1You have to watch PDF page and page #. Sometimes they are different. PDF page is easier to "Goto".
Monitored contacts:
I'll use a very simple example, ignoring the specifics.
Suppose the sensors are fed with a 5V supply in series with a 10K resistor. (Panel might be 12 or 24 V, but I'm using 5 here.
Now, the circuit looks like a 5V supply 10K resistor and a 10K (EOL) resistor with a switch across it to common.
So, with no EOL resistor, we would read 5V
With an EOL resistor, we would read 2.5 V
With the contacts closed (Alarm), we would read 0 V.
That's the ideal world, The resistors and power supply have tolerances which have to be taken into account. Matched resistors (10K) probably would not be used,
The 0V level would depend on wire resistance.
We could have (Above 3.5V) - supervisory alarm
Between 1.5 and 3.5) V; - Supervised - not in alarm
Between 0 and 2.5 V ; Alarm
All measured at the panel.
If the contacts were unsupervised, then you would have 0 and 5 V levels to deal with. 0V alarm, 5 V not in alarm. Again tolerances apply, so say under 100 mV alarm, greater than 4 V alarm or use the same definitions above and re-define their meanings.
The levels are basically determined with wire length, wire gauge, power supply tolerances and resistor tolerances. Higher R values mean less power consumption.
EDIT: If I were doing the design, I'd use 10 mA with the contact closed. This provides sufficient wetting current.
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I had to interface to an FAP panel once. My box used the alarm contacts from the FAP. Instead of a monitored contact, I used 3 conductors (An SPDT relay from the FAP). When not in alarm, I would show a LED indication and when in alarm, I would show the LED off. It's not a monitored contact, but if the entire cable was cut, the panel would know about it, We also knew when we could reset the panel. The hydrogen and toxic gas alarm fed the FAP panel and they had EOL resistors.