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| Why doesn't my RMS multimeter agree with my Rigol 1054Z scope on the AC VRMS? |
| << < (3/5) > >> |
| Kim Christensen:
From the manual: 11. Vrms: the effective value on the whole waveform or the gating area Not sure how you'd change the "gating area"... bdunham7's idea of setting your scope to default settings and trying again is probably the easiest. |
| TurboTom:
What's the firmware version of your scope? On my DS1000Z F/W 00.04.05.SP2, the RMS voltage reading is spot-on, verified with a multitude of waveforms, frequencies and voltages. Maybe some early firmwares had a problem with this? DC offset could also be a problem. P.S. Welcome to the forum, by the way :) |
| Fungus:
--- Quote from: mawyatt on August 09, 2023, 06:54:07 pm ---One of the simplest and often overlooked waveforms for RMS evaluation is the squarewave. --- End quote --- Let's walk before running. :popcorn: |
| Fungus:
--- Quote from: Kim Christensen on August 09, 2023, 10:41:55 pm ---11. Vrms: the effective value on the whole waveform or the gating area --- End quote --- And that's another reason why we need screenshots - the DS1054Z works with what's displayed on screen, not from the incoming signal. |
| G0HZU:
On my old HP/Agilent Infiniium scope there is the option for AC Vrms per cycle and that's the one I favour using for stuff like this. It ignores any DC offset in this case. I just set an Agilent sig gen to 500 Hz output at 2 V peak and the Infiniium scope measured 1.411 Vrms for a single cycle as in the image below. This scope always seems to read ever so slightly low but it still does well for such an old scope. The single cycle method is less risky than using all of the screen data as there often won't be an exact number of cycles being measured from the screen data. My Keithley 2015 DMM measured 1.4137 Vrms and my AD2 measured 1.4146 Vrms as below. I don't use the scope mode in the AD2 very much so I don't know how it computes Vrms. I suspect it uses the screen data plus a little bit but I can't be certain. There may be a way to make it measure a single cycle but I don't know how to do this. I tried various timebase settings and it gave a consistent result. I even tried a custom timebase that forced the display to show less than complete cycles but it only made a tiny difference. Much less than 1%. My trusty old Racal 9300 True Vrms meter measured 1.422 Vrms. This is still within 1% of the other readings but this meter is really old and hasn't had a formal cal in many years. |
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