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+--- Thread: Modbus IP Persistent connection and RTU Together Problem (/showthread.php?tid=6296)
Modbus IP Persistent connection and RTU Together Problem - savaskorkmaz - 04.02.2026
Hello,
We have an energy monitoring project with the following setup:
- 36 Modbus RTU Energy Analyzers connected via 5 Modbus RTU to IP converters
- 4 Modbus RTU Rooftop devices connected directly to the LM5 RTU-1 port
- Each energy analyzer has approximately 90 data points
- For the 36 energy analyzers (via RTU/IP converters), we are using Persistent Connection
The Rooftop devices connected directly via Modbus RTU are extremely slow — data updates are almost not coming at all.
Could this behavior be caused by using Persistent Connection for the 36 energy analyzers?
In other words, can persistent connections on the Modbus TCP side negatively affect the polling performance of devices connected on a separate Modbus RTU port?
What would be the ideal communication settings for this kind of project on both sides:
- Modbus TCP (RTU/IP converters)
- Modbus RTU (directly connected Rooftop devices)
Thank you.
RE: Modbus IP Persistent connection and RTU Together Problem - admin - 05.02.2026
First RTU port and TCP are polled together. Devices are polled in a queue one by one. You can potentially speed things up by using the second RTU port.
Persistent mode does not affect the polling speed. It's needed for devices that can handle only a limited number of TCP connections.
General performance recommendations:
- increase poll interval
- remove unnecessary data points
- use block reading where possible (read_count and read_offset profile fields), this can significantly reduce the polling time for each device