Abstract: A moldable material, which either has dipoles or other charged particles therein, or is susceptible to their creation, is introduced into a mold or is passed through a die. The material is then subjected to a polarization medium until either at least some of the dipoles or other charged particles are oriented in the direction of the polarization medium, or until at least some dipoles or other charged particles are created thereby. Thereafter, the material is permitted to cool. Once cooled, the molded material is separated from the mold or die. The effect of polarizing the moldable material is then analyzed by permitting an at least partial relaxation of the dipoles or other charges therein which were polarized or created. This relaxation results in a measurable current which is related to the actual temperature of the material at the time the polarization medium was applied.

Abstract: A method and apparatus for triggering and measuring electrochemiluminescent phenomena using a voltage waveform applied at the voltammetric working electrode which improves the precision and accuracy of measurements. This waveform has a decreasing scan rate in the range of voltages for which electrochemiluminescence is triggered and is substantially sinusoidal in shape in this range. The waveform results from locating the reference electrode of a potentiostat in close potential proximity to its counter electrode, and applying a uniform scanning voltage waveform at the reference electrode. The waveform also can be synthesized digitally, converted to analog form, and applied directly to the working electrode with the reference electrode in close potential proximity to the working electrode.

Abstract: An improved input circuit (9) for accepting a signal from a triboelectric probe (2). The circuitry provides gain, zero and probe contamination information which allows verification of said information without taking the probe and instrument off-line.

Abstract: The build-up of the deposits on surfaces immersed in water in monitored by passing the water through a galvanic cell comprising a pair of dissimilar metal electrodes (5, 6) mounted on opposite sides of a passage (4) for the water in a housing (1,7), and detecting and interpreting galvanic current developed between the electrodes (5, 6).

Abstract: A method and apparatus is disclosed for continuously monitoring the resistance of a grounding conductor to neutral conductor circuit of a power distribution system. The apparatus compares a parameter of a damped sinusoidal waveform from a shock excited resonant circuit coupled to the grounding conductor and neutral conductor at a branch circuit outlet of the power distribution system with a predetermined parameter from the same resonant circuit discharging into an external circuit having a predetermined resistance. The apparatus indicates an undesired grounding conductor resistance.

Abstract: The blood flow measuring apparatus comprises at least three electrodes, namely, a measuring electrode, reference electrode and an active neutral electrode, which are implanted at a predetermined tissue region. The signals of the measuring electrode and the reference electrode are delivered by input lines to a current and voltage isolated differential amplifier, the output of which is connected with a central unit controlling further instruments. What is important for the measuring accuracy of the blood flow measuring apparatus is an opposite feedback of external spurious fields which couple-in spurious potentials into the tissue and the shields of the input lines of the measuring electrode, reference electrode and neutral electrode. Further probes can be provided as an aid for the central unit.

Abstract: A test unit for a monitoring device includes reference and measuring electrodes coupled to a preamplifier and a temperature compensating resistor for the preamplifier. The test unit has components corresponding to those of the monitoring device as well as a power supply and a voltmeter coupled to the output of its preamplifier. Cables are provided for substituting either or both electrodes of the monitoring device for the electrodes of the test device, and a switch is provided for substituting a temperature compensation resistor of the monitoring device for the temperature compensation resistor of the test device. A cable is adapted for connection to either preamplifier for supplying it with operating potentials derived from the power supply and for coupling the output of either preamplifier to the voltmeter.

Abstract: A system and a method for testing the integrity of interconnection networks on a circuit board or substrate are disclosed. To test the continuity of a being tested network, two probes are used. To test the integrity of the being tested network, as it relates to other nets on the circuit board, a rectangular pulse is provided to the being tested network, and a signal in response to the stimulus pulse, provided across an external capacitor and resistor connected to the reference plane of the circuit board or substrate, is sampled by a transient analyzer. The leading edge of the thus sampled response signal provides an indication of whether the being tested net is acceptable, opened, shorted, or has a high leakage resistance to another net.

Abstract: The present invention relates to the protection of a semiconductor active device from thermal breakdown without actually measuring the temperature of the semiconductor active device. Instead, the present invention measures the magnitude of the forward electrical signal generated by the active device and the reflected electrical signal resulting from the interaction of the forward electrical signal and a load. The thermal energy generated by the active device is a function of these electrical signals. The generated thermal energy is transferred out of the active device at a predetermined rate. The temperature of the active device is calculated as a function of the thermal energy generated by the active device and the amount of thermal energy transferred out of the active device. When the calculated temperature is above a predetermined value, the active device is shut off, thereby preventing further generation of thermal energy.

Abstract: A method and apparatus for triggering and measuring electrochemiluminescent phenomena using a voltage waveform applied at the voltammetric working electrode which improves the precision and accuracy of measurements. This waveform has a decreasing scan rate in the range of voltages for which electrochemiluminescence is triggered and is substantially sinusoidal in shape in this range. The waveform results from locating the reference electrode of a potentiostat in close potential proximity to its counter electrode, and applying a uniform scanning voltage waveform at the reference electrode. The waveform also can be synthesized digitally, converted to analog form, and applied directly to the working electrode with the reference electrode in close potential proximity to the working electrode.

Abstract: Disclosed is a novel electrochemical probe and technique to monitor biofilm activity before the biofilm has been permanently established and microbiologically influenced corrosion (MIC) initiated. This probe includes two sets of metal electrodes isolated from each other. A power source is used to apply a potential difference of between 50 and 500 mV on the two sets of electrodes to activate the probe. Programmed timing, measuring and switching equipment and a data recording device monitors the biofilm-caused depolarization effects on the electrode sets by measuring an increase of DC current produced by the applied potential difference. The equipment also monitors DC current generated between the electrodes after removing the power source and records the AC resistance between the electrodes indicating mostly the resistance of the biofilm covering the electrodes.

Abstract: A method and apparatus for detecting changes in the structural strength of bonded joint. Changes in one or more dielectric properties of the bonding adhesive, such as resistance and capacitance, are monitored by a microdielectrometer. A change in a bond dielectric measurement is indicative of a moisture intrusion in the bond and a corresponding weakening of the structural integrity of the bond. A warning or indication of the bond degradation is provided in response to such changes.

Abstract: An apparatus for determining the particle charge and size distribution of particles in suspensions of arbitrary concentration is provided. The apparatus includes a cell for application of an unsteady electric field or an unsteady mechanical force across the suspension of at least two different frequencies for accelerating the particles. The resulting acoustic wave generated by application of the electric field applied to the electrodes, or the electrical response and the acoustic pressure at the electrodes generated by application of the mechanical force is measured. Transducers convert the mechanical forces to electrical forces.

Abstract: A corrosion monitoring system having one or more anode elements made of a suitable anodic material that corrodes preferentially with respect to the structure being protected. The resistance of each anode wire is continuously or periodically monitored. The presence of moisture between an anode and the structure being monitored creates a current path and causes galvanic corrosion. The anode wire will begin to corrode, but the structural members will remain uncorroded until the anode has been completely consumed. The monitoring system uses the rate of change in anode resistance to extrapolate a prediction of the time remaining before the structure being protected begins to corrode.

Abstract: A molten metal inclusion sensor intended for "continuous" use in the testing of steel, i.e. a useful life of at least about 30 minutes, comprises a probe which is detachably connected to a water-cooled support member (35). The probe comprises a tube (30) of heat resistant material, preferably silica, having an inner electrode (31) mounted on its interior wall and an outer electrode (32) mounted on its exterior wall, the molten metal entering the tube interior through an orifice (33) upon its immersion in the molten metal, whereupon the flow of metal with entrained inclusions is monitored by measuring the voltage between the electrodes (31, 32). The electrodes (31, 32) are preferably of graphite and are shaped to fit closely against the walls of the part of the tube (30) that is immersed in the metal and are of a material that retains enough mechanical strength to support the tube (30) as the metal is pumped into and out of interior, the metal remaining hot enough for this pumping to occur.

Abstract: A sensor for use during the construction of a concrete structure to enable an assessment to be made of whether or not a pour of fresh concrete has settled uniformly throughout the placement area. One of two main electrodes is fitted with an auxiliary electrode in parallel such that the polarity of the electrodes is reversed when they are immersed in water and when they are immersed in fresh concrete. By monitoring this function, it is possible to detect the presence or absence of fresh concrete in accordance with the polarity. In the case of a sensor without an auxiliary electrode, it is still possible to monitor changes in the voltage level when the electrodes are immersed in water and in fresh concrete, thereby providing access to a similar mode of assessment.

Abstract: A modular-construction measurement probe comprising a component designed as a diaphragm module and, connected to the diaphragm module, a rod electrode. The diaphragm is made up of at least three layers, the second layer having a much higher permeability than the first or third layer with respect to the gases and/or non-ionic compounds being determined. The first layer and the third layer are made of chemically resistant material. The three layers are preferably permanently bound to each other to give a uniform diaphragm structure, a support material in the form of stainless-steel gauze being mounted in the second layer. The probe is also fitted with a pressure-compensation system which makes it possible to compensate for pressure differences of the order of 20 bar which occur in operation between the measurement medium and the interior of the probe. The probe can therefore be steam-sterilized without problem. It is particularly suitable for use in the amperometric determination of oxygen.

Abstract: A method for analysis of freshness of fuels, food products, and oils, lubricants and other fluids, and other organic materials, is disclosed which quickly analyzes oxidative degradation of a sample off-line by measuring the oxidation products of the material. A sample of the material is dissolved and subjected to single sweep voltammetric analysis to measure the current through the sample as a function of the potential applied. The resulting current-voltage plot reflects the level of oxidation products present in the material sampled. The method results in data which can be used to evaluate the freshness of unused materials which degrade during storage, as well as to monitor deterioration of materials during use.

Abstract: In a method for detecting the fluidity of particles in a vertically extending bed of fluidized particles, an electric charge which is generated on the particles is dissipated through an electrically conductive means in the fluidized bed to give an indication of the fluidity of the particles in the bed.

Abstract: A dynamic precious metal assay which includes the steps of introducing a controlled amount of liquid electrolyte onto a sample of precious metal alloys, placing an inert electrode in contact with the sample in the presence of the electrolyte to create a wet junction, driving a first pulse of electric current through the electrolyte in the wet junction to cause an oxidation/reduction reaction of the alloying materials present in the alloyed sample to form an electrolytic-based paste, terminating the electric current and allowing the current in the paste to decay to an asymptotic level, driving a second pulse of electric current through the electrolytic paste in the junction at an amplitude above the asymptotic level, driving a third pulse of electric current, at a higher amplitude than the second pulse, through the electrolytic paste in the junction, instantaneously measuring the electrolytic conductance of the electrolytic paste, comparing the conductance with an empirical table of electrolytic paste conducta

Abstract: A method and apparatus for performing an enzyme-linked immuno sorbent assay of a biological substance in a fluid substrate wherein an enzyme conjugate is used to react with the biological substance to cause the release of ions into the substrate. The change in the resistivity of the substrate due to the release of ions is measured, and an analog signal is generated in response thereto. The analog signal is converted into a digital signal, which is quantized and output in a human readable form for indicating the quantity of the biological substance present in the substrate.

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 cathodic protection monitoring system which provides IR drop free cathodic protection potential measurements which are indicative of the effectiveness of the cathodic protection system. The system measures the polarized potential between a reference electrode and a coupon subsequent to decoupling the coupon from the protected structure. The present invention controls the time or times at which the potential is measured in order to ensure that the potential is measured only after the polarized potential has achieved a relatively steady state value. More particularly, the cathodic protection monitoring system controllably measures the polarized potential after the potential has stabilized to the extent that there are no inductive or capacitive voltage spikes present, and before the coupon potential decays significantly due to depolarization.

Abstract: A method and apparatus useful in measuring the size, charge, velocity and concentration of particles in polydispersed systems, and particle concentrations of monodispersed aerosols. A particle flow to be evaluated is conducted through at least one active electric field sensor, which may be constructed in an annular, point, or segmented annular configuration. The charge induced by each particle on the sensor is fed to an active charge amplifier. The output signal of the amplifier serves as input signal for a measured value indicator. The amplifier is a component for a measured value evaluation circuit, which consists of at least one capacitor, one resistor and the amplifier and, which is preferably integrated into the arrangement of the sensor. A computer or microprocessor is used in analyzing the sensor output to determine desired parameters descriptive of the particles and their movement. The particle flow may be charged prior to measurement and the particles may also be separated according to charge.

Abstract: An apparatus and method for accurately monitoring the flow and cure rate of a resin material. The method is accomplished through the use and incorporation of efficient sensors as integral components of a composite resin structure material. The sensors used are electrically conductive threads arranged in a non-intersecting, grid-like configuration. They may be placed into or between composite resin materials. These sensors serve as leads which are connected to a computer through a multiplexer/rapid switching system and a scanner. The data obtained for the monitoring of the flow and cure of resin is stored on a computer system and is presented on the computers' graphic window.

Abstract: The invention relates to a device for measuring the electrode potential of the reinforcement in underwater concrete. The device is of the type comprising a reference electrode placed against the facing of the concrete and a voltmeter connected to the reference electrode and to the reinforcement. The reference electrode is disposed in a bell suitable for pressing in watertight manner against a facing of the concrete, thereby delimiting an enclosure. The device further includes means for injecting compressed air into the enclosure and means for enabling the water imprisoned therein to escape.

Abstract: A circuit is described which tests whether an amperometric electrochemical gas sensor monitoring the concentration of toxic gases in an atmosphere is working properly. The sensor has a sensing electrode, a reference electrode, and a counter electrode and in normal operation the potential between the reference electrodes is fixed by means of an operational amplifier. When there is gas in the atmosphere, the gas reacts electrochemically at the sensing electrode, causing the amplifier to supply electrical current to the counter electrode which results in an electrical potential to the sensor that is proportional to the amount of toxic gas in the atmosphere. The sensor is periodically tested to determine whether it is working properly by applying a pulse potential between the sensing and reference electrodes. If a current flow results then a signal is sent to an alarm device.

Abstract: A device for detecting and monitoring the charge condition of finely divided solid charged particles in a fluid-flow is so devised as to accept the continuous and full volumetric flow of the fluid and to automatically and repeatedly sample and measure the charge condition. The full flow is accommodated without restriction in a passageway which intersects a bore wherein a streaming current detector (SCD), located below the passageway, is caused to cyclically sample and measure the charged-particle content of the flow; and at a passageway location downstream from the point point of cyclical sampling a head-creating formation assures that the fluid level will be raised to maintain a filled condition of the sampling bore. The device is further illustratively disclosed in use in a fluid-treatment system, wherein the SCD produces a signal to control flocculant added to the full flow of the fluid.

Abstract: A method of determining the percentage gas content of an insulating glass window unit or the like comprises the steps of applying a voltage to opposed panes of the unit, progressively increasing the voltage, monitoring the voltage and recording the magnitude of the voltage at which a continuous discharge occurs, or is about to occur, between the electrodes and converting the magnitude to a number indicative of the percentage gas content of the gas between the panes.

Abstract: A molten metal inclusion sensor comprises a single use disposable probe which is detachably connected to a support member. The probe may comprise a tube of heat resistant material having an inner electrode mounted on its interior wall and an outer electrode mounted on its exterior wall, the molten metal entering the tube interior through an orifice in its wall past a jet-preventer insert upon its immersion in the molten metal, whereupon the flow of metal with entrained inclusions is monitored by measuring the voltage between the electrodes. Alternatively the tube may be of electrically-conductive heat-resistant material and constitute the inner electrode. The flow may be assisted by a reduced pressure established within the tube, or may be slowed by a positive pressure to maintain the Reynolds number of the flow below 2000.

Abstract: A method and apparatus for compensating for charging current at a working electrode of an electrochemical cell. And a method for measuring faradaic current at the working electrode. Includes measuring the current at the working electrode while a time-varying potential difference is applied between the working electrode and a reference electrode. And while the applied potential difference is held constant for a short time and the working electrode current is again measured, where this current is the faradaic current. The faradaic current is then filtered from the total current to determine the charging current thereby compensating for double layer charging current in the cell.

Abstract: A contact point is estimated by detecting a variation of a potential difference between the first and the second object as the objects approach one another. The method and apparatus are particularly suited for use in an electrical discharge machine (EDM) that is controlled by a numerical control (NC) unit for machining a workpiece.

Abstract: A voltage-to-digital converter comprising a storage circuit for providing a storage capacitance with a plurality of selectable magnitudes. The storage circuit provides a charge output representative of applied voltage input signals and the selected capacitive magnitude. A charge accumulation circuit is coupled to the charge output. The total charge accumulated is proportional to the integral of the amount of charge discharged from the storage circuit. The charge accumulation circuit provides a balance output representative of a comparison of the accumulated charge and a reference charge.

Abstract: An encoder has a reference scale having periodic structure of atoms or molecules in a predetermined direction, a probe disposed in opposed relationship with the reference scale, the probe being used to detect the structural variation information of the periodic structure of the reference scale, and relative displacement amount detecting means for detecting the amount of relative displacement of the reference scale and the probe along a predetermined direction from the structural variation information obtained by the probe.

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: An apparatus for measuring cathodic protection voltage levels on a concealed conductive structure, includes a probe having a standard half cell reference electrode, a working electrode and an auxiliary electrode mounted in a fixed spacial relationship to each other, wherein the reference electrode, working electrode and auxiliary electrode are each in contact with an electrolytic solution. A voltage measuring device is provided for receiving a voltage from said reference electrode. The voltage measuring device provides an indication of the voltage difference between the reference electrode and a common reference point. A switch is included for connecting and disconnecting the working electrode with the common reference point. A voltage detecting circuit detects voltage between the concealed conductive structure, which is subject to a cathodic protection voltage, and the common reference point.

Abstract: The method of determining interactions due to direct currents on adjacent buried metal structures at least one of which is connected to a direct current generator such as a cathodic protection device, consists in placing calibrated specimen test metal pieces in the vicinity of the buried metal structures, the test pieces being made of materials that are analogous to those of the structures. The test pieces are spaced apart from each other by a distance L' equal to the distance L between the structures. Reference electrodes are placed in the immediate proximity of the specimen metal test pieces and simultaneous measurements are performed firstly of the potentials of the specimen test pieces relative to the reference electrodes, and secondly of the currents flowing through the calibrated specimen test pieces when they are electrically connected to respective ones of the structures.

Abstract: Apparatus for measuring electrolyte concentrations in fluid samples. The apparatus includes an ion selective electrode capable of generating a voltage differential having a magnitude related to the concentration of the corresponding electrolyte in the sample. A voltage to optical transducer circuit is provided to convert the voltage differentials to a digital code and then to an optical signal which is related to the concentration of the electrolytes. The optical signals are suitable for detection by conventional optical detector apparatus of assay instruments. A passive duplex transfer is utilized to simultaneously read one optical signal while transferring the next bit of the digital code. The duplex transfer configuration also makes novel use of the photodetection properties of an LED.

Abstract: In an apparatus for on-line particle determination in molten metals, a sample of molten metal is drawn through a calibrated passage while a steady current is established through the passage between two electrodes on opposite sides thereof. Particles moving through the passage produce voltage pulses whose magnitude and rate indicate respectively their size and number per unit volume. The wanted test signal can be obtained between the two current carrying electrodes, or between two other electrodes disposed on opposite sides of the passage. The electrodes form an interference-receiving antenna so that the wanted low signal/noise ratio test signal is overlaid with interference from neighboring sources. This interference is reduced by a cancellation signal produced by a cancellation antenna constituted by a similar pair of electrodes, either separate from the main current-carrying electrodes or having one of them in common.

Abstract: A streaming current detector having a probe with an electrode holder which can be removed and replaced within only about one minute, allowing the probe to be kept on line nearly continuously even in highly contaminated wastewater. The probe also includes a reciprocating piston and a housing with both a cylindrical void and a transverse passageway. In assembled relation, the electrode holder is slidably disposed within the cylindrical void; and the piston is slidably engaged with an inner wall of the electrode holder. Capillary-sized channels formed between this inner wall and the piston communicate fluidly with the transverse passageway. From it, any test flow stream present is partially sucked into the capillary-sized channels during an upstroke of the piston and then expelled from them, back into the transverse passageway, during the succeeding downstroke.

Abstract: A voltage-to-digital converter comprising a storage circuit for providing a storage capacitance with a plurality of selectable magnitudes. The storage circuit provides a charge output representative of applied voltage input signals and the selected capacitive magnitude. A charge accumulation circuit is coupled to the charge output. The total charge accumulated is proportional to the integral of the amount of charge discharged from the storage circuit. The charge accumulation circuit provides a balance output representative of a comparison of the accumulated charge and a reference charge.

Abstract: A digital isolation monitor comprises a digital processing signal processor P1 designed to synthesize a sine wave in real time by a table, and to send the digital values of this sine wave to a digital-to-analog converter of an input channel to generate a low-frequency AC reference signal with a very low, stable phase distortion factor. An acquisition channel is fitted with a switching unit operating in conjunction with a dual measurement circuit to send an injected voltage signal and a leakage current signal to a low-pass analog filter in series with a sample-and-hold circuit and an analog-to-digital converter. The processor P1 then performs synchronous demodulation and transmits the data to a microcontroller P2.

Abstract: Monitoring apparatus (10) of particles in a gas stream comprising a probe (12) and circuit (14) for detecting electrical activity of the probe and an actuator (20) for insertion and retraction of the probe into and out of the stream, the circuit providing periodic measurement of the retracted probe and self-adjustment to compensate for changing probe characteristics. The apparatus also provided probe cleaning and protection means (30, 32, 34, 36), which work in interaction with the self-check instrumentation. The self-check tests include baseline, gain and sensitivity monitoring.

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: A method for the determination of particle size and electric charge or zeta potential of particles dispersed in a fluid medium. The particle size and charge are determined from measurements of (1) the phase lag between an applied alternating electric field and the resulting particle velocity, and (2) the amplitude of the particle velocity. Also disclosed is the measurement of the interaction of sound waves and electric fields in the fluid medium over a range of frequencies to obtain the particle size and zeta potential.

Abstract: An apparatus for detecting the position of a charged particle in a duct pipe has a plurality of electrodes arranged in the duct pipe. Detection signals obtained in the electrodes are phase-delayed by predetermined amounts and then added to form an integral detection signal. The integral detection signal is input to a circuit which determines waveforms representative of the passage of the charged particle: namely, the D.C. component of the detection signal, fundamental wave component and a phase-shifted fundamental wave component. The position of the charged particle are determined from these components. A part of each electrode is formed of a dielectric member. Each electrode and an associated connector are covered by a double-shield structure with inner and outer shields, the electrode, the connector and the inner shield being electrically insulated from the duct pipe.

Abstract: A method of determining the amount of the substances or ions contained in an ionic solution or a non-deionized solution by measuring the frequency of a one side barrier-covered crystal oscillator comprising a crystal oscillator, a barrier to cover over one of the electrodes of the crystal oscillator through a predetermined insulative space so as to prevent the ionic solution or the non-deionized solution from permeating therethrough and an adsorption film cast on the other electrode of the crystal oscillator, in situ in the state that the one side barrier-covered crystal oscillator is dipped in the ionic solution or the non-deionized solution, and the one side barrier-covered crystal oscillator used therefor.

Abstract: The thermal time constant of fine metal wire segments, such as those used to initiate explosive reactions, is measured by passing a variable frequency source of current through the wire. The magnitudes of the sine and cosine components of the third harmonic of the voltage developed across the wire are detected and compared to each other to provide a control signal which is applied to the frequency source to change the its frequency in a direction which tends to make those components equal in magnitude. The magnitude of the control signal, when the third harmonic sine and cosine components are equal, is displayed as a function of the thermal time constant of the wire segment.

Abstract: A control circuit (1) for use in a humidifier (H). A capacitor functioning as a humidity sensor (55) includes a sulphonated fluorocarbon material acting as the dielectric (57) of the capacitor. The material is sandwiched between sheets (59a, 59b) of a screen material which act as plates of the capacitor. An RC oscillator (53) has a variable frequency output and incorporates the capacitor. Changes in the dielectric value of the material due to sensed changes in humidity produce changes in the oscillator output frequency. A DC voltage is supplied to the oscillator. The amount of voltage impressed on the sensor at relatively high-humidity levels is controlled to prevent leakage currents caused when the material is exposed thereto. The generation of such leakage currents otherwise adversely effects sensor operation. Operation of the circuit to control operation of the humidifier is also described.

Abstract: A technique for electrochemical measurement of the corrosion current (corrosion rate) determines the electrochemical parameters that are necessary to calculate the corrosion rate as they are contained in the harmonic current response to a moderate amplitude sinusoidal voltage perturbation applied to the corroding metallic component. The harmonic current response is analyzed at frequencies .sub.1 f, .sub.2 f, .sub.3 f, .sub.4 f, .sub.5 f and the rectification current response of DC current to the presence of a 20-50 mV AC voltage perturbation at a frequency f. The free corrosion current density, the free corrosion potential and the Tafel coefficients are calculated. The Tafel coefficient or Tafel slope is a measure of the exponential dependence at the rate of corrosion in a material. From these data, the dissolution current is calculated, which in turn is integrated with respect to time to yield a cumulative mass loss.