Abstract: A non-contact capacitive proximity detector includes a sensing plate and detection circuitry electrically coupled to the sensing plate. The detection circuitry comprises an oscillator electrically connected to the sensing plate and signal conditioning circuitry electrically connected to the oscillator. The signal conditioning circuitry includes a coupling capacitor C.sub.1, an envelope demodulator, a first comparator, a delay circuit and a second comparator. When an object is within a predetermined proximity to the sensing plate, the capacitance of the capacitor constituted by the sensing plate and the proximal object is at a level which causes the oscillator to generator an oscillating signal having a sufficient magnitude. The oscillating signal generated by the oscillator is applied to the envelope demodulator by way of the coupling capacitor. The envelope demodulator generates an envelope of the oscillating signal and applies the envelope to he first comparator.

Abstract: The spaced plates of a capacitor are immersed in water adjacent water intake grating so that water flowing toward the grating passes between and in contact with the plates so that frazil ice may accrete on the facing surfaces of the plates. As accretion occurs, the capacitance changes to indicate the amount of accretion of frazil ice which is detected thereby providing an indication of the amount of accretion of frazil ice on the grating.

Abstract: A reference ring oscillator circuit (RROC) is used to determine timing characteristics of a test interconnect structure in an integrated circuit. The RROC includes an odd number of inverters coupled together in a ring manner and has defined test segments at which a test interconnect can be loaded. Reference timing characteristics of the unloaded RROC are determined according to a calibration method including the steps of: (a) directly measuring signal propagation delay through each segment of the RROC; (b) modeling each test segment using an RC tree type reference circuit model having reference elements; (c) simulating the reference circuit model to provide a functional relationship between two reference capacitors; (d) defining upper and lower bounds for propagation delay through the test segment in terms of the reference elements; (e) determining values for the reference capacitor elements; and (f) measuring a reference frequency of oscillation of the unloaded RROC.

Abstract: The present invention relates to a device for the contactless detection of the position of a moving webs. The web has on one side of the web a detector electrode covering its entire width and on the other side in the area of the web edges transmission electrodes fed by an oscillator in phase opposition, so that the capacitive couplings between the transmission electrodes and the detector electrode respond in opposing fashion to deviations of the web from the central position. The signal received by the detector electrode is processed by a current to voltage converter with a very small input impedance so that the potential of the detector electrode remains at zero, and virtually no capacitive displacement currents flow to a screening electrode In this way, the sensitivity of the measurement array is independent of the web width.

Abstract: A capacitive proximity or limit switch comprises a capacitive probe having a sensor electrode and a guard electrode. The sensor electrode is connected to an oscillator formed by a feedback system of two operational amplifiers, of which one operational amplifier is configured as a differential amplifier, the other operational amplifier as a voltage follower. The probe electrode is connected to the inverting input of the differential amplifier, in the feedback circuit of which a capacitor is provided, as a result of which the AC gain is determined. An adjustable portion of the output voltage of the differential amplifier is applied to the non-inverting input of the voltage follower, the output of which is connected to the non-inverting input of the differential amplifier to which the guard electrode is connected.

Abstract: A method and apparatus for monitoring thermal processing of a workpiece using a sensor electrode which can be positioned relative to the workpiece and to which an alternating electric signal is applied in order to determine a measured capacitance (C.sub.meas) present between the sensor electrode and workpiece by evaluating a change in the alternating signal as a consequence of the measured capacitance (C.sub.meas). A measured capacitance frequency distribution is formed from a number of determined measured capacitances (C.sub.meas). The measured distribution is compared with a reference distribution. If a deviation is present between the two distributions, process parameters can be appropriately readjusted. It is preferable to use a laser beam for processing the workpiece.

Abstract: The fast sampling method for taking a position measurement with an electronic measurement system incorporating a capacitive position transducer of this invention allows such capacitive position transducers to be used in contaminant filled environments, such as on a shop floor or in the outdoors. By sampling the output signals within 25 ns-35 ns from when the input signals were applied to the capacitive position transducer, the adverse effects of resistive contamination can be avoided.

Abstract: A conductive strip detector comprises a capacitor defined by an elongate, electrically conductive element (5) and a laterally spaced, electrically conductive member (1). Monitoring circuitry (15,16) monitors changes in the capacitance of the capacitor when an electrically conductive strip substantially parallel with the element is passed by the capacitor and indicates when a change in capacitance is due to the presence of an electrically conductive strip.

Abstract: A fuel gauging system for use in determining the level of fuel in a tank. The system incorporates a resonant circuit for measuring the resonant frequency of at least one probe immersed in the fuel located in the tank. From measurements of variations of the frequency of resonance, the level of liquid in the tank is determined, and the fuel quantity is then calculated and displayed.

Abstract: A method and apparatus for calculating a ratio, R, having a first capacitance value, C.sub.1, in inverse relation to a second capacitance value, C.sub.2, where C.sub.1 and C.sub.2 are the capacitance values of a first capacitor and a second capacitor respectively. The first and second capacitors each have an independent electrode and share a common electrode. An AC voltage is applied to the common electrode producing first and second AC current signals at the two independent electrodes. A dual switched-capacitor integrated circuit and two current to frequency converters respectively convert the first and second AC current signals to first and second frequency signals having values f.sub.1 and f.sub.2. A microprocessor receives the first and second frequency signals and calculates R from f.sub.1 and f.sub.2.

Abstract: A method and apparatus for determining surface characteristics of a layer (e.g. anodised aluminum) by measuring electrical impedance thereof and solving specified equations.

Abstract: A capaciflector sensor system scanned in frequency is used to detect the permittivity of the material of an object being sensed. A capaciflector sensor element, coupled to current-measuring voltage follower circuitry, is driven by a frequency swept oscillator and generates an output which corresponds to capacity as a function of the input frequency. This swept frequency information is fed into apparatus e.g. a digital computer for comparing the shape of the capacitance vs. frequency curve against characteristic capacitor vs. frequency curves for a variety of different materials which are stored, for example, in a digital memory of the computer or a database. Using a technique of pattern matching, a determination is made as to the identification of the material. Also, when desirable, the distance between the sensor and the object can be determined.

Abstract: A capacitive measuring device or apparatus; in particular, a length-measuring apparatus, which incorporates a scale portion and a scanning unit which is movable relative to the former and which supports transmitting electrodes and at least one receiving electrode. Herein, a transmission circuit applies transmitting signals at a basic frequency to the transmitting electrodes, and with the receiving electrode being connected to a reception circuit, to the output side of which there is connected an evaluating circuit for the receiving signals. The transmitting signals are applied to the transmitting electrodes through a pulse width modulator and a synchronous modulator and the receiving signal is conducted through a demodulator.

Abstract: An apparatus for determining the position of a movable object is disclosed. A pair of fixed elements having spaced electrically conductive surfaces form a capacitor. A movable element having an electrically nonconductive composition is connected to the movable object. The movable element is disposed between the fixed element pair. In response to the movement of the movable element, the capacitance value of the variable capacitor changes. A circuit detects the change in capacitance and determines the relative position of the movable object.

Abstract: The assembly comprises an electrically insulated linear array of a plurality of active plates working in conjunction with common return plate means to provide a line of capacitors. The electrically insulated active plate array and common return plate means extend through a column of multi-phase fluid. A discrete oscillator circuit is positioned adjacent to and is permanently connected to each active plate for charging and discharging it. Means are provided for sequentially enabling the oscillator circuits to produce signals which are each indicative of the dielectric constant of the thin horizontal slice of fluid extending between the active plate and the return plate means. The signals are collected by a microprocessor which analyzes them to provide a dielectric constant profile of the fluid column. Interfaces of phases can be located from the profile and the composition of the fluid phases can be determined.

Abstract: A cable length indicating arrangement which utilizes the capacitance of a two wire cable (10) to determine its length. The arrangement includes an oscillator stage (14) having a frequency setting capacitor (16) across which the cable is connected. The frequency of oscillation is converted into a voltage which is provided as the input to a comparator network (70, 72, 74, 76, 78, 80) which compares this voltage against voltages derived from a voltage divider network (96, 98, 100, 102, 104, 106, 108). The comparator network includes a "ladder" of comparators each having their non-inverting inputs coupled to receive the frequency dependent voltage and their inverting inputs each connected to a respective point in a resistive divider string. The outputs of the comparators are connected to respective light emitting diodes (82, 84, 86, 88, 90, 92).

Abstract: It is an object of the present invention to prevent variations in sensitivity of the sensor circuits of the respective channels by equalizing the power of oscillation frequency signals to be distributed/supplied from one oscillation circuit to the sensor circuits of the respective channels. Multi-channel sensor circuits are arranged with a common oscillation circuit. A high-impedance conversion circuit is connected to the output terminal of the oscillation circuit. A first impedance matching circuit for performing impedance matching of resonance circuits of the respective channels with reference to the oscillation circuit is arranged on the output side of the high-impedance conversion circuit. Second impedance matching circuits for performing impedance matching of the oscillation circuit with reference to the resonance circuits are connected at the input terminals of the resonance circuits of the respective channels.

Abstract: A dosimeter with reproducible changes in .epsilon.', .epsilon.'', or their equivalent two parameter circuit representations, under a given treatment regime that correlate directly with changes in physical attributes of a material or fluid, such as strength, modulus or viscosity, is used to monitor the deterioration of the physical attributes of the material or fluid.

Abstract: An apparatus for analyzing the dielectric properties of a sample. A thin planar sample having a hole therein is positioned over two bottom electrodes having the hole over one of the bottom electrodes. An oscillator provides a first signal to one of the bottom electrodes and a second signal 180.degree. out of phase with the first signal to the second bottom electrode. A differential signal is obtained on the top electrode representative of the dielectric properties of the sample with the elimination of edge effects. A phase sensitive demodulator synchronized with the oscillator extracts the two components of the conductance and susceptance of the sample. A position sensor measures the thickness of the sample and is used to calculate the dielectric constant of the sample. Thereby, an accurate measurement of the dielectric properties of the sample is obtained without a complicated structure in order to eliminate edge effects.

Abstract: Measurements of the permittivity of samples over a very wide frequency range and a wide temperature range have previously involved such problems as changing parts of the measuring equipment in different regions of the frequency range, substituting one of the components of a bridge used as part of the equipment to obtain bridge balance, and limited permittivity resolution. The present invention employs a capacitance bridge formed by a sample held between electrodes, a series capacitor and a detector comprising a high input impedance amplifier and correlators. The bridge is balanced by applying voltages of known relative amplitude and phase constructed from outputs having relative phases of 0.degree., 90.degree. and 180.degree. of two phase-locked oscillators. The voltages are constructed using phase shifters, attenuators and summer-driver circuits. At low frequencies the applied voltages are obtained from a waveform synthesizer.

Abstract: Disclosed is a method of detecting a variation in stray capacitance by use of a PLL circuit.

Abstract: A phase discriminating capacitive sensor array system which provides multiple sensor elements which are maintained at a phase and amplitude based on a frequency reference provided by a single frequency stabilized oscillator. Sensor signals provided by the multiple sensor elements are controlled by multiple phase control units, which correspond to the multiple sensor elements, to adjust the sensor signals from the multiple sensor elements based on the frequency reference. The adjustment made to the sensor signals is indicated by output signals which indicate the proximity of the object. The output signals may also indicate the closing speed of the object based on the rate of change of the adjustment made, and the edges of the object based on a sudden decrease in the adjustment made.

Abstract: Apparatus and an associated method are described for testing liquid crystal matrix displays that can be performed prior to the assembly of the display. This display procedure involves applying of square wave signal to the control elements and a sine wave signal to the input terminal of an active element associated with the pixel under test. By selection of the sine wave signal frequency, the modulation products resulting from the combination of the square wave signals and the sine wave signal fall between the components resulting from the application of the square wave signal alone. As a result of the symmetry of the modulation components, a comb filter can be used to select the modulation components. The power of the transmitted modulation products provides a figure of merit for the active element associated with the pixel.

Abstract: An improved oscillator circuit and method for measuring capacitance and small changes in capacitance is described. The circuit provides a digital output signal that has a frequency inversely proportional to the capacitance being measured, is substantially immune to stray capacitance, has low sensitivity to noise and temperature variations, is relatively simple and inexpensive to implement and provides a high precision measurement. One embodiment of the oscillator includes a capacitor to be measured, an integrator, an inverting amplifier, a comparator, a summing amplifier and a digital output circuit. A second embodiment of the oscillator further provides compensation for the non-linear response of a parallel plate capacitive transducer.

Abstract: An improved oscillator circuit and method for measuring capacitance and small changes in capacitance is described. The circuit provides a digital output signal that has a frequency inversely proportional to the capacitance being measured, is substantially immune to stray capacitance, has low sensitivity to noise and temperature variations, is relatively simple and inexpensive to implement and provides a high precision measurement. One embodiment of the oscillator includes a capacitor to be measured, an integrator, a comparator, a resistive attenuator, a summing amplifier and a digital output circuit. A second embodiment of the oscillator further provides compensation for the non-linear response of a parallel plate capacitive transducer.

Abstract: Apparatus and method for detecting the presence and surface location of or the absence of an electrically conductive solar coating on a pane of glass. A capacitor is formed by placing a probe against one surface of the glass. The value of the capacitor is determined by the presence or absence of a conductive coating on the glass and by the location of any coating relative to the probe. Variations in the value of the capacitor are detected to selectively illuminate lights which indicate either the absence of a surface coating, the presence of a surface coating on a near surface or pane of the glass or the presence of a surface coating on a far surface or pane of the glass.

Abstract: A differential capacitive pickoff detector circuit for measuring the difference in spacing of a pair of differential pickoff capacitor plates. Current sources are provided for each output terminal of each of the pair of differential capacitors so that for each capacitor output terminal a current signal alternates between a first current level and a second current level at a predetermined carrier clock switching rate. The capacitors are varied to provide DSB-LC voltage signals across each of the capacitors. The average value of each of the alternating voltages and their amplitudes are automatically adjusted to predetermined levels. The two DSB-LC voltage signals are combined to provide a DSB-SC signal. The DSB-SC signal is synchronously demodulated using a quadrature reference carrier clock signal to provide an output baseband signal which represents the difference between the spacing of the first and second differential capacitor plates.

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: In a hot gas turbine engine a capacitive probe clearanceometer is employed to measure the clearance gap or distance between the continuous surface of a compressor or turbine wheel such as, for example, a shroud ring turbine and its confining casing under operating conditions. The probe positions a capacitor electrode at the inner surface of the casing adjacent the continuous surface path. Electrical power is supplied to the probe through an oscillator having a tuned circuit in which the probe is a component. A high frequency signal of the oscillator is amplitude modulated by changes in electrical capacitance between the probe capacitor electrode and the passing continuous surface. The modulated oscillator signal is processed to provide an electrical signal which is proportional to the distance between the casing and the continuous surface. A preferred combination of high temperature and contamination resistant metal and ceramic materials are combined in an improved gas tight braze sealed probe tip.