Fastbus TDC Gain and Offset Calibrations

The Fastbus TDC gains and offset are calibrated using a time calibrator. The time calibrator sends a START signal to the TDCs and a STOP signal to the TEST inputs of the discriminators. The time difference between START and STOP is a multiple of 10 ns, with a maximum of 640 ns. The Fastbus TDCs have a dual range: in the lower range, the resolution is about 25 ps/channel while the resolution of the upper range is about 200 ps/channel. For more details, please refer to the TDC manual.

The procedure used to calibrate the TDCs is as follows:

Collect Fastbus data using the time calibrator as a trigger.

Set up the gain calibration super module. This is done by executing the following command:

.x $PHATHOME/phatplastic/macros/FBGainCalc_Setup.C

This command produces the following output:

::ListModules():

Module #0: TPhModule:FBGeoInitMod (Enabled)

Module #1: TPhModule: FBInitMod (Enabled)

Module #2: TPhModule: FBunpackerMod (Enabled)

Module #3: TPhModule: FBIndexMod (Enabled)

Module #4: TPhModule: FBGainCalcMod (Enabled)

Module #5: TPhModule: VerifyFBGainMod (Enabled)

Setup for Fastbus gain/offset calculation completed successfully!

Run the super module. This is done by executing the following command:
```
.x $PHATHOME/phatplastic/macros/FBGainCalc_SM.C(6060,0,"/data/cr01/data")
```
where the arguments are:
- run number (in this example 6060)
- sequence number (in this example 0)
- location of the data file (in this example /data/cr01/data)
This command produces the following output:
```
Poor fit for FB = 0 Slot = 9 Channel = 55 Sensor = GX07 
```
```
Low range: Slope = 0.0242124 +/- 0.000286517
```
```
           Offset = 232.076 +/- 0.644101 
```
```
High range: Slope = 0.0254266 +/- 5.26649e-05 
```
```
            Offset = 168.47 +/- 0.682932 
```
```
FBGainCalcMod(TPhFBGainCalcMod): Gain/Offset calibration objects are store    
in object manager FBGainCalcModObjs 
```
```
VerifyFBGainMod(TPhVerifyFBGainMod): **** VERIFYING FASTBUS GAINS 
```
```
VerifyFBGainMod(TPhVerifyFBGainMod): Accept? [y/n] 
```
Before accepting the calibrations please look at the two canvases created by this macro. The results of the analysis of run 6060 are included here.

The canvas with the two dimensional histograms shows the raw TDC data (top) and the calibrated TDC data (bottom) for the low-range (left) and the high-range (right). Two things needs to be checked:
- All TDCs must respond (a total of 10 vertical bands should appear). For run 6060, only the 8 TOF TDCs responded and where thus calibrated.
- A successful calibration should produce horizontal bands in all TDCs.

The calibration parameters calculated are displayed in a second canvas. An example obtained for run 6060 is shown below. The gain parameters (in ns/channel) are shown on the left for the low-range (top) and the high-range (bottom). The offset parameters (in ns) are shown on the right for the low-range (top) and the high-range (bottom). Three things should be checked:

Calibration parameters should be calculated for all TDCs ( again, in this example, the trigger TDCs are missing).

The gains calculated should be similar for all channels and about 0.025 ns/channel for all channels.

The offsets for all channels should be similar of all channels. Variations of up to 50% are expected, but significantly larger variations, like the spike observed in the TDC located in channel 9 must be brought to the attention of the experts.

After examining the histograms displayed decide whether or not to accepts the calibrations. If you accept the calibrations, the calibration parameters will be written to the database. You will see the following information on the screen after accepting the calibration:

VerifyFBGainMod(TPhVerifyFBGainMod): Authenticating TOF DB as phatwriter...

VerifyFBGainMod(TPhVerifyFBGainMod): Writing FB Pedestals for Run, Seq          #6060, 0

VerifyFBGainMod(TPhVerifyFBGainMod): ...Revoking FB Database

Writing object manager to FBGainCalc006060s000.root

fbgaincalc: Real Time = 346.36 seconds Cpu Time = 178.01 seconds

All done!

Frank Wolfs, University of Rochester, June 2001