Pco Expression Editor

[Former Member]

Hi Experts,

I m working on PCo 2.3 Expression Editor.

How i can check any attribute of any subscription tag in Expression Editor?

Thanks in advance.

Please guide.

Regards,

Neha

[former_member196557 · Accepted solution]

Hi Neha,

Rather than depend on Tag Quality, I would recommend that you use the connectivity data that is exposed in the OPC Server, which can be subscribed or queried just like any ohter OPC Tag.  For example, in the Kepware OPC Server, the <channel>.<device>._System.Error tag is a boolean that is false normally, and true when the communications between the opc server and the PLC is broken.  There are other tags that count failed reads and writes that can also be used as well. Here is a screen shot from the OPC Client that shows the tags and values when the connection between Kepware and the PLC is failed:

Other OPC Servers will most likely have equivalent system tags as well.

Regards, Steve

[Former Member · Accepted solution]

Hi Steve,

Thnaks for quick reply.

I have tried same thing. Its perfectly working for PLC with polling state but for unsolicited PLC there is no error tag state change.

So may be attribute like date time or something will help.so checking for the same.

Is there other option for unsolicited PLC?

Regards,

Neha

[former_member196557 · Accepted solution]

Hi Neha,

All you have to do is set up a separate solicited OPC Connection and then subscribe to the tags; I usually do this anytime an unsolicited connection is set up. You need to subscribe to at least one PLC tag so that the server will actually try to read the tag data and keep the system tags updated.

Regards, Steve

[Former Member · Accepted solution]

Hi Steve,

Thanks you for your help.

I have followed same approach.

Regards,

Neha Jadhav

[former_member196557]

Hi Neha,

The PCo Expression Editor cannot access any subscription tag attribute other than the tag value.

What are you trying to accomplish with examination of tag attributes?

Regards, Steve

[Former Member]

Hi Steve,

Thank you for reply.

I m trying to check connectivity loss between PLC and PCo using tag quality attribute.

Now m achieved that in MII.

But still checking is there any option available in PCo expression editor?

Regards,

Neha