Re: Reverse Loops and Occupancy Detection

Vollrath, Don <dvollrath@...>



If you use a current transformer occupancy sensing device like the NCE BD20 and arrange for it to measure track current between the A-R unit output and the track it will work just fine. It doesn’t matter which track lead goes through the transformer hole of the BD20, nor the actual direction/polarity of the A-R track. Other brand products using the isolated current transformer measurement technique will work equally as well.


Other schemes that measure current to the input side of an auto-reverser will indicate continuous A-R track occupancy due to the small but continuous measurable current flow it takes to operate the A-R unit. Diode drop type occupancy sensors will have the same issue. Also, diode drop type occupancy sensors are usually not isolated from rail power making them difficult to deal with the rail swapping connections of the A-R controller if/when attempted to be connected to the output side of the A-R controller.


However – If the polarity of your A-R section is controlled by a relay or DPDT switch contacts of a turnout machine… you might be able to measure only track current flow as it goes into (only) the DPDT switch and be compatible with almost any type of track current occupancy sensing device.  




From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Sunday, July 10, 2016 6:59 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Reverse Loops and Occupancy Detection


I would like to add occupancy detection to an existing hidden reverse loop.  Is the detector affected by the reversing operation? In other words, when the loop reverses does it cause a current to flow in the power leads that would cause the detector to change its reading?


Ed Robinson


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