Mastering PLC: Comprehensive Guide to Industrial Networking and Routing

Industrial network communication relies on switching and routing. Today, we will use Siemens PLC to configure industrial network switching and routing management, while discussing common issues and optimization solutions.

Project Requirements and Common Issues

Industrial networks need to ensure that devices such as PLCs, HMIs, inverters, and IO modules can communicate with each other, while also ensuring stable and efficient data transmission. Network switching distributes data within the same subnet, while routing transmits data across different subnets.

Common Issues

1. 1. Network Conflicts: With too many devices and improper IP address allocation, conflicts can easily occur, leading to severe data packet loss.

2. 2. Subnet Communication Failure: Improper configuration of cross-subnet devices can result in data not being sent or received.

3. 3. High Communication Latency: Improper switch configuration can cause data to take longer routes, affecting real-time performance.

4. 4. Maintenance Challenges: Complex network topology can make it difficult to determine where to troubleshoot when issues arise.

Solutions with Siemens PLC

Using the Siemens S7-1200 PLC and SCALANCE industrial switch, we can achieve network switching and routing. This can be divided into three steps: network planning, switch configuration, and routing setup.

1. Network Planning

First, plan the network structure. For example, a production workshop has two production lines, each using a separate subnet (segment). The PLC and IO modules are in the same subnet, while the HMI and upper computer are in another subnet, interconnected through a router.

IP address allocation:

• • Subnet 1: 192.168.1.0/24 (PLC, IO modules)

• • Subnet 2: 192.168.2.0/24 (HMI, upper computer)

• • Router IP: 192.168.1.1 and 192.168.2.1

After planning the addresses, avoid duplicate allocations to facilitate future operations.

2. Switch Configuration

The main function of the switch is to distribute data packets, ensuring that devices within the same subnet can communicate with each other. We use the SCALANCE switch to configure VLANs (Virtual Local Area Networks) to isolate different production lines and reduce broadcast storms.

VLAN Configuration Code (SCL Language for Dynamic VLAN Allocation):

// VLAN configuration logic
DATA_BLOCK VLANConfig
VAR
    VLAN1_Devices : ARRAY[1..10] OF INT; // VLAN1 device port numbers
    VLAN2_Devices : ARRAY[1..10] OF INT; // VLAN2 device port numbers
END_VAR
END_DATA_BLOCK

FUNCTION_BLOCK VLANSetup
VAR_INPUT
    PortID : INT;      // Switch port number
    VLAN_ID : INT;     // VLAN number
END_VAR
VAR_OUTPUT
    ConfigStatus : BOOL; // Configuration status
END_VAR
BEGIN
    // Assign port to corresponding VLAN
    IF PortID IN VLAN1_Devices THEN
        VLAN_ID := 1; // Assign to VLAN1
    ELSIF PortID IN VLAN2_Devices THEN
        VLAN_ID := 2; // Assign to VLAN2
    ELSE
        VLAN_ID := 0; // Not assigned
    END_IF;

    // Simulate configuration completion
    ConfigStatus := TRUE;
END_FUNCTION_BLOCK

This code can dynamically manage switch ports, ensuring devices are assigned to the corresponding VLAN.

3. Routing Configuration

Cross-subnet communication requires routing configuration. For instance, if the HMI is in the 192.168.2.0 subnet and wants to access the PLC in the 192.168.1.0 subnet, a static route must be added in the router.

Static Route Configuration:

• • Destination subnet: 192.168.1.0/24

• • Next hop address: 192.168.2.1

Routing Configuration Code (Simple Routing Logic Implemented via PLC):

// Routing forwarding logic
DATA_BLOCK RoutingTable
VAR
    Destination : ARRAY[1..10] OF STRING[15]; // Destination subnet
    Gateway : ARRAY[1..10] OF STRING[15];     // Next hop address
END_VAR
END_DATA_BLOCK

FUNCTION_BLOCK RouteForwarding
VAR_INPUT
    SourceIP : STRING[15];       // Source IP address
    TargetIP : STRING[15];       // Target IP address
END_VAR
VAR_OUTPUT
    NextHop : STRING[15];        // Next hop address
END_VAR
BEGIN
    // Check routing table
    FOR i := 1 TO 10 DO
        IF TargetIP = Destination[i] THEN
            NextHop := Gateway[i];
            EXIT;
        END_IF;
    END_FOR;

    // If no match, return default gateway
    IF NextHop = '' THEN
        NextHop := '192.168.1.1'; // Default route
    END_IF;
END_FUNCTION_BLOCK

This logic is a simplified version of routing functionality; in actual projects, it can be expanded based on device requirements, such as supporting dynamic routing protocols.

Optimization Solutions

1. 1. Using Ring Network Redundancy: Stability is crucial for industrial networks, enabling ring network protocols in switches can prevent communication interruptions due to single points of failure.

2. 2. Adding Network Monitoring: Use WinCC or third-party tools to monitor network traffic in real-time, identifying congestion or device offline issues.

3. 3. Automatic IP Allocation: Configure a DHCP server to manage IP addresses uniformly, reducing the hassle of manual allocation.

Conclusion

Industrial networks are not complex; with practice, you can understand them. Feel free to use the code provided, and if you have any questions, leave a message, and we can discuss it together!