Abstract: A power latch circuit uses first and second bipolar transistors responsive to an actuate voltage to latch into a conductive state with power supplied to a computer and a third bipolar transistor powered by the latch circuit and responsive to a deactivate voltage from the computer to place the first and second transistors in a deactivated state to remove power from the computer and itself. It further uses an FET in parallel with the third bipolar transistor and activated directly from the DC power supply when the second transistor is deactivated to latch the first and second transistors in the deactivated state in spite of voltage fluctuations on the deactivate line which might otherwise cause the latch circuit to reactivate. As an FET, it uses little current through its gate compared to alternative bipolar devices while the latch circuit is deactivated.

Abstract: A short circuit protection device for a unitary voltage gain signal transducer circuit (G.sub.v) and for a load impedance (R.sub.L) coupled to the transducer circuit includes a first (A.sub.1) and a second (A.sub.2) threshold comparator circuit and an actuator circuit (ACT). The input terminals of the first comparator (A.sub.1) are coupled to the transducer circuit input and output terminals and the output terminal of the first comparator is coupled to an activation terminal of the actuator circuit. The input terminals of the second comparator (A.sub.2) are coupled to the ends of the load impedance and the output terminal is coupled to an inhibit terminal of the actuator circuit. A first output terminal of the actuator circuit is coupled to an inhibit terminal of the transducer circuit, while a second output terminal of the transducer circuit is used to deliver a small current I.sub.1 to the load impedance.

Abstract: A fail-safe electronic coincidence detecting circuit including a multiple winding saturable core reactor having a first and a second input winding and an output winding. An NPN transistor amplifier supplying a first pulse train to the first input winding and a PNP transistor amplifier supplying a second pulse train to the second input winding. The output winding producing signal pulses only when the first and second pulse trains are in synchronism.

Abstract: A scheme for determining the operational state of a control turn-off semiconductor, of the type having an anode, a cathode and control electrode to which signals are applied to control the conductive state of the semiconductor, utilizes the extant voltage at the control electrode to determine the actual conductive state of the semiconductor. A first signal representing the desired operational state of the semiconductor and a second signal representing the actual operation of the state of the semiconductor and appropriately combined in one embodiment to generate an indication of the operational state of the control turn-off semiconductor. A further embodiment, employed in a series connection of two such control turn-off semiconductors beteen dc buses, uses the second signals in a cross-coupled arrangement between the two semiconductors to inhibit the application of control signals to a first semiconductor if the second semiconductor is conductive.

Abstract: A protective relay for detecting power arcing faults on a low-voltage spot network. The protective relay can monitor the voltage difference between each phase conductor, the voltage difference between each phase conductor and the neutral conductor, or the current on each phase conductor. Using one of these three sets of values, the protective relay first filters the input signal so that only frequencies indicative of a power arcing fault on the low-voltage spot network are analyzed. The signals passed by the filter are amplified, rectified, and averaged and the peak of each signal detected. If the peak has a duration longer than a predetermined value, a fault indication is provided.

Abstract: A protective device for a power element of an integrated circuit includes a circuit element for detecting and processing the value of the current flowing through the power element and the voltage supplied to the power element. The circuit element generates a measuring signal which, when it reaches a predetermined limit value, activates a threshold circuit which reduces the current level in the power element. The protective device also includes a circuit element for amplifying the measuring signal when it reaches the predetermined limit value.

Abstract: Subject high-frequency lighting system comprises the following principal component parts:(a) a power-line-operated power supply operable to supply a high-frequency (30 kHz) output voltage;(b) a plurality of lighting fixtures--with each such fixture comprising one or more gas discharge lamps and series-resonant ballasting means operative to derive the requisite lamp operating voltages and currents from the power supply's high-frequency voltage output; and(c) a bus wire means operative to distribute said high-frequency voltage from the power supply and to each of the fixtures. To protect against circuit failures, which might occur due to excessive socket voltages resulting upon removal of a lamp or toward end-of-lamp-life, a Varistor voltage-limiting means and a self-latching circuit breaker means are used with each series-resonant ballast.

Abstract: In an X-ray generator system having a pulse-width-modulated transistor inverter with associated flywheel diodes, method and apparatus is provided to sense when a diode associated with a non-pulse-width-modulated transistor is conducting and for inhibiting the turning on of that transistor during such period, to thereby avoid the transition from reverse conduction to direct conduction in an uncontrolled manner.

Abstract: In an X-ray generator operating with a pulse-width-modulated transistor inverter, circuitry is provided to sense the collector-emitter voltage of each of the transistors and to responsively turn off the transistor when that voltage level reaches a predetermined threshold level which is indicative of a problem. Provision is included to inhibit the operation of the protective circuit during the time period in which the transistor is turning on so as to thereby allow for higher voltages during that critical period.

Abstract: A solid state power switch includes a gated switch for connecting electrical power to a load whenever the actual load current is less than selected current reference values.

Abstract: This invention relates to apparatus which can detect both interruptions and reductions in an alternating current input extremely quickly. This allows an orderly shut down of the equipment before the output of the equipment power supply decays. The device can be utilized in any application requiring detection of changes in an alternating current input.

Abstract: A protection circuit for a push-pull amplifier includes two sensing transistors arranged in respective feedback circuits. The output signals of such sensing transistors, which are indicative of the output voltage, are used to limit the output current of the amplifier in such a manner that the output current is limited to a first threshold decreasing with a steeper slope as a function of the output voltage of the amplifier between predetermined two output voltage values, and a second threshold decreasing with increasing output voltage at a lesser slope above the higher one of the two predetermined output voltage values. This characteristic response can be overridden by appropriate circuitry so long as the temperature of the amplifier is below a predetermined maximum value, so as to make the output current threshold independent of the output voltage.

Abstract: A microcomputer utilizing a crystal controlled clock and a power line responsive clock operates both the control system and into a safety timing means. The safety timing means can take the form of a pair of retriggerable monostable multivibrators that are operated to monitor the microcomputer along with a feedback circuit from a load control means. The feedback from the load control means senses the status of a safety switch means and provides the microcomputer with the ability to monitor and be monitored for safe operation.

Abstract: A MOS type output driver circuit including an output circuit having first and second MOS type output transistors connected between a voltage supply and ground. The gates of the first and second output transistors are respectively, supplied with first and second drive signals that are mutually inverted. The MOS type output driver circuit further includes a protective circuit for preventing the output transistors from being damaged by overcurrent when the output is shorted to ground.

Abstract: An output transistor protection circuit in a power amplifier comprises a limiter circuit which limits a collector power dissipation of the output transistors to a predetermined magnitude in accordance with an output voltage level of the amplifier and a current level of the output transistors. For sure limitation operation with a low cost construction, and without destruction of signal waveform, limitation characteristics of the limiter circuit is varied in accordance with detection results of an output voltage level detection circuit which detects whether the output voltage level is smaller than a predetermined magnitude, and a clipping condition detection circuit which detects whether an output stage of the amplifier is clipped.

Abstract: A protective circuit for a switching transistor is disclosed in which the base-emitter voltage of the switching transistor is compared in a comparator with a reference voltage. If the collector current of the switching transistor increases, the base-emitter voltage also increases, with the base current remaining constant. As soon as the base-emitter voltage exceeds the reference voltage, a signal is delivered at the output of the comparator. A switching-off device for switching off the driving pulses of the switching transistor responds to this signal so that a switching-on pulse present at the base of the switching transistor is switched off. The reference voltage is fixed so that the switching transistor is protected against overload by excessively large collector currents.

Abstract: A reset circuit which monitors the voltage of the power supplied to a microprocessor unit, and produces a low resistance to ground at the reset terminal of the microprocessor whenever the supply voltage changes from a low value to a high value, or from a high value to a low value. It is based upon the combination of two RC circuits of different time constants, such that when the supply voltage is constant, no current flows in these circuits. A transistor is connected to the RC network such that it carries current only when there is a changing voltage of the power supply. If the voltage increases or decreases, a second transistor acting as an electronic switch grounds the reset terminal, and when the voltage becomes constant again, either at a high value or a low value, the switch opens and the reset voltage goes high.

Abstract: A device for protecting a battery driven electrical appliance against reversal of battery polarity comprises switching means, for connection into the supply circuit of the appliance to be protected, and a series combination of an electrical control for the switching means and a unidirectional semiconductor means, said combination having a first terminal connected to a supply terminal of the switching means and a second terminal for connection to a supply from the battery of polarity opposite that of the said supply terminal, for operating the switching means to interrupt supply of current to the appliance in the event of reversal of battery polarity.

Abstract: An electrical safety switch for protecting an electrical appliance requiring a ground, an on/off switch disposed in series with a resistor and primary coil of a transformer between the ground line and the B+ line of the appliance, and a triac connected in series with the load of the appliance between the B+ line and the neutral line with the gate triggering the triac connected to the transformer to be energized thereby upon a current being present through the on/off switch.

Abstract: A switching circuit has a solid state power switch (9) which is either a PNP or NPN transistor or a VMOS p- or n-channel device. Three individual sensing circuits (2, 3, 4) are set to indicate whether a predetermined operating characteristic of the switch (9) is greater or less than a given threshold value and thus to indicate if a fault is present in the switch (9) or the load (L) it supplies. Digital logic circuit means comprising three logic circuits (5, 6, 8) produce two digital signals from the output signals of the sensing circuits respectively indicating if a fault exists and if it is a serious fault or not. A circuit (7) comprising gating means disables the switch (9) in the event of a serious fault and a delay circuit (33, 34) is provided associated with the logic circuit means to prevent current surges due to short circuit faults being confused with normal operating current surges in switch on.

Abstract: Transistor switching means in which a principal transistor (T.sub.5) feeds into a load (R.sub.c) when a control signal saturates a control transistor (T.sub.1), a resistance bridge (R.sub.3,R.sub.4) fed by a source (V.sub.AL) then polarizing the base of the principal transistor (T.sub.5).An auxiliary transistor (T.sub.3 a) has its base coupled to the collector of the transistor (T.sub.5) by means of a diode (D.sub.2 a) and one of the two polarization resistances (R.sub.10 -R.sub.11). When the collector-emitter voltage of the principal transistor becomes too strong as a result of a short-circuit in the load, the auxiliary transistor (T.sub.3 a) is saturated and blocks the principal transistor (T.sub.5).Application to detectors of the type having an electro-luminescent diode excited by pulses; these pulses, applied to the auxiliary transistor (T.sub.3 a) block it momentarily in order to ensure the re-setting of the circuit when the overload has disappeared.

Abstract: A circuit for assuring the supply of voltage to an electronic circuit can be switched to an auxiliary voltage source via a series-connected, self-conducting field-effect transistor when the supply source fails. The circuit, which is realized with very little circuitry, has a voltage divider connected across the load; a tap on the voltage divider is connected to the gate electrode of the transistor. The invention is useful, for example, for protecting data in C-MOS memories of microprocessors.

Abstract: Power supply sensing circuitry comprises a first comparator for determining whether the power supply potential voltage exceeds by a predetermined amount the voltage required to operate a data processing system connected to the power supply potential, and a second comparator for determining whether the power supply potential is at least the voltage required to operate the connected data processing system.

Abstract: A semiconductor circuit for protecting battery powered electronic devices from damage due to polarity reversal. A metal oxide semiconductor is employed in series with the power source to switch the power input as appropriate. A first embodiment simply disables the power source input upon improper polarity. A second embodiment actually reverses the effective polarity to the load. Because the source-to-drain impedance of the metal oxide semiconductor device is resistive, a number of protection devices may be used in parallel to achieve an arbitrarily low voltage drop between power source and load for a given current drain.

Abstract: A protective current mirror, with a reflection ratio greater than one, is connected as the active load of an input differential amplifier of a power amplifier. This mirror is provided in addition to the usual current mirror which has its output connected to the drive transistor of the output power amplifier stage. The protective mirror senses the imbalance due to a voltage peak which occurs at an inverted input of the input differential amplifier at the very beginning of the descending portion of a sawtooth input signal ramp voltage and the protective mirror operates a protective transistor which is connected to the base of the power amplifier drive transistor so as to keep one power transistor of the final power amplifier stage in its inactive state. Protection of the output power transistor occurs before the output of the power amplifier has reached its maximum voltage level.

Abstract: A dual-switch transformer-coupled switching regulator is provided with a non-dissipative snubber circuit arrangement wherein the resonant elements thereof include an inductor serially connected between two capacitors through a diode switch. The snubber has two other diode switches that are connected on mutually exclusive ones of the same sides of the capacitors that are connected to the inductor. Each of the last two mentioned diode switches connects the respective aforementioned side of the particular capacitor to the outer main terminal of a mutually exclusive one of the dual transistor switches of the regulator. The other side of the particular capacitor is connected to the other main terminal of the other one of the dual transistor switches. The arrangement minimizes any deleterious effects caused when the dual switches are being switched.

Abstract: A protective circuit for a class B OTL circuit such as a vertical deflection circuit and a sound output circuit of a television set. The protective circuit comprises a first voltage comparator circuit having one input terminal applied with a detection signal in the form of an average voltage of an output signal of the OTL circuit and the other input terminal applied with a first reference voltage, and a second voltage comparator circuit having one input terminal applied with the detection signal and the other input terminal applied with a second reference voltage which is different from the first reference voltage. Either one of the voltage comparator circuits is operated when the output terminal of the OTL circuit is short-circuited to either the power supply voltage line or earth.

Abstract: A safety device is included in a circuit comprising a power source and a user device. The power source has one terminal connected to ground, as does the user device, with the safety device connected in a conducting path leading to the ground in the user device. In the event of an incorrect polarity connection between the power source and user device, a current path through the safety device and to ground is established.

Abstract: A protecting device includes a discriminating circuit and a protecting circuit. The GTO thyristor is operated in such a manner that a carrier storing is completed from a first time point at which the supply of a negative gate current is started to a second time point, an anode-cathode voltage increases from the second time point to a third time point and decreases from the third time point to a fourth time point, and increases again from the fourth time point. The discriminating circuit includes a circuit for obtaining an amount of change between the anode-cathode voltages at the third and fourth time points, a circuit for obtaining a ratio of the amount of change to the anode-cathode voltage at the third time point, and a comparing circuit for producing a control signal when the ratio is smaller than a given value. The protecting circuit, when receiving the control signal, stops the conduction of the GTO thyristor.

Abstract: A circuit for protecting the transistor of a high current transistor chopper from damage due to inductive energy stored in the chopper circuit when the transistor is biased nonconductive. The inductive energy charges a capacitor connected in parallel with the transistor, and a return circuit returns the energy stored in the capacitor to the source while the transistor is nonconductive and to the load when the transistor is subsequently biased conductive.

Abstract: A circuit is disclosed which performs two functions: (1) it develops a D.C. voltage signal which is proportional to the difference between the D.C. voltage components of a first and a second voltage, each comprising a D.C. voltage component and an A.C. voltage component impressed thereon, and (2) it filters the A.C. voltage components of both the first and second voltages. This circuit comprises cascade-connected first and second networks, each comprising an operational amplifier, with the output of the first network coupled to the input of the second network. Said first voltage is supplied as an input to the first network, and said second voltage is supplied as an input to the second network. The second network develops a D.C. output signal that is representative of the difference between the D.C. voltage components of the first and second voltages.

Abstract: A circuit tester is disclosed which automatically open-circuits a main lead to an input circuit in response to an excessive overcurrent. The circuit tester of the present invention will automatically sense the existence of an excessive current which, in turn, open-circuits a main lead to the input circuit, actuates a buzzer and energizes a light-emitting diode. Since the main-lead to the input circuit has been open-circuited, the base voltage at a first transistor drops. This renders this transistor non-conductive and tends to cause the main-lead to the input circuit to short-circuit. This tends to restore the circuit tester to its initial condition. However, if the excessive current is continuing, the above sequence will re-commence, the sequence continuing until the excessive current no longer exists or until the tester is adjusted to a higher range of operation.

Abstract: A high voltage generator of a television display is responsive to an alternating voltage, such as a retrace pulse voltage, for developing an ultor voltage at an ultor terminal. A protection circuit for the high voltage generator includes a comparator that develops a television display disabling signal when activated. A circuit that develops a sense voltage representative of the ultor voltage is coupled to an input terminal of the comparator so as to develop the disabling signal when the ultor voltage exceeds a predetermined level. To provide an overload disabling capability, an ultor beam current sensing circuit is coupled to the input terminal of an operational amplifier. The output terminal of the amplifier is coupled to a bias voltage source and to an input terminal of the comparator.

Abstract: A current limiting circuit is provided wherein the monitored voltage is applied to the base of first and second transistors, the first transistor having a substantially larger emitter area than the second transistor. Impedance means are connected to the emitters of the first and second transistors such that they function in conjunction with the emitter area ratio causing the current flowing through the first transistor to be higher than that flowing through the second transistor at low base voltages, while at higher base voltages the current flowing through the second transistor is higher than flowing through the first transistor. At some intermediate voltage the current flowing through both the first and second transistors is equal. This property may be used, for example, in a voltage regulator so as to divert base drive current from the output transistor at the point where the first and second currents are equal.

Abstract: An H-switch driver circuit includes two pairs of opposed drive transistors each pair being selectively energized to control the polarity of power applied to a load. Each pair of transistors is energized by a power current mirror that includes an NPN transistor that supplies base drive current to the remaining transistors in the power current mirror. The emitter of the NPN transistor is coupled to the load. The NPN transistor is biased off to inhibit base drive current to the circuit transistors in the event of a short to plus fault at one of the load terminals.

Abstract: This switch monitoring circuitry is particularly applicable to switching circuitry for operating a bipolar load device, frequently an inductor, on a source of direct current with four switches arranged to alternate the polarity of potential across the load device in a predetermined periodicity. Such circuitry often is arranged with diode devices individually connected across the switches, especially where the load device is an inductor. The monitoring circuitry specifically described comprises basic logical circuitry having coincidence gating circuits for activating status indicating circuitry; or for controlling associated circuitry for protecting or for compensating the switching circuitry; or for alarming operating personnel of malfunctioning switches.

Abstract: A protection and fault detection circuit for an electrically isolated semiconductor power driver acting as a switch to connect a load such as a relay coil to a source of voltage employs logic circuitry responsive to input signals indicative, respectively, of the desired state of driver operation and the conductive condition of the driver itself to effect a rendering of the device to the nonconducting state when an overload or other fault condition exists. A monitoring circuit responsive to specified operating parameters of the semiconductor power driver and its associated circuitry provides an output fault signal which is indicative of a fault condition and may be employed for remedial and/or indicating purposes.

Abstract: An output from an OCL type power output circuit is applied to a loudspeaker load through a switching means such as a relay. A first detector circuit and a second detector circuit detect a first operating status (e.g., output d.c. level) and a second operating status (e.g., output current level of an output transistor) of the OCL type power output circuit, respectively. The detection output signals of the first detector circuit and the second detector circuit are respectively applied to a first detecting transistor and a second detecting transistor. In the normal operation status of the OCL type power output circuit, the first detecting transistor and the second detecting transistor are respectively biased into "on" states by the first detector circuit and the second detector circuit so as to permit predetermined currents to flow. When the first and second detecting transistors are in their "on" states they control a driving transistor into an "on" state.

Abstract: Faulted bipolar transistors in a voltage source transistor inverter are protected against shootthrough fault current, from the filter capacitor of the d-c voltage source which drives the inverter over the d-c bus, by interposing a small choke in series with the filter capacitor to limit the rate of rise of that fault current while at the same time causing the d-c bus voltage to instantly drop to essentially zero volts at the beginning of a shootthrough fault. In this way, the load lines of the faulted transistors are effectively shaped so that they do not enter the second breakdown area, thereby preventing second breakdown destruction of the transistors.

Abstract: Electronic logic circuitry operates to detect and correct a short circuit condition, be it a short to system ground or supply voltage, in a circuit output. In one application, the short protection circuitry is incorporated into a high power CMOS driver. If the circuit output is shorted to ground, the short is detected and a signal is fed back to the input. This feedback signal forces the output to ground thus eliminating the excessive current flow. Conversely, if there is a short to supply voltage, V.sub.DD, a signal is fed back to the input that forces the output to supply voltage V.sub.DD, again eliminating the excessive current flow.

Abstract: A protection system circuit which senses and responds to abnormal gap voltage condition. The circuit is operable in either positive or negative polarity of the gap. The circuit includes two branches, one relating to positive gap polarity and the other to negative polarity. The appropriate one of the two branches is selected by enabling one of two comparators in the respective branches.

Abstract: The output derived from an electric circuit such as an OCL type power amplifier circuit is delivered to a load such as a speaker, through a switching means such as a relay. When the operation of the electric circuit has come out of a predetermined range of operation, the switching means is operated to break the connection between the electric circuit and the load. A detection circuit for detecting the operation of the electric circuit includes a detecting transistor constructed in a semiconductor integrated circuit. The detecting transistor is connected at its base to the input terminal for external connection of the semiconductor integrated circuit, so as to receive a signal representative of the operation state of the electric circuit. The detecting transistor is so biased as to allow a predetermined electric current to flow therethrough, when the electric circuit is operating within the predetermined range of operation.

Abstract: A monitoring device for semiconductor rectifiers which are located in a three-phase current bridge circuit, in which the bridge circuit is provided with two semiconductor rectifiers per rectifier branch, including a current-sensitive detector circuit connected to each pair of semiconductor rectifiers of each branch through a resistor, wherein when the semiconductor rectifiers are intact, the sum of all current flowing through the resistors is zero, as detected by the current-sensitive detector circuit.

Abstract: The collector-emitter voltages (V.sub.ce) of each one of the two transistors of a single-pole-double-throw transistorized switch are independently sensed by a sensing circuit for producing a fault signal, whenever the V.sub.ce of each transistor concurrently approaches or exceeds the magnitudes of first and second DC reference voltages, respectively, by predetermined differentials. Control logic is responsive to the fault signal for removing the base drive from the conducting one of the transistors. An RC network is included in the sensing circuit, for delaying the production of the fault signal, both to avoid false triggering of the control logic, and to provide time for sequentially turning off one transistor and turning on the other transistor.

Abstract: Control circuit system wherein low level signals are delivered through small (miniature) gauge control conductors to remote control circuit breakers to control connection of load devices to load bus through use of solid state circuitry. Such control may be used between the flight station of an aircraft and the various load centers remote therefrom, in an automobile or in an industrial or utility system. The circuitry is also responsive to faults in the load circuits, and current limiting warning lights (CLWL's) located in the power supply of the control conductors may limit current and indicate the status of faults in the control and/or remote power circuits. A large number of CLWL's for the different circuits may be arranged in a matrix at a control station and means with corresponding load identifying indicia are provided to facilitate changes and correlation of lighted CLWL's with respect to the controlled load switching device.

Abstract: Individual rectified phase voltages are produced and applied to individual opto-isolator units whose output photo diodes are connected in a series string. Each photo diode has a zener diode connected across it with the zener diodes mutually connected in series. A direct voltage applied to the photo diode string is blocked unless one of the photo diodes is made conductive by having received radiation indicative of an overcurrent condition. The responsive photo diode forms a current conduction path with the zener diodes across each of the other photo diodes, which latter may remain nonconductive, for developing at terminals a direct voltage upon occurrence of a predetermined overcurrent, which voltage is useful for application to a trip circuit or the like for interruption of the load circuit in which the overcurrent occurs.

Abstract: A safety test circuit for a combustion control apparatus. This safety test circuit is used to check the off-failure of a safety transistor actuating a safety relay which acts to stop the operation of controlled units in the event of mal-combustion or the like, and also to check the on-failure of a control transistor actuating a control relay which controls the controlled units. An operation instruction signal and the collector potential of the safety transistor are applied to a logic circuit including a flip-flop and logic gates so that the off-failure of the safety transistor can be driven to check, utilizing the electrical signal propagation delay time of the elements constituting the logic circuit, before the propagation delay time has elapsed. The logic circuit is also used for similarly checking the on-failure of the control transistor.

Abstract: Arc detection and control apparatus for a high power high voltage gas laser with a constant current power supply comprises a circuit responsive to changes in voltage across the laser electrodes for disconnecting the power supply when the voltage change exceeds a predetermined limit. The circuit monitors a small proportional value of the interelectrode voltage through an optical coupler and has a multiplier circuit for converting detected voltage changes and the differential thereof into pulses with a constant amplitude for fixed percentage changes of the electrode voltage and into pulses with increasing amplitudes for proportionally greater electrode voltage changes. This circuit normalizes and filters the resultant pulses and permits them to be compared to a reference voltage in a comparator circuit. When the pulse amplitude exceeds the value of the reference voltage a control apparatus is actuated which disconnects the power supply from the laser electrodes.

Abstract: A sensing device is connected to an intermediate tap point on each phase leg of a polyphase system such as a grounded wye-connected capacitor bank to detect faulted capacitor units and thereby control a switching device to isolate the capacitor bank. The intermediate tap point is selected in each phase leg such that the number of series units (such as parallel capacitor groups) above the tap point equals (or exceeds by one) the number of series units below the tap point. The outputs of these sensing devices are coupled through a calibration network to a summing amplifier which operates to add the three signals vectorily to produce on AC output signal that is filtered by a 60 Hz band pass filter to attenuate unwanted harmonics and noise which might introduce error into the measurement. Initial balance is achieved by adjusting the magnitude of each phase to ground signal to equalize those signals from each of the intermediate tap points.

Abstract: A computer based control system having a protection circuit including a bistable circuit arranged to disable the outputs of the control system at the end of a scan period of the system. The bistable circuit is operated through logic gates arranged to monitor fault in the control system.