Abstract: An apparatus in accordance with the present invention comprises an electronic component, a sensing element, a power supply element, and logic. The sensing element is coupled to the electronic component. The sensing element is configured to sense an occurrence of an event and to transmit a data signal indicative of the occurrence. The power supply element is configured to receive energy from the sensing element and to power the electronic component with electrical energy. The electrical energy is derived from the energy received from the sensing element. The logic is configured to receive the data signal from the sensing element and to control operation of a component of the system based on a value of the data signal.

Abstract: A protective relay utilizes a mechanism that averages a buffer of anticipated optimal closing times to provide for a more accurate method of determining when to permit the issuance of a breaker close signal. This is used in a Breaker Close Time (BCT) feature of performing synchronism checking in the electrical power industry (for example, in a generator protection device).

Abstract: A trip unit connection tester (10) is arranged to test the electrical connections (12) and (14) between a trip unit (16) and actuator (18) mounted within a circuit breaker (20). Tester (10) includes a power source (64) including a positive lead (68), and a negative lead (70). The positive lead (68) is coupled to a two-loop switch (58). The two loop switch (58) toggles between a first loop (98), and a second loop (100). The first loop (98) includes the power source (64), the two-loop switch (58), and the energy storage element (82) wherein the energy storage element (82) stores energy coming from the power source (64). The second loop (100) includes the two-loop switch (58), and the energy storage element (82), connections (12) and (14), and the actuator (18), wherein energy stored within the energy storage element (82) is released to the actuator (18).

Abstract: A relay test set of reduced size and weight includes a small, highly efficient voltage and current source. The test set incorporates a Class D switching amplifier design that greatly reduces the size of the power source needed to inject the correct voltage and current into the secondary inputs of a protective relay. To further reduce the size, weight and cost of the relay test set, a single voltage amplifier is used to drive both voltage and current secondary inputs of a protective relay. In so doing, this test set then becomes both a voltage transformer and current transformer simulator utilizing a single voltage power source at reduced size, weight and cost. To make the power source variable while maintaining accuracy, a microcomputer module is used to monitor both current and voltage being injected into the protective relay.

Abstract: A method is provided for determining magnetic characteristics of an electrically controlled solenoid. The method includes providing an electronically controlled solenoid having an armature, a stator and a coil operatively associated with the stator. The armature, stator and coil define a magnetic circuit. The armature is spaced from the stator to define an air gap between the armature and the stator. Current to the coil is ramped in a generally linear manner over a period of time to define a known current curve. A resulting rate of change of flux in the magnetic circuit is observed and recorded at certain points along the current curve. In accordance with another aspect of the invention, flux in the magnetic circuit is ramped in a generally linear manner over a period of time to define a known flux curve. A resulting current in the coil is observed and recorded at certain points along the flux curve.

Abstract: A method and apparatus for determining the position of the main contacts of an automatic transfer switch, without need for special position contacts, by monitoring for the presence of voltages at the normal source voltage contacts, the alternate source voltage contacts, the normal source coil control voltage contacts and the alternate source coil control voltage contacts of the automatic transfer switch, and providing an indication of switch position in response thereto.

Abstract: Electrical consumers receive load current from a supply voltage via two or more power switches. A false-closure detection device includes a measuring device and a diagnostic device for the detection of faults. The measuring device is connected parallel to the power switches and the electrical consumer lying in series with the switches. A diagnostic voltage is compared as the output signal of the measuring device with a reference value for the detection of false closures in the load circuit.

Abstract: In the present method and apparatus for processing a vibro-acoustic signal emitted by a high-voltage switching system, the vibro-acoustic signal is converted into a digital signal. The digital signal is rectified and the resulting rectified signal is applied to a convolutional filter with a spectral window to produce a smoothed signal. The smoothed signal is decimated to produce a decimated signal representing an envelope of the vibro-acoustic signal. A time realignment of the decimated signal is carried out with respect to a reference signature to produce a realigned signal. Time deviation values generate an alarm if they exceed a limit threshold. The realigned signal is added as a factor of means providing a reference signature and an actualized signature. Variances of the realigned signal are calculated with respect to the reference and actualized signatures.

Abstract: An electromagnet exhibits in its energization curve (I=f(t)) a characteristic feature or indicator, for example, in the form of a dip (1′, 2′) in the energization current. This indicator is used to control the operation of the magnet, for example, to synchronize its operation with that of another magnet. In a loom the operation of a weft stop magnet positioned next to a weft prewinder may be synchronized with the operation of a solenoid driving a valve that supplies air to the main weft insertion nozzle and/or relay nozzles. A magnet may also be controlled with reference to rated operation values so that its actual operation value coincides with the rated value or values or at least is maintained within a permissible tolerance range of rated values. The control takes place in closed loop fashion, for example, through the main loom control.

Abstract: A device for detecting a fault in a solenoid valve prevents a feeding system from supplying a drive current to a solenoid valve coil which actuates the solenoid valve from being damaged at the time of detection of the fault. The feeding system is provided with a first switch installed between one end of the solenoid valve coil and a battery, a second switch installed between the other end of the solenoid valve coil and a ground, and a plurality of wires for connecting the battery, the first and second switches and the solenoid valve coil. A test power supply system is connected to one end or the other end of the solenoid valve coil and supplies a micro test current to the solenoid valve coil when a current from the battery to the solenoid valve coil is cut off.

Abstract: The present invention relates to a method of monitoring electrical wear on selector switch disconnectors in a bay of a high voltage station that includes a set of distribution busbars connected to at least three electrical circuits constituted by an inlet bay, an outlet bay, and a bay for coupling together the busbars.

Abstract: A sensor is provided for automatically detecting the presence or absence of an electronic device which interfaces with other devices via an information signal. The sensor comprises a receiving connector which receives a mating connector associated with the electronic device to electrically and physically connect the device to the sensor and to another device. The receiving connector includes a terminal to which the information signal is applied. The sensor also comprises a sensing circuit connected to the terminal of the receiving connector for detecting whether the information signal is present at the terminal. The sensing circuit generates an output signal which indicates when a mating connector is received within the receiving connector, and thus whether the electronic device is present, in dependence upon whether the information signal is detected at the terminal.

Abstract: A solenoid actuation detection device for detecting actuation of an armature of a solenoid includes a sensor for sensing electric current flowing through a solenoid, a peak detector for receiving the sensing signal and for creating a peak signal from the sensing signal, and a comparator for comparing the two signals to determine when an armature of the solenoid was actuated.

Abstract: A short between terminals of a linear solenoid controlled by an electronic control in an automatic transmission is detected by sensing when a PWM duty ratio set by a feedback control operating the linear solenoid is less than a reference duty ratio. The reference duty cycle is calculated to be between a range of expected normal duty ratios in the absence of the short and a range of expected short duty ratios in the presence of the short.

Abstract: Switching components with contact parts that are mounted on a contact carrier in a switch housing may include devices for monitoring the contact erosion. The contact carrier may be split (sub-divided) and contact parts can be slotted at the rear and mounted on the sub-divided contact carrier. Thus, the oscillation response (vibration response) of the contact carrier in particular can be used as a measure of the erosion of the contact parts.

Abstract: An apparatus for remotely operating an ignition switch mounted on the steering column of an automobile includes a motor mounted on the floor or other surface of the automobile away from the steering column, such that the steering column does not bear the weight of the motor. A drive cable is connected to the motor, and the drive cable is also connected to a coupling which is mounted on the steering column and which is connected to the ignition switch. The coupling translates rotational motion of the drive cable 90.degree., so that the coupling and drive cable do not unduly project straight out from the steering column and hence do not interfere with other components, e.g., shift levers, that are mounted on the steering column. A position sensor generates a signal representative of the position of the ignition switch, and the signal is received by a controller. In turn, the controller activates the motor as necessary to establish and/or maintain a desired position of the ignition switch.

Abstract: A device for monitoring the switch position of a switch including an auxiliary voltage source, which is connected to the switch, a device for converting the switch position into an electrical signal, a device for transmitting the electrical signal and a device for evaluating the transmitted information. The converting device uses a pulse-duration modulation, the duty cycle of which becomes higher as the voltage U.sub.0 of the auxiliary voltage source becomes smaller. This enables the monitoring device to be used for different auxiliary voltages, without any need for adaptation.

Abstract: In order to provide a dependable check on the reliable functioning of contacts of switches or relays which control a control device, to ascertain whether they occupy the desired rest contact position and/or have a sufficiently high mains voltage, the rest contacts of the two switches can be connected in parallel by way of a respective electrical resistor to a pole of the voltage source and both resistors can be connected in series to a charging capacitor which, upon the attainment of a given electrical charge or voltage (threshold voltage) activates the control device and in particular feeds a threshold switch or itself serves as such.

Abstract: A method for determining mechanical parameters of an electric switching device exposed to environmental influences in which a measuring transmitter is provided for detecting the speed of a component of the drive means of the switch device at at least two consecutive times. In the case of vacuum power switches, the time of contact of the switch members and the time of the latching in the switched-on condition are preferably considered. If measurement values from comparative measurements of a given number of switches are available, the maximum intensity of a given environmental influence at which test sample can reliably operate is determined from a measurement of a test sample under normal environmental conditions.

Abstract: A method for sensing the on/off status condition of a power switch in an appliance includes applying a series of alternating current (AC) voltage pulses to an appliance with an on/off switch that are synchronized to a source of AC power, sensing the presence of any series of AC current pulses that result if said appliance switch is closed, analyzing any AC current pulses detected in the step of sensing to determine if they resulted from the application of the AC voltage in the step of applying, and outputting an on/off status indication for the appliance switch.

Abstract: Electrical and mechanical operation of a bistable magnetically latching solenoid is diagnosed by monitoring induced voltage across the one of a pair of solenoid coils not energized. Energization of one of the pair of coils induces voltage across the other of the coils not energized and plunger actuation in response to energization induces another voltage therethrough. The various induced voltages are distinguishable as between those caused by energization of a coil or motion of the plunger.

Abstract: A method for testing a valve being driven by an electromagnet having a electromagnet armature, includes determining a value of current in the electromagnet as a response current, at an instant when motion of the electromagnet armature of the valve begins during a switching action of the valve. A force acting through the electromagnet upon the electromagnet armature is determined from the determined response current, at the instant when motion of the electromagnet armature begins, by means of a calibration function, as a response force and as a standard for the condition of the valve. An apparatus for testing a valve being driven by an electromagnetic having a electromagnet armature and an electrical circuit, includes a current meter in the electrical circuit of the electromagnet. A computer is connected to the current meter.

Abstract: A circuit which gives a continuous voltage output indication of whether a contact is open or closed. The circuit senses the voltage across the contact to detect whether the contact is open or closed. When there is a significant voltage, the circuit indicates that the contact is open. When the voltage is negligible, the circuit indicates that the contact is closed. Alternatively, the current through the contact can be sensed to provide an indication of whether the contact is conducting or not. The circuit can be used to indicate the welding close of a relay contact in which case power to the load can be turned off or the contact can be opened by other than normal corrective actions. One application is to discontinue closing movement of a garage door when the motor relay switch does not open as desired, but there are innumerable other applications.

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: An apparatus and method for testing a switch having an actuating plunger, the switch undergoing a switch event in response to the actuation of the actuating plunger includes a switch nest and clamp assembly for holding the switch at a precise and predetermined location and a motor driven plunger actuator for applying force to the plunger thereby to actuate the switch. The switch test station further includes a pressure sensor coupled to the plunger actuator which measures the force being applied to the plunger during switch actuation. An electrical sensor couples to the switch nest and measures the electrical characteristics of the switch while a microcomputer responsive to the pressure sensor and the electrical sensor determines the mechanical displacement of the actuating plunger at a switch event.

Abstract: The invention relates to a data input module for inputting data, by means of electrical contact, to a monitoring/control module, the module including a first voltage feed input (1) and a second voltage feed input (2), which inputs are intended to be subjected to a potential difference which is optionally variable, and a plurality of contacts (3) each of which has a first terminal (4) connected to the first input via a first resistor (14), and a second terminal (5) connected to the second input (2), each contact being designed to open or to close an electric current path between its terminals. The module further includes detection members (7) respectively associated with the contacts. Each detection member is organized to detect the presence or the absence of current flowing between the terminals of the contact with which the detection member is associated.

Abstract: The present invention is directed to a method for determining actual tripping characteristics with the aid of a test apparatus in which test parameters are input with the aid of an input unit. The aim is to specify an appropriate method which works particularly quickly and precisely. This can be achieved when a theoretical tripping characteristic of the respective protective relay is stored in the test apparatus. Each measurement point of the actual tripping characteristic is determined on a locating straight line, the starting point for the measurement being a point of intersection of the locating straight line with the theoretical tripping characteristic. In this case, the locating straight line dissects the theoretical tripping characteristic at an angle. The angle is situated in a range from 60.degree. to 120.degree., 90.degree. being preferred.

Abstract: A method of using calibration instrumentation for determining the operating and reset points for a device having an input and an output. An initial courts test is conducted with a first variable input to establish value areas wherein device state changes occur. The method is suited for calibration testing of industrial instrumentation and is effective when operating and reset points need to be accurately searched over a wide range while minimizing the time required for testing.

Abstract: Load driver system (10) preferably uses a microprocessor controller (20) to generate write/read signals and command signals received by a circuit at write/read and command/status input terminals (16, 17). The circuit (15) responds to the input signals and controls a semiconductor switch (11) that controls the operative state of a load (14). The circuit (15) includes a load shorted high detector (28), a load shorted low detector (29) and a load open detector (30) which are used to detect various faults and provide a predetermined sequence of logic states at the command/status input terminal (17) during read cycles implemented by the controller (20). Thus one input line (terminal 17) is used to both send commands to the semiconductor switch (11) and receive a sequence of logic states indicative of various fault modes. This permits the controller to determine which of several types of faults, if any, has occurred, while minimizing the number of controller-circuit interconnections.

Abstract: A circuit configuration is provided for monitoring an electromagnetically actuated device, such as an electromagnetic clutch. The circuit comprises a switchable power source connected to the winding of the electromagnet; the power source supplies a composite voltage formed of a direct voltage part and a periodic alternating voltage part superimposed on one another. Engage and disengage signals are issued for the clutch and the direct voltage part assumes distinctly different levels in dependence on the engage and disengage signals. A precision resistor is connected in series with the winding of the electromagnet and a voltage sensor is connected at a node between the winding and the precision resistor. An evaluation circuit is connected to the voltage sensor for evaluating the alternating voltage part acting on the precision resistor and receiving therefrom information regarding the functionality of the electromagnetic device.

Abstract: The invention relates to a synthetic equivalent test circuit which can generate a 4-parameter transient recovery voltage TRV, for verifying a large current breaking performance of a power circuit breaker. A current source current is supplied to only a testing circuit breaker which is to be tested and an auxiliary circuit breaker. A small current with respect to the current source current is transmitted to the first and second auxiliary switches from a power source. When the small current form the current source or the resonance circuit flows, the first auxiliary switch is opened almost simultaneously with the auxiliary circuit breaker, the testing circuit breaker and operates so as to break the current at the time point of the final zero point of the current source current.

Abstract: A tester for a vehicle engine idle air control system includes an air bypass valve operated by a solenoid which receives a pulse width modulated signal to control the degree of opening of the valve. The tester is inserted in the vehicle wiring harness and includes a manually controlled pulse width modulator for generating a test voltage to the solenoid. A switch is connected within the tester to switch between engine computer control or manual modulator control of the solenoid. A bar graph display monitors the voltage supplied to the solenoid to indicate the magnitude thereof. The bar graph display also indicates the occurrence of short or open circuits.

Abstract: A computer-controlled apparatus (1) for electrical testing of the make-and-break characteristics of electrical switches (15), including characteristics when the switches are actuated very slowly. The apparatus automatically feeds the switches into a test position (16), "breaks them in" by cycling them through many operations, and tests their switching parameters. The amount of hysteresis (54) between a switch actuator's (38) positions at actuation (30) and deactuation (56) is a criterion for sorting the switches. Switches are automatically classified and marked (14) according to their tested characteristics, and sorted into bins (28, 29). Any undesirable electrical "deadbreak" (an excessive transfer delay) during the operation of a double-throw switch's contacts is detectable by both a Timer Method and a Limit Switch Method, and faulty switches are reliably rejected. The apparatus increases accuracy in the testing of switches and reduces human errors such as those caused by fatigue.

Abstract: A seat belt buckle monitor switch has a cooperative circuit for indicating the closed state of a seat belt buckle in a motor vehicle. Due to high-grade monitorability, it has a high sensory reliability. The device is structurally designed such that it allows an operation of additionally provided circuit elements in at least one monitoring current loop. If a contact element is at an erroneous potential due to interruption of a current path outside or inside the switching component, this is detected in the test circuit.

Abstract: A mini-relay signal tester designed to simplify, speed up, and test the operation of "mini" or "reed" relays which are suspected of intermittent failure. These types of relays are extensively used in memory and gate-array testing systems and their failure can cause the semiconductor devices being tested to be erroneously rejected. The relay tester dynamically exercises the relay being tested by application of a square-wave input signal to its coil. The square wave input "reference" signal driving the relay coil is then compared to a square wave output "test" signal which is generated by the contacts of the relay being tested. The signals are compared on a dual-trace oscilloscope. When difference between signals exceeds acceptable standards the relay is rejected.

Abstract: Disclosed is a gas insulated switch device comprising at least two hollow cylindrical containers each accommodating top end portions of a system of line cables, and a disconnector having contacts coupled to the line cables via detachable conductors, wherein electrical tests on the cables, etc. in a first container can be conducted from a test window formed in a side wall of an adjacent second container, by means of a test tank attached thereto. The side walls of the first and second containers comprise a pair of opposing windows that are coupled to each other, via an electrically insulating spacer; branch conductors, which are disposed within the first container and have inner end portions that can be selectively coupled to the line cables or the contacts of the disconnector within the first container, comprise outer end portions projecting into the second container through the electrically insulating spacer disposed between two windows coupled to each other.

Abstract: A fuel cell/battery hybrid power system is disclosed which has a microprocessor based control system. The control system enables the fuel cell to be taken out of the system by a switch when its predetermined maximum desired energy output is about to be exceeded by load requirements. The battery is protected from overcharging by a switch which is activated responsive to the sensing of state of charge, load current and fuel cell current.

Abstract: By providing control logic for initiating a predetermined test sequence depending upon the known state of a relay, a unique testing circuit is attained whereby the relay drivers connected to the opposed sides of the relay coil are fully evaluated without causing the relay to be activated. In the preferred embodiment, the relay comprises a latching-type relay and the relay drivers comprise separate high-power CMOS devices. In this configuration, the control logic separately activates each transistor of each of the high-power CMOS devices without causing the relay to be switched between its two alternate configurations. Furthermore, the control logic originally sets the latching-type relay into one of its two configurations and then shuts off the power until activated for initiating the test sequence. In addition, the control logic is employed to check each transistor during the test sequence and assure its operation.

Abstract: A protected digital output circuit coupled to a programmable controller, for controlling a load supplied through alternating-current (ac) power lines, including a fuse and a single controlled output switch connected in series with the load, and a pair of series-connected crowbar switches connected together across the ac power lines. The crowbar switches can be commanded closed together in the event that the output switch is commanded open but fails to open, thereby shorting the ac power lines and disconnecting the load by blowing the fuse. In routine diagnostic testing, the crowbar switches can be commanded closed separately to check their operation without blowing the fuse. A current detection circuit is used to check for current in the closed crowbar switch. A current sensor is also used to detect current through the output switch, when commanded closed for switching the load on, or for diagnostic turn-on testing when the load is disconnected.

Abstract: A method and system for monitoring the condition of a plurality of electrical devices, particularly electrical switches actuated by sensors, to determine the condition of each and the location of e.g., a malfunctioning device. The electrical devices are connected in parallel across a pair of line conductors. A voltage-dropping element is inserted in series with the line at the input side of each device, and a current-limiting element, passing a fixed current independently of voltage above a predetermined threshold, is inserted in series with the respective device. Initially, a voltage is applied to the line of greater magnitude than the sum of the predetermined threshold and the voltage of the first device, and is sequentially increased in a plurality of steps, while the current passing through the line initially and after each of the voltage steps is measured.

Abstract: To check the presence of operating vacuum in vacuum switches, high voltage can be applied between the contacts at a given contact spacing and the dielectric strength can be tested. According to the invention, the procedure for vacuum monitoring is that a contact spacing (h) below the nominal stroke of the vacuum switch is selected and that the X-radiation generated at this contact spacing (h) and high voltage (U) in vacuum due to the field electron emission between the contacts by the contact surfaces acting as anode is acquired and evaluated as proof of the presence of operating vacuum inside the switching tube. This method can preferably be applied to encapsulated vacuum switching tubes, in particular to SF.sub.6 -insulated switching facilities.

Abstract: A system for testing the conditions of at least one pair of contacts to determine if the contacts are opened or closed comprising a transmit circuit and a receive circuit. The transmit circuit generates and outputs a test signal having a known frequency and the test signal is optically coupled to the contacts. The receiving circuit receives the test signal from the contacts and outputs one output indication indicating the contacts are closed in response to receiving the test signal and outputs one other indication indicating the contacts are opened in resposne to not receiving the test signal. The receiving circuit also optically couples the test signal from the contacts to the indicating means.

Abstract: A circuit arrangement is disclosed for monitoring the connecting lines of a switch or sensor open in the normal condition, with a first ohmic resistance connected in series with the switch or sensor. That together with the switch or sensor and a second ohmic resistance connected in parallel to both forms a parallel circuit, whose first connecting line is connected to ground and whose second connecting line is connected, on the one hand, to a voltage supply by way of a third ohmic resistance and, on the other, with a voltage discriminator unit. The second ohmic resistance is adapted to be disconnected.

Abstract: Apparatus for testing an electrical switch responsive to fluid under pressure and a solenoid valve that controls the flow of fluid under pressure. Fluid under pressure is injected into a socket holding the switch to be tested. The magnitude of the pressure is predetermined in accordance with the rating of the switch. An electrical circuit is connected to the switch to determine whether the switch opens and closes at the rated range of the switch. A solenoid valve communicates with the socket. Fluid under pressure is conducted along a path. The solenoid valve is disposed in the path of fluid flow to control the flow of fluid under pressure. The electrical circuit is connected to the solenoid valve to energize and deenergize the same, thereby opening and closing the valve. A meter communicating with the flow of fluid under pressure indicates whether the solenoid valve is operating properly.

Abstract: The invention is directed to a portable test device for an electronic trip unit which is electrically powered from the internal power supply of the trip unit being tested. The test unit utilizes three leads connected to the trip unit. One of the leads connects to the voltage source for the trip unit and another lead connects to the ground potential to acquire power from the test unit. The voltage is selectively adjusted within the test unit by resistors and a potentiometer to vary the input voltage which is to be carried by the third lead into the trip unit.

Abstract: An automatic transfer switch is taught which includes as part thereof a voltage sensing device which is interconnected with one of the lines to be monitored and controlled by the automatic transfer switch and neutral. This voltage may vary over a wide range and it is desired to provide a universal transfer switch control for operation over the wide range. The output analog voltage is provided to an analog-to-digital converter which has a maximum number of output bits. In order to keep the resolution of the output digital signal from the analog converter as high as possible, it is necessary to range the input voltage according to a menu of potential ranging values which are stored in the memory of a microprocessor. A programming device is utilized to input the line voltage and the microprocessor determines the maximum value for the ranging constant as a function thereof. The output analog voltage is reduced by this factor then provided to the analog-to-digital converter.

Abstract: A rotatable one-piece lens assembly that may be rotated relative to the instrument housing comprising a lens boss, integral with the lens, moving with the rotated lens to move the pointer to engage and test the switches. After the switch test the lens may then be rotated back to its normal position. In this manner the switches are tested without removing the lens from the instrument housing.

Abstract: A valve analysis and testing system includes various devices for measuring the operating characteristics of a valve and its operator and the corresponding imposed valve stem load, which devices are attached to the valve operator. These devices include a switch position indicating circuit for purposes of detecting the open and close positions of limit and torque switches within the valve operator; which circuit includes a coil wrapped with two independent current conducting wire elements, each wire element in series with a different switch; and one wire element being wrapped about the coil core more times than the other wire, wherein a coil output induced by current flowing through one wire element will be of different magnitude than the coil output induced by current flowing through the other wire element; and, preferably, wherein current flowing through both wire elements at the same time will have an additive effect on the coil output.

Abstract: In a protection system for a complex process control system which generates three independent actuation signals, the power circuit includes three pairs of switches arranged in three groups connected in series with each other and with a load device and a voltage source. Each group of switches includes two switches selected from different pairs of switches and connected in parallel. The same circuit topography is used for normally energized and normally deenergized loads with normally closed siwtches used with the former and normally open switches used with the latter. For testing the circuit, each group of switches is shunted by a resistor to form a leakage path through the configuration of switches. The impedance of each resistor is several times that of a closed switch such that the leakage current is insufficient to energize the load, but sufficient to be detected by a current detector which measures the current drawn from the voltage source.

Abstract: Each of the either normally closed or normally open switches, in an n out of m voted power interface circuit having parallel connected groups of serially connected switches, is shunted by a high impedance resistor to form a leakage path through each group of switches. A detector associated with each group of switches, and responsive to the change of impedance produced by actuation of a resistor shunted switch in the group, generates an output signal, preferably a one bit digital signal, indicative of the state of the switches in the group in response to a sequence of test signals which selectively actuate fewer switches than are required to actuate the load controlled by the power interface. Compensation for large variations in supply voltage is provided by incorporating each group of switches into a resistance measuring bridge circuit in which the digital output signal is generated by a comparator connected across the bridge. Preferably, the bridge circuits share common reference voltage generating legs.