Topic | miscalibration after measuring high voltage

Home Forums Mooshimeter Support miscalibration after measuring high voltage

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    • #8757 Reply
      Anonymous
      Inactive

      Hello. I attempted to measure a high frequency high voltage transformer with the Mooshimeter using a 1000 Megaohm probe. But when attempting the measurement, the Mooshimeter reset itself. You could tell that it reset itself because the blinking orange light turned off and it got disconnected from my mobile phone. After a few seconds, the orange light began to blink again, and I could connect to the Mooshimeter again. However, the AC voltages are higher than before. For example, the Mooshimeter used to measure 131 VAC RMS from the wall outlet, but now it measures 165 VAC RMS. The Mooshimeter appears to be operative but its measurements are miscalibrated.

      I have already tried the following: pressing the reset button, and removing the batteries. But neither worked. Is there anything else I could try? Or did I damage my Mooshimeter permanently?

      The high voltage source is 3500 Volts. But I was never able to measure it with the Mooshimeter using the 1000 Megaohm probe. Not only was I not able to measure it, I now have a miscalibrated Mooshimeter. Could you please help?

    • #8761 Reply
      admin
      Keymaster

      Hi Luminus,

      I’m sorry to say that sounds like permanent damage. I am surprised though… the internal resistance of the voltage input is 10MΩ, so a 1000MΩ probe should divide down the input voltage by a factor of roughly 100 to ~35V, which is very safe. Is it possible there was a source of arcing that cause the meter to be exposed directly to the 3500V source? The meter is designed to measure up to 600V, and fail safely when exposed to voltage up to 4000VAC on the voltage input.

      Would you be interested in a replacement meter? I can offer you a 50% off coupon for a replacement, let me know and I’ll send it to the email address you have registered.

      Best
      ~James

    • #8764 Reply
      Anonymous
      Inactive

      Thanks for your reply, James. In that case, I am interested in a replacement meter so I would take your offer. But I still wonder what happened because I have made sure that there was no way the meter could be exposed to the high frequency 3500 VAC. I know the 3500 V source has a frequency between 6000 Hz and 20,000 Hz. So perhaps there was an impedance problem due to the high frequency. Or perhaps the high frequency damaged the sampling components of the Mooshimeter since it is limited to 8000 Hz. Anyway, if you could send me the coupon, I should be grateful!

    • #8769 Reply
      Anonymous
      Guest

      At such frequencies the reactance of the probe will have been much less than 1 Gohm. The slightest capacitive coupling, even just 1pF, would be enough to send kV into the poor Mooshimeter.

    • #8771 Reply
      Anonymous
      Inactive

      Supposedly, the impedance of the probe does not go lower than 1 Gohm until after 1 Mhz. So, in theory, it should have been able to withstand 20 khz. But most likely it didn’t.

    • #8772 Reply
      Anonymous
      Inactive

      I also wonder why the Mooshimeter’s surge protection did not work. After all, the voltage of the source is not greater than 3500VAC, which is below the Mooshimeter’s surge protection.

    • #8773 Reply
      Anonymous
      Guest

      In that case I don’t know how the Mooshimeter could have been damaged. But the probe sounds interesting, and I may have use for such a device. Would you mind sharing the details?

    • #8784 Reply
      admin
      Keymaster

      Hi Luminus+Tim,

      Lowered probe impedance at higher frequencies had not occurred to me, thank you Tim for pointing that out. I think it’s difficult to know exactly what happened in this case, especially remotely, so I don’t want to speculate too much. Luminus if you get more information please let me know. The meters were tested to withstand 4000VAC surges, but I think those tests were only 1-second long exposures (meant to simulate a lightening strike outside the house while touching mains inside).

      Best
      ~James

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