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Visualizing PWM (mean) voltage ?

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Visualizing PWM (mean) voltage ?

Postby nurber » Thu Oct 19, 2017 7:44 pm

Hi Forum. I'm sure there is an easy way, but I'm missing it. Want to see the mean of a PWM signal such that Picoscope is showing the same as a DMM set to VDC. Ideally this voltage is shown graphically along with the PWM signal itself although it also would be useful to see in Measurements table at bottom. For the maths, I tried different combinations of Duty(D) * Max(D) * 0.01, etc, but unsuccessful. Thanks.
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Re: Visualizing PWM (mean) voltage ?

Postby Gerry » Fri Oct 20, 2017 9:21 am

Hi nurber,

If you measure a voltage with a DMM set to AC, the single value displayed is the RMS voltage. The equivalent DC voltage level that would provide the same amount of power when driving a resistive load over many cycles of the PWM waveform is referred to as TRUE RMS (not all DMM's perform this measurement, some will give you AC RMS, which assumes that the waveform your measuring is a sinewave, and would be likely to give you an incorrect value of RMS for your PWM waveform).

We have TRUE RMS as a measurement in PicoScope 6 (and you can increase the size of the font to make it more readable, as it would be on a DMM, by changing the 'Grid Font Size' in the measurements menu). We also have a Math Channel that can converge to TRUE RMS over the duration of a capture (provided certain conditions are met). The TRUE RMS Math channel is discussed here: topic29531.html (to use it you need to see the conditions mentioned lower down on the post).

Regards,

Gerry
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