The coarse cathode planes will be read out with a latch so they
will not require as good of a calibration as the fine cathode
planes. However, the threshold levels should be set uniformly
across a given chamber, so the strips should be pulsed at a
given voltage with several threshold settings to calibrate the
system. Either the strips can be pulsed directly, or the
front end electronics can be pulsed. There are approximately
8000 coarse cathode channels, and we would like to pulse the
system at one voltage and five threshold settings, with 300 data
points at each threshold setting. This gives a total of
1.2x10
data points required for calibration.
In addition, we would like to have the capability to pulse
the coarse cathodes at different voltage levels for test
purposes, but will probably only need a single voltage level
for a standard calibration run.
The data stored for each coarse cathode strip is the threshold value at which the channels fire 50% of the time (8000 calibration constants). The calibration should be performed approximately monthly or on the same schedule as the fine cathode calibration.