[Halld-cal] Proposed change to timing offsets for BCAL

[Michael Staib]

Hi All,

I have been dragging my feet a little on applying George’s relative timing offsets, since the currently the timing constants are all added together and adjusting them for all runs could be exhausting. The following was a suggestion I made to Elton and George a few weeks ago that might be worth discussing at tomorrows meeting:

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There are essentially 4 different per channel offsets that have to all be accounted for. 

Align the TDC and ADC to each other (1152 constants) = tdc_adc_relative_offset
Align the double ended channel to the global time (768 constants) = channel_global_offset
Relative timing offsets of the ADC/TDCs upstream/downstream (768 constants) = relative_offset == tdiff

It may be useful if we were to break these all up into their own table. Currently we just store 1152 TDC and 1536 ADC constants. There are also the per-detector base times. It would take a little work, but I might propose the following definition of the times that could break all of this up. 

t_adc = (t_adc_raw [ns]) + base_time_offset_adc - channel_global_offset   - 0.5 * tdiff * (-1*end) 
t_tdc = (t_tdc_raw [ns]) + base_time_offset_tdc - tdc_adc_relative_offset - channel_global_offset  - 0.5 * tdiff * (-1*end)

where end {0,1} = {upstream, downstream}. This does assume that the same tdiff values are used for the TDC and ADC times. Unfortunately there is still some room for the numbers to interfere. For example, if I change the tdc_adc_relative_offset I might inadvertently change the time difference between the two ends and spoil the global offset. There isn’t any great way I can think of to leave complete flexibility of the values without some constants affecting others. Or at least I should say the tdc_adc_relative_offset must be fixed before channel_global_offset and tdiff are calculated. 

--
Michael Staib
Graduate Student, Dept. of Physics
Carnegie Mellon University
mstaib at cmu.edu
phone: 412-268-2983

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