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| Re: South Ferry Inner Loop Station. (1385518) | |||
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Re: South Ferry Inner Loop Station. |
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Posted by Stephen Bauman on Sun Feb 14 12:38:53 2016, in response to Re: South Ferry Inner Loop Station., posted by Jace on Sun Feb 14 11:34:54 2016. The NTT trains use the equivalent of "fly-by-wire" that is used by AirBus planes. Instead of individual wires running between a switch or indicator light and the physical device, there is a 2-wire serial bus (think party line) that runs between all the devices. There's a microprocessor at each of the devices that monitors the serial bus and responds to messages that are directed to the device the microprocessor is controlling. The fly-by-wire approach is a lot cheaper to implement and maintain. It is also more reliable, given there is error detection/correction built into the serial communications.I'm also not sure what you mean by 'messages' The TA chose LonWorks as the car network at the time the first NTT cars were being designed. There was a NYCTA bulletin board that described the system in some detail. One of the items on the bulletin board was a listing of all the messages and their format. I downloaded that item at that time (probably 20 years ago.) I reviewed the messages realized the weaknesses of their systems engineering approach. Their approach was to copy the existing hardwired commands (door open button pressed, door open, etc.) There was a message for door open pressed, door status, etc. This approach's shortcomings are its inflexibility and equipment dependency. A different approach would have been to have the messages be functional and not hardware specific. Additional microprocessors would have translated the functional command into the specific hardware commands required to implement the functional command. This would permitted complete coupling interchangeability between rolling stock. I pointed out this shortcoming at that time. I also believed that NYCT erred in choosing LonWorks. The LonWorks message format was too restrictive. I would have opted for a system that used TCP/IP as the message protocol and an IEEE 802.11 physical layer. It was obvious to me that this was the direction that control engineering was heading. The "technology" part of the NTT trains was obsolete before the first units were designed. |
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