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Why is the accuracy of multifunction testers so low

Alan B

I am working on a scenario at the moment where my customer has an EV charger cutting out due to low and also possibly high voltage.
My KT65DL is indicating voltage as low as 214V and seeing swigs from 214 to 246 in a 1 hour period. The DNO are saying they don't trust the values being given and are declining to put a voltage logger in, asking for data from the EVCP manufacturer, which is unlikely to be available as it's Tesla and probably no more accurate.

But it's accuracy is +/- 2% plus 4 digits, so effectively +/-5V, which means it has very little value for checking the supply voltage is in range, also doesn't help that the sampling is quite slow and I assume minimums are being missed.

To my knowledge it's not that expensive to build reasonably accurate voltage meters, maybe AC meters cost more? But given multifunction testers cost £500 or more why is the accuracy so low?

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    errata - I thought I had posted this a few hours ago, but it sat here unloved, given other answers that have come in , it is now slightly out of order, but may still be informative .

    Portable Multi function testers  are a compromise, as there is neither the space nor the budget to incorporate  all the bits for a lab grade instrument, that also has to be battery powered, and rugged enough for regular van  transport, and work on a cold day or a hot one.

    Consider a 'good' lab bench meter may be one of these, but skip to pages 7(DC) and 8 (AC) to see how the accuracy may vary with temperature and over one year after cal.

    And the price tag is not that inexpensive - expect to pay over £1k for one of those.
    PDF
    A really 'precision'  meter is a few times that times that...

    https://www.keysight.com/us/en/product/34470A/digital-multimeter-7-5-digit-truevolt-dmm.html

    a snip at 4k

    example from Le Croy  Idare not ask the price

    But additional accuracy is harder than it looks.

    Mike

Reply
  • 0

    errata - I thought I had posted this a few hours ago, but it sat here unloved, given other answers that have come in , it is now slightly out of order, but may still be informative .

    Portable Multi function testers  are a compromise, as there is neither the space nor the budget to incorporate  all the bits for a lab grade instrument, that also has to be battery powered, and rugged enough for regular van  transport, and work on a cold day or a hot one.

    Consider a 'good' lab bench meter may be one of these, but skip to pages 7(DC) and 8 (AC) to see how the accuracy may vary with temperature and over one year after cal.

    And the price tag is not that inexpensive - expect to pay over £1k for one of those.
    PDF
    A really 'precision'  meter is a few times that times that...

    https://www.keysight.com/us/en/product/34470A/digital-multimeter-7-5-digit-truevolt-dmm.html

    a snip at 4k

    example from Le Croy  Idare not ask the price

    But additional accuracy is harder than it looks.

    Mike

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