IEC 60051-3-2018 pdf free.Direct acting indicating analogue electrical measuring instruments and their accessories – Part 3: Special requirements for wattmeters and varmeters.
This part of lEC 60051 applies to direct acting indicating wattmeters and varmeters having ananalogue display.
NOTE For multi-function instruments, see lEC 60051-7.lt also applies to:
non-interchangeable accessories (as defined in 3.1.23 of IEC 60051-1:2016)used withwattmeters and varmeters;
a combination of the instruments and the accessories provided that the adjustments havebeen made for the combination;
direct acting indicating electrical measuring instruments whose scale marks do notcorrespond directly to their electrical input quantity,provided that the relationship betweenthem is known;
instruments and accessories having electronic devices in their measuring and/or auxiliarycircuits.
This document does not apply to:
special purpose instruments which are covered by their own lEC standards;
special purpose devices which are covered by their own lEC standards when they areused as accessories.
2 Normative references
The following documents are referred to in the text in such a way that some or all of theircontent constitutes requirements of this document.For dated references,only the editioncited applies. For undated references, the latest edition of the referenced document (includingany amendments) applies.
IEC 60051-1:2016，Direct acting indicating analogue electrical measuring instruments andtheir accessories – Part 1: Definitions and general requirements common to all parts.
5.2.3Fiducial value
5.2.3.1 The fiducial value for a wattmeter or varmeter 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 theelectrical zero;
instruments with the electrical zero outside the scale irrespective of the position of themechan-ical zero.
The class index for these wattmeters or varmeters is marked using Symbol E-1 given inTable 6 of lEC 60051-1:2016 (see Clause 6 of lEC 60051-1:2016).
5.2.3.3 The sum of the absolute values of the upper and lower limit of the measuringrange when both the mechanical and the electrical zeros are displaced within the scale.
The class index for these wattmeters or varmeters is marked using Symbol E-1 given inTable 6 of IEC 60051-1:2016(see Clause 6 of lEC 60051-1:2016).
5.2.3.4 The span for an instrument whose scale marks do not correspond directly to itselectrical input quantity.
The class index for these wattmeters or varmeters is marked using Symbol E-10 given inTable 6 of lEC 60051-1:2016 (see Clause 6 of lEC 60051-1:2016).
This does not apply to a wattmeter or varmeter designed to be used in conjunction with one ormore shunt(s), series resistor(s) (impedance(s)) or (an) instrument transformer(s). Theseinstruments are treated in accordance with 5.2.3.2 or 5.2.3.3 as appropriate.IEC 60051-3 pdf download.