Showing papers on "Capacitive sensing published in 1973"

Capacitive detector device

Abstract: A stray field capacitor with three plates edge to edge in a row has its center plate grounded, and normally most of the stray field of a signal applied to one of the end plates is between that end plate and the center plate which shields the other end plate A reverse phase signal of proper amplitude may be used to reduce to zero the quiescent output of a receiver attached to the other end plate of the capacitor If the capacitor plates are mounted on the inside of the windshield of a motor vehicle, the receiver will switch on the windshield wipers when moisture collects on the windshield

Two threshold level detector using a capacitive or inductive probe for sorting

Abstract: The specification discloses apparatus for sorting a succession of objects which are passed through a probe on a conveyor. The probes comprise one or two capacitors or inductances whose impedances are varied by the objects passing through. The probe is included in an a.c. bridge circuit whose output is detected by a phase sensitive detector. A discriminator is coupled to the detector by an a.c. coupling, to minimize drift. The discriminator discriminates relative to two threshold levels, the first corresponding to the presence of an object in the probe and the second corresponding to a minimum value of its magnetic or dielectric properties. Embodiments are disclosed in which the second threshold level is a peak amplitude (FIGS. 1 to 5), an integral (gross) magnitude (FIGS. 6 to 8) and an aggregate value of the time for which the instantaneous amplitude exceeds a third threshold (FIGS. 9 to 11).

Capacitive weighing mat

Abstract: A weighing mat adapted to be loaded by a range of forces which preferably includes three elastomeric, conductive layers. The outer conductive layers are separated from the central conductive layer by two dielectric, elastomeric layers having ribs of trapezoidal cross section to form a capacitance which varies with compressive loading. The mat provides linear changes of capacitance with changes of compressive load, has increased load capacity, and has improved resistance to shear forces.

Multielectrode capacitive liquid level sensing system

Abstract: A bridge circuit has in one branch a long capacitive probe and in the other branch a plurality of parallel capacitive probes of different lengths, the probes to be mounted in a storage tank. Inductors used across the respective probes function to subtract the values of capacitances equal to the value of the capacitances of the respective probes when no liquid is present in them, thereby to obtain capacitance readings indicative of only increased capacitances resulting from the presence of liquid. The outputs of the branches resulting from the presence of liquid are compared, and a control voltage is developed for application to a capacitive diode in the one branch of the bridge circuit to maintain the bridge circuit substantially balanced. The control voltage is measured to indicate the level of the liquid in the tank, and the use of a plurality of probes in the other branch extends the useable range of the curve for observable voltage changes. The effect of different densities of liquids is balanced out.

Fluid mixture analyzer using a capacitive probe and voltage divider

Abstract: A sensor device for ascertaining water content of a petroleum flow in a well-pipeline including a capacitive sensing head between the plates of which the petroleum flows and an electrical assembly to measure the dielectric constant of the petroleum flow between the plates and to provide an output representing said dielectric constant which is indicative of the water content of the petroleum.

Capacitive pressure transducer

Abstract: Pressure responsive diaphragms, in their movement with respect to fixed plates, constitute variable capacitors. Dual diaphragms, on opposite sides of a substrate carrying the corresponding fixed plates, eliminate flexure of the substrate as a factor in the performance of the device. An electrical circuit for converting the varying capacitance to a correspondingly varying electrical signal is housed in the space between the diaphragms. The pressure transducer so formed is contained in a casing which communicates by tubing to any desired source of pressure; such pressure in the interior of the casing is imposed on the transducer. Terminals for external electrical connections are formed by screws which hold the casing members together, and which are electrically continuous with internal conductors.

Capacitive sensor for measuring displacement or position

Abstract: A scale reading apparatus operating by capacitive sensing of a scale position is provided with at least one electrical screening layer adjacent the conductive patterns that provide the capacitance measurements, but electrically insulated therefrom, the screening layer being arranged to act to screen stray capacitances. Each screening layer is preferably given a form similar to that of the conductive pattern relative to which it is fixed but 180* of phase therewith.

Techniques for the measurement of air-bearing separation -- A review

Abstract: Various techniques for the measurement of air-bearing separation are described. Examples are given in the specific area of self-acting air-bearing sliders on rotating disks. The techniques can be categorized as capacitive, inductive and optical. The optical technique lacks frequency response but can provide an accurate and convenient way of calibration for the typically nonlinear but versatile capacitive and inductive gap sensors.

A Microminiature Solid-State Capacitive Blood Pressure Transducer with Improved Sensitivity

Abstract: A microminiature pressure transducer is described utilizing a variable air capacitor driven by a pressure-sensitive deflectible silicon membrane as the detection mechanism. Silicon integrated circuit technology is used throughout for economical batch fabrication of the device. Prototype devices have been fabricated and initial test results under static pressure conditions are reported. Equivalent gauge factors of over 500 for this variable capacitance device are about a factor of 5-10 better than the best theoretically designed silicon strain gauges in the size range necessary for catheter insertion. Temperature independence and increased linearity are also important advantages of this variable capacitance sensor head.

Capacitive keyswitch sensor and method

Abstract: Each of the inputs of an analog multiplexer are connected to a plurality of capacitive keyswitches and a reference capacitor. At the first multiplexer scan position, the reference capacitor is charged through a charging resistor and when a predetermined voltage is reached a threshold amplifier is caused to respond. The time period required to charge the reference capacitor is stored and compared with the time period required to charge each of the keyswitches. A control signal is generated in response to this comparison providing a signal representative of the capacitive value of the keyswitch in relation to the reference capacitor and thus the operative condition of the keyswitch.

Capacitive displacement transducer

Abstract: A simple rugged capacitive displacement transducer for use in dirty and severe shock environments has a conductive sleeve that is preferably lined on the inside and outside with an insulating material. The sleeve slides over the free end of a rod whose displacement is to be measured and as the rod moves within the sleeve, the capacitance between the sleeve and rod is changed. The change in capacitance is converted by an electronic circuit into a current signal representing the displacement of the rod. If the rod does not have a free end, the conductive portion of the sleeve is made in the form of two opposing triangular areas and a cylindrical ground plate disk is attached to the rod in the region of the conductive portion of the sleeve.

Capacitive wire gauge

Abstract: An apparatus and method for gauging the cross sectional configuration of a conductive wire at a ground potential where the wire is placed within or passed through a tubular insulator having a tubular sensing electrode thereon and a pair of end electrodes located adjacent opposite ends of the sensing electrode. The sensing and end electrodes are surrounded by a conductive guard and all the electrodes and the guard are energized by alternating electric current. Measuring the capacitance between the sensing electrode and the wire provides an indication of the wire''s cross sectional configuration. The energized guard and a shield maintained at ground potential and surrounding the guard eliminate the effects of stray environmental capacitance. The pair of end electrodes eliminate the fringe effects of the capacitive field at the ends of the sensing electrode.

Capacitive transistorized signaling device

Abstract: An electronic device incorporating a circuit for providing a signal with respect to an on or off mode dependent upon the degree of capacitance. The invention comprises a first and basic embodiment utilizing a signal source having a slope of a step function or specifically one having a fast rise time initiated for example by a clock element. The operative signal criteria demands that the length and slope thereof respectively have an effective amplitude and an effective frequency compatible with the circuit components. The signal source is fed to a transistor or suitable amplifier having its base connected to a capacitance sensing means. Resistors are provided for appropriate biasing, current limiting and drain functions as well as capacitors for capacitance balancing purposes. The capacitance sensing means can comprise a touch switch which when touched has its capacitance increased causing the device to function. The transistor or amplifier is connected to a load so that when a change of capacitance is sensed, the change will be registered. Other embodiments can incorporate differential amplification means and means to drive the active components with the voltage of the signal source or the clock voltage. Alternative embodiments of this invention incorporate capacitance sensing means in the form of transducers which can operate in a linear or a sequential mode. The transducers functionally incorporate a change of capacitance by means of moving mechanical elements so that when such change in capacitance is detected by the circuit it will provide an on or off sensing for the circuit or an analog of the change in capacitance. Thus, a reading of the extent of mechanical movement of a mechanically moving object can be transduced into an electrical function or output having substantial linearity. In summation, the circuit of this invention can be used for a transducer, or a solid state switch.

Level sensing device with capacitive gaging transducer

Abstract: A fuel level measuring system with gaging transducers in the form of probes having an outer, capacitive element and an inner, profiled element which may be continuous, representing an infinite number of capacitive plates, or divided into discrete plates whereby a single probe, operating as a three dimensional probe, performs the function of a multiplicity of probes for various attitudes of a vehicle. An attitude-responsive switch may be used to selectively energize distinct plates of the element.

Capacitive voltage-dividing arrangement for high voltage measuring apparatus

Abstract: In a capacitive voltage-dividing device of the type having a high-voltage capacitor connected in series with a low-voltage capacitor for high voltage measurements, particularly in connection with fully insulated, metal clad, high voltage switchgear, an improved arrangement comprises an inner electrode connected to the high voltage bus of the switchgear and extending through an opening in the metal cover; an intermediate or measuring electrode surrounding the inner electrode; and an outer electrode forming a cap-like extension of the metal cover and surrounding the measuring electrode in spaced, insulated relation. The measuring electrode in combination with the inner electrode forms the high voltage capacitor, and the measuring electrode in combination with the outer electrode forms the low voltage capacitor of the arrangement.

On linear parasitic array of dipoles with reactive loading

Abstract: Center loaded linear parasitic arrays of dipoles are examined. It is shown that capacitive loading increases the phase velocity of the slow wave on the structure while inductive loading reduces it. For the infinite array, used as a transmission line, this has the effect of modifying the cutoff frequency and the bandwidth. This is experimentally verified for the capacitive loading. For a simple finite array without a reflector, due to end effects only a small bandwidth widening is observed. However, when the finite array is attached with a suitable reflector, a significant widening of bandwidth is observed. In both these cases the loading causes a significant shifting of the center operating frequency. This effect is utilized to build a tunable Yagi array with varactor loading. With variable bias this loading can effectively be adjusted to double the operational bandwidth. Also it is shown that it is possible to sustain the optimum array directivity over a very wide bandwidth without bias adjustments, by a special loading network.

Theory of cylindrical antennas with lumped impedance loadings

Abstract: A method is presented for the analysis of a thin symmetrical cylindrical antenna with lumped impedance loadings along its length. The loadings can be resistive, inductive, capacitive, or mixed, and their physical size is assumed to be of the order of the antenna radius. The values of admittances of such structures obtained by the theory are in good agreement with available experimental results.

Disk-shaped record carrier on which information is recorded in the form of an optical structure

Abstract: A record carrier for, for example, video and/or audio information, which information is recorded in an optical structure, and an apparatus for reading the record carrier are described. By means of an additional electrically conducting plate which together with an electrically conducting highly reflecting coating of the optical structure forms a capacitive element the distance by which the image-forming objective system and the optical structure are spaced from one another can be measured.

A Capacitive Integration System for the Precise Measurement of Isotopic Ratios in a Mass Spectrometer

Abstract: An automated data collection system has been developed and applied to the measurement of O16/O18 ratios with high precision. The design is based on the simultaneous capacitive integration of two ion beams from a mass spectrometer. The results obtained have shown a consistent precision of 10–20 parts per million.

Method and means for measuring the phase angle between current and voltage

Abstract: Methods and means for measuring the phase angle between current and voltage associated with an insulator are disclosed utilizing voltage and current transducing means and means for nulling parasitic capacitive and resistive current flow. Logic means responsive to the voltage and current transducing means provides an output pulse waveform having a pulse width dependent on the relative phase relationship between the voltage and current and this output pulse waveform may be filtered to provide a relatively constant output signal having a magnitude indicative of the insulation dissipation factor.

Modified Nodal Iterative Load Flow Algorithm to Handle Series Capacitive Branches

Abstract: This paper presents a modification of the well known Nodal Iterative load flow algorithm. The modification is shown to be capable of giving a significant improvement in convergence in routine applications and to give good convergence in a wide range of cases involving series capacitive branches. The modification causes no significant increase in program complexity.

New Touch Actuator Based on the Foil-Electret Principle

Abstract: A new touch actuator is described that consists of a single metalized foil electret, a number of independent metal backplate sections aligned with the holes of a front cover, and air gaps separating electret and backplate sections. The metal layer of the foil forms a transducer with capacitance C a with each backplate section. The actuator is operated by touching the foil electret through one of the front-cover holes. For a trapezoidal displacement (duration 2T ) of the foil electret, the electrical output signal across a terminating resistor R consists of a pair of oppositely poled spikes with duration comparable to RC a , if RC a is smaller than T . If RC a is larger than T , the electrical output approximates the displacement. For an electret with a charge density of 10^{-8} C/cm^{2} , the measured pulse amplitudes due to touching are of the order of 0.3 to over 100 V depending on the applied force, and on the resistive and capacitive loading. The touch actuator is mechanically simple, reliable to use, inexpensive to produce, and can be made with an overall thickness of less than 0.5 cm. Apart from its potential use in telephone dials, it may also find applications as a key transducer in digital devices.

Electric discharge machining circuit incorporating means for pre-ignition of the discharge channel

Abstract: An electric discharge machining circuit utilizing for the production of erosive current pulses, discharges delivered by electric energy accumulation means, at least a part of which consists of a capacitive type element based upon the voltage/current ratio and intended to store and return the energy, wherein the voltage provided with the inception of each discharge is higher than the voltage used to charge said element.

Capacitively tuned dipole

Abstract: Capacitive tuning of a dipole of almost any electrical length is demonstrated with an antenna configuration that is similar to the folded dipole. If variable-capacitance diodes are substituted for the capacitors, tuning over a very wide band of frequencies is possible.

Vehicle door proximity detector system

Abstract: A proximity detector for use on vehicle doors provides a pair of parallel connected branch circuits each providing an antenna mounted along the leading edge of a vehicle door and a serially connected input winding of a transformer with both antennae providing a capacitive coupling to the electrical ground of the elevator structure. The pair of transformers each provide an output winding which are serially connected in electrical opposition and provide an output in response to a change in impedance to ground of one antenna with respect to the other. The pair of branch circuits are connected to a source of periodic voltage and are further connected to a shunting circuit having a variable impedance which electrically shunts each antenna to the electrical ground through variable resistive and capacitive type elements. A variable capacitor is parallel connected across one transformer input winding while a control circuit is connected to the output windings and includes an interconnected operational amplifier, an AC to DC conversion circuit, an electrical comparator circuit providing a dis-connect and trigger-level control, and a switching circuit providing a controlled rectifier and an output relay.

Capacitive weighted acoustic surface wave filter

Abstract: A new technique for weighting acoustic surface wave filter interdigital transducers in which transducer pads are first deposited on a substrate, a dielectric layer deposited thereover and interdigital fingers deposited atop the dielectric layer with the fingers having a variable and selectable area where they overlap the dielectric to thereby effectively vary the amount of capacitive coupling of each finger and resulting in an acoustic wave which is uniform across its beam width.