s7-1200 modbus RTU - advice on first time user

Hi!

I have worked with s7-1200 before so I'm familiar with the system. However I have never worked with modbus, nor TCP/IP or RTU.

Now I might and since I'm a newbie at modbus I would like to ask this:

I want my s7-1200 to be master and connect to:

http://www.produal.com/folders/Files/Käyttöohjeet EN/FLTA_user_guide_en.pdf

If I buy the CB 1241 (communicationscard for RS-485), can I easily recieve information from this device?

My issue with this is that I could just buy regular sensors and wire it to an analoge module. To save installation time I could use this system that has wireless sensors and this reciever module, but I don't want to buy it (expensive) and then spend several days to program it (profit lost compared to regular sensors)

thanks in advance /Tim

I think you can. We used the same communication board to communicate with 15 frequency drives in Modbus RTU and worked the way we wanted (turn on/off and change the speed).

Sweet, and there is nothing strange with the module I want to communicate with as seen in the pdf link?

rQx said:

Sweet, and there is nothing strange with the module I want to communicate with as seen in the pdf link?

Click to expand...

I don't think so. Good luck

My problem was with the RS485 module, not board. Replaced a 200 (had 2 built-in RS485 ports) with a S7-1200 and RS422/485 module. Talking Modbus to 3 Chinese VFDs.
Had to add time delays between each read and write FB. Modbus comms take time, and the S7-1200 is too fast.
From page 6 of your manual:
"NOTE: The Modbus commands must have at least 500 ms interval."
That's half a second.

Make sure you put in code to monitor status and faults from the FB. In my case, the FB was accurate in detecting faults.

The original code from the Chinese 200 had 6 blocks. 3 reads, and 3 writes. They were using the "Done" bit to trigger the next block. This had problems in the 1200. "Done" wasn't done yet. Apparently, I wasn't waiting for the reply from each VFD to complete.

I just updated a previous thread on this. See it for more info.

rQx said:

Sweet, and there is nothing strange with the module I want to communicate with as seen in the pdf link?

Click to expand...

To me, it is weird that you are talking obout sensor and reciever module and in the pdf the device has only AO. Not specified, but I guess it is Analog Output and not Input.


S7-1200 and modbus work fine..

Thanks alot for all the tips!

@m_turk : This is the wireless reciever module that recieves the signals from the sensors I have in the building. I can also redirect my wireless sensors to the 8 analog outputs on the reciever module to interface it with my PLC. But if I can use rs485 it saves me a "8 analog input" module to the s7-1200 and thus making it even cheaper to use