Common mode voltage rejection circuit

DETAILED DESCRIPTION The principal object of the invention is to minimize the common mode excursions experienced by a differential measurement instrument such as an amplifier by balancing its input leads and by establishing the zero reference point of the instrument at a well-defined impedance relative to earth.
A second object of the invention is to eliminate the switching of the input leads shield in multi-transducer systems thereby limiting the multiplexer to a two-pole switch for each channel, and reducing its costs.
A third objet of the invention is to maintain an effectively high input impedance for the measuring instrument by a judicious choice of absolute and relative values of the components of a front end common mode voltage rejection circuit.
A fourth object of the invention is to realize and maintain high common mode rejection over a wide temperature range using inexpensive components such as carbon and metal film resistors.
These and other objects are achieved by a simple voltage divider circuit which generates a driving potential for the Faraday cage and the instrument zero reference point, and provides a potentiometer for adjusting the effect of imbalance in the path resistance of the input leads.