RRI Aspect Flash

[ewsclass]

Hey all just wondering if anyone can shed some light on something I've noticed on some RRI regions. Sometimes when a route is set and the signal has cleared with appropriate route indicator and green aspect, once the train has proceeded past the overlap and the signal reverts to danger, the signal will sort of 'flash' through the aspects. For example I saw at Westbury recently, the route indicator went out, then the main aspect flashed to single yellow then red. I was wondering if somebody could explain why it stepped through yellow instead of just reverting straight to danger? I'm guessing its something to do with how the relays are wired.

Cheers

 

[ComUtoR]

RRI ?

 

[Elecman]

Remote Relay Interlockings?

 

[ewsclass]

Route relay interlocking

 

[Railsigns]

RRI is Route Relay Interlocking.

 

[ComUtoR]

Ta

 

[Annetts key]

I presume the OP saw the signal go back to red with the passage of a train…

The relay controlling the (single) yellow (and hence the red aspect) is a slow to drop type (known inside signalling engineering as ‘slugged’). It’s required to be slow to drop so that other circuitry works correctly.

The relays that control the double yellow (top yellow) and green aspect do not need to be slow to drop, hence operate slightly faster compared to the relay controlling the yellow aspect.

The above only applies to controlled signals. You should not see the effect on automatic signals. You also don’t see it on non-climbing aspect designs which use a different arrangement of control circuitry.

The effect is far more noticeable on LED signals compared to conventional filament lamp signals. With these, the more common comment was “why do they go black when changing aspect”.

If the signal was put back to red by the signaller cancelling the route with no train, it may be that they put the next signal back first, then cancelled the route for the signal you were looking at.

 

[ewsclass]

Thanks for your reply, would you be able to go into more detail about why the slow to drop type is required in this circumstance?

 

[Taunton]

Sort of related, but the old searchlight signals, I think the last were on the GE main line, were electro-mechanical, they had the colour filters in a U-shaped slide, yellow at one end, green at the other end, red in the middle, which were controlled by a single pair of wires from the interlocking. Positive current swung it to green, negative to yellow, and no current meant it was weighted to fall to the middle, red aspect. It was a common traditional way to give three indications with just a single pair of wires.

What it did mean was as the interlocking stepped up from yellow to green, the slide went from one end to the other and the aspect would briefly pass through the red (similar to what was described above). Drivers were used to this. However, when TPWS came along, its introduction overlapping the last of these signals and whose older technology maybe had not been initially considered, someone thought the way to do it was to attach the TPWS connection to the physical slide in the signal. This caused a problem that if the train was transiting the TPWS grid at just the moment the signal changed from yellow to green, passing the red, something quite common on the GE main at high frequency, it would get a transient TPWS trip. Caused some dislocation until identified and overcome.

 

[Crossover]

Hey all just wondering if anyone can shed some light on something I've noticed on some RRI regions. Sometimes when a route is set and the signal has cleared with appropriate route indicator and green aspect, once the train has proceeded past the overlap and the signal reverts to danger, the signal will sort of 'flash' through the aspects. For example I saw at Westbury recently, the route indicator went out, then the main aspect flashed to single yellow then red. I was wondering if somebody could explain why it stepped through yellow instead of just reverting straight to danger? I'm guessing its something to do with how the relays are wired.

Cheers

Out of interest, does the same happen in reverse (when a signal goes off)?

I think it was Dewsbury (Leeds bound platform) where, pre-LED, if the route was cleared, the signal would step up from red, to yellow briefly, before going green. I can't remember if it did the same when it went from off to on, though

 

[MarkyT]

The relay controlling the (single) yellow (and hence the red aspect) is a slow to drop type (known inside signalling engineering as ‘slugged’). It’s required to be slow to drop so that other circuitry works correctly.

The relays that control the double yellow (top yellow) and green aspect do not need to be slow to drop, hence operate slightly faster compared to the relay controlling the yellow aspect.

The above only applies to controlled signals. You should not see the effect on automatic signals. You also don’t see it on non-climbing aspect designs which use a different arrangement of control circuitry.

The effect is far more noticeable on LED signals compared to conventional filament lamp signals. With these, the more common comment was “why do they go black when changing aspect”.

With filament lamps, the original green would take a little while to cool down and the intermediate yellow a little time to warm up so you may not see the latter light up at all during the cascade. By contrast, LEDs are nearly instantaneously illuminated and extinguished once power is applied and removed respectively. Most, if not all, colour light signals are LED illuminated by some means today, regardless of the age of the underlying installation.

Thanks for your reply, would you be able to go into more detail about why the slow to drop type is required in this circumstance?

I think it may be to cover aspect change at the next signal in advance, whose lamps are always proved illuminated by means of current detection, along with any TPWS equipment functioning correctly. There are also swinging overlap controls, but I think that's covered by a separate 7.5 second timer that bridges out appropriate point detection in the HR (yellow or 'Home Relay' - DR is green or 'Distant Relay') while the switches are moving from one valid position to another. I think the 'climbing aspects' is the more modern style of aspect circuitry provided from the 1980s if not earlier.

 

[Annetts key]

Out of interest, does the same happen in reverse (when a signal goes off)?

I think it was Dewsbury (Leeds bound platform) where, pre-LED, if the route was cleared, the signal would step up from red, to yellow briefly, before going green. I can't remember if it did the same when it went from off to on, though

For signals where the design is of the climbing aspect type, the green control relay can’t operate until the double yellow control relay has energised. The double yellow control relay relay can’t operate until the single yellow control relay has energised. Hence these signals always step through the aspects when cleared from a red to a green (or indeed any change up in aspect) even if all the relevant sections ahead are clear of trains.

SSI (and systems developed since) also use the climbing aspect principles even though no relays are (normally) involved.

Climbing aspect designs have replaced the previous designs. Some of the older designs would just step straight up without going through the intermediate aspect(s). Unless of course the signaller set each route in sequence from the red signal in sequence.

Thanks for your reply, would you be able to go into more detail about why the slow to drop type is required in this circumstance?

That’s going deep into the design of the interlocking, and there are variations between different interlocking systems. Hence I don’t want to go into any detail. But it’s related to guaranteeing that the interlocking sees the correct sequence of operations. That is, when a train passes the signal, the track circuit (or axle counter) goes occupied and the signal is detected as red a short time later. If the signal control relay was not designed to operate slightly slower, it would create uncertainty in the interlocking. This is especially important if the control circuitry is split between two or more physical places (for example the signal is miles away from the signal box) and the communication system may cause a slight difference in transmission between different control signals.

 

[ewsclass]

Thanks guys for the replies, I had a feeling it would be something to do with the positioning of relays within the circuitry and for proving in a fail-safe manner that the correct aspect is shown.

 

[MarkyT]

That’s going deep into the design of the interlocking, and there are variations between different interlocking systems. Hence I don’t want to go into any detail. But it’s related to guaranteeing that the interlocking sees the correct sequence of operations. That is, when a train passes the signal, the track circuit (or axle counter) goes occupied and the signal is detected as red a short time later. If the signal control relay was not designed to operate slightly slower, it would create uncertainty in the interlocking. This is especially important if the control circuitry is split between two or more physical places (for example the signal is miles away from the signal box) and the communication system may cause a slight difference in transmission between different control signals.

Going back 30+ years to my circuit design days, this is ringing a bell. In Western Region 'E10K' standard circuitry (of which Westbury is a late example) the slow-to-release feature may help ensure correct operation of the SR (stick relay) in the panel circuitry and ALSR (approach locking stick relay) in the interlocking. Both of these are used to determine that a train has correctly passed a signal and ultimately permit the sectional route locking to start to disengage, once the signaller has normalised the entrance switch. Unfortunately, I haven't any circuit diagram examples here at home to examine.

 

[Annetts key]

Going back 30+ years to my circuit design days, this is ringing a bell. In Western Region 'E10K' standard circuitry (of which Westbury is a late example) the slow-to-release feature may help ensure correct operation of the SR (stick relay) in the panel circuitry and ALSR (approach locking stick relay) in the interlocking. Both of these are used to determine that a train has correctly passed a signal and ultimately permit the sectional route locking to start to disengage, once the signaller has normalised the entrance switch. Unfortunately, I haven't any circuit diagram examples here at home to examine.

Yes, that’s the correct reasons for the Western Region 'E10K’ interlocking. The Westbury signalling dates from the mid 1980s.
If the sequence is incorrect at the signal box, it completely messes up the operation of the SR. Then the signaller is quickly reporting a failure….

 

[172007]

Everyday is a school day. If I watched a signal do that at work an NR3185, chat with a signaller and a delay incurred as even of the signal wasn't mine I would take it as an irregularity; even a brief flash of yellow.

 

[Annetts key]

Everyday is a school day. If I watched a signal do that at work an NR3185, chat with a signaller and a delay incurred as even of the signal wasn't mine I would take it as an irregularity; even a brief flash of yellow.

There is a difference between theory and practically…

In the case of when a signal is changing aspects with the passage of a train, the train is fully protected because the signal in rear is at red,

I’ve been on plenty of reported failures where the equipment was found to be operating as designed, hence the fault was closed down.