| Long before the modern PTC concept of automatic train control, this Richmond, Fredericksburg & Potomac 4-8-4 Northern used a simpler version called Pulse Code Cab Signal. The system was developed by Union Switch & Signal Company for the PRR. The system had two 60 Hz signals. The break-sensing “track” signal was fed down one rail towards the oncoming train and crossed through its wheels, returning in the other rail. The pickup just ahead of the wheels would sum the approaching current from one side with the returning current on the other. The externally returned ”loop” signal was fed into and out of the mid tap of a resistor across each end of the track circuit. The pickup would sum the approaching current on each side as it carried on past to the far end of the track. This signal was shifted 90 degrees from the other. The signals were applied one or both continuously to give Approach or Clear aspects while no signal was a Restricting aspect. The test installation eliminated wayside block signals, and trains relied solely on cab signals. A very early, primitive forerunner of the modern PTC system. No photographer or date was given for the photo. |
| Date:
6/1/1950 |
Location:
Alexandria, VA Map  |
Views:
322 |
Collection Of:
 
Gary Everhart |
| Locomotives: |
Author: Gary Everhart
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| Picture Categories: Roster,Yard,Steam |
This picture is part of album: RFP "Pulse Code Cab Signal" |