An inexpensive circuit for monitoring photomultiplier anode current

Abstract

An 8-channel current-to-frequency converter module has been developed for measuring photomultiplier anode currents in the range of 1-100 [mu]A. Although this circuit was designed specifically for monitoring photomultiplier currents in a ground-based very high energy gamma-ray telescope, it would be useful in many other applications where cost is a consideration. An interesting consequence of this technique is that, by measuring the pulse-to-pulse time interval, it is possible to synthesize the kind of measurements usually performed with lock-in amplifiers. Tests show that with a few seconds integration time, a 1 kHz modulated signal can be detected at a level of 10-5 of the ambient current.