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The Possible SPAD alert is designed to fire when a signal appears to be passed whilst at danger. This will often fire in the event of a signal reversion, which could be caused by various conditions (e.g. Track Flick).

The alert is deliberately named "Possible SPAD" as it should be used to indicate a possible fault in the signalling system rather than a driver fault.

Real Example

(The train occupying AB track circuit enters AC track circuit while 101 signal is at danger)

Input Channels

Berth Track Circuit TPRDigital input channel for the berth track circuit (TPR immediately before signal)
First Track Circuit TPRDigital input channel for the first track circuit (TPR immediately after signal)
Signal RGKDigital input channel representing the red (danger) state for the signal

Logic

The alert will fire when the First TPR goes occupied whilst the Berth TPR is occupied and the Signal RGK is at danger.

 

This alert will not currently work for some junction layouts.

 

 

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