1、 CEN EN*IS0*655L 95 3404589 Ol120398 TT m A BRITISH STANDARD Petroleum liquids and gases - Fidelity and security of dynamic measurement - Cabled transmission of electric and/or electronic pulsed data The European Standard EN Is0 551 : 1995 has the status of a British standard ICs 76.200 .I_._-/ .,.
2、. II.- .- . . . ._. - . _. . BS EN IS0 6551 : 1996 Incolporati?lg Amendment No. 1 BS6439:IWrenumered - CEN EN*ISO*b55L 95 3404587 0120399 906 Issue 2, March 1996 A BS EN IS0 6551 : 1996 Contents National foreword Committees responsible Rearmmendations O. Introduction 1. Scope and field of applicatio
3、n 2. Definitions 3. Levels of security 4. System design Level E pulse security system; Levei D pulse security system; Level C pulse security system; Level B pulse security system; Levei A Page CEN EN*ISO*b55L 95 3404589 OL20400 458 A A Issue 1, March 1996 BS EN IS0 6551 : 1996 Summary of pages The f
4、ollowing table identifies the current issue of each page. Issue 1 indicates that a page has been introduced for the first time by amendment. Subsequent issue numbers indicate an updated page. Vertical sidelining on replacement pages indicates the most recent changes (amendment, addition, deletion).
5、Front cover inside front cover a b EN cover page iib 1 2 3 4 Issue 2 2 1 blank 1 1 Originai Original Originai Originai 5 6 7 8 9 10 11 12 hide back cover Back cover Issue Original Original Onginai Original original Originai Original Original blank 2 Change of identifier Wherever BS 6439 : 1983 appea
6、rs in this standard, it should be read as BS EN IS0 6551 : 1996. A ExJRoPEANwANDm EN IS0 6551 NOIWIE EUR0PEE?E EUROP it may or may not be resettable to zero (see 4.4). 2.2.4 noise : Unwanted signals which may impair fidelity, and which occur for periods exceeding 0.2 s. 2.2.5 primary indication : Th
7、e combination of the transducer(s) outputs), the transmission cabling, the signal conditioning, processing and scaling, and the indicator with or without totalizer and their readings, the whole of which pro- duces the final reference for the transaction. 2.2.6 secondary indication (auxiliary or anci
8、llary indica- tion) : Any equipment which separately or in combination pro- vides indication of the quantity measured, but which does not form part of the primary indication. 2.2.7 security : The state or means of ensuring fidelity. The degree or level of security given by a minimum basic arrange- m
9、ent, can be increased by additional equipment. 2.2.8 transients : Disturbances having a duration of 0.2 s or leCs. 2.2.9 pulse transmitter : A device for converting the output from a transducer into a pulsed signal of low source impedance over the full operating frequency range (with pre-amplificati
10、on if necessary). 2.2.10 unrevealed error : Any lack of fidelity outside the prescribed limits of error, including errors caused by functional failure and by externa influences. 3 Levels of security 3.1 Designation of security levels In this International Standard, five levels of security are iden-
11、tified and designated, of which leve/ represents the minimum acceptable level. Typical examples of these five levels are shown diagrammatically in figures 1 to 5, and are described below. 3.1.1 Level E Error reduction is achieved solely by correctly installed ap- paratus of good quality. This is a s
12、traightforward scaler totalizer system. 3.1.2 Level D Manua/ error monitoring at, specified intervals by methods of comparison. This level of security is intended to give protection against functional errors and failures and is a method of verification by manual action. It has the means for checking
13、 the read-out visually against an independent totalizing system. 3.1.3 Level C Automatic error monitoring and error indication at specified in- tervals by methods of comparison. 2 CEN EN*ISO*b553 95 3404589 0320405 T3T Module Pulse tramminer Signai conditioner This level of security is intended to g
14、ive protection against functional errors and failures and this may be achieved by design methods acceptable to an approving authority (if ap- propriate). The time intervals for error monitoring are subject to revision in the light of experience gained. .-c Scder .-c Totauer 3.1.4 Level 6 Continuous
15、monitoring, error indication and alarm signalling by methods of comparison. This level of security is intended to give warning of transients and other spurious influences, supply borne and radiated, in addition to functional errors and failures. 3.1.5 Level A Continuous verification and correction b
16、y methods of comparison. Errors must be signalled even though they are corrected. This level of security is intended to give protection against tran- sients and other spurious influences, supply borne and radiated, in addition to functional errors and failures. -BS 6439 : 1983 For this level of secu
17、rity, alternative transmission lines follow- ing two different routes should be provided, together with bat- teries for back-up power supply. 3.2 General note on security levels 3.2.1 A metering system may comprise sections having the same or different levels of security. figures 1 to 5 show typical
18、 functional arrangements of modules required to achieve the specified levels of security. 3.2.2 In the examples, emphasis has been placed on the transmission system as this is considered to be the most vulnerable area of the whole. 3.2.3 Security for the scaler totalizer is not illustrated and is co
19、nsidered to be acceptable to Levei for the majority of ap- plications. It may, however, be considered necessary in some cir- cumstances to duplicate the scaler and/or the totalizer section. 3.2.4 The factors contributing to the integrity of the functions are considered in clauses 4 to 8. messure- im
20、pedance signai over fun operating frequency range Isee 6.1 and 6.2) frequency raw limiting. pub shap- ing. co(MywI mode inberference rejection r- - 1 counts to readout units Function I II Quantin, readout Figure 1 - Typical functional arrangement for pulse security system Level E. The diagram illust
21、rates a simple system with no built-in provisions for error monitoring. Only good quality components and sub-units, correctly installed, will lead to confidence in the security of the system. The use of a pre-amplifier transmitter to drive the transmission line is con- sidered beneficial for the maj
22、ority of applications, a5 is the provision of signal conditioning. The system, though simple, does not differ in hardware quality from more secure systems using the same elements. (Note that the modules and functions shown in full are essential. Those shown dotted are optional.) 3 BS 6439 : 1983 Sig
23、nal conditioner Row transducer II il Puise transmitter CEN EN*IS0*6553 75 = 3404589 O320406 976 c Scaler Totalizer Transmuuion 1-1 line I II r- Mmule Secondary readout lpemnen: or temporary. local or I remote) FlW measure mt Function Manual comparison with primary readout r-l at specified interva(s
24、impedance signais over fu operating frequency range 1 I- I I i Preampiir I I L - I Transmis- sion of. signai (see 6.1 and 6.2) L Amplification end frequency range limiting. pulse shap- ing, common mode interference rejection Conversion of pu198 counts to readout units U readout Figure 2 - Typical fu
25、nctional arrangement for pulse security system Level D. The diagram illustrates a simple system with means of making a periodic manual assessment of security. The secondary readout may be permanent or temporary, local or remote. Manual comparison made during a periodic check will monitor the integri
26、ty of the transmission and totalizer elements. It may be less convenient than the provisions of Level C as the system may have tobe stopped for readings to be taken. Overall security is mainly inferred from the performance during the error monitoring period. (Note that the modules and functions show
27、n in full are essential. Those shown dotted are optional. The modules and functions boxed in double line indicate the difference from Level E). 4 CEN EN*ISO*b551 95 3404589 0120407 802 . BS 6439 : 1983 Channel “A* Transmission lines Flow transduce Pulse transmitter SbMI COnditbIWi w Scaler c Totalue
28、r Module I r- - - - - 1 I Channel “E U t measure- FuKtim impedance *MIS over full operating frequency mnge Transmis Sion Of isee6.1 and 6.21 *Ml frequency range limiting, pulse shap- ing, common mode interfeien rejection Numerica( com Pansai of pulre trains automatically but not continuouaiy I icomp
29、aratormaybe aharedl U r- 1 I Highllowllowalarm I I Rateindication I L- - -A I I r- i readout Figure 3 - Typical functional arrangement for pulse security system Level C. The diagram illustrates a dual transmission system with a dual pulse comparator of simple design. If the pulses delivered become n
30、umerically out of step, warning will be given by the comparator (differential counter). Level C security will be defeated by other disturbances dealt with by higher level security systems, e.g. simultaneous interference superimposed on both channels will not be detected because a numerical differenc
31、e between channels is not caused. It is intended that this form of error monitoring is carried out periodically, the monitoring equipment may thus be shared with other metering systems. Level C security is inferred from the results obtained during the monitoring period. (Note that the modules and fu
32、nctions shown in full are essential. Those shown dotted are optional. The modules and functions boxed in double line indicated the difference from Level D.i 5 .- -. , - . . . .a ., . . . -. CEN EN*ISO*b551 95 = 3404589 0320408 747 L Pulse transmitter Signal condither Scaler -c BS 6439 : 1983 Totaliz
33、er I I L -_-_ J Channel “8“ t I -rt+- Pulse transmitter Sign4 conditioner - Comparator - - r- 7 i Preamplifier I I L -_ J supplies low impedance Ygnals over full operating frequency range channel “4 and “B“ pulses to difier in phase and/or frequency 1 I Preamplifier I ! r- Transmis- sion of signai (
34、see 6.1 and 6.2) AmplifiCath and frequency ringe limiting, pulse shap ing, common mode intaderence rejection Continuous com- parison of pulse treifm for number, frequency. phase an sequeme rmr 71 indica- counts to readout units I r-i Alarm if frequency I 1 fails outside the set I I limits I c _ 4 I
35、I I Rate readout I L _-_ J Quantity readout Figure 4 - Typical functional arrangement for pulse security system Level B. The diagram illustrates a dual transmission system with a dual pulse comparator in which the pulse trains are continuously monitored for number, frequency, phase and sequence and
36、any irregularity is indicated. Simultaneous interfering pulses must be detected and indicated. Alarm is given if pulses are lost or gained on either channel. (Note that the modules and functions shown in full are essential. Those shown dotted are optional. The modules and functions boxed in double l
37、ine indicate the difference from Level C.) 6 L Scaler - transducer Comparator and Pule transmitter Signal conditioner -c . signai analyser Module Totalizer Function I Channel “6 Pulse transmitter impedance signals frequency range channel “A“ and “B“ pu b) etc.; heavy rain, high pressure water, water
38、 cleaning hoses, c) electrical interference from mobile compressors and generators; d) local radio and television transmitters, particularly mobile hand-held sets; e) local electrical sub-stations with transformers and/or relay control systems. 4.5.2 Inclusion of arrangements to enable the electrica
39、l in- tegrity of the system and the power supply to be checked, should be considered at the design stage. 4.6 Signal pre-amplifiers A signal pre-amplifier may be introduced into the transmission system at the transducer, if transmission distances or manufac- turers requirements so dictate. 4.7 Typic
40、al causes of error Typical causes of error which should be taken into considera- tion are as follows : 4.7.1 4.7.2 4.7.3 4.7.4 4.7.5 4.7.6 4.7.7 4.7.8 Transients. Power supply variations. Power supply interruption. Inadequate signal level as a result of line loss. Common-mode noise induced in cablin
41、g. Series-mode noise induced in cabling. Noise introduced from ground-lwp problems. Excessive gain and frequency response of the system elements. 4.7.9 Spurious signals induced from other meters sharing the same muiticore cable. CEN EN*ISO*b5CL 75 m 340q587 OL2OYLL 233 m 4.7.10 Short circuit or open
42、 circuit of conductor pair or short circuit of either conductor to ground or shield. 4.7.11 Bad connections, temperature variations and ex- tremes, vibration, shock and adverse environmental con- ditions. 5 Precautions 5.1 General 5.1.1 Sensitivity controls on pre-amplifiers, scalers, etc., should n
43、ot be capable of unauthorized adjustment. 5.1.2 No malfunction of any measuring equipment should be caused by the following interruptions to the power supply : al Zero voltage for 10 ms or less; b) 50 % of normal voltage for 20 ms or les; c) 80 % of normal voltage for 50 ms or less. 5.1.3 The totali
44、zed pulse counts existing at the time of any power failure, should be retained. 5.1.4 The gain and frequency response of the system elements should be restricted to that required by the applica- tion. 5.2 Warning of metering system fault Notwithstanding that this International Standard deals with th
45、e electronic signal system only, where the output of the transducer is likely to be degraded at the extremes of its useable range the metering system may be fitted with a device to give alarms at the limiting flow rates. 5.3 Protection against electrical storms It is essential that cable pairs and t
46、he instrument input circuit should be isolated; this will effectively increase the degree of protection of the equipment from damage by excessive common-mode voltages (electrical storms). 6 Installation 6.1 Signal amplitude The following points should be ohserved CO that the signal amplitude from th
47、e transducer to the receiver can be main- tained at a high level. 6.1.1 The installation recommendations specified by the manufacturers should be carefully followed, whilst complying fully with statutory requirements and/or codes of safety. 6.1.2 The length of transmission lines from the meter to th
48、e read-out device should be minimized, bearing in mind the re- quirements of 6.2.1 to 6.2.8 inclusive. BS 6439 : 1983 6.1.3 Proper impedance matching should be ensured, 6.1.4 Signal transmission cables that are technically cornpat- ible with the duty should be used. 6.1.5 The supply voltages to pre-
49、amplifiers and constant amplitude pulse generating systems should be checked to en- sure they are of proper magnitude and do not exceed noise or ripple maxima as specified by the equipment manufacturer. 6.2 Signal-to-noise ratio The following points should be observed so that the signal-to- noise ratio can be optimized. 6.2.1 Transmission cables with correctly grounded shielding should be provided from meters and meter prover detectors
