SSM-LE Series
Operations Manual
Eberle Design Inc.
Page 10
may still produce improper signal displays. These input conditions are differentiated by their
longer time constant and fault response times.
The figure below shows a simple example of a Recurrent Conflict fault. Channel 2 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. Because normal Conflict detection requires a
continuous fault of at least 350 ms typical, this event could go undetected. The Recurrent
Pulse detection algorithm will process these pulses into one event and trigger a Conflict
fault once the longer recurrent timing threshold is exceeded.
When triggered by a recurrent pulse fault condition, the SSM-LE Series
will enter the fault
mode, transfer the Output relay contacts to the Fault position, and display the appropriate
CONFLICT, DUAL INDICATION, or RED FAIL status screen along with RP STATUS. 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 typically range from 1000 ms minimum to 10 seconds maximum.
3.11 FLASHING YELLOW ARROW PROTECTED-PERMISSIVE MONITORING (FYA)
The SSM-LE Series is designed to monitor an intersection with up to four approaches using
the four section Flashing Yellow Arrow (FYA) movement outlined by the NCHRP Research
Project 3-54 on Protected/Permissive signal displays with Flashing Yellow Arrows. For
monitoring purposes an FYA approach is logically defined as a four input “channel”
consisting of the solid Red Arrow, solid Yellow Arrow, flashing Yellow Arrow (permissive),
and solid Green Arrow (protected).
