American District Telegraph Company

William J Lautzenheiser

James B Edson

Kenneth E Beeson

Martin E Henderson

Richard A Simonetti

A system for providing a distinctive indication that a system, such as a security system, is in a test mode in which the distinctive indication includes audible and/or visual indications that a test sequence has been initiated, followed by testing of the system during the test sequence, with test results being indicated by altering the format of the audible or visible signal. In one embodiment involving a security system, a periodic signal is changed to a steady state signal when a sensor has been violated, thereby to provide a reminder that the system is in the test mode followed by instantaneous communication to the user of not only the operability of the sensor but also both the transmission of the sensor's output to a central control unit and the operability of this control unit itself.

System for test sequence annunciation

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.

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North Billerica, MA, United States of America

William J Lautzenheiser