What's reading for multimeter set to read dc voltage and bandwidth of 10khz

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Discussion Overview

The discussion revolves around the interpretation of voltage readings from a multimeter set to measure DC voltage in the context of an AC signal, specifically addressing the effects of bandwidth on the readings. The scope includes conceptual clarification regarding RMS and DC measurements, as well as the implications of bandwidth on voltage readings.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant proposes that the reading for a multimeter set to read DC voltage with a bandwidth of 10 kHz would be 0.2 mV, based on a calculation involving the ratio of bandwidths.
  • Another participant emphasizes the need to carefully consider the definitions of "rms" and "dc" in the context of the question.
  • Some participants argue that the voltage reading should not change, suggesting that RMS and DC values are equivalent under certain conditions.
  • It is noted that RMS and DC are not the same when measuring a voltage that varies with time, particularly for AC signals, where a DC meter would measure an average value that could be zero for symmetrical waveforms.
  • A participant suggests practical experimentation with a DC voltmeter connected to an AC signal generator to illustrate the differences in readings.

Areas of Agreement / Disagreement

Participants express differing views on whether the voltage reading should change when switching from an RMS measurement to a DC measurement, indicating that the discussion remains unresolved.

Contextual Notes

There are unresolved assumptions regarding the nature of the "noise" mentioned in the original question and its characteristics as an AC signal, as well as the implications of bandwidth on the measurement outcomes.

chipmunk22
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Happened to come across this qn:

Noise from receiver is measured by rms voltmeter with bandwidth 100khz, and voltmeter reads 2mV. what will be the reading for multimeter set to read dc voltage and bandwidth of 10khz?

My ans is 10/100 x 2 = 0.2mV. cos smaller bandwidth reduced by a factor of 10.

Can anyone comment whether my answer is correct? tks
 
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Read the question carefully - in particular, the abbreviations "rms" and "dc".
 
so u mean the voltage reading shdnt change? since rms value and dc value are the same.
 
RMS and DC are not the same if you are measuring an voltage that varies with time.

A DC meter measure the average (mean) value of an AC signal, which is zero for a symmetrical wave form like a sine wave or a square wave.

Connect a DC voltmeter to a low voltage AC signal generator sometime, and see what reading you get - zero.

The "noise" in the question is basically an AC signal so its average value measured on a DC meter will be 0.

Check out what "root mean square" means, and how it is different from "mean" or "average".
 
Oh now i get it. Thanks for the explanation! ;)
 

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