CMU-24VDC-ITL Cabinet Monitor Unit
Operations Manual
Eberle Design Inc.
Page 7
When a transition from the inactive state to the active state or a transition from the active
state to the inactive state is absent for greater than 2500 milliseconds, the CMU-24VDC will
set a status bit in the Type 189 frame. This alarm condition will not cause a FSA. It should
cause the appropriate response in the ATC. This status is non-latching such that once a
status bit has been set, the sensing of five valid transitions of the input will clear the status
bit.
2.12 CMU POWER FAILURE
The CMU-24VDC will monitor the +24VDC POWER input and the NRESET and
POWERDOWN cabinet control inputs to determine a CMU Power Failure response. The
POWERDOWN signal in the False (low) state indicates loss of power in the ATC. A CMU
Power Failure will be recognized when both the POWERDOWN and NRESET signals are
False (low) for greater than 100 ms or the 24VDC POWER voltage is less than the DC
Power Level Sense Dropout defined in 5.1.
2.12.1 24VDC POWER LEVEL SENSE
The CMU-24VDC will monitor the CMU 24VDC POWER input and AMU 24VDC POWER
inputs reported by each AMU-24VDC. When any 24VDC POWER voltage is less than the
DC Power Level Sense defined in 5.1 for greater than the DC Power Fail Monitor timing
defined in 5.2, the CMU-24VDC will cause a NFSA. Once NFSA has been set, the
POWERDOWN and NRESET signals will not be monitored until all DC voltages have
exceeded the DC Power Level Sense Restore level defined in 5.1.
2.12.2 POWER INTERRUPT
The CMU-24VDC will disable monitoring of the +12VDC and +24VDC power supply inputs
when either the POWERDOWN or NRESET input is False (low). When the POWERDOWN
and NRESET signals are both False (low) the CMU-24VDC will cause a NFSA.
2.12.3 POWER RECOVERY
When the POWERDOWN input is True (high) and the NRESET signal goes from False
(low) to True (high) the CMU-24VDC will begin timing the programmed Minimum Flash
Interval. During the Minimum Flash Interval the CMU-24VDC will be in NFSA.
2.12.4 POWER UP
Following initial application of 24VDC voltage the CMU-24VDC will maintain a NFSA until
the POWERDOWN input is True (high) and the NRESET signal goes from False (low) to
True (high). The CMU-24VDC will then begin timing the programmed Minimum Flash
Interval. During the Minimum Flash Interval the CMU will be in NFSA.
2.12.5 MINIMUM FLASH INTERVAL
During the Minimum Flash Interval the CMU-24VDC will be in NFSA. The Minimum Flash
Interval will be programmed in the Datakey between the limits of 6 seconds to 16 seconds
with an incremental adjustment of 1 second. The CMU-24VDC will not set a FSA during the
Minimum Flash Interval.
2.13 FIELD OUTPUT CHECK
The Field Output Check is a continuous verification that the field signal output states set by
the ATC are properly driven to the signal loads and correctly sensed by the AMU-24VDC
and CMU-24VDC. It is an enhanced function made possible by the Serial Bus #1
communications between the ATC and CMU-24VDC. The CMU-24VDC will receive a Type
61 message from the ATC that contains an image of the controller output commands to the
load switches. When a fault condition triggers the CMU-24VDC, the Type 61 message
information received while the fault condition was being timed will be used by the CMU-
24VDC to determine whether the sensed field signal input status corresponded to the ATC
