filiberto.clara@LIGO.ORG - posted 09:12, Wednesday 06 November 2024 - last comment - 08:36, Friday 08 November 2024(81097)
3T Gurulp seismometers Huddle Test - LVEA
WP 12139
Entry for work done on 11/5/2024
Two 3T seismometers were installed in the LVEA Biergarten next to the PEM area. Signals are routed through the SUS-R3 PEM patch panel into the CER. Signals are connected to PEM AA chassis 4 and 5.
F. Clara, J. Warner
There are 2 of these plugged in, they are 3 axis seismometers, serial numbers T3611670 and T3611672. The first one is plugged into ports 4,5 & 6 on the PEM patch panel, the second is plugged into ports 7,8 & 9. In the CER, T3611670 is plugged into ports 21,22 & 23 on PEM ADC5 and T3611672 is plugged into ports 27,28 & 29 on PEM ADC4. In the DAQ, these channels are H1:PEM-CS_ADC_5_{20,21,22}_2K_OUT_DQ and H1:PEM-CS_ADC_4_{26,27,28}_2K_OUT_DQ. So far the seismometers look like they are giving pretty good data, similar to the STS and the old PEM Guralp in the biergarten. The seismometers are oriented so that the "north" marking on the their carry handles is pointed down the X-arm, as best as I could with eyeballing it.
I need to figure out the calibrations, but it looks like there is almost exactly -15db difference between these new sensors and the old PEM Guralp, but maybe the signal chain isn't exatly the same.
Attached images compare the 3T's to the ITMY STS and the existing PEM Guralp in the biergarten. First image compares asds for each seismometer. Shapes are pretty similar below 40 hz, but above that they all have very different responses. I don't know what the PEM guralp is calibrated to, if anything, it looks ~10x lower than the STS (which calibrated to nm/s). The 3T's are about 5x lower than the PEM sensor, so ~50x lower than the STS.
Second image are tfs for the X,Y & Z dofs between the 3T's and the STS. These are just passive tfs between the STS and 3T's to see if the have similar response to ground motion These are generally pretty flat between .1 and 10hz. The X & Y dofs seem pretty consistent, the Z tfs are different starting around 10hz. I should go and check that the feet are locked and have similar extension.
Third image are tfs between the 3T's and the exist PEM Guralp. Pretty similar to the tfs with the STS, horizontal dofs all look very similar, flat between .1 and 10hz, but the ADC4 sensor has a different vertical response.
I'll look at noise floors next.
The noise for these seems almost comparable to T240s, above 100 mhz, less certain about noise below 100mhz, these don't have thermal enclosures like the other ground sensors. Using mccs2 in matlab to remove all the coherent noise with the STS and PEM Guralp, the residual noise is pretty close to the T240 spec noise in SEI_sensor_noise. Attached plots are the asds and residuals after finding a scale factor that matches the 3T asds to the calibrated ITMY STS asds. Solid lines are the 3T asd, dashed lines are the residuals after coherent subtraction.
For convenience I've attachd the response of the T240 and the STS-2 from the manuals.
These instruments both have a steep fall-off above 50-60 Hz.
This is not compensated in the realtime filters, as it would just add lots of noise at high frequency, and then we'd have to roll it off again so it doesn't add lots of nasty noise.
T240 user guide - pg 45
https://dcc.ligo.org/LIGO-E1500379
The T240 response is pretty flat up to 10 Hz, has a peak at ~ 50 Hz, then falls off rapidly.
STS-2 manual - pg 7
https://dcc.ligo.org/LIGO-E2300142
Likewise the STS-2 response is pretty flat up to 10 Hz, then there is ripple, and a steep falloff above 60 Hz