Dissolved oxygen sensor calibration, monitoring and reporting system

Claim 1

A test and monitoring system for providing automatic on-line, real-time calibration and monitoring of the condition of a dissolved oxygen sensor comprising: (a) said sensor having a housing, an anode electrode, a cathode electrode, an electrolyte, and a permeable membrane, said sensor immersed in a process solution; (b) a test electrode immersed in said process solution adjacent said permeable membrane; (c) generator means for generating a low level, time varying signal, an output of said generator connected between a system ground and said test electrode for producing a time varying current through said membrane to said cathode electrode, and through a resistor to said system ground; (d) means for measuring a voltage drop across said resistor from said time varying current and a dc reference current in which a time varying component is proportional to the impedance of said membrane; (e) a pair of electrolysis electrodes disposed within said sensor and immersed in said electrolyte solution in a closely spaced relationship, a first one of said electrolysis electrodes connected to said system ground; (f) a pulsed direction current source connected between a second of said pair of electrolysis electrodes and said system ground for producing electrolysis in said sensor electrolyte solution to thereby release a pulse of a predetermined volume of oxygen within said sensor, said oxygen producing a controlled increase in dissolved oxygen relative to dissolved oxygen due to the process, wherein said oxygen sensor produces a voltage pulse, from said dissolved oxygen increase, superimposed on a process oxygen level voltage; and (g) means for comparing the rise time, magnitude, and decay time of said oxygen voltage pulse with calibrated values and for detecting deviations from calibrated values indicative of deterioration of said dissolved oxygen sensor.