We faced with the same situation on different Modbus datasources. What do you mean for exact timestamps?
@terrypacker tolerance config is set 0.1. The difference between the data point log shown in red box on the picture is 0.01.
If interval is set to 5 minutes and 0.1 tolerance for point value changes, point should be logged maximum 5 minutes intervals. But there are some logs with 6 minutes interval.
We have some other points with the same issue.
@Nurr it is possible that you are seeing a rendered value which makes it look like there was a difference of 0.01 but if you look at the raw data you might find the difference to be slightly larger and being rounded by the TextRenderer on that point. Just a thought, the logging in your scenario works like I said about.
@terrypacker if the scenarios is like you said, value should be logged earlier than 5 minutes. But the point log shows that it is 6 minutes between two logs.
We should explain the situation to our customer asap.
@Nurr I see what is happening as Terry explained here
@Nurr never mind about the timestamps. You are using "Interval logging and point value changes". This type of logging will log every 5 minutes AND when the value changes.
if you want the point to log on a 5min interval. then just use the interval log.
The interval and value change log will also trigger a log if the point changes by the tolerance after a data source poll.
@CraigWeb I would like to log both every 5 minutes and when current point value is 0.1 higher/lower than previous value.
Is the logging configuration is wrong for this purpose?
In this configuration, point should not wait to log point value for 6 minutes.
Interestingly i have just tested it out and it seems that there is some kind of a rounding thing coming up with values being exactly the threshold value. If value changes next fraction of the threshold then this does not happen.
A quick test
Create a virtual point with exact settings
Current value 1
Set point to 1.01
Set point back to 1.0
Set point to 1.011
If going to other way around
Current value 1.01
Set point to 1.00
I am guessing datalogging does not happen if new value is greater than current value in the defined threshold but if new value is lower then current value in the defined threshold then logging works correctly.
I might also fish out an idea that @Nurr polling time is related to the issue (I guess it might be once per minute?) where the cached value is the new over threshold limit but it does not get logged but still triggers a reset for interval logging and then it has been the same for 5 minutes and then it gets logged by the interval logging sequence.
But still even though this happens, interval logging still works in my instance so I guess this information is not actually so relevant.