2K2 End of Line resistor in home alarm system

[Jason]

For my learning, my home alarm (NESS D8) calls for a 2K2 (2200 Ohm) end of
line resistor to be placed within the loop for each PIR, tamper switch,
etc. What is the usage of these resistors for? It also says that each zone
PIR input must have one of these resistors even if the input is not in use
(ie. no PIR connected to it) - why is that?

Is it common practice in alarm installations to wire the resistor at the PIR
end of the wire or at the 'heart/brains' of the alarm system? If the
latter, if more than one PIR is connected into a zone input is it still
acceptable (one resistor accomodating 2 or more PIR inputs), or should a
resistor be in place at each PIR (more than one resistor on a single zone
input).

Asking because in the middle of connecting up my new home system now. (Ness
D8 - www.ness.com.au). Thanks.

 

[Russ]

"Jason" <jallen@pobox.DELETE.THIS.TO.SEND.EMAIL.com> wrote in message
news:bj7f65$3ls$1@gnamma.connect.com.au...

For my learning, my home alarm (NESS D8) calls for a 2K2 (2200 Ohm) end of
line resistor to be placed within the loop for each PIR, tamper switch,
etc. What is the usage of these resistors for? It also says that each
zone
PIR input must have one of these resistors even if the input is not in use
(ie. no PIR connected to it) - why is that?

Is it common practice in alarm installations to wire the resistor at the
PIR
end of the wire or at the 'heart/brains' of the alarm system? If the
latter, if more than one PIR is connected into a zone input is it still
acceptable (one resistor accomodating 2 or more PIR inputs), or should a
resistor be in place at each PIR (more than one resistor on a single zone
input).

The end of line resistors are part of the anti-tamper precautions. They
allow the panel to detect both an open or short-circuited loop. To work
effectively in this role, the resistors need to be installed at the sensor.

Unused loops need to have a resistor across the connections at the panel,
otherwise it will think there is some kind of fault or tampering on that
zone.

Logically, if you have a NC loop with 2 or more sensors in series, a
*single* resistor should be installed at the furthest sensor (thus the "end
of line" term), so that if anyone tries to short the wires at any point on
the loop, the panel will detect their attempt. If you install multiple
resistors, the panel will see 4k4 or greater on the loop - it may accept
this, but shorting one sensor may just drop the resistance from 4k4 to 2k2
and may not be detected by the panel (depending on how smart it is).

R.

 

[Jason]

On Fri, 5 Sep 2003 12:46 am, Russ wrote:

The end of line resistors are part of the anti-tamper precautions. They
allow the panel to detect both an open or short-circuited loop. To work
effectively in this role, the resistors need to be installed at the
sensor.

Unused loops need to have a resistor across the connections at the panel,
otherwise it will think there is some kind of fault or tampering on that
zone.

Logically, if you have a NC loop with 2 or more sensors in series, a
*single* resistor should be installed at the furthest sensor (thus the
"end of line" term), so that if anyone tries to short the wires at any
point on the loop, the panel will detect their attempt. If you install
multiple resistors, the panel will see 4k4 or greater on the loop - it may
accept this, but shorting one sensor may just drop the resistance from 4k4
to 2k2 and may not be detected by the panel (depending on how smart it
is).

R.

Fantastic info. Thanks, much appreciated.


Cheers,
Jason