An astatic A-C ¿ D-C comparator with wide frequency range

THE NEED for the accurate measurement of a-c quantities, that is, for current, voltage, and power, has been steadily increasing, Moreover, since power supplies at frequencies up to 2,500 cycles per second (cps) have been coming into use it has become necessary to measure these higher frequencies accurately. Pointer instruments with accuracies of 0.2%, or in some cases 0.1%, of full scale are available, but with a limited range of application. Consequently, more accurate measuring equipment has become necessary, not only for national standardizing laboratories where various types of equipment have long been in existence and are continuously being developed and improved, but also for industrial requirements both in research laboratories, in the instrument manufacturer´s laboratories, and in industrial standardizing labhratories, if only to check and to calibrate portable instruments.