Current-to-Voltage Amplifier with a High Voltage Isolated Input.

摘要

The measurement of currents in the picoampere-to-nanoampere range that are collected on electrodes held at a few kilovolts above ground potential is a commonly encountered experimental problem. While studying the long-term behavior of electron multipliers of the type used in cesium-beam atomic clocks. Measuring the first dynode conversion coefficient gamma requires floating a picoammeter at high voltage. The input of commercially available instruments can be typically held at only about 100 V from case potential, thus preventing us from performing the measurement. One possible way around this difficulty would be to isolate the electrometer from the ac power line and to then float it at the first dynode potential. However, this procedure is somewhat risky for both experimenter and electrometer. Therefore, we have designed and built an instrument to measure safely small (pA-nA range) currents collected on electrodes held at high voltages (a few kV). This instrument allows us to measure y at the normal electron multiplier operator voltage, but, more generally, it is a low-cost, flexible replacement for a commercial electrometer in many applications, with the added advantage of the floating input. (JHD)