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ACM 150
Relay terminals and activation options
Relay terminals
Since the output relays are DPDT, they may be connected to two separate devices,
and each device can have a separate DC or AC power loop, wired through the
common (labeled COM) terminals. Each set of terminals provides the choice of wiring
to the normally open (NO) or normally closed (NC) contacts. Since the relay state is
NC when de-energized and NO when activated, most users wire to the NO terminals.
However, if your control logic allows you to trip on loss of signal, you can wire to the
NC terminals. This has the benefit of alarming if a wire is broken or disconnected.
Fail safe configuration
The software can be configured to reverse the relay logic so all of the output relays
are normally energized. You would wire to the NO terminals. An Alarm 1 or Alarm 2
condition, a broken or disconnected wire, or a failure of the relay would activate
the alarm device, shutdown sequence and/or control logic for that relay. This is a
fail-safe implementation, and it requires a change in the ACM 150 monitor software
configuration by Honeywell Analytics.
NOTE
If you use the fail-safe configuration, all of the ACM 150 monitor output relays
will activate on loss of power, which is likely to cause wide-spread alarms and
gas shut-downs. Even a reboot of the computer will cause this to occur. It is
essential that a bypass switch be utilized to maintain power in the wire loop so
that the ACM 150 monitor can be shutdown for service or when loading new
software.
Non-latching vs. latching configuration
The ACM 150 monitor output relays are non-latching in the standard configuration.
This means that they reset automatically when the condition (alarms, malfunction,
power loss) returns to normal.
The software configuration allows a change to latching relays. When the condition
returns to normal, the latching relay contacts will remain activated. They can only be
reset from the ACM 150 monitor touchscreen or via network remote computer. This is
not recommended if you have latching relays in your control logic, because it would
require a manual reset at two locations to silence alarms. However, if your control
logic does not latch, i.e. holding the condition until manually reset, you should have
the ACM 150 monitor configured with latching relays. This is especially important if
the ACM 150 monitor alarm relays will directly activate automatic gas shutdown in
your facility.
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