1、BRITISH STANDARD BS 7194:1990 Incorporating Amendment No. 1 Specification for Direct-current and low-frequency electronic measuring instruments with a digital display UDC 621.3.037.37:621.317.331:621.3.027.2:621.3.08:006.3/.8BS7194:1990 This British Standard, having been prepared under the direction
2、of the Power Electrical Engineering Standards Policy Committee, was published underthe authority of the BoardofBSI and comesintoeffecton 31 July 1990 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference PEL/13 Draft for comment 88/22932 DC ISBN 0 580 1758
3、1 2 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Power Electrical Engineering Standards Policy Committee (PEL/-) to Technical Committee PEL/13, upon which the following bodies were represented: Association of Consulting Engineers Asso
4、ciation of Supervisory and Executive Engineers Department of Energy (Electricity Division) Department of Trade and Industry (National Physical Laboratory) Department of Trade and Industry (National Measurement AccreditationService) Electrical Power Engineers Association Electricity Supply Industry i
5、n England and Wales Engineering Teaching Equipment Manufacturers Association GAMBICA (BEAMA Ltd.) General Electric Company Ltd. Institution of Electrical Engineers Ministry of Defence Amendments issued since publication Amd. No. Date of issue Comments 6892 May 1992 Indicated by a sideline in the mar
6、ginBS7194:1990 BSI 09-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Classification 4 4 Reference conditions and intrinsic errors 4 5 Nominal range of use and variations 4 6 Electrical and mechanical requirements 7 7 Constructional requirements
7、 8 8 Information, general markings and symbols 9 9 Markings and symbols for terminals and connectors 10 Appendix A Recommended tests 13 Appendix B Permissible errors and variations 20 Figure 1 Test apparatus for variation due to common mode voltage 16 Figure 2 Test apparatus for variation due to pea
8、k factor of the measurand 17 Figure 3 Effect of temperature 22 Table 1 Reference conditions and tolerances for testing purposes relating to the influence quantities 5 Table 2 Limits of the nominal range of use and permissible variations 6 Table 3 Symbols for marking instruments and accessories 11 Ta
9、ble 4 Overloads of short duration 20 Publications referred to Inside back coverBS7194:1990 ii BSI 09-1999 Foreword This British Standard has been prepared under the direction of the Power Electrical Engineering Standards Policy Committee and is based on BS 89 1) , the format of which it generally fo
10、llows for ease of use. A 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 T
11、his document comprises a front cover, an inside front cover, pages i and ii, pages1 to 22, 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. 1)
12、Revision in preparation.BS7194:1990 BSI 09-1999 1 1 Scope This standard specifies requirements for the performance of electronic measuring instruments with a digital display intended for measuring analogue quantities of voltage and/or current. It also applies to instruments for indicating other quan
13、tities including non-electrical quantities, provided that the relationship between the indicated quantity and the measurand is known. This standard applies to self-contained instruments having their own enclosure, terminals, etc., and also to instruments for fitting in an enclosure where the enclosu
14、re is not provided by the supplier of the instrument original equipment manufacture (OEM) instruments. This standard applies only to instruments measuring current and voltage at d.c. and at a.c. at distribution system frequencies and their harmonics. It applies to the digital parts of an instrument
15、having a combined analogue/digital display. This standard does not specify requirements concerning dimensions of instruments and does not apply to instruments having a digital or coded measurand input. It does not apply to special purpose instruments which are covered by their own British Standards
16、and contains no requirements for the visibility of the display. It also does not apply to accessories. NOTE 1The values of a.c. quantities given in this standard are r.m.s. values unless otherwise stated. NOTE 2The publications referred to in this standard are listed on the inside back cover. 2 Defi
17、nitions For the purposes of this Part of BS7194, the definitions given in BS4727 apply, together with the following. 2.1 General terms 2.1.1 measurand a quantity subjected to measurement 2.1.2 digital display instrument a measuring instrument that provides a display in digital form. (Referred to her
18、einafter as instrument) 2.1.3 indicating instrument a measuring instrument that displays at any time the value of the measurand without recording it NOTEThe indicated value may be different from the value of the quantity measured by the instrument and may be in units of a different quantity. 2.1.4 e
19、lectronic measuring instrument a measuring instrument intended to measure an electrical or non-electrical measurand using electronic means 2.1.5 single function instrument a measuring instrument intended for the measurement of one kind of measurand only 2.1.6 multi-function instrument a measuring in
20、strument with a single means of indication intended for the measurement of more than one kind of measurand (e.g. an instrument measuring current, voltage and resistance) 2.1.7 fixed instrument a measuring instrument designed to be permanently mounted and which is intended to be connected to an exter
21、nal circuit(s) by means of permanently installed conductors 2.1.8 portable instrument a measuring instrument specifically designed to be carried by hand and to be connected and disconnected by the user 2.1.9 instrument with magnetic screen a measuring instrument shielded by ferro-magnetic material f
22、rom the influence of a magnetic field of external origin 2.1.10 instrument with electric screen a measuring instrument shielded by conductive material from the influence of an electric field of external origin 2.1.11 accessory an element, group of elements or device associated with the measuring cir
23、cuit of a measuring instrument in order to confer specified characteristics to the measuring instrument 2.1.12 instrument lead a lead comprising one or more conductors, specially designed for connecting measuring instruments to external circuits 2.1.13 calibrated instrument lead an instrument lead w
24、hose resistance has a specified valueBS7194:1990 2 BSI 09-1999 2.1.14 distortion factor (total harmonic distortion factor) of a measurand the ratio of the r.m.s. value of the harmonic content to the r.m.s. value of the non-sinusoidal measurand NOTERatio where 2.1.15 ripple content of a measurand the
25、 ratio of the fluctuating current to the value of the d.c. component NOTERatio where 2.1.16 peak factor the ratio of the peak value to the r.m.s. value of a periodic measurand 2.1.17 common mode voltage that part of a voltage measurand which exists between each of the voltage circuit terminals and a
26、 reference point NOTEThis reference point may be the frame terminal, the signal terminal or another defined point. 2.1.18 series mode voltage an unwanted part of the input voltage which is superimposed on the voltage produced by the measurand 2.2 Description of instruments according to their method
27、of operation 2.2.1 rectifier instrument a measuring instrument that combines a measuring instrument sensitive to direct current and a rectifying device whereby alternating currents or voltages may be measured 2.2.2 r.m.s. responding instrument a measuring instrument that, over a specified frequency
28、range, provides an indication which is intended to be proportional to the root-mean-square value of the measurand, even when it contains a d.c. component or is not sinusoidal 2.3 Constructional features of instruments 2.3.1 measuring circuit (of an instrument) the part of the electrical circuit inte
29、rnal to the instrument, together with the interconnecting leads, if any, which is energized by a voltage or a current, one of these quantities being a prime factor in determining the value of the measurand 2.3.2 current circuit a measuring circuit through which flows a current that is a prime factor
30、 in determining the value of the measurand NOTEThe current may be either directly involved in the measurement or a proportional current supplied by an external current transformer or derived from an external shunt. 2.3.3 voltage circuit a measuring circuit to which a voltage is applied that is a pri
31、me factor in determining the value of the measurand NOTEThe voltage may be either directly involved in the measurement or a proportional voltage supplied by an external voltage transformer or an external voltage divider. 2.3.4 external measuring circuit the part of the electrical circuit external to
32、 the instrument from which the value of the measurand is obtained 2.3.5 auxiliary circuit a circuit, other than a measuring circuit, required for the operation of the instrument 2.3.6 auxiliary supply an auxiliary circuit that provides electrical energy 2.3.7 indicating device the part of a measurin
33、g instrument that displays values corresponding to the measurand 2.3.8 electrical zero the indication given by the instrument when the measurand is either zero or a stated value 2.3.9 electrical zero adjuster the mechanism by means of which the instrument may be adjusted so that the electrical zero
34、coincides with the appropriate indication H is the value of the harmonic content; M is the value of the non-sinusoidal measurand. C f is the value of the fluctuating component; C dc is the value of the d.c. component. H M - = C f C dc - =BS7194:1990 BSI 09-1999 3 2.3.10 electrical span adjuster the
35、mechanism by means of which the instrument may be adjusted so that the lower/upper limit of the measuring range coincides with the appropriate indication 2.4 Characteristic features of instruments 2.4.1 span the algebraic difference between the upper and lower limits of the measuring range which is
36、expressed in units of the measurand 2.4.2 measuring range the range defined by two values of the measurand within which the limits of error of a measuring instrument are specified NOTEA measuring instrument may have several measuring ranges. 2.4.3 response time the time taken for the indication to r
37、each, and remain within, a band centred on the final steady indication, when the measurand is abruptly changed from zero (the unenergized condition) to a value such that the final steady indication is a specified proportion of the span 2.4.4 display update time (rate) the time interval between succe
38、ssive occasions on which, in response to a changing measurand, the display is changed NOTEWhen the time interval is short, it is usual to give the display update rate, being the quantity of updates per second. 2.4.5 sampling time the time interval during which the value of measurand is being investi
39、gated in order to produce the display 2.4.6 sampling rate the number of times per second that the measurand is investigated in order to produce the display 2.5 Characteristic values 2.5.1 nominal value a value of a quantity indicating the intended use of an instrument. The intended characteristics o
40、f instruments and accessories are also nominal values 2.5.2 rated value a value of a quantity assigned, generally by a manufacturer, for a specified operating condition 2.5.3 fiducial value a clearly specified value to which reference is made in order to define the fiducial error NOTEThis value may
41、be, for example, the upper limit of the measuring range, the scale length or another clearly stated value. 2.5.4 fiducial error the ratio of the absolute error to the fiducial value 2.6 Influence quantity, reference conditions, nominal range of use and preconditioning 2.6.1 influence quantity any qu
42、antity, generally external to the measuring instrument and/or accessory, that may affect its performance 2.6.2 reference conditions the appropriate set of specified values and specified ranges of values of influence quantities under which the permissible errors of an instrument are specified NOTEEac
43、h influence quantity may have either a reference value or a reference range. 2.6.3 reference value a specified value of one of a set of reference conditions 2.6.4 reference range a specified range of values of one of a set of reference conditions 2.6.5 nominal range of use a specified range of value
44、s that an influence quantity can assume without causing a variation exceeding the specified amount 2.6.6 limiting values of an influence quantity extreme values that an influence quantity can assume without the instrument being damaged or permanently altered in such a way that it no longer satisfies
45、 the requirements of its class index NOTEThe limiting values may depend on the duration of their application.BS7194:1990 4 BSI 09-1999 2.6.7 warming-up period the interval between the energizing of the auxiliary circuit and the instant when the instrument may be used, as specified in the manufacture
46、rs instructions 2.6.8 preconditioning the action whereby a specified value of the measurand is applied to the measuring circuit prior to carrying out testing or use of the instrument, generally for a specified period 2.7 Errors and variations 2.7.1 (absolute) error for an instrument, the value obtai
47、ned by subtracting the true value from the indicated value NOTESince the true value cannot be obtained by measurement, a value obtained under specified test conditions and at a specified time is used instead. This value is derived from national measurement standards or measurement standards which ha
48、ve been agreed. 2.7.2 intrinsic error the error of an instrument when under reference conditions 2.7.3 variation the difference between the two indicated values for the same value of the measurand of an instrument when a single influence quantity successively assumes two different specified values w
49、ithin the nominal range of use 2.8 Accuracy, accuracy class and class index 2.8.1 accuracy for a measuring instrument the closeness of the indicated value to the true value NOTEThe accuracy of a measuring instrument is defined by the limits of intrinsic error and by the limits of variations. 2.8.2 accuracy class a group of measuring instruments which meet certain metrological requirements intended to keep permissible errors and variations within specified limits 2.8.3 class index the number that designates the accuracy class NOTESome instruments may
