Abstract: In order to improve a proximity switch insensitive to interference fields r detecting the position of a machine element with at least one sensor which generates in the proximity of a machine element standing in a position to be detected a total signal having a detection field signal component caused by the machine element and an interference field signal component caused by the interference field and transmits it to a circuit which converts the total signal into an output signal, such that both the gradients of the detection field generated by the machine element and the gradients of the interference field do not affect response of the proximity switch, it is suggested that the conversion of the total signal into the output signal be carried out by the time dependence of the interference field being determined, by a corresponding sequence of scanning pulses being obtained therefrom and the first signal being scanned with these, and by a value which is determined thereby resulting in an output signal indicatin

Abstract: A low power switching circuit for delivering electrical power to a load includes a rectifier network connected between the hot leg of the AC utility supply and the earth ground of the utility supply. A neon lamp interposed in the rectifier supply limits the current drawn through the rectifier to less than the 500 .mu.a code limit for current flow to ground. A high sensitivity, dual coil, bistable relay is connected between the hot leg of the AC supply and the load, which is connected to the neutral leg of the same supply. A capacitor network is connected to the DC output of the rectifier to store sufficient power to operate the relay, and a transistor switching network is connected to deliver the power from the capacitor network to the relay upon receipt of a trigger signal. A "smart" switch such as an area occupancy sensor may be connected to the transistor switching network to provide the trigger signal to cause the relay to switch AC power to the load.

Abstract: The present invention is a safety feature in an automatic garage door operator. In the prior art a single momentary contact push button, either directly connected to the automatic garage door operator or connected via a radio transmitter, is used to control door operation. In accordance with the present invention, closing the garage door requires continuous actuation of the momentary contact push button from the time the operation is begun until the door is fully closed. Any interruption in this continuous operation causes the automatic garage door operator to reverse and fully open the door. Thus continuous attention of the operator is required, thus enhancing safety because of the attention of the operator.

Abstract: An overload protector for a robot arm has an open-topped cylinder into which a piston is inserted. The piston is held against a circumferential stop surface of the cylinder by compression springs.

Abstract: The invention relates to a type of proximity sensor. In one form, two sinusoidal signals travel along two transmission lines near an object. When the distance between one or both of the lines and the object changes, the speed of travel of one or both of the signals changes. There is a correlation between the speed change and the distance, thus allowing one to infer distance from speed change. One way to measure the speed change is to measure the phase relationship between the two signals.

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

Abstract: A safety system for an electrical panel assembly providing receptacles for use with cable connectors. The connectors and receptacles are of the known type having single contacts which lock together when the connector is mated with its receptacle and rotated a partial turn. Polarizing devices are provided in association with each receptacle and connector to assure proper mating. The panel assembly is provided with mechanical interlocking devices determining the order in which the connectors are connected to and disconnected from their receptacles to assure that ground makes first and breaks last. The safety system comprises an AC to DC converter/voltage regulator capable of converting 120 volts to 600 volts AC or DC to 12 volts and 115 volts DC. The converter/regulator has a pair of inputs connected to the contacts of any two power receptacles or the contacts of a neutral receptacle and a power receptacle of the panel.

Abstract: A method and apparatus for sensing the proximity of a target object includes a sensor inductor (L.sub.S, 38) connected in series with an identical reference inductor (L.sub.R, 36) between an input and ground to form an inductive divider network. The sensor inductor is positioned so that its inductance can be varied in response to the proximity of a target object (14, 40) while the inductance of the reference inductor remains constant. Voltage pulses are periodically applied to the divider network from a source (32, 34) and divide across the reference and sensor in accordance with the ratio of the inductances, as varied or not by the presence of the target object. A detector (30) monitors the output of the divider network and provides a target status signal indicative of the proximity of the target object. For low-power operation, the detector circuit and conductive divider network are periodically and momentarily energized in synchronism.

Abstract: The present invention utilizes a latching relay having on and off inputs for controlling power to a load. The on and off inputs of the relay are controlled by pulse generators which are in turn controlled by an occupancy sensor circuit. These pulse generators provide pulses when movement is initially detected in a room and when no movement has been detected for a predetermined time, respectively. The outputs of the pulse generators are coupled to an isolation circuit which isolates the power supply for the occupancy sensor from the pulses during each pulse to prevent damage to the power supply.

Abstract: A proximity switch has at least three Hall effect magnetic field sensitive transducers mounted in a transducer housing and has at least two magnets mounted in a magnet housing. The transucers produce logic signals, and a logic circuit responsive to these logic signals activates an electrical switch only when the magnets are in a proper position relative to the transducers. The electrical switch may be used to control a machine, and the machine is not activated until the proximity switch is activated.

Abstract: A control device for controlling the operation of an object of cooking such as a stove or the like. The presence of a user in the area of the stove is detected. When the user is present, the stove operation is enabled. After the user has been absent from the area for a first predetermined time, the stove is temporarily disabled, an again enabled when the user enters the area. If the user is absent from the area of the stove for a second predetermined time, the stove is permanently disabled, so that it cannot again be enabled until manually reset.

Abstract: A non-contact proximity switch with an oscillation circuit (L 1, C 1) which is activated in a step-like manner, has a reference voltage source (6) which produces at least one reference voltage level (U.sub.ref) and has at least one comparator (5) which compares the amplitude of the transient response with the associated reference voltage level (U.sub.ref) in order to be able to detect at least one value that is distinctive for the time curve of the decaying oscillation from at least one transient response of the oscillation circuit (L 1, C 1) after such an activation. At least one counter (7, 10) counts, at least within a portion of the decay period of the transient response, the number (DA) of the half-waves of the transient response, the peak of which deviated from the associated reference voltage level (U.sub.ref) in one of the two directions.

Abstract: A protective housing and mounting apparatus for simultaneously protectively enclosing, and mounting to a given surface, a generally cylindrical capacitive-type proximity sensor having a substantially solid and unbroken external surface and an electrode member at one axial end thereof. The protective housing and mounting apparatus comprises a one-piece integrally formed member of a durable, moldable plastics material, including an end surface configured for complementary mounting upon a given surface and a protective body portion extending from this end surface for surroundingly housing an end part of the sensor proximate the axial end thereof at which the electrode member is located. The body portion has a cylindrical open-ended bore therein for receiving an end part of the sensor and this bore extends to a point closely spaced behind the end surface.

Abstract: A proximity switch operating on a non-contact basis including a terminal-side main part set in a base housing and a sensor part set in a probe. To enable a selection of the response direction, the probe may be adjusted in different positions on the base housing, to which the probe is designed or arranged as a component insulated on all sides which, by way of individual in-built core coils is inductively coupled with a core coil set in the base housing.

Abstract: A movable storage unit control system is provided with: a leading edge safety tape switch for contacting it to bring a driven unit to a stop; a processor for generating move and stop command signals; a plurality of circuits through which test signals are transmitted under control of the processor and which are returned to the processor coincidentally with their transmission through a current sensor if the circuit tests good; a procedure for having the processor address a test signal to a nonexistent circuit to determine if the current sensor has failed and is allowing return of signals when it should not; circuits for setting minimum and maximum speed of the motors that drive the storage units; a circuit for setting the intensity of dynamic braking of the drive motors; and, a watchdog circuit that shuts down the processor upon occurrence of intense temporary electrical noise or software execution errors and is involved in causing the processor to shut down and block all commands to the system if the processor

Abstract: An isolation transformer is provided by a primary conductor formed on an insulating layer above a secondary conductor formed on a chip therebelow, with flux lines coupling between the primary and secondary conductors to provide transformer action through the insulating layer therebetween. The primary is formed by a serpentine pattern having a plurality of parallel strips transverse to a plurality of parallel strips forming the secondary conductor. The secondary conductor may be formed on an extra insulating layer on the chip substrate.

Abstract: A cutting machine comprising a housing having a base, a motor carried by the housing, a knife blade having a cutting edge and carried by the housing for reciprocal motion generally normal to the base in response to operation of the motor, a presser foot movably carried by the housing located in spaced relation to the blade cutting edge and movable toward and away from the base, and characterized by an elongated guard connected to the presser foot and located closely adjacent the blade edge and guided supported in the housing for movement along the blade edge in response to movement of the presser foot toward and away from the base. There is included an arrangement for releasing the presser foot when the motor is turned off allowing the pressure foot to rest on or near the base and maintain the guard in place along the blade edge when the motor is off.

Abstract: A touch operated electronic switch for alternating current including a full wave rectifying bridge and two unidirectional current electronic switches one being mounted in parallel with said bridge input and the other being mounted in parallel with said bridge output, each unidirectional current electronic switch being such a silicon controlled rectifier which can be triggered by a touch plate. Said bridge input poles are the two external connections of said A.C. switch. Said unidirectional current electronic switch inserted between said bridge output poles is combined with a low inertia accumulator of electrical energy such as a capacitor mounted in parallel or an inductance mounted in series therewith. A device comprising a neon indicator and its dropping resistor is mounted in parallel with said bridge input so as to faintly light in transparency the touch operated electronic switch for A.C. when it is turned off.

Abstract: In a controlled-access apparatus for agricultural food industries, means is provided within the space located between the rotary tool-holder and the edge of the opening of the vessel of the apparatus for a protection and access-control device which performs a double function, namely that of protecting the user against accidental bodily injuries and that of allowing penetration of/or access to agricultural food products or ingredients, utensils or instruments having predetermined characteristics such as zero electrical conductivity and nonmagnetic properties.

Abstract: A proximity switch comprises two magnetic field sensors for detecting an roach of a machine having a magnet. The two sensors are arranged in such a way that one of the sensors is at a smaller distance from the machine than the other sensor when the machine is in a detectable distance so that each of the two sensors responds to the approach of the magnetic field of the machine and outputs a detected signal based on the electrical output characteristics of the sensor. The detected signals from both sensors are fed to a differential circuit for generating a differential signal. In order to compensate interference field, the differential signal due to the magnetic field of the machine is set greater than the differential signal generated from the interference field. A circuit for converting the differential signal into an output signal is provided for the proximity switch.

Abstract: An electronic switch of the type having two external lines, one of which is connected to one pole of an operating voltage source in series with a load and the other of which is connected with the load. The switch comprises a sensor, e.g. an oscillator, responsive to proximity of an object thereto and has an output transistor operated by the sensor with blocking and conductive states selectively controlled by the transistor in response to the oscillator. A MOS-FET power transistor is in series with the output transistor and, to reduce the voltage drop in a conducting state of the electronic switch, a self-conducting MOS-FET is used as the MOS-FET power transistor.

Abstract: The position sensor constitutes a fixed planar board having disposed on the surface serpentine coil structures of relatively low resistance and inductance. The coils are driven in a resonance mode which provides a frequency output according to the position of a moving planar member. The second movable planar board has disposed on the surface thereof planar loop coil structures. The second board is moved in proximity to the first board to vary the resonance characteristics of the first coil according to the position of the second board with respect to the fixed board. In this manner the frequency output of the system is a function of the position of the boards with respect to one another. Other embodiments depict means for compensating the thermal drifts of the frequency with respect to temperature.

Abstract: An electronic switch includes a detector head in the form of a rectangular parallelepiped having a detecting surface and connecting members disposed on a corner thereof including a surface opposite to the detecting surface, the connecting members being identical in shape when the detecting surface is oriented in either a forward or lateral direction, the connecting members being symmetrically arranged with respect to an edge of the detector head, a head joint having an end to which the detector head is connectable by the connecting members and also having a rotatable annular connector on an opposite end thereof, and a switch box having engagement means for slidable engagement with the annular connector of the head joint so that the head joint can be rotatably mounted on the switch box. The detecting surface can be oriented in all of lateral directions by rotating the head joint.

Abstract: A device for interrupting electrical current flow in an automotive lighting system, whereby a squeezing action of an operating means having a fluid or gas contained in a sealed structure mounted on the circumference of the rim of a steering wheel, produces pressure differentials therein, which are converted into flashing signals emanating from the automotive lighting system, thereby eliminating the hazard occasioned by vehicle operator having to remove a hand from the steering wheel and eyes from the road in order to effectuate a flasher signal to nearby drivers, therewhile allowing a vehicle operator to effect the same from any point on the circumference of the rim thereof, by the squeezing action.

Abstract: This circuit includes a DC source in series with a load to be energized, the DC source also being coupled to a constant-current circuit coupled to the input of an output-signal-generating means. The latter produces an output signal in response to the detection by an associated sensor of a changing condition monitored by the sensor. When the signal-generating means detects a change, an SCR coupled to the DC source is turned on thereby by-passing all of the DC from said source around said constant current source. Simultaneously, the signal-generating means causes an associated LED to emit a light signal.

Abstract: A wire detector for semi-automatic wire stripper which responds to capacitance changes caused by sensing a capacitive object such as an exposed wire end and includes signal processing through an oscillator and amplifier circuit providing timer control for activating a relay driver circuit for an adjustable duration time period. The wire touch sensor circuit relay driver is then coupled through a mercury wetted relay which provides electrical isolation from external (switched) voltages to an air solenoid which, when actuated, allows the pneumatic mechanism of the wire stripper to cycle through its function of wire stripping.

Abstract: In a continuous printing plant a timer unit is provided with indication whenever a first control is operated to supply power to the printing plant and whenever a second control is operated to inch a new batch of paper into the printer. The timer unit commences a first timing operation of a first predetermined period whenever indication is received from the first or second controls and switches off power to the entire printer if no reset signal is received within the first predetermined period. A sensor detects the movement of a printed paper web between the printer and a set of takeup rollers and indicates the movement to the timer unit. The timer unit initiates a second timing operation whenever it receives indication from the sensor and switches off power to the takeup rollers if indication is not received from the sensor or from the first and second controls within a second predetermined period, thereby independently switching off the takeup rollers in the event of a failure in the printer.

Abstract: A high frequency oscillation type proximity switch, being an approach switch adapted for detecting the approach to or departure from the detector coil of a metal body, based on the change in output of the high frequency oscillator circuit, with the oscillator coil of the oscillator circuit as the detector coil, in which a small-diameter housing case is inserted in the cable interconnecting the detector head and the power source, the printed substrate for use as the signal detector circuit is provided in housing case and the housing case is filled with an insulation resin.

Abstract: An electronic pressure responsive switch comprises an activating element and at least two sensors. The activating element and the sensors are arranged to be relatively displaceable with respect to one another whereby the sensors each generate signals when the activating element assumes a predetermined position relative to a respective sensor. The switch further has an elastic diaphragm having a first face exposed to pressure to be sensed and a reverse second face carrying either the activating element or the sensors. The diaphragm is deformable by the pressure whereby the relative position between the activating element on the one hand and the sensors on the other hand is varied as a function of the pressure.

Abstract: An initiator for a contactless switch comprises a support section (3) and an adjacent, conical-shaped control section (5), which has a sensor surface (11) and is free to move into several positions with respect to the front side of the support section. In one position, the sensor surface is turned away from the support section and in other positions it is parallel to the lateral surfaces of the support section. The control section is equipped with a prism-shaped recess in which is fitted a fastening element (4). The fastening element can be rotated about a longitudinal axis (6) that is perpendicular to the front side of the support section, and the control section can be rotated with respect to the fastening element about a central axis (7) which extends in the direction of a diagonal across the lateral face of the control section.

Abstract: A motor brush wear indicator includes a probe embedded in a brush and connected in the primary circuit of a transformer for completing the secondary circuit when the brush has worn to a predetermined degree. An oscilator is coupled to the secondary of the transformer which in turn is connected to the gate of an SCR for providing a gate signal when the primary circuit is completed. A relay is connected to the anode-cathode circuit of the SCR for operating an indicating device when the SCR becomes conductive.

Abstract: The disclosure generally relates to a protective device for an electronic instrument wherein input and output lines to and from the instrument are always isolated from calibration input and output terminals. This is accomplished by placing reed switches on or closely adjacent the non-magnetic instrument front panel, the switches being arranged to connect one of the input lines and terminals to the instrument circuitry while disconnecting the others therefrom, this being accomplished under control of a magnet placed adjacent the switches during a calibration procedure. The switches are further arranged to short circuit the output test terminals in the unenergized switch state to prevent insertion of unwanted signal current or voltage in that state.

Abstract: A control apparatus for a pivotal/sliding roof panel powered by a reversible electric drive motor operative to move a roof panel from a closed position in a roof opening in a vehicle to either of a venting or an open position. The control apparatus includes a first, operable switch which connects electrical power in one of two opposite polarities to the electric drive motor. A sensor detects when the roof panel is in the closed position. A control device, energizable by the activation of the first switch and the output of the sensor when the roof panel reaches the closed position from either of the venting or open positions, switches its output to disconnect the drive motor from the source of electric power.

Abstract: A monitor for an electrically-controlled system is provided. A threshold detector senses the voltage variations in the system by means of an optocoupler. The system is disabled by a relay if a voltage level does not meet a predetermined parameter.

Abstract: A proximity switch, operable without physical contact and having an elongated columnar housing which has, perpendicular to its principal axis, a cross-sectional shape with two orthogonal axes of symmetry. The housing is divided into at least two parts and the parts are joined at three abutting surfaces. One of the abutting surfaces extends in the plane of the principal axis and the others intersect the first surface, extending at angles of 90.degree. thereto. The greatest length of the first abutting surface, measured in the direction of the principal axis, is the same as the distance between the principal axis and the outer surface of the housing. With this arrangement, it is possible to arrange the sensor head carrying the sensor operating surface so that the operating surface lies on the longitudinal axis or at 90.degree. to the longitudinal axis in such a manner that the sensor surface does not extend beyond a generatrix of the outer surface.

Abstract: A radio transmitter is protected against the possibility of initiating transmission without the radio being connected to a load by having a switch that controls a push-to-talk key line that is only enabled when the antenna load is connected to the transmitter.

Abstract: An electrical switching device for use on machinery to prevent machine operation unless safety guards or the like are correctly positioned comprises two separate parts one part including at least two Hall effect devices which respond to magnetic poles of opposite polarity and electronic switching means which is actuated only when all the Hall effect devices are triggered simultaneously, and the other part including a corresponding number of magnets positioned to actuate the respective Hall effect devices when the two switch parts are placed in close proximity and predetermined orientation. The switch is substantially tamper proof and a control circuit can detect any unauthorized attempt to override the switch.

Abstract: Inspection apparatus is especially useful to verify the presence of metal parts such as pull tabs on can-production lines and to shut down lines not only if parts are missing or misplaced, but also if the sensors are shorted or the timer switch or circuit operation has otherwise been disturbed. Four stages of operation are coordinated with the mechanical progress of the machine, regardless of its speed of operation; these stages are the activating and deactivating of sensors (usually just before and just after a mechanical operation), then on switching a timing switch to low, and then on switching it back to high just before the sensors are again activated. At and after the stage of deactivation, the sensors are read for actual lack of signals, and latches of their signals during activation are also read to determine whether the parts were actually sensed. The signal to read is turned off when the timing switch goes high.

Abstract: A fail-safe relay system for use in infrared security barriers or other apparatus producing a sensing signal so as to control the de-activation and permit the re-activation of an interconnected device; such as a machine press. The relay system uses two relays with contacts in series in conjunction with electronic circuitry. Safe-start operation for preventing reactivation of the interconnected device if any unsafe condition exists, including failure of either pair of relay contacts to open when an unsafe condition is sensed, is also accomplished.

Abstract: In a crane system for moving a cargo container, an improved system for maintaining the container in a locked relation against a spreader assembly having a plurality of proximity sensors which initially control the ability of said system to lock the container to said spreader, includes a relay connected so as to be actuated by the initial coupling of power to the locking solenoid, such relay acting to maintain power to the locking solenoid even if one or more of the proximity sensors subsequently changes state. The system further includes another relay operatively connected to restore the system to an operative condition after a loss of power has been experienced, such relay functioning to restore power to the locking or unlocking portion of the system, once power has been reestablished, independent of the state of the proximity sensors.

Abstract: Apparatus for monitoring the motion of a movable element, such as a rotatable shaft, comprising sensor means for producing a series of repetitive pulses in response to the motion of the movable element, ramp generator means for producing an increasing ramp signal, the ramp generator means including means for resetting the ramp signal to a starting level in response to each of the pulses, level detector means operable in response to the increase of the ramp signal above a predetermined level, and control means for performing a control function in response to the operation of the level detector means.

Abstract: A switch assembly, especially for electronic contactless or proximity switches comprises a substantially two-part housing including the housing bottom and housing top which are separable from one another. The housing parts interfit to form a generally rectangular parallelepipedal structure provided at one end with a threaded connection for a threaded connector, pipe or conduit through which conductors may be passed to connect to the electronic device within the housing. The bottom housing portion is provided with the connecting circuitry while the top housing portion, interfitting with the bottom housing portion, has a part overhanging the latter and provided with the plug connectors forming a detachable electrical connection with the connecting circuitry permanently received in the lower housing portion. The upper housing portion contains all of the switch circuitry in its receptacle.

Abstract: The control includes approach and safety mat switches to which are applied alternating current voltage. Each of the switches are coupled to respective high gain binary output, solid-state amplifiers which change state upon alternation of two different input voltages being compared. Upon closure of the approach mat switch, the corresponding binary amplifier is caused to change state which in turn changes the state and output signal of a third like amplifier. This output signal causes the energization of an electric motor which opens the door. Opening of the approach mat switch followed by closing of the safety mat switch, the corresponding amplifier changes state and holds the third amplifier in its state which causes energization of said motor, thereby holding the door open. A time delay circuit is connected to the third amplifier for delaying the change of state of the third amplifier after the approach and safety mat switches are opened.

Abstract: A sewing machine is provided with a safety device which protects an operator's fingers from the needle and includes a ring suspended over the presser foot of the machine. The suspended member is movable by finger pressure applied thereto in any direction and when so moved, completes an electric circuit to shut off the machine.

Abstract: Electrical systems (20), such as an electric propulsion system for a vehicle (100) for example, often have electric power available for components of the system (20) when non-operating conditions occur, such as turning off the vehicle key switch (38). An electronic control circuit (10) is provided for controllably interrupting power flow to the system (20) and disabling the system (20) in response to any of a plurality of non-operating conditions.The electronic control circuit (10) includes a transistor (26) having a base (30), an emitter (28), and a collector (32) and being energized to an on condition in response to the base (30) receiving a preselected signal. The signal is controllably delivered to the base (30) in response to a first switch (38) being open and is controllably delivered to the base (30) a preselected time after a second switch (68) is opened.

Abstract: In a two-wire proximity detector, a supply to a probe and auxiliary apparatus is obtained from a bridge rectifier through two regulating circuits of which the first operates when an inhibitor transistor is conducting, while the second operates when the inhibitor transistor is blocked. The first regulating circuit is of the ballast type. The second regulator circuit is of the type which produces a delay in the triggering of a switch thyristor (9). The detector can be fed with an alternating voltage variable over a wide range.

Abstract: Load and socket arrangements are disclosed wherein contacts within a socket are connected to an electrical energy source by a magnetic reed switch responsive to magnetic material carried by the load. The socket is disconnected from the source and incapable of producing electrical shock when the load is removed. In one embodiment, a lamp has a magnetic insulator separating its shell and base terminals. In another embodiment, a connector plug has a magnet carried within the body of the plug. Various sockets and circuits for connecting reed switches in the sockets are disclosed. Also disclosed are magnetic adapters for attachment to conventional lamps or plugs so that conventional loads may be used in the sockets.

Abstract: There is disclosed an automated flush system which senses the approach and departure of an object or person and produces control signals indicative of said approach and departure, respectively. A discriminator unit receives and decodes the approach and departure signals to produce a flush control signal which controls a flush valve in the flush system as a result of the occurrence of the departure signal following the occurrence of the approach signal.

Abstract: A can lid forming apparatus includes means for attaching a can opening key. A proximity field sensor is mounted in a doming die of the apparatus and generates a pulse logic signal as a can lid with a staked key is formed by the doming tool. A timing disc rotates in synchronism with each cycle of the tool and generates a pair of logic signals. A key monitor circuit is connected to respond to the signals to establish a latch, check latch and reset latch sequence for each cycle of the tooling. If the latch is not set, an appropriate output signal is generated indicating a key is missing from the lid. If the latch is not reset after being set, indicating a build-up of aluminum fines or the like on the probe, an appropriate signal is generated by a preconditioned probe monitoring curcuit.

Abstract: A machine guard installation makes use of a proximity detector system including a passive time circuit on the guard. The timed circuit includes a coil which is magnetically coupled to a further coil only when the guard is in its operative guarding position. The further coil forms a part of a positive feedback loop of an amplifier in an active detector circuit, which oscillates only when the coils are coupled as aforesaid.