Recommendations for Optimizing Networks with Modbus Devices

Optimize the Panel Server configuration:

Set appropriate timeouts for the following:
- Modbus serial client timeout: increase the response timeout to accommodate slower devices
- Message timeouts for Modbus client and Modbus server
Set an appropriate Modbus serial client frame delay (default setting 50 ms)to prevent communication errors on the serial bus. Refer to Modbus Serial Client Configuration Settings.
When used as a transparent gateway, do not the devices in the Panel Server.
In a parent-child architecture, avoid discovering the devices in the child Panel Server. Discover the devices at parent level.

Optimize the configuration of connected devices:

Disable unused features to reduce processing time.
Use the Registers read function available in Panel Server webpages to check connectivity and register response from the connected device.

Monitor performance and diagnostics:

Monitor error rates. Check for CRC (cyclic redundancy check) errors and timeouts, which can indicate wiring or configuration issues. CRC error information is available as follows:
- For the Panel Server: available on the webpages. Refer to Panel Server Diagnostics.
- For devices: through Autodiagnostics logs. Refer to Exporting all logs
Use diagnostic tools, for example protocol analyzers or dedicated software like ModScan or Modbus Poll.

Test and tune the system:

Start with conservative sampling frequencies. Gradually reduce them while monitoring for the following:
- CRC errors
- Timeouts
- Missed responses
Adjust sampling frequencies based on actual device response times and network conditions.

Follow best practices for network design:

Minimize the number of devices per serial network to avoid overloading the bus. Try to stay below 32 devices per RS485 segment.
Use repeaters or bridges for long distances or for high numbers of devices.
Terminate the bus correctly. Use 120 ohm resistors at both ends of RS485 lines.
Use shielded twisted-pair cables to reduce noise and interference. If available, connect shield and 0 Volt.

Understand the impact of baud rate. Baud rate determines how fast data is transmitted over the network:

Higher baud rates (for example, 115200 bps) allow faster sampling but are more susceptible to noise.
Lower baud rates (for example, 9600 bps) are more stable over long distances but reduce throughput.

Match the baud rate to the network conditions:

Use higher baud rates (for example, 38400–115200) in electrically clean environments with short cable runs.
Use lower baud rates (for example, 9600–19200) in noisy environments or long-distance setups.

Optimize the connected device configuration:

Set unique server IDs for each connected device to avoid conflicts.
Use consistent baud rates and parity settings across all devices connected on the same segment.

Optimize data sampling strategy:

Read/write multiple contiguous registers in one request to reduce traffic.
Adjust sampling periods to avoid sampling too frequently. Aim for a balance between responsiveness and bandwidth.
Consider all devices in the serial network. The presence of a device with a slower response can impact the overall performance of the network.
Consider using multiple gateways if you have high numbers of serial devices or high volume data.
Avoid overloading the serial line with too many requests.

Manage Modbus TCP clients as follows:

Limit the number of simultaneous Modbus TCP clients to avoid overloading the Panel Server.
Use persistent TCP connections instead of frequent connect/disconnect cycles.
When establishing multiple simultaneous TCP client connections to the Panel Server, configure higher response timeouts on the client side. This helps ensure reliable communication and prevents premature disconnections or timeouts due to increased load during concurrent connections.