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| BM235's strange V and mV value |
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| lionel:
Hello everyone, I recently bought a BM235 (from Welectron) and noticed a strange behaviour on it. When selecting the V or mV fonctions without electrical contact, the reading value isn't at zero (especially in mV) and keeps changing. This happens with no probes connected when i move the multimeter, but especially when i move the probes in the air. In A or mA mode, on the contrary, the zero is dead on. Nevertheless, measuring an AA mignon, tension shows 1.610V without any fluctuations. Is this an expected behaviour or should I consider my multimeter faulkty ? PS: I can try posting a video showing what happens if needed. |
| EEVblog:
All multimeters have an upper tolerance to electric fields. Perhaps you are in a particually high electric field environment? |
| Fungus:
--- Quote from: lionel on April 25, 2023, 07:40:55 am ---Is this an expected behaviour --- End quote --- Yes. Any high-impedance circuit will pick up radio waves. That's what your meter is showing. Try putting some leads in and shorting them together. It will zero. |
| lionel:
--- Quote from: EEVblog on April 25, 2023, 07:54:12 am ---All multimeters have an upper tolerance to electric fields. Perhaps you are in a particually high electric field environment? --- End quote --- Not to my knowledge, but who knows ? And no high tensions lines (that, I am sure of). --- Quote from: Fungus on April 25, 2023, 08:41:45 am --- --- Quote from: lionel on April 25, 2023, 07:40:55 am ---Is this an expected behaviour --- End quote --- Yes. Any high-impedance circuit will pick up radio waves. That's what your meter is showing. Try putting some leads in and shorting them together. It will zero. --- End quote --- I can confirm that shorting the probes together put the Brymen back to zero. What kind of high-impedance circuit could that be ? I mean, what kind of equipment in an individual house could cause such radio waves ? Anyway, these are good news, I won't have to send it back for RMA. |
| EEVblog:
--- Quote from: lionel on April 25, 2023, 08:52:12 am ---I can confirm that shorting the probes together put the Brymen back to zero. What kind of high-impedance circuit could that be ? --- End quote --- He's talking about the multimeter, it has a high impedanc input. Every meter will pick up stray electric fields on the mV range. Some high end meter even have near infinite imput impedance input on the mV range, and these meter will often display overload when the leads are just open. This is perfectly normal, once you measure a circuit that circuit will have vastly lower impedance and not be inpacted by any surrounding stray fields. |
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