Abstract: Means and method are disclosed for providing an alarm signal upon the event of a suicide attempt. All regions at which a confined individual may be located in normal use of a confinement area are sensed for the presence of the individual at the corresponding locations. Absence logic responds to a failure to sense the individual at any of the locations, to signal a possible suicide attempt.

Abstract: This invention concerns an inductive proximity switch having an oscillator and a resonant circuit which is dampable by outside objects, as well as an electronic switch controllable by the voltage across the resonant circuit. From the signal of the electronic switch a switching hysteresis is derived. A device for changing the frequency, when the resonant circuit is damped, as a function of the signal of the electronic switch allows the adjustment of the hysteresis in such a way that there is essentially no effect on the sensitivity of the oscillator.

Abstract: The invention relates to a monitoring and warning apparatus for automatic processing apparatuses, in particular robots. Reactance-determining elements are arranged as sensors on the movable parts of the robot. If the robot arm approaches an object, detuning of the sensor circuit occurs. In that way, it is possible to produce a monitoring or stop signal. A central supply with HF-signals and current permits central monitoring of the function of the sensor circuits and at the same time triggering of warning signals when the sensor approaches an object. That is achieved in that the warning signals derived from sensor signals are used to connect additional loads into the circuit which is supplied from the central current supply means. Therefore, by monitoring the current consumption, it is possible to detect both failure of individual sensor circuits and also the approach of an object to a sensor.

Abstract: The drain voltage of an IGFET having a channel responsive to the change in physical quantity to be measured is negatively fed back to the gate terminal of the IGFET. The negative feedback loop includes series connection of a first amplifier having an amplification factor larger than unity and a second amplifier having an amplification factor smaller than unity. The interconnection point between the first and the second amplifiers is connected to the output terminal. There is provided a stable, highly sensitive and highly reliable semiconductor sensor.

Abstract: Apparatus and method for detecting changes in capacitance of an antenna due to intrusion into the antenna field by a body of different dielectric constant, in the presence of induced AC voltages on the antenna from electromagnetic radiation. The apparatus includes four operational amplifiers connected in a circuit for processing the production of voltage pulses. The first amplifier operates to rectify the AC voltages from the antenna to a DC fluctuating voltage, which voltages are averaged to produce a constant voltage above ground potential so long as there is no intrusion of the field. During this period no signal voltage is transmitted to the second amplifier.

Abstract: A system for monitoring the operation of an input transducer of a central control unit for machines employed in production and product packaging lines, the system having a first circuit for detecting operating defects of the input transducer including a first subcircuit for producing a change in the operating condition of the transducer to produce a corresponding change in the logic signal of the transducer, and a second subcircuit for detecting the change in the logic signal and operating a control alarm based upon the detected change in the logic signal, the system also including a second circuit for providing a signal from the transducer to the central control and monitoring unit based upon the operating condition of the transducer.

Abstract: A personnel identification system for controlling access to restricted equipment or restricted areas comprises a portable device such as a wrist watch (10) in which a unique digital identification code is stored, and a static control unit having a conductive touch element (12) and a code signal receiver (14) for comparing the identification code with a stored access code. The watch (10) includes a transmitter for transmitting the identification code as a modulated alternating signal by electrical conduction through the wearer's body to the touch element (12), so as to provide resistance to interfering radiated signals.

Abstract: A machine tool safety system having a signal induced in a capacitive receptor antenna by the action of an electric field capacitively coupled thereto includes a receiver having an array of linear amplifiers with fast response times, a network connected to the output of each amplifier and responsive to a first command to sample the amplifier output signal, an analog-to-digital converter associated with the sampling network to quantize the signal from the first amplifier in the array that is not saturated, and a network responsive to a second command to dump the sampled signal value prior to the occurrence of the next sample time.

Abstract: A proximity detector includes a crystal which is coupled to an impedance circuit having a value selected to sustain or prevent oscillation of the crystal. At selected points in the impedance circuit, a sensing line is coupled to add capacitance to initiate or terminate crystal oscillation. A detector circuit coupled to the amplified output of the oscillator signal is used to control an alarm circuit. By coupling the sensing line so that capacitance is added to the impedance circuit when the proximity of an individual or other animal tissue is sensed, oscillation of the crystal is initiated or terminated to control the alarm circuit. The oscillator circuit provides improved stability and sensitivity for use of the circuit in a variety of environments.

Abstract: An inductive proximity switch with a built-in testing circuit for monitoring movable elements in which an oscillator has an inductive control element, the impedance of which varies in response to approaching elements with a built-in electrical tester for monitoring the correct functioning of the proximity switch wherein the tester has an electrically switchable damping circuit for damping the oscillator for test purposes.

Abstract: A microstrip antenna is incorporated in a floor mat, the latter consisting of a conductive grid laminated to a conductive sheet with a layer of dielectric material therebetween to form a capacitor. The microstrip antenna is connected to a source of microwave energy for the purpose of radiating a microwave signal through a surveillance area. A low frequency signal is applied to the capacitor section of the mat for direct capacitive coupling through the body of a pedestrian to any surveillance tag carried thereupon.

Abstract: An intrusion warning system for indicating the presence of an intruder to a given area includes an antenna provided around the area and which is insulated from the ground. An oscillator is provided for feeding an alternating current signal to the antenna, and a coupling impedance is connected between an output of the oscillator and the antenna. The coupling impedance includes an arrangement to vary the impedance to an appropriate value such that the voltage fed to the antenna is approximately 50% of the voltage fed from the oscillator to the coupling impedance. By this arrangement the detection sensitivity is always kept at an optimum. The system also includes a signal processing apparatus for producing an output signal responsive to a change in the voltage of the alternating current on the antenna exceeding a predetermined level.

Abstract: An intrusion warning system for indicating the presence of an intruder to a given area comprises a single antenna line encircling the area insulated from the ground, a high frequency oscillator (e.g. of 1 kHz to 10 kHz) for feeding a high frequency signal to the antenna, a coupling impedance, for example, a capacitor, connected between the output terminal of the oscillator and the antenna, and a signal processing part which produces an alarm when detecting a voltage change over a predetermined level of the antenna induced by a proximation of the intruder.

Abstract: This intrusion alarm apparatus has a housing suspended from a metal doorknob such that the housing is tilted when the doorknob is turned. A 100 kHz. oscillator is synchronized with a single shot which produces narrower pulses than the oscillator. An exclusive OR circuit subtracts the single shot pulses from the oscillator pulses. When the door is of wood or other electrically non-conductive material, the body capacitance of a person touching the doorknob increases the width of the pulses produced by the single shot and this change is reflected through the exclusive OR circuit, an integrator, a level detector and a flip-flop to turn on an audible alarm device. When the door itself is metallic, a selector switch can disable the alarm device from responding to the body capacitance of a person touching the doorknob, in which case the tilt switch in the housing will turn on the alarm device when the doorknob is turned.

Abstract: A method for detecting the change in the capacitance of an antenna caused by the approach of a person to the antenna, including the step of charging said antenna to a predetermined voltage relative to ground or a reference antenna, the step of discharging the antenna through a capacitor such that the voltage developed across the capacitor is proportional to the initial charge on the antenna, said charging and discharging steps being sequentially repeated, and the step of comparing the instantaneous voltage across the capacitor to the long term average voltage to detect transient changes caused by an increase in the antenna capacitance resulting from the approach of a person.

Abstract: A self-contained pre-intrusion detection and alarm system for doors and other closures, the system including an rf oscillator circuit incorporating a tank circuit which includes an antenna. The system also includes a detection and processing circuit effective to detect and amplify a change in the voltage in the rf oscillator circuit caused by a change in the antenna to ground capacitance; an audio oscillator circuit; time delay circuitry connected between the detecting and processing circuit and the audio oscillator circuit and controlling the energization of the audio oscillator circuit; and an alarm electrically connected to and controlled by the audio oscillator circuit for alerting occupants of potential danger of intrusion and also deterring potential intruders from continuing their activities toward intrusion.

Abstract: A capacitive motion sensor placed under a mattress or the like for monitoring the movements of a person. The sensor uses an active layer consisting of two courses of dielectric material placed in contact with one another. Movements of a person on top of the mattress cause the courses to move relative to one another, thereby generating an electric change in the active layer which is detected by a pair of spaced elements which form a capacitive antenna means.

Abstract: A directional detector of changes in a local electrostatic field comprising two parallel flat coils of copper wire, separated by an electrically grounded plane rectangular conductor that is coated on both sides with an insulator, and associated signal conditioning electronics has been constructed. The combination of coils and plane rectangular conductors forms two independent wideband antennas which, when placed in an unobstructed electromagnetic radiation field, have induced in them electric currents of equal peak-to-peak values. When the combination was brought near an ungrounded body, such as a person standing on an insulator to earth, a coupling of high frequency potentials of the ungrounded body and the nearest coil occurred, while the coil farthest away from the body, due to the presence of the electrically grounded plane rectangular conductor, was unaffected.

Abstract: An improved safety method and apparatus for sensing individuals adjacent a vehicle utilizes a balanced bridge circuit. The method and apparatus provides for rebalancing the bridge circuit at a first rate during vehicle motion to compensate for topography and environmental changes as the vehicle proceeds and for varying the rate to a second relatively lower rate, and, alternatively inhibiting rebalancing of the bridge circuit when the vehicle is stationary during proximity detection of individuals adjacent the vehicle. A delay in restoring the rebalancing rate to the first rate is provided as the vehicle prepares to proceed. An improved electrode, detection assembly employed in the method and apparatus is described.

Abstract: A capacitance intrusion detection system for use with a metal object or objects insulated from ground comprises a circuit for cyclically charging and discharging the object at a relatively low frequency, for example, less than 500 Hz, and simultaneously integrating the charge on the object to develop a DC voltage proportional to the capacitance of the object. The integrating network is AC coupled to a bandpass filter which passes signals having frequencies corresponding to changes in capacitance of the object caused by an intruder and these signals are applied to a threshold circuit for activating an alarm when an intrusion occurs. Tamper alarm circuits are provided to detect unauthorized disconnection of any portion of the protected object (decrease capacitance) or the addition of capacitance in an attempt to defeat the system.

Abstract: The alarm system comprises a sensing circuit 12 which includes two electrical conductors 10, 11 spaced from but adjacent each other and adjacent to the predetermined position to be occupied by at least one item when in use. The sensing circuit includes a signal generator responsive to the capacitance present between the two conductors to provide a first output condition indicative of a substantially constant capacitance value present between the electrodes due to the undisturbed presence of the item and to provide a second output condition indicative of a change in capacitance value due to the disturbance of the item or items present. The output of the sensing circuit is received by an alarm actuating circuit 13 which causes actuation of an alarm element when the output condition from the sensing circuit changes significantly to cause the actuating circuit to trigger due to the movement of the item from its predetermined position.

Abstract: The alarm device includes a resilient metallic spring strap which is received over a doorknob and against the shank of the doorknob and which forms an input contact to the device. The device further includes an oscillator which outputs a signal through a coupling network having a capacitive branch to ground that includes a capacitive path extending through the strap to the doorknob. When a person touches the doorknob, a capacitive path to ground is established that causes increased attenuation of the signal level. A self-initializing and self-compensating amplifier in the device detects such drops in the signal level and triggers a pulsating alarm. The circuit needs no manual adjustment.

Abstract: A data input device for use in an electrically noisy environment incorporates a plurality of conductive strips, arranged in rows and columns, mounted on a transparent body in front of a display device. Electrical noise is induced constantly in the conductive strips. When an operator places his finger in close association with one or more of the rows and columns, the amplitude of the electrical noise on such strips changes markedly. The change in noise level is detected and used to provide an output identifying the row and/or column in the vicinity of the operator's finger.

Abstract: A water level control system for use with bath tubs includes a capacitive proximity switch disposed external to one wall of the bath tub. The vertical position of the switch is adjustable. The switch generates a signal when the water level is approximately that of the switch. The signal is used to control a water supply solenoid and/or an alarm indication.

Abstract: A detecting capacitive structure undergoes changes in capacitance value depending upon whether it is detecting, in the sheet transport path of a printing machine, a normal or single sheet, an absent sheet, or a double or stuck-together sheet, so that corrective action can be initiated, such as the skipping of a printing cycle. The detecting capacitive structure and also a reference capacitive structure constitute the capacitances of two RC circuit stages to which an input signal is applied and then removed. The variations with respect to time of the output signals from the two RC circuit stages are then compared, both during application of the input signal and subsequent to removal of the input signal. This comparison of time responses of the two RC circuit stages serves as the basis of the detection.

Abstract: A method and apparatus for delivering energy to an oscillatory system in a signal transmitter to maintain the system in a state of oscillation. A component of the oscillatory system that affects the oscillation frequency is influenced by the magnitude of a measured condition which is to be transmitted by the signal transmitter. The oscillatory state of the system is sensed through a signal path, and energy is delivered to the system through substantially the same signal path, said energy being delivered in the form of pulses at time intervals longer than a whole period of oscillation of the system to maintain the system in a state of oscillation.

Abstract: A system for detecting the presence of more than one document along a path during the processing of the documents. A capacitance is introduced by the plural documents in contact with each other and wherein a delay signal is combined with an original signal to generate a multiple document detect signal for indicating the presence of the multiple documents.

Abstract: A field sensor control mechanism for doors and the like has two or more insulated electrodes mounted at different levels in the leading edge of a door or the like. A first oscillating circuit is connected with one of these electrodes and a second oscillating circuit, separate from the first one and serving as a comparison circuit for the same, is connected to the other electrode. The two circuits have base oscillating frequencies which are either identical or differ only slightly from one another. The circuits are so coupled to one another that the oscillations of the first circuit vary as a function of capacitance changes taking place in the electrodes.

Abstract: Each of an array of capacitive touchpad sensors has a single touchpad electrode fabricated upon a substrate and accessible to user personnel, with series coupling and shunt capacitance being provided respectively between a driving generator and the touchpad electrode, and the touchpad electrode and an array ground. Each capacitive touchpad sensor operates with a sense amplifier to provide a high density sensor array requiring relatively low driving voltage amplitudes and may be utilized with driven shields and a normalization network to provide reliable capacitance sensing with reduced sensitivity to contamination of the surface of the sensor array.

Abstract: A capacitive shift fire detection device having a sample circuit and a reference circuit, each circuit having an air capacitor connected to an oscillator and a counter. The presence of particles of combustion in the ambient environment results in a change in the dielectric constant of the air dielectric of the sample capacitor, thus changing its capacitance. This change in capacitance is detected by an oscillator in the sample circuit, the mismatch of oscillators in the two circuits causing an exclusive OR-gate to go high, activating an alarm system.

Abstract: A proximity detector comprises a pair of antennae being disposed along the front edge of a door and at a space therebetween, a pair of coils constituting series resonance circuits, together with each electrostatic capacities of the antennae which are connected in series with the coils, an AC power source for supplying voltages to the series resonance circuits; rectifying circuits for rectifying the voltages produced on the antennae by the AC power source, and a differential amplifier circuit for amplifying difference between the outputs of the rectifying circuits, the output of the differential amplifier controlling the movement of the door.

Abstract: A specially configured cable, which, in use, has a cross section which is mmetrical to a vertical line, but asymmetrical to a horizontal line, is used for an intrusion detection system. It comprises an external sheath, which may be round or rectangular in cross section. An inner conductor is positioned below the center of the cable. It is supported in place by a thin, substantially flat, sheet of insulating material, which is attached to the inner surface of the outer sheath. This particular configuration maximizes the change in capacitance caused by an intruder passing over the cable. The cable is connected to a time-domain reflectometer, which can display on a screen the location of the intrusion with respect to an end of the cable as well as the probable type of intrusion.

Abstract: In a conductor cable for seismic exploration, where the cable will have very high resistance transducers connected to it for transmitting signals from one or more transducer stations to a recording station, there is a controllably conductive path connected across the transducers. The path is only conductive at a voltage greater than the maximum of the signals. And, a constant current source is applied at the recording station. Also, a voltmeter is employed to measure the continuity of the cable.

Abstract: An electronic security device includes an insulated loop shaped antenna which capacitively couples to any objects which intrude into a zone surrounding the antenna. The loop shape allows the antenna to be placed onto a doorknob of the room to be secured, and the insulation prevents electrical contact-bounce between the antenna and the doorknob. A detector circuit connects to the antennna and generates output signals indicating the amount of capacitive coupling. An alarm circuit connects to the detector circuit and sounds an audible alarm for a predetermined time interval when the coupling as indicated by the output signals implies that an object has intruded into the zone. A test circuit connects to the alarm circuit for temporarily decreasing the time interval of the alarm in response to a manually activated switch to allow the security device to be tested prior to being fully activated.

Abstract: An intrusion alarm having an oscillator which is turned off by the body capacitance of a would-be intruder operates in the frequency range of 17-65 MHz. At this frequency, reliable discrimination between body capacitance and stray capacitance is possible and therefore sensitivity is increased while false alarms are reduced. Battery life is increased by providing a high resistance load in the stand-by mode to reduce battery drain to 500 microamperes or less. Latching and nonlatching embodiments are disclosed.

Abstract: Protected objects are connected together to form an antenna. Preferably, the cabinet for the detector circuitry is also included in the antenna. The antenna is excited by a voltage controlled oscillator (VCO). The capacitive reactance of the antenna changes when an intrusion occurs. This causes the frequency of the VCO signal to undergo an instantaneous change. A phase comparator compares the phase of the VCO signal with the phase of a reference oscillator signal. An instantaneous change in the frequency of the VCO signal due to a change in the capactive reactance of the antenna when an intrusion occurs is reflected by a shift in phase between the VCO signal and the reference oscillator signal. This causes the phase comparator signal to change.

Abstract: An intrusion detection unit comprises a compacitance having an "active" field, the coupling of which is significantly increased when an intruder comes into conductive relation with a doorknob. The unit is hung on the inside doorknob and is so arranged that the doorknob is the transmitting element of the capacitor, while a separate plate is the receiving element of the capacitor. The capacitor field is maintained actively charged by a battery driven oscillator which operates at a substantially uniform frequency and amplitude. The intrusion detector circuit is complete in itself and is not externally grounded by the intruder. The signal receiving portion of the circuit incorporates a square law amplifier, and also has means for adjusting the reference level to which the signal is compared.

Abstract: A motion detector comprising a self-excited oscillator operating in the megacycle range which is maintained at a substantially fixed frequency by way of a constant current source. By virtue of the constant current input changes in inductance and capacitance associated with the motion of the intruder are registered as changes in oscillatory amplitude rather than frequency change. This change in amplitude is passed through a low band pass filter, i.e. a filter operating in the range of frequencies normally associated with the motion of a human, and the changes in this filtered signal are then passed through a coupling capacitor to a comparator. In this manner, the DC level, which often drifts in a linear circuit is taken out. The output of the comparator is then applied to a coded transmitter which on the occurrence of an intrusion will set off an alarm at a remotely held receiver.

Abstract: A method and apparatus for providing output indications in response to the presence of an electromagnetic energy receptor within a predetermined distance of a glow discharge device the electrodes of which have a voltage applied thereacross at least equal to the maintaining voltage but less than the breakdown voltage, including an excitor for generating an electromagnetic field around the glow discharge device at a strength less than the ionization level but sufficient to ionize the gas when the electromagnetic energy receptor is within the predetermined distance of the glow discharge device.

Abstract: A contactless motion detector, such as an oscillator sensitive to an approaching metallic element, is connected across a storage capacitor which can be charged from a source of pulsating direct current through a constant-current unit with two parallel branches, one of them including a voltage divider controlling an emitter-follower transistor in the other branch. A Zener diode, shunting the storage capacitor and part of the constant-current unit in series therewith, throttles the flow of charging current through that unit by stabilizing the base voltage of the emitter-follower transistor when the capacitor reaches a predetermined charging voltage. Connected across the series combination of storage capacitor and constant-current unit is an ancillary thyristor forming part of a firing circuit for a main thyristor in parallel therewith; that firing circuit further includes another Zener diode and a stabilizing resistor in series with the ancillary thyristor.

Abstract: A contactless motion detector, such as an oscillator sensitive to an approaching metallic element, is connected across a storage capacitor charged from a source of pulsating direct current through a current-limiting device and shunted by a Zener diode. Connected across the series combination of storage capacitor and current-limiting device is an ancillary thyristor, triggerable by the detector, forming part of a firing circuit for a main thyristor in parallel therewith; that firing circuit further includes another Zener diode and a stabilizing resistor in series with the ancillary thyristor. Conduction of the main thyristor, upon the triggering of the ancillary thyristor, reduces to near-zero the resistance in series with a load, such as a relay, which is traversed by the current drawn from the source.

Abstract: A human touch on an etched copper electrode produces a capacitive change to vary the time constant of an RC network as a part of an oscillator. The variation in the capacitance of the sensor changes the time constant of the RC network which results in a change in frequency of the output signal of the oscillator. This change in frequency thus varies with the human touch to the copper electrode. To develop a directional indication of the touch position, four electrodes are arranged in opposed pairs along orthogonal axes. Each electrode is part of an RC network connected to an oscillator with each of the four oscillators identified with one of the four positions along the orthogonal axes. The output signal from each of the oscillators is transmitted to timing and control circuitry that generates four separate pulse trains, one pulse train identified with each of four positions along the orthogonal axis.

Abstract: A contactless motion detector, such as an oscillator sensitive to an approaching metallic element, is connected across a storage capacitor which can be charged from a source of pulsating direct current through a constant-current unit. A Zener diode, shunting the storage capacitor and part of the constant-current unit in series therewith, throttles the flow of charging current through that unit when the capacitor reaches a predetermined charging voltage. Connected across the series combination of storage capacitor and constant-current unit is an ancillary thyristor, triggerable by the detector, forming part of a firing circuit for a main thyristor in parallel therewith; that firing circuit further includes another Zener diode and a stabilizing resistor in series with the ancillary thyristor. Conduction of the main thyristor, upon the triggering of the ancillary thyristor, reduces to near-zero the resistance in series with a load, such as a relay, which is traversed by the current drawn from the source.