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Entry  Fri Feb 19 15:12:38 2016, Koji, Summary, PEM, Guralp Health Check Guralp_Raw_PSD.pdflow_vel_comparison.pdfGuralp_TF.pdf
    Reply  Wed Mar 23 15:23:12 2016, Steve, Summary, PEM, Guralps as connected GUR_A.jpgGUR_B.jpgGUR_Interface_Box.jpg
       Reply  Thu Mar 24 08:20:52 2016, Steve, Update, PEM, Guralp-A calibration sheet 
       Reply  Fri Mar 25 19:17:28 2016, Nikhil, Update, PEM, Guralp Seismometers 16x
          Reply  Fri Mar 25 23:54:04 2016, rana, Update, PEM, Guralp Seismometers 
       Reply  Wed Aug 3 14:52:37 2016, Steve, Summary, PEM, Guralps as connected 
          Reply  Tue Aug 9 13:53:57 2016, babbott, Update, SEI, long Guralp EX cable repaired on the D-sub side 
             Reply  Tue Aug 9 19:35:49 2016, rana, Update, SEI, both Guralp seismometers are functioning and being acquired 1goodday.png
                Reply  Wed Aug 10 10:32:44 2016, Steve, Update, SEI, working Guralps as they are 6x
                   Reply  Fri Aug 12 14:37:34 2016, Steve, Update, SEI, working seismometers as they are eq_2.1m_Geysers_CA.pngeq2.1m_GeysersCA.pngoscillations.png
Message ID: 12047     Entry time: Fri Mar 25 19:17:28 2016     In reply to: 12044     Reply to this: 12048
Author: Nikhil 
Type: Update 
Category: PEM 
Subject: Guralp Seismometers 

Calibration of Guralp Seismometers


  • 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.



  •  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.                                                                                                                        


                                                                            CMG-40T Guralp A Calibration Sheet                                                           

  Velocity Output: V/m/s (Differential) Mass Position Output (Acceleration Output) : V/m/s^2  Feedback Coil Constant : Amp/m/s^2
Vertical 2 x 400 19 0.00397
North/South 2 x 398 23 0.00486
East/West 2 x 401 23 0.00479                 

Calibration Resistor: 51000

                                                                            CMG-40T Guralp B Calibration Sheet                                                           

  Velocity Output: V/m/s (Differential) Mass Position Output (Acceleration Output) : V/m/s^2  Feedback Coil Constant : Amp/m/s^2
Vertical 2 x 401 19 0.00408
North/South 2 x 400 20 0.00421
East/West 2 x 404 22


Calibration Resistor: 51000 

Attachment 3: VelSens_XArm_Guralp_A.png  60 kB  | Hide | Hide all
Attachment 4: VelSens_XArm_Guralp_A.png  60 kB  | Hide | Hide all
Attachment 5: VelSens_YArm_Guralp_B.png  35 kB  | Hide | Hide all
Attachment 8: Vel_PSD_XArm_GurB_E.png  37 kB  | Hide | Hide all
Attachment 9: Vel_PSD_XArm_GurB_N.png  36 kB  | Hide | Hide all
Attachment 16: Guralp_PowerSpectrum.pdf  45 kB  | Hide | Hide all
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