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I'm working on a school project, just measuring the Vrms of two different waveforms at different frequencies. The function generators output is connected directly into an oscilloscope therefore the waves don't go through any circuitry.

Frequency - pulse output(Vrms) - sinusodial output(Vrms)

50 Hz --- 5.49V --- 3.10V
500 Hz --- 5.45V --- 3.08V
5 kHz --- 4.84V --- 2.60V
50 kHz --- 0.326V --- 0.217V

As you see the output rms voltage has changed, however it shouldn't and that is the question. The only possible reason i could find is about multimeters not being trustworthy enough(?)

May there be any other explanation for this case, and could that drastic voltage drop from 4.84V to 0.326V mean we have gone far too out of the multimeters range?

Thanks in advance for all the help!

Multimeter i have used for measurements: UNI-T ut33a+
Link for the multimeters details(pdf file link): here

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  • \$\begingroup\$ Please edit your question to include a model number and link to the user manual for your multimeter. What are the specifications for the frequency range on AC true RMS range? \$\endgroup\$ – Transistor Nov 9 '19 at 19:23
  • \$\begingroup\$ Are you measuring with an oscilloscope or a multimeter? \$\endgroup\$ – JRE Nov 9 '19 at 19:29
  • \$\begingroup\$ Added the details about the multimeter, thanks for pointing out @Transistor \$\endgroup\$ – Curious Student Nov 9 '19 at 19:41
  • \$\begingroup\$ With a multimeter, just added extra info on it @JRE \$\endgroup\$ – Curious Student Nov 9 '19 at 19:43
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The link to the multimeter manual explains the problem:

enter image description here

It says "frequency response 40Hz to 400Hz."

For any frequency outside of that range, the meter will not meet its specifications.

Despite the upper limit of 400Hz, it appears to respond normally to at least 500Hz.

Your meter is fine. It just can't do what you thought it could.

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  • \$\begingroup\$ That explains the case in detail. Thanks for the help. \$\endgroup\$ – Curious Student Nov 9 '19 at 20:02

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