Showing papers on "Capacitive sensing published in 1985"

Frequency dependence of ion bombardment of grounded surfaces in rf argon glow discharges in a planar system

Abstract: The energy distribution of positive ions incident on a grounded surface in a low‐pressure argon planar rf glow discharge system has been measured as a function of excitation frequency from 70 kHz to 13.56 MHz for both capacitive and direct coupling of the rf power to the excitation electrode. The results are interpreted by taking into consideration both the transit time for the ion to traverse the sheath relative to the period of the rf excitation voltage, and the resistive or capacitive characteristics of the sheaths. The importance of system geometry and of the dc potential of the excitation electrode (as determined by external circuitry) on the maximum energy of ions incident on grounded surfaces is shown.

A polyimide-based capacitive humidity sensor

Abstract: The design of a relative humidity sensor is studied in which the principle of operation is based on the change of dielectric constant of a thin film of polyimide. The design of the sensor is established in such a way that it would be suitable for an integrated-circuit type of fabrication. The studies have shown that the experimental data are described well by the use of the Looyenga equation for dielectric constant behavior coupled with the Dubinin equation to describe the absorption as a function of relative humidity.

Method and apparatus for capacitive keyboard scanning

Abstract: A capacitive keypad (24) is scanned in such a manner that the capacitance value (C) of an individual key in a given row is multiplied by the sum of the relative capacitance values of all the other keys in the same row by means of an amplifier (32) to generate a combined pulse. The combined pulse is then compared by a comparator (28) to a threshold voltage (Vref 3) to verify whether the individual key in question is in the closed or open position. The verification can be made independently of keypad-to-keypad variations in the capacitances of the keys, since the combined pulse value does not depend upon the absolute capacitance value of the keys, but only upon their relative values. Also disclosed is a method for scanning to determine the presence of multiple key closures. This involves comparing the capacitance of an interrogated key to not only the sum of the other capacitors of its row, but also to the sum of the capacitors of the other rows and columns and a comparison of the resulting value to that generated by previous scans to detect change.

Capacitive measuring system for measuring the distance between two relatively movable parts

Abstract: A capacitive measuring system for measuring the distance between two relatively movable parts based on measurement of capacitative charge comprising a measuring sensor which forms one plate of the capacitor whose gap is to be measured. With the position of the sensor face in the fixed part of casing being known, the plate distance of the gap capacitor provides a direct measure of the gap.

High pressure capacitive transducer

Abstract: A high pressure capacitive transducer includes a capacitive pressure transducer having an insulating diaphragm, and a high pressure fitting for housing the transducer. The high pressure fitting includes a flexible metal diaphragm bonded to the fitting, with the metal diaphragm in engagement with the insulating diaphragm. The metal diaphragm may be boned to the fitting around the periphery of the metal diaphragm to block the high pressure fluid from the transducer. The insulating diaphragm may be relatively thick, such as one-twentieth, one-tenth, or one-fifth of an inch thick, for example.

A high-performance silicon tactile imager based on a capacitive cell

Abstract: An 8 × 8-element silicon-based tactile imager fabricated using integrated-circuit process technology is described. The imager consists of an X-Y organized array of capacitive force sensors on 2-mm centers. Each transducer has a zero-pressure capacitance of 1.6 pF, an average sensitivity of 60 mV/g, and a maximum operating force of about 10 g/element. The operating force can be scaled over a wide range without changing the process or lateral array dimensions. The array is read out using a switched-capacitor charge integrator which has been shown capable of a resoiutionof about 1 fF(5 fC), giving a resolution for the imager itself (pad excluded) of more than 8 bit. The readout scheme permits off-chip electronics to be used so that the fabrication sequence requires only five noncritical masks. The array is addressed as a memory, with an access time of less than 20 µsec for 8 pixels. Scaling of the array size to other dimensions is examined and performance limitations are discussed.

A High-Resolution Capacitance-to-Frequency Converter

Abstract: This paper describes an integrated sampled-data sinusoidal oscillator with AGC amplitude stabilization, the frequency of which is proportional to an external low value capacitor (2-20 pF). The circuit, based on a switched-capacitor two-integrator loop, is insensitive to stray capacitances between sensing nodes and ground and features high resolution (16 bits) and excellent linearity (better than 0.1 percent) as well as very low power consumption (less than 0.1 mW). Such a "capacitance-to-frequency converter" is particularly suitable for interfacing variable-capacitance sensors (pressure transducers, accelerometers,... ) in applications requiring high accuracy but where signal bandwidth is limited to a few hundred hertz.

Silicon strip detectors with capacitive charge division

Abstract: Measurements of the behaviour of various high-resolution silicon strip detectors with capacitive charge division have been made in a high-energy particle beam. The results are compared with an electrostatic model which calculates the charges deposited on the strips after the passage of a minimum ionizing particle. Good agreement is found and the model is used to propose a method of improving the charge-division properties of such detectors.

An electrostatic dust precipitator

Abstract: An electrostatic dust precipitator comprises a separation filter (5) having emitter and collector electrodes (4,6), means (1-3) for maintaining a substantially constant d.c. voltage between the electrodes (4,6) during opera­tion of the precipitator, and pulse-generating means (1-3, 7-11) for generating at a given frequency in the order of 30-500 Hz voltage pulses or voltage pulse trains which are superimposed on the d.c. voltage and which are of short duration in relation to the aforesaid frequency. The pulse­generating means (1-3, 7-11) includes capacitive and in­ductive elements (7,8) which together with the capacitance of the separation filter (5) form an electrical oscillation circuit, and a switching device (9) which is incorporated in said circuit and which is periodically actuatable by a control means (11) for activation of the oscillation circuit (5,7,8). The pulse-generating means (1-3, 7-11) further in­cludes a known voltage-controlled frequency converter (1) which is arranged to generate an a.c. voltage having a frequency which is at least three times higher than the frequency of the voltage pulses or voltage pulse trains, and a singel-phase transformer (1) which is connected down­stream of the frequency converter (1) and followed by a rectifier (3).

Capacitive pressure sensor with low parasitic capacitance

Abstract: A plurality of two-plate capacitive pressure sensors with low parasitic capacitance and easily accessible plates are made with microcircuit and thin film technology by depositing a thin layer of glass over a plurality of thin, rigid plates and thin, narrow electrodes previously deposited on a thick glass dielectric substrate, by etching cavities in the thin layer of glass over the plates, and by anodically bonding, in vacuum, thin, doped silicon diaphragms to the thin layer of glass to form variable capacitors each of whose capacitance varies with the pressure outside the sensor.

Capacitive sensing employing thin film inductors

Abstract: A capacitive variation sensor includes one or more elements providing inductive reactance in the form of thin film coils. This enables a capacitive variation sensor to be integrated on a substrate along with a thin film magnetic read/write head. One element of the capacitive variation sensor is a sensing electrode, and in some embodiments of the invention a dedicated sense electrode can be eliminated by employing the pole tips of the thin film magnetic read/write head as the sense electrode.

Capacitive detector for absolute pressure

Abstract: A capacitive detector for absolute pressure, which comprises a base and a stationary capacitor plate (7) attached onto the base (3). An aneroid capsule (4) is arranged in connection with the base (3) and provided with a mobile capacitor plate area (5, 6) directed towards the base (3) and changing its distance from the stationary capacitor plate (7) by the effect of pressure. A silicon plate (2) is attached onto the base and has membrane-like middle portion (5, 6) acting as a mobile capacitor plate. A plate structure (1) is attached hermetically onto the silicon plate (2) such that the space of the aneroid capsule (4) is located between the plate structure (1) and the silicon plate (2).

Adaptive cancellation bridge circuit

Abstract: The invention relates to an adaptive cancellation bridge circuit (ACB) for use in a single medium full duplex line termination equipment such as modems where signals are transmitted and received simultaneously along a pair of wires, the transmit and receive signal being separated in frequency. The bridge comprises a bridge network including transconductance cells (TC1, TC2 and TC3), to provide resistive, capacitive, and inductive components and these cells are electronically controlled by a current control device CC driven from a received signal (RXS) inphase and quadrature components to adjust the bridge network so that it becomes balanced and cancels a transmit signal (TXB) completely.

Capacitive circuit for measuring a parameter having a linear output voltage

Abstract: A capacitance pressure measuring circuit includes a pressure sensitive capacitive transducer and a reference capacitor that are configured in a differential mode to alternately charge and discharge in response to square wave signals. An integrator receives signals from the capacitors and outputs two voltage levels. These voltage levels are provided to a synchronous clock driven selectable sample and hold stage and then to a differential amplifier. The amplifier provides a linear voltage signal proportional to the change in the difference in capacitance of the transducer divided by the capacitance of the integrator.

Fringe field capacitive sensor for measuring profile of a surface

Abstract: A fringe field, capacitive distance sensor for measuring the distance between a probe and the surface of the conductive body. The sensor comprises a conductive plate element mounted by the probe, the thickness of the plate element being substantially less than the height and width of the plate element. The plate element is positioned adjacent to and normal to the body surface, and the fringe field capacitance between the plate element and the body is measured, to thereby determine the distance between the probe and the body surface. The probe may be in contact with and scanned across the body surface, to provide surface profile measurements. A probe including a plurality of plate elements may be positioned inside an opening such as a hole, to measure the geometry of the hole. By maintaining the hole probe adjacent one electrode in electrode in contact with the hole wall, both profile and geometry measurements may be made. A noncontacting probe including one or more plate elements may be used to measure surface topography.

Transfer calibration system

Abstract: A method and apparatus for calibrating a liquid level measurement system of the type having capacitive sensors, by simulating the electrical effects of sensors in an empty condition and their interconnecting cables, at a time when the sensors are full or partially filled. By a sequential balancing technique, using a conventional bridge circuit, a precision, highly stable variable impedance device is adjusted to individually simulate the effects of each sensor and cable combination with the sensor in an empty condition. The settings of the variable impedance device are recorded, and at a later time when the sensors are no longer empty, these settings are reproduced, so as to recreate the electrical effects of each sensor cable combination one at a time. The individual effects are separately transferred into a network having a plurality of variable impedance channels, until each channel simulates the effects of a corresponding sensor and cable. This allows all of the earlier characterized effects to be simultaneously imposed on the measurement system.

Arrangement for detecting spatial inhomogeneities in a dielectric

Abstract: The arrangement includes a capacitive probe comprising pairs of sensor electrodes, arranged in a pseudo-random sequence, with which a common transmitting electrode is associated. The transmitting electrode is fed by an electrical voltage source and to the sensor electrodes of each pair an electrode circuit is connected which generates an output signal which corresponds to the difference of the displacement currents induced in the sensor electrodes. The electronic circuit is constructed such that it maintains the sensor electrodes at any time at a virtual ground potential. For this purpose each sensor electrode may be connected to the inverting input of an operational amplifier whose non-inverting input lies at the potential at which the sensor electrodes are to be held with respect to the supply voltage. The sensed signal is used in a correlative measurement of speed or travel time.

Solid state ballast for gaseous discharge lamps

Abstract: A solid state ballast for starting and operating a plurality of fluorescent lamps comprises a plurality of parallel connected, series LC circuits each coupled by a capacitor to a lamp so that voltage existing across the series capacitors is applied across the lamps and driven by an inverter at a DC power source voltage and at a selected frequency high enough to develop a lamp starting voltage but substantially below their resonant frequency. After starting the resonant frequency of the LC circuits is reduced substantially below the selected frequency by the added capacitive reactances of the coupling capacitors whereby the destructive high voltage at the upper and lower resonances is avoided and the independent selection of the values of L and C and the coupling capacitors to control starting voltage and conduction after starting at the selected frequency is provided.

Capacitive transducer and method

Abstract: An integrated circuit capacitive transducer (10) measures at least one parameter of a medium to which it is exposed. A variable capacitor (12) has a capacitance (C1) which varies as a function of the measured parameter and is charged by source of reference potential (Vr). The charge on the variable capacitor (12) is then transferred to a second capacitor (14) having a fixed reference capacitance (Cr). The voltage (V1) developed across the second capacitor (14) by the charge transferred thereto is then a function of the capacitance (Vr) of the first capacitor (12). Therefore, the voltage (V1) is also a function of the parameter being measured. The capacitive transducer may also include a further variable capacitor (32, 34) for measuring the difference of parameters between two mediums.

Measurement of minimum-geometry MOS transistor capacitances

Abstract: A technique for measuring the gate and substrate capacitances of small-geometry MOS transistors is described. On-chip circuits are used to sense small capacitive currents across a reference capacitor. A low impedance signal is produced which can be interpreted using a commercial bus-addressable gain-phase instrument. The technique has been demonstrated using a 5-µm CMOS process, and experimental capacitance data from several devices (as small as 4 µm by 4 µm) are presented which show short- and narrow-channel capacitance effects. The technique is scalable, which will permit measurement of the minimum-geometry devices of future process technologies. In addition, the technique could be used to measure small-geometry inter-level capacitances. Finally, the limitations of the technique for device modeling and process evaluation are discussed.

Capacitor sensor and method

Abstract: A method and apparatus are described for converting variations in a measured variable (such as pressure) to corresponding variations in an electrical output signal. The preferred method utilizes a capacitive sensor whose capacitance changes to reflect changes in the measured variable. The changes in capacitance are preferably used to vary the gain of a switched-capacitor amplifier whose signal input receives a relatively constant DC reference voltage. The amplifiers' output may be sampled and further amplified to provide an output signal which is indicative of the value of the measured variable.

Capacitive type converter device

Abstract: A capacitive type converter device, such as used for measuring pressure, comprising first and second rectifying circuits, each including an operational amplifier with a non-inverting input terminal connected to a reference point, to which a variable condenser is connected, the variable condenser having a capacitance which varies in response to a force being measured, such as pressure, and to which a reference condenser is connected, the reference condenser having a capacitance which is fixed independent of the force being measured. The device further comprises an oscillator, whose oscillation output is applied to the variable and reference condensers,and which is controlled by a control means in response to output of the first rectifying circuit, or in response to the output of the second rectifying circuit together with the output of the first rectifying circuit, whereby an output responsive to the capacitance of the variable condenser is obtained from the output of the second rectifying circuit, or an output relating to the difference between the capacitances of the condensers is obtained from the outputs of the first and second rectifying circuits. The device eliminates adverse influences of stray capacitances, non-linearity, offset signals, and parallel capacitances and forward voltages.

Harmonic Resposnse Tests on Voltage Transducers for the New Zealand Power System

Abstract: This paper presents the results of harmonic response tests carried out on capacitive voltage transformers, as used on the New Zealand 220 kV a.c. network. It is shown that the harmonic response measured using low voltage test equipment is considerably different from that obtained at high voltage. The latter is highly non-linear and is affected by the specific magnetization characteristic of the CVT tested. It is concluded that for field measurement of harmonics at rated voltage, the transformer of a CVT unit should be disconnected and the CVT used as a purely capacitive or resistor-capacitor divider.

Improved spatial resolution measurement system and method

Abstract: The present invention discloses means and method for obtaining an increased spacial resolution from a sensor that includes a probe having a characteristic physical dimension that limits its spacial resolution. Such a probe may include a rectangular sensing surface wherein the probe sensitivity increases with surface area while the spacial resolution decreases with increasing surface area. The probe and an object to be measured are controllably moved relatively to each other in such a way as to define preselected increments of relative movement that are selected to be a fraction of the characteristic physical dimension of the probe. Data is collected at each of the increments that is representative of a preselected characteristic of the object to be measured with a spacial resolution that is determined by the characteristic probe dimension and the data is digitally filtered to provide processed data representative thereof having a spacial resolution that is determined by the fractional increment of relative motion. In a preferred embodiment, the object measurement system and method of the instant invention has exemplary utility in a wafer profiling station having a capacitive sensor and operable to provide thickness data for regions of the wafer located within one probe-width of its edge. The capacitive sensor includes two capacitive probes each having a generally-rectangular sensing element that is surrounded by a generally-rectangular guard.

Capacitive devices for measuring the diameter of a dielectric fiber

Abstract: The improvements relating to capacitive devices for measuring the diameter of a dielectric fiber are based on a particular shaping of the capacitor plates, such as to allow electric field reductions at the edges to be compensated for and hence capacitance measurements to be unaffected by fibre vibrations

Simple nanosecond capacitive voltage divider

Abstract: The construction of a simple and inexpensive capacitive voltage probe by using coaxial cable is described. The probe has been tested to a frequency response of better than 30 MHz for sinusoidal voltage input and a rise time of <20 ns for single‐pulse input. The probe is ideal for applications in small experiments involving low‐energy and high‐voltage capacitor discharge of nanosecond rise time.

Device for electrostatically suspending a body or sample

Abstract: A device for electrostatically suspending an electrically charged body coises at least two spherical electrodes serving simultaneously for capacitive position detection and electrostatic positioning control for the body.

Computer-Aided Studies of Complex Soil Moduli

Abstract: Low-cost microcomputers and new electronic components make it possible to measure accurately the phase and amplitude of mechanical waves in the frequency domain at a small fraction of the cost that prevailed only a few years ago. Both laboratory and field experiments benefit from this capability and this paper presents examples of both. In a series of new laboratory experiments the authors have measured the phase and amplitude of both the driving torque and the resulting torsional motion of a cylindrical specimen. Motion is sensed with a capacitive, noncontact probe and torque is measured by use of a torque beam instrumented with a silicon strain-gage bridge. The microcomputer and Fourier transform techniques are also used in the interpretation of some of field work involving Rayleigh and Stoneley waves.

Capacitive elements with reduced stray capacitance

Abstract: A capacitive element of a semiconductor integrated circuit comprising a first conductor provided in the input side and a second conductor provided in the output side further includes a third conductor to be connected with the first conductor. The front and back surfaces of the second conductor are entirely covered by the first and third conductors. Portions connecting the first and third conductors are arranged along the peripheral edge portions of the second conductor excepting a signal extracting portion.

Dual cathode beam mode fluorescent lamp with capacitive ballast

Abstract: An improvement in dual beam mode fluorescent lamps in which a capacitive ballast is provided integral with the lamp structure in the form of a cylindrical laminate of metal and insulator coaxial to the lamp's major axis.