Abstract: Compensation for the temperature sensitivity of the output of a potentiometrically operated ISFET probe whose drain-source voltage and drain-source current are held constant is provided by using a Nernstian temperature correction of the difference between the ISFET output and the isopotential voltage of the probe and offsetting the resulting difference by the isopotential pIon value. An ISFET/NISFET pair provides a cancellation of variations due to manufacturing.

Abstract: There is provided a system for measuring a selected ion in a solution so as to avoid noise pickup from AC parasitic currents and measurement offset from DC parasitic currents, such as are frequently found in pH measurements on low conductivity grounded solutions like high purity water. The system in one form has an operational amplifier with an ion selective electrode connected to its inverting input, a counter electrode connected to its output, and circuit common connected to the non-inverting input, so that the potential of the ion selective electrode is continuously driven to circuit common. The reference electrode of the system is connected to a high impedance measuring circuit for measuring the voltage level of that electrode with reference to circuit common as a measure of the concentration of the selected ion in the solution.

Abstract: The membrane of an ion selective electrode is tested for damage while it is being used for continuous measurement by sending a test current through the electrode system and measuring the voltage change produced. If the voltage change does not reach the value expected with an intact high resistance electrode, a defective electrode is indicated. A reverse current of the same magnitude and duration is then sent through the electrode system.

Abstract: An electrochemical cell and method for monitoring toxic compound atmosphe contamination comprising a coiled measuring electrode means, an elongated reference electrode means, a reaction chamber means, an oxime electrolyte means, and a thermal compensating network means; said cell being connected to an electric circuit and alarm means to monitor said contamination.