| Description: | The number of laser pulses averaged per profile, or shot count, exhibited erratic behavior
during the periods in question. The values reported in the sgprlC1.a0 datastream were
incorrect and varied radically from profile to profile. Shot counts are used in the Merge
VAP to compute photon count rates, which are then used by all the other RL VAPs. Thus, the
shot count problem renders all of the RL VAPs bad or suspect during the periods in question.
It appears that the problem was caused as the signal on the line between two triggering
units got noisier over time, causing the second unit to occasionally trigger on noise. The
second unit triggers the Licel electronics. So the false triggering on the second unit
caused false shot count readings. On 6 October 2011 the trigger level was adjusted by the
on-site technician, and this solved the problem.
On 3 May 2012 the DG535 pulse generator, which is used to trigger the Licel data
recorders, was swapped out with a spare. After installation of the spare, the system started
recording erroneous values of shot counts. The problem was fixed on 12 June 2012 when the
on-site tech increased trigger level on the DG535. |