User's Manual

2015-07-31
V029627_02_WOFS_Installation_Guide.docx Page 9 of 20
7 Determining if a Device Requires a Normally Open, or
Normally Closed State
Before connecting the Receiver to an alarm panel or other external device, the user must
determine if the alarm system panel (or other device) requires a Normally Open (N/O) or
Normally Closed (N/C) state.
Note: For the rest of this section, it will be assumed that the device being connected is
an alarm panel, but the theory and steps are the same for a different external device.
The external device, such as an alarm panel, when used to connect to the WOFS will dictate
either the use of Normally Closed or Normally Open TID configuration. In some cases, this may
be configurable in the alarm panel.
 In the N/C case, a high voltage at the alarm panel indicates an alarm (one or more of the
TIDs has opened) or the wiring has been cut. A low voltage at the alarm panel indicates
the wiring has been shorted.
 Conversely, in the N/O case, a high voltage indicates a wiring fault (wire has been cut)
and a low voltage indicates an alarm or wire short.
1. In configuring the connection between the WOFS Receivers, and an alarm panel or iRMS,
end-of-line (EOL) resistors are used at the termination of protected loops or “zones” to allow
for differentiation between an active alarm and secure states, in addition to wiring faults or
wire tampering.
2. As shown in the Figures 9-11, an EOL resistor is used in series with a resistor internal to the
alarm panel to create a voltage divider. Intermediary voltage values indicate a secure (non-
alarming state), high or low voltages indicate an alarm or fault – the actual alarm or fault
state being dictated by whether the Normally Closed (N/C) or Normally Open (N/O)
configuration of the Tamper Indicating Device (TID) is used. The value of the selected EOL
resistor is dependent upon the alarm panel’s specifications.
Figure 8 - Alarm Panel