The PLC (Programmable Logic Controller) has been and still is the basic component of the industrial automation world. PLCs are usually pretty expensive pieces of hardware, which led many people who know micro-controllers to come up with their own ideas to implement similar functionality.
Arduino is a kind of universal programmable controller, although it is only the “core” and in any case it has been built for general applications; with a little of external hardware (essentially interfaces capable of transferring signals from sensors and to actuators, reducing the EMI which may damage the microcontroller) and an appropriate software may, however, become something very similar to a PLC. For output you can use Arduino Relay modules. For input you can use varying Arduino sensors of build your own adapter for some industrial sensors.
Arduino as a programmable logic controller (PLC) tutorial we will explain how to “convert” our Arduino board in a PLC-like controller. There are several ways to turn Arduino into a Programmable Logic Controller, and Arduino as a programmable logic controller (PLC) tutorial presents two: Ladder Logic for PIC and AVR software and ladder.h Generator for LDmicro → Arduino. Also OpenPLC project has a OpenPLC Ladder Editor that can generate code for a standard arduino from a ladder diagram.
In some applications PLCs are more used as IO interfaces for SCADA systems more than doing the controlling. If you want to make Arduino board to look like PLC from SCADA point of view, you can put in software that make it to communicate with MODBUS or other suitable SCADA protocol. One easy way to experiment is to try SCADA for Arduino that includes both Arduino software and SCADA software. I tried it and you can read my experiences with it at Experimenting with SCADA for Arduino posting.
If you are worried if your Arduino based rat’s nest would survive in industrial environment or would be accepted by industrial control people, it is a good idea to to consider available Arduino compatible products designed for industrial control applications. There are now several commercial products built for Arduino PLC applications:
CONTROLLINO advertises to be first software Open-Source PLC. It is ARDUINO compatible.It started as Kickstarter project, but is now available directly from manufacturer web site. It advertises to be designed to control your Internet of Things and be CE & UL certificated. For more details check the video ARDUINO + PLC = CONTROLLINO
Industruino is an Arduino compatible industrial controller. Industruino is a fully featured Arduino Leonardo compatible board housed in a DIN-rail mountable case + prototyping area + onboard LCD + membrane panel. With this product you will be able to permanently install your Arduino application to industrial. Industruino is a pre-built solution offering a range of industrial voltage level I/O. All controlled with the ease of Arduino coding.
Industrial Shields has a selection of Arduino compatible industrial PLC hardware that can be plugges to DIN rail. The ARDBOX PLC, as it uses an Arduino UNO or Arduino LEONARDO, lets you program it through the USB. M-DUINO family is based on Arduino Mega. This PLC can be programmed using the Arduino IDE platform
BieMme Italia offers Soft PLC Arduino which is based on Advanced Arduino Relay Shield. You plug your Arduino to this shield, and it should be then industrial compatible with the control voltage and electrical protection. BieMme Italia also has Bmini All-in-one that has 4 optoisolated 24V digital inputs, 4 high quality relays, 8 analog inputs, PWM, I2C, RS485, Ethernet and more.