ERROR IN POTENTIAL MEASUREMENTS DUE TO NON-UNIFORM CONTACT IMPEDANCE OF ELECTRODES

When an electrode is used to measure electric potential at a point in an electrolyte (or other weakly conducting medium) the non-uniform distribution of contact impedance over its surface coupled with a potential gradient in the electrolyte can result in a deviation of the measured potential from that expected. The calculation of this error in the case of high contact impedance has been considered elsewhere. In this paper the error is calculated in the other extreme case of low contact impedance. Here Laplace's equation has to be considered under mixed boundary conditions. Using results from the theory of an electrified disc the error can be expressed as an integral over the electrode surface of the contact impedance multiplied by a simple weighting function. Values of the error for particular impedance distributions are calculated. 1