40m
QIL
Cryo_Lab
CTN
SUS_Lab
TCS_Lab
OMC_Lab
CRIME_Lab
FEA
ENG_Labs
OptContFac
Mariner
WBEEShop
|
40m Log |
Not logged in |
 |
|
Tue Dec 26 17:24:24 2017, Steve, Update, General, power outage
|
Thu Dec 28 17:22:02 2017, gautam, Update, General, power outage - CDS recovery
|
Thu Jan 4 14:39:50 2018, gautam, Update, General, power outage - timing error
|
Fri Jan 5 21:54:28 2018, rana, Update, General, power outage - timing error
|
Fri Jan 5 22:19:53 2018, gautam, Update, General, power outage - timing error
|
Sat Jan 6 18:27:37 2018, gautam, Update, General, power outage - IFO recovery 
|
Mon Apr 16 22:09:53 2018, Kevin, Update, General, power outage - BLRM recovery 
|
Tue Apr 17 09:57:09 2018, Steve, Update, General, seismometer interfaces 
|
Wed Apr 18 20:33:19 2018, Kevin, Update, General, seismometer interfaces  
|
Fri Apr 20 23:36:28 2018, Kevin, Update, PEM, Seismometer BLRMs  
|
Tue Apr 24 21:19:08 2018, Kevin, Update, PEM, Seismometer BLRMs   
|
Wed Apr 25 17:44:39 2018, Arnold, Update, PEM, PEM Anti-Alias wiring
|
Thu Apr 26 09:35:49 2018, Kevin, Update, PEM, PEM Anti-Alias wiring 
|
Thu Apr 26 20:22:21 2018, Kevin, Update, PEM, ADC common mode rejection with new seismometer connections 
|
Wed May 16 21:02:22 2018, Kevin, Update, PEM, ADC common mode rejection with new seismometer connections
|
Thu Jun 14 15:24:32 2018, Steve, Update, PEM, ADC DAC In Line Test Boards are in
|
Tue Jan 2 15:43:35 2018, Steve, Update, VAC, pumpdown after power outage
|
Wed Feb 7 15:50:42 2018, Steve, Update, VAC, IFO pressure monitoring
|
|
Message ID: 13794
Entry time: Thu Apr 26 20:22:21 2018
In reply to: 13790
Reply to this: 13849
|
Author: |
Kevin |
Type: |
Update |
Category: |
PEM |
Subject: |
ADC common mode rejection with new seismometer connections |
|
|
Yesterday I wired the outputs from the seismometers directly to the ADC input bypassing the old AA board circuit as is described in this elog. The old circuit converted the single-ended output from the seismometers to a differential signal. Today I looked at whether 60 Hz noise is worse going directly into the ADC due to the loss of the common mode rejection previously provided by the conversion to differential signals.
I split the output from the BS Z seismometer to the new board and to an SR785. On the SR785 I measured the difference between the inner and outer conductors of the seismometer output, i.e. A-B with A the center conductor and B the outer conductor, with grounded input. At the same time I took a DTT spectrum of C1:PEM-SEIS_BS_Z_IN1. Both spectra were taken with 1 Hz bandwidth and 25 averages. The setup is shown in attachment 1.
The spectra are shown in attachment 2. The DTT spectrum was converted from counts to volts by multiplying by 2 * 10 V/32768 cts where the extra factor of 2 is from converting from single-ended to differential input. If there was common 60 Hz noise that the ADC was picking up we would expect to see less noise at 60 Hz in the SR785 spectrum measured directly at the output from the seismometer since that was a differential measurement. Since both spectra have the same 60 Hz noise, this noise is differential. |
|
|
|
|