The LED monitoring system is based from single ultra bright blue (470nm)
LED and optical fibers to transmit the light on PM.
The LED modification type MARL-110106
(Farnell
code 884-923) with diameter 5mm and maximal light intensity 4-5mkd is
used. The LED flashed from avalanche generator 35ns length and 10-15V
amplitudes pulses. The avalanche generator is activated
from artificial trigger type out of spill (or in) with frequency 10-30 pulses
per spill. This value is determined automatically every run or manually by help
of script from COMPASS
on-line PC:
echo T 0 13 30 1 | sockclient.pl pccofe02 9876 - out of spill;
echo T 0 13 30 2 | sockclient.pl pccofe02 9876 - in of spill;
echo T 0 13 30 3 | sockclient.pl pccofe02 9876 - never;
echo T 0 13 30 0 | sockclient.pl pccofe02 9876 - in & out of spill;
The digits values is: 13 – the TCS number; 30 – the pulse rate per second.
The LED light is distributed on 464 channels by plastic optical fibers. The diameters of the plastic kern
from PMMA (organic glass) is equal 1mm. The fibers are
covered in black with outer diameter 2.2mm. The single LED light is distributed on 464 by two steps:
-
1 to 34;
-
4 fibers
from first stage are going to PIN-diode;
-
30 fiber are distributed on 460 channels by 16 per group.
The PIN-diode used
to light monitoring in independent from PM way. The PIN-diode allow controlled the
light intensity and normalized it if LED intensity can be changed due to
temperature conditions or pulses shape (amplitude or with) from avalanche
generator.
HCAL1 is
controlled in time of data taking by LED with artificial trigger type.
In generally the LED plots can be in on-line with COMPASS
monitoring if is selected “CALIBRATION_EVENT”
in main menu in “Setup” window.
To obtain normalized LED amplitude is
used reference table in ~/onl/hcal1/referens/
which can be selected by script ./norm (or ./ref if it not normalized).
After this selection the monitoring with normalization can be started
from ~/onl/hcal1/ by script:
source ./led @pccoebXX: or as usual with data
files.
The LED reference
table can be obtained in start of data taking after
last HCAL1 calibration procedure in muon halo beam.
The on-line LED signal normalized to references allow controlled HCAL1 long time stability in time of data
taking very easy by eye. To more convenience can be loaded configuration files led.cfg from ~/onl/hcal1/ in time data taking after “source ./led”
was done.
mail to:Oleg.Gavrishchuk@cern.ch