Hi!

My problem (problem to solve):
The company has a SCADA system for measuring and electric control. There are 13 meters (RS 485 devices) and they communicate with PC where SCADA is installed. SCADA communicates with those devices over Modbus RTU protocol. So PC is a Modbus master and the meters are Modbus slaves.

I would like to read parameters from meters with a Twido PLC (Modbus RTU). But I can not connect a TWIDO to the node because there will be 2 Modbus masters.

The question is: can be this problem solved vith a 174 CEV 300 10 bridge?

If I connect 174 CEV 300 10 bridge to the RS485 node. My PLC Twido has a ethernet port and I can send a Modbus TCP request over the ethernet and then the bridge will handle those requests and send responses from RS485 devices back to TWIDO?

So what is with the SCADA system who communicates over RS232/Rs485 converter with meters (RS485 device)?
Can there be a problem? Do I need to connect the SCADA system also over another bridge or should I just leave it?

 

You should only really have one Modbus master on a Modbus network. So adding a gateway where the gateway will be a Modbus master talkng to modbus slaves ,is exactly the same as using another directModbus master.

what is the point of connecting the Twido in the network any way?

It would make more sense to by a Ethernet embedded Twido. The Twido could be a Modbus master to the meters. The SCADA could link to the Twido over Ethernet (Modbus TCPIP), Modbus RTU is not very good for a scada, it's a bit slow.

 

A 174-CEV-300-10 will permit multiple master to poll him on the ethernet side, and act as a single master on the serial side. If your Twido PLC need to read data directly from the meters and you don't want him to act as a mail box to your scada, then you should put your SCADA on Modbus Ethernet too, so PLC and SCADA will act as Modbus Ethernet masters to the CEV but CEV will be the unique master on the modbus serial side.

We tested this configuration and as long as you are aware of data transfer rate limitations, it will work very well. If your SCADA don't support Modbus Ethernet, you could use a second CEV, configured as slave on the serial side from wich each modbus adress transaction is redirected to the other CEV (CEV Mapping Configuration).

On Jun 10, 2008 3:00 am, Jaka Dolenec wrote:
Hi!

My problem (problem to solve):
The company has a SCADA system for measuring and electric control. There are 13 meters (RS 485 devices) and they communicate with PC where SCADA is installed. SCADA communicates with those devices over Modbus RTU protocol. So PC is a Modbus master and the meters are Modbus slaves.

I would like to read parameters from meters with a Twido PLC (Modbus RTU). But I can not connect a TWIDO to the node because there will be 2 Modbus masters.

The question is: can be this problem solved vith a 174 CEV 300 10 bridge?

If I connect 174 CEV 300 10 bridge to the RS485 node. My PLC Twido has a ethernet port and I can send a Modbus TCP request over the ethernet and then the bridge will handle those requests and send responses from RS485 devices back to TWIDO?

So what is with the SCADA system who communicates over RS232/Rs485 converter with meters (RS485 device)?
Can there be a problem? Do I need to connect the SCADA system also over another bridge or should I just leave it?

( Complete thread: http://www.control.com/thread/1026246993 )