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Last update: February 17, 2020, at 01:26 PM
Version: pmwiki-2.2.126

     NNSN - Norwegian National Seismic Network


Department of Earth Science
    Allé gt. 41, N-5007 Bergen, Norway&nbsp   
0.5  For review/testing  Added section on Mass Centering voltage calibration, and example calibration of Trillium 120QA sensor using built-in signal generator of DM24-EAM digitizer.  24 Jan, 2017  OM OM -
0.4 For review/testing Added section on test results; prototype cable diagram. 30 Jun, 2016 OM OM -
0.3 For review/testing Added section on interfacing mass centering control signals. 22 Jul, 2015 OM OM -
0.2 Withdrawn Initial version, for production 28 Jan, 2011 OM OM -


1.1 Nanometrics Trillium 120P User Manual

  1. From p. 4 in Trillium 120P Seismometer User Guide (version dated 2006-04-27):
  2. From p. 8:
    Ensure that the digitizer case is solidly earthed, and that the outer shield of the cable and the sensor case are thereby earthed.
Trillium 120P connector pinout, p. 29:
Trillium 120P/PA connector pinout, p. 57 of Trillium120P-PA_UserGuide_15149R6.pdf:
  1. Trillium 120P generic cable wiring diagram (p. 32 in Trillium 120P User Manual):

    The four signal groups used in normal operation is highlighted on the right side.

    NOTE: We are using the sensor in traditional mode, where the three outputs reflect the Z, NE and EW-component.

1.1.1 Connector pin-out:

From page 8 in Amphenol datasheet (click to open):

NOTE: Front face of pin inserts illustrated.

1.2 Güralp Digitizer mod. DM24-EAM User's Manual

  • Link to CMG-D24 User's Manual -- Issue T - January, 2020
  • Güralp digitizer mod. CMG-D24120 sensor input pin-out; p. 119 in DM24-EAM User Manual, Issue T - January, 2020:

    The four signal groups used in normal operation is highlighted on the right side.

1.3 Conclusions

According to advice in Trillium 120P manual, the general interconnection between sensor and digitizer should be like this:


In order to determine optimum earthing/shielding method, we performed a series of measurements. The aim was to determine the configuration (if any) that provided the lowest 50 Hz interference from mains power supply.

With regard to cross coupling between the three seismic channels X, Y and Z, we adhere to advice of sensor manufacturer by terminating the shields of the three twisted, shielded signal pairs at one point only - on the digitizer side.

In addition, it is useful to establish a standard for use of Güralp "Scream!" spectrogram software which can be used during sensor/digitizer installation, in order to ensure that seismic signals have a reasonable shape, and that mains 50 Hz interference is at lowest possible level.

2.1 Instruments used, location

Instrument Details
Power supply
  • Mfr: GW INSTEK
  • Model: GPS-303000
  • S/N: EH-855255
  • Mfr: Güralp
  • Model: CMG-D24-2000
  • S/N: C402
  • Sampling frequency: 200 Hz
  • Mfr: Nanometrics
  • Model: Trillium 120PA
  • S/N: 1136

Sensor was placed on pier in "Seismo-lab", basement of "Realfagbygget".

Measurement setup, sensor in foreground, placed on pier in "Seismo-lab".

2.2 Results


2.3 Conclusion

With the Güralp "Scream!" program (ver 4.5), it was not possible to detect any change in 50 Hz interference with different shielding / grounding configuration. This is a testament to the superb noise cancelling properties of differential signal transmission technique.


Based on measurements outlined above, we will use this interconnection between Trillium 120PA sensor, Güralp CMG-D24 digitizer and power supply. Note that only the three seismic components, power supply and grounding/shielding is shown - see complete wiring diagram and -list below.

Interconnection of Nanometrics Trillium 120PA, Güralp CMG-D24 digitizer and power supply
Interconnection of Nanometrics Trillium 120PA, Güralp CMG-D24 digitizer and power supply.


4.1 Assembly photograph

Click to see details of rightmost signal cables:

Junction Box, Trillium 120PA(P) side, as of 12 January 2011
Junction Box, Trillium 120PA(P) side, as of 12 January 2011.

4.2 Cable to Güralp Digitizer Sensor input

4.3 Parts list

Link to Excel part list with hyperlinks to spesific part:


View of part list-link



It's not very tempting to perform Trillium 120PA recentering using laptop in adverse weather conditions, if the sensor enclosure is exposed to the elements. Trials with a RS-232/Bluetooth adapter were successful - this means you can have remote terminal access to the 120PA from approx. 100 meter distance (the two Bluetooth devices are both of Class 1 category = long distance).

6.1 Bluetooth adapter, Trillium side

LM Technologies Bluetooth/RS232 adapter, mod. LM-058
LM Technologies Bluetooth - RS232 adapter, mod. LM-058.


The adapter must first be configured by connecting to it's serial port from a PC, and using a terminal program (e.g. like TeraTerm).

Important: During software setup, place the DCE/DTE switch to the DCE position (towards the DB9-connector).

Configuration commands Interprettion
at+name=Trillium 120PA
    //Set serial speed 9600 bit/second (to match Trillium 120PA setting), and power off/on the device
//Disable RTS/CTS flow
//Set name of Bluetooth device, visible when you scan for BT devices
//Set new PIN code

6.2 Bluetooth adapter, PC side

To obtain longest range, use a Class 1 USB/Bluetooth adapter. During testing, we used an older adapter manufactured by Billionton (P/N: UBTCR3C1A-B) which is obsolete now; any current device (e.g. this SDM USB Bluetooth 2.1 Adapter Class 1) should work fine.

After installing the adapter, scan for Bluetooth devices in the neighborhood, and select "Trillium 120PA".

The adapter on the Trillium side will automatically announce it's serial port capability, and you will be notified on the specific COM port assigned during the Bluetooth session.

Note that connection could be a two-stage process: First the "bridge" between the two Bluetooth devices is established, and then you have to actually make the connection.


The "SENSOR A" connector on the Güralp CMG-DM24 digitizer is furnished with 12 V output, intended to power the manufacturer's own brand of sensors. In our case, using sensor and digitizer from different manufacturers, we must ensure this power supply meets the sensor requirements.

The CMG-DM24 User's Manual does not provide any specifications regarding the 12V power output on the SENSOR A connector. Instead, clues must be sought after in the specifications of those sensors that are intended to be used with the digitizer.

The CMG-3T compact three-component broadband sensor is clearly a candidate for DM-24 partnership, as sensor output and digitizer input matches. This sensor has worst case current consumption during locking and unlocking; value is 490 mA. However, a footnote states that

"Because centering, locking, and unlocking consume varying amounts of power, it is recommended that you use a power supply capable of delivering 1 A at 12 V."

From this we must conclude that the voltage output of the DM-24 sensor connector is capable of supplying at least 1 A at 12 V - assuming, of course, that voltage supply feeding the digitizer itself can provide this amount of current - and then some for the digitizer itself, worst case.


The Trillium 120PA provides three "State-of-health" signals - U_MP, V_MP, W_MP - that indicates how well centered the three masses are. Maximum values are +/- 4.0 volt. The voltages reflect the amount of feedback coil DC current needed to keep the masses in center positions. If any voltage approaches 3.5 V, mass centering should be performed.

Principles of Velocity Broad Band seismometers are described in chapter 5 of New Manual of Seismological Observatory Practice (2002), revised version, electronically published 2009

Fig 5.17, p. 26, ch 5, NMOSOP

Reprinted fig 5.17, p. 26, ch 5 of the NMOSOP

The force-balance principle will in effect make the displacement transducer output ground acceleration. In fig. 5.17, the stage labelled "Displacement transducer with integrator" outputs Velocity - which is used as the seismic signal after transformation to X,Y,Z reference frame. Yet another integration yields Position - which reflect the amount of DC current applied to the Force Transducer in order to keep mass in centered position.

From this figure, one should conclude that the Velocity signal should NOT contain any offset that reflects the mentioned DC current in the Force Transducer. Of course, when the mass imbalance is so great that the DC current is unable to keep the mass centered, the Velocity signal will be influenced.

This argument is confirmed by observation - we can have large signals on the Mass Position output, and no offsets on the Velocity signals (keeping in mind the transformation needed to compare the two signal groups).

To summarize: We should not be able to see mass imbalance on the Velocity signals - until the imbalance is very great.

8.1 Auto-centering on Power-up

An electronic circuit placed in the junction box could automatically activate the Mass Centering line on power-up.

However, there are some problems with automatic centering when power is applied to the seismometer:

  1. Power supply ground is isolated from Digital ground - and mass centering command line is referenced to Digital ground. Digital and Power supply grounds can be connected - but we must prove that the seismic signals are not affected.
  2. Mass centering line is shared with RS-232 serial input line (from computer), some minor issues must be addressed here.
  3. The Mass Position signals are not stable until several minutes after power up - if there is an imbalance, the signals rises gradually from zero. Most likely, mass centering will not be executed properly if the command is given when power is applied - because mass position signals are not stable.


9.1 Connector pin-out, and setting the digitizer to ACTIVE HIGH mode


Trillium 120P/PA connector pinout, p. 57 of Trillium120P-PA_UserGuide_15149R6.pdf:

NOTE: Manual error - MASS POSITION SIGNALS specified to +/-4.0 V in table above, whereas specifications on p. 47 says +/-4.5V outputs.

Güralp DM24 sensor connector pinout, p. 284 of MAN-EAM-0003.pdf Issue E - Feb 2014:

And on page 224 there is the following explanation:

How to support ACTIVE HIGH sensors, as the Trillium 120PA.

9.2 Digitizer mass centering command

Mass centering can either be controlled by the digitizer web interface, or through the command line interface.

The command line provides both a high and low level interface. Ref page 227+ of the MAN-EAM-0003.pdf Issue E - Feb 2014 manual.

One question remains: How long is the duration of the MASS CENTERING command signal sent from the digitizer - and does it satisfy the requirement of the Trillium 120PA sensor? This must be determined by experiment - it's not stated in the digitizer documentation.

The sensor requires a MASS CENTERING signal of at least 1 second duration. Ref p. 35 in Trillium120P-PA_UserGuide_15149R6.pdf.

If the MASS CENTERING signal duration is not compatible with sensor requirement we can consider using the MASS UNLOCK signal instead, which is subject to direct on/off control.

9.3 Mass position interfacing

The Trillium 120PA sensor outputs single-ended UVW MASS POSITION signals in the +/- 4.5V range.

Digitizer specifications are given on p. 120 in the MAN-D24-0004.pdf manual. The MASS POSITION inputs are, however, not mentioned explicitly; one must assume they are categorized as MUX CHANNELS since they are single ended and not differential, thus they have +/- 10V input range, which accommodates the sensor MASS POSITION signal output range.

9.4 Using ANALOG or DIGITAL GROUND as reference for the MASS POSITION / CENTERING signals.


9.5 Draft specification, June 2015


9.6 Calibration test results

Click to enlarge.

Trillium / DM24 interface - calibration test. Click to enlarge.


10.1 Mass centering session, via DM24 web interface

Open DM24 web interface and examine mass position status:

Mass position status before mass centering.

Log in and click "Instrument Control" menu. You should see this:

DM24 web interface - instrument control page.

Allow some time for the system to complete mass centering - let's say 5 minutes - and check mass position status again. Notice the improvement.

Mass position status after centering.


11.1 When should Mass Centering of Trilllium seismometer model 120PA (or -QA) be initiated?

DM24 web "system status" shows mass positions as e.g. "-0.9% -- status 99%" (if good) and "-19.7% -- status 80%" (if not so good). However, we need to "calibrate" what these figures really mean in terms of voltage, because our authoritative guide with respect to allowed mass position ranges is the Trillium 120PA "User Manual" [Nanometrics P/N: 15149R6, release date 2009-05-06], and there everything is specified in terms of voltage levels. Quoting:

Page 33: "Trillium 120P/PA seismometers have three analog voltage outputs representing the DC currents applied to each of the three channel feedback coils. These are the mass position outputs, which cover a range of ±4 V."
Page 34: "Choosing When to Initiate Mass Centering: When the voltage of any of the three axis mass positions (analog signals U_MP, V_MP, and W_MP, referenced to AGND) approach ±3.5 V."
Page 34: "As one or more of the masses in a Trillium 120P/PA seismometer approach the range limit of ±4 V, the seismometer is subject to some degradation in performance. Low frequency self-noise increases by approximately 2 dB per V of mass position. Below ±1 V, the effect on noise is negligible. However, as the mass positions approach ±4 V, the noise level goes up to –173 dB m2/s4/Hz at 100 s period. Depending on the site and the type of study being conducted, this increase in the noise level may or may not be an issue."

Our emphasis. So we should attempt to limit any mass position voltage to ±1 V, just to be sure.

11.2 Measurements - calibration values

Applying voltages to Z-ch Mass Position (MP) input of DM24-EAM (cylinder version)
S/N: 3400/A2970
Test no. Input voltage
MP Z-ch only
Output reading
(on Web interface)
Screenshot documentation
Güralp DM24-EAM web interface
1  1.00 V   "10.3% -- status 89%"  Link
2 3.50 V "36.7% -- status 63%" Link
3 4.00 V  "41.5% -- status 58%" Link
4 5.00 V  "51.8% -- status 48%" Link
5 9.00 V  "93.3% -- status 6%" Link
6  -1.00 V   "-10.6% -- status 89%"  Link
7 -3.50 V  "-36.8% -- status 63%" Link
8 -4.00 V  "-42.0% -- status 58%" Link
9 -9.00 V  "-94.1% -- status 5%" Link
Highlighted: Recommended maximum level of Mass Position deviation from zero.


  • Seismometer: Trillium model 120QA, S/N: 2581
  • Digitizer: Güralp mod DM24-EAM, S/N: 3400_A2970
  • Link to digitizer data:
  • Interface cable documentation: Trillium120PA-DM24-EAM-Interface-draft-June2015.pdf
  • NOTE: Sensor is switched to raw UVW mode before calibration signals are injected, and set to ordinary XYZ mode afterwards. This transition can be seen as large signal transients on all three channels. However, the DM24-EAM calibration web interface refers to each channel as "Z", "E" and "N" and this channel designation is used in table below.
  • By: O.M., 17 January 2017
Test no. Time [UTC] Conditions Screenshot documentation
Güralp "Scream!" software
1 08:32:00
(repeated 08:52:00)
Broadband noise, all channels, amplitude 10%, duration 30s Click to enlarge.

Click to enlarge.

2 08:37:00 Broadband noise, all channels, amplitude 20%, duration 30s Click to enlarge.

Click to enlarge.

3 08:41:00 Broadband noise, Z only, amplitude 10%, duration 30s Click to enlarge.

Click to enlarge.

4 08:45:00 Broadband noise, N only, amplitude 10%, duration 30s Click to enlarge.

Click to enlarge.

5 08:48:00 Broadband noise, E only, amplitude 10%, duration 30s Click to enlarge.

Click to enlarge.

6 08:57:00 Sine, 10 Hz, all, amplitude 10%, duration 30s Click to enlarge.

Click to enlarge.

7 09:01:00 Sine, 10 Hz, all, amplitude 20%, duration 30s Click to enlarge.

Click to enlarge.

8 09:04:00 Sine, 10 Hz, Z only, amplitude 10%, duration 30s Click to enlarge.

Click to enlarge.

9 09:06:00 Sine, 10 Hz, N only, amplitude 10%, duration 30s Same as #8
10 09:08:30 Sine, 10 Hz, E only, amplitude 10%, duration 30s Same as #8
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Page last modified on February 06, 2020, at 02:21 PM
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