Page top

Lead Contents

Programmable Controllers

Introduction Features
Principles Classifications
Engineering Data Further Information
Explanation of Terms Troubleshooting

Related Contents

Primary Contents

What Is a Programmable Controller?

A programmable controller (PLC) has a microprocessor and controls devices through custom user programs.
A PLC receives signals from input devices and makes decisions based on custom programs to control output devices.

Ladder logic is a graphical programming language and commonly used for PLC programming. Programming software, such as CX-Programmer, is used for programming on a PC.

Inside a PLC

I/O devices are connected to the input and output sections of the PLC. The user program determines how output devices work based on the state of input devices. The user program and the state of I/O devices are stored in the internal memory of the PLC.

Types of Data

The types of data used by a PLC can be classified into three major groups.

Input to PLC inputOutput from PLC output
ON/OFF state
(discrete I/O)
Pushbutton switches
Thumbwheel switches
Photoelectric sensors and proximity sensors
Input relays
Seven-segment displays
Relays and contactors
Pulse train
(series of rapid ON/OFF)
Rotary encoders
Pulse motors
Analog value
Displacement sensors

Types of PLC

OMRON programmable controllers are classified as follows.