|
|
| Re: TA is obsessed with CBTC, and ''New'' tech for no reason. (579226) | |||
 |
|||
| Home > SubChat | |||
|
[ Read Responses | Post a New Response | Return to the Index ] |
|
||
|
Re: TA is obsessed with CBTC, and ''New'' tech for no reason. |
|
|
Posted by Jeff H. on Sun Mar 2 01:54:40 2008, in response to Re: TA is obsessed with CBTC, and ''New'' tech for no reason., posted by Stephen Bauman on Sat Mar 1 09:16:28 2008. I respectfully disagree with regard to cab signals.You are quite correct that the "sensing" of the train's position is discrete and delimited by the IJs. The tranmission of the speed "command" to the train is continuous. Let's say you have just passed a wayside signal point in an ASC cab signal system. The indication of that signal is Approach (proceed not exceeding medium speed prepared to stop at next signal) and when you pass the signal your cab signal displays 30 MPH. That "command" is being sent to you by the next track circuit boundary in front of your train, because the track transformer which is feeding track circuit energy into the rails is "coding" it (100% AM) at a certain rate, typically 75 pulses per minute. Whereas the signal you just passed had been the termination of that track circuit, now that you have occupied it, your front axles terminate the circuit. A modulated AC current is thus flowing through the rails and through your axles, which an inductive loop on your lead truck picks up and decodes using logic which is so straightforward it was possible to do this in the 1920s with relays and tuned transformers. Now, I say it is continuous for two reasons. With ASC, your speed is continuously monitored and compared with the command. With wayside trips, your speed is based on X/T between two points, and could thus go far above the limit during part of your traversal. The other aspect of continuity is that when conditions change, the command changes instantly. You don't have to wait until the next signal for reception and enforcement. This works both ways. When your leader pulls away, you get an upgrade mid-block. Likewise, if a controlled signal is dropped in front of you, you can get a downgrade. As for CBTC, I'll have to look up what the sampling rate is. |
|
|
|