Re: USP End-of-Line Supervision Device, Model R64

["Robert L Bass" <robertbass1@xxxxxxxxxxx>]

> Haven't read this yet, but so far
> it sounds rather complicated.

It really isn't complicated, though one of the images might make it seem so.  To better understand how an EOL supervisory relay
functions it helps if you first know the basics of fire alarm circuits.

Smoke detectors are "open circuit" devices.  When they detect smoke they close the sensing circuit (called a "zone").  This is seen
by the control panel as an alarm condition.  In order to supervise the wiring an EOL (stands for "End Of Line") resistor is placed
across the sensing circuit.  The control panel sees a trickle of current flowing through the zone as a "normal" condition.

Thus there are three possible conditions for a conventional smoke detector circuit:

1. Normal: A trickle of current flows through the EOL relay.

2. Alarm: Lots of current flows because a smoke detector has shorted the circuit.

3. Trouble: No current flows.  The circuit is open because of a break in the wire or some other problem.

An EOL Supervisory relay is connected to the last smoke detector in the circuit.  12 or 24 VDC from the smoke detector is connected
to the coil of the relay, keeping engaged.  The sensing circuit is connected to an EOL Resistor (usually an integral part of the EOL
relay) and then through the contacts of the relay.  With DC power available the relay keeps the sensing circuit complete, allowing
that trickle of current to flow through the EOL resistor and back to the control panel.

If the power is interrupted the relay releases, breaking the circuit.  This is seen by the control panel at the other end as a
"trouble" condition.  Typically, the panel will cause an LED to flash and a sounder to warn folks that a problem exists.  It may
also be programmed to report the trouble condition to a central monitoring service or fire department headquarters.

I have copied System Sensor's diagram, simplified it and for illustration purposes and attached it to this post.  Some servers block
posts with binaries on non-binary newsgroups, so I'll post this message twice: once with and once without the image.  Hope it helps
the OP as much as it's certain to annoy the IB.  :^)

--

Regards,
Robert L Bass

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