Data Change Type in log checkbox

[IA_10816220]

Hi,

there is something that confuses me about the log checkbox and the Data Change Type, 

i have a sensor that sends some parameters, lets say 5 values stored in 5 properties, lets say i have 10 readings received from the sensor, when i try to query these data from the database i get an infotable with more than 10 rows, i know that this thing related to the "fillOption" in the query either it is none or previous,

what i want to do is that: whenever there is any change in any of the 5 values, i want to see a new row in the database  and i want this to happen while i am selecting "None" under the "fillOption" in the query,

the point is,  in another part of the project i query the data and calculate the averages, and with the current setup when i query the data i get some repeated values and thing like that, 
so, I want to know when to choose the Data Change Type inside a property to On or always, i didn't understand the description in the help very well

thank you,

[TonyZhang · Accepted solution]

Hi @IA_10816220,

I'm not clear on the difference between "On" and "Always" myself but if you want to log property history only when there is a change of value, you can select "Value" as the Data Change Type.

For "On" and "Always", according to my small test, as long as there's a property update request comes in, suppose there's no change in value but Time and Quality (TQ in VTQ) might change and that will result in firing a change event and a record will be logged in value stream. 

Also, the fillOption "previous" should not add a new history record in Value Stream, it only fills in the blanks to existing records (if other property changed but this property did not change,  fillOption "previous" will assume the value stays the same and uses the previous value)

Hope that helps.