Abstract: A self-contained and free floating spa chemistry monitor unit is provided for automated checking and adjustment of water chemistry in a spa or hot tub or the like to maintain the spa water in a clean and substantially sanitary state. The spa chemistry monitor unit includes a relatively compact buoyant housing having an on-board controller coupled to a plurality of sensor electrodes in contact with the water, wherein the controller is programmable to cause the sensor electrodes to take water chemistry readings such as hydrogen ion concentration (pH) and oxidation reduction potential (ORP) levels at predetermined time intervals. The monitor unit responds to the water chemistry readings to deliver a selected metered dose of one or more chemicals to maintain water chemistry readings within a selected target range for substantially optimized water clarity and hygiene.

Abstract: In a pair of electrodes where a potential difference is changed in accordance with acidity or basicity of oil, a reference electrode is made of cobalt or a cobalt alloy, and a sensitive electrode is made of tungsten or a tungsten alloy. The sensitive electrode is used in combination with the reference electrode. Accordingly, it is possible to provide a pair of electrodes for detecting the acidity or the basicity of the oil which use a novel electrode material not hazardous to the environment and at the same time, suited for use in a semiconductor fabrication technique.

Abstract: A portable, hand-held fluid tester for testing and analyzing process fluids is provided with a volume controlled fluid reservoir. The test fluid reservoir is connected by a spillway to an overflow reservoir to provide more consistent and accurate fluid volumes for measurement. Improved mounting of electrodes in the test reservoir and connection to a testing printed circuit substrate provides for ease of assembly. A special temperature probe arrangement is also provided in a preferred embodiment.

Abstract: Measuring equipment, such as a portable pH meter system, can include a plurality of probes for measuring different properties of a sample with each of the probes contacting the sample simultaneously. A reference source line connected to an appropriate reference source can be connected to each probe, while a signal line connected to each probe can provide a measurement signal. A switch assembly is provided for each of the probes in order to isolate the respective probes from each other to prevent any interference when measuring the sample.

Abstract: A method and apparatus for measurement of wide dynamic range signals is provided. The method and apparatus is particularly suited to measurement of physical parameters over a wide dynamic range and utilizes a plurality of concurrently operating channels of moderate dynamic range, each of which incorporates a detector. The method has the steps of transducing the physical signal into an electrical signal; amplifying and filtering the electrical signal through a plurality of channels, each of which operating within a preselected range of levels; applying the filtered and amplified electrical signals to a plurality of detectors, one for each channel; averaging, using a first time constant, the electrical signals to create a plurality of outputs; sampling the outputs; determining which channel of the plurality of channels has a valid output; averaging, using a second time constant greater than the first time constant, the resultant series of valid output samples (i.e.

Abstract: A sensor for measuring pH and conductivity for liquids is disclosed. The sensor includes a housing having a pH cell and a conductivity cell. A pH fluid flow path is defined between a pH cell fluid inlet and pH cell fluid outlet. An aperture within the pH cell is adapted to receive an electronic pH probe therein. The aperture is configured to position an end of the pH probe having a pH sensing area therein and juxtaposition to the pH fluid flow path so that fluid flowing within the flow path is exposed to the pH sensing area of the electronic pH sensor. A conductivity cell is adapted for placement of a conductivity sensor therein. The conductivity sensor is disposed between a conductivity cell fluid inlet and conductivity cell fluid outlet so that fluid flowing therethrough contacts the conductivity sensor.

Abstract: A pH sensor based upon spectrophotometric techniques has been developed for in situ analysis of an aqueous medium, e.g., surface seawater. This sensor utilizes a spectrophotometric pH indicator (Thymol Blue), which has been calibrated for use in seawater as a function of temperature and salinity. Shipboard spectrophotometric pH analyses routinely demonstrate a precision on the order of .+-.0.0004 pH units. In situ analysis of seawater pH has demonstrated a precision on the order of .+-.0.001 and an accuracy, using shipboard measurements as a standard, on the order of .+-.0.01. The sensor is a self-contained system that pumps seawater, meters in indicator, and spectrophotometrically determines indicator absorbance cells, each with three wavelength channels, to obtain the spectrophotometric absorbance. The sensor system, rated for depths up to 500 m, provides pH, conductivity, and temperature and can be operated via computer or in a standalone mode with internal data storage.

Abstract: The invention relates to a sensor electrode connected to a card module that can be received within an industry standard plug-in receptacle of a selected computer to enable a combination capable of very exhaustive data detection, processing, storage and the like for whatever the selected data sensor and particular card module.

Abstract: A point-of-care analyzer unit characterized by a disposable sensor module, a capability of cooperation with multiple fluid sources for providing multi-point calibration, which sources are detachably connectable with the sensor module, and a waste reservoir integral with the sensor module operable to receive and house multiple sets of complete test sequences comprising multiple calibration fluids sets and an analyte sample.

Abstract: An oil deterioration detector comprising a sensitive electrode whose electric potential varies in response to acidity and/or basicity of oil to be measured, and a reference electrode associated with this sensitive electrode. An electrically conductive housing accommodates the sensitive electrode and the reference electrode together with the oil. A potential difference detector detects oil deterioration by measuring a potential difference between the sensitive electrode and the reference electrode. And, an insulating member is interposed between these electrodes and the electrically conductive housing for electrically insulating these electrodes from the electrically conductive housing. The reference electrode is grounded together with the electrically conductive housing. An insulating, hydrophilic porous member would be interposed between the sensitive electrode and the reference electrode.

Abstract: An automatic calibrating apparatus for a measurement instrument having a sensor member includes a chamber adapted to hold the sensor member during a storage mode. A controller can respond to the presence of the sensor member and automatically wash the sensor member, and subsequently immerse it in a calibration solution. The output reading of the sensor member, along with the temperature, can then be utilized to calibrate the instrument. The sensor member can be subsequently cleansed with a washing fluid so that it is ready for immediate use.

Abstract: In the method of measuring the pH value of a test solution with glass-electrode measuring cells and of simultaneously calibrating the measuring cells, the potentials occurring at the pH glass electrode and the reference electrode are processed in a pH meter with temperature compensation and measuring-cell slope derivation. The potentials from a reference electrode (4) and two pH glass electrodes (2, 3) having different internal reference solutions (6, 7) are processed in a first (8) and a second pH meter (9). The measuring-cell slope is derived from the processed potential and, together with the slope, the measured value is derived simultaneously.

Abstract: A surface-mounted pH sensor provides continuous pH profiling with depth during standard cone penetration testing (CPT). The pH sensor includes at least two electrodes, one being an antimony electrode and the other being a ceramic electrode. The electrodes are mounted to the shaft of a cone penetration device, and make contact with underground fluids during CPT. The antimony electrode, which functions as a measurement electrode, creates an exchange equilibrium between the hydrogen ions in the underground fluids and the ions of the antimony. This equilibrium creates a potential in the antimony electrode which is measured against the stable reference potential of the ceramic electrode. The resulting potential difference is indicative of the pH level of the underground fluids.

Abstract: Water quality sensor apparatus comprising a substrate on which a plurality of sensors are supported in spaced apart relationship, each sensor being responsive to a different water characteristic and each sensor comprising a sensor region which, in use, is arranged to be contiguous with water the characteristics of which are to be sensed, which sensor regions are electrically connected to connector means via conductors supported on the substrate, the conductors and the connector means being arranged to be non-contiguous with the water in use of the apparatus.

Abstract: An automatic control system for maintaining the quality of water in a cooling tower utilizes a probe (38) which senses the oxygen reduction potential (ORP) of a soap having a 1:1 stoichiometric equivalent of an organic acid and ammonia in the water. The soap is pumped from a chemical supply means (20) containing the soap in response to the ORP of the soap in the water falling below a predetermined threshold. A second sensing probe measures the conductivity (in MHos) of the water as a factor of the total dissolved solids (TDS) to control the bleed-off or blow-down of the water. The chemicals, which are supplied for maintaining the ORP, permit significantly higher total dissolved solids in the water than with standard cooling tower systems, without the buildup of scale. As a consequence, water consumption is significantly reduced; and the system functions automatically, without requiring periodic visual inspection, water analysis or manual operation.

Abstract: An automatic control system for maintaining the quality of water in a cooling tower utilizes a probe (38) which senses the oxygen reduction potential (ORP) of a soap having a 1:1 stoichiometric equivalent of mineral acid and ammonia or amine in the water. The soap is pumped from a chemical supply means (20) containing the soap in response to the ORP of the soap in the water falling below a predetermined threshold. A second sensing probe measures the conductivity (in MHos) of the water as a factor of the total dissolved solids (TDS) to control the bleed-off or blow-down of the water. The chemicals, which are supplied for maintaining the ORP, permit significantly higher total dissolved solids in the water than with standard cooling tower systems, without the buildup of scale. As a consequence, water consumption is significantly reduced; and the system functions automatically, without requiring periodic visual inspection, water analysis or manual operation.

Abstract: The invention describes a novel device to measure .zeta.-potentials of substances at high temperatures. The device involves packing the substance to be measured into a "RULON" (polytetrafluoroethylene including a heat resistant filler, e.g., fiberglass, quartz, asbestos, ceramic fibers or mica) column and passing an electrolyte through the column. Measurements are taken across the column to measure streaming potential and the pressure drop, and a sensor in series with the column to measure the pH of the electrolyte. .zeta.-potentials are calculated from slopes of the plots of streaming potential (.DELTA.E) vs. differential pressure (.DELTA.P) using a computer controlled data acquisition system.

Abstract: An automatic control system for maintaining the quality of water in a cooling tower utilizes a probe which senses the oxygen reduction potential (ORP) of the water for activating a chemical supply means, in accordance with a pre-established ORP measurement, to maintain the ORP of the cooling tower water between lower and upper limits. A second sensing probe measures the conductivity (in MHos) of the water as a factor of the total dissolved solids (TDS) to control the bleed-off or blow-down of the water. The chemicals, which are supplied for maintaining the ORP, permit significantly higher total dissolved solids in the water than with standard cooling tower systems, without the buildup of scale. As a consequence, water consumption is significantly reduced; and the system functions automatically, without requiring periodic visual inspection, water analysis or manual operation.

Abstract: An apparatus and method for measuring potentiometric electrode impedance for diagnostic purpose while continuously reading the results of the process value. A square wave is applied to an external circuit, which in turn is coupled to an electrode assembly output through a capacitor. The output of the electrode is converted into a pulse width modulated signal and sampled. These sampled values are used to calculate the impedance and process output value.

Abstract: A sensor which may be immersed in a fluid to measure the pH and the ORP potential of the fluid is taught. The sensor has three solid state electrodes, a pH sensing electrode, a reference electrode and an ORP potential sensing electrode, which extend from a fluid-tight enclosure. The enclosure further contains a display means for indicating the pH measurement and the ORP potential measurement.

Abstract: A device for automatically and continually monitoring the pH characteristic of a water based printing ink which uses a housing for a pH probe, which housing is placed in a flow line through which such ink is flowing, the housing having a main channel for ink flow and a recessed channel into which a pH probe member is inserted. A baffle is provided to direct a portion the flowing ink into the recessed channel in contact with the probe to continually monitor the pH of the flowing ink. A portion of the ink remains in the recessed channel when ink flow is stopped so that the probe surface is covered by the remaining ink and cannot dry out and reduce or destroy the effectiveness of the probe.

Abstract: A potentiostat for an amperometric sensor uses a voltage-controlled current source (VCCS), which may be either unidirectional or, preferably, bidirectional. An error amplifier compares the potential of the sensor's reference or counter electrode, relative to ground potential, to a set-point potential. The error voltage serves as an input to the VCCS. The output of the VCCS--a current proportional to the error voltage--is supplied to the sensor's auxiliary electrode. In a steady state, the error voltage is just large enough to supply current that is equal to the current through the sensor's working and auxiliary (or counter) electrodes. The error voltage can either serve directly as an output voltage or it can be amplified without introducing a feed-back loop disturbance. The VCCS permits direct grounding of the sensor's working electrode and operation of the error amplifier at a low or moderate gain, so as to increase the circuit's frequency response and reduce the probability of oscillation.

Abstract: Acid concentrations are determined by the method and apparatus, particularly HCl acid for picking ferrous material. Specific gravity measurements are made on acid samples, diluted acid samples and water. Conductivity measurements are conducted on the diluted acid samples. The water dilution minimizes the influence of the metal salt in the sample to improve the conductivity measurements. The system calculates the acid concentration by a series of approximations using the conductivity data and the acid concentration - conductivity relationships to provide an accurate acid concentration which is easily automated by computer.

Abstract: A reference electrode is formed of lead, zinc, tin, indium, cadmium, magnesium, or any alloy thereof. A pair of electrodes comprising the reference electrode and a responding electrode made of a conductive solid, when placed in oil, develop a potential difference varying with the acidity or basicity of the oil and thus enable the efficient determination of the acidity or basicity.

Abstract: A microprocessor-controlled pH and ion concentration meter is disclosed with improved testing procedures. The meter can be tested for excessive internal bias current by measuring the potential (V1) when the meter is connected to a circuit a known voltage (E1) of low impedance and the potential (V2) when the meter is connected to a circuit of the same voltage source (E1) but of known high impedance and having the meter compare (V2-V1) to a preset limit value. The meter can be tested for low internal impedance by further measuring the potential (V4) when the meter is connected to a circuit of a second external voltage (E2) and the known high impedance (R1). The meter then calculates:(V4-V2)and compares that value to preset limits based upon E1, E2 and R1. Such limits can be derived as (Z.sub.o) (E2-E1) / (R.sub.1 +Z.sub.o) where Z.sub.o is the minimum acceptable internal impedance.

Abstract: A water analyzer having several electrodes of the type which normally interfere with one another. These electrodes include a first electrode which is an active measurement electrode which perturbs the solution in which it is used and a second electrode whose reading is affected by the operation of the first electrode. Accurate readings are provided by sequencing the operation of the electrodes so that they are not always operating at the same time. In addition, further correction of the readings is provided to compensate for the known error resulting from the operation of the active electrode or electrodes. Such electrodes read conditions such as pH, dissolved oxygen and conductivity.

Abstract: A safe failure ion selective combination electrode in which a signal unit provides a signal if combination electrode output falls outside a predetermined range.

Abstract: A system comprising a disposable device and hand held reader can perform a variety of electrochemical measurements on blood or other fluids. In operation, a fluid sample is drawn into the disposable device through an orifice by capillary action. The orifice is sealed off and the disposable device is inserted into the reader. The reader which controls the test sequence and flow of fluid causes a calibrant pouch located inside the device to be pierced, releasing the calibrant fluid to flow across the sensor arrays to perform calibration. Next an air bladder located in the device is depressed, forcing the sample across the sensors where measurements are performed and read by the reader which performs the calibrations. Once the measurements are made, the device can be withdrawn from the reader and discarded.

Abstract: A pH-measuring system using a Barnacle electrode (e.g. Ni--NiO.sub.2) in an electrolyte to abstract hydrogen from a metal electrode in the same electrolyte, and produces data as to the time t.sub.max required for the current density at the exposed surface of the metal electrode to reach its maximum value j.sub.max after an external circuit between the two electrodes is closed. From t.sub.max and j.sub.max the pH in the bulk of the electrolytes is determined, for display or for control purposes.

Abstract: An electrode, preferably of a conductive polymer, has on its surface, preferably over all of its surface, an ion exchange material, preferably of significant thickness. Such a coated electrode may be used for sensing the presence or measuring the concentration of an ionic species, or for removal from or release of an ionic species into an electrode.

Abstract: Several types of new microelectronic devices including diodes, transistors, sensors, surface energy storage elements, and light-emitting devices are disclosed. The properties of these devices can be controlled by molecular-level changes in electroactive polymer components. These polymer components are formed from electrochemically polymerizable material whose physical properties change in response to chemical changes, and can be used to bring about an electrical connection between two or more closely spaced microelectrodes. Examples of such materials include polypyrrole, polyaniline, and polythiophene, which respond to changes in redox potential. Each electrode can be individually addressed and characterized electrochemically by controlling the amount and chemical composition of the functionalizing polymer. Sensitivity of the devices may be increased by decreasing separations between electrodes as well as altering the chemical environment of the electrode-confined polymer.

Abstract: An amperometric method for the direct measurement of acidity in a medium which contains at least one ester of an acid containing oxygen, and whose dielectric constant is lower than 30. The method provides for maintaining a constant voltage between an ultramicroelectrode and a counterelectrode and measuring the current therebetween as an increasing quantity of diphenylphosphoric acid is added to the medium via a microburette. The measured current being indicative of the acidity of the medium under test. A predetermined curve is provided which represents the relationship between the acidity of the medium and the current measured by the system.

Abstract: A circuit is described for applying a potential to an electrode of a biosensing test cell, which electrode, when properly inserted in a female connector, is contacted by a pair spaced apart contacts. The circuit includes a source of excitation potential and an operational amplifier having one input connected to the source of excitation potential. A switching circuit is coupled between the operational amplifier and a first one of the spaced apart contacts, with the switch means exhibiting an impedance. A feedback circuit is connected between the second of the spaced-apart contacts and another input to the operational amplifier, to feed back a potential appearing at the second contact. The feedback is for the purpose of maintaining the output of the operational amplifier at a level which compensates for impedance losses in the swtiching circuit.

Abstract: Apparatus and method are provided to ensure accuracy of a measurement signal obtained using a potentiometric sensor placed in a solution. The apparatus includes an interface amplifier that generates a relatively large turn-on bias current whenever the amplifier is initially powered on. To avoid polarization of the potentiometric sensor by the turn-on bias current, a switch device is used to direct the turn-on bias current along a path away from the potentiometric sensor. The switch device is controlled using a timer circuit that causes a change in position of the switch device after a predetermined time delay. During the time delay, the bias current reduces to a normal value and polarization of the potentiometric sensor has been avoided. An accurate measurement of a physical parameter associated with the solution can then be taken without the detrimental effect of the turn-on bias current on the potentiometric sensor.

Abstract: A method for the automatic line calibration of an electrochemical sensor for measuring the concentration of a liquid phase dissolved electrochemical substance flowing into a pipe and is characterized by the following stages: upstream of the electrochemical sensor, a generator is placed on the pipe, the generator being suitable for delivering standard quantities of the substance; between the generator and the electrochemical sensor, a delay line (3) is placed on the flow with a given volume of this liquid. By way of the generator, successively injected into the liquid pipe are two bursts of known quantities of the electrochemical substance corresponding to the concentration C.sub.1 and C.sub.2 in the liquid flow. From the indications of the electrochemical sensor (4), the delay time introduced by the delay time is determined.

Abstract: Devices and methods are provided for determining the presence and amount of an analyte by measuring a redox potential-modulated photoinducing signal from a photoresponsive element. Further devices and methods are provided for determining the presence and amount of an analyte by measuring a redox potential, pH or ion modulated photoinduced signal from a photoresponsive element, where one signal is a constant system and the other signal(s) is a variable system. The constant system signal is used to standardize the variable system signal. Various protocols may be employed where an analyte may be directly or indirectly coupled to a redox couple, a pH or ion system for detection. The latter devices employ a photoresponsive element having a medium contacting surface, which is partially covered with an electronically conducting layer and partially covered with a protective insulative layer.

Abstract: A hand held sensor body with a manually extendible two-pronged probe contains an ion meter for both chlorine concentration and for pool water acidity. The sensor is D. C. powered and the probe has dual metallic rods extending from the hand-held probe and terminating in alloy sensor tips. The body of the sensor containing the meter also detachably encases the hand-held probe when the probe is not in use. The meter case tapers downwardly in width to a battery chamber with access for the probe cable. The battery chamber has contacts for connection to the meter and an electrical contact for the control knob for an adjustable potentiometer imposed in the electrical circuit between the meter and the probe.

Abstract: An interface circuit for use in a portable apparatus for measuring the electrochemical characteristics of a sample is disclosed. A disposable cartridge, including a plurality of interconnected flow chambers, houses a printed circuit board substrate upon which reference and indicating electrodes are formed. The electrodes are employed in the presence of chemical reagents to aid in the electrochemical determination of a sample undergoing analysis. Such a system provides a high source impedance signal. Interface circuitry is provided between the electrodes and measuring electronics which causes a controllable current loop to be formed through the physical contacts points between the electrodes and the measuring electronics so that low ohmic contact is established. The control circuitry for the current loop is isolated from the measuring circuitry so that measurements taken are not influenced by the current loop formation.

Abstract: A microprocessor-controlled pH and ion concentration meter is disclosed with improved calibration and testing procedures. For calibration (standardization), the meter stores number pairs (pX.sub.a, E.sub.a), (pX.sup.b, E.sub.b) where the pX values may be pH values (e.g., 4.00 and 7.00) and the E values are expressed in mV/deg K. When multiple standard values are stored, remeasuring one (e.g., replacing E.sub.a1 by E.sub.a2) can be used to update the others (e.g., E.sub.b1 to E.sub.b2) without remeasurement by applying the formula:E.sub.b2 =E.sub.b1 +(E.sub.a2 -E.sub.a1).Additionally, the meter can be tested for excessive internal bias current by measuring the potential (V1) when the meter is connected to a circuit of low impedance and the potential (V2) when the meter is connected to a circuit of the same voltage source but of known high impedance and having the meter compare (V2-V1) to a preset limit value.

Abstract: A particle analyzer which comprises a constricted passage for the passage of fine particles contained in a suspension therethrough for isolation, upstream and downstream passages communicated with the constricted passage and positioned on upstream and downstream sides of the constricted passage with respect to the direction of flow of the suspension, a detector including upstream and downstream electrodes disposed in the upstream and downstream passages, respectively, so as to confront with each other for detecting the fine particles being passed through the constricted passage, and a cleansing passage communicated with either one of the upstream and downstream passages for the supply of a cleansing liquid.

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: A three wire amplifier circuit for use with a sensor in which the amplifier output drives the negative supply so that the negative supply becomes the circuit output and the system is capable of diagnosing the condition of the sensor.

Abstract: An improved method of attachment of a pH or p sensor in the recirculation/filtration line for a pool or spa or for forming a T-connection between any two pipes comprises a saddle-clamp modified with an aperture to receive the shank of the sensor with an O-ring and a thinner, harder constricting ring surrounding the O-ring. When the saddle clamp is tightened, the constricting ring forces the O-ring toward the aperture while preventing excessive flattening of the O-ring.

Abstract: A testing method and apparatus for testing the condition of electrodes and their conductors in ion sensitive measuring or controlling systems, wherein the measuring circuit is disruptive and replaced by an impedance measuring circuit containing only one electrode, so that also failures of, for example, reference electrodes, soiling and deposits, and electrolyte loss, can be determined. The arrangement has sufficient accuracy to detect faults, defects and failures as they slowly come into existence.

Abstract: An instrument for measuring the concentration of a wide variety of important chemical and biochemical substances is provided which comprises an enzyme based voltametric sensor, and electronic circuitry for conditioning an output signal from the sensor. The instrument includes one or more aqueous oxidase enzymes mechanically coupled to a polarographic cell oxygen detector wherein the concentration of a substance is inferred from measurement of the depletion of oxygen resulting from an oxidation reaction catalyzed by the oxidase enzyme. The electronic circuitry includes current to voltage conversion, nulling an unneeded base current signal, and temperature compensation.

Abstract: An improved water analysis system for pools, spas, and the like. An oxidation-reduction potential (ORP) sensor is disposed in the recirculation/filtration system for developing an electrical signal directly related to the active form of a sanitizer contained in the water. A pH (PH) sensor is similarly disposed for developing an electrical signal directly related to the acidity/basicity level of the water. A first electrical driver is operably connected between the output of the ORP sensor and a first bargraph display for moving the first bargraph display in step increments between upper and lower limits corresponding to "more than necessary" and "less than necessary" levels of sanitizer in the water. A second electrical driver is operably connected between the output of the PH sensor means and a second bargraph display for moving the second bargraph display in step increments between upper and lower limits corresponding to "lower acidity than optimum" and "higher acidity than optimum" levels of water.

Abstract: An on-line calibration system for calibrating chemical monitors which monitor a selected chemical characteristics of a fluid sample stream, including a conditioning system for conditioning an influent fluid sample stream to produce a conditioned fluid sample stream having a predetermined level of the selected chemical characteristic. By exposing a sensor of the monitor to the conditioned fluid sample stream and calibrating the response of the sensor with respect to the predetermined level of the selected chemical characteristic in the conditioned fluid sample stream, this calibration system eliminates the effects on the response of the sensor of any ionic species in the fluid sample stream which do not affect the chemical characteristic being monitored.

Abstract: The apparatus (10) for determining the activity of an ion (pIon) in a liquid (16) comprises a measuring circuit (10) including an ion sensitive field effect transistor (ISFET 12), a reference electrode (32) adjacent the ISFET (12), a temperature sensor (34) adjacent the ISFET (12), amplifiers (22 and 38) coupled to the ISFET (12) and temperature sensor (34), and control, computing and memory circuits (30, 44, and 46) coupled to the amplifiers and operable to maintain two of the following three parameters, V.sub.gs (gate-source potential), V.sub.ds (drain-source potential) and I.sub.D (drain-source current) at a constant value so that the third parameter can be used for determining the ion activity or pIon. The pIon sensitivity of the apparatus (10), as a function of temperature and/or the variation of the drain-source current, I.sub.D, as a function of the temperature are controlled by controlling the V.sub.gs so that the pIon can be calculated from a formula stored in the memory (46 ).

Abstract: Apparatus for calibrating a conductivity instrument having a conductivity cell and a conductivity measuring instrument operatively associated with the conductivity cell, includes a conduit for supplying high purity water to be measured; a first flow line for supplying the high purity water from the conduit to the conductivity cell; a second flow line for supplying the high purity water from the conduit to the conductivity cell; a mixed bed ion exchanger in the second flow line for de-ionizing the high purity water flowing through the second flow line; and a valve which selectively supplies the high purity water to the conductivity cell, from either the first flow line to provide a conductivity measurement of the high purity water or the second flow line to calibrate the conductivity cell.

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.