OPC UA Polling Rates

Ignition
,
1

Hi all,

I am currently setting up a Perspective system that connects to 5 separate OPC-UA Servers running directly on remote PLC’s.

Because these are remote devices, I would like to reduce the default polling rate from SCADA to the Servers, however am getting a bit confused as to what actually dictates when the devices will be polled.

All tags are attached to a single Tag Group that have the settings as per the attached screenshot. I would like these tags to all poll at 3 minute intervals.

TagGroup
TagGroup716×613 40.5 KB

However when I look at the OPC Connections in the status section in the gateway, it indicates a “Requested Sampling Interval” that matches my Tag Groups rate, but it then indicates a “Revised Sampling Interval”. When I look at the data going to the sites using wireshark, I can see that Ignition is polling the device at the time defined by the “Revised Sampling Interval” and not what I am setting in the Tag Group.

OPCConnection
OPCConnection1200×737 42.9 KB

Where is this “Revised Sampling Interval” coming from, and how do I set the polling rate to match what is being configured on the Tag Group?

Thank you,
Nic

2

OPC/UA doesn’t poll. It “subscribes”, and the server (PLC in this case) pushes only changed data to the client (Ignition) when there are changes to report. Changes are reported no faster than the mutually-agreed sampling interval. “Mutually-agreed” meaning the server (your PLC) can limit or tweak the pace Ignition requests. Look at the specs for your PLCs’ OPC servers.

3

Like Phil said, OPC UA isn’t polling based, the sampling interval in this case is going to be used by the server to internally poll its data sources, not as something that controls frequency of requests between client/server.

If you really want to reduce the frequency that the server can report changes to the client then you can set the Publishing Interval setting to something slow instead. Publishing Interval controls how often an OPC UA Subscription will “execute”, i.e. gather up all queued changes from all its Monitored Items and report them to a client.