The CS511 is a rugged, low-maintenance sensor that is manufactured by Sensorex. It consists of a self-polarizing galvanic cell that generates a millivolt signal proportional to the amount of oxygen present in the measured medium (typically water). Oxygen diffuses through its membrane onto a cathode that produces a chemical reaction. An electrical current is produced by this reaction, which is converted from microamps to millivolts by an in-line resistor. An in-line thermistor provides automatic temperature compensation.