Pedestal and Common Noise in the Test beam data
Rudi Ganz  October 20th 1997

Here are some pictures generated from file #RUN00100.dat from the 1997 test beam data.
Here is for the Telescope number #1    ADC value versus channel number:
 
for the Telescope detector  1 click here
 
 
 
 before the subtraction of pedestals* 
    after subtraction
( *generated as channel by channel average over the "pedestal tagged" events)


The question now is whether there is common noise which we then have to subtract on an event-by event basis. Common Noise means a correlated change of the pedestal. So if one plots one the ADC value of one channel against the other channel (in the same Read-Out chip) one can look for such correlation's:

The histograms (as suggested by Russell) show the correlation of the noise between each channel of one readout chip  with all the others. (So I take the first channel on the chip and plot it against channel 2-128; then I take second channel and plot it against 3-128 and so on ...) Each telescope detector is read out by 5(4) 128 channel VA chips.
 

 
 
Telescope #1   chip 1
Telescope #1   chip 2
Telescope #1   chip 3
Telescope #1   chip 4
Telescope #1   chip 5
 
 
 
 
One can see no significant correlation in this telescope detector -> no significant common mode noise. In fact when one tried to subtract an event-by-event average on the non-hit channels one can improve the already very narrow pedestal peak width (RMS. = 2.1 ch) to an RMS of 1.9ch. As expected from above,  no significant improvement.