Fault Relay or Trouble
• It is a normally-energized, single-pole, double-throw (SPDT) relay.
• During normal operation, the relay contacts are normally closed
(NC) and normally open (NO) as shown in FIGURE A-5.
• When a fault is detected or power is cut or turned OFF, these
contacts change as follows:
• normally closed contacts open
• normally open contacts close.
• Provides an electrical path for fail-safe relay operation. In the
event of any failure, including power loss, the relay will change
to a fault condition
The Fault Relay can remain STEADY ON or PULSED. These
two different modes can communicate different information to any
PLC or DCS connected to the fault relay:
Figure A-5.
Relay Contacts
Appendix A, Internal Relay Option
A-8
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