This is possible to do, but differs depending on where the tag is coming from. In ICU for an interface you can set a scan class to 168 hours in order to have an interface try to update the value of a point once every week. In the case of Analytics in AF, you would need to be a little more creative by having something scheduled once a day (at 7am for example) and then write nooutput() when the day isn't the one you've specified (i.e. Sunday).
Where is the tag coming from/what is the data source for the tag that you're looking to write to only once a week? Perhaps with a little more background we could better assist you.
It is absolutely fine with keeping scan class to 168 in order to have an interface updating data once every week but how can I make sure my data updates only at a particular time e.g. 7 AM every Sunday. For this I don't think so its a viable solution to create a tag at that exact time(e.g. 6-Feb-17
7.00 AM) so that it will update next week at the same time e.g 13-Feb-17 7.00 AM).
The reason why I am asking this is that what is there in our hand is to set the particular scan class in point builder for any tag whereas from what time it should start updating solely depends on time when it is created.
Let me know your comments over this.
Normally, you can use scan offsets to force the updates to occur on a certain schedule, but given that the scan time is longer than a day I'm not sure how this would behave and would need to do some testing on my end.
Another potential solution is to have a tag update once a day at 7 AM (again using scan class offsets) and then use this tag as an input to a performance equation or analytic which only updates if the day is Sunday. This would take two tags, but get the job done.
What is the use case here? Do you really need to only collect it once a week or can't you just collect it more often but then query for that specific time when you get the data out?
It's just that in either way I should be able to get the data once per week. For now I just want to collect the value once per week.
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I would strongly suggest against that approach. It is much more reliable (and efficient) to periodically collect the value, let's say once per hour, then request it in whatever application you are using at your desired time (Sunday 7AM).