CPL history lesson

NW Mailing List nw-mailing-list at nwhs.org
Fri Jan 5 14:27:20 EST 2007

What is driving the use of 'traffic signal' style signals is the
availability of that type of signal (stock item as opposed to now long
obsolete CPL's)and the possibility of connecting the signal system to the
computer driven control system. The signals must use a voltage or a
feed-back voltage (and current requirement too) to supply the signal
'setting' information to the computer program as well as supply the 'bulb
on' or bulb burned out' information. Thus, today's signals are designed to
match up to the available controlling circuit and computer systems.

Using the old CPL style today would be a backward step in capability.

Gary Rolih

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