In module 0, each PACMAN has its own free-running clock that is periodically synchronized with a PPS signal. @mastbaum showed that the two clocks run with slightly (~20-30e-7) different frequencies. This introduces an offset of up to ~mm in the reconstructed drift coordinate, if you use the basic hit timestamps. There are two (or probably more) ways to correct for this:
- instead of using a single, global clock frequency for the two PACMAN, use the measured frequencies relative to the PPS signal and reconstruct drift times / etc independently for each PACMAN based on those
- instead of always using the first external trigger for the t0 in track fitting, use only the trigger generated by each PACMAN to reconstruct the drift time for hits orgininating on the given PACMAN
Both are equally viable options, and probably both should be implemented.
In module 0, each PACMAN has its own free-running clock that is periodically synchronized with a PPS signal. @mastbaum showed that the two clocks run with slightly (~20-30e-7) different frequencies. This introduces an offset of up to ~mm in the reconstructed drift coordinate, if you use the basic hit timestamps. There are two (or probably more) ways to correct for this:
Both are equally viable options, and probably both should be implemented.