1、BRITISH STANDARD BS 6556-1: 1985 Incorporating Amendment No. 1 Low speed digital signals for use in coal mines Part 1: Specification for optical coupling UDC 622.489:621.398.037.37:681.327.8BS6556-1:1985 This British Standard, having been prepared under the directionof the Mining and Quarrying Requi
2、sites StandardsCommittee, was published under the authority ofthe Board of BSI and comes into effect on 31January1985 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference MQE/25 Draft for comment 82/76934 DC ISBN 0 580 14179 9 Committees responsible for t
3、his British Standard The preparation of this British Standard was entrusted by the Mining and Quarrying Requisites Standards Committee (MQE/-) to Technical Committee MQE/25upon which the following bodies were represented: Association of British Mining Equipment Companies Council for Electrical Equip
4、ment for Flammable Atmospheres (BEAMA) Health and Safety Executive National Coal Board National Union of Mineworkers Amendments issued since publication Amd. No. Date of issue Comments 6204 May 1990 Indicated by a sideline in the marginBS6556-1:1985 BSI 10-1999 i Contents Page Committees responsible
5、 Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 General conventions 1 4 Data link configurations 1 5 Channel allocation 1 6 Data rate 1 7 Electrical network parameters 1 8 System performance 2 9 Cable connections 2 10 Environment 2 11 Maximum output parameters 2 12 Marking 2 13 Documenta
6、tion 3 Appendix A Cable parameters used for system performance test 6 Figure 1 Simplex operation 3 Figure 2 Duplex point-to-point operation 3 Figure 3 Multi-drop operation 4 Figure 4 Originate channel 5 Figure 5 Answer channel 5 Figure 6 Core configuration of cable 6 Publications referred to Inside
7、back coverBS6556-1:1985 ii BSI 10-1999 Foreword This Part of BS6556has been prepared under the direction of the Mining and Quarrying Requisites Standards Committee. Control and monitoring activities below ground in coal mines require the transmission of data between items of electrical equipment sup
8、plied by different manufacturers. Data can be transmitted in analogue or alternatively digital form. For analogue, BS 5754:1980 “Specification for electrical analogue and state signals for use in coal mines” was produced with the purpose of promoting compatibility between transducers, recorders, ind
9、icators and data transmission systems of different manufacture and having inputs or outputs, as appropriate, in the form of d.c. voltage analogue signals or signals derived from relay contacts or a mechanical switch. This standard deals with the digital form. A major disadvantage with control and mo
10、nitoring systems employing the direct transmission of analogue signals is that since a galvanic connection is necessary between the transmitting and receiving circuits, faults, at different points of the system, particularly to earth, can seriously affect overall performance. The avoidance of such f
11、aults, on pit-wide systems, is extremely difficult. The generation of analogue signals within high voltage switchgear, and subsequent transmission for monitoring purposes, also presents difficulty in achieving the required degree of segregation between intrinsically safe and power circuits. A furthe
12、r disadvantage with analogue signals is that the simultaneous transmission of several signals requires either a multicore cable or separate cables. These disadvantages can largely be overcome if the analogue or state information is transmitted in the form of serially coded digital signals. With such
13、 signals complete galvanic isolation between the transmitting and receiving circuits is possible and, within wide limits, only two wires are required for transmission in each direction irrespective of the volume of data. If full benefit of digital signal data transmission is to be realized it is imp
14、ortant that transmission systems of different manufacture conform to a common electrical standard and operate in a uniform manner with identical procedure (or protocol) for handling the data. This standard aims to promote such conformity. It specifies relevant requirements for a low speed digital si
15、gnal link comprising a master and one or more slaves which interconnects the intrinsically safe circuits of one item of apparatus and the intrinsically safe circuits of other apparatus in such a way that units of different manufacture can be interchangeably coupled at the transmission line terminals
16、. This standard is published in three Parts as follows: Part 1: Specification for optical coupling; Part 2: Specification for transformer coupling; Part 3: Specification for message protocols. Parts 1 and 2 of this standard offer alternative methods of achieving galvanic isolation between the intrin
17、sically safe circuits of interconnected apparatus, but the two methods are not compatible. This Part of this standard specifies a600bits/s transmission system which employs optical coupling as the means of achieving galvanic isolation. A system will comprise a master and from1to8slaves connected in
18、point-to-point or multi-drop modes, with two cable conductors being used for each direction of transmission. Transmission from the master to a slave is achieved by the master acting as a switched current source which activates a light emitter at each slave. Transmission from slave to master is achie
19、ved by the master acting as both a current source, which is switched at the slave by a light dependent device, and a current monitor which senses the switched current.BS6556-1:1985 BSI 10-1999 iii Part 2 of this standard specifies a600bits/s transmission system which employs transformer coupling as
20、the means of achieving galvanic isolation. A system will comprise a master and from1to15slaves connected in point-to-point or multi-drop modes. Transmission between master and slaves is achieved by frequency shift keying (FSK) techniques, one pair of cable conductors being used for each direction of
21、 transmission. Part 3 of this standard defines the message protocols to be used by systems complying with Parts1or2. It does not, however, place any restrictions on the application data contained in transmitted messages, although industry standards may exist to regulate this. It is envisaged that fo
22、r high voltage applications optical coupling will be employed due to the relative ease of meeting segregation requirements. The optical system, however, has a limit of8slaves and a range of2km while the transformer method has a greater range and can handle up to15slaves. For intermediate application
23、s either system may be suitable. In Parts 1 and 2 of this standard slaves are the physical interface between the transmission line and one or more addressable logical slaves specified in Part 3 of this standard. A British Standard does not purport to include all the necessary provisions of a contrac
24、t. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Attention is drawn to the Health and Safety at Work etc. Act1974, the Mines and Quarries Act1954, the Regulations made under thes
25、e Acts, and also any other appropriate statutory requirements or byelaws. These place responsibility for complying with certain specific safety requirements on the manufacturer and the user. The address of the recognized certification authority in the United Kingdom for Group1(coal mining) apparatus
26、 for intrinsic safety purposes is as follows: Health and Safety Executive HSE (M) Certification Support Unit Harpur Hill, Buxton, Derbyshire SK179JN. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to6, an inside back cover and a back cover. This s
27、tandard 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.iv blankBS6556-1:1985 BSI 10-1999 1 1 Scope This Part of BS6556specifies the electrical input and output characteristics for the optical cou
28、pling of intrinsically safe transmitting and receiving circuits for use in coal mines. These form a low speed digital data transmission link in which data is transmitted using current loop techniques. A data transmission system comprises a master and up to eight physical slaves so arranged that the
29、transmission line is energized only from the master and galvanic isolation is achieved by optical coupling at each slave. NOTE 1Each physical slave may support more than one addressable logical slave as specified in Part3of this standard up to a maximum of15addressable slaves for the complete system
30、. This Part of BS6556only applies to apparatus where the circuits connected to the transmission lines are designed to be intrinsically safe in accordance with BS1259, BS5501-7or BS5501-9as appropriate. NOTE 2 Where apparatus, which is intended to be used in potentially explosive atmospheres, contain
31、s other circuits which are not intrinsically safe, those circuits will have to be given an alternative form of protection in accordance with BS229, BS4683or BS5501as appropriate. NOTE 3 The titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For
32、 the purposes of this Part of BS6556the following definitions apply. 2.1 duplex the transmission of data simultaneously in opposite directions through a system 2.2 simplex the transmission of data in one direction only 2.3 bit the element of digital information taking the value1or0 2.4 binary having
33、 only two states (of numbers). A system of numbering where each digit has only two possible values,0or1 2.5 channel a circuit carrying information in one direction 2.6 current loop a transmission technique where the presence or absence of current represents binary data 3 General conventions The foll
34、owing conventions shall apply: a) space = value 0 = current flow = start; b) mark = value 1 = no current flow = idle. 4 Data link configurations The data link shall allow data to be transmitted between a master and up to8slaves. The master and slaves shall be interconnected to form data links in the
35、 following ways: a) point-to-point simplex using a single twisted pair transmission line (see Figure 1); b) point-to-point duplex using a four-wire transmission line (see Figure 2); c) multi-drop duplex using a four-wire transmission line with up to8slaves (see Figure 3). 5 Channel allocation Transm
36、ission from master to slave shall be via the originate channel. Transmission from slave to master shall be via the answer channel (see Figure 1 and Figure 2). For multi-drop operation the channel allocation shall be the same but with multiple slaves (see Figure 3). 6 Data rate The data rate shall be
37、600bits/s 0.1%. 7 Electrical network parameters 7.1 General Data shall be transmitted by means of current switching. The transmission lines shall be energized from the master only. Galvanic isolation shall be achieved by optical means at each slave. The common lines of the originate and answer chann
38、els shall be connected together at the master. 7.2 Originate channel (see Figure 4) 7.2.1 Master transmitter. The master transmitter shall take the form of a switched source of current connected to the transmission line. The maximum open circuit voltage at the output terminals of the transmitter sha
39、ll not exceed+12V. The transmitter shall be capable of producing25mA minimum into a2607 resistive load.BS6556-1:1985 2 BSI 10-1999 The mark condition current shall be less than2504A into a1.2k7 resistive load. The transmitter shall have a slew rate of20mV/4s 10%between10% and90% levels across2607. 7
40、.2.2 Slave receiver. The slave receiver shall monitor the transmission line current. The transmission line side of the optical link shall be a current limited light emitter. The receiver input current shall be between2.5mA and3mA at+4.5V and a current of2.5mA or greater shall be recognized as a spac
41、e condition. In this condition the receive circuit shall have an active impedance greater than12007. A receiver current of less than1mA shall be recognized as a mark condition. 7.3 Answer channel (see Figure 5) 7.3.1 Master receiver. The master receiver shall supply and monitor the transmission line
42、 current. The master receiver shall present an impedance to the line of between1507 and2507. The open circuit voltage at the input terminals of the receiver shall not exceed+10V. The master receiver shall recognize any current in excess of5mA as a space condition and any current less than4mA as a ma
43、rk condition. The master receiver shall be capable of delivering a minimum of10mA into an external resistive load of2207. When the receiver line terminals are short circuited the resulting current shall not exceed40mA. 7.3.2 Slave transmitter. The slave transmitter shall switch the transmission line
44、 current. In the space condition the slave terminal voltage shall be less than1.5V when sinking6mA. The leakage current in the mark condition shall not exceed2504A with+10V applied at the line terminals. 8 System performance Master and slaves shall be capable of operating on a data link configuratio
45、n comprising8slaves on a single cable at a distance of2km from the master, using cable as specified in Appendix A, with zero bit errors over a test period of2h. 9 Cable connections The cable connections shall be designed to allow the electrical continuity of the armouring or screens to be maintained
46、. 10 Environment The equipment shall be able to operate within an ambient temperature range of 5 C to+40 C in humidity up to95% normally not condensing. Other environmental conditions of temperature and humidity may be specified by agreement between supplier and purchaser and shall be deemed to comp
47、ly with this standard, provided that the requirements of all other clauses are met and that the agreed conditions shall be so marked on the equipment. NOTECondensation may form when, for example, the equipment is first installed and this should not permanently affect the operation of the equipment.
48、11 Maximum output parameters The maximum output parameters and limiting characteristics measured at the line terminals under the fault conditions of clause4 of BS5501-7:1977for category “ia” apparatus shall be: a) for the combined outputs of the masters transmitting and receiving circuits: V oc= 17
49、V; l sc= 200 mA; C eq= 100 nF; L eq= 0 b) for the slave: V oc= 0; l sc= 0; C eq= 100 nF; L eq= 0 where 12 Marking In addition to any marking required by a certifying authority, apparatus having input or output circuits complying with this standard shall be marked externally with the number and date of this standard, i.e. BS6556-1:1985 1)and “MASTER” or “SLAVE” as appropriate. V oc is open circuit voltage; l sc is short circuit current; C eq is equivalent capacitance; L eq is equivalent inductance. 1) Marking BS 6556-1:1985on or in relation to a product is
