Abstract: A circuit and method for measuring the conductivity of an aqueous sample, as used in an improved instrument for measuring the total organic carbon content of water, provides substantially instantaneous TOC measurements that are repetitively calibrated, and provides substantially improved accuracy of results in a circuit providing improved noise rejection, allowing faster response.

Abstract: An improved instrument for measuring the total organic carbon content of water provides substantially instantaneous TOC measurements that are repetitively calibrated, provides substantially improved accuracy of results in a circuit providing improved noise rejection, allowing faster response, and provides controlled dilution of the sample stream to extent the useful range of the instrument.

Abstract: An improved instrument for measuring the total organic carbon content of water provides substantially instantaneous TOC measurements that are repetitively calibrated, provides substantially improved accuracy of results in a circuit providing improved noise rejection, allowing faster response, and provides controlled dilution of the sample stream to extent the useful range of the instrument.

Abstract: An improved NDIR instrument as used for measuring the carbon dioxide content of a gas sample includes an electrically modulated incandescent lamp disposed at one end of a sample cell for containing the gas to be analyzed, and a first pyroelectric detector at the other end of the cell. The intensity of modulated radiation incident on the detector is measured using paired dual-slope integrators, each integrating the signal on alternate half-cycles of the signal provided by the detector, to determine the concentration of infrared-absorptive gas in the cell. At intervals, the cell is purged by an infrared-transparent gas, and a similar measurement made, allowing correction for long-term drift in the optical characteristics of the instrument.The instrument correctly determines the concentration of CO.sub.2 despite "leakage" of the broad-band infrared radiation emitted by the lamp through the sample to be analyzed.

Abstract: An improved measurement cell and circuit for measuring the electrical characteristics of a liquid sample during exposure to radiation includes a glass cell formed of a main tube extending generally parallel to an elongated lamp emitting the radiation, and a pair of electrodes disposed axially within the sample tube. In the preferred embodiment, the ends of the cell are formed of glass twinbore tubing fused to the glass main tube, the bores retaining ends of the electrodes. Inlet and outlet tubes and a temperature sensing well may also be fused to the main tube. In an implementation for measurement of TOC in water by oxidation to CO.sub.2, the source comprises a low pressure mercury vapor lamp, and the electrodes are formed of solid Ti with catalytic TiO.sub.2 surfaces.

Abstract: An apparatus for removal of organic materials from water includes a reactor for photocatalytic oxidation and/or ionization of organics in the water stream and an ion exchange column for removal of CO.sub.2, dissolved acids, and ionized organics formed in the reactor from the water stream. The reactor includes an elongated flow chamber having an inlet at one end and an outlet at the opposite end. A photocatalytic material is provided as a surface layer on a number of solid members in the chamber, typically a number of rods extending generally parallel to the axis of the flow chamber. The catalyst may be TiO.sub.2 formed by oxidizing the surface of Ti rods. An elongated UV lamp fitting within a tubular quartz window extends along the axis of the reaction chamber. An external circuit connects the electrodes and the water, such that a current flows in the water in the reaction chamber. A potential of up to 600 VDC may be applied between the solid electrodes and water in the chamber.

Abstract: Improved circuits for measuring the conductivity of a solution confined between two electrodes in a cell compensate for series capacitance and parallel capacitance between the electrodes. A bipolar square-wave signal is applied to the cell. In one embodiment, the current through the cell is measured by an op-amp in current-to-voltage converter configuration. A feedback resistance employed with the op-amp in a feedback loop is controlled to a low value to ensure that the parallel capacitance is fully charged during an initial portion of each half-cycle of the drive signal. The feedback resistance is then selected so that the gain of the feedback loop is responsive to the range of the resistivity of the solution, and the measurement is made.

Abstract: Apparatus and methods for measurement of total organic carbon content of water, particularly of low relative organic content, are described, featuring a single sample cell for exposure of a static sample to ultraviolet radiation and comprising electrodes for measuring the conductivity of the water. The conductivity is monitored as a function of time and the second time derivative of the conductivity signal is monitored to indicate when the oxidation reaction has been completed. Compensation for the contribution to conductivity of the water sample made by the instrument is achieved by subtracting a quantity proportional to the first time derivative of the conductivity at a time when the second time derivative reaches zero, indicating that the oxidation reaction is complete, from the change in the total conductivity measurement, the remainder being equal to the contribution to conductivity made by oxidation of the organic content of the water.

Abstract: Improved circuits for measuring the conductivity of a solution confined between two electrodes in a cell compensate for series capacitance and parallel capacitance between the electrodes. A bipolar square-wave signal is applied to the cell. In one embodiment, the current through the cell is measured by an op-amp in current-to-voltage converter configuration. A feedback resistance employed with the op-amp in a feedback loop is controlled to a low value to ensure that the parallel capacitance is fully charged during an initial portion of each half-cycle of the drive signal. The feedback resistance is then selected so that the gain of the feedback loop is responsive to the range of the resistivity of the solution, and the measurement is made. The period of the bipolar signal is selected responsive to the selected loop gain, to ensure that a filter capacitor across the op-amp is fully charged, and to limit distortion caused by the series capacitance.

Abstract: Apparatus for measurement of total organic carbon content of water, particularly of low relative organic content, is described which features a single sample cell for exposure of a static sample to ultraviolet radiation comprising electrodes for measuring the conductivity of the water. The conductivity is monitored as a function of time and the second time derivative of the conductivity signal is monitored to indicate when the oxidation reaction has been completed. Compensation for the contribution to conductivity of the water sample made by the instrument is achieved by subtracting a quantity porportional to the first time derivative of the conductivity at a time when the second time derivative reaches zero, indicating that the oxidation reaction is complete, from the change in the total conductivity measurement, the remainder being equal to the contribution to conductivity made by oxidation of the organic content of the water.

Abstract: Apparatus and methods for measurement of total organic carbon content of water, particularly of low relative organic content, are described, featuring a single sample cell for exposure of a static sample to ultraviolet radiation and comprising electrodes for measuring the conductivity of the water. The conductivity is monitored as a function of time and the second time derivative of the conductivity signal is monitored to indicate when the oxidation reaction has been completed. Compensation for the contribution to conductivity of the water sample made by the instrument is achieved by subtracting a quantity proportional to the first time derivative of the conductivity at a time when the second time derivative reaches zero, indicating that the oxidation reaction is complete, from the change in the total conductivity measurement, the remainder being equal to the contribution to conductivity made by oxidation of the organic content of the water.