PLC Networking Made Easy: Boost Efficiency with Multi-Device Collaboration

How to Seamlessly Connect Multiple PLCs via Network? Multi-Unit Networking Communication is Key. When done right, it’s not difficult for multiple controllers to work together.

What is Multi-Unit Networking Communication?

In simple terms, it allows multiple PLCs to communicate data over a network to achieve coordinated work. This can be used for distributed control, for example, one PLC collects data while another PLC is responsible for control, and the data must be transmitted via network communication. Common communication methods include Industrial Ethernet (Profinet) and Point-to-Point (P2P) communication.

Project Implementation Process Breakdown

1. Hardware and Software Preparation

• Hardware: Two Profinet-supporting PLCs, such as S7-1200 or S7-1500, a switch, and several network cables.
• Software: TIA Portal V14 or higher.

2. PLC Network Configuration

• Assign IP Addresses
• PLC1: 192.168.1.1
• PLC2: 192.168.1.2. Both PLCs need to be on the same subnet and connected to the same switch.
• Check Connectivity: Use a computer to Ping these two IPs to ensure network smoothness.

3. Establish Communication Connection

• Set Communication Partners: In PLC1, add communication partner PLC2, input PLC2’s IP address, and select Profinet communication. Conversely, add PLC1 as a partner in PLC2.
• Define Communication Data: Set the data to be sent in PLC1, such as variables in Data Block DB1. In PLC2, define the receiving data block, and the structure must match the sender’s.
• Data Block Example:

  DATA_BLOCK DB1
  STRUCT
      Motor_Status : BOOL;      // Motor Status
      Temperature : INT;        // Temperature Value
      Alarm_Flag : BOOL;        // Alarm Flag
  END_STRUCT;
  

4. Write Communication Program

• Send Data (PLC1): In the main program of PLC1, use Profinet communication instructions, such as<span>TCON</span> and <span>TSEND</span>, to periodically send data to PLC2:

  CALL "TSEND"
       ID := 1
       SEND_DATA := DB1
       DONE := M0.0
       BUSY := M0.1
       ERROR := M0.2
  

• Receive Data (PLC2): In PLC2, use<span>TRECV</span> instruction to receive data and store it in local variables:

  CALL "TRECV"
       ID := 1
       RECV_DATA := DB1
       DONE := M1.0
       BUSY := M1.1
       ERROR := M1.2
  

Issue 1: Data Loss or Reception Failure

• Reason: Sending and receiving cycles are out of sync.
• Optimization: Introduce a handshake mechanism, using a signal bit to confirm whether the data has been received.

Issue 2: Slow Communication Speed

• Reason: Data block size is too large or refresh cycle is too long.
• Optimization: Reduce the amount of data transmitted each time and adjust the communication cycle, for example, from 200ms to 50ms.

Issue 3: Communication Errors

• Reason: Duplicate ID numbers or incorrect network configuration.
• Optimization: Ensure each connection’s ID number is unique and check the network configuration to avoid IP conflicts.

Advanced Optimizations

1. Increase Monitoring Mechanism: Use a heartbeat signal to detect whether communication is normal. The sender sends a fixed signal at intervals, and the receiver verifies whether the signal frequency is stable.

2. Hierarchical Communication Structure: If multiple PLCs are networked, a “master-slave” structure can be designed, allowing one master PLC to aggregate data while other PLCs act as sub-stations for collaboration.

3. Data Buffering Mechanism: To prevent data loss due to network fluctuations, a data buffer can be added on the sender side, using a FIFO queue to store sending data, ensuring every piece of data can be received.

Multi-Unit Networking Communication is very practical. Once mastered, your PLC control system will become more flexible and efficient! If you have any questions, feel free to chat!