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| Ladder logic program. © Eugene Brennan |
Just
found this among documents I was going through after getting the oil
boiler serviced last week. I had forgotten all about it. The electrician
made a minor cockup when wiring the controls for the dual oil/solid
fuel heating system 9 years ago. So I had to go off and look for a CAD
package to draw a ladder logic diagram for him, showing how it should
have been wired. (He had his own ladder logic diagram, but it made more
sense for me to draw a new one, rather than trying to explain the error
in English). Ladder logic is a schematic system for showing the wiring
in an electrical/electromechanical system, input devices such as
switches and sensors and output devices, e.g. motors and relays being
shown as symbols on a diagram. It has evolved into a graphical
programming language, the graphical program used to control programmable
logic controllers (PLCs). These are basically modular, industrial
control computers, built into a box, with terminals for connecting
inputs and outputs. A computer can be connected for programming and they
can be linked-to by various computer networks.
I'm
rusty on this stuff. It's a shame when you learn stuff, and then forget
it all if you're not applying the knowledge on a daily basis (I never
really used this practically, even though I studied industrial
automation).
See if you can understand what this does. Hint: MV1, 2 & 3 are zone valves, R1 & R2 are relays. SF is solid fuel.