The Sounds of PRR Signaling

This topic has come up a few times in other articles, but one of the neat things about non-solid state signaling technologies are the sounds.  Relays click, air hisses, motor generators....motor-generate?  One of the things I try to do on my documentary trips is capture any interesting sounds that might be escaping from one of the old relay huts or air plants.  My digital camera takes video just as well as stills so it doesn't take much extra effort and I then assemble the results into compilation videos for YouTube.

The following videos were taken mostly along the PRR Main Line or some of its connecting branches.  The sounds can be broken down into the following categories.

Air Hiss: Where switch points are operated by air, there is always a hissing leak somewhere.  Always.

Compressor Chug: When the pressure gets low enough, a compressor trips on.

Something Turning: Motor generators  or flashing relays typically have rotating parts.  When they get worn out, you can hear them.

Cab Signal Code Generators:  The most common sound I capture, electro-mechanical CSS generators generate pulses of current between 1 and 3 times a second. Code rates are 70 pulses per minute for Approach, 120ppm for Approach Medium and 180ppm for Clear. Generators are typically only active when code is being supplied.

The sounds are pretty self explanatory so I won't go into much detail.  Part of the fun is trying to determine which cab signal codes you can hear or what that rotating thing is doing inside the relay cabinet.

In the first video we have sounds from:

MP 53.1 signal on the Enola Branch in Cly, PA
CP-JEB on the Royalton Branch
ALTO interlocking in Altoona, PA
CP-SLOPE in Altoona, PA
MP 277 automatic signals at Fostoria, PA.



In the second video we have sounds from:

CP-PORT in Newport, PA
MP 131 automatic signals
MP 142 automatic signals
CP-MIFFLIN in Mifflin, PA
CP-HAWSTONE near Lewistown, PA



Anf finally in the third video we have:

MP 124 automatic signals
MP 196 automatic signals
HOLMES Interlocking, Holmesburg, PA



As you can see, "noisy" signaling components were installed up through the 1980's, but since then there was been a pretty much wholesale move to solid state.  After all, pulsing current is pretty much the hallmark of of what semiconductors can do :-\