Hi everyone,
I’m working on a project involving the AXL SE RS485 module within my PLCnext setup, focusing on reading data from an EC (Electrical Conductivity) sensor and possibly managing sensor calibration through the PLCnext/HMI interface.
While I’ve delved into the manual and explored the examples provided in the library, applying this to my project practically—especially concerning reading/writing to registers—remains a challenge. A specific question I have is about the necessity of using both the Master and Slave Function Blocks for my application.
My search on the forum for RS485 and Modbus topics showed sparse responses, with few threads offering the depth of discussion I hoped for.
I’m reaching out for insights or advice on how to effectively integrate and utilize the RS485 module in a project context. In particular, how can I retrieve a parameter for EC measurement (for instance, Register Addr. (HEX/DEC): 0x0002, Data Type: UINT16 RO, Modbus Function Code (DEC): 3/4, with a Range of 0-20000 for 0-20000us/cm)? Or, how do you extract or capture the desired data? Furthermore, regarding the Modbus_RTU library’s documentation, it specifies support for baud rates >= 1200 and <= 38400, with a cycle time <= 50 ms and a bus cycle time <= 32 ms. Does this mean the entire PLC program needs to operate with a cycle time of <= 50 ms, or is it possible for the main PLC program to run at 100 ms while managing a separate task for the Modbus part at <= 50 ms?
I’d like to transform this abstract query into a tangible example project, particularly focusing on the use of the RS485 module to efficiently read sensor data. Any practical examples, advice, or insights from those who have navigated similar challenges would be immensely helpful.
Thanks in advance for your support and guidance.