Elements of general theory of null-balance circuits

The null-balance method of output indication is widely used in instrumentation techniques and sensor applications. Yet, the theorems and methods of general circuit theory that are the basis of the null-circuit analysis and design have nearly disappeared from the modern books on network theory. In this paper the elements of general theory of null-balance circuits are presented. The relationships between two-port parameters of passive null-balance circuits are described, and the applications are demonstrated using bridge circuits. The systematic calculation of null-balance circuit sensitivity is given, and this procedure shows the importance of the theory of autonomous two-ports and the compensation theorems in the theory of null-balance circuits.