An Amplifier-Wattmeter Combination for the Accurate Measurement of Watts and Vars

As part of a program of im-provements made to the network analyzer in the electrical-engineering research laboratory at the Massachusetts Institute of Technology, an instrument to measure watts and vars has been devised which imposes a negligible burden upon the network, is rapid in response, and has an error less than one-half per cent of full scale. The instrument consists of (1) a semistock electrodynamic wattmeter, (2) a negative-feedback vacuum-tube amplifier, and (3) a phase-shifting network. When the equipment is once assembled the presence of the amplifier may be ignored and the instrument used thereafter as any portable instrument. The principle of instruments of this kind has other important applications in the field of electrical measurements.