mrfs42
71E25683904T 172E6538094T
Big Hair Day
Posts: 5,922
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NADB.
Jun 11, 2008 19:24:20 GMT
Post by mrfs42 on Jun 11, 2008 19:24:20 GMT
Further to the discussion at districtdave.proboards39.com/index.cgi?board=newfuturetrains&action=post&thread=7425"e=159800&page=2, which anyone interested in the developments with the NADB is recommended to peruse. Could someone knowledgeable please expand the following abbrevia: NADB. MEMS. RPBR. RTTC. And is LowMin 'Lowest Mininum EP (air) brake application; rather than 'Rheo' (rheostatic) braking? Many thanks, I'm following this discussion with mild fascination but am a bit bogged down with these points - expansion would enhance my understanding.  |
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Deleted
Deleted Member
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NADB.
Jun 11, 2008 19:47:24 GMT
Post by Deleted on Jun 11, 2008 19:47:24 GMT
New Auto Driver Box - replacement of the original ADB and the RADB (Replacement Auto Driver Box) |
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towerman
My status is now now widower
Posts: 2,886
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NADB.
Jun 11, 2008 20:11:50 GMT
Post by towerman on Jun 11, 2008 20:11:50 GMT
Rheo was always set at low min with assistance from EP retarders as required,the low min EP brake is the pressure switch brake mainly used to hold train in platforms and when running at controlled speed ie 270 code.
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NADB.
Jun 12, 2008 20:23:35 GMT
Post by tubeprune on Jun 12, 2008 20:23:35 GMT
New Auto Driver Box. It's a replacement for the RADB (Replacement Auto Driver Box) which was the 1988 replacement for the ADB (Auto Driver Box) Are you having fun yet? |
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NADB.
Jun 18, 2008 20:11:48 GMT
Post by tubeprune on Jun 18, 2008 20:11:48 GMT
I "did" ten trains yesterday and monitored the brake control performance to see if I could tell which had the NADB. I reckoned that 3110, 3179 and 3127 had the NADB. The performance is only just noticable though. 3127 was a bit "lumpy" on the stop. It's quite difficult to tell but the driver didn't have to cosh it at the last minute on any of them.
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NADB.
Jun 19, 2008 17:50:20 GMT
Post by georgedishman on Jun 19, 2008 17:50:20 GMT
I "did" ten trains yesterday and monitored the brake control performance to see if I could tell which had the NADB. I reckoned that 3110, 3179 and 3127 had the NADB. The performance is only just noticable though. 3127 was a bit "lumpy" on the stop. It's quite difficult to tell but the driver didn't have to cosh it at the last minute on any of them. Those three all have the NADB fitted. Was 3127 arriving in CSR (Controlled Speed Running for those not yet familiar with the TLA  )? The brake system response is slower without the rheo (which is disabled at low speed) so there's a deliberate bit of hunting to ensure there's no risk of overshoot. |
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NADB.
Jun 19, 2008 18:30:45 GMT
Post by georgedishman on Jun 19, 2008 18:30:45 GMT
For some reason which I never go to the bottom of in 5 years of teaching 67TS braking, there is a RTTC (Round The Train Circuit) which switches off the rheostatic brake on the whole train if it fails to register on one car. I'm guessing here but I suspect the reason might be that the unit with the failed rheo would give less braking effort while the others would have to compensate by producing more. They might reach the upper limit venting air and the disparity would put undue stress on the couplings. The first three had rheo at a high current. Min was just a little air in addition to the rheo, enough to ensure there was still a degree of control because if the rheo alone produce more than the retarder wanted, it would be impossible to avoid an undershoot without dropping the rheo. Normal and max added more air but the rheo level was the same. LowMin does two things, it changes the rheo current to a lower value and replaces the retarder control with having a fixed air pressure in the cylinders. All of that remains the same with NADB control, it is just used (IMHO) in a more imaginative way. It's a little more complex so I'll take it in bits. As a fallback measure aganst failure of the MEMS device, the system can work happily without it. <snip> ... sorry, on second thoughts I posted a bit too much detail </snip> That is used as the demand to the servo and the accelerometer (or tacho derived backup) is compared to the demand to control the application and holding wires, and to the profile value to control LowMin. I've got to go now but the rheo has a built-in variable resistance system based on a stepped cam thingy which is unchanged in the train but is used in a novel way I described in another in another post. |
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NADB.
Jun 19, 2008 18:59:35 GMT
Post by tubeprune on Jun 19, 2008 18:59:35 GMT
Brilliant. It almost all falls into place now. The only bit I don't follow is the "servo". What is this. Again, it's not something I remember from my teaching days.
This is an interesting thought. The rttc wasn't provided on the C Stock and that had (maybe still has) a bad surging problem.
Thanks for the time you spent on this NADB guru. Much appreciated.
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NADB.
Jun 19, 2008 19:06:37 GMT
Post by tubeprune on Jun 19, 2008 19:06:37 GMT
Those three all have the NADB fitted. Was 3127 arriving in CSR (Controlled Speed Running for those not yet familiar with the TLA )? The brake system response is slower without the rheo (which is disabled at low speed) so there's a deliberate bit of hunting to ensure there's no risk of overshoot. No. Car 3110 was though and that was the one where the new control was most noticable. It was the first one I rode on on my way to a meeting. I was on it from Kings Cross to Victoria. I was convinced from the moment I rode on it that it had the NADB. The others were less convincing because they were lightly loaded and didn't have to struggle with stopping but they were detectable - just. I think it was the operation of the Low Min and the controlled fade which gave them away. |
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NADB.
Jun 19, 2008 23:13:03 GMT
Post by georgedishman on Jun 19, 2008 23:13:03 GMT
Brilliant. It almost all falls into place now. The only bit I don't follow is the "servo". What is this. Again, it's not something I remember from my teaching days. I find that hard to believe  A servo system is typically one where the output of an actuator is measured by a sensor in a control loop to improve the performance:
|\ op amp
| \
demand -------|+ \ ----------
| \ | |
| >--->---| actuator |----*-----> output
| / error | | |
----|- / ---------- |
| | / v
| |/ |
| --------
--------------<--------------| sensor |
feedback --------
The error signal is based on the difference between the demand and the feedback and drives the actuator to reduce the error. In our case the 'demand' is what is calculated from speed and distance using the equation I gave earlier, while the 'feedback' signal is the measured acceleration from the accelerometer or tacho. The actuator is of course the braking system. To stop the system flickering the control lines when the feedback is close to the demand, there is a hysteresis so there needs to be a minimum error magnitude before action is taken, and the lines are activated for at least a minimum time once that point is reached. Pleasure, I'm sure there are a lot of rumours about the box and it's good to get a chance to put the record straight. |
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NADB.
Jun 20, 2008 7:05:45 GMT
Post by tubeprune on Jun 20, 2008 7:05:45 GMT
Brilliant. It almost all falls into place now. The only bit I don't follow is the "servo". What is this. Again, it's not something I remember from my teaching days. I find that hard to believe Well, I'm the resident electro-mechanical dinosaur. I come from an era when railway fitters had two skills - hit it and if that fails, oil it. Electronics is a bit of a struggle but I want to learn more. The nearest I got to a servo was a self-lapping brake valve, like A Stock. |
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NADB.
Jun 20, 2008 19:18:33 GMT
Post by 100andthirty on Jun 20, 2008 19:18:33 GMT
I find that hard to believe Well, I'm the resident electro-mechanical dinosaur. I come from an era when railway fitters had two skills - hit it and if that fails, oil it. Electronics is a bit of a struggle but I want to learn more. The nearest I got to a servo was a self-lapping brake valve, like A Stock. Ithink you know far more than you let on about; you play the innocent to lull us tekkies into a false sense of security. Incidentally I once simulated a self lapping brake on an analogue computer - in about 1971. Analogue computers are museum pieces now - to be survived by self lapping brakes! |
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NADB.
Jun 20, 2008 21:16:19 GMT
Post by tubeprune on Jun 20, 2008 21:16:19 GMT
There are some modern systems which I struggle with. The MEMS is one such. I am still struggling with the concept that something in a microchip can accurately and consistently measure constantly changing deceleration in a vibrating mass like a 67TS motor car.
Something else which occurs to me is the blowdown valve. Is this controlled at all or is the servo so good it makes it unnecessary in Auto?
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NADB.
Jun 22, 2008 11:21:53 GMT
Post by georgedishman on Jun 22, 2008 11:21:53 GMT
There are some modern systems which I struggle with. The MEMS is one such. I am still struggling with the concept that something in a microchip can accurately and consistently measure constantly changing deceleration in a vibrating mass like a 67TS motor car. It is nothing more complex than a weight on a springy arm, just very small so the gap between the weight and the chip can be measured by its capacitance. The train systems are almost unchanged so the blowdown is still there with the same properties. The system (rather than the servo) should be good enough that it never operates but as always, there is more to it than that. The spec. for the NADB stated the braking requirement in m/s 2 so the brakes have to work harder on a downhill approach than an uphill station entry. The old mercury retarders measured a combination of the slowing and also the gradient and the effect was to apply about the same retardation regardless of track slope, the actual deceleration was greater on an uphill approach and reduced if the track was downhill. The NADB tries to achieve the same retardation regardless so needs more pressure in the cylinders if the track is downhill - if that exeeds the blowdown then the braking system cannot deliver and an overshoot results. I believe a change to a pressure valve on the train has been included to resolve this. The "servo" part is quite simple and in fact the retarders were part of such a system. The brakes don't have an input whereby you can ask for X m/s 2 of slowing, the controls are Application and Holding which mean "give me more" and "give me less" repectively. The retarders were the "sensor" in the loop and controlled those wires to produce a desired braking effort. The NADB system is the same in that the measured deceleration is compared to the demand and if the difference is large enough either Application is energised or Holding is de-energised to correct the discrepancy. When you said you used to teach, I assumed you would be familiar with the term but of course we all have our specialist areas. For example I have no idea what a "self-lapping" valve is  , and I wouldn't have a clue how to lap one if it wasn't self-lapping. |
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NADB.
Jun 22, 2008 12:06:02 GMT
Post by tubeprune on Jun 22, 2008 12:06:02 GMT
When you said you used to teach, I assumed you would be familiar with the term but of course we all have our specialist areas. For example I have no idea what a "self-lapping" valve is , and I wouldn't have a clue how to lap one if it wasn't self-lapping. I now lecture on railway systems and management in a couple of universities but I was a rolling stock engineering instructor in the late 70s. A small team of 8 people used to teach what were called car examiners (now train technicians) and some workshop grades about rolling stock systems. We did classroom and practical training in depots, so we had a good idea of how all the train systems worked. There was very little electronics apart from the original ADBs on the 67TS and these were handled by specialists at Acton Works (now REW). We learned everything ourselves. When the D Stock was being built we went to Met Camm. and Westinghouse to see what they were building and how it worked. We then wrote the instructional material and prepared courses. I remember trying out meggering on a D Stock for the first time in Ealing Common Depot to see if my theoretical procedure actually worked. I had the electrical trade union rep. with me because he didn't believe anyone without a ticket could do such a thing. Luckily, I proved him wrong but we got along just fine. We worked together to solve a number of technical issues as the stock entered service. As for the self-lapping brake valve, very simply, it is a device provided to give the driver proportional brake control. It is used on those stocks which have separate traction and braking controllers. The A Stock is the only stock still with it. Brake application is achieved by moving the brake controller handle from OFF towards FULL APPLICATION, the application achieved by the brake being proportional to the handle position chosen in the segment. The cut-off is achieved by a feed back from the brake cylinder to an air cylinder in the brake controller. I don't suppose you want me to bore you any more with further details. In its later form, the self-lapping e.p. brake controller (self-lapping is a misnomer, it's really a proportional brake controller) was the best tool a driver could have for train braking. It allowed accurate control and very precise stopping. Combined with the mercury retardation controllers, it was a good system. |
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NADB.
Jun 24, 2008 15:56:43 GMT
Post by ratfink on Jun 24, 2008 15:56:43 GMT
Hi guys
What percentage of 67TS running have NADB as oppose to ADB?
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NADB.
Jun 25, 2008 7:13:01 GMT
Post by tubeprune on Jun 25, 2008 7:13:01 GMT
My informed sources tell me that there are four DMs fitted with the latest version of the NADB. If I told you which ones, I'd have to shoot you and I've run out of bullets so I can't :-)
The challenge set to me was to find a train with the NADB. I managed to get three of them in an hour. Pure luck actually, but you do have to know the Vic line travelling expereince quite well to detect which ones have it.
The ADB is long gone. It became the R (Replacement) ADB in 1988-89.
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NADB.
Jun 25, 2008 20:24:40 GMT
Post by edwin on Jun 25, 2008 20:24:40 GMT
So is the new NADB in service? I could of sworn the other day that my usual bouncy Victoria line journey felt more gentle...
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NADB.
Jul 1, 2008 14:37:19 GMT
Post by georgedishman on Jul 1, 2008 14:37:19 GMT
My informed sources tell me that there are four DMs fitted with the latest version of the NADB. If I told you which ones, I'd have to shoot you and I've run out of bullets so I can't :-) The challenge set to me was to find a train with the NADB. I managed to get three of them in an hour. Pure luck actually, but you do have to know the Vic line travelling experience quite well to detect which ones have it. My informed source told me that, as of the 8th June, 56 cars had been fitted with the current version and AFAIK they continue to be rolled out so the challenge may soon be to find an RADB ;D |
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)? The brake system response is slower without the rheo (which is disabled at low speed) so there's a deliberate bit of hunting to ensure there's no risk of overshoot.
, and I wouldn't have a clue how to lap one if it wasn't self-lapping.
