Abstract: An instrument for measuring cathodic protection voltage levels receives a signal representative of an externally applied, full-wave rectified power line frequency cathodic protection potential, which is subject to electrical interference. The fundamental power line frequency component and odd harmonics of that fundamental component are removed to produce a filtered signal. Selected parameters of the filtered signal are measured to provide an indication of the adequacy of the cathodic protection potential.

Abstract: A method of producing an exhaust gas sensor incorporating BaSnO.sub.3. Stannate ion and barium ion are reacted in a strong alkali to precipitate water-containing crystals of BaSnO.sub.3 such as BaSnO.sub.3.3H.sub.2 O, BaSnO.sub.3.5H.sub.2 O or the like. When thermally decomposed, the precipitate gives BaSnO.sub.3 free from segregated Ba and Sn elements. The product was then molded and thereafter sintered to obtain the sensor.

Abstract: Apparatus for measuring the interfacial impedance in an electrochemical cell having a pair of electrodes in contact with an electrolyte medium that includes circuitry for measuring the interaction current flowing between the electrodes at a series of predetermined external impedance values and an analyzer for determining the interfacial impedance based on the current measurements.

Abstract: In a resistive-sensor type indicator having a resistive sensor whose resistance changes according to a quantity to be measured and an indicator for indicating a sensor output voltage developed across the resistive sensor, when the resistive sensor is open due to disconnection or malconnection of the resistive sensor, the indicator indicates a maximum reading, thus resulting in a problem such that the user cannot recognize the abnormal state. To overcome this problem, a novel trouble detecting circuit is additionally incorporated in the indicator. The circuit comprises a comparator for outputting an abnormal signal when the sensor voltage exceeds a reference voltage and a transistor for grounding the resistive sensor in response to the abnormal signal. Therefore, the indicator indicates a minimum reading in case of resistive sensor trouble.

Abstract: In a particle counter of the Coulter Counter type the orifice size can be varied by the insertion of an insert into the orifice. This enables particles of a wide ranged of sizes to be effectively detected.

Abstract: Apparatus and methods for winding a wire around a periphery of a structure. The wire is connected to the structure and then pulled around that structure in a manner that produces a high tension in a portion of the wire and that winds that high tension portion of the wire around the structure. The high tension portion of the wire is monitored to detect any flaws in the wire coating or cover, and the locations of these flaws are recorded.

Abstract: A protected, lipid membrane-based device useful as a chemoreceptive transducer is provided. The device includes a porous, membrane-protective layer attached to an underlying, lipid membrane. Also provided is a process for using the protected device to determine the concentration of a specified chemical species.There is additionally provided a lipid membrane-based gas sensor. The sensor includes a gas-permeable, hydrated upper layer attached to an underlying lipid membrane. Furthermore, the invention includes a process for using the gas sensor to determine the concentration of an inorganic ion formed from an inorganic ion-forming gas.

Abstract: The electrochemical sensor, which is designed more especially for monitoring the correct function of exhaust gas cleaning means in exhaust gas systems, has a solid electrolyte and a diffusion barrier of porous material and is arranged downstream from the exhaust gas cleaning means in the exhaust gas pipe. The sensor operates in a temperature range of -50.degree. C. to 500.degree. C., throughout which it functions substantially independently of temperature. Preferably nitrogen oxides are used as representative components for monitoring the efficacy of the exhaust gas cleaning means and a signal is produced when the signal from the sensor exceeds a given value.

Abstract: A general purpose potentiostatic test system, used to provide potentiostatic control of test electrodes using a multiplexer in both the anodic and cathodic regimes. A built-in data switching and measurement subsystem enables rapid and precise determination of the set potentials as well as the test electrode currents. All the test electrodes can be placed in the same test tank and use a single auxiliary electrode.

Abstract: A method and apparatus for measuring the remaining charge of a galvanic cell effects the measurement of the remaining charge by superimposing an AC voltage or current on DC voltage or current issuing from the cell to produce a higher harmonic current or voltage, determining the value corresponding to a higher harmonic component of n'th order from the higher harmonic current or voltage, and comparing the value thus measured of the cell under test with that measured previously in the same manner of a reference galvanic cell. Since the corresponding value of the higher harmonic current or voltage of n'th order varies notably with the decrease in the remaining charge of the galvanic cell, the comparison of the found corresponding value with the reference characteristic is effected with ease and the measurement can be carried out accurately and simply.

Abstract: Method for the protection and/or monitoring of a reference system with reference electrode in analytical measuring techniques, and reference system therefor, wherein an additional monitor electrode is provided for self-monitoring the outer bridge electrolyte (16) for contamination, the additional monitor electrode being arranged to permit measuring of the pH value (pX value) of the bridge electrolyte which is adjusted to the same pH value (pX value) as the reference electrolyte. A fault signal is released when a potential difference occurs between the additional electrode and the real reference electrode of the reference system. Further, the bridge electrolyte is preferably connected with the measured solution in pressure-balancing relationship via a flexible diaphragm arranged in the wall of the vessel containing the bridge electrolyte which diaphragm may also be designed to serve as mounting for the said first diaphragm.

Abstract: In a cathodic protection system for protecting a metal structure in contact with a surrounding electrolytic medium, method and apparatus are provided for directly measuring current density. A small metal sample cathode of a like material as the metal structure having a predetermined surface area exposed to the electrolytic medium is located adjacent the surface of the metal structure. A direct electrical path is completed between the sample cathode and the metal structure that is substantially IR free. At least a portion of the electrical path between the sample cathode and the metal structure is insulated from the surrounding electrolytic medium and the metal structure. A voltage directly proportional to the current passing through the electrical path is generated by disposing a toroidal coil in the insulated space by detecting the flux field associated with the current flow through the sample cathode.

Abstract: A predetermined amount of erosion of a material conveying conduit or the like is detected by inserting a probe in the conduit wall, from the side opposite to that subjected to the wear, to a predetermined depth. The probe comprises an insulated conductor which is in electrical contact, at the base of the blind hole, with the conduit. Wear of the conduit down to the level of the probe may be determined by periodic continuity measurements, a lack of continuity indicating that the inserted end of the probe has been exposed.

Abstract: An apparatus for monitoring a cathodic protection system on a structure which is positioned in water such that a portion of the structure is beneath the surface of the water, such apparatus comprising: an insulating means positioned adjacent to the structure below the surface of the water; a metallic body positioned adjacent to the insulating means so that the body is electrically insulated from the structure; means for electrically connecting the body to the structure at a point above the surface of the water; and means for measuring the amount of current flowing through the electrical connecting means.

Abstract: Apparatus for measuring electrical potential in a cell, especially at a point close to a sample electrode, comprises an accommodation for a reference electrode, a modified luggin tube, elements for locating the sample electrode, and supports for both the luggin tube and the locating elements, respectively, the supports being fixed relative to each other. The apparatus requires less skill in the positioning of the sample electrode close to the point at which electrical potential is measured and is less vulnerable to inadvertent disturbance.

Abstract: Method and means for determining the corrosion status of a coated undergrd metallic object without the necessity of excavation. An electrical charge is produced on an area of the pipe, and the rate at which the charge decays is measured. The degree of corrosion of the object is measured as a function of the rate of decay of the charge and the area charged.

Abstract: The clogging of junctions of electrochemical reference cells by contaminants is prevented by a triple junction design incorporating dual, independently operative flushing conduits. The first conduit flushes the exterior of the first junction and the exterior of the second junction, and the second conduit flushes the interior of the second junction and the exterior of the third junction. When the cell is used in-line on a chemical process stream, pressure equalizing means are employed between the stream and the standard electrode, of which the third junction is an element. Elevation of the exits of the flushing conduits above the junctions releases air from the cell which may collect at the junctions and impair the accuracy of the readings.

Abstract: The polarized potential at the boundary between a submerged pipe and a medium is measured unaffected by the presence of a distributed IR drop in the medium due to an impressed current from a corrosion protection system. The voltage between the pipe and a reference electrode in the medium is measured when the protection system current is zero. This is accomplished with a sample-and-hold circuit controlled by a trigger signal derived from the input signal and having a variable phase for controlling the phase angle at which the sample is taken.

Abstract: The present invention relates to a wheel electrode suitable for use with a device for making an electrical survey of a structure contained in an electrolyte. The wheel electrode includes a chamber which contains electrolytic solution and a porous rim. The rim includes a dielectric rim structure having at least one recess in its axial surface, a plurality of apertures passing through the rim structure into the recess, and at least one porous member securable in the recess and having a predetermined rate of permeation. A metal electrode is positioned in the chamber in contact with the electrolytic solution. An elastic porous rim cover is securable about the rim for making contact with the electrolyte. The rim cover is adapted to carry an electrically conductive solution to the electrolyte during wheel rotation. Generating mechanisms are spaced about the wheel electrode at predetermined intervals for generating a series of electrical signals as the wheel electrode rotates.

Abstract: In an apparatus or installation having a metal part corroding in an electrolyte contacting the part, that part is a first electrode electrically insulated from a second electrode, for example another part of the apparatus, also contacting the electrolyte. No external electrical power is applied to the electrodes/electrolyte system. The low frequency voltage between the electrodes is observed. This voltage is a low frequency noise signal. Amplitude values of the signal are measured and subjected to an averaging computation yielding data indicating the corrosion rate of the first electrode and the nature of the corrosion.

Abstract: A device for sensing the presence of and measuring the concentration of a specific non-aqueous particle or gas material in an environment, the device comprising an interdigitated capacitor having at least a pair of selected covering layers thereupon, said pair of layers comprising a first passive electrically insulative layer and a second material layer having a spacial relationship to said first layer, said second layer selectively permeable to the specific material to be sensed and measured; said second coating, when juxtaposed said first coating, selectively permitting permeability of the particular material sought to be sensed and measured, and when spaced apart, permitting passage through of the specific material in order that the material may migrate to the proximity of the first coating and thereby be sensed and measured.

Abstract: In the formation of a paper web from stock fed to a Foudrinier wire, the Zeta Potential is an important parameter. A measure of Zeta potential is made by measuring the streaming potential developed in a vertically-arranged cell having a horizontal mesh therein on the underside of which a pad of fibres and fines is formed by pumping stock into the lower part of the cell. Electrodes located in the cell above and below the pad are used to obtain a measure of streaming potential at a given pressure differential across the pad. A pressure transducer is mounted in the lower part of the cell. Corrections are made for temperature and conductivity by sensors in the stock feed path to the cell. A microprocessor control and measuring circuit is disclosed which sequences valves for controlling the flow of stock and flushing fluid to the cell and which measures the relevant parameters.

Abstract: An electrolysis test station terminal (10) support for use in connection with measurement of electrical properties of an underground pipe (12). The terminal support includes an elongated web structure (21) formed of nonconductive plastic material and including at least one longitudinal rib (17, 18, 19) integrally formed as part of the web structure. A hollow core (30, 31, 32) is formed within the longitudinal rib and provides a housing for conductive wire (37, 38) to be concealed therein. An opening in the longitudinal rib provides access to the core to enable physical contact (37a, 38a) for measurement of electrical properties as conducted from the underground pipe through the wire into the terminal support.

Abstract: The intrinsic time constant .tau. of liquids is measured directly by using he apparatus of the present invention termed a "taumeter". The taumeter impresses a predetermined voltage, level between a pair of electrode immersed in the liquid to be measured. The taumeter then measures the time it takes for the foregoing voltage to decay from a predetermined value V.sub.A to a predetermined value V.sub.B. Comparator logic produces a gate pulse having a leading edge at a time T.sub.A corresponding to the occurrance of the predetermined voltage V.sub.A and a trailing edge at a time T.sub.B corresponding to the occurrance of the predetermined voltage V.sub.B. The gate pulse is used to gate a system counter which counts the zero crossings of a very accurate system clock to determine the intrinsic time constant of the liquid. The foregoing pulsing is repeated as determined by a duty cycle generator.

Abstract: An E-Log I field computer includes a controlled power supply, timers, and a current level stepping relay for circulating cathodic current through a buried metal structure, interrupting the current to allow the decay of residual polarization of the structure and electrolytes within the surrounding ground, and measuring the circulated current and the voltage of structure relative to the ground. The circulated current, voltage of the structure to the ground, and other parameters of interest, such as, the output voltage of the power supply are printed. Then the current level is increased by the stepping relay, and the process is repeated. When a sufficient number of readings have been taken, the data is plotted as a semi-log graph, resulting in an E-log I curve from which the corrosion current and therefore the cathodic protection voltage can be determined.

Abstract: An apparatus for monitoring ion concentrations in an aqueous solution comprises a plurality of electrodes insertable into the solution. At least two of the electrodes are ion-selective for particular ions. Each ion-selective electrode is electrically connected to a corresponding impedance buffer, which generates a low-impedance output signal having the same voltage as the electode. A plurality of operational amplifiers in full differential configuration is provided, each operational amplifier receiving a particular pair of output signals generated by the impedance buffers. Each differential amplifier generates an output signal indicating the potential difference between the impedance buffer output signals received as inputs by the differential amplifier.

Abstract: An optical fiber joint type ion-concentration measurement apparatus in which electrical signals which are detected by an ion selective electrode are transformed into optical signals which are transmitted to a receiving side of the apparatus by means of optical fibers. The detected signals from the electrode are frequency modulated by a voltage/frequency converter and the output of the voltage/frequency converter is used to control an electronic switch. The electronic switch controls a series circuit including a power source and a charging-discharging capacitor and a light emitting diode. The frequency modulated transformed detected signals therefore cause the light emitting diode to emit optical signals which are then transmitted by means of optical fibers. On the receiving end of the apparatus, the optical signals are transformed into electrical signals by a photo diode and then demodulated by a frequency/voltage converter to reproduce the original detected signals from the ion selective electrode.

Abstract: An electrochemical instrument for use with an electrochemical cell that provides IR compensation while operating as either a galvanostat or a potentiostat. The instrument includes an electronic circuit having two output terminals, an input differential amplifier circuit, an output differential amplifier circuit, a control differential amplifier circuit, a reference differential amplifier circuit, a resistor, electric circuitry connecting the input terminal of the control amplifier to the instrument output terminal and a double pole, double throw switch means. In a preferred embodiment, the electric circuitry connecting the control amplifier to the instrument output terminal is a potentiometer.

Abstract: A circuit arrangement is disclosed for correcting the output of a sensor which experiences changes in sensitivity due to the presence of one or more influencing factors, such as the concentration of a material to be sensed, or the passage of time. The circuit arrangement includes a correction network which generates a simulated sensitivity curve which simulated curve is combined with the output of the signal to produce a corrected output signal which has apparent constant sensitivity.

Abstract: A system for assessing the effectiveness of a water softener or comparable liquid-processing apparatus whose effectiveness is related to the difference between the electrical conductivity of the liquid supplied to the apparatus and the electrical conductivity of the liquid that has passed through the apparatus includes two inductance loop conductivity sensors excited by a common signal generator. The outputs of the sensors, which typically include unwanted quadrature components, are applied directly to the inputs of a differential amplifier. The resulting difference signal is then applied to a detector that is gated by the common excitation signal, so as to produce a detected signal that is substantially unaffected by the unwanted quadrature components. In a preferred embodiment, each of the inductance loop conductivity sensors includes two electrodes connected by a conductor that links two toroids.

Abstract: An apparatus for monitoring a cathodic protection system on a structure which is positioned in water such that a portion of the structure is beneath the surface of the water, such apparatus comprising: an insulating means positioned adjacent to the structure below the surface of the water; a metallic body positioned adjacent to the insulating means so that the body is electrically insulated from the structure; means for electrically connecting the body to the structure at a point above the surface of the water; and means for measuring the amount of current flowing through the electrical connecting means.

Abstract: A backelectromotive force of an aluminum electrolysis cell is measured by the steps of: (a) repeatedly measuring voltage V and current I of the cell at a short interval; (b) forming groups of data each including measured values thus obtained within a relative short period; (c) calculating a constant e and its variance Ve with reference to each data group according to a linear regression expressed by an equation:V=r.multidot.I+ewhere r represents an internal resistance of the cell; (d) calculating a backelectromotive force E and its variance V.sub.E at a given time based on the constant e and its variance Ve calculated at the step (c), a backelectromotive force E' and its variance V'.sub.E with reference to a data group preceding the given time and a constant V.sub.T, and according to the following equations:P=(V'.sub.E +V.sub.T)/(Ve+V'.sub.E +V.sub.T)E=P.multidot.e+(1-P).multidot.E'V.sub.E =P.sup.2 .multidot.Ve+(1-P).sup.2 .multidot.(V'.sub.E +V.sub.

Abstract: A measuring device for measuring the potential, relative to the earth, of a metallic structure buried in the earth, and cathodically protected by an externally applied DC voltage. The measuring device includes the combination of a metallic, rod-shaped probe adapted to be driven into the earth, a major portion of which is coated with an electrically insulating material. A small portion of the probe near the bottom end thereof is left uncoated and constitutes a measuring electrode. A reference electrode is situated in a transverse bore near the bottom end of the probe, and is electrically insulated therefrom. The probe is adapted to be electrically connected to the metallic structure, for measurement of and the potential difference between the measuring and reference electrodes.

Abstract: A reference electrode (102), standard calibration solutions (72 and 76) and a sample solution (80) are all placed in liquid contact with one another and a reference solution (70). Contact between the reference solution (70), the sample (80) and the calibration solutions (72 and 76) is made through salt bridges (82, 74 and 78). A special conical shaped solution container (FIG. 5) having a porous plug or other salt bridge extending through the container wall at the apex provides special advantage.

Abstract: A method for controlling the electro-deposition of metal from an aqueous electrolyte containing two organic polarizing agents is disclosed. The method requires measuring the nucleation overpotential, the plating overpotential, and the difference between these potentials. By relating these measurements to predetermined values, optimum process control can be obtained by changing the concentration of the various organic polarizing agents in the process electrolyte.

Abstract: Apparatus for use in determining electric potentials underwater includes Luggin tubes of small diameter which are open to the water at outer ends thereof. The outer ends are arranged at known spaced positions relative to one another. The potentials at the ends of the tubes are connected selectively via fluid in the tubes to a reference electrode. The potential at the reference electrode relative to a further electrode is measured.

Abstract: An arrangement for monitoring the potential of a cathodically protected buried metallic structure. The apparatus includes a measuring electrode to be inserted into the soil and electrically coupled to the metallic structure to be measured, a reference electrode placed on or in the soil, and a measuring circuit for measuring the potential difference between the measuring and reference electrodes. The measuring circuit also generates a reference potential to generate a pulse signal having a frequency proportional to the amount by which the measured potential exceeds the reference potential. A counter counts the number of pulses during a measuring cycle that is measured by a timer. A computer computes from timer and counter output data, the average value of the amount by which the measured potential exceeds the reference potential during a measuring cycle.

Abstract: Disclosed herein is an apparatus for charging a battery including a case containing at least one cell formed of a pair of electrodes immersed in an electrolyte. The apparatus includes a transducer associated with the battery and operable without sensing gas pressure in the battery case for providing a variable signal output in response to electrolyte gassing within the battery case. The apparatus also includes a control circuit arrangement coupled to the signal output for providing a variable control output in response to the signal output, and a battery charger connected to the battery electrodes and operable for charging the battery at a rate subject to the variable control output. In one embodiment of the invention, the transducer is a sound transducer, preferably a ceramic microphone, which provides a variable signal output in response to sound generated within the battery case.

Abstract: An apparatus and method of conducting continuous or closely spaced buried structure-to-soil electrical surveys uses a soil contact cell adapted to be worn on the bottom of the walking field boots of a surveyor walking over the right-of-way of the buried structure such as an underground pipeline. The cell is in the form of a sandal which may readily be secured to and removed from the bottom of the boot. The cell includes an impervious upper plate and a pervious lower ground contacting flexible sole plate forming with the upper plate a flat chamber which may be filled with a loose silica sand fill or sponge material. A copper rod or strap is imbedded in the material and electrically connected through a meter carried by the surveyor to the structure through a length of economically disposable wire.

Abstract: An apparatus for testing the pipe-to-soil potential of a buried pipeline having a plurality of rectifiers electrically connected to it in spaced-apart intervals for applying an electrical potential to the pipe includes a plurality of interrupter units electrically connected to the rectifiers for turning them on and off at intervals. A clock reference unit is electrically connectable to each of the interrupters for synchronizing them for turning all of the rectifiers on and off in unison. A portable sensing device produces signals indicative of the pipe-to-soil potential of the pipe and directs these signals to a demultiplexer unit which is also synchronized with the clock reference unit for separating the signals corresponding to the ON and OFF potentials which are then separately recorded.

Abstract: In the preferred embodiment, an electrochemical method of detecting the presence of tetraalkyl lead (or other organometallic antiknock additive) in an automotive gasoline sample comprises contacting the gasoline with an immiscible methanol solution containing KOH, which solution is the electrolyte of an electrochemical cell. The cell includes a stainless steel anode and a zinc cathode. Tetraalkyl lead is extracted from the sample into the methanol solution and metallic lead is deposited onto the zinc cathode. Thus, the lead deposit is evidence of the presence of tetraalkyl lead in the gasoline. The method is preferably adapted to be carried out on board a vehicle to monitor the fuel used therein.Devices are presented which are adapted to be incorporated into the fuel tank or fuel line of a vehicle for detecting tetraalkyl lead by this method. In one embodiment, the detection device features a cathode comprising two closely spaced zinc surfaces.

Abstract: Apparatus is disclosed for measuring the electrochemical activity of a liquid, for example, the hydrogen ion activity or pH value of blood. A disposable cartridge includes spaced indicating and reference electrodes which develop electrical properties as a function of the electrochemical activity. The cartridge carries a capsule containing an electrolyte solution. A machine for measuring the electrochemical activity includes a socket in a pivoting door for receiving the cartridge. When the door is pivoted into a closed position, the capsule is automatically crushed thereby covering the electrodes with the solution. The breaking of the capsule triggers an electronic measurement of the resultant electrical properties that develop between the two electrodes. This calibration factor is stored and used to compute the electrochemical characteristics of the sample when it is introduced into the cartridge to cover the indicating electrode.

Abstract: A chemical substance detection apparatus comprising a plurality of chemically sensitive elements constructed as an insulation gate field effect transistor formed on one or different substrates and including chemically sensitive portions selectively sensitive to different specified substances and one reference electrode, at least the chemically sensitive portions as well as the one reference electrode being brought into contact with the same test substance so as to detect various specified substances in the test substance, characterized by comprising reference resistors, first amplifiers operative to adjust gain thereof, a differential amplifier in common to all of said amplifiers and applying its output voltage to the reference electrode and a reference gate bias voltage source connected to the input terminals of the differential amplifier and supplying the reference gate bias voltage thereto.

Abstract: A simplified system for practical use in the measurement of specific ion concentrations. A probe for introduction into a fluid stream to measure the ion concentration thereof and said probe comprising an ion sensitive electrode for immersion in a fluid stream in combination with an annular elongated electrode having a noble metal, such as one of the platinum group of metals, on an end surface thereof for immersion in the fluid stream. The combination of the ion sensitive electrode, and the annular elongated electrode having an end thereof with the noble metal is placed in the fluid stream to be measured and is electrically connected to a measurement and/or indicating instruments.

Abstract: An anode depletion detector includes a current carrying probe member which projects into a water heater tank. The probe is normally connected with electric energy storage means which is charged during contact with the probe. To test the level of anode protection, electric energy from the storage means is discharged through a detector. Alternative embodiments for circuits which permit storage and discharge of electrical energy are shown.

Abstract: A test instrument for an electrochemical cell generates a current which counteracts the cell current so that it is briefly reduced to zero thereby allowing the electrode potential or cell potential to be measured free from the IR or ohmic polarization loss. A sample and hold circuit is enabled shortly after the current is interrupted to sense the voltage level of the electrode or electrochemical cell which has only experienced the voltage change due to the IR polarization losses. When cell current is restored, the IR corrected potential stored in the sample and hold circuit is compared to the control potential, and the difference between the two causes automatic adjustment of the average cell current such that the IR corrected potential of the cell is maintained despite any changes in IR polarization.

Abstract: The invention provides apparatus for testing the condition of a battery comprising a load, means to connect the battery to the load for a predetermined interval and means to measure the battery voltage at least at the end of the interval.The invention further extends to apparatus for successively testing the condition of a plurality of batteries comprising means for connecting one of the batteries to a given load for a predetermined interval, means for measuring the voltage of the battery at least at the end of the interval, means for determining the condition of the battery from the voltage measurement, and control means for connecting a fresh battery to the load and repeating the testing of the batteries until all the batteries are tested.The invention also provides a method of testing the condition of a battery including the steps of connecting the battery in a charged condition to a load for a predetermined interval, and measuring the battery voltage at least at the end of the interval.

Abstract: A sensor and method are disclosed for measuring electrokinetic effects across a double layer formed at the boundary between a solid wall and an ionic liquid flowing through a channel. In one embodiment, a passive electrode is located in a cavity forming a tee section with the channel through an orifice of approximately the same size as the channel. A passive second electrode in electrical communication with one side of the double layer is placed on the other side of a porous plug which is located in a second cavity directly opposite the orifice and which is flush with the channel walls. The double layer being investigated is formed on the flush portion of the porous plug. Thus both electrodes are out of the flowing liquid. An electrokinetic potential, labeled the K-effect potential, was measured by the two electrodes.

Abstract: A method and apparatus for measuring a chemical characteristic of a liquid such as its hydrogen ion activity or pH value. A disposable cassette having a reference and indicating electrode therein utilizes the same solution to first calibrate the device and then as an electrolytic bridge from the liquid sample to the reference electrode. The solution has the properties of a buffered pH and also provides a stable electrochemical environment around the reference electrode. In one embodiment, a volume of a liquid sample is placed into a capillary tube and the open end of the tube is then placed over the indicating electrode immersed in the solution. The electrical potential between the indicating electrode and the spaced reference electrode in the electrolyte solution provides a measurement of the pH value of the liquid when compared to the calibration potential previously measured without the liquid sample contacting the indicating electrode.

Abstract: A device for measuring a quantity which influences a field-effect transistor which is included in a measuring circuit as a variable resistance. To compensate for temperature-dependent changes of the field-effect transistor, an auxiliary signal, having a frequency located outside the frequency range of the quantity to be measured, is applied to the transistor. The two signals are separated from one another again after having been processed by the measuring circuit.