New generations of current transducers using Hall-effect sensors and closed-loop systems, Fig. 8-6, are advertised to operate within 1% amplitude error. Such transducers can measure dc and subharmonic currents as well as components in the tens of kHz range. Based on the published data, it is still difficult to ascertain how the accuracy of such units compares with current transformers. For dc measurements however, it is the transducer of choice.
This is a most accurate method if the shunt impedance is properly built and calibrated, Fig. 8-7. The impedance of the shunt must be included in the value of ZS. This method is conveniently applicable in the laboratory in situations where the supply source and the analyzer can share one common point of connection.