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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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    Chris Pearson mentioned using an AVOmeter (I now have two).

    Twenty four years ago, along with my Robin KTS1620 I bought a Seward Checkbox 16 to check the calibration, checking the resistance measurements and RCD is straightforward, checking the voltage is a bit more airy fairy, as it’s still dependent upon the mains voltage, there is a voltage output on the front of the check box, but it tells you the test results will be significantly different measured with digital and analogue meters.

    I just happen to have a modern conventional moving-coil analogue meter, so here’s a comparison of voltage when measured using the check box with both types of meter.


    and here is a comparison measuring the mains directly 


    Which is in line with what is to be expected having taken note of what it says on the back of the check box.

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  • 0

    Chris Pearson mentioned using an AVOmeter (I now have two).

    Twenty four years ago, along with my Robin KTS1620 I bought a Seward Checkbox 16 to check the calibration, checking the resistance measurements and RCD is straightforward, checking the voltage is a bit more airy fairy, as it’s still dependent upon the mains voltage, there is a voltage output on the front of the check box, but it tells you the test results will be significantly different measured with digital and analogue meters.

    I just happen to have a modern conventional moving-coil analogue meter, so here’s a comparison of voltage when measured using the check box with both types of meter.


    and here is a comparison measuring the mains directly 


    Which is in line with what is to be expected having taken note of what it says on the back of the check box.

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