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Accessing previous values from data points to work out flow rate


  • Hey Guys, I'm trying to work out if there is a way to access previous values in a data point's history from the scripting data sources so I can work out flow rate from water level data point in tanks.

    0_1605745395981_59e88e1e-f71b-4b9d-ae67-6f30c6867031-image.png

    I'm thinking I should be able to look at the difference in the values and work out the flow rate in litres per hour or litres per minute, then just update a virtual data point to display it. It's probably so simple I can't see it for looking :O)

    I know PREVIOUSVALUE(datapoint) exists as I use it frequently, but is there one for say a minute ago?
    Or could I simply mirror a data point value but only update it once a minute, then just work out the flow rate by comparing the current value to the previous only.

    Cheers
    Dan


  • use pt.pointValuesSince(timestamp)
    or:

     pointValueAfter(timestamp, cache) 
    //function returns the nearest point value/time object after to timestamp, or null if there is not one.
    
    pointValueAt(timestamp, cache) 
    //function returns the a point value/time object that was recorded exactly at the timestamp, or null if there is not one.
    

    Fox


  • Thanks mate, I'll give it a go.


  • Anytime