Auxiliary Red Aspects

[Deleted]

On a forum now dead, Harsig and BAET once described the inner workings of the auxiliary red aspects in use on the LU MAS installed on the Met Main in 1961 during the quadrupling and electrification.

Now that Harsig has kindly posted his awesome diagram of the Harrow to Amersham and Watford signalling, could someone describe again how these auxiliary reds worked, and why the standard red-lamp-proving circuitry was not deemed sufficient to protect a signal?

[Tom]

I don't remember the ins and outs of the circuitry, but the principle is that LT do not prove any aspect other that route lights. The auxillary reds were provided so that BR stock working without tripcocks would have something to stop them in the event of a main red aspect failing, and stock with tripcocks would now about a power failure before they came to be tripped on the (by now raised) trainstop.

[Deleted]

tom said:

I don't remember the ins and outs of the circuitry, but the principle is that LT do not prove any aspect other that route lights. The auxillary reds were provided so that BR stock working without tripcocks would have something to stop them in the event of a main red aspect failing, and stock with tripcocks would now about a power failure before they came to be tripped on the (by now raised) trainstop.

Oh, I see - I was assuming that a main red aspect failure would mean that the previous MAS signal in rear would drop to red, and thus up the chain, preventing the majority of BR trains from reaching it - except for any unlucky enough to be near the broken signal.

I suppose the circuit that lights this red aspect was triggered by a back contact on the filament detector of the main red, right? Or did the filament detector simply open one of the track circuit relays and induce a partial right-side failure and light the red that way?

[Harsig]

Having glanced again at the circuit for the auxiliary Red Aspect on an Auto signal (No A869, a three aspect signal) I find that the auxiliary Red Aspect, referred to as 869REE is illuminated when 869RECR is down (de-energised) AND 869HR is down (de-energised). Alternatively it is also illuminated if 869HECR is down (de-energised) AND 869DR is down (de-energised) AND 869HR is up (energised).

869HR & 869DR are the relays which control the aspect displayed by the main signal. When 869HR is down the signal is at Danger. When 869HR is up the signal either displays yellow or green and this is determined by the state of 869DR. In this case if 869DR is down the signal is yellow, if it is up then the signal is green

869RECR & 869HECR are the lamp proving relays for the main red and yellow aspects respectively. The relevant relay is Up when the lamp it is proving is illuminated. Thus when the main signal is at Danger 869RECR is Up AND 869HR is down. This is not one of the conditions to illuminate the auxiliary red aspect.
Likewise if the signal is correctly showing a yellow aspect then 869HECR is Up AND 869DR is down AND 869HR is up, again not a condition to cause the auxiliary red aspect to illuminate.

869RECR is included in the TQ circuit for track circuit 871^C.This is the replacing track circuit of signal A869. In other words when a train occupies this track circuit it causes signal A869 to be replaced to Danger. Before this track circuit will pick up again 869RECR must pick up proving the Main Red Aspect has illuminated. If the Main Red Aspect has failed 869RECR will not pick up and so 871^C track circuit will also not pick up after the train has cleared it. This causes A869 to remain at Danger but more importantly signal A871, the previous signal will also remain at Danger. This is exactly the same way in which train stop proving is achieved and in fact the contact on 869RECR is in series with the train stop proving contact. Note however that once 871^C track circuit has pickked up it will stay up even if the main red aspect subsequently fails.
The failure of the yellow aspect will not in any way cause the signal in rear (A871) to remain at danger.

[Deleted]

Awesome! ;D ;D ;D

I am surprised that the auxiliary red would be lit by (869HECR)' AND (869DR') AND (869HR) - if I read the Boolean expression correctly, this would mean that the auxiliary red would be lit by the failure of the single yellow.

Why bother doing this if only 869RECR is needed to hold 871^C down? You would end up with a green at A871 followed by a _red_ at A869 - right?

[Harsig]

theonekea said:

Awesome! ;D ;D ;D

I am surprised that the auxiliary red would be lit by (869HECR)' AND (869DR') AND (869HR) - if I read the Boolean expression correctly, this would mean that the auxiliary red would be lit by the failure of the single yellow.

Why bother doing this if only 869RECR is needed to hold 871^C down? You would end up with a green at A871 followed by a _red_ at A869 - right?

You've understood that exactly right. Remember that in the case of a failure of the yellow aspect it is perfectly safe if a driver is unable to stop at the illuminated Auxiliary Red aspect because the signal would have been showing a proceed aspect but for the failure of the main yellow aspect. While it would have been perfectly straight forward to provide an auxiliary yellow aspect as well as an auxiliary red there is a cost implication in doing so for what is after all only a back up system. By using only a red aspect the signal should always have some sort of aspect displayed, (except in the case of a failure of the green aspect which being the least restrictive aspect is not protected against) and if it does not follow the normal aspect sequence then it should draw the driver's attention to the failure meaning that it is reported and fixed. Another reason for not causing the signal in rear to remain at danger when the yellow aspect has failed is that eventually the signal with the failed aspect will step up to Green and trains will go by under clear signals.

The relevant circuits for signal A869 can be seen here

Auxiliary Red Aspect Circuit for A869

[Deleted]

harsig said:

theonekea said:

Awesome! ;D ;D ;D

I am surprised that the auxiliary red would be lit by (869HECR)' AND (869DR') AND (869HR) - if I read the Boolean expression correctly, this would mean that the auxiliary red would be lit by the failure of the single yellow.

Why bother doing this if only 869RECR is needed to hold 871^C down? You would end up with a green at A871 followed by a _red_ at A869 - right?

You've understood that exactly right. Remember that in the case of a failure of the yellow aspect it is perfectly safe if a driver is unable to stop at the illuminated Auxiliary Red aspect because the signal would have been showing a proceed aspect but for the failure of the main yellow aspect.

Indeed.

But in NR land, the situation you describe would make a S/T engineer blanch - my reading of some of the generalised information available on the subject states that in an MAS area, it is patently illegal for the signalling sequence to skip aspects. Thus, in this case, green at the 'previous peg' followed by a red would be considered a failure, not a feature. Despite the fact that the red is the 'aux' aspect, thus indicating a problem, the little I know about on this subject implies that at the very least, the signal in rear would be forced to red too (you probably know otherwise, since you know everything about signalling )

Even though 869HECR is not part of the Boolean matrix that raises/drops TQ track circuit, is it part of the trainstop release mechanism? That would explain why what you describe isn't a problem - despite the auxiliary red illuminated, the trainstop would still be down.

(Your diagram doesn't include the trainstop linkage for 869RECR - if it does, I'm too thick to see it...)

harsig said:

While it would have been perfectly straight forward to provide an auxiliary yellow aspect as well as an auxiliary red there is a cost implication in doing so for what is after all only a back up system. By using only a red aspect the signal should always have some sort of aspect displayed, (except in the case of a failure of the green aspect which being the least restrictive aspect is not protected against)...

So if 869DR was picked but the green bulb did not display, the only indication of a clear signal would be the lowered trainstop, right?

harsig said:

... and if it does not follow the normal aspect sequence then it should draw the driver's attention to the failure meaning that it is reported and fixed. Another reason for not causing the signal in rear to remain at danger when the yellow aspect has failed is that eventually the signal with the failed aspect will step up to Green and trains will go by under clear signals.

Certainly - but as I alluded to above, it breaks the aspect sequence.

harsig said:

The relevant circuits for signal A869 can be seen here

Auxiliary Red Aspect Circuit for A869

;D ;D ;D

[Tom]

theonekea said:

Even though 869HECR is not part of the Boolean matrix that raises/drops TQ track circuit, is it part of the trainstop release mechanism? That would explain why what you describe isn't a problem - despite the auxiliary red illuminated, the trainstop would still be down.

869HECR wouldn't be in the signal selection (which feeds the proceed aspects and trainstop valve) but 869HR will be - all the HECR does is prove the HE has illuminated after the HR which feeds it has picked up.

(Your diagram doesn't include the trainstop linkage for 869RECR - if it does, I'm too thick to see it...)

Do you mean how the RECR is tied with the trainstop proving? The symbol labelled 869V 'ON' represents an on (raised) contact of 869's Trainstop.

So if 869DR was picked but the green bulb did not display, the only indication of a clear signal would be the lowered trainstop, right?

To the best of my knowledge that is what would happen - while a blank signal is undesireable (and should be taken as a danger aspect anyway) a signal with no green is less critical than a signal with no red or yellow.

[Tom]

harsig said:

The relevant circuits for signal A869 can be seen here

Auxiliary Red Aspect Circuit for A869

That wouldn't pass in the Design Office ;D ;D

[Tom]

theonekea said:

tom said:

I don't remember the ins and outs of the circuitry, but the principle is that LT do not prove any aspect other that route lights. The auxillary reds were provided so that BR stock working without tripcocks would have something to stop them in the event of a main red aspect failing, and stock with tripcocks would now about a power failure before they came to be tripped on the (by now raised) trainstop.

Oh, I see - I was assuming that a main red aspect failure would mean that the previous MAS signal in rear would drop to red, and thus up the chain, preventing the majority of BR trains from reaching it - except for any unlucky enough to be near the broken signal.

It would - I was looking at the aspect itself from the second scenario of a train near the signal with the failed red.

[Colin]

harsig said:

You've understood that exactly right.

Which is more than can be said for the rest of us, I suspect ;D ;D

[Deleted]

tom said:

theonekea said:

Even though 869HECR is not part of the Boolean matrix that raises/drops TQ track circuit, is it part of the trainstop release mechanism? That would explain why what you describe isn't a problem - despite the auxiliary red illuminated, the trainstop would still be down.

869HECR wouldn't be in the signal selection (which feeds the proceed aspects and trainstop valve) but 869HR will be - all the HECR does is prove the HE has illuminated after the HR which feeds it has picked up.

Oh, I see now - so in this case, (869HR OR 869DR) provides the closed contact on the signal selection for the trainstop release, but only the failure of 869HECR with 869HR up will cause the selection to fail, thus lighting the red.

Reading the digram provided by Harsig, I can't quite trace the completed circuit with an open contact of 869RECR with 869HR open, or with an open contact of 869HECR with 869HR closed. Could you describe it to me?

tom said:

Do you mean how the RECR is tied with the trainstop proving? The symbol labelled 869V 'ON' represents an on (raised) contact of 869's Trainstop.

Ah - I must really go and dig out the signalling alphabet and forcibly remind myself that V is a trainstop!

tom said:

So if 869DR was picked but the green bulb did not display, the only indication of a clear signal would be the lowered trainstop, right?

To the best of my knowledge that is what would happen - while a blank signal is undesireable (and should be taken as a danger aspect anyway) a signal with no green is less critical than a signal with no red or yellow.

Thanks. What are the rules taught to Met/Chiltern drivers upon sighting a blank signal with lowered trainstop - especially now that the aux reds have been decommissioned?

tom said:

theonekea said:

Oh, I see - I was assuming that a main red aspect failure would mean that the previous MAS signal in rear would drop to red, and thus up the chain, preventing the majority of BR trains from reaching it - except for any unlucky enough to be near the broken signal.

It would - I was looking at the aspect itself from the second scenario of a train near the signal with the failed red.

Indeed.

[Tom]

theonekea said:

tom said:

869HECR wouldn't be in the signal selection (which feeds the proceed aspects and trainstop valve) but 869HR will be - all the HECR does is prove the HE has illuminated after the HR which feeds it has picked up.

Oh, I see now - so in this case, (869HR OR 869DR) provides the closed contact on the signal selection for the trainstop release, but only the failure of 869HECR with 869HR up will cause the selection to fail, thus lighting the red.

They provide the conditions for the trainstop to lower - trainstop release is the phrase used fro wrong-road release of a trainstop.

869HECR down with 869HR up will cause the signal to display a dual aspect: yellow and aux red.

Reading the digram provided by Harsig, I can't quite trace the completed circuit with an open contact of 869RECR with 869HR open, or with an open contact of 869HECR with 869HR closed. Could you describe it to me?

Not at this time in the morning. Maybe after some coffee and/or sleep?

Oh and BTW, when you're looking at the Alphabet next see what a TQ is (it's not a track circuit name, but is related to track circuits.) ;D

[Deleted]

tq = track local coil

[Deleted]

tom said:

theonekea said:

Oh, I see now - so in this case, (869HR OR 869DR) provides the closed contact on the signal selection for the trainstop release, but only the failure of 869HECR with 869HR up will cause the selection to fail, thus lighting the red.

They provide the conditions for the trainstop to lower - trainstop release is the phrase used fro wrong-road release of a trainstop.

869HECR down with 869HR up will cause the signal to display a dual aspect: yellow and aux red.

Huh?

I thought 869HECR was in series with the bulb and would open if the bulb was not drawing current.

(869HECR)' AND (869HR) AND (869DR)' illuminates 869REE, as Harsig stated...

tom said:

Reading the digram provided by Harsig, I can't quite trace the completed circuit with an open contact of 869RECR with 869HR open, or with an open contact of 869HECR with 869HR closed. Could you describe it to me?

Not at this time in the morning. Maybe after some coffee and/or sleep?

Not a problem...

tom said:

Oh and BTW, when you're looking at the Alphabet next see what a TQ is (it's not a track circuit name, but is related to track circuits.) ;D

aetearlscourt spoiled your fun

[Harsig]

theonekea said:

tom said:

Oh and BTW, when you're looking at the Alphabet next see what a TQ is (it's not a track circuit name, but is related to track circuits.) ;D

aetearlscourt spoiled your fun

Only if you can explain what aetearlscourt meant by

tq = track local coil

[Deleted]

harsig said:

Only if you can explain what aetearlscourt meant by

tq = track local coil

Well....

My knowledge of track circuits stops at the fact that each circuit has a supply feed at the start of the block which charges the running rails with a 50v DC/AC electrical current, and a detector at the end of the block, just before the blockjoints, which detects this electrical current and provides a closed contact which helps to pick a signal's HR or DR relays.

Since aetearlscourt was kind enough to state that TQ was a 'track local coil', a quick read of (withdrawn) GK/RT0205 implies that a TQ is the 'local winding' for a track circuit. My interpretation is that the TQ is the part of the relay mechanism which actually detects the electrical current being sent by the supply mechanism.

Of course, I'm probably wrong...

[Harsig]

theonekea said:

harsig said:

Only if you can explain what aetearlscourt meant by

Well....

My knowledge of track circuits stops at the fact that each circuit has a supply feed at the start of the block which charges the running rails with a 50v DC/AC electrical current, and ...

Remind me not to go anywhere near track fitted with one of your track circuits

[Phil]

harsig said:

Remind me not to go anywhere near track fitted with one of your track circuits

I'll second that - and I'm a scientist, not a LU employee!

[Deleted]

harsig said:

theonekea said:

Well....

My knowledge of track circuits stops at the fact that each circuit has a supply feed at the start of the block which charges the running rails with a 50v DC/AC electrical current, and ...

Remind me not to go anywhere near track fitted with one of your track circuits

Oh my...

So what is the voltage then? Some of BAET's posts state that the running rail voltages are all over the place, depending on where you are in the system and whether or not there are any earth faults

[Tom]

The Track Circuit Relay has two coils - the TQ and TR. Normally the voltage across the TR coil is 5-15v AC. The TQ coil is 100v AC. However, the supply to the TR coil comes from a 100v supply and the majority of that voltage is dropped across the track circuit capacitor. If you get an open circuit condition on the TR coil you can read nominally 100v across it, once the capacitors start charging that can go up considerably (I had 180v across one once). Traction earths and other types of Track Circuit make the situation more complicated again, but we won't go into those yet. ;D

[Deleted]

5 - 15v on a 125hz supply
10 - 30v on a 33 1/3 hz supply

[Deleted]

tom said:

The Track Circuit Relay has two coils - the TQ and TR. Normally the voltage across the TR coil is 5-15v AC. The TQ coil is 100v AC. However, the supply to the TR coil comes from a 100v supply and the majority of that voltage is dropped across the track circuit capacitor. If you get an open circuit condition on the TR coil you can read nominally 100v across it, once the capacitors start charging that can go up considerably (I had 180v across one once). Traction earths and other types of Track Circuit make the situation more complicated again, but we won't go into those yet. ;D

Thanks BAET.

I assume then that when 869RECR is open, the TQ coil is discharged and the TR coil (which I am assuming is part of the receiver assembly) discharges too, thus dropping the track circuit. Right?

aetearlscourt said:

5 - 15v on a 125hz supply
10 - 30v on a 33 1/3 hz supply

Thanks. What frequency is used on the Met Main?

[q8]

All this technicackle talk is doing my head in. I'm glad I'm higgerant.

[Deleted]

q8 said:

All this technicackle talk is doing my head in. I'm glad I'm higgerant.

Sometimes I feel the same way!

[Deleted]

should be 125hz but thats just a guess theres not many sites left now with 33 1/3hz the biggest area is cambell road (bow road) to upminster

[Tom]

The met north of Wembley is 33 1/3 territory still.

[Deleted]

Is this due to the cabinet and track linkages with Network Rail?

[Colin]

How much is a mars bar these days?

[Deleted]

colin said:

How much is a mars bar these days?

*blink*

IDGI.