Measurement different in scope and script

[denis.dantas]

Hello,

I'm starting to work with custom scripts on my discovery 2 (with oscilloscope extension + probes). I'm trying to setup a measurement environment using the AnalogIn_Acquisition.py sample script. I have a power supply with output voltage at 4V. When I run the scope at WaveForms I get 4V reading, however, when I run the acquisition script I get 2.72V as average voltage. I also tried with the AnalogIn_Sample.py script and also get 2.73V. I wonder why such different results. Pictures bellow:

 

 

[attila]

Hi @denis.dantas

The Scope channels on Analog Discovery have two input gains with pk2pk ranges of ~5V and ~50V. To make sure this ranges are covered after calibration the hardware is designed for a bit higher range of about 5.5V and 60V.
In your script the range is probably at 5V pk2pk and the offset at 0V. The input enters in limitation at about +/-2.75V.

You can increase the range to 50V:
dwf.FDwfAnalogInChannelRangeSet(hdwf, c_int(0), c_double(50.0))
or set offset for 0..5V range:
dwf.FDwfAnalogInChannelOffsetSet(hdwf, c_int(0), c_double(-2.5))
dwf.FDwfAnalogInChannelRangeSet(hdwf, c_int(0), c_double(5.0))

[denis.dantas]

I increased the range to 50V and it worked. Thank you attila!