Difference between revisions of "RF Calibration"

Revision as of 10:45, 15 May 2015

Overview

TI-Time Uniformity

• As detailed in GlueX Doc 2686, a copy of the global system clock time is present on each ROC (on the Trigger Interface (TI) board). To check whether they are all consistent with each other, run the RFMacro_ROCTITimes.C macro:

root -l hd_root.root
.L $ONLINE_PLUGINS/RF_online/calib_scripts/RFMacro_ROCTITimes.C
main();

TI-TIME UNIFORMITY CHECK: 1) Confirm that the copies of the global system clock present on each ROC are consistent with each other: "ROCTIs" directory

TDC->TIME CHECK: 1) Confirm that the tdc->time conversion is accurate for each system: "DeltaT_RF_FirstTime" directory - TOF & TAGH RF signals read out 1/128 times: expect first delta-t peak at 128*1000/499 ns - PSC & FDC RF signals read out 1/64 times: expect first delta-t peak at 64*1000/499 ns

RF TIME CALIBRATION: 1) Confirm that the RF signal is arriving at approximately 499 MHz: "RF_SignalPeriod" directory 2) Study the resolution of each source of the RF signal: "DeltaT_RF_Itself" directory. Check in these constants. 3) Do a rough alignment of each RF system with respect to the TOF signal: "AbsoluteDeltaT_RF_OtherRFs" directory & FitMacro_RF_CoarseOffsets.C Macro. Check in these constants. - This is important in case the RF signal period is not exactly 499 MHz. If it's slightly wrong, add the time offsets are huge, then propagating across several micro-s will result in a many-ps error in the time. 4) Study the resolution when taking the difference between RF times at different sources: "DeltaT_RF_OtherRFs" directory. - If these resolutions are much larger than the individual system uncertainties, then do not average the system times together. - This is the default behavior of the DRFTime factory (for the signals in the data stream, only uses the system with the best time resolution) 5) Do a detailed alignment of each RF system with respect to the TOF signal: "AverageDeltaT_RF_OtherRFs" directory. Update these constants (and the uncertainties).

CONFIRM ALIGNMENT TO TAGGER HODOSCOPE: 1) Once the tagger hodoscope has been aligned to the RF, confirm the alignment: "DeltaT_RF_TAGH" directory.

     - If it is out-of-line, realign the tagger to the RF (outside the scope of this plugin)