The Model 499ADO sensor is intended for the continuous determination of dissolved oxygen between 0-20 ppm. The primary application is flue gas scrubbers and wastewater treatment.
The Model 499ADO is a membrane-covered amperometric sensor. The sensor consists of a gas-permeable membrane stretched tightly over a gold cathode. A silver anode and an electrolyte solution complete the internal circuit. During operation, oxygen diffuses from the sample through the membrane to the cathode. A polarizing voltage applied to the cathode reduces the oxygen to hydroxide. The reaction produces a current, which the analyzer measures. The current is directly proportional to the rate at which oxygen reaches the cathode, which is ultimately proportional to the concentration of oxygen in the sample.
Because the rate of diffusion of oxygen through the membrane depends on temperature, sensor response must be corrected for changes in membrane permeability caused by temperature. A Pt 100 RTD in the sensor (Delta-compatible sensors use a thermistor) measures the temperature, and the analyzer automatically performs the correction.