125-0117

Check Active Network Connections

Press MOD key, navigate to 'Network Settings' or 'System Information', and review active connections. Check for multiple simultaneous TNCremo or LSV2 client sessions that may be consuming connection resources.

On TNC 640 controls, use the extended diagnostic view in MOD > TeleService > Connection Overview to see detailed connection statistics.

Disconnect Unused Clients

Close all unnecessary DNC software, tool management applications, and remote monitoring tools. Verify each application properly disconnects from the control rather than leaving sessions open.

Coordinate with production to ensure no active DNC transfers are interrupted during disconnection.

Implement Connection Limits

Configure the LSV2 connection limit in system parameters. Access MOD > System Parameters > Communication and set appropriate maximum connection values to prevent resource exhaustion.

Typical reliable operation uses no more than 3-5 simultaneous LSV2 connections on TNC 530/620/640 controls.

Restart Control

Perform a controlled shutdown and restart of the TNC control to clear the connection list and release all allocated connection resources.

Ensure machine is in safe state and all programs are stopped before restarting the control.

Review PLC Program Communication Blocks

Open the PLC program in TNCopt or PlcEdit and identify all communication function blocks (TCP/IP clients, server connections, file operations). Verify each OPEN or CONNECT function has a corresponding CLOSE function in all program paths including error handling.

Search for function blocks like TCP_OPEN, TCP_CONNECT, FILE_OPEN without matching CLOSE operations in conditional branches.

Check PLC Error Handling

Verify that PLC error handlers properly close connections when communication errors occur. Review all exception handling code to ensure connection resources are released even during error conditions.

Missing CLOSE operations in error paths are the most common cause of PLC-related connection leaks.

Monitor Connection Allocation

Add PLC debug variables to track connection handle states and monitor whether connections are being properly opened and closed during operation. Use PLC variable monitoring in Test Run mode.

Create a counter that increments on OPEN and decrements on CLOSE to verify connection balance over time.

Update PLC Program

Modify the PLC program to ensure proper connection lifecycle management, then compile and transfer the corrected program to the control. Test thoroughly in simulation mode before production use.

Always backup the existing PLC program before making modifications.

Review OPC UA Server Status

Navigate to MOD > OPC UA Server Settings and check the number of active client connections and subscription count. Note any unusually high numbers of monitored items or rapid connection/disconnection patterns.

TNC 640 OPC UA server typically supports 5-10 simultaneous clients; exceeding this may require connection management optimization.

Reduce Monitoring Frequency

Configure OPC UA clients to use longer sampling intervals and reduce the number of simultaneously monitored variables. Group similar data into fewer subscriptions where possible.

Coordinate with SCADA or MES system administrators before changing monitoring configurations.

Configure Connection Timeout

In OPC UA server settings, reduce the session timeout value to automatically disconnect inactive clients. Set appropriate keepalive intervals to detect and clean up dead connections.

A session timeout of 30-60 seconds with 10-second keepalive intervals provides good balance between responsiveness and resource management.

Restart OPC UA Service

Stop and restart the OPC UA server service from MOD menu to clear all current sessions and reset the connection table without full control restart.

OPC UA service restart will disconnect all monitoring clients temporarily.