Showing papers on "Capacitive sensing published in 1977"

Electronic wall stud sensor

Abstract: A portable sensor adapted to be moved along a wall to indicate a change in the dielectric constant of the wall thereby to signal the presence of a wall stud within the wall. The sensor incorporates a capacitor plate positioned adjacent the surface in contact with the wall and a circuit for detecting any change in the capacitive charge on the capacitor. Any change in capacitive charge as the sensor is moved along the wall is due to a change in the dielectric constant of the wall because of the presence of a wall stud behind the wallboard. The sensor visually indicates any change in the dielectric constant in a manner to permit selection of the center of the change in dielectric constant thereby indicating the center of the wall stud. An additional feature of the circuit permits automatic calibration of the sensor to a level corresponding to the dielectric constant of the wallboard so that any change in the dielectric constant of the wall due to the presence of a stud is readily observable.

Capacitive means for measuring the level of a liquid

Abstract: Electrodes are disposed on portions of a container comprising dielectric material, an electrical signal is capacitively transmitted between said electrodes, said electrical signal is shunted by the presence of a liquid in close proximity to said electrodes, and said shunting is detected.

Finite element solution of complex potential electric fields

Abstract: A computer program is described, which calculates electric fields in configurations with both capacitive and resistive distribution of potentials. Resistive coating on the surface of the insulation as well as conductivity in the insulation itself can be handled.

High fidelity pressure transducer

Abstract: The capacitive fluid pressure transducers described herein comprise quartz bodies and diaphragms having suitable electrodes deposited thereon to form both sensing and reference capacitors in appropriate configurations for high fidelity measurement of relative blood pressure, said transducers being substantially unaffected by temperature and other environment factors.

Multiple-frequency permittivity tester

Abstract: As in prior testers, a capacitive cell in which material is placed to be tested is connected in a voltage divider circuit. However, signal generating means connected to the voltage divider applies voltages at different predetermined frequencies selected for the material being tested, and frequency selective means connected to the cell develop voltages at the applied frequencies having values dependent on the impedance of the filled cell at the respective frequencies. These voltages developed across the cell are applied to a computer that provides an output according to an equation that has been derived statistically from many samples of the material being tested for the substance or quality of the material being measured.

Calibrating and measuring circuit for a capacitive probe-type instrument

Abstract: A calibrating and measuring circuit is disclosed for a capacitive probe-type instrument. The capacitive probe, in contact with a surface to be measured, is connected to an oscillator which generates pulses, the frequency of which is adjustable, the number of pulses generated being a function of the texture of the surface being measured. A digital counter is connected to receive, count and present the resulting summation to a visual numerical display. In order to calibrate the instrument the capacitive probe is placed on a known specimen, the digital magnitude of which is loaded into the counter through a number of thumb switches. The counter first counts down to this number, and then counts up to the number of remaining pulses. The resulting count, called the offset number, is then transferred to a memory. During measurement the memory loads the offset number into the counter, the counter then counting the offset number down to zero, before counting up to the amount of the received pulses, which are then displayed. A logic arrangement initiates and controls both calibration and measurement.

Capacitance-to-voltage transformation circuit

Abstract: A capacitance-to-voltage transformation circuit for providing an output voltage proportional to capacitive variations includes a variable capacitor, a reference voltage source, and circuit means for charging the variable capacitor to the reference potential. A switch means alternately connects the variable capacitor to the charging means and to ground at a cyclical rate determined by an oscillator clock. An impedance means coupled between the charging and switch means, develops a voltage drop thereacross of a magnitude directly proportional to capacitance variations of the variable capacitor. In accordance with another aspect of the invention, the circuit includes a compensating means for nullifying any fixed capacitance component of the variable capacitor.

Capacitive touch-pad devices with dynamic bias

Abstract: A dynamic biasing capacitance is formed between a transmitting electrode and a receiving electrode of a capacitive touch-pad device to couple a portion of the scan voltage signal into the sense node of a voltage comparator circuit, coupled to the receiving electrode, to offset the comparator circuit threshold voltage. The dynamic biasing capacitance may be formed by overlapping portions of the electrodes, with a dielectric layer positioned therebetween, or by the parasitic capacitance between aligned end surfaces of the two electrodes, with the magnitude of the dynamic biasing capacitance being adjusted by variation of interelectrode geometries.

Device for continuously measuring the liquid level in a container

Abstract: A device for continuously measuring the liquid level in a container, wherein a capacitive sensor is disposed in the liquid to be measured and is connected with an oscillator as the frequency controlling element thereof, the output of the oscillator being connected with a suitable indicator or control, and wherein the capacitive sensor is formed of an elongate flexible strip of insulating material having opposite faces, with a plurality of elongate conductive elements embedded in the strip of material spaced approximately equidistantly from the opposite faces so that an electric field generated between the conductive elements can be substantially equally acted upon simultaneously on both sides of the device by the liquid to be measured, thereby enhancing the sensitivity of the sensing element, and enabling linear gauge characteristics to be obtained in irregularly shaped containers.

Laminated capacitive touch-pad

Abstract: A laminated capacitive touch-pad having a thin film touch-plate electrode deposited upon a first (exterior) surface of a first, relatively thin dielectric layer and having spaced transmitter and receiver electrodes deposited upon a second surface of the first layer within the outline of and opposite to the touch electrode, with a relatively thick backing layer of dielectric material laminated upon the second surface to provide a total thickness, as measured between the furthest opposed surfaces of the first and second layers, as required for high voltage insulation purposes and to provide additional impact strength The touch, transmitter and receiver electrodes may be of thin film construction

Apparatus for detecting water in oil

Abstract: In an apparatus for detecting water in oil a capacitive probe is filled with the oil under test. This probe and a reference capacitor are alternately connected in the frequency determining network of an h.f. oscillator, the output of which is connected to a frequency to voltage converter. A sample and hold circuit gated in synchronism with switching of the capacitors and an amplifier a.c. coupled to the sample and hold circuit provides an a.c. output, a change in the amplitude of which indicates changes in the dielectric constant of the oil.

Liquid level sensor

Abstract: A pair of wires are encased in a non-absorbing corrosive-resistant material such as Teflon and disposed vertically inside a tank or the like with the wires brought out to a capacitive sensing device to provide a liquid level sensor operable in almost any liquid and some dry granular materials.

Steady-state analysis of sinusoidal time-variant networks applied to equivalent circuits for transmission networks

Abstract: This paper describes the analysis of time-variant networks in the frequency domain applied to resistive, inductive, and capacitive sinusoidally varying networks. It leads to a common equivalent circuit. This equivalent circuit is based on some previous work done by Desoer and by the author. The equivalent circuit is applied to the analysis of resistive modulators, parametric amplifiers, and frequency multipliers. It is shown how simple time-invariant two-port equivalent circuits can be derived for these transmission networks, such that the practical engineer can obtain quick insight into their behavior. The derived linear two-port equivalent circuit can be used as a basis for a small-signal nonlinear analysis of the above mentioned transmission networks.

Electronic watch control device for manual actuation

Abstract: An electronic watch control device for manual actuation is disclosed. It comprises a capacitive sensor including a conductive layer on the inner surface of the watch-glass, which is actuated by placing a finger-tip on the outer side of the watch-glass. The sensor is part of a capacitive voltage divider to which a high frequency voltage is applied. Synchroneous detection means are arranged for detecting the high-frequency voltage drop across the sensor in synchronism with the high-frequency. Comparison means are provided for comparing the value of the said voltage drop to a reference voltage and producing a control signal depending on the condition of the sensor.

Pulse power source

Abstract: In a pulse power source for applying a pulse voltage to a capacitive load; a series resonance circuit capable of generating transient oscillation is formed of the capacitive load adapted to be applied with the pulse voltage, an inductance for generating transient oscillation and a power source capacitor; the capacitive load is charged from the power source capacitor by first closing one of two switch elements provided in the midway of the resonance circuit, that is, a load charging switch element to make the voltage across said capacitive load rise up to about twice the voltage across the power source capacitor after a period equal to about 1/2 of a transient oscillation period of said series resonance circuit, to form a rising edge of the desired pulse voltage; then reversely, the power source capacitor is charged from the capacitive load by closing the other switch element, that is, a charge recovering switch element after first said one switch element has been closed to make the voltage across said capacitive load fall down, to form a falling edge of the desired pulse voltage; and further a residual charge on said capacitive load is discharged by closing still another switch element provided in parallel to said capacitive load, to improve the falling edge of the desired pulse voltage; whereby a steep pulse voltage can be applied to said capacitive load with a low power loss.

Digital level indicator

Abstract: A level indicator providing a digital display of gravity-related attitude comprises a capacitive gravimeter pickup assembly the complementary capacitor pair of which are alternately switched, on an equal-time basis, into an RC oscillator circuit Concurrently, each oscillator pulse train is switched, respectively, into the up- and down-mode of reversible counting means to yield a net oscillator frequency difference directly, digitally indicative of the degree of departure from a gravity-referenced level condition

Recognition and identification key having adaptable resonant frequency and methods of adapting same

Abstract: A recognition and identification key comprising a substrate formed from an electrically insulating material, a first sheet of conductive material formed on a first surface of the substrate in a looping pattern so as to provide an inductive element, and a capacitive element coupled to the first sheet such that the elements are resonant at a first frequency, at least one of the inductive and capacitive elements capable of being changed such that the key is resonant at a second frequency, and a method of adapting the resonant frequency.

Steady-state analysis of sinusoidal time-variant networks applied to equivalent circuits for transmission networks

Abstract: This paper describes the analysis of time-variant networks in the frequency domain applied to resistive, inductive, and capacitive sinusoidally varying networks. It leads to a common equivalent circuit. This equivalent circuit is based on some previous work done by Desoer and by the author. The equivalent circuit is applied to the analysis of resistive modulators, parametric amplifiers, and frequency multipliers. It is shown how simple time-invariant two-port equivalent circuits can be derived for these transmission networks, such that the practical engineer can obtain quick insight into their behavior. The derived linear two-port equivalent circuit can be used as a basis for a small-signal nonlinear analysis of the above mentioned transmission networks.

Capacitive-type nonlinear emphasis circuit

Abstract: A video signal processing circuit includes an amplifier with a circuit connected to it to emphasize the amplification of some frequencies relative to others. A non-linear circuit is also connected to the amplifier and comprises a capacitor connected in series with non-linear elements that change the amplification of positive and negative overshoots of the signal relative to the middle amplitude range. The result is non-linear modification of emphasis and can be used to pre-emphasize video signals before using them to modulate the frequency of a carrier and, in the playback section to de-emphasize the signals to minimize FM noise. Use of the capacitor prevents direct current from flowing and thus affecting the threshold levels of the non-linear elements. Component values can be selected to effect temperature compensation.

Solid state switch

Abstract: A solid state switch is provided which has four terminals, two for the A.C. power which is to be switched and two for signal input. The circuit comprises a full wave bridge rectifier having a light-activated silicon controlled rectifier connected across its D.C. terminals. A capacitor and a light-activated transistor are added to a zero-cross firing circuit whereby the solid state switch is protected from high voltage transients and is applicable for use with resistive, capacitive, and inductive loads.

High speed, radiation hard complementary mos capacitive voltage level shift circuit

Abstract: A complementary MOS voltage level shift circuit which can be used as a memory buffer circuit, for example, is disclosed. The circuit utilizes both N-channel depletion mode devices and P-channel enhancement mode MOS devices preferably fabricated on silicon-on-sapphire. Both types of devices are operated with only negative or zero gate-source voltage in order to minimize threshold voltage shifts in radiation environments. A capacitive voltage level shifting technique is used to obtain push-pull operation with driver type devices in order to reduce power consumption and increase switching speed while feeding into a capacitive load. Load type devices are used to prevent discharge of a capacitive load.

Elimination of transducer bond corrections in accurate ultrasonic‐wave velocity measurements by use of capacitive transducers

Abstract: A capacitive‐driver–capacitive‐detector system for generation and detection of ultrasonic waves has been developed. This eliminates the necessity of bonding piezoelectric transducers to solid samples. With the capacitive‐driver–capacitive‐detector system, free–free boundary conditions exist at the sample surfaces and longitudinal ultrasonic‐wave velocities in solids can be measured accurately without correcting for ultrasonic‐wave phase shifts due to sample‐bonded transducer interfaces. The capacitive driver has a mica dielectric which increases the breakdown potential, but maintains the free–free boundary conditions at the solid specimen surfaces. This allows for a larger‐amplitude ultrasonic signal to be generated in the sample than is possible with an air‐gap capacitive driver. This improves the precision of the measurement. The accuracy of the method is comparable with that of bonded‐transducer methods, after bond corrections are made.

Crack opening displacement gage

Abstract: An electrical transducer for measuring changes in the size of crack openings. The device is designed to operate at temperatures up to and exceeding 1500° F., is portable, compact, easy to use and reuseable. The device comprises a differential capacitive sensing assembly, arm-like members each including an arm assembly for transmitting the change in crack opening from the crack to the sensing assembly, a flexural pivot to facilitate movement of the arm-like members with changes in the crack opening and means for anchoring the device in the crack. The differential capacitive displacement assembly comprises a plurality of capacitor plates, with the reference excitation plates coupled to one arm assembly and the movable sensing plate coupled to another arm assembly. A bridge circuit couples to the differential capacitive sensing assembly for electrically sensing capacitive variations occasioned by crack opening displacements.

Capacitance-compensated cable

Abstract: This invention relates to the transmission of electric power and in particular provides an electric power-transmission system having reduced vector regulation, voltage drop, and power loss through the inclusion of capacitance in the cable in series between the generator and load by utilizing electric conductors, i.e., connective links, having capacitance distributed along the length of the cable. Such capacitance is achieved by dividing a conductor into two parts which are separated by dielectric material such that the two conductor parts are in capacitive relation along the length of the cable and by connecting one conductor part to the generator and the other conductor part to the load such that the distributed capacitance is in series with the generator and load.

Low power dissipation crystal oscillator

Abstract: A low power dissipation crystal oscillator which comprises an inverter circuit including a pair of complementary insulated gate field-effect transistors and an excitation circuit connected between the output and the input of the inverter circuit. The excitation circuit comprises a crystal resonator and a pair of capacitive loads, wherein different DC bias potentials are applied to the gates of the field-effect transistors, respectively, in order to cause the power dissipation to be extremely reduced.

Tapered hole capacitive probe

Abstract: A tapered capacitive probe embodies vertical stripes for detecting irregular flaws in metal holes. Horizontal stripes are added to the probe and connected in a one-to-one relationship with the vertical stripes to detect and measure flaws with angular uniformity. Invention allows flaws to be detected in vertical, horizontal or angular direction and discloses approximate shapes and locations.

Capacitive bolometer effect in the paraelectric phase of triglycine sulfate

Abstract: Capacitive bolometer detectors using Ferroelectric materials and operating in the paraelectric phase with an external bias are investigated. Their responsivity is directly proportional to the induced polarization. The measured specific detectivity D*(0.9μ, 100 Hz, 1 Hz) for a TGS device, 4 mm2 in area and 325 microns thick, was 1.6 × 108 cm√Hz/W, slightly better than the D* of 1.2 × 108 cm√Hz/H' when the same device was used as a pyroelectric detector at room temperature. Theoretical considerations indicate that by going to high frequency ac bias, the capacitive bolometer detectivity can be increased to an extent where temperature fluctuation limit becomes realizable.