Showing papers on "Capacitive sensing published in 1980"

Capacitive fingerprint sensor

Abstract: The sensor incorporates a sensing member which has a sensing surface for receiving a fingerprint and sensing means for sensing the ridges and valleys of the skin of the finger under investigation. The sensing member contains a multitude of small capacitors. When the finger is pressed against the sensing surface, the capacitances of the capacitors are locally changed in accordance with the ridges and valleys. The information about the capacitance distribution is transformed into an electric signal.

A monolithic capacitive pressure sensor with pulse-period output

Abstract: A new microminiature monolithic capacitive pressure transducer (CPT I) is 20 times more sensitive than piezoresistive strain-gauge pressure transducers, requires one percent of the power, and can be batch fabricated through current integrated circuit technology. A second device (CPT II) incorporates bipolar signal-processing electronics on the same silicon chip to produce a low-duty-cycle pulse-mode output with period related to pressure. This output format helps to re-solve the problem of shunting between leads, which is one of the principal causes of long-term drift in piezoresistive transducers designed for implantable medical applications. Because this device uses capacitance change as a transductional mechanism rather than piezo-resistivity, it is not susceptible to drift caused by temperature variations in the piezoresistive coefficient. Optimization for totally implantable biomedical applications places special emphasis on small size, high sensitivity, improved long-term baseline stability, and greatly reduced power consumption. These properties are also important for a wide range of pressure-sensing applications-from automotive to general industrial use.

Apparatus in medicine for the monitoring and or recording of the body movements of a person on a bed, for instance of a patient

Abstract: A capacitive motion sensor placed under a mattress or the like for monitoring the movements of a person. The sensor uses an active layer consisting of two courses of dielectric material placed in contact with one another. Movements of a person on top of the mattress cause the courses to move relative to one another, thereby generating an electric change in the active layer which is detected by a pair of spaced elements which form a capacitive antenna means.

Capacitive systems for touch control switching

Abstract: In capacitive systems comprising a dielectric sheet 11 having a first electrode 12 on one side, and on the other side in capacitive relation with the first electrode 12, second and third electrodes 13, 14 which are mutually spaced by a gap 15 especially for use in touch control switches, it is desired to achieve a favorable compromise between high capacitance modification as between touched and untouched condition of the first electrode 12, and the total amount of material used to form the electrodes. To this end, the third or outer electrode 14 is shaped to surround at least the major part of the periphery of the second or inner electrode 13, and the ratio of the area of the inner electrode 13 to the area of the outer electrode 14 is greater than 0.25 to 1.

Capacitive switch and panel

Abstract: A user, touch actuable switch panel of the capacitive type that includes one or more touch actuable capacitive switches, each switch including at least two capacitive plate elements formed on a dielectric panel. Conductive paths formed on the dielectric panel interconnect the capacitive plate elements to a source for applying signals to the capacitive plate elements forming said capacitive switches and sensing a resulting change in signal level when a selected switch is actuated by the user. Trim tabs formed on the dielectric panel are provided to balance the effect of stray capacitance between the conductive paths and the capacitive plate elements to maintain the level of change of signal at a determined value upon the actuation of each of said one or more capacitive switches.

Capacitive switching panel

Abstract: An improved selection panel having a plurality of touch-actuated capacitive switches thereon Each capacitive switch in the panel includes a transparent glass substrate having transparent conductive coatings on opposite sides thereof to form a capacitor A display support is positioned behind and adjacent to the plurality of capacitive switches, and provides a separate display card support for each capacitive switch A removable display card is positioned in each separate support in a manner such that each of the display cards may be changed periodically

Anomalous low-frequency grain-boundary capacitance in silicon

Abstract: The admittance of silicon bicrystals has been measured as a function of temperature, frequency, and dc voltage. In some cases the low‐frequency capacitance is anomalously large. The ac response of a simple double depletion layer structure is calculated. The anomalous capacitive currents are due to an out‐of‐phase modulation of the barrier height caused by charge injected into grain‐boundary traps.

Capacitive sensor control system

Abstract: An electronic control system for controlling the operation of electromotive apparatus utilizes a capacitive sensor for sensing human touch and producing a command signal whose magnitude corresponds to the contact area of the contact. The sensor command signal is applied to an oscillator which produces a series of output width pulses having a frequency corresponding with the magnitude of the sensor command signal. A discriminator detects the trailing edge of the oscillator pulses and produces a series of fixed width pulses and an integrator produces a D.C. voltage signal corresponding to the discriminator output, which voltage signal corresponds to the area in proximity to and thereby stimulated by the human body. A comparator is employed to produce a pulse-width modulated rectangular pulse output whose duty cycle corresponds to the integrator D.C. voltage by comparing the integrator D.C. voltage with a reference triangular waveform. The comparator output is applied via power circuit to drive the electromotive apparatus which may typically comprise one or more D.C. electric motors.

Adaptive video processor

Abstract: In a pattern recognition system the video output signal is a signal representative of either black or white. The shading effect of the video camera is minimized by using a high pass filter to accentuate the high frequency components of the signal by partially differentiating the substantially square wave input video signal and feeding forward a sample of the undifferentiated signal thereby retaining some low frequency components of the video signal and thereby minimizing the shading effect of the video camera without increasing detected noise components. Positive and negative-going zero crossings with respect to ground are detected through a capacitive coupled comparator circuit. In the absence of zero crossings the discharge circuit and charge circuit of the capacitor is interrupted thereby maintaining the value of the voltage on the capacitor with respect to ground. Changing the charge and discharge rate of the capacitor reduces the probability that noise on the signal will cause a false zero crossing.

Control system for a capacitive level sensor

Abstract: A capacitive system for sensing the level of material includes a conductive member electrically connected to ground potential, a probe including a sensing element arranged to establish a capacitance between the sensing element and conductive member which is determined by the level of the material and a shielding element interposed between the conductive member and the sensing element to form an electrically neutral zone therebetween to thereby reduce the effect of a conductive buildup of the material on the probe on the capacitance between the conductive member and the sensing element, and a first circuit electrically connected to the sensing and shielding elements for applying generally the same electrical potential to both the sensing and shielding elements, the first circuit having an output which varies in response to a change in the capacitance between the conductive member and the sensing element. A device for measuring an electrical characteristic of the shielding element which is related to the conductivity of the buildup of material on the probe is electrically connected to a second circuit which, through a feedback loop connected to the first circuit, automatically adjusts the sensitivity of the first circuit in response to changes in the electrical characteristic to compensate for a highly conductive buildup of material on the probe.

Apparatus for capacitive filling-level measuring, particularly in a motor vehicle tank

Abstract: An apparatus for measuring the level of fluid in a container by the use of measuring electrodes forming a measuring condenser, and compensation electrodes forming a compensation condenser by which the effect of various dielectric constants of the medium upon the measuring result can be compensated in an evaluation circuit, wherein the measuring electrodes and compensation electrodes are arranged on an oblong common line in such a manner that the compensation electrodes are located near at least one suction channel for the medium and the measuring electrodes are near the medium to be measured.

High capacitance multilayer bus bar and method of manufacture thereof

Abstract: A high capacitance bus bar is presented having at least two separated conductive plates (12, 14) between which a plurality of capacitive ceramic dielectric chips (20) are positioned and adhered. The outer surfaces of the dielectric chips are metalized (22) and have a roughened or coarse finish to provide contact between the dielectric chips (20) and the conductive plates (12, 14), thereby permitting use of nonconductive adhesive (18) to bond the parts of the assembly together.

Method of making a capacitive force transducer

Abstract: A capacitive force transducer, particularly suited for use as a microphone or as a phonograph needle pick-up cartridge, comprises a diaphragm electrode insulatively held to a lip portion of a recess in a second electrode, thereby forming a capacitive detector. The lip structure of the second electrode structure has a capacitive face region diverging from a virtual pivot region at the lip where the diaphragm is pivotably affixed to the recessed electrode. In this manner, the quiescent capacitance is defined predominantly by the capacitance near the lip, which is relatively small and defined and the change in capacitance for a given deflection of the diaphragm is relatively large, thereby improving the sensitivity of the transducer. In the case of a phonographic pick-up cartridge, the pick-up needle is coupled to the diaphragm so that vibrations induced in the needle produce corresponding vibrations of the diaphragm. A batch method of fabricating the transducers comprises recessing a semiconductive wafer through a major face to define a plurality of capacitive regions around the margins of the recesses. The diaphragm is conveniently formed by a layer deposited over an insulative layer deposited on the non recessed face of the wafer. The wafer is diced to provide a batch of the transducers.

Capacitive switching circuit for energizing remote controlled device

Abstract: The casing (12A) of a hand-held instrument (12) provides a contact surface for a capacitive switching circuit for energizing a controlled device (63). The switching circuit and device are remote from the contact area. The switching circuit includes an input circuit (80) incorporating the body capacitance (C B ) and a variable capacitor (81) which is adjusted to balance the circuit in the presence of only stray capacitance (C E ) without body capacitance so that the switching circuit remains unactuated. The addition of body capacitance will actuate the switching circuit. In the illustrated embodiment, the input circuit (80) is energized by a periodic signal. An output signal is coupled from the switching circuit to the controlled device through a delay off circuit (88) which has a delay time longer than the period of the periodic signal so that if contact with the instrument is lost momentarily, there is no interruption in the controlled function. This is particularly advantageous in the case of a medical device or dental handpiece where light from a high intensity source is coupled back to the instrument for illuminating the work area.

Current sensing of capacitive keyboard arrays

Abstract: Current sensing circuits especially adapted for use with either capacitive touch plate or mechanical switch keys. The circuits include a transistor whose base is connected to a constant voltage source and whose emitter-collector circuit is connected between the touch plate or switch keys and an input to a comparator. A second transistor and a capacitor are interconnected with the first transistor to provide transient surge protection. The circuits distinguish between differing values of current and activate the comparator which produces a signal indicative of the existing condition.

Filter circuit utilizing charge transfer device

Abstract: A filter circuit of the type utilizing a charge-transfer device, such as a bucket brigade device, comprises a clocking signal drive circuit for supplying a clocking signal; a clock signal generator at whose output a clocking control signal is provided; a transistor whose base is connected to the output of the clock signal generator; a plurality of successive capacitive storage stages for sequentially holding a charge level representing a time-sampled input signal, each of the capacitive storage stages having a clocking electrode for receiving the clocking signal so that the charge level is transferred from one to another of the capacitive storage stages in succession, and at least one of the capacitive storage stages being formed of first and second parallel-connected capacitive circuit portions, and the first and second capacitive circuit portions having respective clocking electrodes coupled to the clock signal generator and to the emitter of the transistor, respectively; and a current feedback circuit, such as a current mirror circuit, for detecting the current flowing through the collector of the transistor and applying a corresponding current to a capacitive storage stage in advance of that stage which is coupled to the emitter of the transistor.

Analog-to-digital converter using half range technique

Abstract: In a successive-approximation charge-redistribution analog-to-digital converter which includes a binary weighted capacitive ladder network, an unknown analog input voltage is sampled only on the largest capacitor representing half the capacitance. The conversion phase proceeds utilizing all the capacitance and only half the reference voltage. This not only reduces circuit complexity, but also reduces problems associated with disruption of the charge stored on the capacitor.

Capacitance-level/density monitor for fluidized-bed combustor

Abstract: A multiple segment three-terminal type capacitance probe with segment selection, capacitance detection and compensation circuitry and read-out control for level/density measurements in a fluidized-bed vessel is provided. The probe is driven at a high excitation frequency of up to 50 kHz to sense quadrature (capacitive) current related to probe/vessel capacitance while being relatively insensitive to the resistance current component. Compensation circuitry is provided for generating a negative current of equal magnitude to cancel out only the resistive component current. Clock-operated control circuitry separately selects the probe segments in a predetermined order for detecting and storing this capacitance measurement. The selected segment acts as a guarded electrode and is connected to the read-out circuitry while all unselected segments are connected to the probe body, which together form the probe guard electrode. The selected probe segment capacitance component signal is directed to a corresponding segment channel sample and hold circuit dedicated to that segment to store the signal derived from that segment. This provides parallel outputs for display, computer input, etc., for the detected capacitance values. The rate of segment sampling may be varied to either monitor the dynamic density profile of the bed (high sampling rate) or monitor average bed characteristics (slower sampling rate).

Liquid gaging system null balance circuitry

Abstract: Circuitry for nulling a signal from a capacitive sensor apparatus with a signal from a reference. The invention includes capacitive sensor apparatus for providing a liquid measurement signal. Also included is reference apparatus for selectively providing a series of reference signals having predetermined amplitudes, the reference apparatus having terminal apparatus for receiving rebalance approximation sequence control signals for selectively controlling the signal amplitudes. The invention further includes null detecting apparatus for detecting the presence of a null, the null detecting apparatus being connected to the capacitive sensor apparatus and the reference apparatus.

High precision 3He‐vapor‐pressure gauge for use to 0.3 K

Abstract: The design and performance of a compact, high precision, capacitive, vapor‐pressure gauge is described. The gauge was constructed using a thin electrodeposited copper diaphragm.

Device for capacitive level measurement

Abstract: A device for measuring the fill level of a liquid medium in a container byeasuring the capacitance between electrodes contained in the medium is disclosed. A pair of electrodes in which one of the electrode is divided over its height into two partial surfaces (F1, F2) which are insulated from one another. Each surface forms a partial capacitor (C1, C2) with the other electrode. The divided electrode is characterized in that at least one of the surfaces (F1) or (F2) has a width which increases or decreases over the height of the electrode. By the appropriate combination of the partial capacitances, the level of the medium can be determined as well as a separate determination of the fluid's susceptibility (K).

Apparatus for video disc stylus electrode reconditioning

Abstract: The invention describes a method and apparatus for reconditioning a video disc signal pickup stylus electrode to prevent electrode-disc electrical shorts. An AC or DC potential is repetitively applied during a predetermined period between the stylus electrode and the disc to produce electrical breakdown at the electrode-disc interface and vaporize a portion of the electrode material. In the capacitive type video disc system, the capacitance sensing pickup circuitry is repetitively tuned to couple excessive amounts of rf potential to the stylus electrode.

Laminated capacitive element

Abstract: PURPOSE:To increase stored electric charge in a capacitive element of a MOSRAM cell and make the element smaller by a method wherein three or more conductive layers are formed on a thick selectively oxidized film with insulation layers in between and every other conductive layers are connected together. CONSTITUTION:In the case of, for instance, a n-channel 1 transistor type RAM, three phosphorus doped Si layers 5, 7, 12 are formed and piled with insulation films 6, 11 in between. The layer 5 and the layer 12 are connected together and compose a capacitive element with the layer 7. One electrode, for instance, the layer 7 (or the layer 5), of the capacitive element is connected to a n diffused layer 2 to be used as a charge storing electrode and another electrode, for instance, the layer 5 (or the layer 7), is used as a grounding electrode. With above configuration, if the occupied area is the same as the conventional cell, the charging capacity can be increased and the large read out signal can be obtained, so that the malfunction can be avoided. If the capacity is the same as the conventional cell, the dimensions of the said cell can be decreased.

Location of Partial Discharges in Power Transformers by Computation and Measurement of Capacitively Transmitted Voltage Pulses

Abstract: The voltage distribution in a power transformer after a partial discharge has occurred is calculated. The results are compared with voltages, measured at the terminals of the transformer. A partial discharge prediction curve, based on the calculated capacitive distribution is constructed, by which the location of partial discharges is improved. The location method is based on peak values or capacitive pulses measured at the terminals. Calculation of the complete winding resonances after a partial discharge is found not to be accurate enough for internal corona location purposes.

Multisegment liquid crystal indication system

Abstract: A circuit is described here for liquid crystal indication systems made up of segments which, using the capacitive performance of the indication system, automatically reveals errors that arise in the segments or due to short-circuits between segments. The invention is adapted for use especially in scales that are to be guaranteed against functional errors.

Seal acting simultaneously as pressure monitoring sensor - consists of multilayer annular or coaxial electrodes and of dielectric

Abstract: A seal which acts simultaneously as a pressure sensor and consists of a single component of simple construction. The signal produced may be used directly as an active signal without requiring the use of expensive auxiliary measurement techniques such as high frequency methods as are used in capacitive accelerometers. A dielectric arranged between two electrode layers (13) is subjected to the measurement pressure. The signal occurring between two outer electrodes (12) when a load is applied is fed to an amplifier (15). The seal can be made as a multilayer annular seal or as an 0-ring. In the latter case, the electrode layers and the dielectric are coaxial. The seal can be used for sealing tubes, and containers operating with a certain defined internal pressure which the seal monitors.

Capacitive blood pressure transducer.

Abstract: A capacitive transducer was developed to measure blood pressure using a catheter interfaced to the body. The transducer was made of fused quartz in order to achieve a low temperature coefficient and it consists of a circular body and a 1.25 mm thick sensing diaphragm that mates concentrically with the body. The body of the transducer has a 10 micron deep circular cavity, plasma etched into it. One of the electrodes of the sensing capacitor is vacuum deposited in the etched cavity and the other, which is an oversized electrode, is similarly deposited on the underside of the diaphragm. To obtain a stable reference capacitor, a ring electrode is also deposited in the cavity that forms a capacitor with the oversized electrode. The diaphragm and body are brazed together using a tin-gold alloy. A typical transducer has a full scale of 300 mm of Hg with an overpressure capacity of 3000 mm; a TC sensitivity of 0.015% of FS/degrees C; a thermal zero drift of 0.01% of FS/degrees C; linearity and hysteresis of 0.5% of FS; a volume displacement of 0.02 mm3/100 mm Hg. The pressure module is 29.3 mm in diameter and 7.6 mm high.

Liquid gaging system sensor calibration

Abstract: The present invention is part of a liquid gaging system and comprises an apparatus for measuring and storing a value related to an unwetted capacitance of a capacitive sensor, the stored value being available for use in liquid measurements. Included is a capacitive sensor for mounting in a tank, the sensor having an unwetted capacitance variable in dependence on manufacturing tolerances. The sensor capacitance is also related to stray capacitance in the system. The invention further includes apparatus for measuring the sensor unwetted capacitance including the sensor capacitance contributed by the stray capacitance in the system. The apparatus for measuring is connected to the sensor. The invention also comprises apparatus for storing a value related to the sensor unwetted capacitance measured by the apparatus for measuring, the apparatus for storing being connected to the apparatus for measuring.

Capacitive rotational position detector

Abstract: A capacitive rotational position detecting apparatus includes a stationary disk plate and a rotatable disk plate in opposite relation. The stationary plate has a first and a second electrode on one surface, each of which is electrically connected through apertures by a metal film formed on the other surface of the stationary plate to reduce a distribution capacitance formed between metal films of the stationary and rotatable plates.