Modbus RTU to Ethernet using PLC

cpkarthiksai

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Join Date
Feb 2013
Location
Madurai
Posts
2
HI

I am still new to PLCs and therefore please excuse and correct me if I am wrong anywhere. I work in a solar energy industry and as part of a new product we are working on.. We need to be able to convert RS485 2 wire data from the current sensor to Ethernet so that it can be read on PC and HMI. As of now we are using a gateway to convert the RS485 to ethernet. Can this be done using a PLC alone like Siemens S7 or so? Or do we still need a seperate RS485 to ethernet converter?
 
Not sure about Siemens, but you could certainly use any plc that has a modbus port to scan your device, place the data into a set of holding registers and read those registers directly from the plc. If it was me I would use a Schneider M340 it has both a Modbus port and ethernet port built into the cpu, and a simple in built function block to read from a Modbus network.
 
yes but i would look more into a lower cost plc because replacing a gateway by a m340 won't be a cost saving...Siemens S7- 1211 or 12 could do that. Just add a 485 serial module and program it to be Modbus master and then exachange the read value thru the plc ethernet port. Their is also a web server in it so you could directly read data without any other software.
 
If you are using a Siemens PLC, depending on which one, you may have RS485 available already. If you are using Profibus there are RS485 / RS232 I/O modules. If you just want to go RS 485 or 232 directly to Ethernet you can use a Blackbox, stand alone for less than $400.
http://www.blackbox.com/Store/Detai...Serial-Servers-RS-232-or-RS-485-RS-232/LES41A

If you are using PCS7 or T-3000 you may have to use a CM-104.
 
Thanks a lot guys.. Ya it depends on the costs too.. I don't want a PLC solution which costs almost same as or more than the gateway i am using of course. I will look into what you have said
 

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