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Old November 24th, 2021, 03:20 AM   #1
DigiWaste
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S7-1500 communication with SCADA system

I'm working with a client who are in the process of installing a smart waste solution in a new building. This solution will be using s7-1500 PLC and ET200SP as remote I/O units. The communication between PLC and I/O units will be using modbus master/slave (CM PtP, RS485). This system needs to communicate with a top system (central operation) based on Schneider teknology running with modbus. My question: what is the best way to setup this communication between ths PLC and the top system?
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Old November 24th, 2021, 04:17 AM   #2
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It is a new system in a new building ?
The choice of Modbus RTU puzzles me.
Even if there is an existing SCADA that uses Modbus RTU, then it should be evaluated if a more recent fieldbus standard would be a better choice.

Quote:
This solution will be using s7-1500 PLC and ET200SP as remote I/O units. The communication between PLC and I/O units will be using modbus master/slave (CM PtP, RS485).
So the S7-1500 PLC will communicate as master with the ET200SP as slaves via Modbus RTU (??). That is a weird decision if any. The natural choice would be Profinet for an all-Siemens system. If it must be a serial RS485 protocol (like Modbus RTU), then Profibus would be the natural choice.
It is as far as I know not possible to setup ET200SP as Modbus RTU slaves. There is an Interface Module for Modbus TCP though.
You can install an CM PtP which will can communicate via Modbus RTU. But it will be the Profinet controller (i.e. the S7-1500 CPU) that communicates, not the ET200SP station.

I think you are mixing things up. You probably mean that you need an Modbus RTU connection to the Schneider SCADA system, and you intend to use a Modbus RTU module (CM PtP) in the Siemens PLC to achieve that.
If that is the case it is certainly possible, but it would be an arcaic and cumbersome design; definitely not the 'best way'.
If the Schneider SCADA do not have a Siemens S7 driver, then at the very least it should be possible to be an OPC DA or OPC UA Client.
So the 'best way' in my opinion is to get an OPC DA or OPC UA Server (can be Siemens Simatic Net, or it can be a 3rd party vendor) to provide the OPC Connection to the Schneider SCADA as OCP Client.
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Old November 24th, 2021, 07:20 AM   #3
hagos
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Agree with what Jesper said.
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Old November 24th, 2021, 11:45 AM   #4
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Also agree with everything Jesper said.



Quote:
Originally Posted by JesperMP View Post
It is as far as I know not possible to setup ET200SP as Modbus RTU slaves. There is an Interface Module for Modbus TCP though.
You can install an CM PtP which will can communicate via Modbus RTU. But it will be the Profinet controller (i.e. the S7-1500 CPU) that communicates, not the ET200SP station.
Possibly it's an et200sp PLC, in an RTU kind of setup? ALSO possible it's just unfounded optimisim, someone selecting parts without knowing how the system actually works.



Quote:
Originally Posted by JesperMP View Post
So the 'best way' in my opinion is to get an OPC DA or OPC UA Server (can be Siemens Simatic Net, or it can be a 3rd party vendor) to provide the OPC Connection to the Schneider SCADA as OCP Client.
Another option would be to use the built in OPC UA server on the 1500s, although I think something like Simatic Net becomes more cost efficient with many PLCs.
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Old November 24th, 2021, 12:11 PM   #5
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Quote:
Originally Posted by mk42 View Post
Another option would be to use the built in OPC UA server on the 1500s, although I think something like Simatic Net becomes more cost efficient with many PLCs.
Also one must consider that on the lower-end S7-1500 PLCs, incl. 1511SP and 1512SP, the integrated OPC UA Server is really lame.
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Old November 24th, 2021, 05:50 PM   #6
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Quote:
Originally Posted by JesperMP View Post
Also one must consider that on the lower-end S7-1500 PLCs, incl. 1511SP and 1512SP, the integrated OPC UA Server is really lame.
What's the lowest model 1500 you'd recommend with an integrated OPC UA Server?
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Old November 25th, 2021, 04:53 AM   #7
DigiWaste
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Yes it is a new system in a new building.
And as you correctly mentioning, I'm mixing things up here. As you put it, we need an Modbus RTU connection to the Schneider SCADA system, and my client intend to use a Modbus RTU module (CM PtP) in the Siemens PLC to achieve that.

You probably understand I'm a pretty new in this field, but I also waswondering about the choice of my client, and I will discuss this further with him. As I understand the PLC1500 have OPC UA Server included (licens), in which can serve an OPC UA client on the Schneider side.
Thanks a lot JespepMP for your quick replay.

By the way, this is a greate place for novices like myself
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Old November 25th, 2021, 05:12 AM   #8
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Quote:
Originally Posted by the_msp View Post
What's the lowest model 1500 you'd recommend with an integrated OPC UA Server?
This may give you a hint of what is possible:
https://support.industry.siemens.com...view/109755846
And you can play around with this:
https://perfdata.public.siemens.com/...ion=34&lang=en
My estimate is that what is possible via an S7 connection on an 1511 CPU will need a 1517 CPU to achieve the same via OPC UA.
edit: If the data volume is very low, OPC UA will be OK even on a small CPU. So it depends on what is required in the actual case.
edit: Even on a high-end CPU, it seems that you will reach transfer times of approx 250 ms unless the data volume is very low. I use down to 100 ms for data that is used to visualize movements, and I want a smooth animation on the screen. This is not a problem for an S7 connection, even on smaller CPUs.

Quote:
Originally Posted by DigiWaste
we need an Modbus RTU connection to the Schneider SCADA system, and my client intend to use a Modbus RTU module (CM PtP) in the Siemens PLC to achieve that.
Who says that you 'need' that ?
If the Schneider SCADA is not completely outdated, then it should support some other protocols than Modbus RTU.
Today, Modbus RTU is very rarely used, mostly as the last option when nothing else is possible. I.e. to connect a modern PLC to a legacy device.
Modbus RTU is never used as the main data connection between a SCADA and a PLC.
It is like sending an important document by fax.
I would challenge the clients decision, and ask if either OPC DA or OPC UA are possible. What exactly is the Schneider SCADA ? Name, and version ?

edit: Do not be confused by the above discussion about the OPC UA server integrated into the S7 CPU.
The OPC UA server can be installed on a PC, either the SCADA PC or another PC, and then there will not be any performance issues.
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Last edited by JesperMP; November 25th, 2021 at 05:52 AM.
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Old November 25th, 2021, 05:57 AM   #9
DigiWaste
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Thanks again JesperMP.

I have a meeting with my client next week and come back to you on "What exactly is the Schneider SCADA ? Name, and version ?" and other stuff.
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Old November 25th, 2021, 02:58 PM   #10
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Even that it would be modbus comms from scada there is no need to use that for ET200SP Remote IO from 1500CPU.
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