Simplex 4100-0136 Installation Instructions Manual page 9

How the Decoder Works,
Decoding the Coder
Loops
Continued
In Method Two, the decoder acts as the "monitor zone" for the loop. A critical limit with this
method is that the line resistance from the "plus" loop output to the "return" must not exceed 800
Ohms through any alarm contact on the loop. This 800-Ohm limit includes line resistance to the
contact plus contact resistance plus line resistance back to the panel. It cannot be assumed that the
further away the coder is from the panel, the higher the resistance. It is very possible that a coder
close to the panel has contact resistance that exceeds the wire resistance. Some coder contacts may
have high "ON" resistance, especially after having been used in AC loop applications. These
contacts can be rubbed/polished to remove carbon buildup or oxide coating, and thus lower
contact resistance. Figure 4 illustrates Monitoring Method Two.
Note: If you determine that the coder contacts cannot be used for direct connection,
use Monitoring Method One.
Figure 5. Monitoring Method Two
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4081-9002 3.3 K, 1 W
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RESISTOR
HARNESS