Date: Mon, 19 Apr 2004 15:54:36 +0200 (MEST)
Subject: ECAL anomaly

Dear Sirs,

while investigating the spurious alerts sometimes produced by j_calib_adc
(the electronic calibration checking program), I discovered something rather
strange in one set of calibration data that had triggered such an alert.
Attached are pertinent parts of the Rev. 167 electronic calibration data: 
jmx1.rev167.anodeswitch.all.ps shows how the electronic pulse amplitude (red)
and the anode switch value (blue) vary from line to line in the raw ECAL data.
jmx1.rev167.anodeswitch.detail1.ps is just a detail of this figure, showing
the change over from the second to the third anode segment. There should be
a complete set of pulses with the full range of amplitudes for each anodeSwitch
value.


In all other cases
of ECAL data I've looked at the change in anodeSwitch occurs exactly where the
amplitude drops to its lowest value, but for this single case, the anode value
switches in the middle of the penultimate series of pulses for the second anode.

It seems likely that this is just an incorrect report of the value of the anode
switch, but questions arise: where did this incorrect changeover occur?
Onboard or in ISDC Preprocessing? Is it truly a single isolated incident, or
does it cover up a more serious problem either onboard or in Preprocessing?
Shall we ignore it, or should we investigate it further?

Version 2.2 of j_calib_adc can handle this problem ('if a change in anodeSwitch
occurs without a HUGE drop in pulse amplitude, stick with the old anodeSwitch
value'), so it is possibly academic. However, if there's someone out there
who can explain why this has happened, just once as far as I know, I'd like to
hear from them.

Best wishes,

Carol Anne



.DANISH.SPACE.RESEARCH.INSTITUTE.DANISH.SPACE.RESEARCH.INSTITUTE.DANISH.
Dr. Carol Anne Oxborrow
Email: oxborrow@dsri.dk	Homepage: http://www.dsri.dk/~oxborrow
Telephone (direct): +45 35 32 57 33
Telephone (secretary): +45 35 32 57 01
Fax: +45 35 36 24 75