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1、BRITISH STANDARD AEROSPACE SERIES BS G 242:1989 Specification for Data bus interconnecting systems Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 242:1989 This British Standard, having been prepared under
2、 the direction of the Aerospace Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 31 October 1989 BSI 01-2000 The following BSI references relate to the work on this standard: Committee reference ACE/6 Draft for comment 86/72596 DC ISBN 0 580
3、17108 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Aerospace Standards Policy Committee (ACE/-) to Technical Committee ACE/6, upon which the following bodies were represented: British Airways BEAMA Ltd. British Cable Makers Confeder
4、ation British Rubber Manufacturers Association Civil Aviation Authority Electronic Components Industry Federation Ministry of Defence National Supervising Inspectorate Society of British Aerospace Companies Limited Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: Lond
5、on South Bank University, London South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 242:1989 BSI 01-2000i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2Definitions1 3Cable1 4Coupling1 5Couplers3 6Connectors4 7Terminators4 8Splices4
6、 Appendix A Surface transfer impedance measurement5 Appendix B Data bus cable, dimensions and performance7 Appendix C Transformer waveform integrity: droop test11 Appendix D Concentric trinax removable contacts: intermateability dimensions11 Figure 1 Data bus interface using direct coupling for type
7、 A or type B systems2 Figure 2 Data bus interface using transformer coupling for type B systems3 Figure 3 Surface transfer impedance test fixture for testing cable screens and cables containing splices6 Figure 4 Ancillary test fixture for measuring surface transfer impedance of mated connectors6 Fig
8、ure 5 Ancillary test fixture for measuring surface transfer impedance of coupler housing7 Figure 6 Typical construction details for data bus cable optimized single screen, multiplex, for type A systems8 Figure 7 Typical construction details for data bus cable optimized double screen, multiplex, for
9、type B systems9 Figure 8 Typical construction details for data bus cable superscreened, multiplex, for type B systems10 Figure 9 Coupling transformer11 Figure 10 Intermateability dimensions for size 8 male contacts11 Figure 11 Intermateability dimensions for size 8 female contacts12 Figure 12 Interm
10、ateability dimensions for size 10 male contacts12 Figure 13 Intermateability dimensions for size 10 female contacts13 Publications referred toInside back cover Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS
11、 G 242:1989 ii BSI 01-2000 Foreword This British Standard, having been prepared under the direction of the Aerospace Standards Policy Committee, gives guidance on the interconnection of data bus systems of all types used on aircraft, either civil or military. The data bus systems have been divided i
12、nto type A and type B. Type A is intended to comply with the general requirements of ARINC 429, which is usually called up for civil aircraft. Type B will comply with the appropriate requirements of Def. Stan. 00-18 and/or MIL-STD-1553 B, which are generally the requirements for military systems. A
13、British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a
14、front cover, an inside front cover, pages i and ii, pages 1 to 14, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South
15、 Bank University, London South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 242:1989 BSI 01-20001 1 Scope This British Standard establishes requirements for data bus interconnecting systems for aerospace applications. It defines the characteristics of the data
16、 bus line and components up to the interface with electronic components of the system. Digital data transmission systems fall basically into two categories working at data rates either above or below 100 kilobits/second. The electrical requirements of the components of the transmission systems in th
17、ese categories are different and the categories are classified in this standard as follows: type A systems, operating at rates of 100 kilobits/second or less; type B systems, operating at rates greater than 100 kilobits/second. NOTEThe titles of the publications referred to in this standard are list
18、ed on the inside back cover. 2 Definitions For the purposes of this British Standard the definitions given in BS 9520 apply. 3 Cable 3.1 The cable used for the mains bus and all stubs shall be a two-conductor screened and jacketed twisted pair having a mutual capacitance not exceeding 98.4 pF/m at a
19、 frequency of 1 kHz. The cable specification used shall include requirements for insulation and screening efficiency. 3.2 The cable shall be formed with not less than 13 twists per metre, where a twist is defined as a 360 rotation of the wire pair. 3.3 The nominal characteristic impedance (Z0) of ca
20、bles for type A and type B systems shall be 77 7. When measured at a frequency of 1 MHz, the impedance shall be 77 7 7 for type A systems and 77 3 7 for type B systems. 3.4 The cable attenuation shall not exceed 4.92 dB per 100 m at a frequency of 1.0 MHz. 3.5 The effectiveness of the cable screenin
21、g shall be determined by measuring the surface transfer impedance (Zt) at a frequency of 30 MHz. Zt shall be not greater than 100 m7/m, at a frequency of 30 MHz unless a higher screening efficiency is called for in the detail specification. NOTE 1A typical method for the determination of surface tra
22、nsfer impedance is given in Appendix A and may be used pending publication of a definitive method which is under consideration. NOTE 2See Appendix B for typical cable constructions. 3.6 Cable classed as suitable for air frame use shall satisfy the electrical performance characteristics of this stand
23、ard and shall be suitable for use in the temperature ranges 65 C to 135 C, 65 C to 150 C, 65 C to 200 C, or 65 C to 260 C. The physical dimensions of these cables and their performance shall be as given in Appendix B and shall be in accordance with the appropriate test requirements of BS G 230. 3.7
24、The two ends of the data bus line shall be terminated with a resistance equal to the nominal characteristic impedance (Z0) 2 % (see clause 7). The termination shall be screened and the effectiveness of the screening shall be determined by measuring Zt, which shall be not greater than 10 m7 at 30 MHz
25、 for use on type A or type B systems. 4 Coupling 4.1 Cable stub connections for type A systems 4.1.1 Cable stub connections for type A systems shall be direct, as shown in Figure 1, and shall not exceed 0.3 m in length. 4.1.2 The electrical connections of the conductors of the stub to those of the b
26、us shall be soldered in accordance with an acceptable quality standard, or crimped, in which case the connections shall comply with the applicable performance requirements of BS 4G 178-1. 4.1.3 The screening of the connection shall be continuous and provide 360 coverage. The effectiveness of screeni
27、ng of the stub connection shall be determined by measurement of the surface transfer impedance (Zt) of an assembly at a frequency of 30 MHz. Zt shall be not greater than 100 m7/m for type A systems and 10 m7/m for type B systems. 4.2 Cable stub connections for type B systems Cable stub connections f
28、or type B systems shall be as shown in Figure 2. Transformer coupled stubs (see Figure 2) shall be as short as practicable and shall not exceed 6.1 m in length. NOTEThe distance between stubs and their lengths may have to be adjusted so as to avoid digital errors arising from spurious pulse reflecti
29、ons. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 242:1989 2 BSI 01-2000 Figure 1 Data bus interface using direct coupling for type A or type B systems Licensed Copy: London South Bank University, Londo
30、n South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 242:1989 BSI 01-20003 5 Couplers 5.1 No resistors or transformers shall be used in type A systems. 5.2 For type B systems, couplers shall consist of a coupling transformer and two fault isolation resistors c
31、ontained within a screened, environmentally sealed and corrosion resistant enclosure. NOTEThe enclosure may contain more than one coupling transformer and associated resistors. When an enclosure contains more than one coupling transformer particular attention should be paid to the stub lengths (see
32、4.2). Couplers may be connected to the data bus and stubs with connectors or may be provided with cables installed during manufacture. These may be connected to the system with permanent splices, as specified in clause 8. 5.3 The screening effectiveness of the enclosure shall be determined by measur
33、ing the surface transfer impedance (Zt) at 30 MHz of a length of data bus cable connected to the enclosure. Zt at 30 MHz for the assembly shall be not greater than 10 m7 plus 10 m7/m for the length of cable used. 5.4 The transformer in the coupler shall comply with the following requirements: a) tur
34、ns ratio: 1.41 to 1, 3 %; b) input impedance: 3 k7 minimum (75 kHz to 1.0 MHz) measured with a 1 V r.m.s. sine wave; c) droop: 20 % maximum (250 kHz), measured in accordance with Appendix C; d) overshoot and ringing: 1.0 V peak (250 kHz square wave, 27 V peak to peak with 100 ns maximum rise and fal
35、l time); e) common mode rejection: greater than 45.0 dB at 1.0 MHz measured with a 10 V r.m.s. sine wave input; f) fault protection: resistors in series with each connection equal to 0.75 Zo 2 % 7; Figure 2 Data bus interface using transformer coupling for type B systems Licensed Copy: London South
36、Bank University, London South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 242:1989 4 BSI 01-2000 g) transformer leakage inductance: not greater than 5 4H measured with 1 V r.m.s. sine wave at 1 MHz. NOTECare should be taken to ensure that couplers incorporati
37、ng transformers are not installed in areas subject to upper temperatures in excess of their capabilities as declared. 6 Connectors 6.1 Connectors 6.1.1 Connectors shall comply with the applicable requirements of BS G 202. 6.1.2 Inserts of single cavity and multicavity connectors employing concentric
38、 twinax contacts shall be of one of two types: a) those retaining the isolation of the screens of the concentric twinax contacts; b) those earthing to connector shell the screen of the concentric twinax contacts. 6.1.3 Connectors shall maintain 360 screening and continuity of screening over their en
39、tire length. 6.1.4 The effectiveness of screening shall be determined by measuring the surface transfer impedance (Zt) at 30 MHz. Zt shall not exceed 100 m7 for type A systems and 10 m7 for type B systems. 6.1.5 The connector shall be capable of operating within the preferred temperature range 65 C
40、to 135 C, 65 C to 150 C, 65 C to 200 C, or 65 C to 260 C. 6.2 Contacts Contacts shall comply with BS 9521. NOTEPreferred contact interface dimensions should be as given in Appendix D for sizes 8 and 10. 7 Terminators A terminator shall be a self-contained device for terminating each end of the data
41、bus line as required by 3.7. It shall take the form of a screened housing containing the necessary resistor and shall be joined to the data bus line by means of a connector or permanent splice (see clause 8). 8 Splices 8.1 Splices, incline or multiple, shall comply with BS G 180. 8.2 Splices in the
42、cable shall maintain 360 screening and continuity of the screen over the entire length of the splice. 8.3 The effectiveness of screening shall be determined by measuring the surface transfer impedance (Zt) at 30 MHz of a length of data bus cable containing a splice. Zt at 30 MHz shall not increase b
43、y more than 5.0 % when compared with the parent cable. 8.4 The impedance mismatch at the splice, as measured on a time domain reflectometer, shall not exceed the tolerance allowable for the characteristic impedance of the cable (Zo) given in 3.3. 8.5 The completed splice shall be fully insulated and
44、 environmentally sealed. After being subjected to the immersion (low air density) test given in clause 10 of BS 5772-7:1981 at 4 kPa the measured insulation resistance shall be not less than 1 000 M7. 8.6 The splice shall be capable of operating within the same temperature range as the cable. Licens
45、ed Copy: London South Bank University, London South Bank University, Sat Dec 09 02:31:31 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 242:1989 BSI 01-20005 Appendix A Surface transfer impedance measurement A.1 General The method is generally in accordance with IEC Publication 96, except that some
46、 changes have been made to the apparatus to allow irregularly shaped components to be tested. A.2 Apparatus A.2.1 General. IEC Publication 96 describes a coaxial arrangement for testing cable screens. This is satisfactory for rigid cables but not always for flexible cable where sagging of the cable
47、can cause difficulty in achieving reproducible measurements. It is not possible to test irregularly shaped components exactly as given in IEC Publication 96. Modifications of the apparatus to accommodate all anticipated types of components are described in A.2.2 to A.2.4. A.2.2 Cables and splices. T
48、he outer coaxial tube used as a circuit drive line is dispensed with and replaced by a length of tinned copper braid drawn down onto the cable jacket. The braid accommodates varying cross sections, e.g. splices in the cable, and also minimizes problems caused by flexible cables sagging inside a coax
49、ial tube which can cause difficulties in achieving reproducible results. When measurements are being taken on a cable sample, it should be kept as straight as possible as bending may give inconsistent results. The test fixture for testing cable screens and cables containing splices is shown in Figure 3. A.2.3 Connectors. Each half of a mating pair of connectors, complete with contacts, is mounted by use of suitable adaptors on a copper extension tube. Each connector has a length of cable connected to
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