Difference between revisions of "CDC 06 02 2008"
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[[Image:test3noise2.jpg|thumb|none|400px|figure 2.8: Noise on straw 2.]] | [[Image:test3noise2.jpg|thumb|none|400px|figure 2.8: Noise on straw 2.]] | ||
[[Image:test3noise3.jpg|thumb|none|400px|figure 2.9: Noise on straw 3.]] | [[Image:test3noise3.jpg|thumb|none|400px|figure 2.9: Noise on straw 3.]] | ||
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+ | And why not? Test 4: | ||
+ | *) Shielding over the upstream end plenum + preAmp: yes | ||
+ | *) Extra shielding over the straws: yes | ||
+ | *) Shielding over the downstream end plenum: yes | ||
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+ | |||
+ | The oscilloscope traces of straw 1,2, and 3 are shown in figure 2.10, 2.11, and 2.12. | ||
+ | [[Image:test4noise1.jpg|thumb|none|400px|figure 2.10: Noise on straw 1.]] | ||
+ | [[Image:test4noise2.jpg|thumb|none|400px|figure 2.11: Noise on straw 2.]] | ||
+ | [[Image:test4noise3.jpg|thumb|none|400px|figure 2.12: Noise on straw 3.]] | ||
== 3 Some studies concerning noise and shielding - with shaper == | == 3 Some studies concerning noise and shielding - with shaper == |
Revision as of 13:27, 28 January 2008
Contents
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 1 was used for this test.
2 Some studies concerning noise and shielding - without shaper
Setup:
- ) HV = 1800 V
- ) NO shaper
Three straws are observed. We'll call them straw 1,2, and 3 (those are the same straws as in previous section).
Test 1:
- ) Shielding over the upstream end plenum + preAmp: yes
- ) Extra shielding over the straws: no
- ) Shielding over the downstream end plenum: no
The oscilloscope traces of straw 1,2, and 3 are shown in figure 2.1, 2.2, and 2.3.
Test 2:
- ) Shielding over the upstream end plenum + preAmp: yes
- ) Extra shielding over the straws: no
- ) Shielding over the downstream end plenum: yes
The oscilloscope traces of straw 1,2, and 3 are shown in figure 2.4, 2.5, and 2.6.
Test 3:
- ) Shielding over the upstream end plenum + preAmp: yes
- ) Extra shielding over the straws: yes
- ) Shielding over the downstream end plenum: no
The oscilloscope traces of straw 1,2, and 3 are shown in figure 2.7, 2.8, and 2.9.
And why not? Test 4:
- ) Shielding over the upstream end plenum + preAmp: yes
- ) Extra shielding over the straws: yes
- ) Shielding over the downstream end plenum: yes
The oscilloscope traces of straw 1,2, and 3 are shown in figure 2.10, 2.11, and 2.12.