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Micro-g LaCoste FG5, Manual

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Concept and History of the FG5 

1

 

 
 
Geophysical Survey (GSC), the University of Hanover Institute for Earth 
Measurement, Germany, the Finnish Geodetic Institute, Finland, and the 
University of Vienna Institute for Metrology and Geophysics, Austria.  
 

1.3. FG5 Design Features 

 

The FG5 incorporates a number of significant advancements in design which 
reduce or eliminate systematic errors identified in the earlier versions, and 
which make the FG5 easier to use.  These improvements are: 

• An inline interferometer beam path which eliminates systematic errors 
from tilt-induced path length changes. 
• Complete redesign of the Superspring, a device for providing an inertial 
mass that contains a retroreflective corner cube.  The new Superspring has 
improved performance, and at the same time greatly reduced size.  The 
drift problems of earlier designs have been reduced substantially. 
• Completely new tripod design, which supports the test chamber, for 
extra stability.  The tripod is now built symmetrically with respect to the 
drop line. 
• The system controller has been updated to a 486-type personal 
computer with a standard language interface. The decision to use 
standard PC technology has allowed the FG5 to offer more computing 
power while reducing the size of the instrument. 
• Improvements to the electronics  reflect new technology and make the 
instrument smaller and easier to use.  
• A user-friendly full-featured real-time software program takes 
interferometer data and environmental data. This software provides an 
immediate value for the local gravity in real-time. 
• A user-friendly full-featured post-processing software program that 
allows complete ability to vary data analysis procedures and to vary 
environmental corrections. 
• This absolute gravimeter is designed to work with a new rugged iodine-
stabilized laser system (WEO model 100) traceable to the BIPM.

 

 

 

1-2 

 
 

Summary of Contents for FG5

Page 1: ...ing 2 13 2 3 1 SUPERSPRING MASS 2 13 2 3 2 SPHERE DETECTOR SYSTEM 2 13 2 4 The System Controller 2 15 2 4 1 REQUIRED HARDWARE 2 16 2 4 2 OPTIONAL HARDWARE 2 16 2 4 3 SOFTWARE 2 16 2 5 Electronics 2 17 2 5 1 TIMING SYSTEM 2 17 2 5 2 DROPPER CONTROLLER 2 19 2 5 3 SUPERSPRING CONTROLLER 2 19 2 5 4 LASER CONTROLLER 2 20 2 5 5 POWER SUPPLIES 2 20 2 5 6 OPTIONAL SYSTEMS 2 21 2 5 6 1 ENVIRONMENTAL SENSOR...

Page 2: ... 1 COMPUTER 3 20 3 3 2 SUPERSPRING 3 22 3 3 3 INTERFEROMETER 3 22 3 3 3 1 OPTION 1 Model AL 1 Laser 3 22 3 3 3 1 3 22 3 3 3 2 OPTION 2 WEO Model 100 Laser 3 22 3 3 3 2 3 22 3 3 4 DROPPING CHAMBER 3 23 3 3 5 POWER 3 23 3 4 Disassembling and Packing the FG5 3 23 3 4 1 ELECTRONICS 3 23 3 4 2 SYSTEM CONTROLLER 3 24 3 4 3 ROTATION MONITOR IF INCLUDED 3 24 3 4 4 DROPPING CHAMBER 3 25 3 4 5 TRIPOD 3 25 3...

Page 3: ...er and make beam vertical 4 14 4 2 2 12 Adjusting the Superspring position and final adjustment mirror 4 15 4 2 2 13 Final Mirror Translation Getting Beams Overlapped In Fringe Viewer 4 16 4 2 2 14 Adjusting the APD signal detector 4 16 4 2 2 15 Adjusting The Fringe Amplitude 4 17 4 2 2 16 Replace all covers and tighten all screws 4 17 4 3 The Superspring 4 18 4 3 1 REPLACEMENTS AND ADJUSTMENTS 4 ...

Page 4: ...ocity 4 39 4 5 2 3 Sphere Servo 4 39 4 5 2 4 Active Sphere Servo 4 40 4 5 2 5 Feedforward Sphere Servo 4 40 4 5 3 Superspring Controller 4 40 4 5 3 1 SUPERSPRING CONNECTIONS 4 41 4 5 3 2 MOTOR DRIVE SELECTION 4 42 4 5 3 2 1 OFF 4 42 4 5 3 2 2 AUTO 4 42 4 5 3 2 3 WINDOW 4 42 4 5 3 2 4 REMOTE 4 43 4 5 3 2 5 MANUAL 4 43 4 5 3 3 Active Servo 4 43 4 5 3 4 Coil Drive Current Driver 4 43 4 5 4 Maintenanc...

Page 5: ...aser 6 1 6 2 UTIC 6 1 6 3 MAIN POWER SUPPLY 6 2 6 4 Portable Ion Pump Power Supply 6 2 6 5 Computer 6 3 6 6 Docking Station 6 3 6 7 IOtech ADC16 6 3 6 8 Turbo pump 6 3 7 PUMPING BAKING THE CHAMBER 7 1 7 1 Choosing the Pumping Method 7 1 7 1 1 Cold Pumping the Chamber 7 1 7 1 2 Baking Out the Chamber 7 1 7 2 Connecting the Turbo Pump to the Dropping Chamber 7 2 7 3 Heating the Chamber 7 3 7 4 Start...

Page 6: ...eplacing V plate 9 14 9 4 7 Replacing the Linear Bearings 9 16 9 4 7 9 16 9 4 8 Replacing Shaft Bearings Drive Pulley 9 18 9 4 9 Replacing Shaft Bearings Top Pulley 9 19 9 4 10 Replacing Rotary Shaft Encoder 9 20 9 5 Interferometer Alignment 9 22 9 5 9 22 9 6 Superspring Maintenance 9 23 9 6 1 Removing Superspring Cover 9 23 9 6 2 Replacing Superspring Cover 9 23 9 6 3 Removing Service Ring 9 24 9...

Page 7: ...asuring gravity is absolute because the determination is purely metrological and relies on standards of length and time The distance scale is given by a frequency stabilized helium neon HeNe laser used in the interferometer A rubidium atomic time base provides the time scale used for the accurate timing The value of gravity obtained with the FG5 can be used without the loop reductions and drift co...

Page 8: ... designs have been reduced substantially Completely new tripod design which supports the test chamber for extra stability The tripod is now built symmetrically with respect to the drop line The system controller has been updated to a 486 type personal computer with a standard language interface The decision to use standard PC technology has allowed the FG5 to offer more computing power while reduc...

Page 9: ...rometer is used to monitor the position of the freely falling test mass The Superspring is an active long period isolation device used to provide an inertial reference for the gravity measurement The System Controller computer allows a flexible user interface controls the system acquires data analyzes data and stores the results The Electronics provides high accuracy timing necessary for the measu...

Page 10: ...mber which houses the Test Mass A Drive Mechanism is used to drop track and catch the test mass inside the drag free chamber Laser light Figure 2 1 passes through a window in the bottom of the Dropping Chamber to the corner cube inside the test mass then is reflected back down through the window to the interferometer 2 2 Figure 2 2 Front view of the dropping chamber ...

Page 11: ... 2 3 The cart drag free chamber Figure 2 4 and Figure 2 5 houses the test mass The purpose of the drag free chamber is to reduce the residual air drag inside the evacuated dropping chamber The chamber also reduces magnetic and electrostatic forces on the test mass and provides a convenient method for ...

Page 12: ...o mounted on the cart This system senses the position of the cart with respect to the test mass A servo motor drive belt system Figure 2 2 moves the cart inside the Dropping Chamber using active feedback from the position sensor to maintain the cart in a constant position relative to the test mass during free fall Since there is essentially no relative motion between the test mass and the drag fre...

Page 13: ... and balanced at the optical center of the corner cube The corner cube is a three surface mirror which has the special optical property that the reflected beam is always parallel to the incident beam In addition the phase shift of the reflected beam is virtually constant with respect to any slight rotation or translation of the corner cube around its optical center1 2 5 1 Peck Edson J Opt Soc Amer...

Page 14: ...al evacuation of the vacuum system A Ferrofluidic rotary vacuum feedthrough which connects the motor shaft to the cart drive mechanism A servo motor rotary shaft encoder assembly which moves the cart and senses its position An electrical vacuum feedthrough which allows connection of the test mass tracking electronics to the controller An ion pump mounted on a 2 Conflat flange which maintains the v...

Page 15: ... top flange of the dropping chamber directly above the viewing port When the rotation monitor is not mounted a cover for the port is used to exclude ambient light from the interior of the dropping chamber during measurements 2 1 5 THE DROP 2 7 In drop mode a signal from the computer to the dropper controller initiates the drop sequence The cart drag free chamber is driven slowly from its bottom po...

Page 16: ...city Approximately a million fringes are generated during a single drop A zero crossing discriminator comparator transforms the sinusoidal fringe signals from the APD into a series of square Transistor Transistor Logic TTL pulses The pulses are scaled i e divided by a user defined factor typically 4000 which is set in the scaler counter A universal time interval counter UTIC measures the time inte...

Page 17: ...nlike the WEO Model 100 Iodine Laser it must be periodically calibrated to achieve the best accuracy However it is more rugged than the iodine laser 2 2 2 OPTICS AND BEAM PATH The laser beam Figure 2 8 and Figure 2 9 is directed by mirror 1 through the isolator plate to mirror 2 From there it passes through the focusing optics microscope objective and the collimating lens where the beam is expande...

Page 18: ...re produced at beamsplitter 2 The vertical recombined beam is reflected by mirror 7 and is focused by a lens The focused beam strikes the detector APD and the interference fringes are converted to continuous wave CW signals and transmitted to the scaler counter The other recombined beam travels horizontally until it reaches the attenuator or rattler plate This beam is split and reflects rattles be...

Page 19: ...Design Components and Function 2 Figure 2 8 Top view of interferometer optics and beam path 2 11 ...

Page 20: ...Design Components and Function 2 Figure 2 9 Side view of interferometer optics and beam path 2 12 ...

Page 21: ...cube retroreflector and an optical glass sphere 2 3 2 SPHERE DETECTOR SYSTEM The Superspring sphere detector system Figure 2 11 senses motions of the Superspring mass relative to the support housing An infrared light emitting diode LED located on the support housing directs light through an optical glass sphere attached to the Superspring mass The sphere focuses the light onto a split photodiode d...

Page 22: ...Design Components and Function 2 Figure 2 10 The Superspring 2 14 ...

Page 23: ...e related length changes of the mainspring are compensated with an aneroid wafer assembly Figure 2 10 2 4 The System Controller 2 15 The system controller is an IBM compatible notebook PC with docking station which is used to control the gravimeter initiate drops as well as collect data distance and time for computing the gravity value It is also used to collect environmental and rotation monitor ...

Page 24: ...s the user to customize the data acquisition for each site including input output files printing options and session control The software also allows user input of site specific information such as site name code geodetic coordinates and elevation nominal air pressure and gravity gradient In addition the software allows the user to apply or not apply all the gravity corrections independently These...

Page 25: ...atible with most background TSR s and disk caching programs These restrictions do not apply to the post processing program REPLAY since it is not a real time application See the FG5 Software Manual for additional information 2 5 Electronics 2 5 1 TIMING SYSTEM The timing system Figure 2 12 consists of four main components Avalanche Photo Diode APD Rubidium Oscillator Universal Time Interval Counte...

Page 26: ... absolute time of occurrence of the scaled fringes The Scaler Counter uses a zero crossing discriminator to transform the sinusoidal signals from the rubidium oscillator to square wave TTL pulses It keeps track of the number of fringes that have passed by counting the TTL signals from the APD It also scales divides the fringes and the 10 MHz TTL clock pulses by user defined scale factors Nominal s...

Page 27: ...on of the test mass to the cart during free fall is provided by a sphere detector system An LED and a linear detector are mounted on opposite sides of the cart and an optical glass sphere is mounted on the test mass The sphere focuses a beam of light from the LED onto the linear detector indicating the precise location of the center of the sphere relative to the cart The dropper controller uses th...

Page 28: ... fine control The main servo electronics control the coil magnet forcer moves the main spring support in such a way to keep the main spring length constant This active servo acts to effectively weaken the main spring synthesizing a long period isolation device The active period of the Superspring is nominally about 60 seconds 2 5 4 LASER CONTROLLER The laser controller supplies power and enables o...

Page 29: ... local barometric pressure attraction correction while the system is operating The primary components of the environmental sensors package are A D Converter A 16 bit 100 kHz IEEE488 A D converter is mounted on the front of the electronics case It is used to convert all analog signals which are monitored and logged by the system controller BNC Signal Connection Box A signal connection box is mounte...

Page 30: ...ranslation and is only sensitive to rotation The diode laser beam reflects off mirror 1 and the beamsplitter mirror mount 2 The beam then passes down through the dropping chamber viewing port where it reflects off a flat mirror which is mounted to the top of the test mass The return beam from the test mass mirror passes through the beamsplitter and reflects off mirror 3 The beam then passes throug...

Page 31: ...Design Components and Function 2 Figure 2 13 Rotation Monitor 2 23 ...

Page 32: ......

Page 33: ... mount on the foam case insert and attach the three legs It is best to use two people so one can steady the interferometer while the other is attaching the legs Carefully raise the interferometer to its upright position and place on the floor Tighten each leg by sliding the steel rod through the hole in the leg and turning until the legs are snug There is no need to over tighten the legs since the...

Page 34: ...ar cover 8 Check the input voltage settings and make sure they are set to the proper AC line voltage If the instrument is not set to the correct voltage see appendix A for instructions on how to change the voltage selection 9 Make sure the following switches are off Main AC power rear Main DC power rear Laser power main AC power and key switch Universal Time Interval Counter Superspring coil Porta...

Page 35: ...h and the key switch for the laser tube HV Both lights on the laser controller panel should come on Set the heater current to 0 3 using the front panel monitor to view current Allow the laser to warm up for at least half an hour before locking 3 1 2 1 2 Operation After the laser is warm the LOOP switch should be closed The control switch should be set to REMOTE so that the computer can control the...

Page 36: ...ter BIAS Bias Voltage Set to 0V meter Allow the laser to warm up for at least two hours or until the temperature of the laser has stabilized before beginning observations 3 1 3 DROPPING CHAMBER TRIPOD 14 Remove the tripod tray from the Superspring case and place it carefully upside down on the floor 15 Remove the three tripod legs from the dropping chamber case and attach them to the tray 16 Turn ...

Page 37: ...refully remove the dropping chamber from its case by the handles and gently place it into the pocket in the top of the tripod tray allowing the two vertical alignment pins in the tray to engage the sockets in the dropping chamber base Orient the dropping chamber so the ion pump is on the side of the interferometer which is opposite the laser head directly above the beam blocker controls on the int...

Page 38: ...g chamber has remained intact since the previous use the ion pump alone may be sufficient to pump down the chamber The ion pump will probably start if it has been off for two hours or less 25 Before turning on the ion pump set the front panel meter select knob to PUMP VOLTAGE kV Turn on the pump and check the meter The voltage should be at least 2 kV within 5 minutes after turning on the ion pump ...

Page 39: ...l is adjusted first it will change when the cross level is adjusted When the cross level is adjusted first it does not change when the long level is adjusted 28 Remove the blue pads and brass tripod feet from the Superspring case Make sure the pads are clean 29 Place a tripod foot under each leg of the tripod Raise each foot and slide a blue pad under the foot 30 Center the cone in each foot under...

Page 40: ...of the three alignment pins do not slide freely the tripod is still in contact with the interferometer If this happens slide the alignment pins out and lower the tripod leveling feet turning clockwise until the cones are no longer in contact with the tripod leg balls Return to step 30 and repeat steps 30 33 to raise the tripod THERE MUST BE NO CONTACT BETWEEN THE TRIPOD DROPPING CHAMBER ASSEMBLY A...

Page 41: ...legs until the two points are coincident in the telescope This is most easily done by first adjusting the interferometer leg nearest the telescope eyepiece moving the spot diagonally until the test beam spot is on the vertical crosshair which passes through the reference beam spot either above or below it Then adjust the single leg on the side of the interferometer opposite the telescope to move t...

Page 42: ...How to Set Up and Run the FG5 3 3 10 ...

Page 43: ...Measuring Scale 3 11 42 The brass V posts on the bottom of the tripod are marked with concentric rings 1 mm apart the red ring being 0 see Figure 3 2 Estimate the distance the tripod has moved upward or downward and add this to the value read with the scale If our setup procedure has been followed correctly the dropping chamber will be 1 ring 1 mm above the zero position Record this value the Supe...

Page 44: ...How to Set Up and Run the FG5 3 Figure 3 2 V Post 3 12 ...

Page 45: ...ears are directly above the nearest leveling screws then gently lower the Superspring into place so the v grooves on the underside of the ears are resting on the leveling screws VERIFY THAT THE THREE V GROOVES IN THE SUPERSPRING TOP FLANGE ARE CORRECTLY SEATED ON THE ADJUSTMENT SCREWS CHECK THAT EACH V GROOVE IS ENGAGED IN EACH LEVELLING SCREW IT IS VERY EASY FOR ONE LEVELLING SCREW TO RIDE UP ON ...

Page 46: ...el lock just touches the spring support structure Then slowly return the knob to the unlocked position 3 1 12 CONNECT REMAINING SYSTEM CABLES 48 Attach the rest of the system cables as described below Both ends of all cables are labeled with the proper location for each connector When connecting cables to the computer make sure the power is off MAKE SURE THE DROPPING CHAMBER IS IN STANDBY HIT RESE...

Page 47: ...ct the 37 pin PIO cable to computer Connect the IEEE cable to computer If the FG5 is equipped with the environmental sensors package connect the 9 pin barometer cable to computer Connect the temperature cable from the temperature probe to the BNC 16 1F 49 Recheck the verticality of the interferometer by placing the alcohol pool on the top of the Superspring Level the interferometer if necessary by...

Page 48: ... with a front panel mounted trimpot labeled MOTOR The middle of the trimpot marked 5 applies no voltage Numbers above the middle 5 10 cause the motor to lift the mass increasing positive voltage on the sphere BNC and numbers below the middle 0 5 lower the mass Decreasing the voltage on the sphere BNC AUTO causes the motor to seek the zero position automatically NOTE IN AUTO THE DC MOTOR IS ALWAYS ...

Page 49: ...E voltage is positive 52 Once the desired zero position is reached SPHERE output between 0 20mV deactivate the motor by turning the front panel knob to OFF The spring should again be allowed to settle down for at least two minutes Set the coil switch to ON This switch activates the Superspring main servo loop for normal operation At this point there may still be a rotation in the test mass three s...

Page 50: ...adjust the beam translator until both beams are coincident in the periscope Note Only the horizontal axis in the periscope can be made coincident using mirror mount 6 Vertical coincidence must be accomplished with the translator plate or using step 57 for a coarse adjustment 57 Horizontal coarse adjustment of the test beam in the fringe viewer If the twiddler is not sufficient to move the test bea...

Page 51: ...ns off the motor and lets the cart drop to the bottom It is preferable to wait until the cart is near the bottom before hitting RESET Make sure the cart is resting at its bottom position and the red STANDBY light is on Set the trigger source switch to EXT and turn the rotary knob to AUTO Press RESET then INIT The dropper is now waiting for an external signal from the computer to initiate a drop 3 ...

Page 52: ...trol codes and filenames C56 C61 3 Check the FG5PARAM DAT file and make changes if necessary 4 If peak detection is enabled P32 check the 1f signals and correct if necessary NOTE Make sure the laser is warm and the meter select switch of the WEO Model 100 laser controller is set to 1f see WEO manual After reading the 1f signals be sure to reconnect the BNC cable between the signal monitor connecto...

Page 53: ...How to Set Up and Run the FG5 3 1 Backup the data 2 Shut off computer power 3 21 ...

Page 54: ...cs 3 3 3 INTERFEROMETER 3 3 3 1 OPTION 1 Model AL 1 Laser 6 a Set the switch on the front panel of the laser controller to MANUAL b Turn the fine gain control off fully counterclockwise c Set LOOP switch to OPEN d Turn the key switch off The green indicator light should turn off e Turn power switch off 3 3 3 2 OPTION 2 WEO Model 100 Laser 6 a Set servo control to OFF recommended but not required b...

Page 55: ...the AC and DC power rear of electronics rack 3 4 Disassembling and Packing the FG5 NOTE Please follow these instructions carefully Care in packing the components properly will result in easier and faster set up in the field and will help protect the instrument from damage 3 4 1 ELECTRONICS Unplug cables from the electronics rack and components 1 APD power cable 2 TTL fringe BNC cable 3 Laser signa...

Page 56: ...ble from the computer and printer and place in the system controller case 14 Close computer lid and place computer docking station in the system controller case 15 Close the system controller case and secure all latches 3 4 3 ROTATION MONITOR IF INCLUDED 16 Unplug all BNC and power cables from the rotation monitor detector box and electronics rack and store in the rotation monitor case 17 Remove t...

Page 57: ...6 Carefully remove the tripod from the interferometer base Remove the legs from the tripod Place the legs in the dropping chamber case and the tripod tray in the Superspring case large 3 lobe knobs toward the outside of the case 27 Place the brass tripod feet in the Superspring case and the blue pads in the dropping chamber case 28 Close dropping chamber case and secure all latches 3 4 6 SUPERSPRI...

Page 58: ...padded surface One person should steady the interferometer while the other person unscrews the legs 35 Place the legs in bottom of the interferometer case and cover with the foam pad provided 36 Gently place interferometer base in the case above the legs 37 Fold the handles down on the interferometer base 38 Close interferometer case and secure all latches 3 4 8 TURBO PUMP IF USED 39 Make sure the...

Page 59: ...res before reassembly When performing repairs in the field it is sufficient to wipe or flush the contaminated parts with alcohol Whenever possible vent the chamber with dry nitrogen rather than air This will reduce the pump down time after the chamber is reassembled To vent the dropping chamber remove the clamp and blank flange from the vacuum valve on the service ring Loosen the vacuum valve lock...

Page 60: ...nubber screws on the top rod ring out until they come in contact with the inside of the chamber cover walls Tighten the screws equally an additional 1 8 turn and lock in position with the locking nuts Inspect the top flange O ring and sealing surfaces Coat the O rings with a very light film of Apiezon L grease if necessary and mount the top flange to the chamber cover NOTE Whenever the chamber cov...

Page 61: ...ut there should be a minimum clearance of 1 mm between the belt and the side walls of the pulley housing yoke 4 1 1 4 Adjusting the Drive Belt Tension Adjust belt tension using the set screw on the top pulley assembly located on the top rod ring Tighten the belt adjustment screw until the slack has been taken out and the belt is straight Then tension the belt by tightening the screw approximately ...

Page 62: ...oupling from the feedthrough and unscrew the feedthrough from the Conflat flange Lubricate the O ring on the new Ferrofluidic vacuum feedthrough with a light coat of Apiezon L grease Use pliers with padded jaws e g blue pad to gently tighten the feedthrough to the Conflat flange Reverse the procedure for reassembly 4 1 1 6 Replacing the V Plate The V plate contains three tungsten V s which support...

Page 63: ...n balls from which the test mass is held are part of the top hat assembly If these balls need replacement send the entire mass assembly to Micro g Solutions for installation and rebalancing Reassemble the test mass using the three beryllium copper M3 screws and pack it carefully before shipping All the pieces must be included for the balancing to be done correctly 4 1 1 7 Replacing the Linear Bear...

Page 64: ...e above procedure to replace the cart 4 1 1 8 Replacing the Shaft Bearings Drive Pulley Refer to Figure 4 1 Drive pulley assembly Remove the drive belt as described previously Disconnect the Helical coupling between the pulley shaft and the ferrofluidic vacuum feedthrough Remove the five screws holding the bottom rod ring to the bottom flange Rotate the guide rod structure so that the shaft clears...

Page 65: ...rings Top Pulley The procedure for the top pulley is similar to the drive pulley except that there is no Helical coupling and no Woodruff key To access the top pulley assembly remove snap rings on upper bump stop and slide down shaft Remove two small retaining rings on top of upper pulley yoke and slide pulley down to remove Reverse procedure for replacement of upper pulley assembly When reassembl...

Page 66: ...nap the new encoder over the encoder back plate which was left attached to the travel lock plate Tighten the set screw and remove the Allen wrench from its hole Rotate shaft to check that the encoder disk is rotating freely inside the encoder Loosen and retighten set screw if necessary until the disk rotates freely 4 1 1 11 Pumping Down the Dropping Chamber See Appendix B for instructions on pumpi...

Page 67: ...he beam should be collimated approximately 5 7 mm in diameter On a card or paper placed in its path it should make a round uniform spot The beam should hit the center of mirrors 3 and 4 without being clipped by the button head screws It should then pass through both the dropping chamber and the Superspring and return intact The recombined beam should be centered in the fringe viewer It should also...

Page 68: ...m with oversized through holes to allow a height and tilt adjustment of the polar angle There are also 2 screws on the top plate of the mount with oversized through holes to allow adjustment of the azimuthal angle These are M3 screws which require a M2 5 socket head hex wrench Note that there is a 1 6 mm horizontal translation of the beam through the Faraday isolator 4 2 2 4 Optical Isolator Repla...

Page 69: ...This procedure may require several iterations to get the alignment perfect Figure 4 2 Beam expander with alignment pinholes mounted 4 2 2 6 Beam Expander 4 2 2 6 1 Focusing lens Remove the alignment pinholes and put the focusing lens 25 4 mm focal length into the first lens holder The lens should be inserted so that curved surface is towards the input beam Figure 4 3 4 11 ...

Page 70: ... that they are aligned with the cart travel inside the dropping chamber First re install the top middle cover on the interferometer base leave the two end plates removed for access Pull the alignment pins out and make sure that the interferometer base handles are in the upright position Put the tripod tray onto the interferometer base without the feet Place the dropping chamber onto the tripod tra...

Page 71: ...that the laser beam coming back from the dropper cornercube does not translate as the cart travels up and down The laser spot can be monitored by eye but is much better if monitored using a quadrant photodiode such as the translation detector supplied with the FG5 Put the translation detector on the floor and attach X and Y outputs to channels 1 and 2 on an oscilloscope Set the scope on XY 200 mV ...

Page 72: ...sening the M3 screw with a 2 5M socket inside the outer brass screw and adjusting the brass screw then locking the assembly using the internal screw see Figure 4 4 The thread on the outer brass screw is delicate and can be damaged easily by turning the brass part when the internal screw is tight locked This procedure will ensure that the rods on which the cart travels are vertical when the bubbles...

Page 73: ...er the dish of alcohol and adjust mirror 3 farthest from the first beamsplitter until the beam is traveling through the dropper system cleanly Remove the card and look into the telescope and you will see the reference beam and the return beam from the alcohol dish Adjust mirror 4 until they overlap in the telescope this adjusts the verticality of the beam DO NOT ADJUST THE LEGS OF THE INTERFEROMET...

Page 74: ...y to overlap in the fringe viewer with the reference beam it is sometimes necessary to translate the final adjustment mirror underneath the interferometer base Before doing so look through the telescope and adjust the mirror until the two spots are coincident in the telescope This will ensure that the angle of the reference and test beams are the same even though they may not yet be coaxial Then y...

Page 75: ...s 4 2 2 15 Adjusting The Fringe Amplitude Put the dropper tripod back on the interferometer base Level the interferometer base to the bubble levels on the dropper and raise the tripod by one full turn of the tripod feet Mount the Superspring Align the test beam and reference beam in the fringe viewer Put the dropper into OSC mode and maximize the fringes using the last mirror adjustment and twiddl...

Page 76: ...pring cover may be removed as a unit by removing the six screws holding the cover to the top of the service ring and lifting the cover assembly straight up Most routine maintenance can be accomplished at this point except for replacing the coil linear actuator the mainspring itself and its upper hanger To accomplish these tasks the service ring and bottom flange must be removed 4 3 1 2 Removing th...

Page 77: ...tructure to the bottom flange 4 3 1 3 Replacing the Coil Linear Actuator The permanent magnet assembly of the coil is attached to the base plate and the voice coil pusher is attached to the emitter detector block of the support structure Remove the service ring as described previously Remove the base plate by loosening the three 3mm barrel clamp screws that secure the rods to the plate Carefully l...

Page 78: ...st mass to drop BE VERY CAREFUL NOT TO BEND THE FILAMENT WIRE IN THIS ASSEMBLY It is highly recommended that this procedure be done at Micro g Solutions 4 3 1 5 Replacing the Flexures Necessary tools and fixtures A small table with leveling screws that can hold the Superspring in the field one could use the entire tripod or just the leveling feet A pulling tool music wire 16 long with m 1 6 thread...

Page 79: ...ock fork assembly off main rod Unhook three support springs from O rings and remove lower triangular spring plate This plate is held on by four 3 mm screws Be careful not to cut or score the O rings Note orientation of emitter detector block and remove block six 3mm screws in deep counter bore holes Note The test mass spring and flexure will come out with the emitter detector block Wear plastic gl...

Page 80: ...spring assembly into service ring Insert 6mm screws but don t fully tighten Replace the travel lock assembly Rotate the main spring assembly in the service ring so that the travel lock fork has equal clearance around the two shoulder screws then tighten 6mm screws Install electrical feedthrough Re connect all electrical connections Level the Superspring by viewing on each side of copper mass and c...

Page 81: ...stment screw and lock in position by tightening both top and bottom nuts Note 1 This will take time as the Test mass must settle down after each adjustment Note 2 Be careful not to let dust or debris fall onto corner cube Re check the level of the test mass and set level bubbles by turning brass screws Lock position with center lock screw Replace the Superspring cover as previously described 4 23 ...

Page 82: ...ment motor by changing the position of the set screws in the actuator arms The limit switches should shut off the zero positioning motor ZPM when the gap between the focus lever and the fulcrum plate is 4 8mm 4 3 1 9 The Aneroid Wafer Assembly To compensate for the thermal expansion and contraction of the Superspring an aneroid wafer assembly adjusts the position of the top hanger The position of ...

Page 83: ...es statistics and computes a gravity value including certain corrections e g for the tides and the gradient Optical fringes are produced in the interferometer by combining the portion of the laser beam hitting the freely falling and reference retroreflectors the corner cubes with the portion traveling directly through both beam splitters A fringe is produced every time the falling object traverses...

Page 84: ...umber of fringes that have passed can be expressed as a time and distance pair The data are then fit to a parabola by the computer to determine a best value for the acceleration a gravity value 4 4 1 1 Avalanche Photo Diode Printed Circuit Board This circuit detects the optical fringes produced in the interferometer The FG5 uses a 50 MHz APD which is powered by a high voltage module mounted inside...

Page 85: ...s the board through an SMA connector and is available outside the interferometer on a BNC connector labeled TTL The TTL signal is used for timing by the gravimeter electronics All on board voltages are derived from the 15V supply with linear regulators 6 volts for the APD and 5 volts for the discriminator and 50Ω TTL driver APD SIGNALS CONNECTOR TYPE DESCRIPTION Digital SMA output TTL fringe signa...

Page 86: ... fringe scaling circuit 4 is identical to that of the clock scaler The scaled fringes are counted by a 4 bit accumulator 5 and are passed on to the UTIC via a front panel BNC connector The leading edge of the latch pulse from the UTIC latches 6 the current values of the scaled clock and fringe accumulators into buffers along with the states of the data_valid and up down status lines The accumulato...

Page 87: ...Adjustment and Maintenance 4 4 29 ...

Page 88: ...ntroller indicating object in free fall Up Down Status TTL signal from controller indicating object is in the ascending descending phase of throw trajectory Spring Status TTL signal from Superspring indicating proper operation not implemented Laser Status TTL signal from the Laser indicating lock status Stat 1 undedicated TTL compatible status inputs to computer BNC OUTPUTS DESCRIPTION Spring Zero...

Page 89: ...output latched fringe count bit 0 7 VALIDL output latched data valid status bit 8 U D_L output latched up down status bit 9 DL9 output latched clock count bit 9 10 DL8 output latched clock count bit 8 17 GND power ground connection 19 GND power ground connection 21 GND power ground connection 22 CTL1 input laser control signal 23 CTL0 input spring zero signal 24 DIS input fringe output inhibit 25 ...

Page 90: ...ccurate time information The oscillator is split by a 50 Ω POWER splitter From there the clock is sent into the 10 MHz IN BNC on the back of the UTIC and also into the Clock In BNC on the back of the scaler counter 4 4 1 5 Universal Time Interval Counter To measure the time between a scaled fringe and the next scaled clock the FG5 uses a Universal Time Interval Counter UTIC The scaler counter SCAL...

Page 91: ...Adjustment and Maintenance 4 4 33 ...

Page 92: ...d the clock frequency to be 10 MHz The UTIC is set to measure positive mean time intervals only The trigger levels for A and B are set at 1 8 V 4 4 2 DATA ACQUISITION 4 4 2 1 Computer Interface Cards 4 34 The computer running the system is a 386 DX machine or better To interface the computer to the scaler counter the FG5 uses a Metrabyte PIO 12 SET TO 380 HEX This card provides 24 bits of I O It i...

Page 93: ...e setting of trigger and hold points within the dropping chamber One bit of the second EPROM is also used to control the time out circuitry a safe guard that protects the motor and the test apparatus Eight bits address the two EPROM s giving a total of 256 programmable states One bit is reserved for a fail standby state reducing the system to 128 non standby states These remaining states are subdi...

Page 94: ...cating failure 4 5 1 1 2 Function The controller is in standby The motor is turned off 4 5 1 1 3 To Deselect Press the front panel INIT button Note The initialize function can also be executed remotely through the INIT BNC connector WARNING IT IS DANGEROUS TO ALLOW THE COMPUTER REPEATED INITIALIZE CAPABILITY THE SYSTEM CAN ENTER THIS STATE THROUGH TIME OUT WHICH MAY INDICATE SYSTEM FAILURE 4 5 1 2...

Page 95: ...the computer or from the internal timer selected on front panel 2 Lift The cart servos to a constant lift velocity until the cart comes within the window of the hold position 3 Hold The cart servos to a constant hold position 4 Track The cart servos to track the test mass with a separation of about 3 mm This is adjustable 5 Soft catch The cart tracks the test mass with a very slight separation 6 C...

Page 96: ...logic GAL chip called the AXQD2X The outputs of the AXQD2X are glitch free clock pulses and an up down bit The resolution of the shaft encoder is multiplied by two giving 1000 counts per revolution The AXQD2X also has logic that helps clear the counters and keeps them from an overflow or underflow condition The sixteen bit counters feed a twelve bit digital to analog chip DAC for use in the analog...

Page 97: ...allows an offset to be added using the trim pots labeled THROW OFFSET and CATCH OFFSET These ramps are used to accelerate the cart during the throw phase and decelerate the cart during the catch phase The gain for the velocity servo is set by the VELOCITY GAIN trimpot on the PC board 4 5 2 3 Sphere Servo The sensor for this servo is an LED focused spot sensor The operational principle is a simple ...

Page 98: ...is made with a ramp waveform The slope of the ramp is given by the trimpot called RAMP SLOPE The zero point which should be at the top of the drop or throw is set by the ramp offset 4 5 3 Superspring Controller The Superspring electronics comprise a system for locating the Superspring mass relative to the support housing a motor driven mechanical lever system for raising and lowering the mainsprin...

Page 99: ...ller which controls a motor The motor drives a lever system that raises and lowers the mass and mainspring Two micro switches and diodes keep the motor from raising or lowering the mass beyond a specified range A linear actuator coil and magnet system pushes and pulls the mainspring support structure to track the Superspring mass The Superspring controller has six main parts 1 LED driver 2 Sphere ...

Page 100: ...elative to the main bracket The position may need to be adjusted as the main spring slowly stretches over time or due to temperature or gravity changes The DC motor can lift lower the test mass so that the sphere position becomes more positive negative This motor should only be used to position the mass but should not be activated during the Superspring operation as a long period isolation device ...

Page 101: ...pass HP and then a low pass LP filter The Q value and frequency of each filter is adjustable via the on board trim pots The phase lead and lag and the servo gain are also adjustable 2 4 5 3 4 Coil Drive Current Driver The filter section feeds the coil driver which produces a current for the coil using a high power op amp The signal feeding the coil driver can be viewed at COMP OUT The signal retur...

Page 102: ... replace and adjust the cart drive belt Inspect replace and lubricate the drive system bearings Inspect and replace the tungsten support contacts on the test mass and cart Reassemble the vacuum system and test for leaks Pump down and bake out the vacuum system Test and adjust the system electronics Clean and align the optics 4 5 4 2 Semi annually Calibrate the He Ne laser to an iodine standard 4 4...

Page 103: ...ring set up and observation Conscientious recording of system information e g laser power ambient temperature and atmospheric pressure Superspring position ion pump current fringe signal amplitude dropping chamber and Superspring level positions etc can be extremely helpful in diagnosing problems The Micro g Solutions Environmental Sensor Package is highly recommended for monitoring system status ...

Page 104: ...Troubleshooting 5 5 2 ...

Page 105: ... needs to be adjusted Noisy catch Catch offset and ramp need to be adjusted Hum at the top of the drop Hold servo gain needs to be reduced Shaft encoder is dirty and needs to be blown clean with high pressure air Upward or downward trend in gravity values time series plot Ion pump is not turned on Time or date on PC controller have been set incorrectly Tide correction flag has not been set in the ...

Page 106: ... snubbers tightened asymmetrically or because of stress from bad alignment of rods in the top ring Table 5 1 Dropping Chamber Problems and Solutions 5 2 2 INTERFEROMETER AND LASER To achieve the best possible results the interferometer optics must be clean and correctly aligned In some cases it is possible to detect alignment problems during setup The operator should always be extremely observant ...

Page 107: ...not aligned properly with interferometer Superspring not leveled or not aligned properly with interferometer Cannot obtain 200mv amplitude on analog fringe output with alignment optimized Rotate λ 4plate lens in front of faraday isolator to increase beam intensity Analog fringe output clipped with alignment optimized Rotate quarter wave plate lens in front of faraday isolator to decrease beam inte...

Page 108: ...t file No fringes at all No power to APD One both beam blockers are pushed in Very bad alignment of the test reference beams Look into the telescope and make sure that the test and reference beams are overlapped Also make sure that the beams are overlapped in the fringe viewer with the twiddler Fringe amplitude varies as the cart is moved up or down The iodine stabilized laser is running multi mod...

Page 109: ...up into range If the change in gravity is negative the spring should be driven down into range It is always very important to monitor the voltage at the front panel BNC of the Superspring controller marked SPHERE OUT while the servo loop is still open The sphere position should be moving substantially voltage when the loop is open and the Superspring is unlocked This indicates that the test mass i...

Page 110: ...lexure delta rod has been damaged and needs replacement The lock on the controller is locked Gravity is extremely noisy mGal It is possible that there is an earthquake event occurring somewhere on earth The Superspring is very sensitive to earthquakes no matter where they occur The gravity will continue to be noisy for hours or even days when the earthquake event is close to the gravimeter locatio...

Page 111: ...d disconnect and reconnect the serial cable Use the GETBAR program to test the barometer Olivia ends with the Error Number 00308 Original Command OUTPUT 16 The UTIC is not connected to the system or it is turned off Olivia ends with the Error Number 00308 Original Command OUTPUT 14 The IOtech ADC 16A is not connected to the system or is not turned on OLIVIA locks and the UTIC displays BINARY DATA ...

Page 112: ...setup 5 10 Problem Solution The Stanford Research Instruments SRS Model SR620 UTIC has momentary power outages and loses programmed configuration A voltage regulator is shorting out against the case Call Micro g for detailed instructions The SRS UTIC displays an error See UTIC manual The SRS UTIC has excessive jitter Make sure that the voltage selection is correct for the AC power This unit will n...

Page 113: ...usoidally varying gravity value Rubidium standard is warming up or will not lock VCXO trim may need adjustment Large noise often looks like a Superspring problem Poor system grounding Sometimes it is necessary to ground the system electronics rack to an earth ground like a water pipe in the laboratory Table 5 5 Electronics Problems and Solutions 5 11 ...

Page 114: ...ate to better than one µGal can still be computed and applied during post processing Possible problems and solutions pertaining to the environmental sensors package are shown in Table 5 6 Problem Solution Room temperature reading incorrectly Change battery in thermocouple mounted on tripod tray Turn on temperature probe Attach thermocouple to temperature probe Attach BNC between temperature probe ...

Page 115: ...o determine if there is excessive rotation of the test mass about a horizontal axis i e if the balls and or v grooves are worn and need to be replaced Possible problems and solutions are shown in Table 5 7 Problem Solution Excessive Rotation 10mrad sec Alignment of the dropper is not correct Ball Vee contacts for the test mass need to be replaced Table 5 7 Rotation Monitor Problems and Solutions 5...

Page 116: ...s much as possible A basement with a thick concrete floor is usually best Avoid floors with composition materials if possible and set up the instrument on a solid tile or concrete floor 5 3 3 ENVIRONMENTAL NOISE Heavy heating or cooling equipment as well as bipedal or vehicular traffic can cause vibrations which tend to increase the drop to drop scatter of the observations This can usually be seen...

Page 117: ...Troubleshooting 5 5 15 ...

Page 118: ...s always best to use voltage stabilizers and or uninterruptible power supplies to minimize problems with unreliable line voltage Some system components especially the WEO Model 100 iodine laser are more sensitive to line voltage fluctuations than others so it is always best to stabilize line voltage well enough to satisfy the requirements of the most sensitive component 5 16 ...

Page 119: ...MAGE TO THE TRANSFORMER INSIDE THE LASER CONTROLLER 3 Rotate the drum voltage selector until the proper line voltage is visible make sure the drum is removed from the power entry module 4 Replace the drum voltage selector making sure the proper line voltage is visible and plug the AC power cord into the power entry module 6 1 2 AL 1 Laser Possible voltage selection positions 50 60Hz 115 and 220 VA...

Page 120: ...amber Superspring scaler counter translation detector printer voltage and ac power strip 1 Remove AC plug 2 Remove selector by pulling straight out 3 Flip or rotate selector to correct voltage 4 Reinsert the selector and the AC power cord Check to see if the correct voltage is visible before reconnecting to mains power 6 4 Portable Ion Pump Power Supply Possible voltage selection positions 50 60Hz...

Page 121: ...NO SWITCHING IS NECESSARY IF SWITCHING BETWEEN 100 ÅÆ 115 VAC OR IF SWITCHING BETWEEN 220 ÅÆ 240 1 Remove the unit from the electronics rack and remove the top lid of the box 2 Flip the red selector switch between 110 or 220 VAC 3 Install the appropriate fuses 6 8 Turbo pump The Varian Model V 60 Turbo Pump was included with the FG5 prior to February 1996 Since then the Varian Model V 70 Turbo Pum...

Page 122: ...onnector Cable Connector Cable L1 No Connections L1 No Connections 3 Blue 3 Violet 4 Orange 4 Orange 5 Violet 5 No Connections L2 Red L2 Red and Blue Table 6 1 Turbo Pump AC Voltage Select 2 To complete the voltage switching it is necessary to select the proper input voltage for the turbo pump control unit This is done by removing the access panel at the rear of the enclosure to access the back of...

Page 123: ...he required pumping time is determined by the time the ion pump has been off power and the temperature at which the dropping chamber has been stored If the ion pump has been off for less than one month a pumping time of 1 hour or less is usually sufficient to start the ion pump When the ion pump has been off for several weeks it is usually best to pump the chamber overnight 12 14 hours In extreme ...

Page 124: ...vacuum fittings have an O ring that fits between the two flanges A clamp holds the two vacuum flanges and O ring assemble together Make sure that there is no dirt or hair on the vacuum flanges or O ring Sometimes it is helpful to use a little high vacuum grease such as Apiezon on the O ring to ensure a good seal There are two different circumstances which dictate whether the bellows valve is to be...

Page 125: ...d wrap separate heat tapes around the dropping chamber and the ion pump The chamber temperature should be maintained at 80 C or less and the ion pump at 100 C This is done by connecting the heat tapes to a variable transformer to control the temperature It is preferable to use separate transformers if possible to allow independent adjustment of the chamber and ion pump temperatures Monitor the bak...

Page 126: ... the base of the dropper Set the meter select knob on the ion pump controller to PUMP VOLTAGE KV Start the ion pump by turning on the AC BAT and HV switches on the ion pump controller Leave the turbo pump running and connected to the dropping chamber until the ion pump starts After turning on the ion pump check the meter on the ion pump power supply The voltage should be at least 2 KV within five ...

Page 127: ...ssible without losing sight of the test mass mirror Use the travel lock pin to lock the mass in this position Adjust only mirror mount 1 so as to put the laser beam back in the center of the test mass mirror Lower the test mass to the bottom and adjust only the beam splitter on mirror mount 2 to put the spot back in the center of the test mass mirror The first mirror is used to translate the beam ...

Page 128: ...OGGING SYSTEM Connect the x y and sum jacks on the detector box to the IOtech patch panel connections as follows X to 5H Y to 6H SUM to 7H Connect the Valid and the Trigger Out signals of the DROPPER Controller to the IOtech patch panel connections as follows Valid to 8H Trigger Out to Trigger 8 3 TAKING DATA The program for taking data from the attitude monitor is turned on and off using line P22...

Page 129: ...e status of the system and document any information e g weather site conditions system status which is noteworthy This information is invaluable in documenting observations performing data analysis post processing and troubleshooting the system This appendix consists of several checklists and logs which are helpful In many cases the user may develop additional or modified procedures which are tail...

Page 130: ...Power Use card in power entry module Ion Pump Power Supply Use drum in power entry module Remove drum from power entry module before rotating Computer docking station Flip red switch on rear panel to 115 or 230 IOtech ADC16 Remove unit and top cover Flip red selector to 110 or 220 Turbo Pump Remove motor access panel and connect cables to proper terminals see owner s manual or table in appendix A ...

Page 131: ...Checklists and Logs Appendix D 9 3 ...

Page 132: ... and remove covers Check AC line voltage Connect main AC power cable Connect signal HV cables from electronics rack to laser head Turn on main AC and DC power switches Assemble dropping chamber tripod and place on interferometer Place dropping chamber on tripod ion pump away from laser head Clamp dropping chamber to tripod Release cart travel lock Connect ion pump cables and start ion pump Rough p...

Page 133: ...per do not touch Check levels on tripod tray and center if necessary If levels are adjusted recheck to make sure interferometer and dropper do not touch Mount telescope and focus crosshairs Adjust verticality of test beam using interferometer legs Measure and record reference height Mount Superspring Verify that all three v mounts on Superspring lid are located properly Connect Superspring cable y...

Page 134: ...rspring cable Connect APD power green Lemo Connect BNC fringe signal to interferometer TTL port and front panel of Scaler Counter Recheck beam verticality Adjust if necessary Adjust Superspring zero position Record Superspring sphere voltage in system check log Close Superspring servo loop turn coil switch on Put Dropper in OSC mode and hit RESET then INIT to make the dropper move smoothly up and ...

Page 135: ...d bottom of the drop Record these values in the system check log When the cart is at the bottom of the drop set the trigger source to EXT Press RESET then INIT Now it waits for the computer to initiate a drop Check the laser output power and record this value in the system check log Verify 1f signal of the WEO and put these values in the FG5param dat file Make sure that the time constant is set to...

Page 136: ...under vacuum keep the bellows valve shut If the dropper has been open to air open the bellows valve Plug in turbo pump power cord and turn on pump keep bellows valve closed Wait to see that turbo pump has reached normal operation Open bellows valve if necessary after evacuating air in flexible tube Remove magnet package from ion pump if heating is required Connect heat tapes and temperature sensor...

Page 137: ...kage Connect HV and ground cables between ion pump controller and ion pump Turn on ion pump controller to start ion pump Monitor voltage at ion pump controller should be 2 KV within 5 minutes and rising Table 9 3 FG5 Pump Down and Bake Out 9 4 Dropping Chamber Maintenance 9 4 1 Removing Chamber Cover 9 9 Removing Dropping Chamber Cover Checklist Remove blank flange from vacuum valve ...

Page 138: ...ean and protect O ring surface Table 9 4 Removing Dropper Cover 9 4 2 Replacing Dropping Chamber Cover 9 10 Replacing Dropping Chamber Cover Checklist Inspect chamber O ring and sealing surfaces Lubricate O ring if necessary Lower chamber cover over dropping mechanism Tighten mounting screws in star pattern Adjust snubber screws and tighten lock nuts Inspect top flange O ring and sealing surfaces ...

Page 139: ...Belt Checklist Remove dropping chamber cover Loosen belt tension Remove belt clamp from cart Remove belt Clean drive and top pulleys and wipe new drive belt Thread new belt around top and drive pulleys Place belt ends over dowel pin and install belt clamp do not tighten clamp Tension belt while moving cart up and down Allow belt to locate natural position Tighten belt clamp ...

Page 140: ...Checklists and Logs Appendix D Table 9 6 Replacing Drive Belt 9 12 ...

Page 141: ... wrench Table 9 7 Adjusting Belt Tension 9 4 5 Replace Ferrofluidic Vacuum Feedthrough Replacing Ferrofluidic Vacuum Feedthrough Checklist Remove dropping chamber cover Loosen 4 40 screws on Helical coupling between motor and feedthrough Remove 28 screws which attach motor to Conflat flange Remove motor mount assembly motor Helical coupling travel lock plate and shaft encoder from Conflat flange L...

Page 142: ...through Gently tighten new feedthrough to Conflat flange use pliers with padded jaws Table 9 8 Replace Ferrofluidic Feedthrough 9 4 6 Replacing V plate Replacing V plate Checklist Remove dropping chamber cover Remove bottom drag free cover from cart Detach LED bracket from cart and pull out of the way be careful not to damage wires Observe position of the threaded post attaching top drag free cove...

Page 143: ...or damage wires connected to it Note orientation of top part of test mass to V plate Remove top part of test mass from posts which pass through V plate Lower bottom part of test mass through V plate Remove old V plate and replace with new one Reverse procedure to reassemble Table 9 9 Replacing V Plate 9 15 ...

Page 144: ...e wires and clamp from cart Lift cart off guide rods Remove two retaining rings for each linear bearing wind off end of bearing Slide linear bearings out of the cart Make sure new linear bearings have venting holes Make sure new linear bearings have been cleaned and lubricated with Krytox 143AC low vapor pressure oil Insert new linear bearings in cart and insert retaining rings Reverse above proce...

Page 145: ...Checklists and Logs Appendix D Table 9 10 Replace Linear Bearings 9 17 ...

Page 146: ...ulley shaft and Ferrofluidic feedthrough Remove screws holding bottom rod ring to bottom flange Rotate guide rod structure so shaft clears service ring Remove guide rod structure Remove pulley yoke from bottom rod ring Remove bowed retaining ring from short end of pulley shaft note orientation Remove retaining ring from other end of shaft don t lose Woodruff Key Remove pulley from bearing mounting...

Page 147: ...ectly and fully seated in groove Table 9 11 Shaft Bearings Drive Pulley 9 4 9 Replacing Shaft Bearings Top Pulley Replacing Shaft Bearings Top Pulley Remove dropping chamber cover Remove drive belt Remove snap rings on upper bump stop and slide down shaft Remove retaining rings on top of upper pulley yoke Remove pulley slide down Remove bowed retaining ring from short end of pulley shaft note orie...

Page 148: ...rse order make sure bowed snap ring is oriented correctly and fully seated in groove Table 9 12 Shaft Bearings Top Pulley 9 4 10 Replacing Rotary Shaft Encoder Replacing Rotary Shaft Encoder Checklist Loosen set screw holding disk to shaft Pry encoder housing off back plate plate remains attached to travel lock plate Snap new encoder over back plate Tighten set screw holding disk to shaft Rotate s...

Page 149: ...Checklists and Logs Appendix D Table 9 13 Replace Shaft Encoder 9 21 ...

Page 150: ...Reinsert 128 mm collimating lens in spatial filter Adjust collimating lens position by minimizing spot in telescope Level the dropping chamber and adjust bubble levels Adjust mirrors 3 and 4 to make the beam travel through dropping chamber vertically Adjust Superspring position top mounting plate Adjust final mirror overlap beams in fringe viewer Steer beam onto the APD Focus beam on APD Adjust fr...

Page 151: ...not remove top flange Lift cover straight up over Superspring mechanism Table 9 15 Remove Superspring Cover 9 6 2 Replacing Superspring Cover Replacing Superspring Cover Checklist Check O ring seat and lubricate O ring if necessary Gently lower Superspring cover including top flange over mechanism Tighten screws holding Superspring cover to service ring Table 9 16 Replace Superspring Cover 9 23 ...

Page 152: ...emove electrical feedthrough from service ring note color coding on connector Remove travel lock knob Remove travel lock assembly from service ring Remove service ring and bottom flange as a unit Table 9 17 Removing Superspring Service Ring 9 6 4 Replacing Coil 9 24 Replacing Coil Checklist Remove service ring Remove base plate Lift rod assembly off bottom plate ...

Page 153: ...ings from O rings Remove lower triangular spring plate do not damage O rings Remove emitter detector block note orientation Remove permanent magnet assembly from base plate Remove coil from emitter detector block Reverse procedure for reassembly Table 9 18 Replacing Superspring Coil 9 25 ...

Page 154: ... Place hard foam or rubber shim between top rod ring and top triangular plate Fasten plates together with cable tie Loosen clamps holding rods to bottom plate Disconnect wires from pre amp circuit board Lift rod assembly off bottom plate Remove travel lock fork from main rod Unhook support springs from O rings Remove lower triangular spring plate do not damage O rings ...

Page 155: ... to main spring Put lower lock nut on new flexure assembly Remove broken flexure anchor Screw new flexure anchor into spring to original position Thread pulling tool through one nut top lever and down center tube Thread tool into top of flexure coarse adjustment screw of main spring assembly Pull tool up until spring hangs Thread test mass onto lower main spring anchor Tighten lower anchor Pull to...

Page 156: ...res 9 6 6 Assembling Superspring 9 28 Assembling Superspring Checklist Replace emitter detector block in original orientation below lever pivots Replace lower triangular spring plate Attach support springs Install travel lock fork assembly on shaft Replace spring assembly into lower plate don t damage coil Make sure rods are seated flush with bottom of lower plate Tighten barrel clamps ...

Page 157: ...ub Replace spring assembly in service ring don t tighten screws Replace travel lock assembly Rotate main spring assembly to equalize travel lock fork clearance Tighten screws holding spring assembly to service ring Install electrical feedthrough Connect all wires match color coding Place Superspring on leveling table Adjust table to center test mass in cage Make sure top of test mass is about 1 5 ...

Page 158: ...lever arms Make sure sphere voltage goes to assure true center position Carefully align beam holes in top lever with holes in test mass Recheck centering of test mass in cage and adjust bubble levels Table 9 20 Assembling Superspring 9 6 7 Replacing Focus Lever Motor 9 30 Replacing Focus Lever Motor Checklist Remove nut on focus adjustment screw Lower focus lever motor assembly off fulcrum lever L...

Page 159: ...ip positions by changing position of set screws in actuator arms Adjust so limit switches shut off ZPM when gap between focus lever and fulcrum plate is 4 8 mm Table 9 22 Adjusting Superspring Micro Switches 9 7 Packing the FG5 9 31 Packing the FG5 Checklist Unplug cables from electronics rack and components Store ion pump GPIB and PIO cables in electronics case Put remaining cables in zippered po...

Page 160: ...on monitor if used Store in rotation monitor case Remove rotation monitor from dropper and store in case Close case and secure latches Secure lids to electronics case Replace screws and viewing port cover on top dropping chamber flange Engage cart travel lock Remove dropping chamber from tripod and place in dropping chamber case Lift tripod from interferometer base and remove legs Place tripod leg...

Page 161: ...t top plug Place Superspring in Superspring case Remove telescope assembly from interferometer base Put lens cap on telescope and place assembly in Superspring case Close Superspring case and secure latches Insert top and side plugs in interferometer base Remove interferometer legs Place interferometer legs in interferometer case and cover with foam pad Place interferometer base in interferometer ...

Page 162: ...ix D Close interferometer case and secure latches Make sure all blank flanges and covers are in place on turbo pump and flexible tube Store flexible tube and power cord in base of turbo pump case Table 9 23 Packing the FG5 9 34 ...

Page 163: ...sion Adjustment 4 3 BNC Signal Connection Box 2 21 Buffer Sphere Signal 4 40 C Cables Connecting 3 13 Cards Computer Interface 4 32 Data Acquisition 4 32 Cart Position 4 36 Cart Velocity 4 37 Cart Drag Free Chamber 2 2 Front View 2 4 Function 2 3 Side View 2 5 Checklist Adjusting Belt Tension 9 11 Adjusting Micro Switches 9 27 Assembling Superspring 9 24 FG5 Setup 9 3 Interferometer Alignment 9 18...

Page 164: ...3 21 Side View 2 3 Troubleshooting 5 1 Venting 4 1 Vertical Alignment 4 13 Dropping Chamber Cover Removing 4 1 Replacing 4 2 Dropping Chamber Tripod Setup 3 4 E Electronics Function 2 1 Troubleshooting 5 9 Electronics Case Setup 3 2 Environmental Sensors Package 2 21 Troubleshooting 5 11 EPROM 4 33 Second 4 33 F Faraday Isolator 4 10 Feedforward Servo 4 38 Feedthrough Rotary Vacuum 2 6 Ferrofluidi...

Page 165: ...ches Adjustment 4 24 Linear Actuator 2 19 Linear Bearings Lubrication 4 6 Micro g Modifications 4 6 Replacement 4 5 Linear Detector 2 4 2 19 Lubrication Linear Bearings 4 6 O Ring 4 4 Pulley Bearings 4 7 M Mach Zender Interferometer 2 10 Maintenance Annual 4 42 Semi annual 4 42 Maintenance Schedule 4 42 Measuring Reference Height 3 10 Micro Switches Adjustment 4 24 Mirror 1 2 9 Adjustment 4 10 Mir...

Page 166: ...ve 2 16 IEEE Board 2 16 Memory 2 16 Parallel Interface Board 2 16 Rotary Shaft Encoder Replacement 4 7 Rotation Monitor 2 7 2 21 Alignment 8 1 Diagram 2 22 Function 2 21 Installation 8 1 Troubleshooting 5 12 Rough Leveling Interferometer 3 7 Rough Pumping 7 1 Rubidium Oscillator 4 31 Function 2 18 S Scaler Counter Circuit Board 4 28 Function 2 18 Scaling Clock Pulses 4 26 Fringes 4 26 Semi annual ...

Page 167: ...ng Travel Lock Releasing 3 13 Switching AC Power AL 1 Laser 6 1 Docking Station 6 3 FG5 System 6 1 Ion Pump Power Supply 6 2 IOtech ADC 16 6 3 Rear Mains Power Rack 6 2 Turbo Pump 6 3 UTIC 6 2 WEO 100 Laser 6 1 System Controller Function 2 1 2 15 Setup 3 18 Troubleshooting 5 8 T Taking Data Rotation Monitor 8 2 Telescope Collimating 2 10 Focusing Crosshairs 3 8 Infinity Focus 3 9 Temperature Senso...

Page 168: ... 9 Vertical Alignment Dropping Chamber 4 13 Verticality Beam 4 12 Dropper 3 8 Viewing Port Function 2 7 V Plate Replacement 4 4 W WEO 100 Laser 2 9 Setup 3 4 Shutting Down 3 20 Switching AC Power 6 1 Window Comparator 4 40 Z Zero Position Superspring 2 20 Zero Crossings Fringes 4 25 Zero Positioning the Superspring 3 15 10 6 ...

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