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First encounters

3.6 Using Baffles

Baffles are a useful tool to prevent convection currents in the borehole from
generating low-frequency oscillations.

The baffle consists of some large, deformable washers and spacer material attached
to a cable clamp. For best results, one should be installed on the signal & suspension
cable, half way between the sensor and the surge arrestor. Once in position, it should
be tightened onto the cable using the socket-head screws.

20

Issue G - November 2019

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Содержание 3TB

Страница 1: ...G ralp 3TB Operator s Guide Document No MAN BHO 0001 Issue G November 2019 Designed and manufactured by G ralp Systems Limited 3 Midas House Calleva Park Aldermaston RG7 8EA England...

Страница 2: ...ts 12 3 3 1 The break out box 12 3 3 2 The hand held control unit 14 3 3 3 The inclinometer monitor unit 16 3 4 Operating the hole lock 17 3 4 1 Disengaging the hole lock 18 3 5 The surge suppressor s...

Страница 3: ...Calibration with Scream 55 5 3 1 Sensor response codes for 3TB instruments 58 5 4 Calibration with a hand held control unit 58 5 5 The coil constant 58 6 Inside the 3TB 60 6 1 The sensors 60 6 2 The c...

Страница 4: ...ble for for any incidental or consequential damages resulting from the use of this document 1 2 Warnings Cautions and Notes Warnings cautions and notes are displayed and defined as follows Warning A b...

Страница 5: ...ss locking are carried out through a surface control box The 3TB s sensors are sensitive to ground vibrations across thee entire seismic spectrum with a flat response to velocity in the frequency rang...

Страница 6: ...ee jaw hole lock mechanism as required a pit head installation including a breakout box and a number of additional optional control units which may be connected to the breakout box to perform installa...

Страница 7: ...rs with identical response characteristics 2 2 Digital borehole installations The G ralp DM24 digitizer is available in a borehole sonde form Connecting a G ralp borehole instrument to a down hole dig...

Страница 8: ...modules mounted above and below it It is designed to maintain a positive pressure on the borehole casing over a prolonged period of time without attention and to fix the sonde in place whilst avoiding...

Страница 9: ...nts are very close to each other You should evaluate the various locking methods available to see which works best in your borehole The spring inside the lock provides around 60 kg of force at its loc...

Страница 10: ...than the single arm lock This is the standard option for uniaxial instruments it can be installed in boreholes between 99 mm 3 9 and 203 mm 8 in diameter The three jaw hole lock consists of a set of t...

Страница 11: ...curely packed and you will need to remove most of the foam packing before it can be removed 3TBs used to be delivered in sections which had to be assembled by the user They are now shipped complete an...

Страница 12: ...t have been supplied with your installation Their functions can be duplicated either by directly grounding control lines see appendixes for pin out information or through a connected G ralp digitizer...

Страница 13: ...boxes However its internal wiring is different from that used for some other instruments For this reason if you are using several instrument types you should mark each breakout box clearly so that it...

Страница 14: ...six seconds If the masses are locked the microcontroller will do nothing Otherwise it attempts to zero the output of the vertical E W and N S sensors in sequence by exerting a small extra force on th...

Страница 15: ...o the component you want to monitor You can set the range of the meter with the RANGE switch When switched to 10 V the meter ranges from 10 to 10 V as marked When switched to 1 V the range is 1 to 1 V...

Страница 16: ...e unlocking the sensor masses since too great a tilt can damage the components To measure the attitude of a 3TB instrument 1 Connect the inclinometer monitor unit to the CONTROL connector of the break...

Страница 17: ...s outlet power To operate the hole lock 1 Connect the hole lock control unit to the HOLELOCK POWER connector of the breakout box and to a mains power supply Alternatively connect a 12 24 V DC power su...

Страница 18: ...the current will drop to zero If using a deep borehole unit return the dial to zero 4 If the current has not dropped quite to zero after 30 40 seconds of operation release the switch wait a few secon...

Страница 19: ...lly be provided with an extra sonde combining a surge suppression system with a cable strain relief arm The surge suppressor sonde has the same connector as the instrument on its top face and a short...

Страница 20: ...llations The baffle consists of some large deformable washers and spacer material attached to a cable clamp For best results one should be installed on the signal suspension cable half way between the...

Страница 21: ...instrument Note In installations with a down hole digitizer the strain relief arm is fitted to the base of the digitizer sonde the phrase strain relief unit in the following instructions should be ta...

Страница 22: ...n page 17 If this fails you should contact G ralp Systems Extend the arm once more 3 If your system does not have a separate surge suppressor sonde fix the main lifting cable to the shackle on top of...

Страница 23: ...relief mechanism extended If not using a separate surge suppressor sonde tighten the cable clamps on the strain relief unit allowing a little slack in the signal cable 7 Fix the signal cable to the m...

Страница 24: ...sensor see Section 4 5 on page 39 so that it can be tested 14 Check that the sensor is functioning correctly by connecting a meter or monitoring device to the sensor outputs If the sensor fails to re...

Страница 25: ...at the bottom of the hole but also reduces noise due to air convection The ideal type of sand to use is the fine kiln dried sand used for children s play sandpits This is readily available in airtigh...

Страница 26: ...given by v r2h Also measure the internal diameter of the borehole 2 Measure and pour in a sufficient quantity of sand to fill the borehole to a depth of around 300 mm 3 Connect the signal cable to th...

Страница 27: ...sor sonde Caution Do not allow the signal cable or the surge suppressor cable to bear any of the sensor s weight 5 Attach the lifting loop to the sensor using four M5 16 screws provided 6 Join the loo...

Страница 28: ...e borehole mouth Set the depth gauge on the winch to zero 11 If using a baffle as described in section 3 6 on page 20 fit it now half way between the sonde and the strain relief 12 Calculate how much...

Страница 29: ...or is hanging vertically within the borehole and is no longer in contact with the sand bed At this point you may wish to use an inclinometer monitor unit to check that the instrument is sufficiently c...

Страница 30: ...G ralp System technical support via an email to support guralp com for advice There are two sections for each leg of the tripod The upper sections are pre attached to the head of the tripod the lower...

Страница 31: ...ing three outer strands from the 7 core cable crossing the two sets and splicing the three outside strands back around the remaining four in the opposite direction Secure the loop with a cable clamp 5...

Страница 32: ...egs in turn to the height you require leaving the leg with the winch attached until last 7 Take the end of the load bearing cable without the loop and screw it to the axle inside the winch using a 4 m...

Страница 33: ...larger hexagonal key 9 Wind the cable onto the winch by rotating the handle Ensure that the cable builds up neatly across the drum Continue winding until the loop on the other end is as high as you ne...

Страница 34: ...m any borehole instrument you must make sure that the sensor electronics its casing and the power supply share a common local ground and that all power and data lines are adequately protected against...

Страница 35: ...f from several suppliers On the sensor side surge protection is installed as standard within all new G ralp borehole sensors and control equipment If your surface installation includes third party ele...

Страница 36: ...best option is often to attach the sensor housing to an earth line brought out to the surface and attached to a metal stake driven into the ground nearby The sensor s load bearing cable is suitable f...

Страница 37: ...cable may make it impractical to use the borehole as an earthing point In these cases you will have to connect the local ground plate to an earth stake near to the enclosure any coupling between this...

Страница 38: ...r supply will couple to the sensor As with AC installations if the borehole is more than around thirty metres from the surface enclosure you will need to provide a second earthing point for the local...

Страница 39: ...point In any case the lightning earth must be well separated from the borehole and its earth if it needs one 4 5 Levelling and Centring Once it is installed you should level and centre the instrument...

Страница 40: ...eed to initiate the centring process several times before the masses are adequately centred 4 6 Down hole orientation Once the sensor is installed inside the borehole you will need to measure its orie...

Страница 41: ...crete base around the top of the borehole If this is present we recommend installing the reference sensor there A good coupling to bedrock is however more important than proximity so if there is a nea...

Страница 42: ...range would contain lots of teleseismic events and very little local noise You should use a period of at least an hour and preferably much longer 4 Hold down and drag across the WaveView window with...

Страница 43: ...and select Relative Orientation from the menu Two small windows will appear a progress window and typically a warning like Scream produces this warning when the reference sensor is not using a standar...

Страница 44: ...ates the N S and E W components of the sensor being tested in small steps It measures first the amplitude similarity and then the coherence between the virtual rotated N S component and the reference...

Страница 45: ...ent is installed with its N S axis at a bearing of 90 from true North 7 The second window shows the result of applying the rotation to the signal i e the time series that a sensor in perfect N S orien...

Страница 46: ...or is in the installation of the reference sensor If you have particular difficulty in deriving a stable value additional information is contained in a third output window which shows a waterfall plot...

Страница 47: ...gure a DM24 mk3 digitizer to apply an automatic rotation to the digitized data and output streams representing ground motion on true North South and East West axes This is done within the DSP to minim...

Страница 48: ...rue North that you measured earlier as a whole number of tenths of a degree This is the same angle with the same sign as that given by the orientation program The 0 tells the digitizer to apply the ro...

Страница 49: ...ore data with the transformation active and carry out another orientation calculation The data from the down hole instrument should now have a maximum coherence with the reference sensor at 0 Check in...

Страница 50: ...ll be twice the true sensitivity of the instrument To remind you of this the sensitivities are given as 2 single ended sensitivity in each case Mass Position Output The sensitivity of the mass positio...

Страница 51: ...t A is calculated at a normalising frequency value fm 1 Hz with s j fm where j 1 H s is the transfer function of the sensor which can be expressed in factored form In this equation zn are the roots of...

Страница 52: ...xperiments Each plot marks the low frequency and high frequency cut off values also known as 3 dB or half power points If you want to repeat the calibration to obtain more precise values at a frequenc...

Страница 53: ...omain The amplitude and phase response can then be calculated using a Fourier transform Because the input signal has predominantly low frequency components this method generally gives poor results How...

Страница 54: ...itizers provide calibration signal generators to help you set up your sensors Calibration is most easily done through a PC running G ralp s Scream software Depending on the digitizer type sine wave st...

Страница 55: ...urated retry using a calibration signal with lower amplitude until the entire curve is visible in the Waveview window 5 If you need to scale one but not another of the traces right click on the trace...

Страница 56: ...the Scream documentation for more information 9 Click The script will return with a graph showing the responsivity of the sensor in terms of amplitude and phase plots for each component if appropriate...

Страница 57: ...nal f is the signal frequency R is the magnitude of the calibration resistor and K is the feedback coil constant R and K are both given on the calibration sheet supplied with the 3TB The calibration r...

Страница 58: ...eleration for each of the tilt angles used and plot a graph of mass position output against input acceleration 5 The gradient of the line obtained gives the sensitivity of the coil in V m s2 if g was...

Страница 59: ...w for simple and accurate assembly The base of each unit includes a double O ring to isolate the sensor from any pressure variations in the atmosphere The 3TB functions by monitoring the position of e...

Страница 60: ...eceives control signals which are used to clamp and un clamp the masses and to run the motors which level and centre the instrument once in position Finally a line is provided for you to apply a calib...

Страница 61: ...the lines are controlled from the break out box Hand held Control Unit or digitizer If you send control signals to the 3TB manually you must ensure that the lines are allowed to float high after send...

Страница 62: ...ring each stage but goes out briefly between stages allowing you to follow the progress of the lock 6 2 2 UNLOCK This command unlocks the sensor masses and prepares the instrument to begin operating I...

Страница 63: ...vel position This process takes rather longer At some point during this stage the mass may flip to the other side as seen in the green trace 5 The N S sensor mass is centred by applying pulses to the...

Страница 64: ...in the controller monitors the mass position sensor and stops the centring process once it reaches its lowest offset This graph shows a typical centring process 1 The BUSY LED pulses to indicate that...

Страница 65: ...nal to the displacement of the mass from its equilibrium position After amplification this voltage generates a current in the force transducer coil which tends to force the mass back toward equilibriu...

Страница 66: ...is flat to ground acceleration above it the response is flat to velocity Other values for the acceleration velocity corner can be provided upon request Hybrid feedback systems provide a stable respon...

Страница 67: ...amping constant of 0 707 1 2 The seismometer can be supplied with an equivalent resonant frequency of 0 033 Hz 30 s 0 01 Hz 100 s or 0 0083 Hz 120 s as required An active low pass filter provides a hi...

Страница 68: ...G ralp 3TB Inside the 3TB MAN BHO 0001 68 Issue G November 2019...

Страница 69: ...nufacturer Suitable mating connectors have part numbers like 12 10P and are available from Amphenol ITT Cannon and other manufacturers Pin Function A Power supply 0 V B Power supply ve 12 24 V DC C no...

Страница 70: ...Z P Calibration signal all channels B Velocity inverting Z R Calibration enable all channels C Velocity non inverting N S S Inclinometer output X D Velocity inverting N S T Inclinometer output Y E Ve...

Страница 71: ...l all channels B Velocity inverting Z R Calibration enable all channels C Velocity non inverting N S S Inclinometer output X D Velocity inverting N S T Inclinometer output Y E Velocity non inverting E...

Страница 72: ...y 0 V V not connected F Mass position Z Y Lock G Mass position N S Z Unlock H Mass position E W a not connected J Velocity non inverting Z b Acceleration Velocity mode K Velocity inverting Z c not con...

Страница 73: ...V ms 2 Controls Mass locking and unlocking remotely operated Mass centring microprocessor controlled Mechanics and electronics Sensors 3 orthogonal sensors each 0 180 kg Lowest spurious resonance abo...

Страница 74: ...of spec would be 30 s 0 033 Hz Sensors are available with a range of sensitivities between 2 750 and 2 10 000 V ms 1 Because centring locking and unlocking consume varying amounts of power it is reco...

Страница 75: ...s 2018 03 12 F Removed direct from pin outs 2017 11 06 E Added baffle details 2016 01 02 Face lift with no significant content changes 2013 04 17 D Added surge arrestor stress relief details 2006 11 1...

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