Anatomy of the Marion Branch. Really OLD stuff.

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LakeATCS
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Joined: Sat Feb 28, 2015 5:37 am

Anatomy of the Marion Branch. Really OLD stuff.

Unread post by LakeATCS »

Since we got to talking about blocks and bits in the other thread and the OK blocks. I wanted to demonstrate how the current of traffic BK blocks work on the Marion District (branch)

I ended up with the Marion branch after two people looked at the MCPs and gave up saying they simply made no sense.
What I found is some of the oldest logic around.

The CTC system is old in that not only does it track occupancy, but the bits also tracks current of traffic. Now to do that they used a clever trick. The same bits are used to track current of traffic AND occupancy. How does that work. Let me show you.

Okay, lets look at the main between CP19 and CP21. There is one bit on each MCP that tracks both current of traffic on both.

Now, lets have the dispatcher line a train south.
Immediately on the dispatcher lining CP19 with a 1SGK (Southbound signal).
CP 21 will display a 1BK bit if it was not high. CP 19 will not display a 1BK

Think of it like this, PITCH and CATCH. By lining the 1SGK at CP 19, It has alerted the CP21 that the current of traffic has been set for southward movement. CP21 says, okay I know that the signals are set southward, so I will display the 1BK ready to "catch"

Now when the train gets past CP19 the 1BK bit will display. This combined the with 1BK bit CP21 will cause the display to throw the block red on the display (A BK is AND logic. For the block to be shown with a red line, BOTH the 1BK bits must be ON. This is different from an OK in that ether bit can cause the block to be shown red)

Now once the train clears the block, CP19 will have the 1BK block drop, CP21 will have the 1BK stay high. This is because the occupancy is clear, but the current of traffic is left in the direction of last movement.

Okay now, lets do a Northbound. Dispatcher will punch the 1NGK at CP21. This will immediately cause the 1BK at CP21 to disappear, and the CP19 1BK to appear. Again pitch and catch. The current of traffic has been set northward. When the train gets past CP21 northward, the CP19 1BK will apear.

The siding between CP19 and CP21 is set up the same way. As is the main and siding between CP 53 and CP54.

CP33 and CP35 are no longer set up this way. When the connection was put in at Claypool. NS changed the blocks to conventional OK blocks.

Now the mainline between the sidings (like CP 33 to CP 53 and CP 78 to CP 58) is set up in a pretty much similar way. Only there are two AK blocks that tell the dispatcher when train is approaching the control point. So you have a CP 33 1NAK / 1BK / 1SAK CP53. The BK works in the same pitch and catch.

CP 3 to CP 19 is also like this, but even more complex due to having the CSX in the middle. It's a nasty hair puller set up.

Now about of a 1/3 of the Marion branch has been upgraded from this logic. CP 421 to CP3, CP 21 to CP 35 and CP54 to CP58 is modern logic.

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