Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 9)

An Introduction to Programmable
Controllers
Chapter 2
2Ć2
Programmable controllers can perform many of the functions of traditional
controls (Figure 2.2). Sensing devices and output devices are located at the
machine and perform the same jobs. The field wiring between the machine and
the control panel provides electrical paths from the sensing devices to the
control panel, and from the control panel to the output devices.
Figure 2.2
Machine Control with a Programmable Controller
Control Panel
Output
Sensing
Devices
Machine
Devices
Programmable
Controller
Conditions Action
Comma
10150ĆI
However, inside the control panel you’ll find a programmable controller rather
than relays or discrete solid state devices. Instead of wiring those devices and
relays together to produce a desired response, you simply tell your
programmable controller how you want it to respond to the same conditions.
you do this with a program.
Programming is telling your programmable controller what you want it to do.
A program is nothing more than a set of instructions you give the programmable
controller telling it how to react to different conditions at the machine.
Let’s take a closer look at a typical programmable controller system. it usually
consists of four major sections:
Power supply
Input section (connects to input devices)
Output section (connects to output devices)
Processor section
Figure 2.3 shows these sections
Programmable Control
The Four Major Sections