[EricQ, Koji, Manasa]

We opened the BS chamber to check the status of the green beams. The X green has 3 steering mirrors before they hit periscope1 and the Y green transmits through all the optics giving no way to steer it.

We agreed to start fixing the Y green. The wedge angle of PR3 is steering the transmitted beam away in both pitch and yaw. Since we are restricted only to yaw movement (done by moving the periscope), we want he wedge angle to be oriented in the yaw as well.

Right now, the wedge is oriented at about 20-30 deg off (The mark on the side of the mirror does not indicate the wedge). So we see a pitch as well as yaw misalignment in the transmitted beam. The pitch misalignment is making the beam fall off the mirrors in periscope2. 

We have decided to get the wedge angle set right for PR3 and redo the alignment for IR. Once we are aligned for the IR, we will modify the green layout.

A cosmic ray struck the RFM in the framebuilder this afternoon, causing hours of consternation.  The whole FE system is just now coming back up, and it appears the mode cleaner is not coming back to the same place (alignment).

rob, jenne

 Jenne, Rana, Koji

The mode cleaner has been realigned, using a combination of techniques.  First, we used ezcaservo to look at C1:SUS-MC(1,3)_SUS(DOF)_INMON and drive C1:SUS-MC(1,3)_(DOF)_COMM, to put the MC1 and MC3 mirrors back to their DriftMon values.  Then we looked at the MC_TRANS_SUM on dataviewer and adjusted the MC alignment sliders by hand to maximize the transmission.  Once the transmission was reasonably good, we saw that the spot was still a little high, and the WFS QPDs weren't centered.  So Koji and I went out and centered the WFS, and now the MC is back to where it used to be.  The MC_TRANS QPD looks nice and centered, so the pointing is back to where it used to be.

Koji and Steve,

We took transferfunctions of each channel yesterday. They were identical ?. I will check the cables from ADC to DAQ next.

As reported previously, the transfer functions of the channels look fine. (i.e. All channels almost identical.)
I checked the chain from the unit input to the DAQ BNC connectors. They were all OK.

Today I have been checking the signals on the unit with the long DB37 cables connected.
I could not see anything on the Gur2 channels on the board. I looked at the DB37 for Gur2 and felt something is wrong.

I opened the housing of the cable and realized that all the pins are not fully inserted.
The wires were crimped improperly and prevents them to be fully inserted.

=> We need to redo the crimping to insert them.
=> We need to check the other side too.

I'm making a new long cable. Both connector ends of this X arm long cable were terrible. It was removed from the cable tray yesterday.

The Y arm Guralp is running fine. The interface box is open in front of 1X1 on a cart and it is alive!    Please be aware of it !

Ara! Onara suru tsu-mori datta keh-do, un-chi ga de-chatta...

The new cable was made this way:

Pins were located with ohm meter for locations and both ends were cut off.The Belden 1424A cable than was soldered to DB37 and Guralp circular connector " IKPT06F16-26S-ND "

This cable will connect the ADC interface box CCD# DO 60506 to Guralp seismometer at the sout end.

The Guralp's each 3 axies will be connected through a twisted pair to the differential input op amp

Gur  ouput  vertical axis + -  on circular connector   A, B  to DB37 pin 1 &20

Gur output        N/S axis + -  on circular connector   C, D to DB37 pin 2 & 21

Gur output       E/W axis + -  on circular connector   E, F to DB37 pin 3 & 22

Power +12 VDC  from DB37 pin 29 to Gur circular connector pin c (lower case)

Power -12 VDC  from DB37 pin 24 to Gur circular connector pin  M Note: this connection was absent at the first test of this cable!

Ground              from DB37 pin 10 to Gur circular connector pin b (lower case)

Summery: I may destored the opamp  at the Guralp A at the south end.

To help find out if Steve really melted the inside of our precious seismometer, lets hook it up using the handheld seismo wand and see if it produces volts when we shake the ground.

Also, please stop using names like GurA or Gur1 or GurSuzy. We have GurX and GurY because they are at those ends. Anything else is confusing.

Atm1, Before cable swap

Atm2, The long cables were swapped at the input of the interface box.

We can conclude that the problem is in the interface box

I wonder if interface box input 3 is wired?

Let's dismantle the I/F unit from the rack and connect the cable with the lid open.
We need to trace the signal.
 

IIRC, the Guralp box's 3rd set of channels do not have all of the modifications that were made on channels 1 and 2.

The Guralp ADC  interface box  D060506 is ready for inspection. It is in front of 1X1 with open top and running.

Obviously c7 as 1 miroF cap is missing.

[Sanjit, Jenne]

Sanjit discovered that the Gur1 channels are all digital 0.  We determined that this began on July8, 04:00 UTC (~9pm on the 7th?).

It's digital zero, so we suspect a software thing.  Just to check, we put a sine wave in, and didn't see anything.  Gur2 seems totally fine, and the sine wave input showed up nicely on dataviewer.  What's going on? Sabotage to prevent this paper from getting done?  Dmass trying to get his paper done before me???

Investigations are ongoing.... Joe claims it's not his fault, since his shenanigans near the PEM rack were on days before, and days after this, but not on the 7th.  

 I just rebooted c0dcu1, which didn't help anything.  Joe said he'd try to give me a hand tomorrow.

In previous elogs, we saw that the X and Y spectra out of GUR2 (X end Guralp seismometer) looked strange (i.e. inconsistent with the GUR1 spectra). 

This morning, Steve and I brought the handheld control unit to the Guralp to center the test mass, by adjusting the centering potentiometers inside the unit while monitoring the voltage readout corresponding to the DC mass position (manual has instructions). 

At first glance, this seemed like the likely culprit, as the offsets for the horizontal directions were much larger than the vertical one. We zeroed all three to within a mV or two. Unfortuntately, the spectra look the same as they did 10 hours ago. 

Since we already had the kit out, we checked the offsets for GUR1. Only the "East/West" had an offset over 50mV, so we zeroed that one, but left the others alone. 

The cables labeled "Gur2" which were connected to channels 2,3,4 of the PEM-ADCU have been moved to the PCIX ADC which is connected directly to the ASS machine.  This means that until I (a) put the cables back or (b) figure out how to route channels from the ASS ADC to the RFM, we won't be able to use these channels for environmental monitoring, nor will they be saved. 

The Gur2_X, Gur2_Y, Gur2_Z channels are now connected to the 2nd, 3rd and 4th ADC channels respectively, on the ASS ADC (the first channel / TP1 is ADC0_0, which is the 1pps signal.).  The sketchy thing about the setup is the connection between the cables and the new ADC board.  The PCIX card is connected to the ASS via a white ribbon cable, and the board is just sitting on top of the computer box.  The 1pps (which has been hooked up for a long time) goes into the board via clip-doodles.  The regular channels have a SCSI cable connector, so I used a SCSI cable to connect up the ADC tester board, and connected my seismometer inputs to this tester board via more clip doodles.  Clearly this is a sketchy solution, and not okay for more than a day or so.  But we'll see how it goes. 

I'm going to, on the SimuLink Diagram, change the input source of these channels, from the RFMN to the ADC.  Then we'll see if that fixes our timing problem, and magically makes everything relating to the OAF work, and subtract huge amounts of noise. 

So that we can use both Guralps for Adaptive stuff, and so that I can look at the differential ground motion spectra, I've reconnected the Guralp Seismometers to the PEM ADCU, instead of where they've been sitting for a while connected to the ASS ADC.  I redid the ASS.mdl file, so that the PEM and PEMIIR matricies know where to look for the Gur2 data.  I followed the 'make ass' procedure in the wiki.  The spectra of the Gur1 and Gur2 seismometers look pretty much the same, so everything should be all good.

There's a problem with DataViewer though:  After selecting signals to plot, whenever I hit the "Start" button for the realtime plots, DataViewer closes abruptly. 

When I open dataviewer in terminal, I get the following output:

allegra:~>dataviewer
Warning: communication protocol revision mismatch: expected 11.3, received 11.4
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: communication protocol revision mismatch: expected 11.3, received 11.4
msgget: No space left on device
allegra:~>framer4 msgget:msqid: No space left on device

Does anyone have any inspiration for why this is, or what the story is?  I have GR class, but I'll try to follow up later this afternoon.

I've been trying for most of the week to get noise measurements on the output of the Guralp box as well as scross the AD640 chip. The measurements haven't really been making sense, and, being at a loss as to what else I should try, I decided to redo the resistors on the N/S 2 and E/W 2 channels. (I had been comparing the VERT1 and VERT2 channels, as VERT1 has been restuffed and VERT2 has not.) I don't need all three of the second set of channels to do more measurements, so it seemed like a good use of time.

The first thing I noticed was that the VERT2 channel was missing two resistors (R24 and R25). I probably should have noticed this sooner, as they are right by the output points I had been measuring across, but it didn't occur to me that anyone did anything to the VERT2 channel at all. So, probably the measurements on VERT2 are no good.

Note the existence of 100 kOhm resistors on the top channel, and none on the bottom channel (VERT2).

Then, while I was soldering in some 100 Ohm resistors, I happened to notice that the resistors I was using had a different number (1001) on them than the corresponding ones on the already redone channels (1003). I checked the resistance, and the ones on the already redone channels turned out to be 100 kOhm resistors, rather than 100 Ohms. So, I double checked the circuit diagram to make sure that I had read it correctly, and there were a number of resistors that had been relabeled as 100 Ohms and several relabeled as 100 kOhms. On the board, however, they were ALL 100 kOhms. Clearly, one of them is wrong, and I suspect that it is the circuitboard, but I don't know for sure.

The diagram clearly shows that R6 should be a 100k resistor, while R5 and R8 should be 100 Ohm resistors, but they are all the same (100k) on the board. I suspect this may have something to do with larger-than-expected noise measurements. But, it's possible the diagram is wrong, not the board. In any case, I didn't really know what to do, since I wasn't sure which was right, so I just replaced all the resistors I was sure about and removed the 100k and 100 Ohm resistors without replacing them with anything. Incidentally, the box of 100kOhm resistors seems to be missing, so I wouldn't have been able to finish those anyway.

There managed to be just enough 100 kOhm resistors to stuff all the "2" channels (VERT2, N/S2, E/W2) with the fancy low-noise resistors. The first six channels (VERT 1/2, NS 1/2, EW 1/2) are now completely done with the thin-film resistors, taking into account the changes that were made on the circuit diagram. I also replaced the C8 capacitor with the fancy Garrett ones and added capacitors on top of R4 and R13 (after painstakingly making sure that the capacitances are exactly the same for each pair) for the "2" channels. It looks like the capacitors on the "1" channels are the cheaper ones. I will compare the noise measurements later to see if there is any difference - if so, I can replace those as well (although, we're out of the 1 uF capacitors needed for C8).

Speaking of, we are now out of or very low on several types of the Garrett resistors/capacitors: 1 uF, 1kOhm, 100 Ohm, 14.0 Ohm, and 100 kOhm. I left the specifics on Steve's desk so that more can be ordered for the eventual time when the third set of channels needs to be restuffed.

I pulled the Guralp breakout box from the rack, and it's sitting on the EE bench here.  The game plan is to check out the Gur2X channel.  

Rana and Steve have been investigating, and found that the X channel has been funky (which has been known for ~a month or two) when the seismometer has been plugged in, and also when the seismometers have been unplugged, but the box is left on.  The funkyness goes away when the box is turned off.  Since it's not there when the box is off, it seems that it's not a problem with the cable from the box to the ADC, or in the ADC channel.  Since it is there when the box is on, but the seismometer is unplugged, it's clear that it's probably in the box itself.  

Preliminarily, I've connected a set of BNC clipdoodles to the input testpoints, and another set to the output.  They're both connected to a 'scope (which is on it's battery so it's not connected to any Ground), and when I tap on the circuit board the input trace is totally unchanged, but the output trace goes kind of crazy, and gets more fuzzy, and picks up a DC offset.  Koji is concerned that some of the big capacitors may have an iffy connection to the board. 

Investigations will continue Monday morning. 

 The Guralp Box appears to be back in working order.  It's reinstalled with the 2 seismometers plugged in.

In order:

* Koji suggested retouching the through-board solder joints on the broken channel (EW2 = Gur2X) with a bit of solder to ensure the connections were good.  Check.

* "C7", one of the giant 1uF capacitors on each channel is totally bypassed, and since that was one of the original suspects, Rana removed the (possibly) offending capacitor from EW2.

* Rana and I isolated the craziness to the final differential output stage.  We tried each of the testpoints after the individual gain / filter stages, and found that the signals were all fine, until after the output stage.

* I started to remove the resistors in the output stage (with the plan to go through the resistors, capacitors, and even the amplifier chip if neccessary), and noticed that 2 of the 1k resistors came off too easily, as if they were just barely connected in the first place.  After replacing only the 4 1k resistors, the craziness seemed to be gone.  I poked and gently bent the board, but the output wouldn't go crazy.  I declared victory.

* I reinstalled the box in its normal spot, and put Gur2 (which had been out by the bench for use as a test signal) back next to the other seismometers.  We are in nominal condition, and should be able to do a huddle test this week.

I looked at the time traces of all the seismometer channels, and they all looked good.  I'll put a spectra in in the morning....I'm too impatient to wait around for the low frequency FFTs.

Attached are the before and after pictures of the output stage of EW2 / Gur2X.  The "before" is the one with the OUT+ and OUT- words upsidedown.  The "after" picture has them right side up.

The Guralp cable has been pulled and put in the corner to the left of the water cooler:

Ben came by today before the cable had been pulled but he said he'll be back tomorrow.

The Guralp cable has been reconnected and powered after having the connector changed out.
 

I measured the guralp raw outputs and the TFs using the handheld unit and an FFT analyzer.

[Setup]

The handheld unit was connected to each guralp with the same cable which is confirmed t be functional with the Yend Guralp.

The signal for Z, N, and E directions are obtained from the banana connectors on the handheld unit. Each direction has mass, low gain velocity, and high gain velocity output. The PSDs of the signals were measured with an FFT analyzer. The transfer function from the mass signal to the low/high gain signals were also measured for each direction.

The adjustment screw for the E output of the Xend does not work. I had to tilt the Xend Guralp using the leg screws to bring the E signal to zero.

[Result]

Attachment 1: Raw voltage PSD for all outputs
Attachment 2: Comparison of the low gain vel outputs

- All of the mass output show similar PSDs.
- Low gain velocity outputs shows somewhat similar levels. I still need to check if the output is really the ground velocity or not.
- High gain velocity outputs are either not high gain, broken, or not implemented.

- We need to calibrate the low gain output using signal injection, huddle test, or something else.

Attachment 3: TFs between each mass output and the low or high gain outputs

- TFs between the mass signal and the low vel signals show the similar transfer functions between the channels.
- The high gain outputs show low or no transfer function with regard to the mass signals.
 

We need to do a new huddle test of the Guralps for the Wiener filtering paper. The last test had miserable results.

I tried to use recent data to do this, but it looks like we forgot to turn the Guralp box back on after the power outage or that they're far off center.

So instead I got data from after the previous power outage recovery.

I tried to use our usual Wiener filter method to subtract Guralp1-Z from Guralp2-Z, but that didn't work so well. It was very sensitive to the pre-weighting.

Instead I used the new .m file that Dmass wrote for subtracting the phase noise from his doubling noise MZ. That worked very well. It does all of the subtraction in the frequency domain and so doesn't have to worry about making a stable or causal filter. As you can see, it beats our weighted Wiener filter at all frequencies.

The attached plot shows the Guralp spectra (red & green), the residual using time-domain Wiener filtering (black) and the Dmass f-domain code (yellow).

As soon as Jenne brings in her beer cooler, we're ready to redo the Huddle Test.

I used some recent better data to try for better Z subtraction.

Dmass helped me understand that sqrt(1-Coherence) is a good estimate of the theoretical best noise subtraction residual. This should be added to DTT. For reference the Jan statistic is the inverse of this.

This should get better once Steve centers the Guralps. 

I mapped out the corresponding pins on both ends of the Guralp seismometer cable. Here is the diagram:

The circular 26-pin end of the cable (that plugs into the seismometer) is labeled as above. The other end (the 39-pin end) is not physically numbered, so I just came up with a numbering system. They are both pictured on the non-cable end of the connector. The colored circles indicate the pin pairs.

FROM JENNE, 30JULY2009:  the Dsub end is 37 pin, not 39.

Calibration of Guralp Seismometers

Objective

• Estimate transfer functions of Guralp A ( near ETMX) and Guralp B ( near ETMY)
• Calibrate the instruments by estimating Velocity Sensitity Parameter
• Convert previously measured Voltage Spectrum to Velocity Spectrum

Instruments Used

• Guralp CMG-40 T Seimometers  : Guralp A (Serial Number: T4Q17)
• Guralp CMG-40 T Seimometers  : Guralp B (Serial Number: T4157)
• Guralp Handheld Control Unit (HCU)
• FFT Spectrum Analyzer: Model SR785: 2 Channel Dynamic Signal Analyzer
• Oscilloscope: TDS 3014B
• Function Generator: DS 345

Procedure & Results

Sinusoidal current of known frequency and amplitude was injected to the Seismometer calibration coil using signal generator and handheld control unit & corresponding Magnitude and Phase response were recorded.  For  Guralp B, system response was also estimated with a FFT Spectrum Analyzer. 

Frequnecy Range: 0.1 Hz to 45 Hz.

Equivalent Input Velocity was derived from the Input Voltage measurements using the relation: v = V/ (2*pi*f*R*K) , V is the peak to peak Calibration Signal voltage, f is the calibration signal frequency, R is the calibration resistor and K is the feedback coil constant.  [See Appendix for R & K values]                                     

Velocity Sensitity at the required frequency is obtained by dividing the Output Response Voltage by the Equivalent Input Velocity.

The obtained Velocity Sensitivity is used to convert the recorded Volatge PSD to Velocity PSD as shown below. The obtained results are compared to gloabl high noise model [NHNM] and USGS New Low Noise Model [NLNM,Peterson 1993] which gives the lowest observed vertical seismic noise levels across the seismic frequency band. Plot legend NLNM shows both the high & low levels.

                                                                    Guralp A [X Arm] Low Velocity Output                                          

                                                                    Guralp B [Y Arm] Low Velocity Output                                          

                                                                            DTT Power Spectrum                                                             

Both the Seismometers were connected to the 40 M Control and Data Acquisition System (CDS) and Power Spectrum was estimated for the Vertical, North/South & East/West Channels using Diagnostic Test Tool (DTT) software.

Comments

•  The transfer function from Guralp A [ETMX] looks similar to that of Guralp B [ETMY] in both magnitude and phase but with a lower gain.                                                                                                                                                                                                  
• Velocity Sensitivity of Guralp A is comparable to the value provided in the Calibration Data Sheet [~ 400] for all the channels [Vertical, North/South, East/West] after 1 Hz. For Guralp B, Velocity Sensitivity is a factor of 2.5 higher [all channels] than the specification [~ 400] after 1 HZ.Below 1 Hz Sensitivity drops down for both sensors. I am not ruling out a missing common factor in the calculation, but anyway, test shows that Guralp B has ~2.5 times better Velocity Sensitivity than Guralp A.                                                                                                                                                               
• The Calibrated Seismic Velocity Spectrum for Guralp B is within the Globally Observed High and Low Noise Seismic Spectrum while Guralp A's Spectrum is more noisier above 1 Hz [Anthropogenic Activity normally contributes the most in 1 Hz to 10 Hz frequency band].                                                                                                                                                                                                                                                                          
• Concurrently acquired Power Spectrum using DTT [Diagnostic Test Tools] shows that Guralp A Spectrum behaves rather strangely. The system response seems to be completely different from the one we obtained locally using signal generator. While Guralp B functionality seems normal. One reason for this erratic beahvior might be faulty cables used for data acquisition from Guralp A. This needs to be verified.                                                                                                                        

Appendix

                                                                            CMG-40T Guralp A Calibration Sheet                                                           

Calibration Resistor: 51000

                                                                            CMG-40T Guralp B Calibration Sheet                                                           

Calibration Resistor: 51000 

Something seems not right. The Guralp response should be flat in velocity from 0.05-30 Hz. Why is there any feature at 1 Hz? Saturation of some kind?

While writing my progress report, I redrew the Guralp breakout box circuit diagram with all the changes marked. Since only one hard copy exists, I thought it might be useful to post my drawing up in case it is needed for any reason. The two drawings are the same - the second has just been broken into two parts to make it easier to fit on a normal 8.5 x 11 or A4 sheet of paper. The gains for each opamp have not been marked, but they could very easily be added in if necessary. The black resistances and capacitances are the originals. All changes have been indicated in blue.

After many issues, I finally have some Guralp box noise. I did not measure every single channel with high resolution at the low frequencies because that would have taken about 3 years, but I could perhaps take some faster measurements for all of them if necessary.

COD_Sugar napolion is due to Steve:  Item delivered, model CMG-SCU-0013, sn G9536

Reward being offered for the safe return of this thing:

 Kate & Jenne

About 2:30 this afternoon, we briefly powered off the Guralp (C1:PEM-SEIS_GUR1_{X,Y,Z}) in order to better align it with the other seismometers along its marked N/S direction. It had been visibly off by a few degrees. 

I plugged the Guralp cables back into the PEM ADCU

       Guralp NS1b ---> #11

       Guralp Vert1b --->#10

       Guralp EW1b --->#12

CMG-40T handheld controller unit is missing its power supply. In order to zero the instrument one has to apply plus and minus DC voltage.

The wiring on this 10 pin Amphenol PT02E-12-10P is shown.

I was checking into the Guralp situation today. I put the rubber balls underneath the granite block (the Q is too high), but found unfortunately that Jenne's styrofoam box is too short to cover the Guralps on top of the granite. If the box was skinny enough to fit on the block or taller by ~6 inches, it would be perfect. We need some new Seismo boxes.

Here's the story of the Gur2 noise so far. We need to pull out and repair the breakout box.

1) At some point we noticed that the Guralp2 X channel was behaving badly.

2) Steve tried recentering with just a +12V supply - this didn't work. Jenne then centered it using the +/- 12V supply. This was OK.

3) Around noon on March 24, the channel 'goes bad' again.

4) On the afternoon of the 25th, most of the channels go to zero, but the GUR2X channel stays bad. There's NO ENTRY in the elog about this. This is UNACCEPTABLE. Apparently, the seismometers were disconnected without shutting off the power to the box. You MUST elog everything - otherwise, go home and sit on your hands.

5) On the evening of the 31st, Steve turns off the Guralp breakout box. From the trend, you can see that the signals all go to zero at that time.

6) From then until today, there is no noise in the GUR2X channel. From these tests we can guess that the problem is in the GUR2X channel of the breakout box, but not in the AA Chassis or the ADC, since those showed no excess noise with the box turned OFF. Its hard to be sure without elog entries, but I assume that 3/25-3/31 was a 'seismometer disconnected', but 'box on' state.

After many, many "it'll be there in 2 weeks" from the Guralp people, our seismometer is finally back!

I have it plugged into the Guralp breakout box's Channel 1xyz (so I have unplugged the other Guralp).  Both of the Guralp's are currently sitting under the MC1/MC3 chamber.

Before we can have both Guralps up and running, I need to stuff the next 3 channels of the breakout box (back in the fall, I only had Caryn do 1x, 1y, 1z, and now I need 2x, 2y and 2z done with the fancy low-noise resistors), so all the gains match between the 2 sets of channels.

I'm leaving the new Guralp plugged in so we can see how it behaves for the next couple days, until I take out the breakout box for stuffing.

Tried swapping cables at the Guralp interface box side. It seems that all of our seismic signal problems have to do with the GUR2 cable being flaky (not surprising since it looks like it was patched with Orange Electrical tape!! rather than proper mechanical strain relief).

After swapping the cables today, the GUR2 DAQ channels all look fine: i.e. GUR1 (the one at the Y end) is fine, as is its cable and the GUR2 analog channels inside the interface box.

OTOH, the GUR1 DAQ channels (which have GUR2 (EX) connected into it) are too small by a factor of ~1000. Seems like that end of the cable will need to be remade. Luckily Jenne is still around this week and can point us to the pinout / instructions. Looks like there could be some shorting inside the backshell, so I've left it disconnected rather than risk damaging the seismometer. We should get a GUR1 style backshell to remake this cable. It might also be possible that the end at the seismometer is bad - Steve was supposed to swap the screws on the granite-aluminum plate on Thursday; I'll double check.

 After seeing all of these spikes in the BLRMS at high frequency for awhile, I power cycled the Guralp interface box (@ 10:21 PM) to see if it would randomly recenter in a different place and stop glitching.

It did - needs to be better centered (using the paddle). Plot shows how the Z channel gets better after power cycle.

I've looked through the Guralp manual to figure out what noise do they declare. They present it in acceleration units in dB relative to 1 m² / s⁴ / Hz. I've converted my measurements to this units and got

They declare much better noise. May be linoleum makes an effort. Do we have any isolation boxes?

I've connected Guralp output to the ADC without readout box. I've got the same noise at low frequencies and even worse noise at high frequencies. However, readout box was still used as DC supply and the signal was read from INPUT test points. I'll do the same experiment without touching readout box at all.

I've checked whether the Guralp noise that we see comes not from seismometer but from ADC or readout box. I did 2 separate measurements . First, I've split 1 signal from Guralp into 2 before the input to AA board and subtracted one from another using Wiener filter. Second, I've connected inputs of channels 1 and 4 of the seismometer readout box and put the signal from seismometer to channel 1.

The plot shows that ADC and readout box do not contribute too much to the Guralp noise.

As I've mentioned in yesterday's elog MC mirrors start to move in a synchronistic manner. I've plotted DELTA_GUR = GUR1_X - alpha * GUR2_X, where alpha = const to make the transfer functions SEISMOMETER -> ADC equal for each channel. I've noticed that DELTA_GUR decreases below 10 Hz compared to GUR1_X as theoretically predicted. But starting from 1 Hz DELTA_GUR starts to increase. I decided that this is Guralp noise floor. Today I checked this, this is indeed the case.

In the frequency range 0.01 - 1.5 Hz Gur noise is comparable to the signal DELTA_GUR. For that reason we see low coherence between MC_F and GUR1_X in this frequency range. 

Guralp noise floor was determined by placing 2 seimometers close to each other and subtracting by Wiener filtering.

Conclusion: To filter seismic noise out of MC_F we need more sensitive seimometeres.