"rail" wrote in message

In message
"Recliner" wrote:

"Chris Read" wrote in message

Thanks all. I had thought that DOO on the tube was a 1980s
phenomenon.

The Victoria stock uses a very simple 1960s system that's quite
different to that used in modern ATO trains. From memory, trains run
at either a standard restricted speed, or flat out, with no finer
controls.



There were four control codes used:

420 ppm up to line speed
270 ppm up to 25mph
180 ppm coasting up to 25mph
120 ppm used in connection with signalling

for the 270 code there is a governor that regulated the speed between
21 and 23 mph. Over 25mph and the emergency brakes would come on
automatically.

A seperate 15kHz signal indicated points where power could be shut
off and the train allowed to coast. As it approached the next
station there were a succession of command codes to slow the train
down. Codes were calculated at 100Hz/mph so 35mph had a code of
3.5kHz. There were 3 rates of breaking providied by mercury retarder
switches down to 4mph at which pont a constant pressure control took
over to ease the braking to a smooth stop.

Very sophisticated for the time; remember, practical ICs were a
decade or more in the future.

OK, that's a bit more sophisticated than I remembered. And, yes, I
agree that it's very impressive, and reliable, for mid 1960s technology.
Mid/late 1960s car or airliner designs would feel a lot more antiquated
compared to today's products than do those elderly 1967 stock trains.
And, unlike those trains, which remain in heavy daily use, such cars and
planes would almost all have been retired long ago.