GROSS ERROR IN D.C. AVERAGE MEASUREMENT IN PICOSCOPE

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Glovisol
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GROSS ERROR IN D.C. AVERAGE MEASUREMENT IN PICOSCOPE

Post by Glovisol » Tue May 10, 2016 12:54 pm

In Picoscope, depending on scan time, the D.C. average measurement can be correct, or can show a very big error.

I found this while monitoring 120 Hz PWM with a peak value of 3300 mV, but the same error happens at any frequency and at any level with a given ratio between Frequency and Pulse Duration.

I am enclosing two PC screens showing exactly the same PWM, but taken at different scan times, one showing the correct value and the other a grossly incorrect D.C. value.
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Picoscope anomaly 2.jpg
Picoscope anomaly 1.jpg

Martyn
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Re: GROSS ERROR IN D.C. AVERAGE MEASUREMENT IN PICOSCOPE

Post by Martyn » Tue May 10, 2016 1:27 pm

The DC average will only be for the data values drawn on the screen.

In the first trace only part of the third cycle is drawn, so a significant part of the zero level is missing. This results in the reading being higher than would be expected.

The second trace shows more cycles, so the incomplete part of the last cycle has less effect on the overall result.
Martyn
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