Showing papers on "Capacitive sensing published in 1987"

Scaling limits in batch-fabricated silicon pressure sensors

Abstract: The scaling properties of silicon capacitive and piezoresistive pressure sensors are described. An evaluation of the various noise mechanisms and pressure offsets in the scaled devices is presented, including Brownian noise, electrical noise, electrostatic pressure variations and pressure offset due to resistor mismatch. The analysis of diaphragm deflection includes the effects of intrinsic stress and the transition from plate theory to membrane theory. Both ultraminiature and ultrasensitive sensors are considered. Ultraminiature piezoresistive sensors with diaphragms measuring 100 µm in length and resolving 1 mmHg should be possible using present technology as well as ultrasensitive capacitive sensors that resolve 1 µmHg.

Capacitive liquid level sensor for automatic chemical analyzer

Abstract: A capacitive liquid level sensor for an automatic chemical analyzer, wherein a pipetting tube approaches a liquid level of the sample to be analyzed and is electrically connected to one terminal of an electrical bridge network. The electrical bridge network is activated by an A.C. current and produces an A.C. signal which has a phase change produced by a change in capacitance between the pipetting tube and the liquid level as the pipetting tube approaches the liquid level. The A.C. signal is converted into a D.C. signal proportional to the phase difference by means of a phase detector. A liquid level is detected by comparison of the D.C. signal with a preselected reference level.

Capacitive separating circuit

Abstract: In the capacitive isolating section for DC isolation of a coaxial cable, a radio-frequency filter, preferably a low-pass filter, is provided in addition to an isolating capacitor in the outer conductor, by means of which the shielding characteristics of the isolating section are considerably improved. The isolating capacitor in the outer conductor can be a part of the radio-frequency filter. The attenuation characteristics of the isolating section can be improved even further by means of several radio-frequency filters connected in the manner of a cascade.

Digital technique for precise measurement of variable capacitance

Abstract: The present invention comprises a circuit for measuring the capacitive differences of small capacitors. The circuit comprises a reference capacitor and a sensor capacitor. Connected to one of the plates of each capacitor is a switch which connects the capacitors to one of two reference voltages. The other plate of the capacitors are connected to an input terminal of a voltage comparator. The comparator compares the input voltage with a third reference voltage. Differences in voltages detected by the comparator are applied to a feedback loop for generating an offset voltage at the input terminal. The offset voltage applied at the input terminal is proportional to the capacitive difference between the reference capacitor and the sensor capacitor. The feedback loop comprises a successive approximation register for digitizing the offset voltages and a digital to analog converter for converting the digitized voltages into analog voltages which are applied at the input terminal. Digitized offset voltages can be measured at the output of the successive approximation register.

DC touch control switch circuit

Abstract: A switching circuit includes a source of direct current for operating an oscillator which in turn applies a signal to a detector circuit including a touch plate. The detector includes a voltage dividing capacitive system or, in one embodiment, a phase detector circuit. In either embodiments, the output signal from the phase detector circuit or the voltage divider provides a control signal which can be used for actuating a solid-state switch such as a transistor or the like for providing control functions.

Pressure sensor with improved capacitive pressure transducer

Abstract: A pressure sensor comprises an improved capacitive pressure transducer having a first capacitor plate secured to a limited portion of a first surface of a relatively rigid ceramic substrate and having a diaphragm with an electrically conductive surface forming a second capacitor plate, the diaphragm being secured to the ceramic substrate at a location spaced inwardly from the periphery of that first substrate surface for disposing the second capacitor plate in spaced, overlying relation to the first capacitor plate to be movable in response to applied pressure for varying the capacitor formed by the plates. Support means bear against opposite surfaces of the ceramic substrate at the periphery of the substrate for mounting the transducer with the diaphragm thereof substantially free of mounting stresses to be exposed to a pressure force in a pressure zone to be monitored.

Capacitance-to-phase angle conversion for the detection of extremely small capacities

Abstract: Much progress has been made over the last few years in scaling down the dimensions of transducers. In particular, silicon micromachining technology has allowed small integrated sensors to be developed. The advantage of scaling of integrated capacitive transducers is mainly restricted by the limitations imposed by the capacitance change that can be resolved by the readout circuits. This paper describes a suitable technique for the readout of capacitive transducers using an ac-operated charge amplifier. The method is based on the compensation of the nominal transducer capacitance using a voltage which is slightly less than 180° out of phase. This setup makes it possible to convert the capacitance to a phase angle and to detect capacitance changes smaller than 1 fF.

Capacitive measuring assembly for determining forces and pressures

Abstract: A capacitive measuring assembly for determining forces and/or pressures includes at least three plane parallel capacitor surfaces with intercalation of a dielectric therebetween. The capacitor surfaces being movable relative to each other against elastic resetting forces of the dielectric, a main surface being in opposing relation to all remaining surfaces and partly covering them with intercalation of the dielectric therebetween. The main surface being movable both perpendicular and parallel relative to the remaining surfaces so that from the individual capacity values between the main and remaining surfaces, there can be measured or eliminated both the forces that act perpendicularly between the main and remaining surfaces and the forces that act parallel with the capacitor surfaces.

Capacitive feed for plasma reactor

Abstract: A capacitive feed is disclosed for the lower electrode in a parallel plate plasma reactor. One plate of the capacitor comprises the lower electrode or a contact to the lower electrode. The other plate of the capacitor comprises an annular member insulated from the lower electrode, or the contact. There are no RF connections directly to the lower electrode.

Partial discharges in voids in solid dielectrics. An alternative approach

Abstract: Partial discharges in voids are traditionally discussed in terms of an equivalent capacitive network, the abc-model [1,2]. A void is represented by a capacitance, and discharges within the void are simulated as a partial or a complete discharge of this capacitance. This simple approach has been so successful with respect to measurement techniques that there is a tendency to identify the equivalent circuit with the actual dielectric system. This may lead to erroneous conclusions, e.g. about transfer of charges within a void, or to concepts which, although they are meaningful with respect to the equivalent circuit, may have no direct relation to the actual dielectric system.

Electromagnetic flowmeter for conductive and dielectric fluids and its applications in particular in oilfield

Abstract: The invention is a non-intrusive system for measuring the flow rates of insulating or conducting fluids in conduits. It results from the combination of an electromagnetic flowmeter, operating with conducting fluids, and of a triboelectric noise cross-correlation flowmeter, operating with insulating fluids. The system is equipped with a non-intrusive device for measuring fluid conductivity. The electronic signal processing unit uses the conductivity value to decide which of the two sensors is providing a signal effectively representing the fluid flow rate. The electromagnetic flowmeter may use electrodes of small cross-section in contact with the fluid or, more advantageously, it may be of the capacitive type using larger section electrodes isolated from the fluid.

Proximity detector between a metallic mass and an element to which is applied an electric voltage

Abstract: The present invention relates to a proximity detector between a metallic mass and an element subjected to an electric voltage, with an electric circuit feeding a safety device such as the coil controlling a circuit-breaker, the feed switch of a motor controlling the displacement of the mass, an auditory or visual alarm, or an emergency ground. The circuit includes an element which is normally non-conductive but made conductive when there is a potential appearing on the metallic mass to be protected, or on the antenna in which the electric circuit is fed by a DC autonomous power source. The conductibility of the element whose conductibility is modified by the variation of the electrostatic potential is controlled by the potential at an intermediate point between the metalic mass or the antenna and a pole of the DC source, with interposition between the intermediate point and the pole of a resistive or capacitive element.

Antenna coupling circuit for magnetic resonance imaging

Abstract: A coupling circuit for coupling an inductive coil antenna of a magnetic resonance imaging system to receiver circuitry is provided which includes capacitive circuitry, resistive circuitry, and capacitive transformer circuitry. The capacitive circuitry is coupled in parallel with the antenna to provide capacitive reactance to the coupling circuitry. Resisitive circuitry is coupled in parallel with the antenna and with the capacitive circuitry to provide resistance R in the coupling circuit when an AC voltage at the resonant frequency of the coupling circuit is applied. Capacitive transformer circuitry is coupled in series with the antenna for transforming the resistance value R of the resistive circuitry into a transformed resistance value R'. This increases the apparent resistance of the coupling circuit in parallel with the antenna without increasing the actual resistance and power consumption of the coupling circuit.

Static response of miniature capacitive pressure sensors with square or rectangular silicon diaphragm

Abstract: The static response of capacitive pressure sensors with a thin rectangular or square diaphragm is studied, assuming small deflections. Lagrange's equation is solved from the virtual displacement theorem and an approximated polynomial solution. It is shown that response can be expressed under a normalized form dependent only on the value of the diaphragm dimension ratio. For a given silicon surface, square sensors exhibit the highest sensitivity whereas rectangular sensors have a more linear behaviour. Finally, the proposed formulation equally allows easy and rapid determination of the four geometric parameters defining this type of sensor Etude de la reponse en regime statique du capteur, dans l'hypothese des deformations faibles

Capacitor array sensors tactile and proximity sensing and methods of use thereof

Abstract: Multiple capacitor arrays which are employed for a diversity of applications, particularly in the field of robotics. The capacitance sensor array is used for proximity and tactile sensing of properties of an object and comprises a plurality of capacitor plate elements formed in a predetermined array, means for actively connecting each capacitor plate element and the object to one of a plurality of oscillating circuits so that the oscillation frequency of each of the oscillating circuit is a function of the capacitance between each capacitor plate element and the object, and means for generating an output from the sensor which is a function of the tactile properties of the object from the plurality of oscillator circuits.

Self-excited induction generator/force-commutated rectifier system operating as a DC power supply

Abstract: The paper presents a new DC energy generation system based on a 3-phase self-excited induction generator coupled to a force-commutated rectifier. This rectifier is switched in such a way that its input current fundamental component is advanced with respect to the corresponding voltage, producing a capacitive characteristic on its terminals. This characteristic helps the self-excitation and improves the direct output voltage regulation, with respect to load variation, to the range of 1 to 2%, for some firing angle. Also, this capacitive effect greatly increases the output power limit, and allows the system to supply a constant direct output voltage over a reasonably wide range of rotor speed variation. The steady-state performance of the system is analysed based on a simplified mathematical model, which is validated experimentally. A study on the influence of the smoothing reactor size is presented and it is shown that the system can operate properly even without this reactor, if there is no limit for current ripple in the load.

Apparatus having capacitive sensor and metal detector for detecting objects concealed behind surfaces

Abstract: A device for detecting concealed objects behind a surface, the device being intended in use to be held near and passed over the surface. The device detects changes in the dielectric constant of the surface resulting from the presence of concealed objects, and also includes metal detector means. The design precludes interference between the two kinds of sensors.

Capacitive sensor for measuring a displacement

Abstract: A capacitive sensor for measuring a displacement comprises a slide carrying groups of emitting electrodes (1 to 32) disposed facing receiving electrodes (51 and 52) carried by a scale. A periodic configuration of signals is applied to the emitting electrodes by electronic circuits (60 to 65h) which permit a separate switching of each group of electrodes. There is thus obtained a more precise definition of the signals received by the receiving electrodes situated facing the scale and thus a greater precision of the measurement of displacements.

Overfill sensing system

Abstract: An overfill sensing system uses a capacitive sensor (12) on the interior of a tank for sensing the presence of a liquid to cease the filling process. The capacitive sensor (12) includes a sensing capacitor (16) and a reference capacitor (18) on separate arms of a bridge circuit (22). An oscillator (28) supplies an AC signal to the bridge circuit (22) divided by a variable resistor (30 ) to balance the bridge (22). A comparator (24) receives the output on each arm of the bridge (22) to sense a differential therebetween. When a liquid reaches the sensing capacitor (16), the capacitance changes from a predetermined capacitance, thereby changing the differential. A control circuit (14) is responsive to the differential at the output of the comparator (24) for visually indicating the status of the filling process and ceasing the filling process from the filling facility when a liquid has been detected.

Noise due to Brownian motion in ultrasensitive solid-state pressure sensors

Abstract: Noise due to Brownian motion of diaphragm in ultrasensitive solid-state capacitive and piezoresistive pressure sensors operating at sub-millimeters of mercury pressures in a gaseous ambient is considered. The statistical properties and spectral characteristics of the noise are obtained as functions of the diaphragm dimensions, temperature, and applied pressure. The results show that the Brownian equivalent pressure noise is substantially less than has been previously reported and is well below 1µmHg for most practical cases of interest. Thus it is not a limiting factor in setting device performance when compared to circuit noise sources.

Monolithic microwave phase shifting network

Abstract: A phase shifting network with multiple outputs between which a constant phase difference is maintained over a large frequency range. The configuration consists of a four branch all pass network which in turn consists of four similar all pass networks one in each branch. An in phase and an out of phase input signal are applied to this network and four signals in phase quadrature, 0°, 90°, 180°, and 270° may be obtained from the network. The network is designed for operation at frequencies of micro and millimeter wavelengths and may be realized from resistive and capacitive elements fabricated upon a common monolithic substrate. A suitable substrate is gallium arsenide, permitting both passive and active elements to be formed and interconnected by lithographic techniques.

Apparatus and method for determining liquid levels

Abstract: A liquid level sensor system well suited for sensing the level of fuel in aircraft fuel tanks includes a plurality of capacitive sensors which provide an output capacitance that is a function of the fraction of the sensor wetted by the fuel. A plurality of sensors are positioned in the liquid-containing tank with each sensor having a first and at least a second probe-specific liquid-quantity profile corresponding to a first and at least a second attitude of the tank. The capacitance of the sensors are determined as function of the length of the respective sensor wetted by the liquid. A memory is provided with a first and second sets of address locations containing liquid-quantity profile information for the sensors for their respective first and second attitudes. The memory is addressed by determining an address offset as a function of the attitude of the system, the relative location of the profile information for the sensor, and the fraction of the sensor wetted by the liquid.

Multilayer capacitor elements

Abstract: Several constructions of multilayer ceramic capacitor elements are presented which provide a low induction parallel-plate type capacitive structure.

Polyimide capacitive humidity sensing element

Abstract: The present invention relates to a humidity sensing element having a polyimide moisture sensing film. It is of a capacitive structure containing, without the use of adhesives, a polyimide film which is either sandwiched between a corrosion resisting metal substrate and a thin moisture permeable gold layer, or vapor deposited on both sides thereof with a moisture permeable thin gold layer.

Capacitive rotary transmitter for controlling and positioning displaced objects

Abstract: A capacitive linear or rotary transmitter for controlling and positioning displaced objects by measuring the displacement, angle or speed of the displaced object is formed, in one embodiment as a rotary transmitter, by two mutually opposed stators defining a reciprocal spacing, their gap having rotatably arranged in it a rotor which is rotatably coupled to a spindle which is coupled to the displaced object. Capacitive values varying during the rotation of the rotor may be measured in the air gaps produced in each case between one stator and the rotor, and the other stator and the rotor. To attain a superior degree of precision and resolution, coatings are so arranged on the rotor and the stators, as to produce at least two concentric annular areas, of which one area forms the measurement track of a coarse measuring system and the other area forms the measurement track of a precision measuring system. The digitally determined values of the coarse measuring system are so combined with the values of the precision measuring system as to yield an unequivocally defined absolute value for the angle of rotation. This is attained by the fact that the coupling capacitances generated by mutually associated coatings of the rotor and stators follow a course during the rotary displacement of the spindle which is sinusoidal in parts and that by addition of several reciprocally displaced capacitance graphs which extend sinusoidally in parts and are provided with different prefixes, an approximately purely sinusoidal capacitance graph is generated with a cycle depending on the number of measurement tracks.

Capacitive probe for use in a system for remotely measuring the level of fluids

Abstract: A capacitive probe for use in a system for remotely measuring the level of fluids. The probe is continuously charged and discharged. The discharge current from the probe is measured and converted to a corresponding voltage rerepresenting the level of fluild. The voltage is then supplied to an indicating device. One embodiment of the probe includes first and second spaced supports which maintain a plurality of spaced parallel wire electrodes which form two capacitive plates. In a further embodiment of the probe, the wire electrodes are positioned on an integrally formed support.