Line monitor for two wire data transmission
AssigneeGeneral Signal Corporation
InventorsRobert W. Right, Hilario S. Costa
Life of this patent
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Abstract
A line monitor uses two wire data transmission in a fire alarm and detection system. A line voltage monitoring mechanism is within each wiring/contact monitoring circuit such that the exact value at any time of varying source voltage is known. The monitoring current resultant from the monitoring arrangement is strictly a function of impedance and not a function of source voltage because a line-monitoring scaling factor is incorporated into the final calculation. The monitoring scheme also results in the alarm and trouble voltage thresholds being suitably altered to take account of changed line voltage conditions.
Claims5
An alarm system for detecting and warning of the presence of alarm and trouble conditions in transponder units located in a plurality of zones, comprising:
- a loop controller having a plurality of signal/power supply lines, including a wiring pair, connected to the respective units;
- a module, including a microcontroller, connected in each of said predetermined zones to said plurality of lines, said module being capable of initiating communication of the alarm and trouble conditions of said circuits to said loop controller;
- a plurality of outgoing circuits extending from said microcontroller, and means within said microcontroller for selectively operating said circuits in a variety of modes;
- and
- means, including a connection extending from said microcontroller to a portion of said selectively operated circuits .and a line, for monitoring the line voltage such that the variable state of that voltage is accurately known, including means for obtaining a resultant monitoring current, which is indicative of the presence of alarm and trouble conditions, strictly as a function of the impedance across said wiring pair, and not as a function of the source voltage.
Dependencies are inferred from the claim text.