus the introduction of packets 29/0 in advance of any more complex Level 2.5 transmissions using objects and DRCS is recommended. Where a service comprises pages in different languages using different alphabets, for example Estonian (Latin) and Russian (Cyrillic), it is recommended to use parallel mode transmissions and dedicate particular magazines to each language. This ensures the correct alphabet is used when the decoder is displaying rolling headers while searching for a page. Broadcasters are encouraged to transmit packet X/29 to define the primary and secondary language sets, particularly if the secondary language set is a Latin set so that the appropriate language option can be set, for instance to display the @ character which is 4/0 in the English options. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.4 Interrupted pages | In order to keep some existing decoders working, it is recommended that Level 1 pages be re-transmitted completely, including all extension packets, after any interruption. Pages carrying enhancement data (MOT, POP, DRCS) may be interrupted and can continue with the transmission of the remaining part of the page following the page header. Special rules apply to the setting of the sub-code and certain control bits under these circumstances. Refer to EN 300 706 [1], clause A.1. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.5 Parallel magazine transmissions | In order for a decoder to maintain the time field at the end of the header row, it is necessary to transmit a page header at least every second. This is particularly important with parallel magazine mode transmissions where a limited number of pages in a magazine and the infrequent allocation of a transmission slot can result in the time field changing erratically. Where the number of pages in a magazine is limited and transmission slots are allocated infrequently it is good practice to terminate explicitly each page with a dummy header (page number FF) if the page is not to be terminated implicitly by the immediate transmission of another page in the same magazine. An example is the transmission of subtitles where the page is the only one in the magazine. The purpose of the dummy header is to terminate the acquisition process within the decoder and prevent corruption of the received data by noise and, at Level 2.5, to activate the processing of any enhancement data required by the page. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 18 The combination of TOP and parallel transmissions is not recommended due to the limited performance of existing decoders. This is caused, amongst other factors, by a lack of memory in a significant number of decoders. Therefore, where a parallel transmission is implemented, the use of navigation via FLOF or the MIP is encouraged. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6 FLOF and TOP Navigation Protocols' | |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.1 Introduction | Navigating a teletext database can be very slow if the user has to keep referring to index pages and then has to select pages by entering 3-digit numbers. If the service provider supplies additional data to categorize each page, i.e. a keyword or indication of the subject matter, and combines this with machine-readable page numbers, navigation can be simplified for the user. Speed of access to pages is usually increased as well when these techniques are used with multi-page decoders. The two navigation enhancement methods in current use are FLOF (Full Level One Facilities) and TOP (Table Of Pages). These are specified in EN 300 706 [1] in clauses 11.1 and 11.2 respectively. Codes of Practice for each are presented in annexes H and I respectively. The two protocols were designed independently and have generally been regarded as being mutually exclusive. In other words, a transmission would adopt one or the other, or neither. Many decoders have been designed on this premise. Clause 10.6.4 summarizes the problem that can occur as a result of using both protocols in the same transmission. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.2 FLOF | |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.2.1 Key points | FLOF requires two extra packets to be transmitted per page. A packet X/24 provides an extra row of text to be displayed at the bottom of the main page. This contains four keywords, each in a different colour - red, green, yellow and blue (or cyan). The viewer is provided with four special keys in matching colours on his remote control handset. These permit single-key access to the corresponding pages. The editor chooses the pages to reflect the likely responses of the viewer once he has read the current page. The decoder is informed of the relevant page numbers by the second additional packet - a packet X/27/0. This defines up to six page numbers. A decoder will normally try and pre-capture as many of these pages as possible, subject to its memory capacity. The first four page numbers map directly to the four coloured keys. The last page number maps to an index page related to the current page. There is usually a dedicated key on the handset for selecting this page. No dedicated key is provided for accessing the fifth link. A full 7-digit page address can be specified by each of the six links in the packet X/27/0. A subcode value of 3F7F indicates that an explicit sub-code value is not being specified and only the 3-digit page number should be used. A page address value of xFF.3F7F indicates that no particular page is being specified and any associated direct access key should be temporarily disabled. The display of the packet X/24 is conditional on the setting of the most significant message bit in the Link Control Byte carried in the packet 27. The packet X/24 should only be displayed if this bit is set to 1. FLOF is fully compatible with both magazine serial and magazine parallel methods of transmitting a page-format Teletext service. EN 300 706 [1] states that a packet 8/30, format 1 is an optional component of a FLOF compliant transmission. This statement should not be interpreted to mean that the presence of the packet implies that packets X/24 and X/27/0 are also being used for navigation purposes. A packet 8/30 format 1 has a stand-alone function and carries various items of data relating to the broadcast channel. The navigation aspects are restricted to recommending an initial page by which the user should enter the service. Other contents include channel identification, time and date. This type of information is important for VCRs and NexTView EPG decoders. Thus the packet is quite likely to be found in a transmission that is not using packets X/24 and X/27/0 for navigation. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 19 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.2.2 Identifying a FLOF transmission | • A FLOF compliant transmission will include some or all pages with a packet X/27/0 with the MSB of the Link Control Byte set to 1. It is likely that such pages will also have a packet X/24. However, it is possible that not all pages in the service will have FLOF components. • The presence of a packet 8/30 format 1 should NOT be interpreted as implying that a service uses packet X/24 and X/27/0 for navigation purposes. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.2.3 Recommendations to service providers | • Since a decoder will normally enter a teletext service via page 100 or the initial page referenced by a packet 8/30 format 1 (if different), it is recommended that these pages have FLOF compliant packets X/24 and X/27/0 when the FLOF navigation protocol is used anywhere within the service. • The combination of FLOF and TOP in the same transmission is not recommended; see clause 10.6.4. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.3 TOP | |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.3.1 Key points | The TOP system transmits additional information that categorizes the Teletext pages. For each page in the service, the page number and a text string describing the theme or content is broadcast in a machine-readable format. Unlike FLOF, this additional data is transmitted via special pages and no packets with addresses greater than 23 are employed. A decoder is free to interpret this additional information in its own way. Typically it constructs and displays menus of pages grouped by theme or content rather than page number. In the background, a multi-page decoder will be acquiring some or all of the pages referenced by the menu currently displayed. The viewer selects a page by theme or content and, if has been pre-captured, it can be displayed immediately. Four coloured keys on the remote control handset are used to move around the menus and select pages. A number of different data pages are allowed for in the TOP specification but common to all implementations is the Basic TOP Table (BTT) page. The contents of this page indicate the page numbers of the other data pages, if used. The BTT information is always broadcast on page 1F0 and is coded Hamming 8/4 throughout packets 1 to 23. EN 300 706 [1] specifies the coding of the Page Function and Page Coding fields of a packet 28/0 format 1 which can be added to the page to define unambiguously that it is a BTT page. However, this is not a mandatory requirement. Identification codes exist for the other types of TOP data pages. The packet should be coded according to table 6 in clause 9.4.2.4 of EN 300 706 [1]: • Triplet 1, bits 4, 3, 2, 1: 1000 - BTT page • Triplet 1, bits 7, 6, 5: 011 - 8/4 Hamming coding throughout • Triplet 1, bits 18 - 8: 00111111111 - Default value for pages which are not level one pages or data broadcasting pages • Triplets 2 to 13 - Do not care (reserved for future use). All bits set to 0 is recommended. The page numbers used to carry TOP data can also be indicated via Magazine Inventory Pages (MIP). The BTT will always be in magazine 1. The code value for a TOP data page is 0xFE. A lack of memory in many decoders means that TOP is not particularly suited for use with parallel mode transmissions. NOTE: There is no minimum cycle time for the BTT page specified in either EN 300 706 [1] or the IRT's TOP specification (No. 8, R5, 2nd edition, 1991). ETSI ETSI TR 100 287 V1.2.1 (2002-12) 20 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.3.2 Identifying a TOP compliant transmission | • A TOP compliant transmission will include, as a minimum, the BTT information on page 1F0. However, further checks ought to be carried out in case this page is actually being used for data broadcasting purposes. A page used for data broadcasting purposes and coded to the Page Format - CA method described in EN 300 708 [2] should include a packet 28/0. This packet 28/0 should be checked to see if the Page Function and Page Coding fields identify the page as carrying TOP data, see above. • If a packet 28/0 is missing from a page 1F0 AND the majority of bytes in packets 1 to 23 pass a Hamming 8/4 check, it is very likely the page carries BTT information. • A decoder should search for the BTT page for a time much greater than the recommended minimum transmission rate. • If present, a Magazine Inventory Page for magazine 1 should indicate whether a BTT page being transmitted. Other TOP data pages should be indicated in the same MIP or in MIP(s) for other magazines, as appropriate. • TOP is unlikely to be used with parallel mode transmissions. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.3.3 Recommendations to service providers | • The BTT page should be transmitted at a minimum rate of once every 10 s. (It should be noted that some older decoders may require a more frequent transmission). • The service should include Magazine Inventory Pages as appropriate to confirm that TOP data pages are present. • An appropriately coded packet 28/0, format 1 should be added to the BTT page to confirm its function. • Where page 1F0 is used for data broadcasting purposes according to the Page Format - CA method described in EN 300 708 [2], a properly coded packet 28/0 should accompany the page. • The combination of TOP and FLOF in the same transmission is not recommended; see clause 10.6.4. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.6.4 Combined FLOF and TOP transmissions | Since the FLOF and TOP navigation protocols introduce different additional components into the transmission, it is possible to add both to the same Teletext service. However, this is not recommended, as some existing decoders may not be consistent in their operation each time they tune to a particular channel. Sometimes they might work in FLOF mode, other times in TOP mode. Their response will be determined by which additional component they find first. Some existing receiving systems have been designed to accept dual-standard transmissions. Usually the user or the dealer is able to configure the equipment so that it always operates in one particular mode if both protocols are encountered. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.7 Preferred use of packets 27/4 | Packets 27/4 links provide a complete definition of the particular POP and DRCS sub-pages carrying the enhancement data required by the associated basic page. (This is in the form of 16 flags for the 16 possible sub-pages). The MOT only provides the page number and an indication of the total number of sub-pages. Thus the transmission of a packet 27/4 can speed up the processing of a Level 2.5 page by a decoder. In some circumstances the transmission of a packet 27/4 is essential, for example to support the "news-reel" type of page where a selection of pages, possibly from different magazines, with different enhancement data (POPs and DRCS) is presented on a single page number as a rotating page. The information available from the MOT is insufficient to identify the requirements of each page. |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.8 Objects in row 24 | The use of objects which spread from rows higher up the screen into row 24 is not recommended, as many decoders will display row 24 below rows 0 to 11 when operating in "page expansion" mode. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 21 |
06b8529f50de00705de57a93f537c8ab | 100 287 | 10.9 The advantages of transmitting a MOT | The MOTs will always be captured by Level 2.5 decoders and stored permanently. Thus the decoder may search for the basic page and the required enhancement data pages simultaneously. With some Level 2.5 decoders the memory will be large enough to pre-capture and store all the enhancement pages. The requested page can then be displayed as soon as the basic page is acquired. If the required enhancement data pages are only indicated through packets X/27/4 appended to the basic page, they can only be requested after reception of the basic page. The default object feature within the MOT allows enhancements to added to any page without the need to append packets 26 to the basic page and thus saving transmission capacity. 10.10 Limiting the use of packets 26 Packets 26 should be used primarily for Level 1.5 data and global (or public) object invocations to minimize the number of packets 26 appended to each basic page. A large quantity of enhancement data should be packed into an object and transmitted in an object page even if the enhancement is to be used only once. This approach will save transmission capacity as the object page can make use of the filler packet space. In addition, the effect on the processing time of some Level 1.5 decoders will be minimized. 10.11 Special characters The Euro currency symbol is invoked at Levels 1.5, 2.5 and 3.5 by local enhancement data (packets 26), or at Levels 2.5 and 3.5 from within objects. A column address triplet is required with a mode value of 01111 (character from the G2 supplementary set) and a data (character) value of 5/6. This assumes the Latin G2 set is the currently selected. The @ symbol as used in internet addresses can be accessed in Level 1 from the character code 4/0 in the English national G0 option set. It is available in Level 1.5 where the Latin G0 character set is used. It is desirable to support the @ symbol in all languages, in the second edition of EN 300 706 [1], the @ symbol replaces the * symbol when invoked with a NULL accent. Manufacturers of Level 1.5 equipment are encouraged to support these symbols. Broadcasters should transmit a suitable default characters on the Level 1 page. 10.12 Packet X/28 format 1 There are two packet 28/0 formats in EN 300 706 [1], format 1 (clause 9.4.2) and format 2 (clause 9.4.3). Format 1 was invented as part of the Level 2.5 development. Format 2 is what remains of the original WST/SPB492 coding scheme. This survived because it is used in Page Format - CA data broadcasting as defined in clause 5 of EN 300 708 [2]. Format 1 has three sub-coding schemes: • Basic Level One pages (LOP) - table 4. • Page Format - Clear data broadcasting pages as defined in clause 4 of EN 300 708 [2], table 5. • Pages other than these two types, e.g. DRCS pages - table 6. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 22 According to table 7, the three fields in the first triplet of a packet 28/0 format 2 accompanying a Page Format - CA page can only have the following values: Page Coding Set to '0' Page Function Bit: 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0 0 1 1 Inspecting bits 1 to 7 of these sequences against table 3 in clause 9.4.2.1 yields: 7 6 5 Page Coding 4 3 2 1 Page Function 0 0 0 7 bits + odd parity 0 0 0 0 Basic level one page 0 0 0 7 bits + odd parity 0 1 0 0 GDRCS page 0 0 0 7 bits + odd parity 0 1 0 1 (Normal) DRCS page Thus the page could be a level 1 page or a DRCS page. However, according to clause 9.4.2.4 it CANNOT be a DRCS page because bits 8 to 18 are not set to 11111111100. Bits 8 to 14 of the first triplet of a packet 28/0 for a level 1 page define the default G0 and G2 character sets, and bit 15 to 18 are part of the second G0 set definition. The bit sequences shown above are all valid when interpreted against tables 32 and 33 respectively. Thus it is not possible for a decoder to distinguish between a level 1 page and a data-broadcasting page solely on the coding of the first triplet of a packet 28/0. The coding scheme for the data broadcasting packet 28/0 cannot be altered because it pre-dates the Enhanced Teletext specification and there are installed decoders that are designed to the current specification. However, a level 1 page is likely to have a number in the range x00 to x99 while a data broadcasting page is likely to have a page number which includes elements in the range A to F. 10.13 Channel identification It is strongly recommended that all teletext transmissions include at least a Packet 8/30 format 1 to enable the channel to be identified. See TR 101 231 [3]. For compatibility with nexTView TR 101 288 [4] reception it is preferable to use Packet 8/30 format 2 or VPS where available for channel identification. 10.14 Date and time setting It is recommended that to enable the accurate setting of time and date a Packet 8/30/1 is included in any transmission. This time shall be UTC with the appropriate time offset bits set. Because of features of some decoders which fall back on the use of bytes 38-45 of a Packet X/0, it is strongly recommend that a packet 8/30/1 is transmitted if any X/0 bytes 38-45 do not contain the current time. The use by decoders of a text string in packet X/0 to determine the date is deprecated and the use of the MJD in Packet 8/30/1 is encouraged. 10.15 Level 2.5 data on magazine 7 Problems have been encountered with some receivers that do not correctly receive Level 2.5 information on magazine 7. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 23 Annex A: Cycle time in serial transmission mode By its very nature cycle time involves a mathematical treatment. A displayable page consists of a header (row zero) and a number of other packets. A full page takes 24 packets. If a row has no information, it does not need to be transmitted. Table A.1 shows the number of vertical blanking intervals (VBIs), each 20 ms in duration, required to transmit pages of between 18 and 30 packets on 1 to 12 VBI lines. Table A.1: VBIs required to transmit pages of different sizes No. of VBIs Number of packets per page 30 29 28 27 26 25 24 23 22 21 20 19 18 1 30 29 28 27 26 25 24 23 22 21 20 19 18 2 15 15 14 14 13 13 12 12 11 11 10 10 9 3 10 10 10 9 9 9 8 8 8 7 7 7 6 4 8 8 7 7 7 7 6 6 6 6 5 5 5 5 6 6 6 6 6 5 5 5 5 5 4 4 4 6 5 5 5 5 5 5 4 4 4 4 4 4 3 7 5 5 4 4 4 4 4 4 4 3 3 3 3 8 4 4 4 4 4 4 3 3 3 3 3 3 3 9 4 4 4 3 3 3 3 3 3 3 3 3 2 10 3 3 3 3 3 3 3 3 3 3 2 2 2 11 3 3 3 3 3 3 3 3 2 2 2 2 2 12 3 3 3 3 3 3 2 2 2 2 2 2 2 Table A.2 shows the number of filler packets per page over the same range of packets per page and VBI lines. Table A.2: Number of filler packets per VBI/page size combination No. of VBIs Number of packets per page 30 29 28 27 26 25 24 23 22 21 20 19 18 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 1 0 1 0 1 0 1 0 1 0 1 1 3 0 1 2 0 1 2 0 1 2 0 1 2 0 4 2 3 0 1 2 3 0 1 2 3 0 1 2 5 0 1 2 3 4 0 1 2 3 4 0 1 2 6 0 1 2 3 4 5 0 1 2 3 4 5 0 7 5 6 0 1 2 3 4 5 6 0 1 2 3 8 2 3 4 5 6 7 0 1 2 3 4 5 6 9 6 7 8 0 1 2 3 4 5 6 7 8 0 10 0 1 2 3 4 5 6 7 8 9 0 1 2 11 3 4 5 6 7 8 9 10 0 1 2 3 4 12 6 7 8 9 10 11 0 1 2 3 4 5 6 ETSI ETSI TR 100 287 V1.2.1 (2002-12) 24 The previous two tables are fundamental - but it is more useful to see how many pages can be transmitted in about 20 s, a typical reading time for one page (see table A.3). Table A.3: Number of pages in 20 s per VBI/page size combination No. of VBIs Number of packets per page 30 29 28 27 26 25 24 23 22 21 20 19 18 1 33 40 50 2 66 66 72 72 77 77 83 83 90 90 100 100 111 3 100 100 100 111 111 111 125 125 125 142 142 142 166 4 125 125 142 142 142 142 166 166 166 166 200 200 200 5 166 166 166 166 166 200 200 200 200 200 250 250 250 6 200 200 200 200 200 200 250 250 250 250 250 250 250 7 200 200 250 250 250 250 250 250 250 333 333 333 333 8 250 250 250 250 250 250 333 333 333 333 333 333 333 9 250 250 250 333 333 333 333 333 333 333 333 333 333 10 333 333 333 333 333 333 333 333 333 333 500 500 500 11 333 333 333 333 333 333 333 333 500 500 500 500 500 12 333 333 333 333 333 333 500 500 500 500 500 500 500 Table A.4 shows the vast number of filler packets that a service using more than six VBI lines per stream contains. The shaded area shows the combination of packets per page and VBI lines per field where there are more than approximately 500 filler packets per 20 s (i.e. corresponding to the maximum amount of Level 2.5 enhancement data at the slowest permitted transmission rate). Table A.4: Number of filler packets in 20 s per VBI/page size combination No. of VBIs Number of packets 30 29 28 27 26 25 24 23 22 21 20 19 18 1 2 66 72 77 83 90 100 3 100 200 111 222 125 250 142 284 4 250 375 142 284 426 166 332 498 200 400 5 166 332 498 664 200 400 600 800 200 400 6 200 400 600 800 1 000 250 500 750 1 000 1 250 7 1 000 1 200 250 500 750 1 000 1 250 1 500 333 666 999 8 500 750 1 000 1 250 1 500 1 750 333 666 999 1 332 1 665 1 998 9 1 500 1 750 2 000 333 666 999 1 332 1 665 1 998 2 331 2 664 10 333 666 999 1 332 1 665 1 998 2 331 2 664 2 991 500 1 000 11 999 1 332 1 665 1 998 2 331 2 664 2 997 3 330 500 1 000 1 500 2 000 12 1 998 2 331 2 664 2 997 3 330 3 663 500 1 000 1 500 2 000 2 500 3 000 ETSI ETSI TR 100 287 V1.2.1 (2002-12) 25 Annex B: Commercial name The term "Hi Text" has been proposed as the commercial name for enhanced Teletext services and decoding products compliant with EN 300 706 [1] and the present document. ETSI ETSI TR 100 287 V1.2.1 (2002-12) 26 Annex C: List of members of the EBU/EACEM Application Group The following members of the EBU/EACEM Application Group contributed to this code of practice ETR: Alexander Kulpok (Chairman) ARD/ZDF-Videotext/Berlin Paolo d'Amato RAI/Rome Dirk Angenendt ARD/ZDF-Videotext/Berlin Frans Collignon NOS Teletekst/Hilversum Doug Eaton VG Broadcast/Crawley Gerhard Eitz IRT/Munich Brian Gill GEC Plessey/Swindon Christian Lappe Bayerischer Rundfunk/Munich Paul Georg Meister CH-TELETEXT/Biel Kjell Norberg NRK/Oslo Danny Payea VG Broadcast/Crawley Werner Roessler Siemens/Munich Rolleiv Solhom NRK TEKST-TV/Oslo David Tarrant Philips Semiconductors/Southampton Peter Tobisch ORF/Vienna Peter Weitzel BBC/London Uwe Welz ARD/ZDF-Videotext/Berlin Otto Wisst Sony/Fellbach Russ Wood Softel/Pangbourne ETSI ETSI TR 100 287 V1.2.1 (2002-12) 27 History Document history Edition 1 October 1996 Publication as ETR 287 V1.2.1 December 2002 Publication |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 1 Scope | Short duration transient disturbances can occur on dc power distributions when a short circuit fault occurs in part of that distribution. The energy contained in the transient can be sufficient to do considerable damage to equipment connected to the distribution unless measures are taken to suppress or absorb this energy. The present document examines the parameters of dc power distributions within the scope of EN 300 132-2 [1] that significantly contribute to the energy contained by a transient, discusses ways in which the transient can be controlled to reduce its harmful effects, and suggests ways in which the immunity of an electronic unit or a substantial telecommunications installation might be tested. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 2 References | For the purposes of this Technical Report (TR), the following references apply: NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee their long term validity. [1] ETSI EN 300 132-2: "Environmental Engineering (EE); Power supply interface at the input to telecommunications equipment; Part 2: Operated by direct current (dc)". |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 3 Definitions, symbols and abbreviations | |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 3.1 Definitions | For the purposes of the present document, the following terms and definitions apply: fault: short circuit of the negative conductors of the power distribution to any earthed part of an equipment or installation interface "A": The definition given in EN 300 132-2 [1] applies. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 3.2 Symbols | For the purposes of the present document, the following symbols apply: A Ampere C Capacitance d separation of conductors dc direct current E Energy I current L inductance l length of conductor n number of ways current is split r diameter of conductor R Resistance t time U voltage (nominal voltage) V voltage (overvoltage) μ magnetic permeability of insulation separating conductors ETSI ETSI TR 100 283 V2.2.1 (2007-08) 6 |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 3.3 Abbreviations | For the purposes of the present document, the following abbreviations apply: EUT Equipment Under Test PDF Power Distribution Frame UB Battery voltage |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 4 Void | |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 5 Typical power distribution | Virtually all equipment operated in telecommunications centres has a battery as a backup source of power in the event of a mains failure. Batteries store very large amounts of energy and under fault conditions are able to deliver very large currents for short periods far in excess of the ratings of fuses or circuit breakers in the path of the fault. Figure 1 shows a typical power distribution (negative conductors only) in a large installation. The current supplied from the power plant and battery is broken down into several lower current feeds at each Power Distribution Frame (PDF). The power cables are sized according to the current they have to carry and the voltage drop that can be tolerated, and are protected by suitably rated fuses or breakers in each PDF. In large installations the conductors close to the battery may be copper or aluminium bus bars. The positive return conductors will be parallel with the negative conductors but will not include current protection devices. Figure 1: Typical power distribution ETSI ETSI TR 100 283 V2.2.1 (2007-08) 7 |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 6 Characteristics of a power fault transient | least affected feeds most affected feeds MAIN PDF SECONDARY PDF RACK FUSE PANEL cable cable bus-bar Figure 2: Power fault applied in an equipment rack Figure 2 shows the fault current path when a fault occurs in a branch of the power distribution. The voltage transient experienced by the branches of the distribution not associated with the fault can be divided into two distinct parts and are shown in figures 4 and 5: - Part 1: begins at the moment the fault is applied (t0) and ends at the instant the protection device clears (t1); - Part 2: begins at the instant the protection device clears the fault (t1), and ends (t2) when the voltage returns to its value before the fault was applied. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 7 The transient, part 1 | When the fault is applied the current rises rapidly at an exponential rate: I= U R (1- e ) R L t B − (1) Where: • UB = the battery voltage in float mode. • R = the sum of the resistances in the fault circuit which include: - (a) fault resistance itself; - (b) total conductor resistance in both negative and return legs; - (c) the resistance of fuses or breakers; - (d) the internal resistance of the battery. • L = the inductance of the fault circuit loop. • t = the time elapsed from the fault being applied. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 8 It can be seen that if inductance is ignored, the potential fault current can be extremely high. I= U R B (2) Currents of in excess of 1 kA are not unusual, depending on where the fault occurs in the distribution. In practice the inductance of the fault circuit cannot be ignored and it plays an important role in the behaviour of the power distribution as will be seen next. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8 Analysis of part 1 | Two things are of concern during this part of the fault transient: a) the magnitude of the fault current; b) the voltage at the input of all other equipment sharing the same power distribution. The magnitude of the fault current largely determines the amount of energy that will be dissipated after the fault is cleared by the protection device. E = 1/2 LI2 (3) Where: - E is the energy (joules); - L is the inductance of the fault circuit (henrys); - I is the fault current at the instant the fault is cleared by the protection device (amps). The voltage at the input of all other equipment sharing the same distribution falls to below the normal, minimum steady state value for some portion of the clearing time of the protection devices, requiring the dc/dc converters to store charge on "hold up" capacitors to ride through this fall in supply voltage. The magnitude and duration of the fall depends on many parameters of the power distribution already mentioned e.g. R, t1 and L. How these can be controlled is explained in clauses 8.1, 8.2 and 8.3. The general objective is to reduce the energy stored in the distribution inductance which from equation 1 means that the distribution inductance itself (L) must be kept to a minimum and the peak fault current (I) must be controlled by resistance in the distribution (R) or by the use of very short clearance time fuses (t1). ETSI ETSI TR 100 283 V2.2.1 (2007-08) 9 |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8.1 Increasing distribution resistance | Resistance would seem to be an undesirable feature to have in a power distribution but used in the right way, there are advantages worth having by its inclusion that more than compensate for the power losses. Figure 3: A controlled resistive power distribution Figure 3 shows a power distribution where the resistance has been concentrated in the most remote branches. The fault current is limited to: I = U (n + 1)R B (4) But the voltage supplied to the other rack power feeds can be reasonably expected to remain above: U = nU 1+ n B (5) after the influence of inductance in the circuit has passed. If dc/dc converters are designed to operate at U volts, only the drop in voltage due to circuit inductance needs to be covered by "hold up" capacitors in the converters. Such a resistive power distribution permits the use of circuit breakers, with their longer clearance times compared to fuses, and at the same time, there is no need to increase the hold up time of the power converters to match the clearance time of breakers. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8.2 Decreasing the fault clearance time | The response of fuses and circuit breakers to fault currents needs to be understood. A fuse needs time to break an excessive current i.e. a current greater than its rated value. The larger the excess current the sooner the fuse element reaches its melting point and ruptures. However, even with very high levels of excess current, a fuse will still have a finite clearance time. Depending on the design of the fuse and the excess current level, clearance times can vary from 1 ms to more than 10 ms. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 10 Circuit breakers have a rather different response to large fault currents. The time needed to clear an excessive current is mainly dependent on the inertia of the moving mass of the breaker mechanism and contacts. The range of clearance times for breakers is usually longer than for fuses, the fastest being 4 ms to 6 ms and the longest extending beyond 15 ms. UB Figure 4: Voltage transient waveform Figure 5: Current transient waveform The importance that these overcurrent protection devices play can be seen in the diagrams of figures 4 and 5 when coupled to the inductance present in the fault circuit. The fault current rises exponentially towards the maximum level already established in equation (2) above, and, depending on the clearance time of the protection device (tx or t1 in figures 4 and 5, battery in float mode UB) being used, the peak fault current may be limited by the inductance of the fault loop. If the clearance time is long, then the peak current is limited only by the resistance of the fault loop. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8.3 Decreasing power distribution inductance | |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8.3.1 Calculating inductance | The inductance of any fault circuit is reduced when all the negative conductors are closely coupled to the earth return conductors, the closer the coupling the less inductance there is. Negative and return conductors made as a bonded pair (e.g. twin cables) provide a good solution with consistent performance figures for inductance per metre length. If this is not possible, then separate conductors run side by side as closely as possible gives good results, or negative conductors tied at frequent intervals to a positive return bus-bar also reduces distribution inductance. The theoretical equation for the inductance (L) of a pair of parallel conductors is shown below: r d ln l = L π μ (6) Where: - r = the radius of the conductors; - d = the separation of the conductor centres; - μ = the magnetic permeability of the insulation that separates the conductors; - l = the length of conductor. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 11 This equation is only approximately correct as it assumes that "d" is much greater than "r" which is not true of a pair of power conductors. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8.3.2 Measuring inductance | A more accurate method of characterizing the inductance of a conductor pair is by direct measurement. This can be done using a representative length of bonded pair cable, shorting the two conductors at one end and measuring the inductance at the other end. As the low frequency inductance is the parameter that stores energy when fault currents flow in the cables, the measuring frequency should be the minimum that permits a dependable reading from the measuring instrument. Higher measuring frequencies will give erroneous readings due to distributed cable capacitance between conductors and from each conductor to its surroundings. Measurements can also be made on an installation during construction or before power is connected. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8.4 Summary | Figure 4 shows a typical transient caused by a fault, as seen at the input to a branch sharing the same secondary PDF, or the same rack fuse panel, as the branch with the fault. The initial large drop in voltage is caused by inductance in those parts of the fault circuit that are shared with the branch being monitored, and the duration is dependent on the value of the inductance. If it is small then the voltage quickly recovers to the value determined by the distribution of resistance in the cabling from the battery to the point of application of the fault (see figure 3). If it is large then the fault current may not reach the value limited by resistance alone before the fuse clears the fault circuit (see figure 5). The time constant for the inductively controlled part of the voltage dip can vary from a few tens of microseconds to perhaps 2 ms. Where it is not possible to reduce distribution inductance, the fault current can be reduced using fuses with very short clearance times. When the design of the whole power distribution can be undertaken, the apportioning of resistance by the selection of cable sizes or other means can both reduce the fault current and reduce the voltage drop for that portion of the wave form controlled by resistance to a value that still permits the normal operation of dc/dc converters. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 8.5 Recommendations | If Interface "A" for a particular installation occurs at a remote point in the power distribution then there is little that can be done to influence the magnitude or duration of the voltage dip, and it would be safest for a supplier of equipment to assume that the voltage drops to an unusable level for the duration of the clearing time of the protective devices. The supplied equipment would at the same time need to be designed to give continuous service during the clearing of the types of fuses or circuit breakers being used on that location. The dc/dc converter's specification for "hold up" time will need to match the clearing time. If the interface is at a point closer to the battery, then the scope for the equipment's own power distribution to adopt some of the measures already outlined is much greater. The use of apportioned resistance in the distribution has the advantage that it allows the use of circuit breakers as the protective device, which is favoured by most network operators today, and the "hold up" time needed by the dc/dc converters only needs to cover the inductive portion of the voltage dip. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 9 The transient, part 2 | The second part of the transient begins at t1 (see figures 4 and 5) when the protection device opens the fault circuit while the fault current is at its peak. With the fault circuit now open, there is much more current flowing in the inductance of the cables than is required by the combined load of the affected branches. The energy represented by this excess current and the cable inductance (see equation 1) must be encouraged to decay without causing damage to any equipment connected to the power distribution. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 12 |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 10 Analysis of part 2 | The analysis of part 1 has shown how energy is stored in the conductors of the power distribution, and how this energy can be kept to a minimum, but the energy that remains can be disposed of in two ways: a) by absorbing it and gently releasing it to the load; b) by dissipating it as heat. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 10.1 Absorbing the energy | The energy can be absorbed by capacitance distributed across the power distribution. This can be in the form of capacitor banks placed in PDFs and rack fuse panels, or it can be in the form of the capacitors that exist at the input to dc/dc converters to provide "hold up" time during part 1 of the transient, or a combination of both. To give an indication of the amount of capacitance needed to keep the rise in voltage below a given value, the following relationships can be used: ( ) 2 0 2 1 2 2 1 2 1 V V C LI − = (7) Where: • V0 = open circuit voltage. • V1 = the overvoltage. ( ) 2 0 2 1 2 V V LI C − = (8) Where V is the overvoltage i.e. the rise in voltage above the supply voltage. Thus if LI2 has been minimized, then for a given value of V the equipment can tolerate, C is the amount of capacitance needed to control the overvoltage. Alternatively, for a given value of distributed capacitance (C), V is the over-voltage: 0 2 1 2 0 2 = V V V C LI − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + δ (9) Again this should only be used as a guide because not all the energy is transferred to the capacitance due to resistive losses in cables and in the capacitors themselves. Figure 6 curve (a) shows a transient between times t1 and t2 that would not be acceptable on a power distribution, which has been transformed by distributed capacitance to figure 6 curve (b) which could be tolerated by most equipment. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 13 150 V 50 V 100 V TIME b a V O L T A G E Figure 6: Alternative transient recovery waveforms; curve a and curve b |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 10.2 Dissipating the energy | The energy can be dissipated quickly by using transient absorbing devices which are essentially like Zener diodes connected across the positive and negative conductors at a number of strategic points in the distribution. The transient absorbing device is chosen to conduct at a voltage safely above the maximum continuous voltage of the power system, and safely below the voltage at which damage might occur to the equipment. These devices need to be rated for very high peak powers. Alternatively, there are fuses and breakers that are specifically designed to produce an arc as the fuse element melts or the breaker contacts separate. These can go a long way to being able to dissipate the excess energy on their own. They are often backed up by lower powered Zener diodes to guard against premature extinguishing of the arc. |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 10.3 Recommendations | The capacitive solution works very well but the consequences of a short circuit failure of such large capacitors, protected by only high current rated fuses or breakers, needs to be considered carefully. The Zener diode solution also can be successful, but the tolerance on the Zener voltage often makes it difficult to meet the conditions given in clause 10.2. Arcing fuses and breakers are relatively new but deserve serious consideration. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 14 |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 11 Testing for immunity to transients | Dependent upon the size of the installation needing to be tested, there are two practical and one theoretical means of demonstrating immunity to power transients: a) By simulating a transient, suitable in scale and energy to the size of the equipment being tested. To do this the power distribution to which the equipment under test will be connected needs to be known in some detail or some form of worst case distribution assumed. The maximum energy available, the equivalent resistance and capacitance of other loads connected to the same distribution, and any voltage limiting devices present in the distribution would all need to be represented in the transient simulating circuit used for this test. b) By applying a simulation of real power distribution faults to an installation model. For large installations or where a large part of the power distribution is supplied with the equipment, this is by far the best way of demonstrating transient immunity. c) By analogue circuit simulation of the whole power distribution under an applied fault and including the extreme limits of the results in the specification of the dc/dc converters or other direct load circuits. The accuracy and validity of the results depends on the integrity of the data used in the simulation. Simulations of this nature usually need some practical testing to give credibility to the results. NOTE: Changing of the distribution network may alter the overvoltage as well as the overvoltage duration achieved. 11.1 Transient immunity test circuit; by applying real power distribution to an installation model (high power systems) Coax - Shunt 1 mOhm Fuse Oscilloscope Oscilloscope Power Relay Interface "A" or DC power supply conductors 50 cm / 16 mm 2 100 cm / 10 mm 2 50 cm / 16 mm 2 Recording Device Recording Device Contactor Figure 7: Test set-up method for testing short circuits behind Interface 'A' of high power systems (e.g. more than 1 kW) Fuse rating has to be determined on DC power supply equipment with distribution and protection, DC power supply conductors or Interface "A". NOTE: The achieved overvoltage and the duration of the overvoltage can depend on the type fuse applied. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 15 11.2 Transient immunity test circuit; by analogue circuit simulation Figure 8 provides a suggested circuit for creating the levels of energy and current that can be found in a faulted distribution. With the values shown, the circuit provides a 4 ms drop in voltage while developing a fault current of 300 A, followed by the release of 10 J of energy. The inductance in the test circuit L1 may be varied to suit the conditions in any power distribution at any position of Interface "A". Similarly the peak current can be varied by the adjustment of R1, Rx and Rs. The diodes D1 and D2 are included only to limit the maximum voltage generated to a safe level when the equipment under test has low capacitance. The test is only valid if the diodes do not conduct significantly during the test i.e. less than 3 A. Conduction of the diodes indicates that not all of the energy is being injected at the interface. If required, the Zener diode voltage of D2 can be varied to match the voltage immunity of the equipment under test, and to avoid diode conduction. The nodes marked A represent Interface "A". At this point can be connected the equivalent circuit of other loads that may be connected to the same Interface "A" as the Equipment Under Test (EUT). L2 and R2 represent the power distribution from Interface "A" to the equipment under test.µ 99 000 µF EUT POWER SWITCH NOTE: The nodes marked A represent Interface "A". Figure 8: Transient immunity test circuit ETSI ETSI TR 100 283 V2.2.1 (2007-08) 16 |
62da74a7e53806ce03036347aa9d4518 | 100 283 | 12 Conclusion | The present document has shown that no standard can be applied to a transient that appears on a power distribution. The energy stored in the cables of a distribution network depends on many factors, several of which may not be under the control of an equipment supplier. If Interface "A" for a large installation is close to the battery then there is the opportunity to design the power distribution and the equipment itself to work together to achieve immunity to power faults by applying the principles contained in the present document. Recognizing this difficulty, each installation or extension will need an understanding between network operator and supplier on how compatibility on either side of Interface "A" may be achieved so that all equipment from many suppliers sharing the same power distribution can each tolerate power faults occurring in the other. The parameters must describe the time voltage relationship of the transient that this equipment will tolerate without deviating from the specified performance. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 17 History Document history Edition 1 May 1996 Publication as ETR 283 Corrigendum 1 March 1997 Corrigendum 1 to 1st Edition of ETR 283 V2.1.1 July 2002 Publication V2.2.1 August 2007 Publication |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 1 Scope | The present document has the aim of giving the user the following information: • an explanation of the main environmental concepts and terminology with examples; • the purpose and use of environmental classes; • the testing philosophy relating to environmental classes and equipment characteristics; • the principles underlying environmental specifications. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 2 References | For the purposes of this Technical Report (TR) the following references apply: [1] IEC 60721 (all parts): "Classification of environmental conditions". [2] IEC 60068 (all parts): "Environmental testing procedures". [3] IEC 60605-3 (all sub-parts): "Equipment reliability testing: Part 3: Preferred test conditions". [4] ETSI EN 300 019-1 (Parts 1-0 to 1-8): "Environmental Engineering (EE); Environmental conditions and environmental tests for telecommunications equipment; Classification of environmental conditions". [5] ETSI EN 300 019-2 (Parts 2-0 to 2-8): "Environmental Engineering (EE); Environmental conditions and environmental tests for telecommunications equipment; Specification of environmental tests". |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 3 Environmental engineering | |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 3.1 Purpose | The purpose of environmental engineering is to make the equipment and the environment mutually compatible. This means that in some instances the equipment has to be modified and/or protected to resist a given environment or, alternatively, the environment itself shall be conditioned to match the equipment. The matching of the equipment to its environment and its effect on the environment needs to be carefully evaluated. Finally, testing reveals whether the equipment and the environment successfully match. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 3.2 Economic and technical aspects | Environmental requirements have a number of economic and technical consequences. These include: • the equipment specification; • the equipment design; • the choice of materials; • the testing procedure and protection, where applicable; • the operational conditions and application. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 8 The environmental requirements relating to equipment specification and design must be considered and stated in an early phase of a project. If this is not done, significant economic and technical difficulties may occur during the later phases of the project. An "overspecification", which results in "overdesign", is costly, complex and may not lead necessarily to a more reliable product. To make the requirements for the environmental conditions at the equipment location too stringent may also be costly and complex. The introduction of protection, whether in the equipment or on the environment, always requires an economic evaluation. This protection shall always be taken into account in any test specification. Thorough testing is both costly and time consuming. Hence selecting the relevant and cheapest test procedures for the equipment is most important. Good environmental engineering practice seeks to balance the above costs against the costs of environmentally induced failures. Such costs arise from: • elimination of the failure; • possible redesign; • operational losses; • possible compensations. The process involves both technical and economic optimization in relation to the selected environment. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 9 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 3.3 Outline of the test requirements | Figure 1 shows a total, but simplified, procedure for preparing an environmental resistibility test based on environmental data. Some main elements of the procedure are described in the following clauses with the emphasis on environmental classes, transformation and the resulting test specification, while taking into account the performance requirements of the equipment. RESISTIBILITY REQUIREMENTS ACCORDING TO EN VIRONMENTAL CLASSES TRANSFORMATION ENVIRONMENTAL PROGNOSIS DESCRIPTION (clause 4.1) CLASSIFICATION (clauses 4.2 to 4.5) TRANSLATION (clause 6.2) FROM ENVIRONMENTAL CLASS TO TESTING SPECIFICATION (clauses 6.1 and 6.3) SPECIFICATION AND TESTING (clause 6.4) NATURE PROTECTION EXTERNAL CONDITIONS ENVIRONMENTAL PARAMETERS WITH CHARACTERISTIC SEVERITIES MODELS PHILOSOPHY FAILURE CONSEQUENCES EXPERIENCE PERFORMANCE REQUIREMENTS TEST SEQUENCES TEST METHODS ENVIRONMENTAL DATA GROUPING IN ENVIRONMENTAL CLASSES ENVIRONMENTAL TEST SPECIFICATION DEFINITIONS OF APPLICATIONS Figure 1: Outline for the preparation of the test specification ETSI ETSI TR 100 035 V2.1.2 (2004-02) 10 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4 Environmental description | |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.1 General | In this context environmental conditions are limited to the physical and chemical conditions to which equipment is subjected at a certain time for (more or less) well-defined locations and applications. Physical and chemical conditions should be considered in a very broad sense. They cover not only the two main areas - climatic and mechanical conditions - but also borderline and transitional areas, e.g. biological and chemical conditions as well. The environmental conditions comprise those conditions appearing in nature as well as "artificial" conditions. The "artificial" conditions may be of a favourable nature, e.g. a house being heated during the winter, but they may also be of an unfavourable nature, e.g. thermal influence from the equipment itself or from other equipment. Typical environmental conditions usually have simple names, such as "outdoors", "in a car". However, such "typical" conditions involve numerous environmental factors (parameters) apparently varying at random in strength (severity) and having complex interactions. These factors determine the actual influence of the environment on the relevant equipment. As a result, only those parameters having a significant effect on the equipment are considered. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.2 Purpose of classification | The main purpose of environmental classes is to establish a number of "standardized" and operational frames of reference for a wide range of applications of (telecommunications) equipment. These classes cover use, transportation, etc. in typical environmental conditions. The classification system arose out of the difficulty of describing environmental conditions in detail and the even greater difficulty of applying the results in practice. Until recently the only tools were some specific tests covering a few environmental effects. The introduction of the concept of environmental classes provides a more powerful approach. The environmental classes cover: • environmental requirements prescribed for the equipment; • resistibility requirements imposed on the equipment (important for the designer and for forming a basis for testing); • emission requirements imposed on the equipment which, in certain situations (e.g. heat dissipation) may need restricting, such that the effect on the original environment is "negligible". NOTE: "negligible" in this context means that conditions defined by the environmental class still remain valid. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.3 Classes | An environmental class is a systematic representation of the environment for a family of locations with "similar properties". This means that the detailed description of the class may be envisaged as an envelope around a group of related environmental conditions. The class itself may not be considered directly as a typical example. A class is composed of the most significant single factors, termed environmental parameters, selected from those factors which may be assumed to influence equipment performance. Severities and other characteristics are appended to the parameters to specify the class (see clauses 4.4 and 4.5). ETSI ETSI TR 100 035 V2.1.2 (2004-02) 11 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.4 Parameters | Environmental parameters represent those physical or chemical properties of an environment which can be distinguished and specified in relatively simple terms. In many instances additional detail parameters should be stated in order to make the specification unambiguous. Table 1 shows typical examples of parameters with their related detail parameters covering both climatic and mechanical conditions. Most detail parameters are quantified by their characteristic severity (see clause 4.5). In a few instances the parameter itself may be qualitatively expressed (e.g. "conditions of condensation"), with the "value" "yes" or "no" and without further details (considered as a characteristic). However, the fact that these conditions may occur should be reflected in both the design phase and the test procedure. Table 1: Examples of environmental parameters and related detail parameters with corresponding characteristics marked with a * or characteristic severities for a class A: Climatic conditions: Humidity Environmental parameter Parameter Detail parameter Characteristics * or characteristic severity for a class Unit High 100 % RH Low 10 % RH Relative humidity Condensation * Yes * B: Mechanical conditions: Vibration Environmental parameter Parameter Detail parameter Characteristics * or characteristic severity for a class Unit Displacement 3,5 mm Acceleration 10 m/s² Vibration, sinusoidal Frequency 2 - 9 9 - 150 Hz |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.5 Severities | The severity of a parameter, or detail parameter, is generally the quantitative measure of the stress introduced by the parameter involved. It may be stated as magnitude, rate or duration. A practical example shows some fundamental aspects concerning the concept of severity. The example considers the climatic parameter "outdoor air temperature" for a defined geographical area. The statistical distribution of the observed temperatures is shown as a histogram in figure 2, where the dashed curve is an approximation to a continuous distribution. The distribution appears to have two peaks and has extremes of about -15°C and +30°C. Considering the definition of severity as a measure of the stress, the parameter "outdoor air temperature" is split into two parameters: • low air temperature; and • high air temperature. This is because either may induce its own stress with its own consequential failure mechanisms on the equipment. The parameters "low air temperature" and "high air temperature" are shown in figure 3. Both show increasing stress and correct fractiles to the right. The values to the left are not defined because they are not relevant. The characteristic severity can thereby comply with the definition that this severity (i.e. the stress) is rarely exceeded. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 12 -15 -10 -5 0 +5 +25 +20 +15 +10 +30 RELATIVE DURATION PER YEAR % 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 TEMPERATURE °C Figure 2: Distribution of outdoor temperature Tu 23,4 °C -10 -5 0 +5 +25 +20 +15 +10 °C +30 20 18 16 14 12 10 8 6 4 2 Severity Stress RELATIVE DURATION PER YEAR % 3(a) HIGH TEMPERATURE (Tu IS THE UPPER CHARACTERISTIC SEVERITY TEMPERATURE) Tl –9,3 °C +10 +5 0 -5 -25 -20 -15 -10 °C -30 20 18 16 14 12 10 8 6 4 2 Severity Stress RELATIVE DURATION PER YEAR % 3(b) LOW TEMPERATURE (Tl IS THE LOWER CHARACTERISTIC SEVERITY TEMPERATURE) Figure 3: Separated distributions of outdoor air temperature showing the boundary value of the upper (Tu) and the lower (Tl) characteristic temperature ETSI ETSI TR 100 035 V2.1.2 (2004-02) 13 Figure 3(a) shows the right-hand - i.e. high temperature - side of the distribution shown in figure 2. The shaded portion of figure 3(a) represents 1 % of the total area under the curve of figure 2 and has been calculated by numerical integration. The left-hand vertical edge of the shaded portion intersects the temperature axis at temperature Tu. The temperature Tu represents the boundary value, for a given distribution, which is acceptable as an upper characteristic severity (in the example shown in figure 3(a), Tu = 23,4°C. Depending upon circumstances a higher severity temperature value may be appropriate, see also figure 8). Figure 3(b) is a mirror-image of the left-hand - i.e. low temperature - side of the distribution shown in figure 2 (the mirror-image allows severity to be shown increasing in value to the right as in figure 3(a)). In figure 3(b) the left-hand vertical edge of the 1 % shaded portion intersects the temperature axis at temperature Tl. The temperature Tl represents the boundary value for a given distribution, which is acceptable as a lower characteristic severity (in the example shown in figure 3(b) Tl = -9,3°C. Depending upon circumstances a lower severity temperature value may be appropriate, see also figure 8). Most other climatic parameters (with the exception of humidity), and all mechanical parameters, induce low stress at low levels. Hence one distribution defines both high and low extremes as shown below. The severity stated for the relevant detail parameters in a class is designated the characteristic severity. This is (in principle) to be considered as an extreme point of the statistical severity distribution for each parameter. The probability of exceeding the characteristic severity is normally (very) low. This is illustrated in figure 4. The above principles of statistical distribution shall be applied when interpreting the climatograms of EN 300 019-1 [4]. The type of distribution curves to be applied is under discussion. CUMULATIVE PROBABILITY OF OCCURRENCE 100 % SEVERITY 99 % 50 % 50 % 99 % FRACTILES 100 % (0 %) CHARACTERISTIC SEVERITY PROBABILITY OF OCCURRENCE (Probability density) 1 % SEVERITY Figure 4: Schematic example showing the occurrence of the severity of a parameter (e.g. level of aggressive pollutant) The characteristic severity represents a degree of severity which is rarely exceeded (often with a probability of less than 1 %). Occurrence refers to time or relevant (geographical) locations. It is important to note that the characteristic severity, although an extreme, may be exceeded from time to time or from place to place. Depending on the equipment this fact should be considered in the test procedure. Thus the characteristic severity determines the resistibility requirements on the equipment and forms the basis for the test specification. The characteristic severity also applies to the requirement on the environment according to the class. Furthermore, the characteristic severity forms the basis for the requirement on the maximum permissible emission. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.6 Limitations and considerations | It must be emphasized that the description of environmental conditions by means of environmental classes provides only simplified models of reality. This affects primarily: • the application of classes and severities; and • the simultaneous occurrence of parameters. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 14 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.6.1 Application | The stated classes apply only to a limited number of "standard" environments and hence "special" conditions are not directly covered. For such conditions new classes may be established - preferably by the modification, or combination, of existing classes. The temptation to apply a very severe standard class should be avoided as it risks over specifying some of the parameters. The characteristic severities stated for a class define the "maximum" short-term stresses on the equipment. However, the severities do not give any information about the long-term (total) stresses on the equipment. These are important for reliability and life/endurance assessments. If these total stresses are to be considered then a better knowledge of the complete distribution is needed. This aspect is covered in more detail in clause 6.5 of the present document. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 4.6.2 Simultaneous occurrence | The parameters of a class are stated individually. But in practice the equipment will be exposed simultaneously to a large number of parameters of varying severities. Some of the parameters are statistically independent, e.g. (normally) vibration and temperature. In such instances the probability that both parameters simultaneously exhibit their extreme severities is very low. If, for example, the probability of exceeding the characteristic severity is 1 % for both parameters, then the probability is only 0,01 % that both severities occur simultaneously. In the case of independent parameters it is reasonable to test individually the effect of each parameter at high severity. Although two parameters might be statistically independent, another aspect occurs if their physical effects on the equipment are dependent. This means that their effects cannot just be superimposed if the parameters are occurring simultaneously. A typical example is the correlation between vibration and temperature where most materials exhibit low fatigue strength during conditions of simultaneous vibration and low temperature. Such phenomena shall be considered during design and, if necessary, shall be reflected in the test procedure. Some pairs of parameters, e.g. temperature and relative humidity, solar radiation and high temperature, are (strongly) dependent. This means that in such instances extremes may (often) occur simultaneously. Such conditions cannot be deduced directly from the specification for the class. However, the corresponding test specification shall reflect the mechanism, e.g. by stating higher test severities than the characteristic ones. Generally the physical influences of environmental conditions on equipment may be the result of a number of parameters. This shall be considered during design. An important example is the surface temperature of equipment which results from a combination of: • surrounding air temperature; • solar radiation; and • heat radiation from other nearby equipment, heating elements and possibly spotlights. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 5 Equipment properties | So far the environments have been treated without too much reference to the equipment which is located in the relevant environment. In order to make an approach to the test philosophy some properties of the equipment need defining. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 5.1 Resistibility and performance | Environmental resistibility is the capability of an equipment to endure, or resist, a relevant environment for a short period of time. This means that the equipment shall be able to fulfil certain performance requirements when or after it is exposed to one or more specific environmental influences. The influence is determined by the severities and the duration of the test. Performance requirements should be understood in a very broad sense. It may, for example, be a requirement for a surface just to "look nice". Another requirement may be that the equipment should fulfil all specified technical functions. A third requirement may be that the equipment should be capable of surviving. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 15 To systematize the relationship between performance requirements and environmental stresses, it may be appropriate to grade the performance requirements against increasing severity of the environmental test conditions in the following way: • normal performance: all specified performance and functional requirements shall be fulfilled, including given tolerances; • reduced performance: all specified primary function requirements shall be fulfilled, possibly with wider margins (primary functions are essential properties which are significant during the use of the equipment); • specified secondary functions are not required to be fulfilled (secondary functions are properties which facilitate/improve the use of the equipment); • intermittent function, which is considered as a functional failure often of short duration. Normal performance is required after recovery from the severe environmental exposure; • cessation of function, which is considered as an irreversible failure, is acceptable under very severe environmental exposure. The equipment is required not to cause any damage to its surroundings, including to other equipment. There is no requirement for the equipment to resume normal performance. The proper use of the different performance requirements is discussed in clause 6.2.2. Sometimes it may be difficult for the specification writer to distinguish between primary and secondary functions. A general rule is that the user cannot dispense with the primary functions without the equipment, or the whole system, being jeopardized. All other functions are secondary. Generally the purpose of introducing "reduced performance" is to see what happens when the environmental conditions occasionally become very severe (e.g. exceeding the characteristic severity). Hence an expensive overspecification requiring normal performance may be avoided. Table 2 shows, as an example, some primary and secondary functions of a telephone set, including some normal performance requirements. Table 2: Example of specification of some suggested primary and secondary functions of a telephone set Performance Function category Equipment characteristic Normal Reduced Send reference equivalent tolerance ±2,5 dB ±5 dB Primary Multi frequency tone signalling tolerance ±5 dB Dialled number Yes Secondary Loudspeaker distortion < 5 % |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 5.2 Failure consequences | Obviously different kinds of telecommunications equipment are not all equally important and hence the significance of proper function and the failure consequences may vary considerably. Within the field of environmental engineering, just as within reliability, failure consequences may range from negligible to catastrophic depending upon the nature and application of the equipment. Important failure consequences may be: • loss of life and limb and other catastrophic situations (all beyond the present scope); • loss of service, e.g. failing alarms; • loss of equipment, e.g. destruction; • loss of revenue, e.g. charges for calls; • loss of reputation, e.g. public criticism; and • expenses, e.g. for repair and modifications. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 16 In order to make failure consequences an operational concept of testing, three degrees of failure consequences are introduced: • moderate failure consequences, which apply to common subscriber installations and equipment, e.g. telephone sets; • severe failure consequences, which apply to essential centralized equipment and to equipment of a system security nature, e.g. central processors and alarm equipment; and • minor failure consequences, which apply to equipment having the characteristic of auxiliary facilities, or where alternative equipment is available, e.g. automatic diallers. Failure consequences shall be taken into account when selecting test severities. The proper use of the three grades of "failure consequences" in relation to the different "performance" requirements is discussed in clause 6.2.2. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 5.3 Emission | Equipment is influenced by the ambient environment, as discussed under environmental resistibility. However, in many instances the equipment will also influence the environment by producing emissions. This means that (in principle) the environmental conditions are changed from what they were before the equipment was brought into service at the location. Emission from the equipment may be: • acoustic noise; • dissipated heat; • mechanical vibration. These emissions raise problems regarding both the specification of and the actual interference to the original environment. The first step to solving these problems is to consider that the emission shall be so limited that the interference to the environment is negligible. This does not necessarily mean that the original conditions shall be unchanged, but that the conditions still remain within the original environmental class, as specified by the characteristic severity. Thus the emission requirements keep the environment within the class boundaries. A second approach considers the problems when the emission is so large that it becomes impossible for the environment to remain within the original class boundaries. In this instance a solution may be to introduce: • separate protection, e.g. shields, filters, or shock absorbers at the location; or • elimination, e.g. a cooling or ventilation system, at the location. In such instances co-operation between manufacturer and end-user is usually needed. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 5.4 Protection | Protection of the equipment environment is an important measure acting in two directions: • it protects the equipment from the surrounding environment by tempering the inside environment (e.g. cover, lightning arrester, filter, shock absorber); and • it protects the environment from emissions from the equipment by suppressing those emissions (e.g. electromagnetic shield, filter, acoustic damping). It is important to notice that all protection defines an interface between two environments with differing conditions. This shall be considered when specifying the equipment requirements and the test conditions by stating to which class the equipment belongs both with and without protection. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 17 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6 Environmental testing | |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.1 Purpose and philosophy | As mentioned in clause 4, environmental classes are one "tool" relating to the specification of resistibility requirements. It must be realized, however, that this "tool" is not particularly useful as far as the verification of resistibility is concerned. Thus another "tool" is needed to prove - or more precisely to render it possible - that the equipment can meet the requirements. Environmental testing is such a "tool". The purpose of testing is to demonstrate that equipment, under defined environmental conditions, can: • survive without irreversible failure; and • perform according to requirements. This means in fact that the test shall demonstrate the potential failure mechanism of equipment. Or more clearly expressed, the test shall attempt to produce the effects of the environment, which is generally far from reproducing the real environment itself. This philosophy is fundamental to the design of most of the testing methods. Examples 1 to 3 below illustrate this philosophy. Generally environmental tests are carried out as laboratory tests. In certain instances the tests may also utilize defined field conditions. However, an approach of trying to let a laboratory test reproduce the real environmental conditions is generally not feasible. EXAMPLE 1: High temperature: A high temperature test on a heat dissipating item of equipment is designed to produce the thermal effect of subjecting it to: - high air temperature; - solar radiation; - heat radiation from nearby sources, etc. Thus the test temperature will be substantially higher than just the ordinary room temperature (see clause 4.6.2). EXAMPLE 2: Shocks: In a shock test an item of equipment is subjected to a simple, half-sine shaped pulse, although the actual conditions are not that simple. To attempt to produce the same mechanical stresses requires a comparison of the two shock spectra. EXAMPLE 3: Moisture: In practice the relative humidity varies within such wide limits and in a manner so complicated that to attempt to reproduce the actual humidity conditions is unrealistic. Instead the preference is to produce - by means of different damp heat test methods - a number of failure mechanisms that may be caused by humidity, e.g.: - Humidity absorption by testing at constant high temperature and high humidity (damp heat, steady state); - Chemical and galvanic corrosion and moisture accumulation by testing in cyclically varying humidity where condensation occurs (damp heat, cyclic). None of the damp heat exposures mentioned above resemble realistic environmental conditions, although their effects try to reflect real conditions. Very often the environmental tests required, for instance by the customer, can be considered as a part of a type qualification approval which is normally a "go, no-go" test. Environmental testing, however, is not confined to this application. During the development phase particularly, environmental testing is a powerful tool both in evaluation and analytical programmes considering, for example, safety margins and comparison between designs and materials. In particular, testing with increasing severity ("step stress"), produces very useful information. Figure 5 shows a general outline of the different purposes, applications, test methods and evaluation principles for environmental testing. In the present document only resistibility tests undertaken as a part of qualification approval have been considered. These aspects have been highlighted. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 18 Endurability and reliability tests are discussed in clause 6.5. Storage Exclusion Selection Comparison Weak Point Safety Factor Objective Approval Non operational: Handling etc. Transporta- tion Operational: Application/ Function Reliability Test Endurability (Life) Test Functional Check Environmental Climatic Mechanical Biological Method Mono Sequence Composite Combined Severity/ Stress level Realistic Accelerated Step-Stress Marginal Selected Evaluation Go, No-Go Trial Statistical Analysis Trend Extrapolation Product Specified Failure Analysis ENVIRONMENTAL TESTING Figure 5: Outline of environmental testing applications |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.2 Transformation from class to test | International and national standards for environmental testing procedures were established long ago. Recently, proposed standards for environmental classifications have been prepared. However, despite great demand, the transformation from class to test has not yet been defined internationally. The principle reason is that the transformation can never operate universally. This is because the transformation largely depends on: • the type of equipment; • the mode of operation; • the significance of proper operation (failure consequences). Some of these aspects have already been considered and will be used together with the "stress-strength" model as elements in the following ETSI transformation proposal. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 19 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.2.1 Stress - strength | For equipment used in applications where failures have severe consequences tests are often carried out with severities which are a little greater than those stated in the environmental class. The reason for this may be briefly described with reference to the so-called stress-strength model. EQUIPMENT STRENGTH PROBABILITY OF OCCURRENCE S SEVERITY ENVIRONMENTAL STRESS 1 2 S Figure 6: Stress-strength curves for an equipment with a reasonable safety margin It appears that there is no influence on the test result whether the test is carried out at the characteristic severity S1 or at the maximum severity S2. In figure 6 the curve on the left shows the probability (probability density) of occurrence (rate or relative duration) for an environmental parameter versus the severity. Point S1 indicates the characteristic value usually about the 1 % (99 %) fractile for the environmental class. The curve on the right shows - for a certain type of equipment - the distribution curve for environmental resistibility. Imagine that this latter curve (normally unknown) has been produced by testing a large sample of the equipment, and that for each result the exact value of the severity has been plotted - e.g. the temperature at which the equipment fails - i.e. the functional requirements are not met. If the test severity is stated as S2 (maximum severity for the environment) it can be seen that the equipment can safely resist even the worst occurring environment within the environmental class and hence a safety margin is obtained. This means that the lower strength limit of the equipment is not close to the severities predicted for the application. This last statement should be viewed in the light of the fact that type testing is normally carried out on very few samples. This may be seen by comparing figure 6 with figure 7, but with the significant difference that figure 7 deals with less robust equipment. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 20 EQUIPMENT STRENGTH PROBABILITY OF OCCURRENCE SEVERITY ENVIRONMENTAL STRESS S S 1 2 Figure 7: Stress-strength curves for an equipment with a lower strength limit which is too low If the test is carried out at the characteristic severity S1, then apparently the exposure of weak points does not necessarily follow. However, if the test is carried out at the maximum severity S2, there would appear to be a reasonable chance of demonstrating the lack of environmental resistibility of the equipment. By testing with the severity S2 (figure 7) there is a probability that either real failures, or merely tendencies for malfunction (i.e. weak design points) will appear. The demonstration of such weak points is of great importance. This is partly because a better knowledge of the product and its application is obtained and partly because - with a small effort - improvements to exposed weaknesses are often possible. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.2.2 Failure consequences and performance | Besides what has already been mentioned about the stress-strength model, two more elements must be considered in order to state the test severity, namely: • failure consequences; and • performance requirements. As mentioned, the failure consequences may vary considerably, depending upon the kind of equipment and its application. Quite often two types of equipment may be placed at locations covered by the same environmental class. However, one type of equipment may be tested under significantly more severe conditions than the other one because of its different failure consequences. Hence two or more different test severities may apply to a certain environmental class. In most cases only "moderate" failure consequences are considered. The grading of performance requirements allows the specification of different test severities for the same type of equipment in the same class. In this way more information from the resistibility test on the equipment can be obtained as well as avoiding an expensive "worst case" test with full normal performance. Based on a schematic (and simplified) model shown in figure 8, the use of the concepts of failure consequences and performance requirements will be explained together with their interrelations. Figure 8 (upper) shows the distribution of an environmental parameter in a class (e.g. temperature) with some fractiles indicated. Figure 8 (lower) shows the different test severities on the x-axis corresponding to the class and with the three grades of failure consequences on the y-axis. For each of the three grades of performance the corresponding test severities are plotted against the failure consequences. The corresponding points are connected with symbolic lines to show the relevant performance. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 21 If figure 8 were really valid (unfortunately it is not that simple), the procedure for stating the test severities for a specific type of equipment assigned to a class would be as follows: • select the failure consequence on the y-axis; • read the corresponding test severities on the x-axis for the three grades of performance - if they are all needed. Generally only moderate failure consequences are considered with a stated test severity for normal performance. In certain instances, however, two or more test severities are stated for moderate and for minor and severe failure consequences as well. Figure 8, as a model, may nevertheless show the use of the different concepts. 10% FRACTILES PROBABILITY OF OCCURRENCE 3% 1% 0,2% 0,04% (PROBALILITY DENSITY) X SEVERITY (IN A CLASS) Y DISTRIBUTION OF AN ENVIRONMENTAL PARAMETER (E.G. TEMPERATURE) IN A CLASS INTERMITTEND FUNCTION FAILURE CONSEQUENCES X TEST SEVERITIES Y SEVERE MINOR REDUCED PERFORMANCE NORMAL PERFORMANCE MODERATE Figure 8: Schematic outline of test severities (x) corresponding to different failure consequences (y) and different grades of performances ETSI ETSI TR 100 035 V2.1.2 (2004-02) 22 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.3 Test methods | First and foremost, test methods shall, of course, be reproducible. Additionally they should also be realistic with regard to failure effect, be relatively simple and be reasonably rapid to perform. Internationally accepted methods, such as those in IEC 60068 [2], usually meet these requirements. In EN 300 019 series [4] and [5], reference has been given as far as possible to IEC Publications. Significant changes in characteristics or performance due to environmental conditions are often brought about slowly. Thus in order to make a test within a reasonable time these changes need acceleration either by increasing the test severity or by "compressing" the time, etc. Many test methods are implicit accelerated tests, such as humidity and mechanical tests, although generally, and unfortunately, these have an unknown "acceleration factor". However these aspects are important when specifying the test procedure. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.4 Environmental resistibility test | |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.4.1 Purpose and limitations | An environmental resistibility test is generally considered as being a part of a type test. The environmental resistibility test demonstrates characteristic properties of equipment regarding its capability of withstanding certain environmental conditions. These conditions are typically specified as different applications and environmental classes with specified performance requirements. The resistibility requirements shall be a part of the basic equipment specification covering all normal applications. Thus the purpose of an environmental resistibility test is to verify - or render it possible - that equipment will survive and perform as intended when it is used, stored and/or transported. An environmental resistibility test has some inherent limitations. The most important one is that the test only covers the equipment type (e.g. the design) and not the complete population. This is because a resistibility test is generally carried out on only a few specimens hence the test cannot be a "guarantee" for production lots. The test can, however, assure that the equipment, considered as a type, is capable of resisting the expected environment. Some other limitation aspects concern the operational life of the equipment. In general a resistibility test is not able to give evidence either about the reliability or the endurability of the equipment. These aspects are discussed in clause 6.5. Finally the information obtained from a resistibility test is limited, partly because of limited evaluation after exposure and partly because of the fixed test severities (e.g. no step-stress), see figure 5, clause 6.1. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.4.2 Test sequence | In order to cover the many different influences of several environmental parameters (concerning operational and non-operational conditions), a resistibility test must comprise a number of different tests. Most tests are performed in either one, or a few sequences. This means that each specific test, after a recovery period, is succeeded by the next, specific test in a relevant sequence. Such a test procedure is truly not realistic, but practical. If required two tests can be carried out immediately after each other (a composite test) or two tests can be carried out simultaneously (a combined test). The sequence of tests is important because a conclusive result to the resistibility test may depend on the test sequence. For example, the result of a final insulation test may change significantly depending on whether the test sequence is a dry heat test followed by a damp heat test or vice versa. The general rule is to choose the most severe sequence - if it is reasonably relevant - because the purpose of testing is to demonstrate the potential failure mechanisms. This rule is valid for resistibility testing. Furthermore another rule shall be considered relating to the objective of obtaining early information about failure tendencies or major failures (in order to obtain the most significant information as early as possible). In this case severe - and preferably short and cheap tests - are conducted at the beginning, while the less severe, prolonged and expensive tests are placed later in the sequence. Naturally some of these considerations and rules may be contradictory and not always applicable. If this is so then the test sequence can be based on what is most likely to occur in practice. Any test sequences suggested in the present document aim to utilize the rules mentioned. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 23 If the testing concerns investigation of a prototype during development only one or a few specimens may be available. In this situation the objective of the test sequence is to keep the specimen "alive" as long as possible in order to obtain as much information as possible before damage occurs. Hence the sequence shall start with the least severe test. |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.4.3 Environmental test programme | Complete environmental testing for a specific equipment type typically employs three environmental test specifications: • storage; • transportation; • in use. Each specification comprises several "individual" tests which can be performed in a stated order, i.e. sequence. In order to realize all the testing activities it is necessary to construct a complete environmental test programme. This programme shall be based on the relevant test specifications, and take into account other considerations and detailed information, such as: • equipment functions, properties and technologies; • available resources, time, test facilities, funds, etc.; • engineering experience and judgement; • common sense. The overall objective is to perform the complete programme in an efficient way e.g. by: • utilizing results from previous tests; • deleting needless tests; • avoiding thorough functional testing, if possible. Thus the environmental test programme requires careful and specific consideration. This means that the programme shall be prepared by the test engineer in co-operation with the engineer responsible for the equipment. Figure 9 shows the procedure and the elements for preparing a complete environmental test programme. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 24 TEST SPEC. TEST SPEC. TEST SPEC. TEST SPEC. TEST SPEC. STORAGE TRANSPORT. IN USE IMMUNITY EMISSION CLIM ./ MECH. CLIM. / MECH. CLIM. / MECH. EMC (see note) EMC (see note) TEST METHODS VARIOUS RESOUCES TEST SEQUENCES TEST ENGINEERING ENGINEERING JUDGEMENT EQUIPMENT ENGINEER RESPONSIBLE EQUIPMENT FUNCTIONS & PROPERTIES TEST PROGRAMME NOTE: EMC has been included for completeness although not within the scope of the present document. Figure 9: Outline for the preparation of a complete environmental test programme |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.5 Testing related to operational life | |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.5.1 General | So far most of the emphasis has been directed towards the performance of the equipment under extremes of environmental conditions. These cover the environmental classes as well as the tests. A natural consideration is how this emphasis is reflected in the "behaviour" of the equipment during its normal operational life (assuming that all environmental requirements are fulfilled). The conclusion is that such equipment is "debugged" in so far as environmentally induced design failures are concerned, thus avoiding problems from these possible failure effects. Thus the behaviour of the equipment has certainly been improved compared with equipment having poor environmental resistibility. In this special context this might be called improved reliability. However, it must be strongly emphasized that an environmental resistibility test - as part of a type test - must never be confused with a reliability test (see clause 6.5.2). Summarizing, it may be concluded that although an environmental resistibility test is very important, it cannot "stand alone". It is a necessary - but not a sufficient - basis to ensure that the user obtains a reliable performance from the equipment. ETSI ETSI TR 100 035 V2.1.2 (2004-02) 25 |
1f7ea7b6418174d53d51b760f9c08c93 | 100 035 | 6.5.2 Reliability | The environmental conditions have a significant effect on the reliability performance of equipment. A typical example is the component failure rate. This normally increases with increasing temperature, where the average temperature is the determining parameter. A proper reliability test is performed under defined environmental conditions. The following typical test conditions differ from a resistibility test in the following way: • many specimens are under test; • prolonged test time; • reasonably mild environmental conditions; • environmental conditions often varying in a cyclic manner; • simulation of typical use is intended; • field tests often used; • random failures are provoked. Thus there is a visibly significant difference between a resistibility test and a reliability test (see IEC 60605-3 [3]). |
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