124
Andover Controls
Normally Open Supervisory Inputs
NO Series Parallel
With this type of input wiring, two external resistors are added to the input, one in series
and the other in parallel. When the door switch is open (normal position) the door is
assumed to be closed. The circuit reads the value of the parallel resistor.
Circuit Action Input Senses Condition
Switch Closed External Resistance
÷
2 Door Closed
Switch Opened External Parallel Resistance Door Open
Wire Cut Infinite Resistance Violation or error
Input Shorted Zero Ohms Violation or error
When the door is opened the switch closes an a reading results that is composed of both
resistances in parallel that works out to be half the value of one of them (5K). If the wires
to the door are cut it appears as an infinite resistance. Shorting the input causes a zero
ohm resistance. Both a short and an infinite resistance (open) should result in an error
condition.
AUX
or
DOOR
or
REX
RET
Contact
Closure
External
Resistors
10 K
Ω
typical
AC-1
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