Guralp-systems CMG-3T Manuel d'utilisateur Page 1

CMG-3TTriaxial Broadband SeismometerOperator's guidePart No. MAN-030-0001Designed and manufactured byGüralp Systems Limited3 Midas House, Calleva

CMG-3Tpower will be supplied through the digitizer, which can also activate the sensor control lines.The breakout box also provides a CONTROL

Operator's guideTemporary installations can be protected against spurious vibrations by• selecting a suitable site,• placing the instrument in a

CMG-3TIf you cannot easily see the pointers, you should align the sensor using the north arrow on the handle. Howe

Operator's guideyou are using one.7. Connect a 12 Volt power supply, either directly or through the breakout box or digitizer.8. Unlock the sens

CMG-3T11.Ensure that the sensor cable is loose and that it exits the seismometer enclosure at the base of the instrument. This w

Operator's guide2. On granite or other hard bedrock, use an angle grinder to plane off the bedrock at the pit bottom so that it is flat and level

CMG-3Tprepare a concrete mix with sand and fine grit, and pour it into the hole. Agitate (“puddle”) it whilst still liquid, to allow it to flow out an

Operator's guideSome installations introduce a layer of ceramic tiles between a rock or concrete plinth and the seismometer (left): However, no

CMG-3TBy following these guidelines, you will ensure that your seismic installation is ready to produce the highest quality data.2.5

Operator's guidecrushed rock, with a high proportion of rock flour and fine particles, makes excellent packing material. Alternativ

CMG-3TTable of Contents1 Introduction...31

CMG-3T3 Calibrating the 3T3.1 The calibration packAll Güralp sensors are fully calibrated before they leave the factory. Both absolute and relative ca

Operator's guidePoles and zeroesMost users of seismometers find it convenient to consider the sensor as a “black box”, which produces an output s

CMG-3TFrequency response curvesThe frequency response of each component of the 3T is described in the normalised amplitude and phase plots provided. T

Operator's guide3.2 Calibration methodsVelocity sensors such as the 3T are not sensitive to constant DC levels, either as a result of their desig

CMG-3Tcalibration will be used to determine the complete sensor response in one action. Please refer to the digitizer's manual for information on

Operator's guidetop left of the window or the cursor keys.Drag the calibration stream Cn up the Waveview window, so that it is at the top.4. If

CMG-3TMost data can be found on the calibration sheet for your sensor. Under Instrument response, you should fill in the sensor respons

Operator's guideinformation is present in higher-rate streams, they also include a large amount of high-frequency data which may

CMG-3TSensor Sensor type codeUnits (V/A)CMG-3T, 360s – 50 Hz responseCMG-3_360S_50HZ VCMG-3TB or 3V / 3ESP borehole,30s – 50 Hz responseCMG-3B_30S_50H

Operator's guide3. Repeat this measurement for several tilt angles.4. For the vertical sensor, the input acceleration is given

Operator's guide1 IntroductionThe CMG-3T is a three-axis seismometer consisting of three sensors in a sealed case, which can measure

CMG-3T4 Accessories4.1 The breakout boxThis unit separates the lines in the signal cable, so you can connect a power supply, a recording system, and t

Operator's guideout, the instrument is ready for transportation.• To re-centre the sensor masses, hold down the ENABLE and CENTRE button

CMG-3Tvelocity output. There is also a RANGE switch allowing you to alter the sensitivity of the meter.CalibrationThe hand-held control unit can be us

Operator's guide• the left-hand two sockets expose the balanced differential outputs representing ground velocity, and• the right-h

CMG-3T• To unlock the sensor masses, hold down the ENABLE and UNLOCK buttons simultaneously for one second. The BUSY LED will light.

Operator's guide5 Inside the 3T5.1 The sensorsThe horizontal and vertical sensors are similar in design. The inertial mass in both cases

CMG-3TThe signal voltages output by the 3T are proportional to ground velocity and are transmitted from the instrument

Operator's guideadjustment motors. It responds to commands sent on three input lines by grounding for 0.2 – 7 seconds.The signals you can send

CMG-3TThe five-stage process comprises locking the Z, N/S and E/W masses, followed by longer periods tilting the N/S and E/W sensor base to their

Operator's guideAgain, you can use the BUSY LED to monitor the progress of unlocking.1. The instrument checks to see

CMG-3TThe seismometer unit is self-contained apart from its 12 Volt power supply. Centring and mass locking can be carried out by

CMG-3Tsensor indicates an offset close to zero. In the case of the horizontal sensors, the sensor frame is tilted on its base plate.

Operator's guideactivating the CENTRE command again. You will probably need to initiate the centring process several times

CMG-3Twith OK. If there was a problem, such as one or more components failing to unlock or centre, the controller will report NG (“no good”.)L LockS

Operator's guideand damping of the sensor is completely determined by a feedback loop which applies a force to the sensor mass opposing any motio

CMG-3TThe hybrid feedback circuit contains a single capacitor in parallel with a resistor, resulting in a single dominant pole. Below this frequency,

Operator's guideThe conventional-response feedback system has an additional parallel feedback circuit, consisting of a non-inverting integrator i

CMG-3T 46 Issue N

Operator's guide6 Connector pin-outs6.1 Sensor and control unit pin outputModels with a 26-pin mil-spec plug (02E-16-26P) have the following pin

CMG-3Tc Power +veIn sensors with the RS232 control interface option, the RS232 ground line (pin H) is isolated from the other ground lines (pins Z and

Operator's guide26 RS232 ground (RS232 control interface option)In sensors with the RS232 control interface option, the RS232 ground line (pin 26

Operator's guideAs an option, the 3T can be supplied with a 26-way “D”-type connector with standard pin assignments (see se

CMG-3T9 RS232 receive at instrument (RS232 control interface option)10 Calibration signal (all channels)11 Calibration enable, N/S channel12 Calibrati

Operator's guide7 SpecificationsHybrid sensors Velocity output bandwidth 0.1 – 50 Hz High pass filter output flat to acceleration0.01 Hz – spec*

CMG-3Tcentring (average) Current at 12 V DC during locking and unlocking490 mA†*spec refers to the quoted frequency response value, e.g., for a “30 s”

Operator's guide8 Revision history2009-07-06 N Added integrated SOH controller2006-10-19 M Added waterproof connector pin-out2006-08-14 L Added R

CMG-3TSensor responseThe 3T can be supplied with a response which is flat to velocity from 100 Hz to any of 0.1 Hz (10 seconds), 0.033 Hz (30 seconds)

Operator's guide2 Installing the 3T2.1 First encountersUnpackingThe 3T seismometer is delivered in a single transportation case. The packaging is

CMG-3TSerial numberThe sensor's serial number can be found on the label stuck to the top lid of the sensor. It is also stamped onto the side of t

Operator's guideboard ADCs.Breakout box and hand-held control unitThe 3T can be supplied with an optional robust breakout box, which provides m