Abstract: A method of noise reduction in electronic measuring circuits is provided wherein two discrete signals (A,B) are separately established, each of which contains the same noise, and the signal P=A-NB is then established, where N is chosen to make P a minimum. The method is particularly useful in a method of pulse detection of the type wherein signals (A) and (B) obtained from two monitoring units (M.sub.1,M.sub.2) in series with respective components (C.sub.A,C.sub.B) are compared in a pulse discrimination device (P.D.S.) in order to detect the occurrence of out of phase pulses in the signals. In this event, increased detection sensitivity can be obtained by operating on the signals (A) and (B) by a difference amplifier arrangement (A.sub.3,A.sub.4) to establish input signals (P) and (Q) for the pulse detection system given by:P=(A-.alpha.NB) and Q=(NB-.alpha.A)where .alpha. lies in the range of 0.5 to 1.0 and N is chosen to make the difference signal (A-NB) a minimum.

Abstract: A circuit arrangement for applying low frequency high voltage waveforms across a load and which includes low and high voltage circuits. The low voltage circuit includes a sinusoidal signal generator for producing a low voltage electrical waveform, and a transmitter circuit having first and second light emitting diode circuits by which first and second light signals are generated which are transmitted to the high voltage circuit by respective fibre optic light guides. The high voltage circuit includes first and second high voltage d.c. supplies and first and second triode valves.