Pedestal and Gain Coefficients of the Test Beam Time

The Problem

• The data acquisition system reads each FastBus QDC channel, subtracts a pedestal value, and puts it into the data stream if it is larger than a threshold value.
• The pedestal values have been determined with a QDC gate width different to the one used for normal events. The pedestal depends, albeit relatively weakly, on the gate width. The net result is, that the used pedestals were different than the true pedestals.
• We used two sets of pedestal values:

      Set 1: run 1001 - 1112
      Set 2: run 1113 - 1167
  

  In both cases the used pedestals were higher than the true pedestals. The difference for set 2 however seems to be much larger than for set 1. The reason for this is still unclear.

The Evidence

• The used pedestals have been determined from the logfiles of the pedestal program and the FastBus parameter events. Set 1 was reconstructed from the parameter events (were available for run 1003, 1008, 1097 and 1109 were all identical). Set 2 was taken from logfiles and was confirmed by the parameter events of runs 1138 and 1160.
• The true pedestals have been determined after the beam time. These pedestals will be correct for all QDC and runs which had the same gate and input as we had at the end of the test beam time.
  This means, we have the correct true pedestals for set 2 runs but only approximate true pedestals for a good part of the set 1 runs.
• The collected evidence is under doc_s117:[fastbus]:
  • The used pedestals as found on 17.2.95 (set 2):

        ped_hodo_950217.dat       gain_hodo_950217.dat
        ped_twal_950217.dat       gain_twal_950217.dat
    

  • The true pedestals (and gains) as determined after the beam time with the correct gate widths with the setup unchanged, all electronics on but detector biases off:

        ped_hodo_950221.dat       gain_hodo_950221.dat          
        ped_twal_950221.dat       gain_twal_950221.dat          
    

  • The used pedestals as reconstructed from parameter events:

        para_hodo_1109.dat        para_twal_1109.dat	set 1
        para_hodo_1138.dat        para_twal_1138.dat	set 2
    

The Calibration Parameters

• The pedestal and gain coefficients in cal_s117:s117.rz have been setup to correct for the difference between true and used pedestal and also for the low/high gain ratios. Depending on the run number you specify with init_online you'll get the default's or the correct values:

      init_online run=1		|  default, no pedestal correction
      init_online run=2		|  ped. corrections for run 1113 - 1167
      init_online run=3		|  ped. corrections for run 1001 - 1112
  

• The pedestal and gain parameters can be setup with the KUMAC's fbgain_set and fbpedestal_set respectively. Example: shell def/job fbpath doc_s117:[fastbus] exec -inc_s117:fbgain_set#set_twal fbpath:gain_twal_950221.dat exec -inc_s117:fbgain_set#set_zdho fbpath:gain_twal_950221.dat exec -inc_s117:fbgain_set#set_hodo fbpath:gain_hodo_950221.dat exec -inc_s117:fbgain_set#set_ptel fbpath:gain_hodo_950221.dat exec -inc_s117:fbgain_set#set_ustr fbpath:gain_hodo_950221.dat * exec -inc_s117:fbpedestal_set#set_twal fbpath:ped_twal_950217.dat _ fbpath:ped_twal_950221.dat exec -inc_s117:fbpedestal_set#set_zdho fbpath:ped_twal_950217.dat _ fbpath:ped_twal_950221.dat exec -inc_s117:fbpedestal_set#set_hodo fbpath:ped_hodo_950217.dat _ fbpath:ped_hodo_950221.dat exec -inc_s117:fbpedestal_set#set_ptel fbpath:ped_hodo_950217.dat _ fbpath:ped_hodo_950221.dat exec -inc_s117:fbpedestal_set#set_ustr fbpath:ped_hodo_950217.dat _ fbpath:ped_hodo_950221.dat
• The parameters have been saved in the parameter database. The following example shows how run 2 was created: rz/file 20 s117.rz ! u * run/set 2 comm beam P001 C001 run/set 2 comm hodo P001 C002 run/set 2 comm ptel P001 C002 run/set 2 comm trig P001 run/set 2 comm ustr P001 C002 run/set 2 comm zdho P001 C002 run/set 2 alad twal P001 C002 L001 Z001 E001 A001 run/lis * para/write comm hodo 2 C002 para/write comm ptel 2 C002 para/write comm ustr 2 C002 para/write comm zdho 2 C002 para/write alad twal 2 C002 * f/clo 20