Abstract: Sensing magnetic flux in an electromechanical actuator having dual axially opposed stators and dual springs, a control system modifies the rise of flux in such a manner to produce a substantially zero velocity landing of an armature against the stators. The flux is sensing by means of a sensor such as a hall effect sensor that is mounted each stator. The control system controls the flux rise when the armature is within the landing zone of the armature against the stator to match the spring rate of axially opposed springs in the actuator.

Abstract: A pulse signal generator comprises a magnetic element capable of causing a large Barkhausen jump, a detector provided in relation to the magnetic element, a magnetic field source provided in the vicinity of the magnetic element to produce a biasing magnetic field which causes a predetermined magnetization of the magnetic element, and a magnetic circuit forming member provided in the vicinity of the magnetic element to produce a main magnetic field which cause a large Barkhausen jump in the magnetic element such that movement of the object to be detected changes the main magnetic field of the magnetic circuit forming member thereby causing a large Barkhausen jump to provide a pulse signal.

Abstract: An inductive proximity switch includes a coil that is supplied with periodic transmitting current pulses. Signals which correspond to voltages induced in the coil after the end of a transmitting current pulse by the decaying current which previously flows in the detected body due to the voltage induced therein by the transmitting current pulse are then processed. The coil is supplied with transmitting current pulses whose direction alternates periodically. The current flow pattern is such that in the first half of a period of the current supplied to the coil, the transmitting current delivered to the coil flows in a first direction and substantially only during a first interval which is shorter than one half of the period of the transmitted pulses. The transmitted current subsequently decays during a time interval and is negligibly small during the remaining time of the first half of the period.

Abstract: In order to identify the position of a movable element, such as a lock bolt, a resonant circuit is subjected to the element or a part that moves with the element. The resonant circuit is thereby damped by the element in a position-dependent manner and oscillates in one end position of the element but is damped too greatly in the other end position. A microprocessor controls the switching on and the respective operating point of a transistor in such a way that switching hysteresis is obtained. The operating point can be automatically readjusted in an adaptation phase.

Abstract: A charge transfer load sensor. A first and second electrode are disposed a fixed distance apart, and a third electrode is disposed between the first and second electrodes. The third electrode is grounded and its position between the first and second electrodes varies in response to an applied force. A switch arrangement applies a predetermined voltage level to the first electrode and couples the second electrode to ground during a first predetermined timing interval. During a second predetermined timing interval, the first electrode is coupled to the second electrode to transfer the charge of a first capacitor formed by the first and third electrodes to a second capacitor formed by the second and third electrodes. An output port coupled to the second electrode provides an output voltage as a function of the applied force.

Abstract: The invention concerns a protective circuit for monitoring an object which can move between two end positions, for example a displaceable safety door (1) of an electric machine. This type of protective circuit has a very simple and distinct design and can consequently be produced economically. In particular, the monitoring system is designed so as to be independent of the start command. According to the invention, at least two end switches (4, 5) are provided for monitoring the end position of the object, at least one switch (18) is provided for activating a first reservoir for a first charge potential, and a multivibrator (8) is provided which is connected to a known driver bridge (9) which has relay outputs and is connected to a consumer, for example an electric machine. The multivibrator (8) is connected to a second reservoir for a second charge potential which keeps the multivibrator (8) activated for a predetermined period of time when the end switches (4, 5) are not in the "off" position.

Abstract: A method and a device for starting a machine, in particular, a printing press, using a sensor or sensor field which emits a start signal during the approach of a part of the body of a machine operator. According to the method, the machine is automatically started if the start signal appears twice consecutively and if the following additional conditions, automatically checked by a machine controller, are met: No start signal is present within a first predefined time period following the instant of the first appearance of the start signal in a predefined time interval, and the start signal reappears within a second predefined time period following the first predefined time period. The device includes a proximity- or touch-sensitive operating surface, which has a first partial surface having the function of a machine starter and second partial surface, which blocks the function of the first partial surface for a predefined period of time in response to proximity or contact.

Abstract: An apparatus to detect the presence of a surgical handpiece is provided. The handpiece is electrically isolated from its source of electric power by a transformer having two primary windings and one secondary winding. The first winding provides power to the handpiece and the second winding is used in the handpiece detection apparatus. The handpiece detection apparatus includes a detection circuit and a comparator that compares the electrical signal input to a standard to determine the presence of the handpiece.

Abstract: A multivoltage (120 VAC to 277 VAC) input, low leakage current type, microcontroller-based, wall switch mounted, IR motion sensor with a latching relay having zero watt load switching capability, provided in a low cost, single PC board design to be mounted in a single gang electrical box. The switching circuit delivers AC electrical power to a load, such as a lighting fixture, from an AC power supply having only a hot lead, a neutral lead and a ground connection. The switching circuit comprises a rectifier, coupled to conduct a leakage current between the hot lead and the ground connection, for converting the AC electrical power to a DC electrical power supply. A relay has a first normally open contact coupled to the hot lead and a second normally open contact coupled to the load, and is powered by a storage capacitor. An IR occupancy sensor generates a signal in response to a detected human presence.

Abstract: A non-contact switch movs from an off position to an on position when a lossy material enters a sensitive area of the switch. The non-contact switch comprises a transmitting element and a sensing element. The transmitting element is capable of radiating a signal. A portion of the signal passes through the sensitive area of the switch. The sensing element is capable of receiving the signal. When the received signal is less than a predetermined level, the received signal represents the lossy material entering the sensitive area of the switch.

Abstract: A detection device associated with an electrical apparatus for detecting by contact the presence of a user, composed of an electronic circuit for detecting a presence of a user by detecting a leakage current traversing, at least partially, a portion of the body of the user using the electric apparatus when the body portion comes into contact with an electric contact providing for the transmission of the leakage current from the electronic circuit to the portion of the user's body.

Abstract: In order to improve a non-contact proximity switch, and a method for programming it, with an resonant circuit that can be influenced by objects approaching from outside and an evaluation circuit to generate an output signal as a function of an output voltage of the resonant circuit that exceeds a predefined threshold value, and with standard terminals, in such a way that the proximity switch can be used at different temperatures and operates accurately independently of the ambient temperature and independently of other trouble influences, it is proposed that a temperature sensor be arranged in the vicinity of the resonant circuit; and that a compensation circuit comprise a circuit unit, downstream from the temperature sensor, which outputs a compensation quantity, dependent on the sensed temperature, that is delivered to a comparator to be compared with the output voltage of the oscillator circuit and, when identity exists, to enable the output signal; and that the compensation magnitude for compensating for

Abstract: The invention relates to an electromagnetic relay drive circuit which generates an electromagnetic relay excitation signal after first verifying that the electromagnetic relay make contact points are off. A forced-operation electromagnetic relay with make contact points and break contact points having complementary relationship with each other is used, and when the break contact points are on, that is to say the make contact points are off, a trigger input signal of logic value "1" with a predetermined level range is applied to a trigger input terminal of a self hold circuit. When an input signal IN of logic value "1" within a predetermined level range is applied to a reset terminal while the trigger input signal is being applied, the relay is excited and the make contact points switch on.

Abstract: A method and apparatus for electromechanically locking a docking station to a computer using an electromagnetic attractive force is disclosed. In a preferred embodiment, the docking station includes a latching mechanism with a ferromagnetic handle, and an electromagnet proximately located to the latching mechanism. The latch mechanically secures the docking station to the PC. The electromagnet is positioned such that, when electrically energized, the electromagnetic field produced thereby attracts the handle with sufficient force to prevent the handle from being used to disconnect the PC from the docking station. Alternatively, the electromagnet can be located in the docking station so that it is near a ferromagnetic plate in the PC when the PC is docked.

Abstract: A safety device and an alarm system controller of a workspace providing bidirectional communication for determining whether the required safety devices are used by the work persons entering the workspace, and whether the safety devices are properly worn. The communication means used allow to associate one or more safety devices to a work person.

Abstract: A proximity switch for controlling lighting devices includes an oscillator operating at a nominal frequency. When a hand is positioned near a sensing antenna, the frequency of the oscillator decreases. The decrease in frequency is detected by a detection circuit which toggles a flip-flop. The output of the flip-flop controls a trigger circuit which provides a trigger input to a triac. When the trigger circuit is active, the triac conducts and provides power to an incandescent lamp. The power is alternatively toggled on and off each time the hand is brought into proximity to the sensing antenna.

Abstract: A safety device and a supply power controller of a machine tool providing bidirectional communication for determining whether the safety device is appropriate for the particular machine tool, and whether the safety device is properly worn. The communication means used allow to associate one safety device to a plurality of machine tools and a plurality of safety devices to one machine tool, as well as relating safety devices to a specified work zone including a plurality of machine tools.

Abstract: A proximity sensor of the electrostatic type has a pulse-generating circuit and first and second delay circuits which are respectively connected to an output of the pulse-generating circuit. The first and second delay circuits are of the integrating type having capacitances which are charged over time. The second delay circuit is a reference circuit and has a delay based on a fixed capacitance. The first delay circuit has its capacitance based on a capacitance of a detection electrode. The first and second delay circuits each have their respective capacitances charged or drained by constant current circuits, each moving the same amount of current. Outputs of the first and second delay circuits are each applied to a respective limiting amplifier such as a Schmitt trigger, each Schmitt trigger then has an output to input to a common phase detector. The phase detector determines the sequence of arrival of pulses generated by the first and second delay circuits.

Abstract: A radio receiver and its power supply are included in a circuit with a switch which is responsive to introduction of a force field, such as a magnetic field. When the field is activated, as by the introduction of a sufficiently powerful magnet, the switch is opened and the radio receiver is deactivated. Removal of the force field automatically restores the radio receiver to operable condition.

Abstract: In one aspect of the present invention, an electromagnetic actuator is disclosed. The electromagnetic actuator includes a plunger adapted to move between first and second positions, a pull coil adapted to receive electrical energy and responsively produce a high electromagnetic force causing the plunger to move from the first position to the second position, and a hold coil adapted to receive electrical energy and responsively produce a low electromagnetic force for maintaining the plunger at the second position. A sensing device is included to detect the magnetic flux density produced by the coils and responsively produce a position signal having a magnitude responsive to the position of the plunger. Advantageously, signal conditioning circuitry receives the position signal, and de-energizes the pull coil in response to the position signal indicating that the plunger is at the second position.

Abstract: A circuit and method for controlling the application of a fastener to a surface and a support, for use with a support sensor and an automatic fastener applying device. In the circuit, a comparator receives a primary signal from the sensor and generates an intermediate signal when a preselected condition is satisfied between the primary signal and the predetermined value. A controller generates a control signal in response to receipt of a secondary signal from the sensor and the intermediate signal. An actuator operates the automatic fastener applying device to apply the fastener to the surface and support in response to the control signal.

Abstract: The operating parameters of a proximity switch can differ depending on the type of switch and also because of manufacturing tolerances. To make it possible for one to react to new developments in ultrasonic transducers and to customer-specific solutions without requiring additional space, data such as operating parameters are able to be input into a microprocessor of a prefabricated proximity switch with little expenditure of time and energy. A proximity switch may contain an enabling input and an overcurrent-detection device including a microprocessor. An overcurrent across the switching output can be identified by a pulse provided to a first input of the microprocessor. A programming device is provided through which such an overcurrent condition is simulated and the corresponding pulse is generated which represents information about an operating parameter in the form of a bit pattern. The microprocessor is loaded with this bit pattern.

Abstract: In an electronic arrangement for initiating an action by means or a key element which includes a coded machine readable data memory and a data processing unit for initiating the desired action which includes a reading head for reading the data stored in the key element data memory, the key element data memory is a single contact storage module and also the reading head includes only single contact sensors through which, when contacted by a key element, data are exchanged in series-bit fashion through a single data transmission line, with the key element under the control of the data processing unit.

Abstract: An actuator movement detector (10) indicates proper engagement of a solenoid (12). The current flowing through a field coil (16) is converted to a sense voltage that exponentially increases and then follows a dip before increases again to a steady state value greater than the first peak value. The exponentially increasing sense voltage is stored across a capacitor (24). Any AC variation about the stored sense voltage sets the output state of comparators (30, 32) and determines a first peak value of the sense voltage. After the first peak, a counter (44) must count to a predetermined value during the low peak before the sense voltage returns to its first peak value. If the counter reaches at least the predetermined count value before returning to its first peak value and count back down to zero before reaching steady state, then the solenoid is considered engaged.

Abstract: Surveillance of signal changes, especially for self-checking control systems. It is essential in self-checking control systems to create equipment to monitor signal changes and allowing to detect all conceivable initial errors or defects and to allow beginning a dangerous state or a dangerous motion of a machine only when the input peripherals evince, not only for instance static signals, but after definitively at least one change of signal has taken place and after this input signal was successfully checked dynamically for its suitability in beginning the dangerous state or the dangerous motion of a machine. For that purpose a special circuitry is proposed in which at least one signal source as well as relays and relay contacts are arrayed in such manner that both self-checking signal detection and voltage-free transfer of at least one checked signal to a higher safety level shall take place.

Abstract: A proximity switch is provided which has a programmable parameter such as a programmable switching threshold and/or programmable switching function. The device is programmable using a digital signal that is applied to a conventional terminal of the proximity switch. For example, the conventional power signal for operating the proximity switch can be modulated by a programming signal for use in programming the proximity switch parameters. The program signal could also be input to a conventional output terminal of the proximity switch.

Abstract: A circuit and method for controlling the application of a fastener to a surface and a support, for use with a support sensor and an automatic fastener applying device. In the circuit, a comparator receives a primary signal from the sensor and generates an intermediate signal when a preselected condition is satisfied between the primary signal and the predetermined value. A controller generates a control signal in response to receipt of a secondary signal from the sensor and the intermediate signal. An actuator operates the automatic fastener applying device to apply the fastener to the surface and support in response to the control signal.

Abstract: A plurality of sensitive high-frequency proximity switches are provided in the bumper of a car and obstacles can be accurately identified. The electronic car bumper includes: a plurality of sensor portions each having sensor plates, first loading coils, and a divided capacitor, and a reference resonance circuit having a reference capacitor, a second loading coil and a divided capacitor. An oscillator drives each of the sensor portions and the reference resonance circuit through switching devices, and a detector detects an output of the oscillator. A discrimination portion discriminates an output of the detector and provides a discriminated signal to an output portion corresponding to the sensors and the reference resonance circuit. A synchronous device switches the switching device and the discriminator portion in synchronization.

Abstract: Detector comprising a sensor and a processing circuit connected to a load by means of two wires. Two switches (I1, I2) are arranged in series in a switching circuit leg (21), the ends of which (C, D) are connected to the detector terminals and the middle point (S) to a terminal (F) of the processing circuit. When operating (I1) is conductive and (I2) determines a parallel regulation of the voltage (V) at the processing circuit (12) terminals ; when in rest position, (I1) determines a series regulation of the voltage while (I2) is blocked.

Abstract: A machine operator control station circuit which uses capacitive proximity switches to replicate the function of mechanical switches used in prior art control stations. A monitoring circuit for monitoring the "on" state of the capacitive proximity switches used in a two hand industrial machine control station is disclosed. The circuit also reduces the chance of unintended operation of the machine being controlled as a result of emitted or conducted radio frequency interference which might be detected by the capacitive proximity switches. An isolation transformer provides an isolated power supply for the monitoring circuit. The monitoring circuit includes a first capacitive proximity switch for detecting the presence of one of the machine operator's hands, and a second capacitive proximity switch for detecting the presence of the other of the machine operator's hands. Each proximity switch has a monitoring circuit for monitoring the length of time the proximity switch remains in the activated or "on" state.

Abstract: A method of operating a relay includes shifting, by a predetermined time increment each time the relay coil is energized, the time in the sine wave of the applied AC power source at which the relay coil is energized. The method further provides for similarly shifting the time in the sine wave at which the relay coil is de-energized. When applied to a system having two relays, the method includes providing such shifting to both relays and further includes providing a predetermined time delay between the time one relay is de-energized and the other relay is energized.

Abstract: The invention prioritizes elevator service by an electronic lock and key circuit which uses a pre-existing capacitive touch button, an electronic key for receiving a 10 KHz first button pulse train from the face of the capacitive touch button and modulating said capacitive touch button pulse train with a signal of a preset frequency. A modulated first pulse train is provided back to the capacitive touch button face and an electronic lock for modulating a demodulated first pulse train received at the capacitive touch button face so as to provide a high priority hall call or a car call.

Abstract: A safety switch having first and second elements intended to be mounted on components of a safety enclosure that are moveable relative to one another. The first and second elements are in a predetermined relative position adjacent each other when the enclosure is in a closed condition and spaced apart when the enclosure is in an open condition. A source of magnetic flux is mounted on one element and a magnetically operable switch is mounted on the other element. The magnetically operable switch is arranged so as to be switched by the magnetic flux generated by the source when the elements are moved adjacent to each other. A pair of tuned circuits are mounted one in each of the elements, and a switching circuit is connected to one of the tuned circuits. The switching circuit is arranged so as to be switched when the elements are moved adjacent to each other.

Abstract: A timed contact switch apparatus has a conventional pushbutton placing a main switch in an actuated state when the pushbutton is depressed. A timing circuit is activated by the pushbutton to provide power to activate an electromechanical latch which holds the main switch in its actuated state while the timing circuit times out. Preferably the timing circuit operation is initiated by output of a Hall sensor which is controlled by a magnet whose position is mechanically linked to the position of the pushbutton.

Abstract: A material level sensing device for detecting when the level of unprocessed material has reached a predetermined threshold includes a contact-type probe extending from a housing into a retaining bowl where unprocessed material is collected before processing. Within the housing is disposed a proximity sensor. The housing itself is suspended from an overhanging support. When the material level reaches the predetermined threshold, the material displaces the material level sensor, which displacement is sensed by the proximity sensor. The proximity sensor then sends a signal to an external system indicating that the material has reached the threshold.

Abstract: A hand brake operated control device of a car includes an electrical control circuit having a normal-open switch positioned under a rear cam portion of a hand brake lever, a normal-close switch formed in a front portion of the hand brake lever to be operatively depressed by a push button of the hand brake lever, and an electromagnetic switch which is powered for protruding a core latch outwardly to retard a depression of an accelerator pedal of the car, whereby upon an upwardly pulling of the hand brake lever for braking the car, the normal-open switch will be closed by the rear cam portion of the hand brake lever to close the electrical control circuit to actuate the electromagnetic switch to protrude the core latch outwardly for retarding a depression of the accelerator pedal for preventing the driving of a hand braked car for protecting the car; and upon a depression of the push button of the hand brake lever, the normal-close switch will be opened as being depressed by the push button to thereby open the

Abstract: An improved electrical panel assembly of the type providing a plurality of receptacles for use with cable connectors and requiring that the connectors must be connected with their respective receptacles in a given order and disconnected therefrom in the reverse of that order. The panel assembly comprises a planar panel element having an opening therein for each receptacle and a receptacle mounting housing element behind each panel opening, constituting an integral, one-piece molding. Each panel opening is provided with a cover swingable between a closed position and an open position. The connectors and receptacles are of the known type having single contacts which lock together when the connector is mated with the receptacle and rotated a partial revolution. Polarizing devices are provided in association with each receptacle and each cable connector.

Abstract: Two opposed poles of a permanently magnetized circuit establish a relatively large air gap. An armature element (15) is displaceably interposed in the gap between these poles. The armature element establishes a first relatively small gap to one of these poles when in a first position of adjacency to the other of these poles, and the armature element establishes a second relatively small gap to the other of said poles when in a second position of adjacency to said one pole. Pole-fringing flux is manifested laterally of that one of the relatively small gaps which uniquely identifies the instantaneous presence of the armature in one of its two positions, and a detector of fringe flux at one of the two gaps (18) provides an indication of the positional status of the armature with respect to the poles.

Abstract: A detector of the two wire type with regulated voltage is disclosed, comprising a sensor and a switching device.The switching device comprises a series voltage regulation circuit, a parallel voltage regulation circuit and switching circuit. The latter receives the output signal from the sensor for alternately activating the series circuit in a first state of the signal and the parallel circuit in a second state of the signal.

Abstract: A proximity switch assembly is provided which has a base with a longitudinal axis. A sensing coil is mounted on the distal end of a probe on a front axial end of the base, and the base is adapted to be mounted to a machine which has a moving part, the position of which relative to the sensing coil is to be determined by the proximity switch. An electrical cable connector is rotatably mounted on the base and may be rotated into a plurality of positions around the axis. Conductors extend between the sensing coil and the electrical cable connector, and at least part are deformed spirally to permit rotation of the cable connector. A series of teeth are on the base and a locking spring moves into engagement with any of the teeth to establish the plurality of locked rotational positions.

Abstract: There is provided a detection system for detecting attempted entry onto the shaft-side roof of an elevator cab which includes a power supply for supplying power to the system, a proximity detector in electrical connection with the power supply which is disposed proximate the roof of the cab for detecting an object entering a zone of detection including the top of the cab, the detector in a preferred embodiment including an optical source for generating a detection beam and a corresponding optical receiver for receiving the detection beam when it is diffused by an object entering the detection zone and for providing a detection signal when the object enters the detection zone, and detection indicator responsive to the detection signal for indicating an attempted entry.

Abstract: Method for determining qualities and/or frequencies of electrical tuned circuits. The method includes the steps of exciting the turned circuit with a switching pulse which has a short rise and fall time as compared with a period corresponding to the resonant frequency of the circuit, and evaluating the oscillation dying out after the switching impulse.

Abstract: A flipper game apparatus comprises an inclined playing surface on which are disposed switches adapted to be operated by balls rolling over the playing surface and encountering the switches. A ball is introduced on to the playing surface by a respective player and rolls down the playing surface towards the outlets, passing the striker switches as they do so. The outlets are flanked by flippers which can be actuated by a respective player. So that two players can play at the same time and in mutual interreaction, the game uses balls of first and second different types, while operatively associated with at least some switches is a sensor which is responsive only to one type of ball. A circuit distinguishes the types of balls from each other upon actuation of a switch, by means of the respective sensors.

Abstract: A control system for a chiropractic adjustment instrument comprising a microprocessor programmable to control various parameters of an adjustor head to be driven against the spinal vertebrate of a patient. A solenoid is associated with the adjustor head which is energized by a capacitor. The capacitor is charged by a charging circuit to the programmed voltage level. The pressure of the adjustor head against the patient is sensed and when the pressure reaches a predetermined level, the capacitor is discharged to the solenoid to drive the adjustor head against the spinal vertebrate of the patient.

Abstract: An apparatus for controlling the intensity and on/off status of an incandescent light bulb as a function of the proximity of an object to a sensing plate. The frequency of a signal is varied from a nominal value when the presence of the object is sensed. A pulse is generated having a duration proportional to the time over which the signal if varied from its nominal frequency. The duration of the generated pulse, in relation to a pulse of predetermined width, is used to control a gated oscillator. The output of the gated oscillator is counted. The count obtained is used to control the operation of a TRIAC, which in turn connects power to the incandescent bulb.

Abstract: A proximity-switch circuit operates a main switch TH1 to pass an ac supply through an external load when a metallic object is near a coil L1 that is part of an oscillator circuit. The oscillator circuit is connected to a level detector circuit controlling the switch TH1. The circuit is powered by a power supply stage that includes a storage capacitor C7, for which the charging current is controlled by a transistor T10 and a MOSFET T11. Upon initial application of the ac supply, the level-detector circuit is overridden by a circuit that includes capacitor C3 and transistor T4 until a predetermined period of time has elapsed, so as to prevent the generation of erroneous "on" signals before the oscillator has stabilized.

Abstract: The circuit operates a main switch SCR to pass an a.c. supply V through a load L when a metallic object is in proximity to coil L1. Coil L1 is driven by an oscillator comprising transistor T2 and associated components. SCR is gated on simultaneous occurrence of an output from level detector T3 and a signal from T5, these being ANDed by T4. The timing of the signal from T5 in the supply cycle is governed by the RC time constant of C4,Z1,R14 and is such that the power supplied to the oscillator and level detector is the minimum necessary, for a wide range of supply voltage and load current.

Abstract: An electronic switchgear operating contact-free, having a presence indicator which can be externally affected, a switching amplifier disposed downstream of the presence indicator an electronic switch controllable by the presence indicator via the switching amplifier a supply circuit for the provision of the supply voltage for the presence indicator and for the switching amplifier and a delay circuit preventing activating pulses. The supply circuit has a voltage and/or current regulator. In the electronic switchgear in accordance with the invention activating pulses are prevented with a higher degree of assurance than in the state of the art, namely based on the fact that the delay circuit becomes active, i.e. the delay time starts, only after the voltage and/or current regulator has started to operate.

Abstract: Proximity sensors for detecting the presence of metal objects such as sheet metal workpieces within workpiece engaging devices such as grippers and shovels. The proximity sensors are jacketed in a stainless steel casing, making them rugged and resistant to impact damage. Monitor circuits are used with the sensor which enable the devices to sense objects through their metal casing.

Abstract: There are provided a first switch which is switched to the on state or the off state in association with a displacement of an actuator which causes a displacement by a contact with an object and a second switch which is switched to the on state or off state later than the first switch in association with the displacement of the actuator. A switch output is produced and an abnormality is detected in accordance with the on and off states of these switches.