Abstract: A method and system for determining dissolved oxygen is disclosed. One or more constant currents are driven through amperometric-type dissolved oxygen probes to develop reference electrode potentials defining the envelope of oxygen electrochemistry. The reference electrode voltage is generally measured at a first current level and at a second current level utilizing the oxygen probe, wherein the first and second current levels define limitations of oxygen electrochemistry. An optimum electrode bias voltage can thereafter be automatically calculated based the reference electrode voltage measured at the first current level and the second level to thereby provide accurate indications of dissolved oxygen thereof.

Abstract: A method and system for determining dissolved oxygen is disclosed. One or more constant currents are driven through amperometric-type dissolved oxygen probes to develop reference electrode potentials defining the envelope of oxygen electrochemistry. The reference electrode voltage is generally measured at a first current level and at a second current level utilizing the oxygen probe, wherein the first and second current levels define limitations of oxygen electrochemistry. An optimum electrode bias voltage can thereafter be automatically calculated based the reference electrode voltage measured at the first current level and the second level to thereby provide accurate indications of dissolved oxygen thereof.

Abstract: Methods, apparatus and chip fabrication techniques are described which provide electrostatic discharge (ESD) protection to ion-sensitive field effect transistor (ISFET) based devices used to selectively measure ions in a liquid. According to one aspect of the invention, an ESD protection circuit, made up of conventional protective elements, is integrated onto the same silicon chip on which the ISFET is formed, along with an interface that is in contact with the liquid being measured and which does not open up paths for D.C. leakage currents between the ISFET and the liquid. According to a preferred embodiment of the invention, a capacitor structure is used as the interface between the protection circuit and the liquid sample. Further aspects of the invention are directed to methods per se for providing ESD protection for ISFET sensors utilizing the interface means (e.g, capacitor structure) referred to hereinabove, and processes for fabricating the novel interface on a silicon wafer.

Abstract: Methods, apparatus and chip fabrication techniques are described which provide electrostatic discharge (ESD) protection to ion-sensitive field effect transistor (ISFET) based devices used to selectively measure ions in a liquid. According to one aspect of the invention, an ESD protection circuit, made up of conventional protective elements, is integrated onto the same silicon chip on which the ISFET is formed, along with an interface that is in contact with the liquid being measured and which does not open up paths for D.C. leakage currents between the ISFET and the liquid. According to a preferred embodiment of the invention, a capacitor structure is used as the interface between the protection circuit and the liquid sample. Further aspects of the invention are directed to methods per se for providing ESD protection for ISFET sensors utilizing the interface means (e.g, capacitor structure) referred to hereinabove, and processes for fabricating the novel interface on a silicon wafer.

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: A transducer housing assembly for an ultrasonic flowmeter made by an injection molding having a pair of pedestals for supporting the transducers at a specific angle while acoustically isolating the transducers from each other and providing an air backing for the transducers to improve the sensitivity of the transducer assembly.

Abstract: An ultrasonic Doppler flowmeter for measuring flowing fluid by reflection of sonic waves from particles in the fluid is provided with a discriminating circuit including a comparator amplifier connected to the received signal that produces a zero-flow output from the flowmeter when the signal received by the receiving means is produced by vibration of the reflecting particles in a zero-flow condition.

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 ultrasonic Doppler flowmeter is provided with a frequency-to-voltage converter comprising a pair of interconnected filp-flops triggered by the Doppler frequency and a submultiple of the transmission frequency which produces a series of output pulses having a repetition rate determined by the Doppler frequency and a pulse duration inversely related to the frequency of transmission of the ultrasonic transmitter.