Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 15)

Chapter
2
2-1
Fundamentals of a Programmable Controller
In this chapter, you review general fundamentals common to our
programmable controllers. This chapter:
describes what a programmable controller does
describe the functions of a programmable controller
describes the four major sections of a programmable controller
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