PRINCIPLE OF SURFACE-CHARGE MEASUREMENT FOR THICK INSULATING SPECIMENS

We discuss the method for measuring surface charge density accumulated on the surface of a solid dielectric (insulating specimen) such as a supporting spacer in gas and vacuum insulated equipment. For such thic k specimens, the probe response does not correspond to the charge dens ity directly below the probe, so the measurement necessitates multipoi nt data together with the aid of numerical field calculations. The pro be gives either induced charge or floating potential in response to th e surface charge. We compare various previously proposed techniques an d give a reasonable procedure for analyzing the data.