Siemens PCS7 + OPC over Modbus TCP/IP

Hello All,

I am not very familiar with the Siemens architecture however, I was looking into a possible application.

The current Siemens PLC is already working and running an OPC server that can be accessed by an OPC Client. I am able to browse the server and get all the required tags.

However, I am trying to get/convert this OPC data from the server to Modbus TCP/IP as I am looking to add a gateway that can only accept Modbus TCP/IP. Is this possible using Siemens tools? Like do I have to create Modbus function blocks and assign each variable to it for every input I want?

Apologies for the lack of information but if someone could lead me in the right direction, I would appreciate it. Thank you.

Hello and welcome to the forum. Not sure I understand your goal. You need to add a gateway which supports only Modbus TCP "client" functionality, and so you need the data served as OPC UA nodes to be mapped into a Modbus TCP server? About the Modbus TCP client gateway, what does it convert the data to?

Thank you. I will try and explain this a little better:

1. The IoT/gateway only supports Modbus TCP/IP communication. This gateway converts the input variables into 1 XML file that is sent to our telemetry server which offers a GUI for the customers to visualize data. The server only accepts XML Files. This gateway is sold by our company so integration is seamless.

2. The current Siemens PLC is running an OPC Server and communicating over Ethernet IP.

3. Since the gateway does not support OPC, I need to convert this OPC data to Modbus TCP. I have successfully done this using Kepware (Modbus + Advanced tags suite license). In the modbus suite I can create registers and using the advanced tags suite I can link the existing OPC tag to the newly created modbus tag.

4. I am trying to eliminate the licensing costs with the additional Kepware server.

Can I approach this differently? Would the only other way would be by using "MB_SERVER" (Modbus server) function block directly in the PLC and having the PLC serve as a slave?

Let me know if this helps. Thanks again.

I still cannot answer your question because the Modbus TCP protocol requires the definition of a client and a server. hence, you need to explain whether the IoT/gateway you mention is a Modbus TCP client or a Modbus TCP server, as the solution will be very different, depending on its Modbus TCP functionality.
If the IIoT gateway is a Modbus TCP client, then ypu need to develop a Modbust TCP server in the Siemens S7 program. You need to an arbitrary assignment of the data currently available as OPCUA nodes but which are internally S7 tags, and map this data to the Modbus database in the PLC program. The Modbus TCP client must access the data periodically, as the client controls the communication in Modbus TCP.
If the IIoT gateway is a Modbus TCP server then the solution is much easier as you will need to develop a Modbus TCP client on the S7 program and decide where to write data to or read data from the Modbus database in the IIoT gateway.

Siemens PCS7 can do Modbus directly, but it must be licensed, installed and configured.

An IoT gateway that only speaks Modbus TCP ?
I think that the solution is to change the IoT gateway.

This gateway is sold by our company so integration is seamless

Click to expand...

Does the fact that you are selling the gateway affect your decision on the technical solution ?

arth608 said:

This gateway is sold by our company so integration is seamless.

Click to expand...

I think your original question is proof to the contrary... particularly for a gateway.

I recently started to work with siemens arhitecture too

If you have redundant processors, you need to purchase the Modbus TCP/IP redundant package from Siemens, last time I purchased was 4 years ago, and it was around 6000.00 US Dollars. Then you configure the Modbus blocks in a CFC chart. You have to add each Modbus connection in NetPro, and then use the connection ID in the CFC block configuration. Then Build a DB to hold the Modbus data. The Modbus blocks sends and receives data to/from the DB. You will need dedicated Modbus blocks and connections for each device. We usually install a dedicated CP-443-1 module just for the modbus communications.

Edit:
Just in case you are new to Siemens all the addresses and DB calls are in HEX.

I think siemenes architecture will be enought during work with create your own IoT application at first. Because usually siemens works on big industrial manufactuing. I knoaw that in Siemens there are different catgeriesof automation products depending upon process like machine toolsinumerik, process integrationTIA etc.