Showing papers on "Capacitive sensing published in 1982"

A batch-fabricated silicon capacitive pressure transducer with low temperature sensitivity

Abstract: A batch-fabricated solid-state capacitive pressure transducer has been developed using silicon integrated-circuit technology The fabricated devices exhibit a dynamic range of 350 mmHg and a pressure sensitivity of about 1100 ppm/mmHg The temperature coefficient of zero-pressure offset is about +50 ppm/°C (less than 005 mmHg/°C) and the temperature coefficient of pressure sensitivity over the -20 to +50°C temperature span is about +275 ppm/°C (less than 004 mmHg/°C) when the device is used with an open or vacuum-sealed reference cavity These temperature coefficients are substantially lower than those of previously reported monolithic devices and are low enough that expensive temperature trims can be eliminated for many applications

A high-sensitivity integrated-circuit capacitive pressure transducer

Abstract: A high-sensitivity capacitive pressure transducer with active processing circuit on the chip has been demonstrated and evaluated. The transducer configuration has been optimized by computer-aided design to achieve highest sensitivity for a given maximum dimension. The measured sensitivity of the devices is in the range of 50-150 µV/ V . mmHg, which is approximately one order of magnitude higher than the sensitivity of the piezoresistive pressure transducer of comparable size. Theoretical analysis also shows that a sensitivity on the order of 1000 µV/V . mmHg is also possible using the capacitive approach if the dimension of the device can be enlarged and the full scale pressure range is lowered. Other characteristics of the devices have been investigated and are presented.

A Temperature Compensated Ultrasonic Sensor Operating in Air for Distance and Proximity Measurements

Abstract: An ultrasonic sensor operating in air was developed to measure distance (up to 100 cm) or to operate as a proximity sensor in a presettable distance range. The error in the measured distance is about ±1 mm while the accuracy is maintained within ±1 percent of the reading in the whole temperature range from -20°C to +110°C, being the temperature dependence of the sound velocity electronically compensated. As a proximity sensor it can overcome most of the drawbacks and limitations of inductive, capacitive, optical, and Hall-effect commercial proximity sensors.

SENSIM: A simulation program for solid-state pressure sensors

Abstract: A simulation program is described which is capable of calculating the output response of silicon piezoresistive or capacitive pressure sensors as a function of both pressure and temperature. A thermoelastic plane-stress formulation is used in calculating the stress and deflection of the transducer diaphragm. Both analytical and finite-difference solution methods are available, depending on the sensor structure. Diaphragm thickness taper, oxide and package stress, and rim effects are simulated. For capacitive structures, the program accurately predicts the diaphragm deflection and pressure sensitivity as a function of pressure and temperature. Stepped diaphragm structures are shown to be capable of improving pressure sensitivity by as much as 50 percent. The package-induced thermal drift for electrostatically sealed glass-silicon devices is typically less than 0.05 mmHg/°C.

Wafer alignment station

Abstract: An automatic wafer alignment station is disclosed for aligning a wafer having flats about its centroid with the flats oriented in a preselected spatial direction. The wafer is held by a vacuum chuck which is operatively connected to a motor driven carriage for controlled movement about an X axis, to a θ actuator carried by the carriage for controlled rotation about the axis of the chuck, and to a Z actuator carried by the carriage for controlled motion about a Z axis. An X capacitive sensor and a Z capacitive sensor are positioned near the wafer. An X processing and Z compensating circuit is responsive to the X and the Z capacitive sensor output signals and provides an electrical signal that has values which exclusively represent the position of the edge of the wafer along the X axis only over a predetermined angular range. Circuit means including an A/D converter and a microprocessor respond to the electrical signal and produce a plurality of corrective signals to the X, Y, and θ actuators for aligning the wafer about its centroid and for orienting the flats of the wafer in a preselected spatial orientation.

Capacitive touch switch arrangement

Abstract: A capacitive attenuator type touch switch cell arrangement employs a touch responsive pad or electrode and a receiver electrode of comparable surface area on opposing surfaces of a dielectric substrate for capacitive coupling therebetween, which capacitive coupling is alterable by the human touching of or proximate to the touch pad. A scan signal is coupled from signal generating circuitry to the touch responsive pad by a separate transmitting capacitor. Signal detection circuitry senses the signal coupled to the receiver electrode to detect attenuation of the coupled signal signifying the touching of the touch pad. The use of a separate capacitor to provide the transmitting capacitance reduces the touch pad area requirement, thereby permitting closer spacing of touch switch cells for greater switch density on a control panel.

Capacitively coupled machine tool safety system

Abstract: A safety system for a machine tool is characterized by a capacitively coupled electric field generator (transmitter) and a capacitive receptor antenna. An electrical signal is induced in the capacitive receptor antenna by the action of the electric field. The magnitude of the induced signal is monotonically related to the distance between the electric field generator and the capacitive receptor antenna. When the magnitude of the electrical signal exceeds a predetermined threshold, a machine tool safety indicator is developed.

Multi-capacitor fluid level sensor

Abstract: A tubular shaped fluid level or fluid volume sensor for mounting in a fluid storage vessel for sensing the level or volume of the fluid within the vessel which comprises: a first pair of like electrically conductive capacitor elements each formed to present two electrically connected capacitive plate areas, the capacitor elements being spaced from one another and shaped and arranged to generally define together the outer periphery of the tubular sensor; and a second pair of like electrically conductive capacitor elements each formed to present two electrically connected capacitive plate areas, the second pair of capacitor elements being positioned within and spaced from the first pair of capacitor elements and being spaced from one another and shaped and arranged to generally define together the inner periphery of the tubular sensor. Electrical insulating material located between the capacitor elements defining the other periphery of the sensor and the capaictor elements defining the inner periphery of the sensor for mounting the pairs of capacitor elements in fixed spaced relationship from one another and for positioning the elements so that each capacitive plate area thereof defines with a capacitive plate area of the next adjacent capacitor element a dielectric space therebetween so that the mounted capacitor elements together form four like dielectric spaces. Material of known constant dielectric value fills two of the dielectric spaces thereby forming with their respective space defining capacitive plate areas two capacitors of known fixed and substantially like capacitive value. The remaining two dielectric spaces are open to receive varying levels of fluid thereby forming with their respective capacitive plate areas, and the fluid within the spaces, two capacitors of variable capacitive value.

Development and test atT=4.2K of a capacitive resonant transducer for cryogenic gravitational-wave antennas

Abstract: The characteristics of a new capacitive resonant transducer developed and tested on a small (M=11.2 kg) cryogenic gravitational-wave antenna at the liquid helium temperature are presented. The resonator frequency can be tuned within 0.1 Hz of the antenna frequency. The system has a mechanical merit factorQ≃5·105 and a ratio between the electrical energy in the transducer and the energy in the antenna β=3·10−3 atT=4.2 K. With these parameters, the transducer allows one to reach an effective noise temperatureT eff≃60 mK using a cooled FET preamplifier, and, if coupled to a r.f.-SQUID, allows one to reachT eff≃10 mK for the 5000 kg cryogenic gravitational-wave antenna of the Roma group at CERN (Geneva).

High-speed capacitive weighing method and apparatus

Abstract: The mass of an object dropped through a capacitive sensing transducer having a pair of spaced plates is determined independently of the spatial orientation of the object as it passes through the transducer, and independently of whether the object is entirely within the transducer at any instant The transducer generates an output proportional to the instantaneous change in capacitance between the spaced plates caused by the sample passing therethrough When the sample is a powder, the transducer output is integrated, and a correction factor is subtracted from the integral for correcting for temperature drift and for accumulation of minute particles of the powder on the plates The spaced plates can be formed in a substantially 90° twist; or, the transducer may be in the form of a plurality of pairs of spaced plates, each pair being oriented at a different angle with respect to the path of a sample through the transducer

Electrostatic bonded, silicon capacitive pressure transducer

Abstract: Electrostatic Bonded, Silicon Capacitive Pressure Transducer Abstract A plurality of silicon pressure transducers 10 are formed by processing two conductive silicon wafers 11, 14, one of the wafers including a layer of borosilicate glass 32, a thin portion of which 17 is on the surface 12 of one of the plates of a capac-itor formed by field-assisted bonding together of the two wafers, the thin layer of borosilicate glass avoiding arcing during the field-assisted bonding process.

A study of capacitance and resistance characteristics of an Al2O3 humidity sensor

Abstract: In this article the fabrication of a humidity sensor employing an Au-poroue Al2O3–Al structure is described. The behaviour of the sensor in both the capacitive and the resistive mode as a function of relative humidity is studied. The effect of frequency on these characteristics is investigated. It is observed that the change in capacitance is small below 30% RH. Above this humidity the capacitance increases rapidly. The dependence of resistance of the sensor on humidity is the reverse of the capacitance dependence. An electrical equivalent circuit model of the sensor based on the structure of the device and the sensing mechanism is developed. The results are interpreted in terms of the model.

Touch sensitive liquid crystal switch

Abstract: A touch sensitive switch with a liquid crystal cell and a circuit for measuring capacitive changes when the cell is deformed by touch The cell has a layer of a liquid crystal material between slides bearing electrodes Capacitive changes are detected for example by a comparator or by a bridge circuit which includes one or more cells Touching one cell unbalances the bridge The area of cell that is touched may be coincident with or separate from a display area For some types of cells extra sensitivity is achieved by maintaining a voltage across the cell between a critical and saturation value

Capacitive system for monitoring the dielectric properties of flowing fluid streams

Abstract: A method and instrument for comparing the dielectric properties of a flowing stream of fluid with the dielectric properties of a reference fluid in which a uniquely configured multi-capacitor sensor, formed of a first pair of capacitors having like dielectric spaces within which the reference fluid is maintained under non-flow conditions as the dielectric material and a second pair of capacitors having like dielectric spaces within which a sample portion of the flowing stream of fluid is continuously passed as the dielectric material, comprises all of the capacitance elements of a Wheatstone bridge circuit in a single cellular unit in which the capacitive elements are all subjected to the same sample fluid, temperature and pressure environment and which is not sensitive to stray capacitances. Each pair of capacitors forms opposing sides of the Wheatstone bridge circuit. A source of alternating current of constant voltage and set frequency is applied across a first set of bridge terminals at opposite corners of the bridge and a current detection circuit is connected across a second set of bridge terminals independent of the first set of terminals and at opposite corners of the bridge. Detection and measurement of the current value of the bridge is translated into a value of dielectric constant for the fluid sample in direct linear relationship with the current value.

Analog integrated circuit pressure sensor

Abstract: An integrated array of pressure transducers capable of producing an analog output voltage representative of the applied pressure is proposed. The individual transducing elements (16) are defined by a three-layer structure including a thin layer of piezoelectric material (10) disposed between a reference potential plate (12) and a plurality of electrodes (15) contained in a silicon substrate (14). A force applied to a localized portion of the reference plate will cause a deflection of the piezoelectric material towards the electrodes on the substrate, inducing a capacitive charge on the electrode in the localized area. This capacitance is stores at a node A associated with the transducing element, and may be interrogated by a sensing circuit (18) located in the silicon substrate. Since the induced charge is directly proportional to the applied force, a measurement of the output voltage from node A will yield a direct indication of the localized force applied to the sensor.

Pulse power supply for generating extremely short pulse high voltages

Abstract: A pulse power supply for generating extremely short pulse high voltages comprizing an ac charging high voltage, rectifier, pulse forming unit as a capacitive energy storage element, and an externally-controlled high speed synchronous switching unit, such as a mechanical synchronous spark switch of rotating type. The capacitive energy storage element, i.e. condenser is charged up by the ac charging high voltage source from zero voltage to its peak voltage through the rectifier without the use of current limiting resistance during its half cycle or desired polarity, i.e. negative one. Then, this charged potential of the capacitive element is kept, with the blocking action of the rectifier, until a desired instant of the next half cycle when the said switching unit is triggered from outside, e.g. by rotation of the rotor disc carrying the spark electrode elements, and the very short pulse high voltages are produced at this instant at the output of this pulse power supply. This charging scheme by an ac charging voltage altering from zero to its peak reduces greatly the power loss in the charging process of the capacitive element. The switching of the charged capacitive element to the load in the next half cycle when the rectifier is blocking avoid the short-circuit current to flow from the arc charging voltage source to the load, making the production of the pulse voltage stable and use of a large protective resistance unecessary.

Distributed Equivalent-Circuit Models for Circular Dispersive Electrodes

Abstract: Analytically solvable distributed equivalent-circuit models have been developed for circular electrosurgical dispersive electrodes which are either resistively or capacitively coupled to the body. Calculations based on these models show that for either electrode type it is possible to define a characteristic length, the magnitude of which governs the current distribution under the electrode. The well-known perimetrical burn problem occurs when the current transfer length is much smaller than the electrode radius: a problem which may arise with either capacitive or resistive electrodes. Design guidelines are given for the optimization of simple circular dispersive electrodes, and suggestions for further improvements are discussed.

Capacitive transducer with continuous sinusoidal output

Abstract: A capacitive encoder utilizing a stationary plate having transmitter elements and receiver elements located on the surface thereof and a moving plate having two conductive areas separated by a sine wave shaped gap. The receiver elements on the stationary plate overlie the gap and provide outputs which vary as a function of the position of the gap with respect to the output elements. Signals from the output elements are differentially amplified and demodulated in order to provide precise sine and cosine outputs, the accuracy of which are unaffected by variations in the input signal.

Displacement transducers based on reactive sensors in transformer ratio bridge circuits

Abstract: Displacement transducers which employ differential reactive sensors in transformer ratio bridge circuits are considered. Archetype models of inductive and capacitive sensors are developed and the performance of bridge circuits containing them is analysed. Aspects of performance which are examined include linearity, discrimination, excitation forces, power dissipation and the effects of stray impedances. Practical design problems relating to long-term stability and environmental influences are also discussed. It is concluded that capacitive transducers are most suitable in applications requiring high levels of accuracy, stability and discrimination and low power dissipation and excitation forces. In situations where these requirements are not so stringent both inductive and capacitive transducers are suitable.

Analysis and Composition of a New Microwave Filter Configuration with Inhomogeneous Dielectric Medium

Abstract: A theoretical study has been undertaken to solve inter-resonator coupling problems, and to design a new structure of microwave bandpass filter. This filter is composed of quarter-wavelength resonators arranged in a housing with the same ends short-circuited. This arrangement of resonators has never been utilized to compose bandpass filters because of the small inter-resonator coupling. The coupling coefficient of TEM resonant lines has been derived theoretically and expressed with capacitive parameters of the coupled lines. The accurate values of capacitances of the lines were obtained by the numerical analysis of the TEM field. By a simple method to make the medium inhomogeneous through removing the dielectric partially, a simplified structure of filter has first been realized based on the theory. Through numerical analysis by the finite difference method, this structure is also shown to have higher unloaded Q of resonator than conventional dielectric-filled coaxial filters to minimize the volume of filters.

Integrated circuit device having internal dampening for a plurality of power supplies

Abstract: The present invention is directed to an integrated circuit device comprising a lead frame having a ceramic capacitor mounted thereon and forming the support for a silicon chip bearing a multiplicity of circuits, including at least two power supply circuits namely a main power supply circuit and a secondary circuit. The capacitor is shunted across the terminals of the main power supply and the main power terminals of said IC chip. A conductive layer disposed atop the ceramic uppermost layer of the capacitor defines with the uppermost electrode of the capacitor, a second capacitive load of lesser value than the main capacitor, the said second capacitive load being shunted across the terminals of the secondary power supply and a secondary set of power terminals of said chip. The provision of internal capacitive shunting for the plurality of power supplies for the chip enables lead length to the capacitors to be maintained at a minimum thereby minimizing inductive reactance and thus enabling small capacitances to effectively dampen noise and pulses in the circuit.

Measuring system for measuring the variation of the capacitive impedance of a bearing installed in a housing

Abstract: The improvement is characterized by a metal measuring ring (6) enclosing the bearing circumference (2) which surface parts facing resp. the bearing outerring (7) and housing (3) of the arrangement (1 -4), being provided with an insulating layer (10). The layerpart (11) contacting the bearing outerring (7) is thinner than the remaining part (12) of said layer (10). Due to this feature the capacity between housing (3) and shaft (4) is substantially reduced which improves measuring.

Capacitive pressure transducer

Abstract: A capacitive type pressure sensing transducer comprised of a housing having a pressure sensitive element which interfaces with an applied pressure force to be sensed and measured and which moves in response to force changes to vary the volume of the housing in direct relation to such changes. The housing is filled with a fluid which is in fluid flow communication with a multi-capacitor fluid level sensor. The sensor is formed of a first pair of plate type capacitors of like fixed capacitive value and a second pair of plate type capacitors having like open dielectric spaces for receiving varying levels of fluid from the transducer housing in response to changes in the volume of the housing. Thus, a change in pressure applied to the pressure sensitive element of the transducer produces a corresponding change in the fluid level within the dielectric spaces of the second pair of capacitors of the sensor and a corresponding change in the capacitance value of such capacitors. The capacitors of the sensor are electrically connected into a classic alternating current Wheatstone bridge circuit and the current flow value of the circuit is measured as a direct, linearly-related value of the pressure force applied to the transducer.

Solid state transmission gate

Abstract: A solid state transmission gate having a low "on" resistance utilizes capacitive devices for partially compensating parasitic capacitance effects, a P-channel device and an N-channel device with a switched tub or substrate to compensate for parasitic capacitance effects When the transmission gate is conducting, the tub or substrate of the N-channel device is switched from one of its current electrodes to a reference potential such as ground Before the transmission gate is opened electrically, a settling time is provided to allow charge which is coupled from parasitic capacitance to settle

Transient Development of Nanosecond Gas Discharges

Abstract: The development of cufrent in gaseous spark gaps has been investigated in the context of a transmission-line pulse system. A simple model, which utilizes the electron continuity equation, provides a description of the formative period as well as the current buildup during the resistive phase. The E-field in the gap is assumed to be spatially uniform and dependent on time through temporal variations in the applied field. We have employed this simple model in analyzing the dependence of the formative time on the initial parameters of the discharge. At the end of the breakdown formation process, space-charge and secondary ionization effects become important. A two-dimensional time dependent model has been developed to include these effects. Current waveforms obtained from both models have been compared with experimental waveforms. Experimental measurements were performed in a 50-? pulse transmission-line system. Incident voltage waveforms of approximately rectangular shape were applied between large electrodes in a nitrogen filled test gap. Incident voltage and transmitted current waveforms were monitored with capacitive dividers and recorded by a fast transient digitizer.

Push-pull microwave oscillator with fundamental and second harmonic outputs

Abstract: A push-pull microwave oscillator circuit, including two transistors, for producing the second harmonic of a fundamental frequency at a symmetry point of the circuit which is connected to the bases of the transistors through identical arrangements of circuit elements. The circuit includes tuning means coupled to at least one of the transistors, an output and an input. The output, which is utilized to provide to a phase comparison means an output signal at the fundamental of the second harmonic frequency, is coupled to the base of at least one of the transistors by a capacitive impedance. The input, which is utilized to receive a tuning signal produced by the phase comparison means in response to the output signal, is coupled to the tuning means.

Position determination device

Abstract: A position determining device has two perpendicular longitudinal magnetostrictive elements. A grid of a plurality of closed loop conductors has two parallel straight legs which form the grid. A flux producing element inductively coupled to at least one of said grid conductors causes an electrical current in that conductor. In turn that current induces a strain wave in the magnetostrictive element. Near the end of the magnetostrictive element is a sensing means to detect the strain wave comprising a lumped inductive capacitive delay line substantially having a plurality of evenly spaced inductive coils aligned with the magnetostrictive elements. The lumped delay line is defined by the formulas ##EQU1## where w is the overall length of the delay line; L is the total inductance, C is the total capacitance, Z is the terminating impedance, c is capacitance of the capacitance associated with each coil, and n is the number of coils.

Fluid level measuring system

Abstract: A system for measuring the level or volume of a fluid within a fluid storage vessel which comprises: a multi-capacitor fluid level sensor formed of a pair of capacitors of fixed and substantially like capacitive value and a pair of capacitors having like open dielectric spaces for receiving varying levels of the fluid within the vessel. The four capacitors of the sensor are connected together to form the four capacitive sides of a Wheatstone bridge circuit. A source of alternating current of constant voltage and set frequency is applied across the bridge circuit to a first set of bridge terminals at opposite corners of the bridge, each of such terminals located between a fixed capacitor and a variable capacitor of the sensor. A detection circuit is connected across the bridge to a second set of bridge terminals (independent of said first set of terminals) and at opposite corners of the bridge, each of such terminals located between a fixed capacitor and a variable capacitor of the sensor. The current value in the detection circuit is measured and indicates the value as a fluid level or fluid volume measurement in direct linear relationship with the current value. The system may be used for volume measurement with respect to a wide variety of multi-component fluid systems as long as the dielectric constants for the two or more components are different.

A communications system

Abstract: A communications system for a device 10 incorporates a conductor 26 extending along a locus near to the device 10, and a transmitter 52 arranged to transmit signals through the conductor 26. The system also includes a receiver 55 at the device 10, arranged to detect the signals by capacitive means. The signals consist of two or more frequencies which are converted to corresponding voltage levels at the receiver 55. The device 10 may be a carriage driven alongside the conductor 26 by a motor receiving drive current from the conductor by inductive coupling.