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Monday, October 6, 2014

Caught on Camera - Episode 4: Relay Logic

Today I have a few photos taken in that brief period of time when the relays are still fluttering about and signals, at least the old school variety, can do some rather..."nonstandard" things.  Today we begin on the SEPTA reading trunk line between the Center City Tunnel and Wayne Junction.  This was re-signaled around 1990 and while heavy use of solid state logic was just around the corner, northeast commuter lines were still hitting things up in the traditional way.  Here we see the LED upgraded 24 automatic on track #2 displaying Clear G/G New York Central style. the 24 auto is totally off the reservation!  I will say that I wish I knew what about LED arrays make certain ones fade out and others exhibit more binary behavior.

Alright, time to lift the veil.  Here's a video of the signal progression. Note the relay lag actually lasts for a second or two.

Here is an example from a recent trip on the Capitol Limited on the former Conrail Chicago Line just out of Chicago.  Here the MP 508 automatic is in the process of flipping from Stop and Proceed up to Approach right after our train passed by.  This is because there was a westbound Wolverine Service train waiting for us to clear the single track at CP-506.

One of my favorite signals with wonky relays is the southbound Southern cantilever at MIDLAND interlocking in Gainesville, GA.  This signal has some serious Conrail envy because when trains pass it at Approach Diverging, it drops first to R/Y Diverging Approach before finally going R/R.  I say Conrail envy because this is somewhat typical on plants where R/Y is used for Restricting.

In this Caught on Camera special you can first see the signal upgrade from Approach to Approach Diverging, then get knocked down  in the manner I just pointed out.

I'm sure I have a few more examples of this sort of behavior captured on still or video, but I'm going to leave it at these for now.  If you have some fun examples of relay logic feel free to post them in the comments.

1 comment:

  1. Regarding Signal 242, the green over green, you would have never seen this back in the Reading days. Yes, there was a relay lag, but the bottom head would turn red first.

    And, just as an aside, the Reading used offset heads for their block signals. And I've seen some of your photos where the green light is on the upper right, such as Newtown and Jenkintown. I think this is a SEPTA thing. I could be wrong, but I spent a fair amount of time around the Reading growing up (at least in Philly) and I always remembered green being on the left.