CalFiles

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Cal Files

Calibration files (cal files) are the files ending in a .cal extension. They are used to perform a variety of functions:

• Map digitizer address to Channel Number
• Set a mnemonic for each channel
• Set a digitizer type (this determines the number of ns per timestamp unit)
• Calibrate energy
• Set a charge integration parameter
• Calibrate CFD, LED and time
• Calibrate efficiency
• Set a time offset for a channel's timestamps (LaBr)

Some of this information is contained in the ODB which is read out by grsisort from the start of the .mid file. The Calibration classes can be used to set these variables in TChannel and create cal files as well.

Using Cal Files

When a cal file is input during the MIDAS sorting stage, the calibration data is saved to the fragment tree. After this, grsisort defaults to reading the cal file from the fragment tree. If a different calibration is desired, TChannel::ReadCalFile("*name_of_cal_file*") can be called to read in a different cal file.

NOTE: This data is not written to the tree unless TChannel::WriteToRoot() is called.

Once a calibration from a cal file is active, access to the various calibrations is straight forward. For example, one can access the calibrated energy for a fragment using the GetEnergy() command.

Finally, if you would like to create a new calibration file from a fragment tree you can run the command TChannel::WriteCalFile("<calibrationfile>.cal").

Cal File Format

Calibration files are in a plain-text format that is easily modifiable. The labels are case-insensitive, but colons must be used to separate labels from values. Lines that begin with // are comments.

The file is a listing of calibration parameters for individual mnemonics, like the listing below for the blue crystal in GRIFFIN clover 1:

GRG01BN00A	{
Name:      GRG01BN00A
Number:    1
Address:   0x00000000
Digitizer: 
EngCoeff:  -0.743423	1.419230	
Integration: 0
ENGChi2:     0.000000
EffCoeff:  
EFFChi2:   0.000000
TIMECoeff:  0.000000	271.279000	-0.739159	
TimeOffset: 0.0
}

Name sets the mnemonic for the data from the address listed with Address (the address is the actual electronic channel this data came from). If this calibration file is read in while sorting a MIDAS file to a FragmentTree, Number will be the ChannelNumber assigned to this address in the FragmentTree.

Beyond these three primary numbers, any additional lines will set calibration values for this channel.

• EngCoeff sets the energy calibration coefficients, assuming a polynomial calibration from charge to energy. The first value is the zeroth-order coefficient (offset, set to -0.743423 in the example above), the second is the first-order coefficient (slope, set to 1.419230 in the example above), etc.
• Integration sets the integration parameter that is used in the energy calibration.
• TIMECoeff or Walk sets the coefficients for the low-energy walk correction of the form t_diff = a₀+a₁E^a₂. In the example above, a₀ is 0, a₁ is 271.279, and a₂ is -0.739159.
• TimeOffset is an offset to be removed from the time stamp from the hit before sorting the fragments into events. Useful for TAC's. The returned value is Timestamp - TimeOffset.
• Digitizer sets the digitizer type which determines how many nanoseconds each timestamp unit corresponds to.
• CFDCoeff similar to EngCoeff this can set parameters for a polynomial function using the CFD value as input. This is mainly used to set an offset for small corrections in the timing after the fragments have been sorted into events.

Other possible calibration parameters include:

• Number
• Stream
• EngChi2
• CFDChi2
• LEDChi2
• TimeChi2
• EffChi2
• LEDCoeff
• EffCoeff
• FileInt

ODB

Using odbgains.C on a cal file writes a bash script that will allows easy setting of the odb gains parameters for GRIFFIN.