Abstract: In a central station alarm system the alarm sensors associated with a particular subscriber's premises are monitored by a local control unit associated with those premises and controllable by the subscriber. The local control unit automatically reminds the subscriber when he is supposed to close the premises and turn on the system. The local control unit allows the subscriber to change his expected closing time. The local control unit may also perform various other functions such as automatically cutting off power to low priority alarm sensors during a prolonged power failure, automatically cancelling any audible alarm indication silence commands when there are no alarms to silence, and automatically forming a bridge connection between the remote ends of two communication circuits when there is a break in either circuit.

Abstract: A security system of the bridge circuit type has in one of its arms a conducting element whose impedance is to be monitored and in its other arms reference and/or compensating elements, for detecting an unbalance of the bridge resulting from a sudden change in the impedance of the conducting element. At least one of the reference elements has a variable impedance. The phase shift of the signal obtained at the output of the bridge circuit is detected, due to the drift of the bridge circuit, with respect to the A.C. supply frequency. The detection signal is then used for compensating the drift by acting on the reference element having a variable impedance in order to bring the bridge circuit back to balanced condition.

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: In a fire sprinkler system a plurality of physically distributed actuators are connected in a normally balanced bridge circuit. The bridge circuit is impressed with a pulsed measuring voltage thereacross to conserve power. LEDs are connected to the bridge for indicating either normal or unbalanced conditions of the bridge as well as indicating which actuator branch of the bridge is causing unbalance.

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 plurality of fire, smoke, security or other detectors of the type which respond to the existence of a predetermined condition are each connected to an input module which monitors the state of the detectors. The input module is connected to an alarm module and when a predetermined number of detectors simultaneously detect the existence of fire, smoke or a breach in security or the like, the alarm module provides a suitable pre-selected command to sound an alarm, commence an interlock and/or activate a predetermined management decision to activate other devices for fire or security protection, such as the automatic discharge of an extinguishing agent, etc. The alarm module may provide different commands depending upon the number of detectors which are simultaneously triggered. In addition, certain preselected detectors may cause the alarm module to provide a command signal regardless of the number of detectors which are simultaneously triggered.

Abstract: A digital alarm system of the type having first and second electrically conductive loops connected by an alarm switch. The alarm switch is normally open, but can be closed when an alarm state exists to electrically short one loop to the other. Currents are generated in each of the loops for use in detecting either the closing of the alarm switch or the occurrence of a fault in one of the loops. Resistors are connected to each of the loops for use in detecting the presence or absence of the currents. A first pair of transistor switches alternatingly short-circuit one resistor then the other; and a second pair of transistor switches, synchronized with the first pair, alternatingly short the ends of one loop then those of the other so that when the alarm switch is closed the first pair of transistor switches simultaneously short-circuit both resistors even if a fault occurs anywhere in one of the loops.

Abstract: An alarm system includes a security loop comprising a plurality of sensors, a circuit connected to the security loop and an alarm. The circuit is responsive to a change in condition within the security loop, and upon any change over a threshold value or substantially any change which is rapid, irrespective of value, the responsive circuit functions to enable the alarm. The alarm may be of audible and/or visual-type with additional capability of signalling a remote control center. The responsive circuit includes a network for self-balance thereby to compensate for changes which are responsive to ambient conditions.

Abstract: A fire detection system includes a single conductor pair for both supplying the energizing voltage to all of the fire detectors in the protected area and receiving back status information regarding the individual detector operation. The system provides individual, successive alarm outputs to regulate successive functions such as "evacuate the area", "dump the fire extinguishing material", and "call in the local fire department", as successive ones of the detectors are alarmed. The system includes a voltage regulator for supplying a well regulated voltage to the detectors, which regulator is switched into a current limiting mode to prevent an inaccurate first alarm signal if the conductor pair is short circuited. This system also provides a trouble-indicating output signal if the system loses supply voltage or experiences a ripple voltage beyond a preset amplitude.

Abstract: A system for displaying the location of an open switch in a series alarm protection circuit containing a plurality of switches. A plurality of independent input monitoring circuits includes a display array to visually indicate the input status of each circuit, the monitoring circuits and visual displays being mounted on a common plate. The high input resistance of the monitoring circuits allows direct connection in a pre-determined sequence to the alarm protection circuit. An unconnected normally closed alarm protection loop has a higher and lower positive voltage value with respect to common voltage of the alarm unit at its input terminals. Designating the higher value as "start" and the lower value as "finish", the monitoring circuits are connected through a sequential order to the finish side of each serially connected switch. As a switch is opened all monitoring circuits that are electrically connected through a closed switch to the start terminals will display a lighted condition.

Abstract: A fire detector provided with a warning system, a reference element and an analysis element whose impedance varies in the presence of a rise of temperature and/or radiation and/or combustion gas, said reference and analysis elements being connected in series or in parallel and constituting two adjacent arms of a Wheatstone bridge assembly. The other two arms are constituted by resistors if necessary variable while the measuring diagonal or bridge, joins, either the common connecting points of the resistors and said elements, or respectively the ends of the detector elements. This device is distinguished in that the two ends of the bridge (X and Y) are connected respectively to the two inputs of two voltage comparators (A.sub.1 and A.sub.2), mounted in parallel and in reverse, each connected to a warning system (S.sub.1, S.sub.

Abstract: An alarm circuit indicating a defect in a car alternator, said circuit comprising a voltage divider formed by two resistors connected between the positive terminal B+ and a negative terminal D- of the alternator, the center point of the voltage divider being connected to the control electrode of a commutation circuit of which the output path is serially connected with a lamp between the terminals of the battery, and rectifier means being provided for preventing the battery to discharge through the voltage divider.

Abstract: An alarm system includes a number of self powered indicating elements each with an integral warning device. Each indicating element includes a control circuit which may comprise a transistor switching circuit, transistor oscillator or part of a wheatstone bridge circuit for example. Each of these control circuits is connected via two lines to a common control element at a position remote from the remainder of the control circuit, such element comprising for example a resistor, a battery or a zener diode dependent on the type of control circuit utilized. A switch is also included to provide, on actuation, either a short circuit or open circuit condition between the two lines. Actuation of this switch or tampering with the lines so as to cause a short circuit or open circuit condition to occur will result in operation of the alarm.

Abstract: Digital interface circuitry is utilized to analyze the condition of alarm detecting loops. The new circuitry is utilized as an alarm system of the type which has a detecting loop extending between a central station and a remote zone at which is provided a normally open detection switch in parallel with a resistor. At the central station a digital high voltage is supplied to the input loop lead and a resistor is connected to ground from a reference point on the return lead, to provide a voltage divider network with the remote resistor. Two voltage-sampling branches connect to the reference point; the first branch has a comparator or pull-up circuit to indicate digitally whether the voltage level is substantially zero or greater, while the second branch has a level detector and pull-up circuit or a comparator to indicate digitally whether the reference point voltae is greater than its normal level.

Abstract: A monitoring device for monitoring incandescent lamps, especially in motor vehicles, is provided. A measuring resistor is connected in series with an incandescent lamp to be monitored. Means for monitoring the voltage drop at the measuring resistor are provided. The monitoring means comprises an operational amplifier to one input of which the connection between the measuring resistor and the incandescent lamp is connected and to the other input of which a voltage divider is connected which is mounted in parallel with the measuring resistor and the incandescent lamp. The voltage divider is formed of ohmic resistors, and the output of the operational amplifier controls an indicator means for generating an indication signal upon missing or excessively low voltage drop at the measuring resistor.

Abstract: In order to assure that an alarm signal is transmitted, whether in the case of a true alarm condition or tampering, whether advertent or inadvertent, without any significant increase in power requirements, an alarm radio transmitter system is provided with a supervised loop which controls an electronic switch for connecting the power source (a single battery) to energize the transmitter for a brief interval of time only when an alarm condition or tampering occurs. The supervised loop is part of a bridge circuit also connected to the power source which draws a minimum amount of current therefrom. The alarm radio transmitter system may be remotely located where attention is not available, since the battery need only be infrequently changed.

Abstract: A device for detecting cable insulation faults while laying underground cables. The device is adapted for attachment to the cable reel, having one lead connected to the metal shield of the cable or to selected conductors and the other lead to the metal reel. A bridge circuit within the device applies a voltage potential between the two leads, with the resulting resistance value serving as one leg of the bridge circuit. Two high impedance amplifiers are connected across the bridge circuit to act as buffers between the bridge and the operational circuitry. A differential amplifier is connected to the outputs of the two high impedance amplifiers to provide an output proportional to the difference between the two high impedance amplifiers. This differential amplifier's output is adjusted to provide an alarm trigger signal when its two inputs differ by a predetermined amount. Preferably the alarm signal is transmitted to a remote location for providing the alarm.

Abstract: A novel method is disclosed for determining the change in tire pressure of a dual wheel tire by detecting a change in the axle housing moment arm supported by the wheel assembly. The preferred apparatus for carrying out the invention comprises one or more strain gauges affixed to the axle housing adjacent the tire assemblies and electronic means for measuring the strain occurring as a result of the underinflated tire.