What is the purpose of the occupancy detectors and why is it gapped? The Digitrax Big Book of DCC has this for the single district wiring but doesn't explain what it is for. Thanks in advance.
DCC Question
Jul 14, 2003
2 Replies
I will be installing occupancy detectors to drive a signal system.
Scott
An occupancy detector detects the presence of a train, engine or cars at a particular location, to operate signals, crossing gates, etc.
The coil-type DCC occupancy detectors work by sensing electrical current flow in the stretch of track they are connected to. In order to detect cars, you have to install a resistor across one (or more) of the car's wheelsets, so some small current flows.
The rails (actually, only one) must be gapped to isolate the occupancy detector from the rest of the layout, otherwise, it will detect trains/engines/cars everywhere and not just within the limits that you want.
The most common installation would be for a signal system (or even CTC) where the mainline would be divided into "blocks" with a signal governing entry into the block. The detector feedback would be used by the signal logic to determine which signals should be red, yellow, or green.
--Dan
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