A general-purpose 50 c/s null indicator, particularly suitable for use with high-voltage bridges
W P Baker · Journal of Scientific Instruments · 1955
When a null indicator is used with a high-voltage bridge the additional requirement must be met of suppressing the output voltage due to discharge currents in the test specimen or connexions. A new approach to the design of a null indicator is described which not only yields a satisfactory solution to the discharge problem but also produces an instrument which is simpler, cheaper and more effective than conventional indicators. The new design is basically a tapered low-pass resistance-capacitance filter in which some of the passive resistive elements have been replaced by the anode impedances of amplifying valves.