Apparatus for Guarded Polarization Measurements

A circuit is presented for making guarded polarization measurements in situ on samples which vary from 10 to 108 Ω over the temperature range of the experiment. The time dependence of the voltage at constant current (or the current at constant voltage) can be followed from less than 1 msec to several days. Combined leakage resistance 105 times smaller than the sample resistance results in less than 1% error in the measurements. The circuit should prove generally useful whenever automatic guarding is required over a wide frequency range (including dc).