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Setting subscription update interval

Setting subscription update interval



I have a couple of questions regarding the subscription update interval.

  1. What is the minimum update interval?
  2. Is there any way to set the update interval for a large number of tags all at once?
    1. I can only see how to set this value for single tags

Frequent Contributor

1. The update interval is defined by the PLC, not by WebIQ. Please note that in OPC UA the server notifies the client on changes - so it's up to the server to support it. Please note also however that you have to consider network latency.

2. & 3. This is only possible by using the XML importer available on the Smart HMI website - you cannot modify multiple items/widgets/entries at once in WebIQ currently.

Regarding #1, the inherited update interval from the ctrlX OPC UA server seems to be 100ms, but if I manually set the update interval to 1ms in WebIQ, I see an update rate of ~50ms. Could you please explain why that might be?

A little background... I am running some communication benchmark testing between ctrlX OS OPC UA Server and WebIQ as OPC UA client.

Frequent Contributor


WebIQ always uses the "Update Interval" setting in Process Data Manager (the subscription interval) and devides that by two resulting in 0ms (it's an integer value) in your case, because 1 / 2 is 0 in this case. However, the OPC UA server in this case tells us "I only support 50ms as the lowest value".
Please note that this is a subscription rather than a pull mode in OPC UA, that means that it's always the server that decides how fast he going to send the data, because the server is sending the data to the client, it's not pulled.
Please also see here for full reference on the sampling interval in OPC UA:

Thanks for the explanation. Why is 100ms inherited as default then when the server is capable of 50ms? When I look at the configuration of the OPC UA server on the ctrlX CORE, 10ms is the minimum publish interval.



Frequent Contributor

We're just querying the OPC-UA server, we've not developed it, as such we cannot tell you why you're only getting an update every 50ms. Although it might be interesting to see the explanation of the asterisk that's now shown. Maybe some expert on this from Bosch Rexroth can provide more information on this?

WebIQ always uses 100ms by default if you add an item to WebIQ Designer, it doesn't use the suggested one by the server, but you're of course free to change it anytime.

Once again let me point out that in OPC-UA a client is only *asking* the server for getting updates in the desired interval, it's up to the server to adhere to that or not as it's not a pull, but a subscription model.

Community Moderator
Community Moderator

@Sgilk See HowTo article WebIQ-Use-Designer-Add-On which provide a tool to set attributes like update interval of an item. It's based on WebConnect API which is documented on the homepage of SmartHMI.