A remote monitor circuit for measuring photomultiplier anode current at high voltage

A system is presented which is capable of monitoring currents in the microamp region at a voltage of up to 2.8 kV. This can be used for measuring the DC anode current of a photomultiplier when operated with the photocathode grounded. The system is based on a voltage-to-frequency converter, the output of which can easily be transmitted to a remote scaler coupled to a computer.