Read and Write to Device Level System Tags with an Allen Bradley PLC

[SW_10030176]

Hello, we do a lot of development on an Allen Bradley PLC and had the question come up wondering if there is a way to read or write to the Device Level System Tags (the ._System tags) that you see in OPC Quick Client. Are there any examples or is there a way to do this? This is a 1756-L72 ControlLogix 5570 with revision 32.11 and using KepServerEx v6.10.659.0, basically the thought is can I create a tag in the PLC that can write to or read to a particular ._System tag? Or anyway to read all of the ._System tags on the PLC side?

[SlidingDownhill]

You can map them as static tags within a Kepware channel and then have the PLC read those... You might need "advanced tags" to read the system tags though... not sure about that... but now I'm interested too. 

[cmorehead]

@SW_10030176

The default access for System tag read/write permissions is disabled. Please take a look at the knowledge base article in the following link to change the access permissions:

https://www.ptc.com/en/support/article/CS280759

Thanks,

*Chris

[SW_10030176]

Thanks for your reply Chris, this is what I received from PTC support ticket as well. I have all the permissions allowed, this does not help me how to setup in the PLC or in the KepServerEx Configuration to make this actually work. Thanks. 

[cmorehead]

@SW_10030176,

I'm not sure I follow you. The _System and _Statistic tags are internal to the KEPServerEX application and do not require plc set up. System Tags in KEPServerEX represent server, channel, and device-level properties only and are not connected directly to any PLC programming. Here is a link to complete list of available system tags with Read/Write or Read Only availability :

https://www.kepware.com/getattachment/e1943820-ef3c-4932-b055-4ef2a80ab863/kepserverex-manual.pdf#page=113

Do you have a specific tag or use case you are having trouble with?

Thanks,

*Chris

[SW_10030176]

My original question is can I read and write to the _System tags that are internal to the KEPServerEx application from a PLC? So on the PLC side I would have a PLC tag where I want to set a _System tag that is read/writeable in KEPServerEx, so an example would be say I want to set the ._System._Enabled kepware tag to 0 from the PLC, can I do that and how? I have the permissions all possible to do that

[SlidingDownhill]

That's interesting, You want the PLC itself to read/write to the system tags? or any Kepware tags?

The PLC might not be able to even address Kepware tags like you can in a SCADA platform (without using Open Sockets and a lot of work perhaps). 

[SW_10030176]

Correct, this is a unique situation where we do a lot of testing and development with a PLC and wondered if the PLC itself can read/write the KepServerEx internal system tags. I understand there are ways for other applications to read/write to them but wondered about the PLC itself. 

[SlidingDownhill]

Other than creating an open socket MSG, which I have yet to do, I can't envision how the PLC can initiate communication with Kepware in that manner.  I'm hoping Chris will prove me wrong. 

I'm gonna poke at a couple other resources I know too. 

You might also talk to Software Toolbox. They are a reseller of Kepware under the brand TopServer (like RXLinx Enterprise is) and they have a lot of other apps for OPC that might be able to help make this happen in a roundabout way if Kepware can't natively do so. 

[cmorehead]

@SW_10030176 

To my knowledge, I have not heard of any PLC's with the capacity to act as Client application and perform writes. Do you have any PLC documentation that supports the ability  for that PLC to perform writes via OPC DA or OPC UA?  

Thanks,

*Chris

[SlidingDownhill]

All I can find to come close is using FTLinx Gateway OPC Topics which has been there for a long time or the newly introduced AB FT Optix application (or a host of other third party apps) but it seems there will be a device or PC doing the intermediate work, nothing direct from PLC to KW I have found. 

I'm guessing that it would just be to chatty for a PLC to deal with.