Flashing Yellows Question

[Step3 Star]

Is it possible to have a Flashing Yellow sequence for the ahead route being set from two different Signal Boxes/Panels?

For example two flashing yellows from a different box/panel to the single flashing yellow and then junction signal??

Thank you in advance for any help and information.

 

[DeparturesBeck]

Yes - an example is approaching Cheadle Hulme North junction from Stockport. The double flashing yellow is Edgeley Junction No. 1's last signal and the flashing single yellow is Manchester South's first signal.

 

[Step3 Star]

Thank you for your help & reply.

 

[Annetts key]

It’s also possible for one or both signals to be automatic signals.

 

[Step3 Star]

It’s also possible for one or both signals to be automatic signals.

Ok thank you for your reply & information.

 

[satisnek]

Are/were flashing yellow aspects driven from the same gizmo which generated flashing panel indications?

 

[Annetts key]

Are/were flashing yellow aspects driven from the same gizmo which generated flashing panel indications?

No. Flashing aspects in relay interlocking areas have their own special flashing units mounted in the equipment location cupboard that feeds the signal. These units are entirely electronic and are in the form of a rack mounting unit. The older design is a square box.

SSI (Solid State Interlocking) TFM (Trackside Functional Module) have support for flashing aspects built in as standard.

This is actually a coded track circuit transmitter that normally would be paired up with a “matching” receiver to be used to form a type of track circuit.

Swindon was likely similar to other Western Region Panels, in that the flashing indications were originally derived from the Western Region design of electro-mechanical Train Describer (TD) equipment. When this equipment was replaced, a coded track circuit transmitter was often used to provide the flashing indication supplies for the flashing panel indications.

 

[Railsigns]

A low-tech method of generating a flashing indication is with a pair of astable relays. Energising the first relay causes the second relay to energise, which cuts the feed to the first relay and in turn de-energises the second relay. The process repeats as long as power is supplied to both relays (which are slow to drop when de-energised, to reduce the flashing rate). A contact of the first relay is cut into the indicator circuit, causing it to flash.

This is what produces the flashing blue indication at the stop boards on the Heart of Wales line, to inform drivers that the TPWS has been disarmed. The co-located flashing red indication is however generated by a flasher unit built into the red LED module. Different methods are used to flash the blue and red lights because the blue can be either steady or flashing, whereas the red can only flash (there's no steady red indication). There's a noticeable difference in how the two lights flash.

 

[satisnek]

That's fascinating - thanks.

 

[Annetts key]

A low-tech method of generating a flashing indication is with a pair of astable relays. Energising the first relay causes the second relay to energise, which cuts the feed to the first relay and in turn de-energises the second relay. The process repeats as long as power is supplied to both relays (which are slow to drop when de-energised, to reduce the flashing rate). A contact of the first relay is cut into the indicator circuit, causing it to flash.

Yes, a similar method to this has been used to produce a flashing yellow aspect in the past. But that particular design was found to have a design limitation - using the relay specifications, the life span of two of the relays was worked out to be only about three months! In practice they often lasted longer, but still a relatively short amount of time compared to normal use. So an economiser circuit was added. This resulted in the signal being held at red until the interlocking detected an approaching train.

Relay based flashers were (and may still be) used for some level crossings to flash the red road traffic lights. An entirely electronic flasher is used in more modern installations. Plus some older installations have been upgraded to use the electronic flasher.

For non-safety critical applications, such as panel indications other than that described in my earlier post (#7), a commercial ‘flashing relay’ may be used.

 

[MadMac]

No. Flashing aspects in relay interlocking areas have their own special flashing units mounted in the equipment location cupboard that feeds the signal. These units are entirely electronic and are in the form of a rack mounting unit. The older design is a square box.

SSI (Solid State Interlocking) TFM (Trackside Functional Module) have support for flashing aspects built in as standard.


This is actually a coded track circuit transmitter that normally would be paired up with a “matching” receiver to be used to form a type of track circuit.

Swindon was likely similar to other Western Region Panels, in that the flashing indications were originally derived from the Western Region design of electro-mechanical Train Describer (TD) equipment. When this equipment was replaced, a coded track circuit transmitter was often used to provide the flashing indication supplies for the flashing panel indications.

Common, although usually in a plug-in relay format, in the US where it “modulates” an AC track circuit with a code (in this case, 75 pulses per minute) to provide speed commands.