Train Direction Detector

The Train Direction Detector senses which direction a (dc/analogue) train is moving. 

It is used for signalling lines with bidirectional running and switching IRDOT-P controlled points for trains travelling in one direction but not the other.

When a line is used for bidirectional running there may be signals to control trains running in both directions. As a train runs along the line all the signals facing away from the train should be at danger (red). If the signals are controlled by IRDASC units then the Train Direction Detector can be wired to the RR (reverse running) terminals of these units to achive this. Similarly the Train Direction Detector can be connected to the I (inhibit) terminal of the IRDOT-P units so that points will only switch for trains running in one direction.

The Train Direction Detector takes a very low current from the track to sense the polarity at the rails (which it remembers even after track power is removed).  The connections from the track are electrically separate from the rest of the wiring (built in opto-couplers provide this separation).  Terminal d1 or d2 switches to 0 volts depending on the direction of the train because the track polarity changes when the train's direction changes.  Terminal d1 or d2 connect to the RR (reverse running) terminals of the IRDASC signalling units. When d1 or d2 switch to 0 volts because of the direction of the train, the RR terminal will be activated causing the signal to remain at red.