I have my PI point setup as follows for exception and compression, I am using 3 minutes scan rate. It is storing data in every 3 minutes for the same value ignoring the following setup. Any help please?
Hi Abu Salam
The exmax tag attribute specifies an amount of time to wait before sending a value across even if it does not vary by more than the exdev amount. That is why you see data coming in about every 10 minutes ot the PI server with exception on and compression off. Exmax is set at 600 in your tags (10 minutes – the default setting).
So too, compmax specifies an amount of time to wait before sending a value to the archive EVEN if that values does not vary by more than compdev. Your tag compmax attribute is set to 2 hours. This means that after waiting 2 hours with no values breaking the compression setting, the current snapshot value will be archived. This current snapshot value could have a timestamp anything up to 10 minutes prior to the 2 hour mark due to the exception settings you have.
is all values stores every 3mn are above +/- 0.1 compare to the previews one? if so it's normal! based on you Exception and Compression Deviation configuration!
Thank you Leonard for replying.
Thank you Lal Babu,
Very clear! So, what is the best way to store value in every 2 hours if there is no change? Change the exdev to 2 hours?
If you are value is not changing frequently then would suggest exception deviation to zero and compression deviation to zero so that it writes same value every two hours. If you are checking for some variation in the value then set compression deviation accordingly.
So, I have few digital tags and values are not changing but it is still storing data every 3 / 10 minutes.
In General, you can increase compression max to number 24 hours and compression deviation to 1 but would recommend to configure all digital tags as Advise in your interface. Location 4=1 and Location 3=1 if you are using OPC interface.
I am sure Advise mode will be the best solution but I believe OPCDA interface has limitations using same itnerface for both Advise and Polled.
There is no problem use polled and advised tags in opcda interface. Be sure to divide them to own scanclasses.
You are awesome! Good discussion...
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