The program in the PLC is not a normal computer-programming language like Java, C or BASIC. Rather, the PLC program uses contact and coil symbols to indicate which switch should control which output. These symbols are similar to ladder-logic diagrams used in electrical relay-logic diagrams. In most systems the program can be displayed on a computer screen where the actions of switches and outputs are animated as they turn motors and other outputs on or off. The animation includes highlighting the input and output symbols in the program when they are energized. Other systems may use LEDs on a hand-held programmer that illuminate when an input or output is energized to show its status.

Briefly, then, the PLC executes logic programs like logic gates found on solid-state ICs, but its programs are designed to look exactly like relay-logic diagrams that electricians have used since the earliest electrical controls were introduced. Read more on PLCs…

This entry was posted on Saturday, July 9th, 2005 at 7:09 pm and is filed under Technology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.