Showing papers on "Capacitive sensing published in 1981"

Capacitive pressure transducer with isolated sensing diaphragm

Abstract: A capacitance transducer has a central chamber with a conductive diaphragm disposed therein to separate the chamber into at least two portions, at least one portion having an electrical conductor disposed thereon to form in combination with the diaphragm at least one variable sensor capacitor, and wherein at least one portion of the chamber is coupled by a passageway to communicate with an isolator having an isolator chamber and an isolator diaphragm which in combination with the conductive diaphragm enclose a substantially incompressible fluid such that when pressure is applied to an exposed side of the isolation diaphragm, the conductive diaphragm is urged to deflect and thus change the sensor capacitance. Configuration of the isolators, spaced from the sensor capacitors, and other factors disclosed herein, eliminate unwanted mechanical and thermal stresses thereby improving the capacitive sensors' response to pressure.

High accuracy differential pressure capacitive transducer

Abstract: A capacitive pressure transducer is disclosed in which a sensing diaphragm bearing an electrode is mounted to flex in response to applied fluid pressure relative to a reference member having an opposed electrode. A thin film or layer of dielectric material such as glass covers the reference member electrode and has formed therein a concavity matching the flexed curvature of the sensing diaphragm at its limit position. The dielectric layer has a high compressive strength and substantially enhances linearity by providing a substantially higher capacitance than the equivalent fluid-filled space. The transducer is retained within a transducer assembly under compressive preload, the assembly further including thermal strain relief means. Also disclosed are methods of making the transducer, which methods include thick film screen deposition techniques for forming concavities having preselected contours in the dielectric layer.

Capacitance pressure sensor

Abstract: A capacitive pressure sensor has a diaphragm means a portion of which is conductive which forms a first capacitor electrode The sensor also has a reference disc means a portion of which is conductive which forms a second capacitive electrode The diaphragm means and the reference disc means are supported in a spaced, over-lying relationship to each other by a peripheral spacer means Responsive to pressure, the diaphragm means deflects relative to the reference disc means thus changing the capacitive spacing of the diaphragm means and the reference disc means The diaphragm means, reference disc means and spacer means are formed from substantially the same material The spacer means is disposed between the diaphragm means and the reference disc means adjacent their outer edges and the diaphragm means, reference disc means and spacer means are then fused together

Linear capacitive pressure transducer system

Abstract: A capacitive pressure transducer system includes a reference capacitor and a capacitor which varies with pressure; and circuitry which involves alternately charging one of the capacitors to a reference voltage level, and then switching to charge the other capacitor; and circuitry for producing an output voltage which varies as the duty cycles of the two capacitors shift; and the output is therefore substantially proportional to the pressure changes. Feedback is provided to incrementally change the capacitor charging and switching timing or duty cycles by changing the charging current or the reference voltage at which switching occurs, to substantially eliminate deviations from linearity in the voltage versus pressure characteristic.

Multiplexed varistor-controlled liquid crystal display

Abstract: An improved varistor-controlled multiplexed liquid crystal display of the type having columns of front electrodes and rows of rear electrodes connected in series with combinations of varistor elements and electrical capacitances, has a capacitance of increased magnitude formed in parallel with the capacitance of the liquid crystal layer in each of the multiplicity of the display cells, for reducing capacitive crosstalk between an addressed and unaddressed cell elements of the display. The increased capacitance is provided by auxiliary data electrodes positioned below, and spaced by a thin film dielectric layer from, the reflective rear cell row electrodes of the display, and spaced from the varistor member by at least one thick film dielectric layer. A pair of thick film layers may support the row scan electrodes therebetween, or the scan electrodes may be formed between a single layer and the varistor surface.

Capacitive transducer for accurate displacement control

Abstract: The underlying theory, design, and operation are presented for an interdigitated capacitive displacement transducer supported on an air-bearing stage. This device provides a purely electrical means of displacement measurement and offers the possibility of being closely matched to the substrate against thermal perturbations. Tests on a prototype system show the basic capacitive transducer to have a sensitivity of 2.6 mV/μm and a position uncertainty of 4 nm set by thermal noise.

Pressure measuring system

Abstract: A digital pressure measuring system with nonlinear resolution is disclosed. The system includes a capacitive pressure transducer with a pressure variable sensing capacitor and a substantially invariable reference capacitor. The capacitors of the transducer are excited by out-of-phase signals and their outputs combined at a summing junction. The output of the summing junction controls the incrementation of a counter whose output is converted to a nonlinear negative feedback signal. A closed loop is formed by applying the feedback signal to the summing junction through a feedback capacitor. The counter is incremented in a direction to null the loop such that its output is representative of the measured pressure.

Angle-position transducer

Abstract: Angle-position is determined by relative angular rotation between a capacitive track and a capacitive pick-up probe. The capacitive track is disposed along the region of angular interest. The pick-up probe is oriented broadside to the capacitive track and closely spaced therefrom thus establishing a measurable capacity thereacross. As the capacitive track moves angularly relatively to the pick-up probe, a geometric asymmetry is produced therebetween causing the capacity that exists thereacross to change unambiguously and in a manner that exhibits analog correspondence with relative angular rotation.

Power line communication system using the neutral and ground conductors of a residential branch circuit

Abstract: At a point on a residential branch circuit downstream from the service entry load center where the termination of the neutral conductor thereof is solidly clamped to ground and the ground conductor is terminated in electrical connection in common with the neutral conductor termination, a transformer is linked with one of the neutral and ground conductors. Downstream from the transformer, a capacitive coupler is connected across the branch circuit neutral and ground conductors. A transmitter of high frequency voltage signals is connected with either the transformer or capacitive coupler and a signal receiver is connected with the other thereof, such as to establish a communications lin between the transmitter and receiver using the branch circuit neutral and ground conductors.

Low cost capacitive accelerometer

Abstract: A capacitive transducer is disclosed which provides a measurement of acceleration. The transducer includes a semiconductor element having a mass ring suspended from an elastic diaphragm which is retained by a support. The mass ring is formed to have opposed parallel planar surfaces, each of which are spaced adjacent a metal layer deposited on a glass substrate to form a capacitive circuit. The metal layers are configured in the shape as the flat surface of the mass ring and are coupled to provide an electrical output. The semiconductor element forms a common capacitor plate disposed between the two capacitor plates formed by the metal layers. Movement of the mass ring in response to acceleration causes a change in the spacing between the mass ring and metal layers thereby changing the capacitance and providing a measure of acceleration.

Combination of analog to digital converter and error correction circuit

Abstract: Error correction circuitry for an analog to digital converter is disclosed which provides for the correction of charge in a charge redistribution converter architecture. This conversion technique as implemented requires that a binary weighted capacitor array be present where the capacitors are accurately binarily weighted in decreasing value. The charge correction circuitry allows for the correction of any deviations of binary weighted capacitance value by adding or subtracting charge from the capacitor array. This is accomplished by the use of a resistor array connected to a capacitor that is equal in capacitance to the smallest capacitor in the capacitor array. The converter includes a microcomputer which determines the charge error for each of the individual capacitors together with the total charge error for the capacitive array coupling with the comparitor. During digitation of the analog input the microcomputer provides correction for each stage of the digitation operation in order to more accurately digitize the analog input.

Capacitance measurement probe

Abstract: An improved probe is provided for surface texture capacitive gauging. One embodiment of the probe comprises a sensor assembly with a thin, flexible dielectric having a conductive coating to provide an active sensor area and integral lead-in which is durable, flexible, and constant. In another embodiment, a bladder-like flexible dielectric contains a conductive media and the bladder is appropriately confined to define the active sensor area. The probe includes a mask to further define the active sensor area and to sense proper seating of the probe on the work surface to be gauged.

Hybrid circuit including capacitive charge-transfer means

Abstract: A hybrid circuit includes a capacitive charge-transfer arrangement, comprising parallel capacitors and series switches,for coupling signals in one or both directions between a four-wire line and a two-wire line. The switches are constituted by VMOS power FETs. In one embodiment, the charge-transfer arrangement is provided in the receive path to give the desired properties of electrical isolation and unbalanced to balanced conversion of receive path signals. Signals from the two-wire line are coupled to a transmit path of the four-wire line via an attenuating and high-pass filtering arrangement and a differential amplifier, thereby providing good common mode rejection of high voltage signals, especially at power line frequencies. In another embodiment, the charge-transfer arrangement is provided, commonly for the receive and transmit paths, for coupling the two-wire line to the remainder of the hybrid circuit.

Linearized electronic capacitive pressure transducer

Abstract: A capacitive pressure transducer 10 with an analog output voltage which varies linearly as a function of sensed pressure is provided. A capacitive pressure sensor C x provides a pressure variable capacitance that determines the frequency of a sensor oscillator 11. The oscillator frequency is combined with a reference frequency by a pair of D-type flip-flops 18 and 19 to provide a resultant signal having a duty cycle related to the sensed pressure. The resultant signal is integrated to provide a first analog signal as an input to a controllable gain amplifier 24 which receives gain control information from a non-linear gain control circuit 40 that receives an analog control signal as an input. The analog control signal varies as a function of sensed pressure in an opposite manner to said first analog signal. Said non-linear circuit provides for non-linearly varying the gain of amplifier 24 as a function of sensed pressure. Preferably the non-linear circuit 40 includes temperature compensating diodes 47. The output of the amplifier is a temperature compensated output signal which has a substantial linear variation as a function of sensed pressure.

Capacitance to voltage conversion apparatus

Abstract: A C-V(capacitance-to-voltage) conversion apparatus usable e.g. for detecting physical parameters such as pressure, distance and angle. The apparatus comprises a capacitive sensor, a C-PW(capacitance-to-pulse width) conversion circuit, and a PW-V(pulse width-to-voltage) conversion circuit. The capacitive sensor converts a physical parameter to a capacitance, but has a non-linear conversion characteristic. The C-PW conversion circuit converts the capacitance to a pulse signal whose mean value is proportional to the capacitance, by controlling a charging-discharging cycle of the capacitive sensor and a reference capacitor. The PW-V conversion circuit converts the pulse signal to a d.c. voltage and at the same time compensates for the non-linearity of the capacitive sensor's conversion characteristic so that the d.c. voltage is proportional to the physical parameter.

Electric surgical scalpel with HF current source - has active and return electrodes, generator and capacitive impedance monitor

Abstract: The appts. has an active electrode (A) which is a scalpel and a return electrode in the form of two plates (P1,P2) placed between the patient (P) and the operating table (B). The plates (P1,P2) are covered in an insulating dielectric film (D1,D2) and are connected by two leads (11,12) to a mixer (T) which is a transformer. A high frequency generator (G) is connected by a lead (10) to the active electrode and by another lead (13) to the transformer. A capacitive impedance measuring device (M) is also connected to the transformer by two further leads (14,15). The capacitive impedance measurement represents the state of the high frequency return signal and is therefore an indication of a good contact between the plates and the patient's skin. The appts. eliminates the risk of electrocution and burning.

Graphical data entry apparatus

Abstract: Improvements in graphic tablets employing resistance planes are disclosed including one or more of the following: a tablet usable both by depression and by capacitive probe, reference connections to side midpoints, automatic gain control for capacitive readings, selective high voltage tablet energization for increased resolution reading of a detected region, forming high resistance edges by bending flaps so that resistance flux deposition is oblique to the flaps, separate overlying substrates with edge connecting resistances, and cursor light and/or infrared positioning beam generators.

LSI Chip carrier with buried repairable capacitor with low inductance leads

Abstract: A carrier for LSI chips includes a built-in capacitor structure in the carrier. The capacitor is located beneath the chip with the plates of the capacitor parallel to the chip mounting surface or at right angles to the chip mounting surface. The capacitor is formed by assembling an array of capacitive segments together to form the first one of the plates of a capacitor with the other plate spanning a plurality of the segments of the first plate. Each of the segments of the first plate includes a set of conductive via lines which extend up to a severable link on the chip mounting surface. The severable via is cut by means of a laser beam or the like when the capacitor must be repaired by deleting a defective segment of the capacitor. Preferably, the structure includes a pair of parallel conductive charge redistribution planes above and below the capacitor plates with connections to the respective plates providing a low inductance structure achieved by providing a current distribution which results in cancellation of magnetic flux. The lower redistribution plane is preferably connected directly to the lower capacitor plate. The upper redistribution plane is preferably connected to the segments of the first capacitor plate by means of the vias which extend first to the chip mounting surface and then down to the redistribution plane which has connections to the chip mounting pads.

Capacitive measurement system

Abstract: A system for independently determining the capacitance and resistance of a capacitive sensor, in which the sensor and a reference capacitor are sequentially energized from two alternating voltage sources of different frequencies, and average sensor and reference capacitor current valves at the two frequencies are measured and supplied to a computer which periodically calculates the sensor capacitance and resistance.

Transmission line model of substrate effects on capacitive mesh couplers

Abstract: To use a transmission line model to calculate the optical properties of a thin metal mesh on a dielectric substrate, account must be taken not only of the different propagation conditions within the substrate and of Fabry-Perot resonances due to reflections at the second surface, but also of the effect of the dielectric on the capacitive component of the equivalent reactance of the mesh. Only when this effect is accounted for, which can be done using a simple formula based on Babinet’s principle, is good agreement obtained with experimental measurements.

Demand defrost sensor

Abstract: A demand defrost system in which a high resistive epoxy resin hermetically seals a capacitive sensor plate and a noise immune phase detector detects a phase shift caused by the build up of frost.

Liquid quantity measuring apparatus

Abstract: An apparatus for measuring the quantity of a liquid such as a fuel in a tank, which comprises liquid level measuring electrodes, comparing electrodes dipped always in the liquid to detect the capacitance inherent to the liquid, an LC oscillator for converting each capacitive value measured by the electrodes into a corresponding frequency signal, reference electrodes constituting a level feeder together with the oscillator to compensate for capacitive variation of the latter, and a microcomputer for calculating a liquid quantity in the tank based on the frequency signals and for displaying the calculated quantity.

Physical Principles of the Displacement Cardiograph Including a New Device Sensitive to Variations in Torso Resistivity

Abstract: The displacement cardiograph (DCG) is a noncontacting device which senses displacements associated with the cardiac cycle through a high-frequency electromagnetic field interaction between a sensing coil and the thorax. The coil is located in the tuning circuit of an oscillator, and perturbations in the oscillation frequency, i.e., frequency quency modulation (FM), resulting from tissue displacements are monitored. The device, originally described by Vas, is similar to earlier devices reported by others. Separation of capacitive and inductive effects with a capacitive shield indicates that the principal interaction is through capacitance, rather than inductance. Experimental and theoretical results suggest that the DCG is relatively insensitive to internal movements as compared to displacements of the precordium. A new technique for monitoring cardiac activity is reported which utilizes the amplitude modulation (AM) of the oscillator. With capacitive shielding, we have successfully recorded waveforms which result from the inductively coupled, reflected resistance in the coil. This AM device does respond significantly to internal movements.

Energy saving circuit arrangement for a piezoelectric positioning element

Abstract: A circuit arrangement for a piezoelectric positioning element is formed of a series connection of a capacitive element, an inductance, and first switch to be controlled, said series circuit being connected across at least one piezoelectric body of the positioning element. The capacitive element, which may be another piezoelectric body of the same positioning element but which is operated in reverse phase, has at least approximately the same capacitance value as a capacitance of the first piezo-electrical body. The inductance is dimensioned sufficiently large in order to magnetically intermediately store substantially an entire energy increment to be transferred between the positioning element and the capacitive element. The first switch is connected to permit termination of a charge transfer. A series circuit is formed of an electrical energy source for charging and recharging and a second switch, said series circuit being connected parallel to the positioning element or the capacitive element. A controllable short-circuit switch is connected parallel to the capacitive element or parallel to the positioning element. In this way, the activation energy of the piezoelectric body is recovered on de-activation, for re-use on the next cycle.

Thyratron Marx high voltage generator

Abstract: Thyratrons are used as the switching devices for connecting capacitive storage devices in series after they have been charged in parallel. In the preferred embodiment, the capacitive device is placed before the thyratron in each stage, so that the output pulse is of the same polarity. The inductors connected to the cathodes have secondary windings to form transformers, for triggering the thyratrons of the following stages.

Capacitance type displacement conversion device

Abstract: A capacitance type displacement conversion device is provided in which a physical displacement resulted from a change of a physical value such as pressure or tension is converted into an electrical signal. The device is comprised of a capacitance sensor and an improved circuitry whereby conversion characteristics are linear and free from erroneous measurements caused by distributed capacitances and other circuit elements related thereto. The type of the sensor may be either a single capacitance or a differential capacitance type.

Bus bar assembly with discrete capacitor elements

Abstract: Constructions of miniature bus bar assemblies which incorporate discrete capacitive elements having a high dielectric constant are presented herein. The capacitive elements are preferably metallized ceramic wafers which are bonded between a pair of bus bar conductors. In one embodiment bonding by strips of solder. In other embodiments, printed circuit elements are employed, both for electrical connection between the capacitor elements and the bus bars and to define the bus bars.

Arrangement for determining the level in a container

Abstract: An arrangement for determining the level in a container includes a capacitive probe disposed in the container, a measuring transducer arranged in the vicinity of the container, and a remote evaluation apparatus. The measuring transducer produces a signal corresponding to the capacitance between the probe and the container. This signal, which is indicative of the level in the container, is transmitted from the transducer to the evaluation apparatus via a two-wire line, which also transmits the current supply DC voltage from the evaluation apparatus to the transducer. The transducer includes a switch for periodically switching from the probe capacitance to a test capacitance. The evaluation apparatus comprises a time control circuit which periodically varies or interrupts the DC voltage on the two-wire line, and the transducer includes a control circuit which responds to the voltage changes to actuate the switch. This permits control of the test operation by the evaluation apparatus over the same two-wire line which also carries the measuring signal and the current supply voltage.

Capacitive touch switch for electrical domestic appliances

Abstract: A capacitive touch switch, preferably for hobs of glass and glass ceramics, exhibits capacitor plates on both sides of a switch panel consisting of dielectric plate-like material. On the side of the switch panel facing away from the operating side, two capacitor panels to be brought into contact with the evaluating circuit are applied; on the operating side, another capacitor plate is arranged as coupling element which causes a capacitive detuning by the approach of an operating element.