IEC 60051 -2:2018 pdf download – Direct acting indicating analogue electrical measuring instruments and their accessories – Part 2: Special requirements for ammeters and voltmeters.
5.2 Limits of intrinsic uncertainty, fiducial value 5.2.1 Limits of intrinsic uncertainty See IEC 60051 -1 :201 6. 5.2.2 Correspondence between intrinsic uncertainty and accuracy class See IEC 60051 -1 :201 6. 5.2.3 Fiducial value 5.2.3.1 The fiducial value for an ammeter or a voltmeter corresponds to the following. 5.2.3.2 The upper limit of the measuring range for the following: • instruments with the mechanical and/or electrical zero at one end of the scale; • instruments with the mechanical zero outside the scale irrespective of the position of the electrical zero; • instruments with the electrical zero outside the scale irrespective of the position of the mechanical zero. The class index is marked using Symbol E-1 given in Table 6 of IEC 60051 -1 :201 6 (see Clause 6 of IEC 60051 -1 :201 6). 5.2.3.3 The sum of the electrical values: The sum of the absolute values of the upper and lower limit of the measuring range when both the mechanical and the electrical zeros are displaced within the scale. The class index is marked using Symbol E-1 given in Table 6 of IEC 60051 -1 :201 6 (see Clause 6 of IEC 60051 -1 :201 6). 5.2.3.4 The span for an instrument: The span for an instrument whose scale marks do not correspond directly to its electrical input quantity.The class index is marked using Symbol E-4 given in Table 6 of IEC 60051 -1 :201 6 (see Clause 6 of IEC 60051 -1 :201 6). Subclause 5.2.3.4 does not apply to a voltmeter or ammeter designed to be used in conjunction with a shunt, a series resistor (impedance) or an instrument transformer. These instruments are to be treated in accordance with 5.2.3.2 or 5.2.3.3, as appropriate. 5.2.3.5 The fiducial value for an ammeter with overload scale or an expanded scale voltmeter: The fiducial value for an ammeter with overload scale or an expanded scale voltmeter corresponds to 5.2.3.2 or 5.2.3.3, as appropriate. The measuring range of an ammeter with overload scale is the upper limit of the non-overload part. The measuring range of an expanded scale voltmeter is the lower limit of the expanded part. 5.2.3.6 The fiducial value for an instrument with a special arrangement of scale marks: For an instrument whose scale has been arranged to produce a special arrangement of scale marks, the fiducial value shall be as agreed between manufacturer and user. The fiducial value does not have to be the same at all points on the scale.
5.3.2 Limits of variations See IEC 60051 -1 :201 6. 5.3.3 Conditions for the determination of variations See IEC 60051 -1 :201 6. 5.4 Operating uncertainty, overall system uncertainty and variations See IEC 60051 -1 :201 6. 5.5 Electrical requirements 5.5.1 Electrical safety requirements See IEC 60051 -1 :201 6. For a fixed ammeter having the upper limit of its measuring range of 1 A to 1 0 A and intended for use with a current transformer having a high over-current capability (Class P protective current transformers as specified in IEC 61 869-2), the measuring circuit shall not open when the ammeter is subjected to 30 times the nominal secondary current of the associated current transformer for a period of 2 s. A portable ammeter intended for similar use shall withstand 1 5 times the upper limit of its measuring range for a period of 2 s. These ammeters need not be functional after application of this overload but shall not then be open-circuit. For the recommended test, see IEC 60051 -9. 5.5.2 Self-heating See IEC 60051 -1 :201 6. 5.5.3 Permissible overloads 5.5.3.1 Continuous overload Ammeters and voltmeters, together with their non-interchangeable accessory(ies), if any, except for instruments fitted with a non-locking switch, shall be subjected to a continuous overload of 1 20 % of the upper limit of the electrical input quantity for a period of 2 h. The upper limit of the electrical input quantity of an ammeter with overload scale is the upper limit of the non-overload part. The upper limit of the electrical input quantity of an expanded scale voltmeter is the upper limit of the expanded part. After removal of the excitation, the sum of the temporary and any permanent residual deflections shall not exceed 1 % of the scale length.