Showing papers on "Capacitive sensing published in 1978"

Single-electrode capacitance touchpad sensor systems

Abstract: Each of an array of capacitive touchpad sensors has a single touchpad electrode fabricated upon a substrate and accessible to user personnel, with series coupling and shunt capacitance being provided respectively between a driving generator and the touchpad electrode, and the touchpad electrode and an array ground. Each capacitive touchpad sensor operates with a sense amplifier to provide a high density sensor array requiring relatively low driving voltage amplitudes and may be utilized with driven shields and a normalization network to provide reliable capacitance sensing with reduced sensitivity to contamination of the surface of the sensor array.

Quantitative measurement with high time resolution of internal waveforms on MOS RAMs using a modified scanning electron microscope

Abstract: The growing packing density of integrated circuits calls, to an increasing extent, for the testing of the functioning of the individual circuits of ICs. If a mechanical prober is used for this purpose, the resulting capacitive loading of the circuit is liable to alter its performance. It is shown in the present work that the electron beam represents an ideal nonloading and nondestructive probe which can be finely focused and positioned on measuring points within the circuit under test. A modified scanning electron microscope allows the recording of waveforms within a circuit with a voltage resolution of the order of 10-100 mV and a time resolution of less than 1 ns. The efficiency of the technique was demonstrated by measuring the internally derived clock pulses and the voltage distributions of a digit-line of a 4096-bit MOS RAM and comparing the results with computer simulations.

Capacitive measuring system with automatic calibration

Abstract: In a device for continuously monitoring the characteristics of a moving filament, such as the denier of an extended synthetic yarn, by passing the filament through a capacitive sensor to develop an electrical signal representing an absolute measurement of the filament with reference to a prescribed datum, the problem of measurement signal drift arising from contamination of the capacitive sensor is obviated by developing compensating signals to be combined with the filament measurement signal. The compensating signals are digitally formed and stored, thereby eliminating drift in the compensating signals themselves. The compensating signals are developed in an auto-calibration circuit, including an auto-zero circuit and an auto-gain circuit, which receives the measurement signal from the capacitive sensor. While the sensor is vacant, the auto-zero circuit digitally counts clock pulses to generate a digital output, converts the digital output into an analog signal varying with the digital count, detects a prescribed comparison between the analog signal and the input measurement signal, and stops the clock pulse count at a zero compensating value when the comparison is detected. Then, the auto-gain circuit applies an unbalanced drive to the sensor, digitally counts clock pulses to generate a digital output, and varies the measurement signal gain with the digital output. The circuit detects a prescribed comparison between the gain-adjusted measurement signal and a standardized output signal, and stops the clock pulse count at a gain compensating value when the prescribed comparison is detected.

Force responsive transducer

Abstract: A differential capacitive force responsive transducer provides a substantially linear relationship between transducer output and input variations. A pressure or load to be measured is applied to one surface of a deflectable diaphragm, the opposite surface of which includes at least a pair of electrodes at different positions, such that when the diaphragm flexes there is a differential deflection of the electrodes. A substantially rigid electrode-bearing plate is secured to the electrode-bearing face of the diaphragm by a spacer or spacers in an intermediate flexure region of the diaphragm, to define separate capacitive elements with the diaphragm electrodes. The plate thus moves with the diaphragm, maintaining a fixed spacing at the spacer elements, but with the spacings between the elements varying in opposite senses. With this construction, the transducer can be of low cost, small size, precision manufacture, and use readily deposited thick or thin film electrodes. Moreover the circuits may automatically be adjusted to provide selected nominal zero and range values, so that the transducer can be utilized interchangeably with other transducers in mass production systems. Furthermore, the differential capacitance values obtained from a single transducer can directly provide digital values to a processor, by oppositely varying two variable frequency oscillators, and using the difference frequency to generate pulse counts during successive time intervals.

Capacitive measuring apparatus

Abstract: Digital circuitry for use primarly in measuring the volume of gasoline in an automobile fuel tank. A measurement capacitor is mounted in the fuel tank to have its capacitance vary with the level of gasoline in the tank and forms part of a multivibrator circuit the repetition rate of which is consequently varied in an inverse manner with the capacitance of the measurement capacitor. Pulses generated in the multivibrator are fed to a counter coupled to a resetting circuit which is triggered by an output of this counter when a predetermined number of the said pulses has been counted so that a train of resetting signals are generated separated by intervals the length of which is a measure of the capacitance of the measurement capacitor. Further pulse generating means of fixed repetition rate is gated by the resetting signals and the resultant batches of pulses supplied to a digital display device which displays a reading representative of the number of pulses in each of the said batches, so that the display number is dependent on the capacitance of the measurement capacitor and hence on the level of gasoline in the tank. The capacitor is so shaped and arranged that the capacitance thereof is determined by the fuel level is representative of the volume of fuel in the tank.

Continuous action capacitive moisture measuring apparatus

Abstract: Capacitive moisture measuring apparatus for continuously measuring the moisture content of granular material, such as grain, includes a series circuit including a measuring capacitor whose capacitance varies as a function of moisture content of granular material in which it is immersed during operation and a resistor coupled to the measuring capacitor, and an oscillator for generating a voltage signal of stable frequency and amplitude which is applied to the circuit. An operational amplifier is serially coupled to a diode to constitute an ideal diode, the latter being coupled across the measuring capacitor.

Device for the capacitive level height measurement of liquids or solids

Abstract: A device for the capacitive level height measurment of liquids in motor vehicle tanks, with a measuring sensor with at least two electrodes which are arranged axially parallel to each other and a carrier, and an evaluation circuit containing an oscillator, with the measuring sensor and an indicator instrument being connected to the evaluation circuit. One electrode is made of an electrically conducting layer which is disposed on the elongated insulating material plate and the other electrode is formed in the shape of a U-shaped elongated metal carrier; on the legs of the carrier there is fastened the insulating material plate contacting another conducting layer in the insulating material plate, and the evaluation circuit is constructed in microelectronic technology, is electrically connected to the conducting layers, and is fastened on that part of the measuring sensor which projects from the liquid or solid, respectively.

Diaphragm formation and pressure sensitivity in batch-fabricated silicon pressure sensors

Abstract: The formation of thin silicon diaphragms for batch-fabricated pressure sensors is examined. Several anisotropic silicon etchants are compared with respect to their etch rates and the surface finishes produced. Concentrated potassium hydroxide and ethylene diamine-pyrocatechol are found to be most compatible with sensor requirements. Both V-groove and boron etch-stop techniques are capable of controlling diaphragm thickness to within one micron or better, the latter removing wafer taper as a major source of variability. The effects of several process-induced diaphragm irregularities on the pressure sensitivities of piezoresistive and capacitive structures are examined using a finite-difference computer program. Diaphragm thickness is the most important parameter influencing pressure sensitivity in these structures, with resistor-diaphragm alignment and plate separation important secondary parameters in piezoresistive and capacitive devices, respectively.

High capacitance bus bar

Abstract: A high capacitance bus bar including at least two separated conductive plates between which a plurality of capacitive ceramic dielectric chips are positioned and adhered. Opposite faces of the chips are coated with a thin, integral and continuous film of conductive material and the coated chips are adhered to the conductive plates with a conductive adhesive.

Capacitive liquid level sensor

Abstract: A capacitive liquid level sensor for sensing the height of liquid in a liquid storage tank at a plurality of locations. The liquid level sensor includes a cylindrical housing which extends along a line perpendicular to a predetermined reference level which is approximately parallel to the expected level of liquid in the storage tank. Several capacitors are included within the housing, each employing an air/liquid dielectric, whereby the capacitance values of the capacitors are individually variable due to any variations in the liquid height at each location. Several alternative cross-sectional structures are shown whereby the cylindrical housings are employed as a common plate to the several capacitors located within each housing.

Solid state tunable capacitor

Abstract: A semiconductor tunable capacitor is described. This tunable capacitor employs a plurality of metal-insulator-semiconductor (MIS) capacitive segments and each element has a first and a second value of capacitance. The solid state capacitor employs a plurality of tuning terminals and a single capacitor terminal. Tuning signals are applied to each of the tuning terminals for switching that capacitive segment into its high or low capacitive state. The capacitor terminal is capacitively connected to each capacitive segment and is employed for summing the individual values of capacitance into a total value of capacitance. An MNOS capacitor is shown as the preferred embodiment.

Apparatus and method for measuring capacitive energy

Abstract: A system for determining whether or not an amount of energy in excess of apecified minimum amount of energy is stored in a capacitor of unknown capacitance includes a capacitive reference device for storing an amount of energy which is known to be no less than the specified minimum. The system further includes a capacitive calibration device selectively coupled to the capacitive reference device and to the unknown capacitor for providing a first voltage when coupled to the capacitive reference device, and for providing a second voltage when coupled to the unknown capacitor. A comparator device which is calibrated by the first voltage receives the second voltage and provides an indication signal when the unknown capacitor has stored an amount of energy which exceeds the reference amount of energy.

A quasi-totally shielded, low-capacitance glass-microelectrode with suitable amplifiers for high-frequency intracellular potential and impedance measurements.

Abstract: The fabrication of a new glass microelectrode for high-speed recording is reported. It consists of a Ling-Gerard microelectrode which is slit into a “spacer” capillary with the tip slightly protruding. Except for the ultimate tip (of ∼30 μm length) the entire assembly is coated with silver and insulated. After proper insertion into the cell the electrode provides a shield, which extends from the surface of the cell membrane up to the input of the amplifier. This electrode has two advantages: 1. it eliminates all capacitive pickup of bath potentials which is of paramount importance in impedance measurements and 2. if used in conjunction with negative capacitance amplifiers, it allows more faithful high-frequency recordings, than was possible with the conventional techniques, because the capacitance neutralization can be properly set even though the non-ideal transmission properties of the electrode tips are not known. Test experiments using a rapid amplifier circuit of own design show that the electrode assembly allows error-free phaseshift measurements of up to 30 kHz to be obtained with electrodes of 20 MΩ or risetimes (10–90%) of squarewave pulses of 10 to 12 μs. The corresponding time constants of 5 to 6 μs indicate that the time resolution of the new technique is superior to the apparent time resolution of the conventional techniques.

Stroboscopic beacons fed from a capacitive source

Abstract: The present invention relates to a system for energizing flash-tubes of beacons by means of the capacitive energy extracted from an insulated section of the overhead wire of power transmission lines. The supply system comprises a circuit for transforming the AC capacitive energy from the overhead wire into DC voltage, the latter feeding at least one flash-tube and a regulation circuit shunted across the transforming circuit for controlling a DC voltage threshold value supplying the tubes. Such regulation is achieved by detecting the predetermined DC voltage threshold value across the lamp terminals and by switching to the earth any capacitive energy extracted from the overhead wire exceeding that threshold value. Moreover, a circuit delivers a pulse at predetermined time intervals to control the firing of each flash-tube when the latter is subjected to a DC voltage corresponding to the predetermined threshold value and regulated by shunt switching.

Capacitive gauging system utilizing a low internal capacitance, high impedance amplifier means

Abstract: A capacitive gauging apparatus in which a single central processing unit is connected to a plurality of gauging heads each gauging head having a further plurality of gauging probes. The system then multiplexes the probes and heads to enable the central processing unit to receive serially the output from each of the heads and produce an analog or digital signal which indicates distance between each of the probes and the work piece. A central microprocessor transforms these signals into an output for visual display or calculates the difference between these signals and an ideal master work piece. Further, a highly temperature stable, low capacitance, high impedance amplifier is used in conjunction with each of the probes so that the output signal from each of the probes is stable and accurate over a wide range of conditions.

Method and apparatus for the determination of signal pickup qualities of a stylus of a capacitive disc video player

Abstract: Stylus suitable for use in a capacitive disc record playback apparatus comprises a wedge-shaped support material and an electrode formed on a flat longitudinal surface of the support material. Signal pickup qualities of such stylus can be determined by supporting such stylus on a silicon dioxide-silicon wafer where the capacitance formed between the electrode bottom and the wafer can be changed at a cyclical rate by energizing the wafer with a low frequency signal. A tuned resonator circuit coupled to the electrode detects those capacitance variations and additional undesired capacitance variations contributed by fringe capacitance between the whole of the electrode and the wafer. Where the wafer is of an n-type silicon material, the contribution of the fringe capacitance to the detected capacitance variations is reduced by growing a large quantity of positive charge in the silicon dioxide layer of the wafer.

Resonant linear frequency modulator

Abstract: A circuit which modulates an r.f. carrier to produce an FM signal having a substantially linear frequency relation to an applied modulating voltage over a selected deviation bandwidth. An r.f. oscillator having an output matching circuit supplies the carrier to a modulator. The impedance of the oscillator is adjusted by the matching circuit to present a desired reactive mismatch to the modulator over the bandwidth. The modulator includes a pair of voltage dependent reactive impedance elements, oppositely biased and separated by a quarter wavelength line which acts as an impedance inverter. A modulating voltage applied to both of the elements causes a reactive imbalance therebetween, affecting either a net inductive or capacitive change in the load impedance presented to the oscillator. The center frequency of the circuit reacts in a substantially linear manner to the modulating voltage over the deviation bandwidth.

Method and device for measuring the variations of the cross-sectional dimensions of a moving thread-like structure

Abstract: Novel method and device for measuring instantaneous changes of the thickness or diameter of travelling yarns and similar structures. The devices comprise sensing means provided with a pair of members contacting the yarn, with one of the members spring loaded toward the other. The distance or the variation of the distance between the contacting members when the yarn travels is detected by a transducer, e.g. of the capacitive type, and translated into electrical sensing signals.

Capacitive force load cell for weighing scale

Abstract: A weight scale includes a capacitive force load cell for linearly transducing force into electrical capacity. A C-shaped spring supports two capacitor plates adjacent the distal ends of the arms with the surfaces of the plates being normally parallel. Weight is transmitted from the platform of the scale to a pin which acts to separate the arms against the spring force. The plates are shaped, preferably triangularly, so that the change in capacitance as they separate is linear. The load cell is connected in circuit with an oscillator so that the change in capacitance is directly proportional to change in frequency as a measure of the weight of the load on the scale's platform.

D.C. to D.C. Converter utilizing resonant inductor to neutralize capacitive losses

Abstract: A d-c to d-c converter utilizing a resonant inductor to neutralize capacitive losses is disclosed. In most high voltage d-c power supplies, a step-up transformer is employed as the conversion element from the low voltage source to the high voltage output. Such transformers exhibit capacitive losses resulting from intra-and inter-winding capacitances. When utilizing a large step-up transformer wherein the turns ratio n=N p /N s is much less than 1, the capacitive losses result in a sharp decrease in the load to source voltage ratio thereby reducing the power available to the load. The present invention compensates for these losses by providing a resonant inductor which forms, at the operating frequency of the transformer, a resonant circuit with the equivalent Thevenin capacitive reactance as viewed from the primary side of the transformer resulting from these losses.

Capacitive thread stopping motion

Abstract: A method and device for detecting the presence of a running thread takes advantage of the inherent physical irregularities of the thread to generate an alternating current signal as the thread passes through a capacitive element. The variations in capacitance resulting from the running thread are detected and amplified as an alternating current electrical signal, which disappears instantly with thread stoppage or breakage.

Capacitive Power Tap-Off from Transmission Lines Using Ground Wires: Calculation of the Equivalent Circuit Parameters

Abstract: The capacitive coupling between the ground wire and the phase conductors of a transmission line can be used to supply small loads in remote regions along the line. A theoretical analysis is presented in this paper to determine the parameters defining an equivalent circuit for the case of single as well as two insulated ground wires. Results are presented to show variations of the equivalent circuit parameters as functions of geometrical parameters of lines in the range of 300- 750 kV. Finally, some results of measurements on Hydro-Quebec's lines are presented and compared with theoretical calculations.

A capacitive instrument for the measurement of a large range of magnetostriction at low temperatures and high magnetic fields

Abstract: An instrument has been constructed to measure a large range of magnetostriction between room temperature and 4K in a superconductive split-coil magnet. A combination of high sensitivity and large range is achieved by using a variable-gap capacitor to measure the magnetostriction. Consideration has been given to the best way of relating the magnetostriction to the fundamental magnetoelastic coupling coefficients, and to the information that can be obtained by measurements in various crystal planes. In the light of this, the instrument has been designed to make the measurements in the plane containing the magnetic field. The use of the instrument is illustrated by preliminary results for the first basal plane magnetostriction coefficient for terbium.

Compensation circuit for trailing edge distortion of pulse-width modulated signal

Abstract: When a pulse-width series modulator is connected to the cathode of an RF radio transmitter tube for the purpose of series modulation, filtration of the PWM switching signal is required to eliminate the switching signal from the output modulating signal. Stray capacitive effects in this filtration generate undesirable distortion in the trailing edge of the signal appearing in the last stage of the PWM thereby producing non-linearity in the modulation of the RF output tube. The present disclosure illustrates circuitry for complimentarily modifying the leading edge of the pulses so as to maintain a linear relationship in the time integral of voltage in the output signal. This modification is accomplished through a plurality of capacitive units each having different time constants for charging and discharging.

Automatic coin checking system - uses capacitive and/or inductive sensors generating signals compared with reference values relating to size, denomination and material

Abstract: Automatic checking of coins of various denominations is made by a collector or sensors, and the basis of size, form and material. The coins are fed past a number of electronic, capacitive and/or inductive sensors. The sensors respond to cause changes in phase, amplitude or frequency of signals. The signals are compared with predetermined reference values. The generated signals are checked in a logic circuit to indicate either acceptance or reflection. The coins to be checked are also passed through the light beams directed at opto-electronic sensors which are arranged to give accurate measurements of size and surface condition.

Multiple, independently actuatable fire suppression devices each having individual actuating power source

Abstract: A fire protection system of the type having a plurality of electrically activatable, parallel coupled fire suppressant units each having a bridge wire type initiating element, produces significantly improved reliability by providing each of the units with an electrically active portion for continuously monitoring the electrical continuity of the associated bridge wire and a discrete capacitive portion for storing an independent, electrical supply of the actuating power therefor, thereby eliminating the dependency of the units on a single, central electrical power supply source while also allowing continuity monitoring of each bridge wire, even though the latter are continuously coupled in parallel relationship with each other. A control circuit associated with each of the suppressant units limits the flow of electrical current in one direction through both the corresponding bridge wire and capacitive portion to a low level in order to effect charging of the latter, but allows a high level current to flow in the opposite direction through the bridge wire upon discharge of the capacitive portion to produce activation of the associated unit. A centrally located, detecting device is operative to sense either the loss of a supervisory current which is allowed to flow through the control lines coupling the units into parallel relationship, due to an open circuit condition in such control lines, or a trouble signal produced by the active portion of one of the releasing units indicating an open circuit condition in the bridge wire associated with an inoperable unit.

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.

Film thickness detection system

Abstract: A film flaw detection system has capacitive sensing members for sensing capacitance changes in correspondence with irregular film variations. The sensing members take two forms. One form senses variation in film thickness by using the film as a dielectric between two plates of the capacitor. Changes in film thickness result in changes in the dielectric and hence in the capacitance. The other form consists of feelers which ride along the surface of the film and which move transversely to the film movement in response to flaws in the film. Each feeler forms a plate of a capacitance, and movement of the feeler changes the distance between this plate and an associated fixed plate which results in a capacitance change. The detecting circuit comprises a phase detection system for measuring phase changes in a high frequency signal. These phase changes correspond to capacitance changes caused by flaws in the film and sensed by either of the two forms of sensing means.

Electrically alterable memory cell

Abstract: An electrically alterable memory cell is described which has a capacitive imbalance for causing the memory cell to assume either of its two stable states, and which uses a capacitor as a non-volatile storage element for retaining the information stored in the memory cell during power down operation. The capacitor has an alterable capacitance-voltage curve which is employed to identify the information in the bistable multivibrator just prior to loss of power. When power is returned, the capacitor causes the bistable multivibrator to assume that stable state in which it was operating at the time power was lost.

Capacitive keyboard for data processing equipments

Abstract: In a capacitive keyboard using a polarized dielectric commonly called an electret, the keys are organized according to a matrix by rows and columns, the signals generated on the column conductors being of opposite polarity with respect to those generated on the row conductors. The movable armatures of the variable capacitors of the keys also act as bridging elements to allow the crossing of the row and column conductors and as snap elements.