Issue
140 March 2002
Replacing
Relays with Ladder Logic
Part
1: Getting Ready for the Climb
by
Fred Eady
What’s Fred
Up To?
Well, if you’re
wondering why I’m on the rungs, I happen to have a real-live
PLC from Triangle Research International in my possession.
The PLC you see all lit up in Photo 1 is a T100MD888+.
This PLC is chock full of relay coils, relay contacts,
timers, counters, sequencers, PWM outputs, analog inputs,
analog outputs, and high-current I/O.
|
(Click
here to enlarge)
|
Photo
1—The T100MD888+ is a simple and rugged piece of hardware
that can fly with some of its parts damaged or missing.
How do I know that? I yanked some ICs and put my assumption
to the test. There are only a couple of parts you
can’t get from normal channels, so your local gurus
can maintain the T100MD888+. |
What really
makes this Triangle PLC shine is its ability to use an
IP network for control and monitoring purposes and its
extended ladder logic programming language called Ladder+BASIC.
Of course, the T100MD888+ understands all of the standard
PLC protocols like OMRON, MODBUS, ASCII, and RTU.
I didn’t get
a schematic diagram with my T100MD888+, however, I recently
completed a job that used some of the components on the
T100MD888+ circuit board. So, I decided not to violate
any of the protective labels, and instead tackle figuring
out what I could about how the T100MD888+ works physically.
Some folks can program blind not caring about what the
hardware is composed of or how it works. I think I gain
a programming edge knowing what the hardware is doing
with my code, or in this case, ladder logic.
