Abstract: A programmable controller (41) based logic system places two electronic output converters (14,18) in series for redundant protection against the inadvertent energization, due to the failure of an image register (66,68) or due to the shorted failure of a triac (10,12) on the output converters (14,18), of an energize-to-start, deenergize-to-stop field device (28). A control and monitor circuit monitors the image registers (66,68) and the output converter (14,18) triacs (10,12) that switch power on and off to the field device (28) to assure that the triacs (10,12) have not failed in an unsafe mode or that the image registers (66,68) have not failed. The monitor circuit continuously monitors both image registers (66,68), the first triac (10) and the series combination of the two triacs (10,12). The monitor circuit intermittently monitors the second image register (66) and the second triac (12). A failure of either or both triacs (10,12) or either or both image registers (66,68) energizes an alarm.

Abstract: Built-in test equipment (BITE) of the electrical/electronic systems of an aircraft is provided in-part by passive fault detection circuitry that is integrated into the electrical/electronic systems for continuous, in flight monitoring of line replaceable units (LRUs), such as temperature and pressure sensors. Both steady and intermittent failures of the LRU components are detected, and the type and location of each failure are identified and stored in a memory for continuous display or for subsequent recall by ground maintenance crews. The primary feature of the disclosed circuitry is its ability to detect and distinguish between an open impedance fault of a critical LRU component and an open wiring fault in the interconnect wiring that is associated with each component and is needed to electrically communicate signals developed at remotely mounted sensor components with a centralized controller, usually located in the avionics bay.

Abstract: An electronic control circuit of the type including a microprocessor, a circuit for monitoring the operational state of the microprocessor connected directly to a first output of the microprocessor, and a warning light of the control circuit and its input and output peripherals. The warning light is connected to a second output of said microprocessor through a starter and protection circuit and thus diagnostic data are available in series at the input terminal of said warning light which is also the output of said starter and protection circuit.

Abstract: A trouble-shooting circuit arrangement for localizing and identifying the first failure in time in a sequence of failures which has a plurality of monitor circuits including trouble detector circuits for producing direct current outputs in response to the occurence of failure or trouble at various contact points and trouble localization circuits for identifying the trouble which has occurred in any of the monitor circuits, identifying such factors as coolant, pressure, temperature, fuel and the like in an engine. The arrangement locates the first failure or trouble in time, which has occurred in any of the circuits so as to remedy the countermeasures of the equipment against the occurence of trouble or failure therein.

Abstract: A fully integrated alarm, communication, and building management system has a central control station and a plurality of remotely located sensing and controlling devices. Each remote device has an individual digital address, which is a parallel address present on a plurality of parallel lines. The parallel address is converted to a serial address and sent to the various remote locations where it is then reconverted to a parallel address and decoded to determine the specific device being interrogated. A multiple amplifier system is provided at the central control unit and provides communication capability involving remotely located loudspeakers and microphones. The amplifiers are provided in a dual channel arrangement so as to provide a fail-safe arrangement and a failure detector is located in each channel such that if a selected amplifier channel fails, the back-up or redundant channel is immediately switched into use.

Abstract: In an intrusion alarm system, an anti-tamper system for detecting the bridging and removal of sensors connected in parallel along an interconnection cable includes means at each sensor for detecting open circuits on or shorting between any of the lines of the cable. Each sensor is provided with a resistance element and the resistance elements are connected in series by virtue of connection to the cable. Should any of the lines be cut or shorted, regardless of any bridging attempt to remove the sensor from operation, this condition is sensed and the series connection for the resistors is interrupted. This causes an imbalance at the comparator utilized to sense the combined impedances of the resistance elements and an alarm condition is indicated. If an attempt is made to bridge the line connecting the resistors together, the removal of the bridged resistor also causes an imbalance at the comparator which results in an alarm indication.

Abstract: A continuous strip sensor for detecting extremely cold temperatures is disclosed. The sensor includes a plurality of series connected sections each of which exhibits a substantial increase in resistance upon exposure to an extremely cold temperature. A detection circuit utilizing the above sensor provides compensation for changes in ambient temperature by means of a compensation-sensor having the same total resistance and resistance-temperature characteristic as the cold sensor. The detection circuit also detects the occurrence of faults in the cold sensor or the compensation-sensor.

Abstract: In an instrument system consisting of a transmitter in one location and a receiver in another location connected by a transmission medium, fail-safe operation is obtained by restricting the output of the transmitter to well-defined levels and interpreting any substantial departure of the received signal from these well-defined levels as a failure. When a failure is detected, alarms or other equipment may be activated, including a control circuit which causes replacement of the defective transmitter or transmission medium, thereby restoring the system to service. An embodiment wherein the transmitter is an admittance-responsive transmitter in a two-wire current loop for monitoring the condition of materials is described.

Abstract: An alarm switch circuit includes an opto-isolator that is used as a high speed switch to control the pulse generation rate of an oscillator circuit which in turn maintains a set of normally open contacts of an interlock relay in the closed condition. The fail-safe design features are not negated should the following conditions occur: (1) a loss of power, (2) one or more independent failures of circuit elements, (3) open or short circuit failures of the set point (SP) or process variable (PV) voltages or their polarity reversals and (4) the background noise masks the PV signal.

Abstract: Conventional warning installations possess electrically interrogated feelers or sensors or generate electrical signals, particularly if they are used for remote monitoring purposes. At the feelers and even more so at the signal lines it is possible for there to be produced spurious signals due to electrostatic charges or electrical or magnetic induction. These spurious signals trip unwarranted warning or alarm signals. The novel warning or alarm installation therefore contains an optical conductor or guide as a signal line, and the feelers are interrogated by means of optical signals. The optical conductor together with an electronic monitoring circuit forms a free-running opto-electronic oscillator which comes to standstill when there is interrupted the oscillating optical signal which is irradiated into the optical conductor and radiated back out of the conductor into the circuit.

Abstract: A flame scanner has a sensing circuit (10) utilizing a photosensitive device (12) for monitoring and a logic circuit (20) which includes a flame detection circuit (22) and a fault detection circuit (24). The photosensitive device produces a current signal (13) indicative of the intensity of the flame. The current signal is fed to a logarithmic amplifier (14) and converted to a voltage signal (15). The voltage signal (15) powers an LED (18) with its output (4) impinging on the photosensitive device (12). The voltage signal (15) is also transmitted to the flame detection circuit and the fault detection circuit for simultaneous and independent processing. The flame detection circuit continuously processes the signal to determine if a stable flame is present, while the fault detection circuit continuously monitors the integrity of the photosensitive device and its associated sensing circuitry.

Abstract: A fail-safe acknowledging circuit having a plurality of relay switching contacts having a predetermined order of more restrictive significance. A differentiating circuit selectively interconnected by certain ones of the plurality of relay switching contacts for establishing a selected one of a plurality of charging potential levels from a d.c. voltage source. A latching circuit is conditioned by a holding voltage and is set by momentarily closure of an acknowledging switch to produce a.c. signals which are fed to one input of a two-input AND gate. A checking circuit monitors the voltage level of the d.c. voltage source and verifies the integrity of the differentiating circuit to produce a d.c. potential which is conveyed to the other input of the two-input AND gate.

Abstract: A standard mechanical lock is provided with an electrical coding system for setting off an alarm in the event that an incorrect key is used or the lock is tampered with. The electrical coding system includes a binary code inscribed in the back edge of the key. A plurality of conductive fingers are mounted on the lock body to contact the back of the key when the key is rotated in the lock. A decoding circuit is provided which sounds an alarm in the event that an incorrect code is presented to the fingers. In the event that an attempt is made to pick the lock, one or more of the fingers will become grounded thus setting off the alarm. Automotive and building applications are disclosed wherein microswitch sensors are placed at strategic locations to set off the alarm in the event that an attempt is made to circumvent the mechanical lock.

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: Self-monitoring seals have ends of fiber optic bundle loops mounted in stressed tamper resistant containers. A battery operates microelectronics to change a display in predetermined sequence. Tampering with the container or interrupting or changing the light transmission through the fiber optic bundle disrupts the predetermined display sequence.

Abstract: The disclosed temperature monitoring and alarm circuit includes a temperature responsive switch which opens when water temperature exceeds a predetermined point. When the switch opens, a relay is de-energized, thereby activating a latch which activates a visual alarm and closes off a solenoid operated valve on the monitored water source until the over temperature condition is corrected and the circuit is reset.

Abstract: A number of remotely mountable transmitting heads each has a transducer driven by a sweep frequency ultrasonic signal for generating an ultrasonic field. A number of remotely mountable receiving heads each processes incident doppler shifted energy reflected by a disturbance by developing therefrom a constant amplitude received signal and multiplying this signal by the ultrasonic signal to generate a pair of noise cancelling differential signals. A processor for generates the ultrasonic signal and further processes the received signals so as to detect the disturbance or system tampering.

Abstract: An alarm system including an alarm which is actuated when a sensor such as a microphone detects an emergency condition. In one embodiment the output of the microphone is fed through a filter circuit tuned to frequencies characteristic of breaking glass. In conventional systems failure of the microphone may remain undetected but in the system of the present invention an alarm is instituted when the sensor detects any emergency signals and when the sensor fails to detect a reference signal. The reference signal is produced at regular intervals but the alarm instituting means includes a delay and is operable to switch off the reference signal within the delay period to avoid false alarms.

Abstract: A monitoring system has a connecting unit that is adapted for connection between a nurse call button and a communication panel in a hospital room and is attached to a movable pressure activated switching means for placement in a bed or chair to operate an alarm in the nurse call system for remotely signaling the absence of a patient.

Abstract: A single terminal detection system of the beam variety is provided with polarizing filters to sense "near-field" problems. One filter polarizes radiation reflected back to the transceiver component and a second filter, positioned within the transceiver, polarizes radiation before it is incident upon one of two radiation detectors. Circuitry, operatively coupled to the detectors, actuates an alarm in the event either an alarm condition or a near-field problem exists.

Abstract: The sensor system senses a drop in the flow of impressed cathodic protection current to a minimum threshold level. A potential difference is developed which is a sample of the cathodic protection current. A comparator receives the sample potential difference and normally produces an output control signal which drops to substantially zero when the cathodic protection current drops to a predetermined threshold level. A relay responsive to the control signal then switches a signaling device to its signaling condition. A standby battery is also coupled to the signaling device through the relay. In the event of any failure in the sensor system or in the primary source of power energizing the sensor system, the standby battery becomes connected to the signaling device to cause it to change to its signaling condition.

Abstract: Process for the automatic signalling of faults of an automatic static safety module and a module realizing said process which can be used in automatic safety systems which can, for example, be used in nuclear reactors.The module comprises at least one pair of identical parallel logic circuits each having a first positive continuous supply connection and a second negative supply connection. The circuit output can have one or other of two logic states depending on whether it is connected to the first or second connection. It comprises means for the automatic signalling of a fault in one module component constituted by a.c. voltage sources of different frequencies inserted in the supply connections. It also comprises means for detecting the presence of beats between the a.c. voltages appearing at the outputs of circuits and for indicating cases of non-agreement of the logic states.

Abstract: An electronic control unit for regulating the air/fuel ratio of an internal combustion engine is disclosed. The electronic control unit has an open loop calibration for regulating air/fuel ratio that is corrected with a closed loop signal developed by an integral controller. The integral controller bases the closed loop correction signal on a signal from an exhaust gas composition sensor located in the engine exhaust manifold. Various conditions of the system are sensed by a closed loop sensor condition detector to provide information on whether the sensor is up to operating temperature and is operative. If the exhaust gas sensor is functioning and the operating system parameters indicate the system operation should move to closed loop control, the loop is closed by the condition detector. Included in the condition detector circuit is a timer whose cycle is RPM dependent.

Abstract: A process control installation has means for sensing a plurality of physical conditions connected to means for comparing the condition to a reference. A differential signal is fed to a corresponding reproduction circuit which in turn feeds it to inputs of a plurality of majority decision circuits. The majority decision circuits are in turn connected to pairs of logic circuit trains which in turn are connected to other logic circuitry for intrinsic security.

Abstract: A monitoring circuit for monitoring a plurality of signals developed by remote sensors which preferably are capacitance probe sensors. The circuit is intended for use with a motor vehicle maintenance system employing capacitance probes to detect low and safe levels of oils and coolants in a vehicle engine. The monitoring circuit includes a constant voltage source with a voltage divider in circuit therewith to develop a plurality of reference voltage signals of predetermined values which are applied to respective inputs of a plurality of voltage comparators that receive, at their other terminals, condition-responsive voltage signals generated by a condition sensing circuit. The condition sensing circuit comprises a liquid level capacitance probe which generates intermediate, high and low voltage signals indicative of safe and low, respectively, levels of sense liquid.

Abstract: An improved a.c. voltage powered warning device for detecting the occurrence of predetermined phenomena, is characterized by battery backup for providing power to the device in the event of interruption of the a.c. voltage. In the disclosed embodiments the warning device is a fire detector having circuitry for supervising the energy level of the backup battery and for providing a warning upon the energy level decreasing to a predetermined value, and for testing a combustion detecting and alarm generating portion of the detector.

Abstract: An improved warning device having a sensor responsive to predetermined phenomena to generate a signal which changes in value upon the presence of the phenomena, and means for comparing the signal with a reference potential and for generating an indication upon a predetermined difference therebetween, is characterized by integrated circuit components which may economically be manufactured and assembled, and which maintain substantially constant the sensitivity of the device to the phenomena despite changes in the level of power supplied thereto. Where the warning device is a battery powered fire detector, the phenomena to be sensed is products of combustion, circuitry supervises the power level of the battery, and means are provided for readily testing the entire combustion detecting and indication generating portion of the detector, whereby a user of the detector may be assured of proper operation of the detector in response to combustion.

Abstract: Both power to and detection signals from a remotely located condition monitoring device are provided via a single wire with return through the vehicle frame. A load switching circuit connected and responsive to the output of the condition monitoring device causes a particular current to be drawn from the line when the device and signal status are normal than when either is not. An indicator circuit connected into the line and responsive to the current drawn by the device and loading circuit provides a failsafe indication to the operator of the monitored condition and/or operational status of the system circuitry.