Setting the BBCal and HCal thresholds

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Rough HCal Discriminator Threshold to Energy Conversion

The conversion between the HCal sum trigger discriminator threshold in mV to energy deposited in the scintillators in MeV is approximately 6.22 MeV/mV.

This was calculated using cosmic rays. The average cosmic ray deposits ~14 MeV in scintillators for a single PMT and this corresponds to an fADC integral of roughly 8 pC. If a spectrum of the cosmic rays' amplitudes is made the peak is at 18 mV in the fADC. Now we track this 18 mV at the fADC back in the electronics to the PMT output. First the 18 mV is multiplied by 2.5 which is the approximate amplitude attenuation due to the 100 m cables connecting the DAQ and FE electronics. This gives a 45 mV signal out of the FE amplifiers. These are 10x amps so this equated to 4.5 mV signals out of the PMTs for the average cosmic ray which deposited 14 MeV in the scintillator.

Now we track the signal forward from the PMT to the HCal sum trigger discriminator on the FE.

How to adjust the VME DAC HCal and BBCAL discriminator thresholds

  • Log into sbs-onl@adaq1 with the usual sbs-onl password
 ssh sbs-onl@adaq1
  • Navigate to /adaqfs/home/sbs-onl/hcal/GUI.
  • To set the environment variables do:
 source setup.sh
  • Execute the following command to open the DAC control GUI: 
 python3 DAC_Control_GUI.py

DAC GUI Startup Output.png

  • After executing the command, the a new DAC GUI should pop up which has instructions to load, initialize and save the settings and adjust the thresholds. The terminal in which the command was executed should also print the previous settings of all the channels.

DAC Control GUI.png

  • Click on "Load mpv04Library tab" to load a library
  • Click on "Initialize mpv04" to initialize the library
  • Click on "Save settings" to save the settings
  • Go to the "Enter DAC Output Voltage Setting (V)" and enter the desired output voltage of the DAC channel.
  • Click on "Set Voltage". Note this sets the DAC output voltage which is not equal to the threshold setting. The predicted threshold setting can be seen in the "Predicted Discriminator Threshold (mV)" column and the actual readback for the HCal sum trigger threshold and BBCal Hi Discriminators 1 and 2 can be seen in the "Threshold Readback (mV)" column.
  • Make sure that BBCal Hi Discriminator 1 and BBCal Hi Discriminator 2 have the same value entered
  • Check the online GUI on to make sure that the threshold readback values are where you want them to be.
  • It is also possible to query the readbacks on aslow@adaqsc using:
 caget SBSDaqPi1:thresh1 - for HCAL threshold
 caget SBSDaqPi1:thresh2 - for BBCAL DISC HI1
 caget SBSDaqPi1:thresh3 - for BBCAL DISC HI2
  • For problems/questions with this GUI contact Scott Barcus (skbarcus@jlab.org).
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