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Formula about accessing the penultimate value of a variable in PiVision or Pi System Explorer

MarcusSchuck

Hello everyone,

I'm currently working with PiVision and Pi System Explorer for data visualization and analysis, and I have a specific query regarding accessing historical data.

Is there a built-in functionality or method within PiVision or Pi System Explorer that allows me to retrieve the penultimate (second last) value of a variable, irrespective of timestamp? I understand that these tools are primarily geared towards visualizing current and historical data, but I haven't found a straightforward way to access the value immediately preceding the current one without relying on a specific timestamp.

 

Aim: We track the feed and product tanks in our DCS and read the values into Pi. Our operators want to see the current tank number and the second last tank number which has been used for the unit.

 

Thank you in advance for any assistance or advice you can provide!

Best regards

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    Since you didn't specify the engine: performance equation or analyses, I will provide a one-line solution that will work in either.

    Assume your tag or attribute is called 'Metered Value':

    TagVal('Metered Value',FindNE('Metered Value','*','*-30d','Metered Value'))

     

    FindNE - Get the timestamp 'Metered Value' between now and 30 days back where the value is not the current value of 'Metered Value'; the search starts at 'now' and goes backwards

    TagVal - Get the value of 'Metered Value' at the timestamp provided by FindNE

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  • 0

    Since you didn't specify the engine: performance equation or analyses, I will provide a one-line solution that will work in either.

    Assume your tag or attribute is called 'Metered Value':

    TagVal('Metered Value',FindNE('Metered Value','*','*-30d','Metered Value'))

     

    FindNE - Get the timestamp 'Metered Value' between now and 30 days back where the value is not the current value of 'Metered Value'; the search starts at 'now' and goes backwards

    TagVal - Get the value of 'Metered Value' at the timestamp provided by FindNE

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