An improved electrothermic instrument

An improved electrothermic instrument for measuring watts, amperes, or volt-amperes, actuated by the thermal expansion of a liquid in a closed system which includes a Bourdon tube, is described in this paper. The new instrument is not subject to the errors inherent in the bimetallic strip type of electrothermic instrument, it has a linear input-deflection characteristic, and its time period may be adjusted readily to any desired value up to at least 60 minutes.