On strategies for automatic bridge balancing

Automatic balancing of coaxial AC impedance bridges asks for simple, robust and efficient strategies suitable to be easily implemented on PC controllers. The paper considers the problem of balancing a bridge with n detectors to be equivalent to the problem of finding the root of a complex-valued vector function F. To avoid electrical modeling of the bridge, F is considered generally unknown except at specific points evaluated by experiment. In this framework, efficient root-finding strategies can be employed; in particular, secant method and two generalizations of it to the case n>1 are proposed. Experimental results on a test circuit are given.