Difference between revisions of "CDC 06 02 2008"
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− | + | After this test point some straws were wrapped with Al-foil. The effect was that the shape of the noise stayed the same but the amplitude of the noise went down from 1.38 to 1.08 mV (average); straw 4 was used for this test. |
Revision as of 20:00, 24 January 2008
1 News on the noise issue
Inspired by Gerard's visit and equipped with his differential probe I had a first look at a non-oscillating preAmp. I put 1900 V on the straws and checked all connected straws and they are all looking good (= I see signals). Time to do some additional noise studies.
Setup:
*) 16 armed straws *) HVDB (HV distribution board) that Gerard brought with him *) new preAmp, also the one the Gerard brought with him *) 1.5 meter cable + differential probe (which attenuates the signal 0.366x) (NO shaper) + scope
The VME crate was switched off, the only thing on (within a radius of 10 m) was a PC and a NIM crate.
I took a first look at the noise on a random straw (shown in figure 1.1):
Pickup with a frequency of 67.80 kHz can be observed. It was coming from a CRT computer screen, so that was switched off.
For further studies i selected 4 typical channels/straws: i will call them straw 1,2,3, and 4. The scope traces of these channels (respectively) are shown in figure 1.2-1.5:
The noise is what it is, this is our starting point. After trying out some things I put Al-foil over the upstream plenum + HVDB. I had most success when the foil was touching the cooling strip of the new preAmp. When the foil was touching the grounding of the cable (between preAmp and differential probe I saw the preAmp oscillating??? again (forgot to take traces of that one, sorry). The scope traces of the noise are shown in figures 1.6-1.9 (for straw 1-4 respectively).
These traces are averages, the sample traces are shown in figures 1.10-1.13
The improvement is vast! I also looked at the signals with this new setting, they are shown for each straw in figures 1.14-1.17.
They look pretty good, I think.
After this test point some straws were wrapped with Al-foil. The effect was that the shape of the noise stayed the same but the amplitude of the noise went down from 1.38 to 1.08 mV (average); straw 4 was used for this test.