Modbus communication help

[Saiesh]

Hi all
I need help on this
As in my project used Schneider TM241 controller.
Now I want to communicate Elite energy meter with controller by modbus serial communication (RS 485).
Using READ_VAR FB but still it is not communicating
Software: Machine Expert 2.1

 

[Corsair]

I'm not familiar with the PLC or meter - but the general things must be checked first. Making sure baud rate, data bits, stop bits, and parity match on both ends. Data bits must be 8 for Modbus RTU. Polarity on the RS-485 must be correct. If everything else is right you may try reversing it. Termination resistors on the ends unless internal resistors on the units can be switched in.

Next verify that the one-byte 'Node' or "Modbus ID' or 'Drop' number of the meter matches what the PLC is sending. Should be a value between 1 and 247.

You haven't said if the meter is responding with anything or if it is silent. If it is responding, then see if it is sending an exception. After that it is time to investigate the usual Modbus issues - data type, address index, byte order, etc.

If you have a 485 connection on your computer it may be easier to get the computer reading the meter first and then try it with the PLC. Lots of software recommendations on this forum for doing that. Some are free downloads.

 

[Saiesh]

I'm not familiar with the PLC or meter - but the general things must be checked first. Making sure baud rate, data bits, stop bits, and parity match on both ends. Data bits must be 8 for Modbus RTU. Polarity on the RS-485 must be correct. If everything else is right you may try reversing it. Termination resistors on the ends unless internal resistors on the units can be switched in.

Next verify that the one-byte 'Node' or "Modbus ID' or 'Drop' number of the meter matches what the PLC is sending. Should be a value between 1 and 247.

You haven't said if the meter is responding with anything or if it is silent. If it is responding, then see if it is sending an exception. After that it is time to investigate the usual Modbus issues - data type, address index, byte order, etc.

If you have a 485 connection on your computer it may be easier to get the computer reading the meter first and then try it with the PLC. Lots of software recommendations on this forum for doing that. Some are free downloads.

But in Modscan data in coming properly....

 

[Corsair]

Could still be a data cable polarity issue with the PLC or a node number in the plc program.