IEC 60051-2-2018 pdf free.Direct acting indicating analogue electrical measuring instruments and their accessories –
Part 2: Special requirements for ammeters and voltmeters.
5.2.3Fiducial value
5.2.3.1 The fiducial value for an ammeter or a voltmeter corresponds to the following.5.2.3.2The 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 theelectrical zero;
instruments with the electrical zero outside the scale irrespective of the position of themechanical zero.
The class index is marked using Symbol E-1 given in Table 6 of IEC 60051-1:2016(seeClause 6 of lEC 60051-1:2016).
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 boththe 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 60051-1:2016(seeClause 6 of lEC 60051-1:2016).
5.2.3.4The span for an instrument:
The span for an instrument whose scale marks do not correspond directly to its electricalinput quantity.
The class index is marked using Symbol E-4 given in Table 6 of lEC 60051-1:2016(seeClause 6 of IEC 60051-1:2016).
Subclause 5.2.3.4 does not apply to a voltmeter or ammeter designed to be used inconjunction with a shunt, a series resistor (impedance) or an instrument transformer. Theseinstruments 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 scalevoltmeter:
The fiducial value for an ammeter with overload scale or an expanded scale voltmetercorresponds to 5.2.3.2 or 5.2.3.3，as appropriate.The measuring range of an ammeter withoverload scale is the upper limit of the non-overload part. The measuring range of anexpanded 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 scalemarks，the fiducial value shall be as agreed between manufacturer and user. The fiducialvalue does not have to be the same at all points on the scale.
5.5 Electrical requirements
5.5.1 Electrical safety requirementsSee lEC 60051-1:2016.
For a fixed ammeter having the upper limit of its measuring range of 1 A to 10 A and intendedfor use with a current transformer having a high over-current capability (Class P protectivecurrent transformers as specified in lEC 61869-2), the measuring circuit shall not open whenthe ammeter is subjected to 30 times the nominal secondary current of the associated currenttransformer for a period of 2 s.
A portable ammeter intended for similar use shall withstand 15 times the upper limit of itsmeasuring range for a period of 2 s.
These ammeters need not be functional after application of this overload but shall not then beopen-circuit.
For the recommended test, see lEC 60051-9.
5.5.2 Self-heating See lEC 60051-1:2016.
5.5.3Permissible overloads
5.5.3.1Continuous 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 continuousoverload of 120 % of the upper limit of the electrical input quantity for a period of 2 h.Theupper limit of the electrical input quantity of an ammeter with overload scale is the upper limitof the non-overload part.The upper limit of the electrical input quantity of an expanded scalevoltmeter is the upper limit of the expanded part.IEC 60051-2 pdf download.