Why do some signals blink?

[slick]

As per title. Just to clarify Im a driver, and this is not to be confused with flashing signals.

Some of the signal aspects on my patch "blink" once in certain situations always usually when a green aspect. Almost as if a clear route has been set over an already clear route. Also happens occasionally in conjunction when being given RA at certain locations. My area is full ARS. Been bugging me for years and wondered if any of you signalling/technician guys/girls can tell me whats actually occurring. Cheers!

 

[chuff chuff]

Is it not some kind if self test going on.

 

[driver9000]

This was covered in one of the now defunct industry magazines a few years ago. It's an automated Power Dispersal Test to prove the electricity to the signal can be switched off. As I remember the test occurs every 5-6 hours or so and is meant to be timed to coincide with an aspect change but this isn't always possible.

 

[MarkyT]

SSI TFMs (trackside functional modules) do this self-test every so often as explained above. They have been installed on most resignalling schemes for the past three decades. I suspect LEDs make the blink more noticeable because they turn on and off so rapidly, while the older filaments would continue to glow for a split second. Relay-based signalling shouldn't ever do it. Some of the latest processor-based schemes have alternative distributed input/output hardware that may not do this or can do it without a noticeable blink.

 

[slick]

Thanks for your replies makes sense! People at my depot just thought I had dodgy eyes

 

[Dieseldriver]

I have noticed it more with the new VMS signals. Some of them it would routinely occur when it was displaying green and you'd just gone over the magnet. I was told that it was down to some kind of self test so that would tie in with what other people have said here.

 

[sw1ller]

There’s one on the Cheshire lines somewhere (I don’t sign it so can’t be specific) that blinks EVERY time when you’re about 600 yards away, so nowhere near an AWS and doesn’t seem to tie in with the self test every 5-6 hours as mentioned above. It’s probably timed to coincide with the aspect change though. It’s good to know what it is.

 

[driver_m]

Thanks for your replies makes sense! People at my depot just thought I had dodgy eyes

I'm surprised at your workmates then. All mine know about where ours blink on the WCML. (Primrose Hill tunnel, Rugby Trent Valley down fast, Aston by Stone, all in SSI area controlled boxes)