Continuous measurement of pH of aqueous solution - uses preamplifier in immediate vicinity of electrodes incorporating integrated operational amplifier

摘要

Continuous measurement of the pH of an aqu. soln. is performed by a device incorporating a pair of electrodes (V) and (R) immersed in the soln. and connected to a preamplifier (A1) which is in the immediate vicinity. A cable (c) interconnects the preamp with a further amplifier (A2) which drives a galvanometer (g) calibrated directly in pH. Amplifier (A1) receives low tension A.C. over conductors (1) and (2) which drives an integrated operational amplifier serially connected to a magnetic amplifier which ensures isolation between input and output of the preamp. The low tension input to preamp (A 1) enters a three winding transformer the output of which is full wave rectified to provide the requisite DC drive currents to the operational and magnetic amplifiers. The amplifier (A2) may feed a data logging device or a system control unit in a feedback system and also comprises an operational amplification stage.