BB Cerenkov T2 timing re-measured, looks good

NEXT
Make New Entry, Make Followup Entry

User name brads

Log entry time 20:58:03 on February 10, 2009

Entry number 260366

keyword=BB Cerenkov T2 timing re-measured, looks good

I gave the Cerenkov group + Shower group AND input timing a pretty thorough check using a different technique than I had used in the initial setup. The overlaps (still) look pretty good: the shower will carry the timing for any legitimate overlap. I measured 30ns of walk in the shower group signal (a composite entity involving 5x17 blocks) relative to a paddle scintillator. Walk in the Cerenkov groups appeared less than a couple ns using the same method.

The minimum overlap (slowest shower vs. Cerenkov) is 10--15ns, significantly larger than the minimum overlap resolving time of the P758, and P756 logic modules. The signal widths at the AND input are 50ns. The output pulses were set to 150ns wide to prevent false doubles with observed ringing in the shower signals with a period of ~100ns.

Two changes were made to the circuit this afternoon. The outputs of the AND units were normalized to 150ns. Most had been set to 50ns previously, one (Cer overlap 9, I think) had a slightly dodgy 30ns wide output. The second change involved shortening the output of the P706 used to fan-out copies of shower row-pairs needed to form the overlapping shower groups. Previously that output had been 150ns; now it is 50ns, consistent with the widths of the other (non-fanned-out) shower-row signals.