Performance characteristics and calibration of the ENDECO pulsed dissolved oxygen type 1125 system

The initial response pattern for a conventional two-electrode, membrane-type dissolved-oxygen probe connected to an ENDECO model 1125 dissolved-oxygen sensor controller is presented. The controller implements a chronoamperometric technique and involves application of the polarizing potential as a pulse. The pulse duration confines the diffusion boundary within the internal electrolyte and the membrane. The time required for readout stabilization is attributed to the establishment of an equilibrium involving diffusion of reactant and product of the electrochemical reaction. A procedure for minimizing the role of membrane stretch in establishing the equilibrium time is discussed. Data obtained on changing the pulse repetition interval are presented in support of the establishment of an equilibrium condition. Sensor response over a 32-day period is noted. Calibration curve data demonstrate the linearity of response with varying oxygen concentrations. Response time data indicate attainment of better than 99% of full deflection within three minutes of a change in oxygen concentration