how S7-1500 OPC UA server communicates with custom

Question

I'm little bit confused regarding how S7-1500 embeded OPC UA server communication works in case of a custom client installed on PC since all examples I've seen so far include a Simatic PC Station as OPC server!!!

On PLC side, I have S7-1511-1PN with OPC UA server activated. This PLC is connected over PROFINET to ET200SP+several AI modules.

On PC side (not Simatic PC Station), I have an application in which there is some kind of OPC UA client functionnality that reads inputs from AI modules, writes some tags on PLC and if necessary sends reconfiguration records of AI modules to PLC (reconfiguration via user program).

What I can't understand, is:

Why the Simatic PC station is always added as OPC server if the PLC already has this feature?

Does/How PLC OPC server communicates directly to my custom client? (Any programming needed on PLC)

For the certificates limitations as defined in "Function Manual, 10/2018, A5E03735815-AG (page 222)", what means "Max number of implementable server methods", "Max number of arguments", "Max number of server interfaces", "Max number of nodes in user-defined server interface", "Max size of loadable server interfaces"?

How can I estimated these numbers from my application?

(Yes/No) Do I need a second communication (TCP for example) between my PC application and PLC to send/receive reconfiguration data?

Answer 1

Why the Simatic PC station is always added as OPC server if the PLC already has this feature?

The SIMATIC PC station is not required. In the days before the S7-1500 PLC had a built in OPC UA server the only way to have an OPC UA server with data from the PLC was to use a SIMATIC PC station. A SIMATIC PC station is a computer running the SIMATIC NET software. The SIMATIC NET software can talk to the S7-1500 via an S7-Connection, the data it reads can be served to OPC UA/DA servers which are also part of the SIMATIC NET software.

Does/How PLC OPC server communicates directly to my custom client? (Any programming needed on PLC)

The OPC UA client must be on the same IP range as the PLC network interface. In the hardware configuration of the S7-1500 the OPC UA server is enabled. The OPC UA client is then pointed to the IP address of the S7-1500 PLC and using the OPC UA discovery will be able to read all the marker memory area, input and output memory area and data blocks. The OPC UA client will be able to subscribe to tags and write values if required.

No programming is required in the S7-1500. In TIA Portal simply acess the hardware configuration of the PLC and in the hardware settings there are options to enable the OPC UA server.

For the certificates limitations as defined in "Function Manual, 10/2018, A5E03735815-AG (page 222)", what means "Max number of implementable server methods", "Max number of arguments", "Max number of server interfaces", "Max number of nodes in user-defined server interface", "Max size of loadable server interfaces"?

In OPC UA it is possible to call methods. Methods can call function code from within the PLC logic. A method can be passed parameters and can return values. This is what the spec is refering to when it dicusses methods and maximum number of arguments. Each data point is considered to be a node in OPC UA, so this is explaining the maximum data points which can be read. As different PLC tags take up different amounts of memory the max size is the total size of all the nodes.

How can I estimated these numbers from my application?

This will be depending on the number of tags you wish to share from the OPC UA server. The update speed on the subscription and the amount of subscriptions allowed. There is no hard and fast method for calulcating this, it is very application dependant.

Do I need a second communication (TCP for example) between my PC application and PLC to send/receive reconfiguration data?

The OPC UA server can be configured to listen on any network interface of the S7-1500. There is no need for extra communication it is all part of the OPC UA protocol.

Siemens provide a nice application example with accompanying documentation which may help you get started. Download the documentation PDF from the link below.

https://support.industry.siemens.com/cs/us/en/view/109737901

Answer 2

Why the Simatic PC station is always added as OPC server if the PLC already has this feature?

OPC UA has quite few advantages over other industrial communication protocol. The communication is/can be secure, the project is Open (Source available on GitHub, Specification are free), ...

Does/How PLC OPC server communicates directly to my custom client? (Any programming needed on PLC)

The communication between your S7-1500 and your computer is an OPC UA End-to-End communication. I don't know the specification of the S7-1500 OPC UA Server neither your OPC UA Client but I guess they use OPC UA Binary over TCP

For the certificates limitations as defined in "Function Manual, 10/2018, A5E03735815-AG (page 222)", what means "Max number of implementable server methods", "Max number of arguments", "Max number of server interfaces", "Max number of nodes in user-defined server interface", "Max size of loadable server interfaces"?

Your Configuration can contains OPC UA Methods. I guess there is some limit given by Siemens for the number of Methods. Same for the number of Arguments available in each Methods. There shall also be some limitation for the number of available Server interface in your controller.

How can I estimated these numbers from my application?

I am pretty sure you can find those limitation in your Siemens's PLC Manual ;)