Problems associated with a.c.-d.c. transfer devices for the precise measurement of alternating currents and voltages.
possible transfer device for the precise measurement
or standardization of an alternating current with
reference to a precisely known direct current. A full
method of operation has been developed and an experimental
and theoretical consideration of the various sources of
error carried out. The performance has been compared
with that of existing a.c. - d.c. transfer devices, and
it is shown that the indirectly heated thermistor is a
valuable addition to this field, particularly in the
measurement of very low frequencies.
The actual idea of using the indirectly heated
thermistor as a transfer device is not original, nor is
the measurement of the thermistor characteristics themselves
(section 2.5). It is believed, however, that all the
work concerning the actual bridge design and operation,
the analysis of its performance, and the investigation
of the sources of error is original, and that, as a
result of this work, this device can be confidently used
for measurements of the highest precision.
During the course of this investigation, comparison
measurements were carried out between the indirectly
heated thermistor and the vacuo-thermo-junction.
Discrepancies which appeared in these measurements were
ultimately attributed to limitations in the existing
theory of transfer errors in vacuo-thermo-junctions,
concerning the effects of Thomson and Peltier heating.
This theory has been reconsidered and a new
generalized theory developed which is shown to be applicable
also to the indirectly heated thermistor. It is
evident, that providing certain precautions are taken in
the construction, the vacuo-thermo-junction is capable of
the highest precision. It is believed that the new
theory and the supporting analysis is largely original.
Some of the work on the indirectly heated thermistor
has been published by the author in the Proceedings of
the Institution of Electrical Engineers, Vol. 103, Part B,