Voltage measuring apparatus employing feedback gain control to obtain a predetermined output and a feedback loop to readout the gain value

Claim 1

Electrical circuit for the direct measurement of input AC voltage signals, comprising: a variable transfer means having a signal transfer factor adjustable in response to an electrical control signal applied thereto; a first comparing circuit receiving a first reference DC voltage signal for adjusting the transfer factor of the transfer means, said first comparing circuit including a signal converter for converting signals received from said transfer means and an amplifier with high amplification for amplifying a first difference signal resulting from the comparison of the first reference signal and the converted signals and passing on the amplified difference signal as said electrical control signal to the transfer means; A second comparing circuit receiving a second DC voltage signal for measuring the transfer factor of the transfer means, said second comparing circuit being adapted to compare signals received from the transfer means which are different from those received by said signal converter with said second reference signal; an amplifier with high amplification receiving a second difference signal resulting from the comparison in the second comparing circuit, the output of the amplifier being applied to the input of the transfer means so that the amplified second difference signals produced are a measure of the input AC voltage signals.