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Entry  Wed Nov 23 08:17:23 2016, Abhishek Rajput, Potential Incorrect Timing Calibration for DRS4 Data 
    Reply  Thu Nov 24 13:24:26 2016, Stefan Ritt, Potential Incorrect Timing Calibration for DRS4 Data drs.pdf
       Reply  Tue Nov 29 23:19:06 2016, Abhishek Rajput, Potential Incorrect Timing Calibration for DRS4 Data 
          Reply  Wed Nov 30 08:53:58 2016, Stefan Ritt, Potential Incorrect Timing Calibration for DRS4 Data 
             Reply  Fri Dec 9 04:17:46 2016, Abhishek Rajput, Potential Incorrect Timing Calibration for DRS4 Data 
Message ID: 573     Entry time: Tue Nov 29 23:19:06 2016     In reply to: 569     Reply to this: 574
Author: Abhishek Rajput 
Subject: Potential Incorrect Timing Calibration for DRS4 Data 

Hello Stefan,

Thank you for the excellent explanation and diagram. This part of the code is now much clearer to me.

My other questions pertain to the "trigger cell". Firstly, what precisely does this mean? Moreover, how does the "trigger cell" relate to the trigger time delay we can set in the DRS4 application? This is causing some confusion for me, because regardless of where you set the trigger time delay on the DRS4 application, there are still points on the waveform that are saved prior to the moment in time when a pulse exceeds some voltage threshold we set in the application. I get the impression that "trigger delay" and "trigger cell" are unrelated concepts, so any clarification you can provide would be greatly appreciated.

Abhishek

Stefan Ritt wrote:

The code in the macro is correct. The misconception lies in the definition what "sample 0" means. Please view the attached picture. This is simplified case with a DRS chip with only 8 cells (instead of 1024). There are two events (blue and red). In the first event, the chip is stopped at trigger cell (tc) 2, in the second case at 5. Since the readout starts with the trigger cell, the first readout sample in the first event belongs to cell #2, the next one to cell #3 and so on. In the second (red) case, the first sample belongs to cell #5, the second to cell #6 and so on. "Aligning cells 0" now means that the physical cell 0 (not the readout sample) is aligned for each channel. In the first event, the 7th readout sample will have the same time in all channels, in the second event the fourth readout cells will have the same time. This is because physical cell #0 is always at different places inside the readout array.

Stefan

Abhishek Rajput wrote:

Hello,

I was running through a particular binary file containing data taken on all 4 channels of the DRS4 and printing out the value of the first time sample for each channel (per event). While doing so, I noticed that some of these times were negative. For this dataset, channel 1 was chosen as the reference channel (which is the default setup in Stefan's DRS4 macro).  From my understanding, the calibration procedure delineated in the DRS4 manual and shown in the code below is supposed to sync the timing of each channel relative to sample 0. However, this does not appear to be the case for when I print out the time value of the first sample, I notice that only channel 1's 0th sample is set to 0. The first sample for the other channels is nonzero (and most often negative). 

Even more strange is when I test another 4-channel dataset with the same code, this issue does not appear. More specifically, the first time sample on each waveform on all channels is set to 0, as should be the case.

My question is therefore whether or not the timing calibration varies from dataset to dataset. My initial thought was that this should not be the case, but I have two different data sets taken on the same set of channels which give different timing calibration results. Are there any circumstances under which this behavior can happen? 

for (ch=0 ; ch<5 ; ch++) {
         i = fread(hdr, sizeof(hdr), 1, f);
         if (i < 1)
            break;
         if (hdr[0] != 'C') {
            // event header found
            fseek(f, -4, SEEK_CUR);
            break;      
         }
         chn_index = hdr[3] - '0' - 1;
         fread(voltage, sizeof(short), 1024, f);
         
         for (i=0 ; i<1024 ; i++) {
            // convert data to volts
            waveform[chn_index][i] = (voltage[i] / 65536. - 0.5);
            
            // calculate time for this cell
            for (j=0,time[chn_index][i]=0 ; j<i ; j++)
              time[chn_index][i] += bin_width[chn_index][(j+eh.trigger_cell) % 1024];            
         }
      }
    
      // align cell #0 of all channels
      t1 = time[0][(1024-eh.trigger_cell) % 1024];
      for (ch=1 ; ch<4 ; ch++) {
         t2 = time[ch][(1024-eh.trigger_cell) % 1024];
         dt = t1 - t2;
         for (i=0 ; i<1024 ; i++)
            time[ch][i] += dt;
      }

 

 

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