Indirect acting electrical measuring instruments using a null balance method, which need an auxiliary electrical power supply. The null balance may be achieved by comparing:
a) Two voltages or two currents (electrical balance);
b) Two forces or two torques (mechanical balance).
These instruments may indicate the value of the measured quantity or record the value of the measured quantity as a function of time. These two functions may be combined in one instrument.
Electrical balance instruments, measuring electrical quantities, as defined in Sub-clauses 20.1 to 20.3 of Section Two; Mechanical balance instruments, measuring electrical quantities, as defined in Sub-clause 30.1 of Section Three.
Receivers of electrically operated measuring equipment of either the electrical balance or mechanical balance type when the conversion function of the non-electrical quantity into an electrical one is known. (See Sub-clause 20.4 of Section Two and Sub-clause 30.2 of Section Three.)
Nole. — For electrically operated measuring instruments, it is not always sufficient to know the conversion function. This is particularly the case for certain pyrometer receivers for which it is necessary to know also the temperature of the reference junction.
Instruments having auxiliary circuits which incorporate amplifiers, photoelectric cells or electronic acces-sories.
This recommendation does not apply to:
Devices which incorporate a direct acting indicating or recording instrument associated with a measuring amplifier; Electrically operated measuring equipment when the conversion function is not known.
Controllers, with an electrical output, containing electrical indicating or recording instruments. For such controllers, the recommendation does not apply to the circuits used for control;
Indirect acting instruments indicating or recording the measured quantity in the form of digits, codes, punched
cards, etc;
Position follower instruments;
Recording instruments in which the chart movement is a function of a quantity other than time (X, Y recorders);
Nole. — Some requirements of the present recommendation may be used for these instruments.
Integrating instruments or auxiliary integrating devices incorporated in instruments which fall within the scope of this recommendation.
Accessories, for which reference shall be made to IEC Publication 51, Recommendations for Direct Acting Indicating Electrical Measuring Instruments and Their Accessories.
The requirements in this recommendation are sectionalized as folfows: Section One: General requirements for indirect acting instruments. Section Two: Special requirements for indirect acting electrical balance instruments. Section Three: Special requirements for indirect acting mechanical balance instruments.