What are PLC and RTU? What is the difference between the two? I believe many people are at a stage where they roughly know what it is, but cannot accurately say it. 

This article will tell you in detail!

What is PLC

PLC (Programmable Logic Controller) can be used as a programmable controller, and its most basic and widespread application field is to replace traditional relay 

circuits and achieve logic control and sequence control. PLC consists of CPU and input/output modules.

It has multiple control functions, data acquisition, storage and processing functions, mathematical operation functions, and input/output interface conditioning 

functions. In addition, there are communication networking functions, human-machine interface functions, and editing and debugging functions. Mainly applied 

in traditional industrial control fields, such as steel, petroleum, chemical, textile, transportation, machinery manufacturing and other industries.

What is RTU

RTU (Remote Terminal Unit) is a remote measurement and control terminal used for monitoring and controlling on-site equipment, mainly used in SCADA systems. 

Similar to PLC, RTU also includes CPU and input-output modules, as well as communication and protocol conversion options.

RTUs typically require excellent communication capabilities and large storage capacity, suitable for harsh temperature and humidity environments, and capable of 

providing computing functions that comply with proprietary standards. It is precisely because of its comprehensive functions that RTUs have been widely used in 

SCADA systems.

Comparison of Differences between PLC and RTU

1. Volume size

RTUs are usually larger than PLCs, and one reason for this is that the added functionality increases the durability and robustness of the equipment, which takes up 

more space.

PLCs are smaller and more compact because they are suitable for industries and factories where available space is often insufficient.

2. Communication function

Due to the fact that RTU needs to transmit the collected analog, switch, and digital information to the dispatch center, which is sometimes thousands of miles away, it 

is required to have remote communication capabilities.

Although PLC also has communication function, it is limited to transmitting data within the factory station at close range, and its communication function is slightly 

inferior to RTU.

3. Usage environment

RTU products are designed for harsh environmental applications, with a typical working temperature range of -40~70 ° C.

PLC is generally used for controlling industrial assembly lines within factories. The working environment temperature requirement is 0-55 degrees, and the air 

humidity should be less than 85%. If the temperature exceeds 55 degrees Celsius, a fan should be installed for ventilation. If the temperature exceeds 60 degrees 

Celsius, a fan or air cooler should be installed for cooling, otherwise it will increase the failure rate of PLC components and even damage them.

6. Data storage

RTU can provide a large storage space of 1-32M, while PLC provides only 6-13K bytes of data storage space.

7. Communication mechanism

RTU products have client/server communication capabilities and can initiate active reporting communication methods.

The communication mechanism of traditional control systems (including PLC) is master-slave mode, which is the communication principle followed in the industrial 

control field under proprietary wiring structure.

8. Communication Protocol and Flexibility

RTUs generally have 3-5 communication interfaces, such as RS485, RS232, etc; Supports multiple communication protocols, such as MODBUS, DNP3, etc., making it 

particularly suitable for SCADA systems.

The PLC communication interface and protocol are single and only suitable for relatively fixed and unified station control systems.