Abstract: An electrostatic sensing device for investigating a surface and/or sub-surface structure comprises a central and square electrically conductive sensor plate, and four side electrically conductive elongated and rectangular sensor plates connected together and each disposed adjacent and parallel to one edge of the central plate. The arrangement of sensor plates is applied to the surface, and the central and sensor plates are then electrically charged at different rates, the charging rate of the central plate being affected by the permittivity of the investigated structure to electric field. A differential amplifier amplifies the difference between the voltages on the central and side plates as these plates charge, and a peak detector detects the highest amplitude of this amplified voltage difference and displays it on a voltmeter.

Abstract: An impedance measurement system including a series circuit having a reference impedance leg and a measurement leg, the measurement leg including first and second spaced apart electrodes defining a region for receiving a sample of material to be tested; an oscillator circuit connected in parallel with the series circuit and providing a reference voltage and a signal voltage proportioned to the impedance of the measurement leg; and a detector circuit producing an output voltage proportional to changes between the reference voltage and the signal voltage.

Abstract: A verification device for a security thread embedded within currency paper includes two or more sensor channels, each channel comprising a sensor plate and a guard plate disposed adjacent to one another. The sensor plate and guard plate of one channel are in a planar relationship with the sensor plate and guard plate of all other channels. A transistor has its base connected to the sensor plate and its emitter connected to the guard plate, thereby effectively removing any stray capacitance between the sensor and guard plates. The output of the transistor at its emitter is indicative of the amount of the electrical charge on the sensor plate. Signal processing electronics disposed after the transistor convert the sensor plate capacitance into an electrical signal whose pulse width is proportional to the amount of sensor plate capacitance. A valid currency having a security thread embedded therein passes by a sensor plate and varies the amount of capacitance of the plate.

Abstract: A verification device for a security thread embedded within currency paper includes a pair of capacitive plates having applied thereto time-varying electronic signals that are 180.degree. out of phase. Disposed between the plates is a sensor element comprising a cylindrical wire dimensionally equal to the security thread. A guard electrode surrounds the sensor; the guard, sensor, and plates comprising a capacitance bridge. When the security thread in the currency is adjacent to the sensor and in proximity thereto, a capacitance imbalance occurs in the bridge. Electronic circuitry is responsive to this imbalance and provides an indication of a valid security thread embedded within the proffered currency paper.

Abstract: A circuit for responding to the output of a capacitive fuel sensor that can distinguish gasoline from methanol and produces an output that is related to the methanol proportion. The response is independent of the conductivity in the sensor resulting from fuel contamination. A square wave is employed to excite the sensor and the circuit provides for stabilizing the square wave amplitude. The circuit includes an amplitude modulation detector that converts the square wave transients into a fuel composition related voltage output that can be applied to an engine control mechanism that will adjust the automotive engine to operate efficiently with the fuel being supplied. Circuits are shown for linearizing the fuel composition to voltage response and a charge dispenser amplitude modulation detector is described wherein the detection occurs only during the square wave transient interval.

Abstract: A flexible fuel dielectric-effect sensor is disclosed wherein three capacitors, immersed in the fuel flow, are connected to define a pi filter.

Abstract: An apparatus for detecting the degree of deterioration in lubricating oil including a grid-like capacitive sensor, that uses the lubricating oil as a dielectric medium, and a magnetic field imposed upon the oil to attract ferromagnetic wear particles into the vicinity of the sensor. Preferably, the magnetic field is generated by a permanent magnet and an electromagnetic aligned such that the magnetic field produced by each magnet acts upon the oil along the same axis.

Abstract: A hand-held test probe is employed which uses a capacitance measuring circuit to measure capacitance as the probe is scanned along a pattern of conductors (pads or pins) at a steady rate. The capacitance measurement is stored in a memory during the scan, then maximums are detected in the stored data, corresponding to the conductor pattern. If a particular conductor has a short or a break in continuity, its capacitance will be more or less than it should be. The detected maximums are compared with recorded values for a known-good printed wiring board for this scan pattern. If the comparison shows a difference greater than a selected threshold, an error is indicated for this pin location. The known-good is scanned in a "learn" mode, in which the capacitance values are stored for each scan, identified by scan number.

Abstract: A fuel composition sensor provides to a voltage divider comprising sensor and reference capacitors a voltage which oscillates between two voltages at a comparatively low frequency, such as 6 KHz, for lower power dissipation, but which switches fast to produce periodic fast voltage changes across the voltage divider to produce voltage spikes at the junction of the capacitors indicative of the capacitance ratio and thus of fuel composition.

Abstract: Apparatus for detecting thickness which includes an electrode detecting unit including a ground electrode and a detecting electrode. The electrodes oppose each other along a paper path. An oscillating circuit provides an oscillation frequency signal. A resonant circuit, having a resonator independent of the oscillating circuit, has a resonance point which changes in accordance with a change in electro-static capacitance corresponding to a change in paper thickness detected by the electrode detecting unit. A resonant circuit outputs a detection signal corresponding to the change in resonance point. By analyzing this detecting signal, a state of two sheets of paper passing through the path is detected as a change in paper thickness.

Abstract: A liquid sensor for detecting, in a non-contact manner, whether an electrolyte solution is flowing through a pipeline. A pair of electrodes, on which an AC voltage is impressed, are mounted on the outer surface of a pipeline formed of a material having a high dielectric constant, such as a ceramic, and a discrimination between the presence and the absence of the electrolyte solution in the pipeline is made based on variations in capacitance between the electrodes. In the presence of the electrolyte solution flowing through the pipeline, the capacitance between the electrodes is high because of the conductivity of the electrolyte solution. In the absence of the electrolyte solution flowing through the pipeline, the capacitance is determined by air and is, therefore, low. Since the electrodes are maintained in a non-contact relation with the electrolyte solution, degradation of characteristics due to corrosion is obviated.

Abstract: A tomographic flow imaging system comprising three or more capacitance electrodes positioned around a pipe through which a flow to be monitored passes. The capacitance between each pair of the electrodes is measured, and an output is derived from the measured capacitances which is representative of the distribution of material within the pipe. A predetermined voltage signal is applied to one electrode at a time, and the electrodes other than said one electrode are connected to sources of equal fixed potential. The capacitance of each pair of electrodes is measured by measuring charge flowing between the said other electrode of the pair and the source of potential to which it is connected.

Abstract: A fuel composition sensor for a fuel line carrying a mixture of two fuels provides a fuel composition signal VOUT to an engine control computer having a computer analog reference voltage ECM referenced to a computer ground EGD. The sensor has a sensor analog reference voltage VREF referenced to a sensor ground GND, which may differ from the computer ground EGD. An input isolation amplifier derives the sensor analog reference voltage VREF relative to GND ratiometrically from the computer analog reference voltage ECM referenced to EGD; and an output isolation amplifier derives the fuel composition signal VOUT referenced to EGD ratiometrically from the difference between a fuel composition responsive sensor signal VSIG and its minimum possible value, corresponding to a sensed fuel composition of only one of the fuels, relative to GND. The sensor may comprise a capacitive voltage divider and provide sensor voltage VSIG also having a maximum value corresponding to a sensed fuel composition of only the other fuel.

Abstract: In a fuel composition sensor in which a fast step voltage is applied to a capacitive voltage divider comprising a sensor capacitance and a reference capacitance in series, a padding capacitor is connected in parallel with the sensor capacitor to produce a more linear output across the full range of fuel composition. The value of the padding capacitor is sufficient to produce a capacitance ratio of the voltage divider substantially less than one and, in particular, less than two thirds.

Abstract: Apparatus and method for determining capacitive and resistive values of an electrical component, such as a fuel level determining probe, includes a waveform generator for subjecting the probe to a time-varying waveform that includes a linearly varying ramp portion and a fixed, constant portion. A selectively controlled sample and hold circuit senses the voltage potential of the probe in response to a zero-crossing detector during the linearly varying ramp portion of the waveform to provide information indicative of the capacitive value and again senses the voltage potential at selected time thereafter during the fixed portion of the waveform to provide resistive value information. The output of the sample and hold is provided to an analog-to-digital converter which provided digital information to a stored-program controlled processor which provides the desired output information.

Abstract: A device for inspecting a glass container to evaluate its wall thickness. The minimum thickness, the maximum thickness and the minimum to maximum thickness ratio are calculated and an inspected bottle is rejected based on one or more of these three parameters.