Programmable controllers, or P.C.s, have been used in industry in one form or another for the past fifteen years. The newest models may not resemble their earlier counterparts, but many of the concepts used in the first units are still in use. The programmable controller is basically a computer-controlled system containing a microprocessor that is programmed with a programming panel, or keyboard. The P.C. is dedicated to receiving input signals and sending output signals in response to the program logic. The program generally consists of contacts, outputs, timers, counters, and math functions. The programmable controllers found in industry today have evolved from the need for a control system that can be easily reprogrammed as changes occur or as new products develop.
For example, the automotive industry is faced
- Another feature of most P.C.’s is their capability of being connected to a printer,so that a hard copy printout can be made of the electrical diagram. The hard-copy printout of program is used for troubleshooting.
The same change in a P.C.-controlled system is accomplished by reprogramming the P.C. Since changes can be made in the program instead of the wiring system, many man-hours are saved.
In the P.C. –controlled system, electrical power comes from the voltage source, through the switch into the input module. The input module senses the presence of this voltage and inturn, sends a small signal voltage into the processor. The voltage from the switch is isolated from the voltage signal that the module sends into the processor. This isolation is necessary since the fragile processor chip operates at a
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