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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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    I see the Fluke 1662 MFT quotes Accuracy 45 Hz – 66 Hz 0.8% + 3digits. I suspect similar from other manufacturers are also available.

    (That said: I will say in answer to your question, having had the misfortune in the past of having to design an AC meter for a specialist market, yes it is very difficult and expensive to guarantee that accuracy! And yes to be high accuracy it has to be slow to average out the rubbish - it's the irony that you can have fast and inaccurate or slow and accurate, which absolutely is a pain with voltages that are jumping around.) 

    On your original point, it does feel a bit as if you're in a vicious circle here if you have to prove what the voltage swings are before the DNO will prove what the voltage swings are... 

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    I see the Fluke 1662 MFT quotes Accuracy 45 Hz – 66 Hz 0.8% + 3digits. I suspect similar from other manufacturers are also available.

    (That said: I will say in answer to your question, having had the misfortune in the past of having to design an AC meter for a specialist market, yes it is very difficult and expensive to guarantee that accuracy! And yes to be high accuracy it has to be slow to average out the rubbish - it's the irony that you can have fast and inaccurate or slow and accurate, which absolutely is a pain with voltages that are jumping around.) 

    On your original point, it does feel a bit as if you're in a vicious circle here if you have to prove what the voltage swings are before the DNO will prove what the voltage swings are... 

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