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Entry  Wed May 2 10:44:17 2018, Alessio Berti, Peak at 0 mV in traces zero_peak_after_spike_removal_ch1.pngzero_peak_after_spike_removal_ch2.pngzero_peak_after_spike_removal_ch3.pngzero_peak_after_spike_removal_ch4.pngzero_peak_after_spike_removal_offset_correction_ch2.png
    Reply  Wed May 2 12:12:42 2018, Stefan Ritt, Peak at 0 mV in traces 
       Reply  Wed May 2 12:23:16 2018, Alessio Berti, Peak at 0 mV in traces zero_peak_after_spike_removal_ch2_1000_bins.png
          Reply  Fri May 4 11:35:20 2018, Stefan Ritt, Peak at 0 mV in traces Screen_Shot_2018-05-04_at_11.36.24_.png
             Reply  Tue May 8 12:15:54 2018, Alessio Berti, Peak at 0 mV in traces 20180508_drs4_drs_exam_1000_events_81_bins_linear.png20180508_drs4_drs_exam_1000_events_81_bins_log.png20180508_drs4_drs_exam_1000_events_23_bins_linear.png20180508_drs4_drs_exam_1000_events_23_bins_log.png
                Reply  Tue May 8 14:43:03 2018, Stefan Ritt, Peak at 0 mV in traces 
Message ID: 686     Entry time: Fri May 4 11:35:20 2018     In reply to: 685     Reply to this: 691
Author: Stefan Ritt 
Subject: Peak at 0 mV in traces 

I tried the following:

- trigger on a 10 MHz sine wave on CH0, CH1 was open

- run drs_exam.cpp program and write data.txt with a few events

- imported the event into Excel

- did a histogram on (empty) CH1

What I see is a nice Gaussian distribution centered around 1mV, but with no spike around zero. See attachment. So I still believe that you have either a binning or a rounding problem. Like you round value -0.99 to +0.99 all to zero mV, and 1.00 to 1.99 mV to one mV.

Stefan

Alessio Berti wrote:

Hi,

thank you for the quick reply. All the bins in the previous histograms have the same width. We also tried to plot the noise histogram for channel 2 with more bins (i.e. 1000, so that we can see almost discrete values), and the peak is still there.

Alessio & Davide

Stefan Ritt wrote:

I note that your peak at zero is exactly twice as high as the bins left and right, so this looks to me like a binning problem in your histogramming. Maybe your bin #0 goes from -1mV to +1mV, which all other bins are just 1mW wide. Can you check that?

Stefan

Alessio Berti wrote:

Hi,

we modified drs_exam.cpp to read all 4 channels from the DRS4 and apply directly the spike removal (taken from Osci.cpp) during the acquisition phase. For test purposes, we don't save the data showing spikes and we focus on the data not having spikes (even if at the end we end up having triple and quadro spikes which are not removed by the spike removal routine, but they are rare). With this modified program we wanted to characterize the noise of the DRS4, so we took 30000 events at 5GSPS, triggering on channel 1 with a 10 MHz sine wave with 100 mV_pp (trigger level set at 10 mV), while channels 2,3 and 4 were left open without any input.

We then took a look at the data and plotted the noise histograms for channels 2,3 and 4, which you can find attached (without offset correction, named zero_peak_after_spike_removal_ch*.png). For completeness, we also attached the plot from ch1 (the sine wave). The selections in time and amplitude we applied had the goal to remove the high oscillations in amplitude occurring in the first and last samples and to discard the quadro spikes we had in the data.

We see that there is a peak at 0 mV in all histograms from all channels and scanning through the data, we saw that indeed the value 0 mV is stored many times for each event, thus originating the peak we see in the histograms. We also applied an offset correction to the data (taking the average of the first three most occuring amplitudes) of channels 2 (as an example) and the problem seems to be only partially removed.

We also noticed that this peak at 0 mV is present also when we acquired the data from the DRS4 with DRSosc saving the data in binary format.

So we had the following questions:

- why is the DRS4 saving so many times the value 0 mV (exactly 0 mV)?

- is there any way (in our case through software, preferably at acquisition time) to solve this problem?

Thank you for the help and best regards,

Alessio & Davide

 

 

 

 

Attachment 1: Screen_Shot_2018-05-04_at_11.36.24_.png  861 kB  Uploaded Fri May 4 12:37:41 2018  | Show | Show all
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