Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 15)

Chapter
2
2Ć1
An Introduction to Programmable Controllers
In this chapter, you review general fundamentals common to our programmable
controllers. This chapter:
describes what a programmable controller does
describe the four major sections of a programmable controller
describes how the four major sections of a programmable controller interact
gives an example of a simple program
You are probably familiar with the traditional methods of machine control.
Control Panel Relays
Machine
Sensing
Devices
Output
Devices
11591
Sensing devices located on the machine detect changes in the machine’s
condition. For instance, a part arriving at a work station contacts and closes a
limit switch, the sensing device. As a result, an electrical circuit is completed
and a signal is sent to the control panel.
At the control panel, the electrical signal enters a bank of relays or other
devices, such as solid state modules. Circuits within the control panel open or
close causing additional electrical signals to be sent to output devices at the
machine. For example, a relay energized by the limit switch closed by the
arriving part may complete another circuit energizing the output device, a
clamp, which secures the part at the work station.
Chapter Objectives
Traditional Controls