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.

--
Graeme Wall

This address not read, substitute trains for rail
Transport Miscellany at www.greywall.demon.co.uk/rail