CMG-5T - Guralp Systems Ltd
Contents
1. 2 2 Initial testing To test the 5T before installation you will need a power source which can deliver 100 mA at 10 to 36 V and a digital voltmeter DVM with 1 and 10 V ranges Also ensure that the supplied cable is connected with the correct polarity see the Appendices To make it easier to measure the output from the sensor you can use a hand held Control Unit or a custom interface box which can be manufactured from a screw clamp connector block This will simplify the connections to the appropriate connector pin outputs 1 Place the 5T sensor on a flat horizontal surface 2 Connect the power supply observing the correct polarity for the cable supplied and switch on 3 Connect the voltmeter to pins L and M of the output connector corresponding to the low gain vertical component Measure the output of the low gain vertical component The steady output voltage should be about zero 10 mV 4 Repeat the measurement for the N S and E W low gain component outputs pins C D and K U respectively 5 Now gently turn the sensor onto its side propping it carefully to prevent rolling 6 The low gain vertical component should now read about 5 V corresponding to 1g 7 Roll the instrument until the N S line is vertical with N at the top 8 The low gain N S component should now read 5 V corresponding to 1g 9 Roll the instrument until the N S line is horizontal 10 The low gain E W component should no2. CMG 5T Triaxial Accelerometer Operator s guide Part No MAN 050 0001 Designed and manufactured by G ralp Systems Limited 3 Midas House Calleva Park Aldermaston RG7 8EA England Proprietary Notice The information in this manual is proprietary to G ralp Systems Limited and may not be copied or distributed outside the approved recipient s organisation without the approval of G ralp Systems Limited G ralp Systems Limited shall not be liable for technical or editorial errors or omissions made herein nor for incidental or consequential damages resulting from the furnishing performance or usage of this material Issue E 2009 12 14 CMG 5T Table of Contents T Tir UCU OW sa oxossadactisiedencnoinntacineathewhe ispa ni e printed aera EEES EEE aE Ea TEENE 3 2 Installation sarre eE E EEEE E eE eE E e ea A rS REE eai 5 2 1 Unpacking and packing eeesseessssssisssriesrrrestrrssrersstesssttesttresttessreeseseesstresrereress 5 2 2 Ipitialtesting serisini i E ENE E E TR 6 2 3 Installing the sensof ononido Ea iea A R a E a i 7 DA Genting the ST eei aeaniee e ii EEE EOE EE A A EEEE AS 8 2 5 Electrical Connet on Senese it ENO OE E E AEN 9 BS Gali br atti M EEE dvasceses 12 3 1 Absolute calibratid Dessiner rset snnisen ates ERE EE EORR 12 3 2 Relative calibration ssesssssesssessessssrerrssssrresssttessstttesssstttessseteeessseeeseteesssss 12 3 3 Calibrating acceleroMeters ys isciisiiscvesiscaisesatarneseeisvirros nevvea
3. Remove the screwed cover protecting the level adjusters The cavity contains three adjustment screws which are arranged as shown in the diagram below SEALED CAP FOR ADJUSTMENT SCREWS OFFSET ADJUSTMENT SCREWS THE OFFSET ADJUSTMENT SCREWS ARE PROTECTED BY A SEALEO CAP UNSCREW AND REMOVE THE CAP TO REVEAL THE ADJUSTMENT SCREWS EACH SCREW ADJUSTS ONE SENSOR WHICH SENSOR CORESPONDS TO WHICH SCREW IS SHOWN IN THE DETAIL ABOVE ENSURE THAT THE CAP tS REPLACED AND TIGHTENED DOWN FULLY WHEN ADJUSTMENT IS COMPLETE TO ENSURE PROPER PROTECTION 2 Power up the sensor and connect a digital multimeter to its low gain vertical outputs pins L and M Alternatively use a G ralp Systems CMG 5T hand held control unit to monitor the outputs more easily 3 Adjust the vertical screw until the output voltage reads zero NNS Repeat steps 2 and 3 for the N S and E W channels pins C D and K U respectively 5 If necessary continue to adjust each channel in turn until consistent results are obtained on all three channels 6 Repeat steps 2 to 5 using the high gain outputs if available and refine the settings as far as possible 7 Replace the protective cover firmly to keep the instrument s electronics protected from water and dust After the cover is installed the accelerometer outputs may drift until the system establishes temperature equilibrium with its environment and the sensor settles down in its position If required the
4. offset adjustment can be repeated to achieve a better output offset With experience it should be possible to reduce the output level to less than 1mV 2 5 Electrical connections Each channel inside the 5T sensor has four output lines a pair of December 2009 9 CMG 5T differential outputs with low gain and another pair with high around x 10 gain Optionally the second gain block can be configured at the factory to act as a high pass filter to remove the DC offset at the output terminal If this is the case the gain at these outputs will be set to x 1 unity with a separate circuit board providing a filter with a corner frequency of 0 05 Hz 20 s or 0 025 Hz 40 s The output offsets of a high pass output cannot be zeroed using the DC offset adjustment screws in any case this offset should not be more than 1 mV The high pass output is likely to take around five times the time constant of the high pass circuit to settle down This time constant is provided on the calibration sheet together with accurately measured frequency values The two pairs of output lines are balanced about signal ground so that either differential drive or single ended drives of opposite polarity phase are available For a single ended drive the signal ground must be used as the signal return path You must not ground any of the active output lines as this would allow damaging currents to flow through the output circuits Also if single en
5. used not connected Low gain ve E W channel Open closed loop all channels High gain ve E W channel Low gain ve E W channel Wiring details for the compatible socket _14 19S as seen from the cable end 22 Issue E Operator s Guide 6 2 5T high pass filter output option The following table applies if the second amplification stage is being used to provide a high pass filter with unity gain The same connector is used and the connector information above in Section 6 1 applies Pin Function geao tomas cme alle de Sanoo ago S High pass filtered acceleration ve N S channel High pass filtered acceleration ve N S channel Acceleration ve N S channel Acceleration ve N S channel Calibration signal all channels Power 12 V all channels Power 0 V all channels Power 12 V all channels Open closed loop all channels Acceleration ve E W channel Acceleration ve vertical channel Acceleration ve vertical channel High pass filtered acceleration ve vertical channel High pass filtered acceleration ve vertical channel High pass filtered acceleration ve E W channel Calibration enable all channels Signal ground essential if a long power cable is used Acceleration ve E W channel High pass filtered acceleration ve E W channel December 2009 23 CMG 5T 7 Specifications 24 Outputs and response Calibration controls Physical Power
6. E S i S EERE macra zo EON qra y g 2 oss Hz anot o sala TS aN 3380 82 Y axis value H of single X Marker on PIN TETEE TRACE B Sensor Serial Number The sensor transfer function Most users of seismometers find it convenient to consider the sensor as a black box which produces an output signal V from a measured input x So long as the relationship between V and x is known the details of the internal mechanics and electronics can be disregarded This relationship given in terms of the Laplace variable s takes the form V x s GXxA xX H s In this equation G is the acceleration output sensitivity gain constant of the instrument This relates the actual output to the desired input over the flat portion of the frequency response e A is a constant which is evaluated so that A X H s is dimensionless and has a value of 1 over the flat portion of the frequency response In practice it is possible to design a system transfer function with a very wide range flat frequency response The normalising constant A is calculated at a normalising frequency value fm 1 Hz with s j fm where j v 1 H s is the transfer function of the sensor which can be expressed in factored form December 2009 19 CMG 5T 20 N Me 5 4 H s N EEE In this equation zn are the roots of the numerator polynomial giving the zeros of the transfer function and pm are the roots of the denominator polynomial giving the poles of
7. Low gain output options Corresponding high gain outputs Dynamic range at 2 g Dynamic range 0 005 0 05 Hz Dynamic range 3 30 Hz Standard frequency band Optional low pass corner Linearity Cross axis rejection Open loop response Closed loop response Step function response External inputs Lowest spurious resonance Operating temperature range Pressure jacket material Power signal connector Weight Current at 12 V DC 2g 1g 0 5g 0 1g 0 2g 0 1g 0 05g 0 01g standard lt 140 dB lt 127 dB DC 100 Hz 3dB point 50 100 or 200 Hz 0 1 of full scale 0 001g g pin on connector pin on connector may be added to open and closed loop calibrations Sine wave step or pseudo random 450 Hz 20 to 70 C hard anodised aluminium Mil spec connector on sensor housing 02E 14 19P 2 2708 8 mA per axis Issue E Operator s Guide 8 Revision history 1009 12 14 2009 10 05 2007 11 20 added 2006 09 22 2006 01 06 December 2009 E Revised calibration section and new internals diagram Additional connector information and some purely cosmetic changes Installation in hazardous environments section Added revision history New document 25
8. ces The CU can also trim DC offsets during installation if required It is available in both rack mounted and water resistant portable formats The accelerometer housing itself is completely waterproof with a hard anodised aluminium body and O ring seals throughout The photograph below shows two instruments under test by long period total immersion in a tank of water 4 Issue E Operator s Guide 2 Installation 2 1 Unpacking and packing The CMG 5T accelerometer is delivered in a single cardboard box with foam rubber lining The packaging is specifically designed for the 5T and should be reused whenever you need to transport the sensor Please note any damage to the packaging when you receive the equipment and unpack on a clean surface The package should contain the accelerometer a signal connection cable if ordered and a connector of type O6F 14 19S Place the accelerometer on a clean surface and identify The signal cable connector on the top of the unit The N S orientation line engraved on the lid The N S orientation pointers studs The bubble level The screw on cover for the output offset adjuster see below December 2009 5 CMG 5T The central hole for the main fixing bolt and The serial number If you need to request the sensor production history you will need to quote either the serial number of the sensor or the works order number which is also provided on the calibration sheet
9. cording to the following diagram Offset adjustment UCC ee TEE PO ee OEE Phase splitter Wien bridge square wave oscillator High gain i amplifier gt or High gain high pass i outputs filter Pre amp Phase Initial sensitive gain detector raf stage gt Low gain Capacitive outputs displacement rt transducer io A Phase i m compensator F Gain OO z resistor Open Ower closed amp loop OD i Constant flux signal force Calibration i transducer enable annnnnunnnsnnnnnnnns December 2009 17 CMG 5T The mass and the capacitor plates are energised by a two phase transformer driver forming a differential capacitor This acts as a capacitive transducer whose signal is then demodulated with a phase sensitive detector The accelerometer feedback loop is completed with a feedback loop compensator and a feedback force transducer power amp The differential output amplifier scales the output sensor sensitivity and a second stage amplifier can be configured at the factory either as a further cascaded gain stage or as a high pass filter with unity gain 4 1 The force transducer The CMG 5T is a force feedback strong motion accelerometer which uses a coil and magnet system to generate the restoring feedback force Such accelerometers inherently depend on the production of a constant strength field in the magnet gap Although the high quality magnets us
10. ded outputs are used the positive acceleration outputs must be interfaced to the recorder For distances up to 10 metres you can connect the sensor outputs using balanced screened twin lines terminated with a high impedance differential input amplifier The sensor outputs have a nominal impedance of 47 Q The 5T is normally powered directly from a connected Giralp digitizer through the 10 way connector although you can use a separate 10 36 V DC power supply if you wish The current consumption from a 12 V supply is about 53 mA An isolated DC DC converter installed inside the sensor housing forms the main part of the 5T unit s power supply its filtered outputs provide the 12 V required to operate the sensor electronics The DC DC converter is protected against polarity reversal The calibration signal and calibration enable inputs are referenced to the signal ground If you are using a G ralp digitizer these lines can be connected directly to its calibration lines Otherwise you will need to provide a 5 V logic level on the calibration enable input in order to calibrate the instrument The signal ground line is used as the return for both calibration enable and calibration signal lines See Chapter 3 for more details Modifying the sensitivity This section applies to instruments before serial number T5225 only 10 Issue E Operator s Guide The primary gain block of the 5T is normally set at x 1 unity If higher sensitivit
11. e response of the sensor traces out a sinusoid over time which is calibrated at the factory to range smoothly from 1g to 1g without clipping 3 2 Relative calibration The response of the sensor together with several other variables is measured at the factory The values obtained are documented on the sensor s calibration sheet Using these you can convert directly from voltage or counts as measured in Scream to acceleration values and back You can check any of these values by performing calibration experiments G ralp sensors and digitizers are calibrated as described below ground movement Calibration Sensor Injection Output Calibration Signal Calibration Digitisation 0 signal Generator Oo Calibration enable 12 Issue E Operator s Guide In this diagram a G ralp digitizer is being used to inject a calibration signal into the sensor This can be either a sine wave a step function or broad band noise depending on your requirements As well as going to the sensor the calibration signal is returned to the digitizer on a full rate channel older digitizers used one of the 4 Hz auxiliary Mux channels The calibration signals and sensor output all travel down the same cable from the sensor to an analogue input port on the digitizer The signal injected into the sensor gives rise to an equivalent acceleration EA on the above diagram which is added to the measured acceleration t
12. ed in the 5T accelerometer are exceedingly stable under normal conditions if the sensor is sited in an area where the background seismic noise is much higher than that of vaults built in seismically stable locations the flux density may be affected by the external magnetic field generated by the feedback transducer coil In order to minimise non linearities in the feedback force transducer the 5T uses a symmetrical system of two magnets and two force coils Any increase in flux in one coil is cancelled by a corresponding decrease in flux in the other thus eliminating any non linearity due to lack of symmetry 4 2 Frequency response The frequency response of each component is provided as amplitude and phase plots When testing the instrument to confirm that it meets its design specification the range of frequencies used are concentrated over about 3 decades i e 1000 1 of excitation frequencies Consequently the frequency plots of each component are provided in normalised form Each plot marks the frequency cut off value often quoted as 3dB or half power point G ralp Systems performs frequency response tests on every sensor at the time of manufacture All records are archived for future reference 18 Issue E Operator s Guide Y axis value Value of single of singleX X Marker Value of single Y Marker X Marker Marker on TRACE A Y Marker a 3413 aB a eT SRT H T TTT Zs dB ain in a D D D
13. ed joints between them and a hole drilled for the connector You can then use high grade glass fibre sealing tape to fix the leads in position and fasten the box to the mounting surface Commercial duct sealing tape is ideal 5 Connect the sensor to your digitizing equipment or Control Unit to start receiving signals Temporary installations 5T sensors are ideal for monitoring vibrations at field sites owing to their ruggedness high sensitivity and ease of deployment Temporary installations will usually be in hand dug pits or machine augered holes Once a level base is made in the floor the accelerometer can be sited there and covered with a box or bucket One way to produce a level base is to use a hard setting liquid December 2009 7 CMG 5T 1 Prepare a quick setting cement sand mixture and pour it into the hole 2 Puddle the cement by vibrating it until it is fully liquefied allowing its surface to level out 3 Depending on the temperature and type of cement used the mixture will set over the next 2 to 12 hours 4 Install the sensor as above cover and back fill the emplacement with soil sand or polystyrene beads 5 Cover the hole with a turf capped board to exclude wind noise and provide a stable thermal environment If you prefer you can use quicker setting plaster or polyester mixtures to provide a mounting surface However you must take care to prevent the liquid leaking away by proofing the
14. eosaipensrstecowesatousens ences 13 4 Inside the STren enean naaa Ete rE E REEE EER 17 4 1 The force trans du Ger reitindcvsissbeveesevsunevevsouastuteecuns vevusensch tevin ack ewevoneternianwasoecevteas 18 4 2 FREQUENCY TESPOTISC ccasssccssvosesvcuspeneduovsnouns uexsseemevenes ve nepesscuepesmevernsasustensbinceeausices 18 5 Calibration informati n erann reae aa 21 5 1 Calta tins MC ts 55 a ascinycnarynvstibeins xi duane eerie a aE E EATEN EE REEERE 21 5 2 Poles and zeroes aississs cessvvevaecevsdsevnctovineatsintu devs duonavaxtbauney coninutoeteastontuniers veepuravinee 21 6 Connector PUNO EG reeeo aeaoe rE Easa hack tiedeacaecdnen tates tev paeeucasebontemeeaiiees 22 6 1 5Ts with high gain output Options cssisiswsceicrssarcudsreosieibieinaasieaia sens 22 6 2 5T high pass filter output Opin pinsynctiavienbacairunsnwesvemreueavinbas 23 7 Specifications cic asicavdecesiericae issn iriiria ieii aianei iirin iise 24 8 Revision Wistory iss ccscccsctisccncaedacecstclasesicl A E A a E 25 2 Issue E Operator s Guide 1 Introduction The CMG 5T accelerometer is a three axis strong motion force feedback accelerometer in a sealed case The sensor system is self contained except for its 10 36V power supply which can be provided through the same cable as the analogue data An internal DC DC converter ensures that the sensor is completely isolated The 5T system combines low noise components with high feedback loop gain to provide a l
15. hole beforehand Dental plaster or similar mixtures may need reinforcing with sacking or muslin Installation in Hazardous environments The fully enclosed aluminium case design of the 5T instrument makes it suitable for use in hazardous environments where electrical discharges due to the build up of static charge could lead to the ignition of flammable gasses To ensure safe operation in these conditions the metal case of the instrument must be electrically bonded earthed to the structure on which it is mounted forming a path to safely discharge static charge Where electrical bonding earthing is required during the installation of a 5T instrument the central mounting hole that extends through the instrument should be used as the connection point This is electrically connected to all other parts of the sensor case Connection can be made by either a cable from a local earthing point terminated in a 8mm ring tag or via the mounting bolt itself 2 4 Centring the 5T Once it is installed you should centre the instrument ready for use The offset can be as much as the entire output range of the accelerometer which corresponds to around 1 from the horizontal or vertical You can check that the 5T is within this range by using the bubble level on the top of the casing as long as the bubble lies completely within the scribed ring the remaining adjustments can be made internally 8 Issue E Operator s Guide 1
16. inear precision transducer with a very large dynamic range In order to exploit the whole dynamic range two separate outputs are provided one with high gain and one with low gain Nominally the high gain outputs are set to output a signal 10 times stronger than that from the low gain outputs The 5T sensor outputs are all differential with an output impedance of 47 Q A single signal ground line is provided as a return line for all the sensor outputs Full scale low gain sensitivity is available from 4 0g down to 0 1g The most common configuration is for the 5T unit to output 5 V single ended output for 1 g 9 81 ms input acceleration The standard December 2009 3 CMG 5T frequency pass band is flat to acceleration from DC to 100 Hz although other low pass corners from 50 Hz to 100 Hz can be ordered A high frequency option provides flat response from DC to 200 Hz Each seismometer is delivered with a detailed calibration sheet showing its serial number measured frequency response in both the long period and the short period sections of the seismic spectrum sensor DC calibration levels and the transfer function in poles zeros notation Installation is simple using a single fixing bolt to fix the sensor onto any surface No sensor levelling is required Optionally you can use a G ralp Control Unit CU and Breakout Box BB to distribute power and calibration signals to the sensor and to receive the signals it produ
17. mation on how to use a DM24 series digitizer please see its own documentation If you are using a third party digitizer you can still calibrate the instrument as long as you activate the Calibration enable line correctly and supply the correct voltages 1 In Scream s main window right click on the digitizer s icon and select Control Open the Calibration pane December 2009 13 CMG 5T 2 Select the calibration channel corresponding to the instrument make any other choices you require and click Inject now A new data stream ending Cn n O 7 or MB should appear in Scream s main window containing the returned calibration signal 3 Open a Waveview window on the calibration signal and the returned streams by selecting them and double clicking The streams should display the calibration signal combined with the sensors own measurements If you cannot see the calibration signal zoom into the Waveview using the scaling icons at the top left of the window or the cursor keys 4 If you need to scale one but not another of the traces right click on the trace and select Scale You can then type in a suitable scale factor for that trace 5 Click on Ampl Cursors in the top right hand corner of the window A white square will appear inside the Waveview at the top left This is in fact two superimposed cursors 6 Drag one cursor down to be level with the lowest point of the signal trace 7 Drag the other dow
18. n to be level with the highest point In the following example a step function of 1 minute duration has been applied to the Z3 stream Note that ground movements continue to be observed superimposed on the returning calibration signal 02 03 2004 12 53 17 Ce 11 gt 44 PE er EB oe amp v Time cursors 704 512 2 44 12 45 12 46 8 14 Issue E Operator s Guide The Ampl Cursors button will now be displaying a value which is the strength of the returning signal in counts doubled if using a sine wave Measure the other two signal strengths in this manner Note that if you have used the Scale option described above you will need to take the scale factor into account to produce the correct number of counts In the example the MB calibration input signal has been scaled by a factor of 40 so the signal strength as measured by the Ampl Cursors must be divided by 40 to yield the correct value 8 Convert to volts using the uV Bit values given on the digitizer s calibration sheet for the various input ports and compare the returned signal with the input calibration signal MB 9 In the example the following data are now known Input calibration signal strength MB 697 221 counts Returning signal strength Z3 701 512 counts The calibration sheets provide us with the remaining values needed to calibrate the sensor Sensor acceleration response 0 254 V ms Equivalent accel from 1V calibration 1 968 ms Digi
19. o provide the sensor output Because the injection circuitry can be a source of noise a Calibration enable line from the digitizer is provided which disconnects the calibration circuit when it is not required Depending on the factory settings the Calibration enable line must be either allowed to float high 5 to 10 V or held low 0V signal ground during calibration this is specified on the sensor s calibration sheet The equivalent acceleration corresponding to 1 V of signal at the calibration input is measured at the factory and can be found on the sensor calibration sheet The calibration sheet for the digitizer documents the number of counts corresponding to 1 V of signal at each input port The sensor transmits the signal differentially over two separate lines and the digitizer subtracts one from the other to improve the signal to noise ratio by increasing common mode rejection As a result of this the sensor output should be halved to give the true acceleration CMG 5T instruments are tuned at the factory to produce 1 V of output for 1 V input on the calibration channel For example a sensor with an acceleration response of 0 25 V ms should produce 1 V output given a 1 V calibration signal corresponding to 1 0 25 4 ms 0 408 g of equivalent acceleration 3 3 Calibrating accelerometers Both the DM24 digitizer and Scream software allow direct configuration and control of any attached G ralp instruments For full infor
20. r If required you can use the poles and zeroes to derive the true ground motion mathematically from the signal received at the sensor The 5T is designed to provide a flat response to within 3dB over its passband For example the following curve describes the frequency response of a 100 Hz sensor Magnitude dB J 9 F L 10 10 10 10 10 Pha December 2009 21 CMG 5T 6 Connector pinouts 6 1 5Ts with high gain output option The 5T sensor has a single connector for both power and signal output The following details apply if the second amplification stage is being used to provide a high 10 x gain output channel This is a standard 19 pin mil spec plug conforming to MIL DTL 26482 formerly MIL C 26482 A typical part number is 02E 14 19P although the initial 02E varies with manufacturer Suitable mating connectors have part numbers like 14 19S and are available from Amphenol ITT Cannon and other manufacturers Function Pin Function High gain ve N S channel L Low gain ve vertical channel High gain ve N S channel Low gain ve vertical channel Low gain ve N S channel High gain ve vertical channel Low gain ve N S channel High gain ve vertical channel Calibration signal all channels High gain ve E W channel Power 12 V all channels Calibration enable all channels Powered v ell chonnelsg Signal ground essential if a long power cable is
21. the transfer function In the calibration pack G is the sensitivity given for each component on the first page whilst the roots z and p together with the normalising factor A are given in the Poles and Zeros table The poles and zeros given are measured directly at G ralp Systems factory using a spectrum analyser Transfer functions for the vertical and horizontal sensors may be provided separately Issue E Operator s Guide 5 Calibration information Every CMG 5T is supplied with a comprehensive calibration pack detailing the characteristics of the sensor 5 1 Calibration sheet The calibration sheet provides the measured acceleration responsivities over the flat portion of the sensor frequency response in units of volts per metre per second squared V ms Because the sensor produces outputs in differential form also known as push pull or balanced output the signal received from the instrument by a recording system with a differential input will be twice the true value For example the calibration sheet may give the acceleration responsivity as 2 x 0 50 V ms indicating that this factor of 2 was not included in the value given Caution You must never ground any of the differential outputs If you are connecting to a single input recording system you should use the signal ground line as the return line 5 2 Poles and zeroes The poles and zeroes table describes the frequency response of the senso
22. tizer input port sensitivity 3 507212 uV Bit Calibration channel sensitivity 3 491621 uV Bit From these we calculate that the calibration signal is producing 697 221 X 3 491621 2 434 431 uV 2 434 V This corresponds to an equivalent input acceleration of 2 434 x 1 968 4 791 ms The sensor s acceleration response is given as 0 254 V ms so that an acceleration of 4 791 ms will produce an output of 0 254 X 4 791 1 217 V 1 216 904 uV which corresponds to a count number at the digitizer s input port of 1 216 904 3 507212 346 972 counts Because this calibration is being carried out with a differential output sensor the count number observed at the December 2009 15 CMG 5T 16 digitizer should be double this 693 944 counts All G ralp Systems sensors use balanced differential outputs The actual signal at the digitizer of 701 512 counts is within 1 5 of this value indicating that the sensor is adequately calibrated 10 If you know the local value of g you can also perform absolute calibration by tilting the sensor by 90 and varying the calibration signal until it precisely compensates for the signal generated due to gravity 11 Calibrate any other sensors connected to the digitizer in the same way You must wait for the previous calibration to finish before doing this clicking Inject now has no effect whilst the Calibration enable relay is open If you prefer you can inject your own signals into the s
23. w read 5 V 6 Issue E Operator s Guide If the performance so far has been as expected the instrument may be assumed to be in working order and you may proceed to install the unit for trial recording tests Most likely however you will need to adjust the mass deflection offset see Section 2 4 page 8 2 3 Installing the sensor You will need a solid surface such as a concrete floor to install the 5T If you are in any doubt about how to install the sensor you should contact G ralp Systems 1 Prepare the surface by scribing a N S orientation line and installing a grouted in fixing bolt around the middle of the line A 6 mm 0 25 in threaded stud is suitable or an expanding nut rock bolt or anchor terminating in a threaded stud The bolt should be about 120 mm 5 in long 2 Place the accelerometer over the stud on the scribed base line and rotate to bring the orientation line and studs accurately in alignment with it The accelerometer has no levelling feet but can use an internal simulated level adjustment to compensate as long as it is fixed to a hard clean surface within 1 of the horizontal 3 Fix the accelerometer in place using a fixing nut with spring washer Do not over tighten 4 If required make a screening box for the sensor to shield it from draughts and sharp changes of temperature A suitable box can be constructed from expanded polystyrene slabs e g 5 cm building insulation slabs with seal
24. y is required the gain of the instrument can be altered by inserting gain setting resistors onto the power supply board of the unit POWER SUPPLY BOARD 7 OPO GAIN RESISTORS R4 VERTICAL R5 NORTH SOUTH 2 9 zi R3 EAST WEST TORROIDAL_ TRANSFORMERS MAIN CONNECTOR DC DC CONVERTOR IS MOUNTED ON THE UNDERSIDE OF THE PCB VERTICAL SENSOR CABLE NORTH SOUTH SENSOR CABLE EAST WEST SENSOR CABLE If G is the gain change you require then the value of the resistors to insert is given by the formula R 10000 G 1 Care must be taken when soldering these resistors to the circuit board as overheating the terminal could easily damage surrounding circuit elements December 2009 11 CMG 5T 3 Calibration The 5T is supplied with a comprehensive calibration document and it should not normally be necessary to calibrate it yourself However you may need to check that the response and output signal levels of the sensor are consistent with the values given in the calibration document 3 1 Absolute calibration The sensor s response in V ms is measured at the production stage by tilting the sensor through 90 and measuring the acceleration due to gravity Local g at the G ralp Systems production facility is known to an accuracy of 5 digits In addition sensors are subjected to the wagon wheel test where they are slowly rotated about a vertical axis Th
25. ystem at any point together with a Calibration enable signal if required to provide independent measurements and to check that the voltages around the calibration loop are consistent For reference a DM24 series digitizer will generate a calibration signal of around 16000 counts 4 V when set to 100 sine wave or step and around 10000 counts 2 5 V when set to 50 Issue E Operator s Guide 4 Inside the 5T The 5T unit is constructed of hard anodised aluminium with O rings throughout ensuring a completely waterproof housing Inside the mass of the vertical and horizontal components is attached to the rigid frame with parallel leaf springs The geometry of the spring spacing together with the symmetrical design ensures large cross axis rejection The sensor mass is centred between two capacitor plates and moves in a true straight line with no swinging motion Feedback coils are attached either side of the sensor mass forming a constant flux force feedback transducer The vertical and horizontal sensors are identical in mechanical construction the vertical sensor s mass spring system is adjusted to compensate for gravity They are mounted directly onto the base with the sensor electronics fixed onto the rigid sensor frame A single row 12 way surface mount R A Molex connector joins each sensor to the main power supply circuit board The signal and feedback circuits inside the 5T accelerometer are arranged ac
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