Abstract: An alarm system includes a controller (20), a plurality of transponders (23-26), and a transducer (50) connected to one of the transponders (23). A voltage reference which is preferably earth ground is established for the entire alarm system. A local loop comprises a pair of electrical conductors (72, 73) connecting the transducer and transponder. The transponder includes a comparator (70, 80, 80-82) having a fixed reference input and a second input which is the voltage level on the local loop. If a ground fault or other abnormal condition occurs, this is sensed by the comparator and an indication provided a loop status portion (60a) of the transducer. The controller includes a communications module (27) by which each transponder is addressed, and the transponder includes an output response portion (60b) by which the transponder identifies itself to the controller as the transponder at which the ground fault or other abnormal condition has occurred.

Abstract: An alarm system including a sensor for providing an output signal upon sensing a given condition, an alarm unit for providing an alarm signal on receipt of the output signal, and a timer, coupled between the sensor and the alarm unit, which is reset to a preset count each time it receives an indication that the sensor has detected the given condition where the timer is allowed to count down from a preset count while no sensor is providing output signals and an arming signal is generated by the timer when it completes the countdown.

Abstract: A relay supervision system is disclosed to check the presence and operability both of a relay and the associated circuitry located at a position remote from the control unit which effects the supervision. The supervision is accomplished by pulsing the relay with energy at a volt-time integral less than that required to energize the relay and displace a contact set, but sufficient to cause current flow through the winding and its associated circuit components. If the relay includes two separate windings, each winding can be separately pulsed at different times, the relay state determined, and both windings effectively supervised without changing the position of the contact sets operated by the windings.

Abstract: A mounting frame for supporting several printed circuit boards in abutting relationship includes a pair of side frame members. At least some of the printed circuit boards have slots along or near the side edges, through which screws extend into the side frame members. The screw heads extend over and retain the printed circuit boards in position. When the screws are loosened for some of the boards, those boards can be displaced from each other but not removed from the frame. Additional loosening of one set of screws allows the removal of that one board, even if that board is not the last board in the run of boards. Cylindrical bores are provided in at least one of the side frame members to afford pivotal mounting of the frame-and-card set in an enclosure. When the frame-and-card assembly is pivoted outwardly, an additional set of cards can be mounted on the back of the frame.

Abstract: A security alarm system includes a transponder having a housing enclosing both a sensor and associated circuit means in a unitary package. The housing base includes barrel-shaped connectors, and a pc board carrying the communications components is carried by the housing cover. Flag-like connectors mate with the barrel-shaped connectors when the cover is attached to the base, and the connectors give both good mechanical indexing and retention, and effective electrical contact. Removal of the cover from the base breaks the electrical contact and thus breaks continuity back to the system controller, indicating someone has tampered with the system.