Why should you use PLCs for network communication?

1 Benefits of PLC network communication

PLCs can exchange data, commands, and status information with other PLCs or devices over a network, such as Ethernet, serial, or wireless. This can improve the efficiency, safety, and performance of your control system by enabling centralized monitoring and control of multiple PLCs from a single workstation or server. Additionally, distributed processing and logic among PLCs helps to reduce the load and complexity of each PLC. Remote access and maintenance of PLCs is possible from anywhere with an internet connection, while integration and interoperability with other systems like SCADA, HMI, or IoT devices is also achievable. Furthermore, data logging and analysis of PLC inputs and outputs can be used for optimization and troubleshooting.

2 Types of PLC network communication

Different types of PLC network communication exist, depending on the protocol, topology, and purpose. For example, peer-to-peer communication allows PLCs to communicate directly with each other without a central controller or server, which is useful for simple and fast data exchange. Master-slave communication involves one PLC acting as a master and sending or requesting data from one or more slave PLCs; this is ideal for centralized control and coordination of multiple PLCs that perform different tasks. Lastly, client-server communication requires one or more PLCs to act as clients and send or receive data from a server such as a PC, database, or web service; this is helpful for integrating PLCs with other systems and accessing data from the internet or cloud.

3 How to program PLCs for network communication

Programming PLCs for network communication requires you to consider a variety of factors, such as the network protocol and standard that your PLCs support, like Modbus, Profibus, or Ethernet/IP. Additionally, you need to configure the network settings and parameters of your PLCs, including the IP address, port number, baud rate, or node ID. You must also define the data format and structure used to send or receive data, such as binary, ASCII, or floating point. This includes specifying the data types and sizes of your PLC variables and registers, like word, bit, or real. Finally, you need to consider the communication method and mode used to initiate or respond to data exchange, such as polling, interrupt, or event-driven. Writing the logic and code of your PLC program accordingly is necessary for this process; this includes read, write, or send instructions.

4 Best practices for PLC network communication

To ensure the reliability, security, and performance of your PLC network communication, you should select the appropriate network protocol and standard for your application and PLC model. This should offer the best compatibility, speed, and functionality for your needs. Likewise, you should choose the data format and structure that offers the best accuracy, efficiency, and readability for your data. Further, you should determine the communication method and mode that offers the best responsiveness, flexibility, and robustness for your data. Additionally, use network diagnostics and troubleshooting tools to monitor and test your PLC network communication for errors, delays, or failures. Finally, employ network security and protection measures to prevent unauthorized access or interference with your PLC network communication; encrypting, authenticating, or isolating your network and data as much as possible.

5 Examples of PLC network communication

To illustrate how PLC network communication works in practice, here are some examples of common applications and scenarios. For instance, a PLC network that controls a conveyor belt system in a factory uses Modbus TCP over Ethernet to coordinate the speed, direction, and stoppage of the conveyor belts. It also communicates with a PC using OPC UA over Ethernet to send and receive data and commands from a SCADA system. Similarly, a PLC network that monitors and controls a water treatment plant relies on Profibus DP over serial to collect and process data from sensors and actuators. It also communicates with a web server using MQTT over Ethernet to publish and subscribe data and alerts from an IoT platform. Finally, a PLC network that operates a solar panel system in a remote location utilizes ZigBee over wireless to control the orientation and output of the solar panels. It also communicates with a smartphone using GSM over wireless to allow remote access and maintenance of the PLCs.