The sensitivity and calibration of partial-discharge detection systems is an important aspect of the general subject of partial-discharge measurements of products or structures involving electrical insulating materials. The primary objective is to perform a measurement, using a detection system having a sensitivity adequate to the purposes of the test, in the presence of inevitable electrical noise. Of equal importance is the matter of calibration which requires that fairly-accurate information be obtained as to the magnitudes of the changes that take place in the insulation system when it is stressed at some particular voltage.