A-C null-type recorder with balancing amplifier which provides damping and suppresses the quadrature component

ELECTROLYTIC conductivity is a good example of a measurement which can be made most satisfactorily by using an a-c null-type instrument. The use of alternating current instead of direct current reduces polarization at the electrodes. The use of a null-type recorder permits the measurement of conductivity directly by means of a Wheatstone bridge, thus avoiding the need for voltage regulation. This paper describes difficulties encountered when an unimproved electronic balancing amplifier is tried for this type of instrument. Theory and performance of an improved amplifier are given.