NI OPC collects PLC data, data is lost in rare cases，Why?

[zdz]

I used NI OPC to collect Siemens S7-1500 data and displayed it in the vi program. The acquisition rate is 50 milliseconds, but after observation, it is found that data is lost in rare cases. Is this a problem with the NI OPC Server or a PLC, or what causes it? Is there any solution?

[GerdW]

Hi zdz,

once you can observe a pattern in those "rare cases" then you might be able find a cause.

How can/should we help with so little information?

[zdz]

What is "pattern in those rare cases"? I use "shared variable value change notification: user registration event" to detect PLC variable changes. Will there be data loss under normal circumstances? Is it because the data is updated too often?

[Ben]

Date rates of 200Hz are a bit high for typical OPC server.

You may want to poke around with the OPC server settings to see if you can bump up the update rate but you are definitely pushing it.

100 Hz is the highest I would depend on an OPC interface.

An aside...

LabVIEW Channel wires come in multiple flavors including a Tag type. The Tag flavor offers the most recent update and are lossy. It is no accident NI chose the name "Tag" since that is what OPC servers and PLCs expose.

Take care,

Ben

[zdz]

Do you mean that NI OPC tags cannot guarantee all data?

[pincpanter]

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@Ben  ha scritto:

Date rates of 200Hz are a bit high for typical OPC server.

Actually it's 20 Hz. Not a rate I'm experienced about, anyway.

[Ben · Accepted solution]

You are correct Paolo!

My bad.

I can not say what the top update rate can be.

OPC is generally used for slow changing values and checking what the value is NOW.

Ben