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NSM-3E Signal Monitor Unit

Operations Manual

Yellow field signal outputs. Any channels which have been selected for Dual Indication

Monitoring by the SSM switches will function as described above in Section 2.2.

GY-Dual Indication Monitoring is disabled when the Red Enable input is not active.

2.2.2 WALK DISABLE (DUAL INDICATION MONITORING)

This option will modify the operation of Dual Indication Monitoring on the NSM-3E Signal

Monitor. When enabled, the Dual Indication monitoring function will not monitor the Walk

field outputs. This function is enabled by the front panel option switch labeled "WALK

DISABLE". See also Section 1.3.1.

This function detects the absence of a minimum 2.7 second period of an active Yellow field

signal output during a Green to Yellow to Red signal sequence. Clearance Monitoring is

enabled concurrently with Dual Indication Monitoring on a per channel basis via the front

panel SSM switches.

Clearance Monitoring is disabled when the Red Enable input is not active.

A Clearance (short or absent Yellow) fault condition will place the NSM-3E Signal Monitor

into the fault mode causing the Output relay contacts to transfer.

This error detection function supplements the normal Conflict, Dual Indication, and Red Fail

monitoring algorithms for sensing faults which are intermittent or pulsing in nature. The

RMS-Engine is designed to filter out short term transients commonly found on the electrical

service and provide noise immunity against false signal detections. The Recurrent Pulse

detection function is designed to respond to fault conditions which are intermittent in nature

and do not meet the continuous timing requirements of the normal detection algorithms, yet

may still produce improper signal displays. These input conditions are differentiated by

their longer time constant and fault response times.

The diagram below shows an example of a recurrent Conflict fault. Channel 1 Green is

detected active due to a malfunction of the load switch which caused the output to "flicker"

On for 100 ms approximately every 200 ms. Since normal Conflict detection requires a

continuous fault of at least 350 ms typical, this malfunction could go undetected. The

Recurrent Pulse detection algorithm will combine these pulses into one event and trigger a

Conflict fault once the longer recurrent timing threshold is exceeded.

When triggered by a recurrent fault condition, the NSM-3E Signal Monitor will enter the fault

mode causing the Output relay contacts to transfer and illuminate the appropriate

CONFLICT, DUAL INDICATION, or RED FAIL indicator along with the RP STATUS

indicator. The unit will remain in the fault mode until reset by the Reset button or the

External Reset input. Fault response times will vary depending on the pulse width and

frequency of the recurrent inputs, but will range from 1000 ms minimum to 10.4 seconds

Eberle Design Inc.

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