PicoScope 7 Software
Available on Windows, Mac and Linux
Mismatch between raw data and PicoScope6 displayed data?
-
EzekielAxel
- Newbie
- Posts: 0
- Joined: Thu Aug 27, 2020 10:16 am
Mismatch between raw data and PicoScope6 displayed data?
Hello,
I am trying to write a short program in C++ to automate some testing I have to do using the PicoScope 5442A. I am using the sine wave generator and two channels in 15-bit mode. I use the Picoscope API to generate and acquire data in block mode. To double check if I am using the API correctly, I have been comparing the data I get from the PicoScope6 software with the raw data I get from the "ps5000aSetDataBuffer()" and "ps5000aGetValues()" functions. However, they don't seem to match up, and it's puzzling.
For example, let's say I apply a 1V 1MHz sine wave to my DUT at point A, and measure output signals B and C to compare the relative amplitude and phase. If I investigate using the PicoScope6 software, I get a relative amplitude of B compared to C of 0.42 and a phase offset of 93º. However, if I use the raw data from my custom program running the PicoScope API, I get a relative amplitude of 0.78 and a phase offset of 79º.
Qualitatively, the system behaves similarly in both cases, and plotting the raw scope data the system-specific waveform distortion I am expecting appears in both sets of data. It just seems like there's some scaling and time-offset issues perhaps...?
I am trying to write a short program in C++ to automate some testing I have to do using the PicoScope 5442A. I am using the sine wave generator and two channels in 15-bit mode. I use the Picoscope API to generate and acquire data in block mode. To double check if I am using the API correctly, I have been comparing the data I get from the PicoScope6 software with the raw data I get from the "ps5000aSetDataBuffer()" and "ps5000aGetValues()" functions. However, they don't seem to match up, and it's puzzling.
For example, let's say I apply a 1V 1MHz sine wave to my DUT at point A, and measure output signals B and C to compare the relative amplitude and phase. If I investigate using the PicoScope6 software, I get a relative amplitude of B compared to C of 0.42 and a phase offset of 93º. However, if I use the raw data from my custom program running the PicoScope API, I get a relative amplitude of 0.78 and a phase offset of 79º.
Qualitatively, the system behaves similarly in both cases, and plotting the raw scope data the system-specific waveform distortion I am expecting appears in both sets of data. It just seems like there's some scaling and time-offset issues perhaps...?
Re: Mismatch between raw data and PicoScope6 displayed data?
Hi Ezekiel,
I'm assuming that by relative amplitude, you mean peak or RMS so, that aside, I have a few questions regarding sanity checks for your coding.
1/ Have you measured the frequency of the API generated waveform just as a double check?
2/ Have you performed a reasonable number of captures for both PicoScope 6 and API generated waveforms, to rule out statistical variation.
3/ Are you swapping the capture points over between channels, and getting consistent variation to rule out any channel transfer issues between DUT and Scope?
4/ How are you evaluating the API waveform (are you plotting it, and if so how/using what, and if not how are you making the measurements)?
5/ Are you able to post API waveform comparisons along with the psdata file, and also an image of the setup, with connections to points A, B, and c in place?
Regards,
Gerry
I'm assuming that by relative amplitude, you mean peak or RMS so, that aside, I have a few questions regarding sanity checks for your coding.
1/ Have you measured the frequency of the API generated waveform just as a double check?
2/ Have you performed a reasonable number of captures for both PicoScope 6 and API generated waveforms, to rule out statistical variation.
3/ Are you swapping the capture points over between channels, and getting consistent variation to rule out any channel transfer issues between DUT and Scope?
4/ How are you evaluating the API waveform (are you plotting it, and if so how/using what, and if not how are you making the measurements)?
5/ Are you able to post API waveform comparisons along with the psdata file, and also an image of the setup, with connections to points A, B, and c in place?
Regards,
Gerry
Gerry
Technical Specialist
Technical Specialist