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Micro-g LaCoste FG5 Manual

Absolute gravimeter
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1. CONCEPT AND HISTORY OF THE FG5 ..................................... 1-1
1.1. The FG5 Absolute Gravimeter .................................................................................... 1-1
1.2. HISTORY...................................................................................................................... 1-1
1.3. FG5 Design Features .................................................................................................... 1-2
2. DESIGN: COMPONENTS AND FUNCTION................................. 2-1
2.1. The Dropping Chamber ............................................................................................... 2-2
2.1.1. TEST MASS ........................................................................................................... 2-5
2.1.2. DRIVE MECHANISM ........................................................................................... 2-6
2.1.3. SERVICE RING ..................................................................................................... 2-6
2.1.4. VIEWING PORT.................................................................................................... 2-7
2.1.5. THE DROP ............................................................................................................. 2-7
2.2. The Interferometer ....................................................................................................... 2-9
2.2.1. LASER.................................................................................................................... 2-9
2.2.2. OPTICS AND BEAM PATH ................................................................................. 2-9
2.3. The Superspring.......................................................................................................... 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 SENSORS.................................................................. 2-21
2.5.6.2. ROTATION MONITOR............................................................................... 2-21
3. HOW TO SET UP AND RUN THE FG5 ........................................ 3-1
3.1. Setting Up the FG5 ....................................................................................................... 3-1
3.1.1. INTERFEROMETER ............................................................................................. 3-1
3.1.2. ELECTRONICS CASE .......................................................................................... 3-2
3.1.2.1. Model AL-1 Laser:.......................................................................................... 3-3
3.1.2.1.1. Warm Up ................................................................................................. 3-3

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Summary of Contents for Micro-g LaCoste FG5

  • Page 1: Table Of Contents

    2.5.5. POWER SUPPLIES....................2-20 2.5.6. OPTIONAL SYSTEMS..................2-21 2.5.6.1. ENVIRONMENTAL SENSORS..............2-21 2.5.6.2. ROTATION MONITOR................2-21 3. HOW TO SET UP AND RUN THE FG5 ........3-1 3.1. Setting Up the FG5 ....................... 3-1 3.1.1. INTERFEROMETER ..................... 3-1 3.1.2. ELECTRONICS CASE ..................3-2 3.1.2.1.
  • Page 2 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.
  • Page 3 Table of Contents 4.1.1.6. Replacing the V-Plate..................4-4 4.1.1.7. Replacing the Linear Bearings ................ 4-5 4.1.1.8. Replacing the Shaft Bearings—Drive Pulley ..........4-6 4.1.1.9. Replacing the Shaft Bearings—Top Pulley............. 4-7 4.1.1.10. Replacing the Rotary Shaft Encoder ............. 4-7 4.1.1.11. Pumping Down the Dropping Chamber............4-8 4.2.
  • Page 4 4.5.4. Maintenance Schedule................... 4-44 4.5.4.1. Annually ......................4-44 4.5.4.2. Semi-annually ....................4-44 5. TROUBLESHOOTING ..............5-1 5.1. The FG5 System ......................5-1 5.2. System Problems ......................5-1 5.2.1. DROPPING CHAMBER ..................5-1 5.2.2. INTERFEROMETER AND LASER ..............5-4 5.2.3. SUPERSPRING ...................... 5-7 5.2.4.
  • Page 5 Table of Contents 5.2.7. ROTATION MONITOR..................5-13 5.3. Gravity Site Selection ....................5-14 5.3.1. GEOLOGIC STABILITY..................5-14 5.3.2. SITE STABILITY ....................5-14 5.3.3. ENVIRONMENTAL NOISE ................5-14 5.3.4. TEMPERATURE STABILITY ................5-14 5.4. AC POWER ........................ 5-16 6. SWITCHING THE AC POWER ............. 6-1 6.1.
  • Page 6 9.6.2. Replacing Superspring Cover................9-23 9.6.3. Removing Service Ring..................9-24 9.6.4. Replacing Coil ....................... 9-24 9.6.5. Replacing Flexures ....................9-26 9.6.6. Assembling Superspring..................9-28 9.6.7. Replacing Focus Lever Motor ................9-30 9.6.8. Adjusting Micro-Switches..................9-31 9.7. Packing the FG5 ......................9-31 10. INDEX..................10-1...

  • Page 7: Concept And History Of The Fg5

    The FG5 absolute gravimeter is a high precision, high accuracy, transportable instrument that measures the vertical acceleration of gravity (g). The operation of the FG5 is simple in concept. A test mass is dropped vertically by a mechanical device inside a vacuum chamber, and then allowed to fall a distance of about 20cm.

  • Page 8: Fg5 Design Features

    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: •...

  • Page 9: Design: Components And Function

    Design: Components and Function 2. Design: Components and Function The FG5 System (Figure 2-1) consists of a: Dropping Chamber, Interferometer, Superspring, System Controller, and Electronics. A test mass is allowed to free-fall inside the evacuated Dropping Chamber. The Interferometer is used to monitor the position of the freely-falling test mass.

  • Page 10: The Dropping Chamber

    Design: Components and Function 2.1. The Dropping Chamber The Dropping Chamber (Figure 2-2 and Figure 2-3) is an evacuated chamber which contains the Cart/Drag-Free Chamber which houses the Test Mass. A Drive Mechanism is used to drop, track, and catch the test mass inside the drag-free chamber.
  • Page 11 Design: Components and Function Figure 2-3 Side view of the dropping chamber CART/DRAG-FREE CHAMBER 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.
  • Page 12 Design: Components and Function dropping and catching the test mass, as well as returning it to the top of the chamber for the next drop. A Light Emitting Diode (LED) , located on the cart, directs light through an optical glass sphere attached to the test mass. The sphere focuses the light onto a linear detector, also mounted on the cart.

  • Page 13: Test Mass

    Design: Components and Function Figure 2-5 Side view of the cart/drag-free chamber 2.1.1.TEST MASS The Test Mass (Figure 2-4 and Figure 2-5) is a retroreflective corner cube surrounded by a support structure and balanced at the optical center of the corner cube.

  • Page 14: Drive Mechanism

    Design: Components and Function 2.1.2.DRIVE MECHANISM The drive mechanism (Figure 2-2) is a support structure inside the dropping chamber on which the cart/drag-free chamber travels up and down, driven by a DC servo motor. 2.1.3.SERVICE RING The Service Ring (Figure 2-6 and Figure 2-7) is the base of the Dropping Chamber.

  • Page 15: Viewing Port

    Design: Components and Function Figure 2-7 Top view of the service ring. 2.1.4.VIEWING PORT The viewing port (Figure 2-2 and Figure 2-3) is located in the top flange of the dropping chamber. It allows visual observation of the dropping chamber interior when the rotation monitor is not fitted to the system.
  • Page 16 Design: Components and Function When the cart has traveled about 5 mm downward from the hold position (as measured by the shaft encoder) a separation of about 3 mm between the cart and test mass has been achieved. The dropper controller then uses feedback from the linear detector to maintain this separation for the remainder of the drop.

  • Page 17: The Interferometer

    2.2.1.LASER The FG5 employs a stabilized helium-neon laser to provide an accurate and stable wavelength used in the interferometric measurement system. There are two lasers which are currently available for the FG5.
  • Page 18 Design: Components and Function The test beam passes through the top window of the Superspring chamber to a corner cube in the Superspring mass. The test beam is then reflected back through the window to the interferometer base, where it hits mirror #5, passes through the translator plate, hits mirror #6, and is recombined with the reference beam at beamsplitter #2.
  • Page 19 Design: Components and Function Figure 2-8 Top view of interferometer optics and beam path 2-11...
  • Page 20 Design: Components and Function Figure 2-9 Side view of interferometer optics and beam path 2-12...

  • Page 21: The Superspring

    Design: Components and Function 2.3. The Superspring The Superspring (Figure 2-10) is a long-period, active vertical isolator used to compensate for small vertical motions of the first beam splitter. The Superspring has a short (20-cm) mainspring with a natural period of about 1 second.
  • Page 22 Design: Components and Function Figure 2-10 The Superspring. 2-14...

  • Page 23: The System Controller

    (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 data if the FG5 is equipped with these systems.

  • Page 24: Required Hardware

    • Micro-g Solutions Environmental Sensors Package • Micro-g Solutions Rotation Monitor 2.4.3.SOFTWARE The FG5 software consists of a bundled set of DOS-based applications. The software provides FG5 data acquisition, real-time processing, post processing, and diagnostic testing. It also allows the user to customize the data acquisition for each site including input/output files, printing options, and session control.

  • Page 25: Electronics

    ® ® incompatible 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: •...
  • Page 26 Design: Components and Function The Rubidium Oscillator is an atomic resonance-controlled oscillator or equivalent which outputs a stable sinusoidal signal of 10 MHz. The Universal Time Interval Counter (UTIC) measures the time interval between the occurrence of each scaled fringe and the next scaled clock pulse. Using this information, the system controller computes the absolute time of occurrence of the scaled fringes.

  • Page 27: Dropper Controller

    Design: Components and Function 2.5.2.DROPPER CONTROLLER The dropper controller uses three modes to operate the dropping chamber. These modes are OSC, AUTO, and MANUAL. The operator also controls the status of these modes and the dropper triggering with the RESET and INIT switches and the trigger source (INT/EXT) switch.

  • Page 28: Laser Controller

    2.5.5.POWER SUPPLIES The electronics case contains all the power supplies which are required to operate the FG5. They consist of two primary units: The Micro-g Solutions Model 125 Portable Ion Pump Power Supply is located in the front of the electronics case. It supplies power to the ion pump for both AC and DC operation.

  • Page 29: Optional Systems

    FG5. 2.5.6.OPTIONAL SYSTEMS There are two optional systems for the FG5: the Environmental Sensors Package and the Rotation Monitor. The environmental sensors package can be added to the system by itself, but if the rotation monitor is purchased, the environmental sensors package must be included in the system.
  • Page 30 Design: Components and Function The rotation monitor (Figure 2-13) is used to monitor and record the rotation of the test mass during each drop. The rotation monitor consists of a rigid anodized aluminum housing mounted on the top flange of the dropping chamber, above the viewing port.

  • Page 31: Rotation Monitor

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

  • Page 33: Setting Up The Fg5

    4, “Adjustment and Maintenance” for instructions, before proceeding with set up. When setting up the FG5, it is helpful to use the FG5 Setup Checklist in Appendix D, page 9-4. 3.1.1.INTERFEROMETER 1. 1. Locate and mark a reference point on the floor where gravity will be measured.

  • Page 34: Electronics Case

    How to Set Up and Run the FG5 AND LEVEL AS POSSIBLE. IT IS BEST TO SET UP THE FG5 ON A CONCRETE OR HARD TILE FLOOR! 3.1.2.ELECTRONICS CASE 6. Place the electronics case in a convenient location within two meters of the interferometer.

  • Page 35: Model Al-1 Laser

    How to Set Up and Run the FG5 3.1.2.1.Model AL-1 Laser: 3.1.2.1.1.Warm Up • Set the LOOP switch to the OPEN position. • Turn the switch on the laser controller to MANUAL. • DO NOT ADJUST THE COARSE GAIN KNOB.

  • Page 36: Weo Model 100 Laser

    How to Set Up and Run the FG5 3.1.2.2.WEO Model 100 Laser • Turn on the power (main power and HV key switches). • Select the proper iodine peak. • Set the servo control to AUTO. • Do not adjust any other controls. Nominal control settings are:...
  • Page 37 How to Set Up and Run the FG5 MAKE SURE THE HANDLES ON THE INTERFEROMETER ARE IN THE UP POSITION AND THE TOP DUST CAP HAS BEEN REMOVED. 17. Slide each of the three horizontal alignment pins on the top of the interferometer radially outward by pulling the 5-lobe knobs until they stop.

  • Page 38: Ion Pump

    How to Set Up and Run the FG5 3.1.4.ION PUMP 22. Recheck the AC,BAT, and HV switches on the ion pump power supply, and make sure they are off. 23. Connect the ion pump HV cable (#9) to the ceramic connector on the pump.

  • Page 39: Rough Leveling Interferometer

    How to Set Up and Run the FG5 3.1.5.ROUGH LEVELING INTERFEROMETER Note: While leveling the interferometer and dropping chamber tripod, note that turning the tripod feet clockwise lowers the dropping chamber tripod and turning the interferometer feet clockwise raises the interferometer.

  • Page 40: Dropper Verticality

    How to Set Up and Run the FG5 3.1.6.DROPPER VERTICALITY 31. After each foot is in contact with the tripod leg, rotate each tripod foot leveling screw exactly one revolution (counterclockwise), using the mark on the top of the adjustment screw as a reference. This raises the tripod off the interferometer just enough to take the weight of the tripod and dropping chamber off the alignment pins.

  • Page 41: Vertical Adjustment Of The Test Beam

    How to Set Up and Run the FG5 35. With both beam blockers pushed in, look through the telescope and focus the crosshairs with the telescope by rotating the eyepiece. It may be helpful to place a white card in front of the telescope to see the crosshairs better.
  • Page 42 How to Set Up and Run the FG5 3-10...

  • Page 43: Reference Height

    Record this value (the Superspring reference height added to the vertical distance indicated by the brass V-posts in cm) in the system check log as the reference height. It must be entered in the FG5COMND.DAT file before beginning observations. Consult the FG5 Software Manual for instructions. 3-11...
  • Page 44 How to Set Up and Run the FG5 Figure 3-2 V-Post 3-12...

  • Page 45: The Superspring

    How to Set Up and Run the FG5 3.1.10.THE SUPERSPRING 43. Remove the dust cap from the top window of the Superspring. Make sure the Superspring locking mechanism is engaged. Then carefully slide the Superspring under the interferometer base. The top Superspring flange has three “ears”.

  • Page 46: Travel Lock

    How to Set Up and Run the FG5 CAUTION: DO NOT ADJUST THE LEVELING VIALS THEMSELVES. They are preset to provide the correct internal vertical reference for the Superspring. 3.1.11.TRAVEL LOCK 46. Release the Superspring travel lock by pulling out the brass travel lock knob until it engages the shaft and slowly rotating it counterclockwise until it reaches the stop (190°).
  • Page 47 • Connect 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).

  • Page 48: Superspring Zero-Positioning

    The Superspring can be left in this condition, but it is still advisable to turn the rotary knob to OFF before closing the Superspring coil loop (switch set to CLOSED on the front panel). WINDOW mode is currently not supported by the FG5 software. 3-16...

  • Page 49: Fringe Optimizing

    How to Set Up and Run the FG5 When setting the zero position, it is very important to make sure that the mass is hanging freely, and is not out of range. A substantial variation in SPHERE OUT voltage when the servo loop is open indicates that the mass is hanging freely.
  • Page 50 How to Set Up and Run the FG5 coincident in the viewing periscope. Adjustment of the translator plate does not affect the appearance of the beams in the telescope. 55. If the two beams can be overlapped using the twiddler, skip to step 58. If the translator plate does not have enough range to make both beams coincident, there are two methods of adjustment.

  • Page 51: Dropper Controller

    3.2. Running the FG5 The FG5 begins observations when the realtime data program, OLIVIA, is executed. Consult the FG5 Software Manual for instructions on operating the program. The software manual also includes information about software features, gravity corrections, output displays, and input/output file descriptions, as well as data analysis and trouble shooting.

  • Page 52: Program Setup

    1f signals, be sure to reconnect the BNC cable between the signal monitor connector on the laser controller and channel 4H of the IO/TECH BNC 16. 3.2.2.PROGRAM SETUP 5. Begin observations by executing the OLIVIA program. Refer to the FG5 Software Manual for instructions. 3.3. Shutting Down the FG5 3.3.1.COMPUTER...
  • Page 53 How to Set Up and Run the FG5 1. Backup the data. 2. Shut off computer power. 3-21...

  • Page 54: Superspring

    How to Set Up and Run the FG5 3.3.2.SUPERSPRING 3. Set the switch on the front panel of the Superspring controller to OPEN. 4. Engage the Superspring travel lock. The arrow on the lock know points down when it is locked and up when it is unlocked.

  • Page 55: Dropping Chamber

    How to Set Up and Run the FG5 3.3.4.DROPPING CHAMBER 7. Press RESET on dropper controller. 8. Disconnect the shaft encoder, motor power, and cart control cables from the dropping chamber. 9. Engage the dropping chamber travel lock. 3.3.5.POWER 10. Turn off the UTIC and any other devices that are still on.

  • Page 56: System Controller

    How to Set Up and Run the FG5 The following cables may be disconnected from exterior components and remain connected to the electronics case. They are rolled up and stored inside the electronic case during shipment. 8. Ion pump HV supply cable 9.

  • Page 57: Dropping Chamber

    How to Set Up and Run the FG5 3.4.4.DROPPING CHAMBER 21. Lock the cart by turning the locking hub counterclockwise using a 4 mm Allen wrench or ball driver until the cart stops moving. 22. Pull and rotate travel lock knob 90°, allowing the pin to drop onto the hub, then rotate the lock clockwise until the pin engages the hub.

  • Page 58: Interferometer

    How to Set Up and Run the FG5 3.4.7.INTERFEROMETER 31. Loosen the three locking screws of the telescope rail assembly. Slide the assembly off the interferometer base and place it in the Superspring case. Make sure the lens cap of the telescope is in place.

  • Page 59: Adjustment And Maintenance

    Adjustment and Maintenance 4. Adjustment and Maintenance NOTE: The FG5 has been engineered to use metric screws and dimensions wherever possible. However, some “off-the-shelf” purchased components use English screws and dimensions. 4.1. The Dropping Chamber 4.1.1.REPLACEMENTS AND ADJUSTMENTS 4.1.1.1.Removing The Dropping Chamber Cover When opening the dropping chamber, take great care not to contaminate the inside surface of the chamber cover or any of the interior parts.

  • Page 60: Replacing The Dropping Chamber Cover

    Adjustment and Maintenance and back out the screws which position the top ring of the dropping mechanism within the chamber cover. Remove the six screws holding the chamber cover and handles to the service ring, and carefully lift the cover up over the dropping mechanism.

  • Page 61: Adjusting The Drive Belt Tension

    Adjustment and Maintenance of the cart with two socket head screws. Remove the clamp and slide the ends of the belt off the dowel pin. Remove the belt. Before installing a new belt, clean both of the pulleys with acetone or alcohol on a cotton swab.

  • Page 62: Replacing The V-Plate

    Adjustment and Maintenance Loosen the English 4-40 clamp screws on the Helical coupling between the motor and the Ferrofluidic vacuum feedthrough by reaching through the access hole in the motor mount. Remove the three ¼-28 English screws which attach the motor mount to the Conflat vacuum flange on the service ring. Remove the motor mount assembly (including motor, Helical coupling, travel lock plate, and encoder) from the Conflat vacuum flange, leaving the Conflat flange and Ferrofluidic vacuum feedthrough attached to the service ring.

  • Page 63: Replacing The Linear Bearings

    Adjustment and Maintenance cover to the cart, observing the position of the post. Gently lift the cover off, being careful not to damage the wires connected to it. To remove the V-plate, the test mass must be partially disassembled. First, note the orientation of the top part of the test mass and the V-plate.

  • Page 64: Replacing The Shaft Bearings-Drive Pulley

    Adjustment and Maintenance Two retaining rings secure each bearing to the cart. To remove the rings, they must be wound off the end of each bearing. Slide the linear bearings out of the cart and slide the new ones in. Replace the retaining rings. NOTE: Venting holes have been added to the linear bearings by Micro-g Solutions.

  • Page 65: Replacing The Shaft Bearings-Top Pulley

    Adjustment and Maintenance Figure 4-1 Drive Pulley Assembly CAUTION: DO NOT DEFORM THE BOWED RETAINING RING. Remove the retaining ring from the other end of the shaft. Slide out the pulley shaft, taking care not to lose the Woodruff key, and remove the pulley from the bearing mounting yoke.

  • Page 66: Pumping Down The Dropping Chamber

    Adjustment and Maintenance main encoder housing off the encoder back plate with a flat blade screwdriver. The back plate must remain attached to the travel lock plate with three screws to maintain proper alignment. To reassemble, snap the new encoder over the encoder back plate, which was left attached to the travel lock plate.

  • Page 67: The Interferometer

    Adjustment and Maintenance 4.2. The Interferometer 4.2.1.TROUBLESHOOTING THE BEAM PATH Periodic adjustments of the beam path can be made with the mirrors. (For a detailed description of the beam path, see Chapter 2). Adjustments of the beam path through the beam expander and the beam splitter assemblies are performed separately.

  • Page 68: 2-Faraday Isolator Combination

    Adjustment and Maintenance The standard optical isolator is attached to the interferometer base by two screws in the bottom. The optical element has a preferred orientation with the linear polarizer first. This can be tested by rotating the optical isolator. You should notice that you can change the light level from very bright to very dim by rotating the isolator.
  • Page 69 Adjustment and Maintenance pass through the first pinhole and then use the second mirror (#2) to adjust the beam angle so that it passes through the second (furthest) pinhole. 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...

  • Page 70: Beam Expander

    Adjustment and Maintenance Figure 4-3 Beam expander 4.2.2.6.2.Collimating lens: Insert the collimating lens (128mm focal length) into the mount and adjust the position of the lens to be about 153.4mm from the optical center of the focusing lens. Look through the telescope at the spot and minimize the diameter of the spot in the telescope by moving the collimating lens back and forth.

  • Page 71: Leveling The Dropper

    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/div.

  • Page 72: Setting The Bubble Levels On The Tripod

    Adjustment and Maintenance Once this procedure is finished, the tripod is adjusted so that the cart is traveling vertically. Without changing anything the bubble levels should now be reset to indicate level. 4.2.2.10.Setting the Bubble Levels on the Tripod Once the cart travel is vertical, the tripod bubble levels should be adjusted to show level.

  • Page 73: Adjusting The Superspring Position And Final Adjustment Mirror

    Adjustment and Maintenance This step assumes that the tripod levels have been set so that level ensures that the cart travel is vertical. Now we will adjust the interferometer so that it is referenced to the tripod tray bubble levels that were set in the last step. This next adjustment will ensure that the beam is vertical and travels cleanly through the dropper when the dropper and tripod are sitting on the interferometer base with the bubble levels indicating level.

  • Page 74: Final Mirror Translation-Getting Beams Overlapped In Fringe Viewer

    Adjustment and Maintenance should be loosened slightly and the Superspring leveled. These M5 screws have a M4 hex socket head. The Superspring should be unlocked mechanically to let free the reference test mass. The translator plate underneath the interferometer base (twiddler) should be put into its mid range position so that the glass surface is normal to the beam.

  • Page 75: Adjusting The Fringe Amplitude

    Adjustment and Maintenance Steering the beam onto the APD: The beam can be steered onto the APD using the mirror mount holding the APD focusing lens. You should notice that the beam is either on or off of the sensitive APD area (there is not a sharp maximum, but a rather flat response) as you sweep the beam across the APD.

  • Page 76: The Superspring

    Adjustment and Maintenance 4.3. The Superspring 4.3.1.REPLACEMENTS AND ADJUSTMENTS 4.3.1.1.Removing the Superspring Cover If it is necessary to remove the top flange for any reason, be sure to replace the flange in the same orientation. Align the large ear of the top flange directly above the travel lock knob on the service ring.
  • Page 77 Adjustment and Maintenance MAKE SURE TO NOTE THE COLOR CODING ON THE CONNECTORS FOR LATER RECONNECTION. Remove the travel lock knob by removing the flat-head screw from the center of the knob and sliding the knob off the shaft. The knob is comprised of three pieces: the brass knob, the control spring retainer, and the internal spring.

  • Page 78: The Mass Mainspring/Hanger

    Adjustment and Maintenance Remove the voice coil by removing its three attachment screws inside the emitter-detector block. Reverse the procedure for reassembly. 4.3.1.4.The Mass Mainspring/Hanger The upper spring hanger assembly has a flexible thin wire member which is soldered into the Superspring hanger and the coarse adjustment screw.
  • Page 79 Adjustment and Maintenance Remove the Superspring cover as previously described. Put a dust cover over top of the main tube to keep dust from falling on the test mass and upward-facing corner cube (a piece of paper or foil over the tube will suffice). Remove the service ring as previously described.

  • Page 80: Assembling The Superspring

    Adjustment and Maintenance lever. Screw on top nut to hold in position then remove the tool. (Set approximately in center of coarse adjustment screw travel). Rotate test mass so beam holes in top lever and copper test mass roughly match. 4.3.1.6.Assembling the Superspring Replace emitter-detector block in the original orientation.
  • Page 81 Adjustment and Maintenance Viewing from top, carefully rotate the corner cube and visually align the beam holes in top lever with the ones in the copper Test mass, adjust by rotating the coarse adjustment screw and lock in position by tightening both top and bottom nuts.

  • Page 82: Replacing The Focus Lever Motor

    Adjustment and Maintenance 4.3.1.7.Replacing the Focus Lever Motor Loosen and remove the nut on the focus adjustment screw. Lower the focus lever motor assembly off the fulcrum lever. Loosen the set screw holding the hex bushing to the motor shaft and raise the bushing out of the way.

  • Page 83: Timing System And Data Acquisition

    Adjustment and Maintenance THE POSITION OF THE DELTA RODS DETERMINES THE CLEARANCE BETWEEN THE VOICE COIL (PUSHER) AND THE MAGNET ASSEMBLY. IT IS IMPERATIVE THAT THE ASSEMBLY NOT RUB OR DRAG! To field check the alignment, measure the gap between the support structure pins and the center tube assembly with a feeler gauge.

  • Page 84: Avalanche Photo Diode Printed Circuit Board

    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 the interferometer base. A high-speed comparator and 50-Ω driver on the APD board minimize noise problems on the long cables between the interferometer base and the scaler- counter board.
  • Page 85 Adjustment and Maintenance The analog output is buffered by an OP AMP directly from the APD. The zero-crossing of the fringe signal is determined by the high speed comparator, which in turn drives a 50-Ω line driver chip. A 40-mV hysteresis is implemented on the discriminator to avoid multiple triggering.

  • Page 86: Scaler-Counter Printed Circuit Board

    Adjustment and Maintenance 4.4.1.3.Scaler-Counter Printed Circuit Board The scaler-counter board has several major functional blocks: Clock discriminator Clock scaling Scaled clock count accumulator Fringe scaling Scaled fringe accumulator Accumulator/computer data latching Miscellaneous I/O interface circuitry The incoming clock signal is converted to TTL levels (1), and then scaled (2) according to a three-digit hexadecimal value selected with three PCB hex switches.
  • Page 87 Adjustment and Maintenance 4-29...
  • Page 88 Adjustment and Maintenance SCALER-COUNTER SIGNALS BNC INPUTS DESCRIPTION Clock In 50-Ω terminated input from 10-MHz Rubidium Oscillator Latch In TTL pulse from UTIC that latches count data for reading by the computer Input Fringes 50-Ω terminated TTL prediscriminated fringe signal from APD board Valid Data TTL signal from controller indicating object in free- fall...
  • Page 89 Adjustment and Maintenance Throw Init TTL control line to controller used to initiate a throw cycle Laser Control TTL signal to laser controller used to indicate which mode to lock (red or blue) Table 4-2 Scaler Counter Signals DB-37 CONNECTOR SIGNALS TO COMPUTER NAME TYPE DESCRIPTION...

  • Page 90: Rubidium Oscillator

    Table 4-3 DB37 Connector 4.4.1.4.Rubidium Oscillator The FG5 uses a rubidium oscillator as a frequency standard (atomic clock). The oscillator generates a 10-MHz sine wave with amplitude of .5Vrms into 50 Ω. It is used by the UTIC and scaler-counter to provide accurate time information.
  • Page 91 Adjustment and Maintenance 4-33...

  • Page 92: Universal Time Interval Counter

    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 is configured for 20 input lines and 4 output lines.

  • Page 93: Dropper Controller

    Adjustment and Maintenance 4.5. DROPPER CONTROLLER The dropper controller is a flexible control circuit (programmable servo controller) that can direct the motor to servo the cart (and test mass) to a specified height in the dropping chamber using a rotary shaft encoder, or to a specific velocity, again using the shaft encoder.

  • Page 94: Dropper Control Modes

    Adjustment and Maintenance critical positions such as launch points or hold points. The set points are well-controlled against environmental variables. The controller circuit board currently supports four different modes of operation: STANDBY, MANUAL, OSCILLATE and DROP. 4.5.1.DROPPER CONTROL MODES 4.5.1.1.STANDBY 4.5.1.1.1.To Select This mode is chosen upon power-up, when the front panel RESET button is pressed, or when a time-out has occurred (usually indicating failure).

  • Page 95: Function:

    Adjustment and Maintenance 4.5.1.2.2.Function: The front panel potentiometer controls a servo position for the cart. The cart servo will not initiate until the trimpot is within a predefined window of the actual cart position. This will time out after 20-30 seconds if the time out is enabled (default).

  • Page 96: Analog Servo

    Adjustment and Maintenance slip can cause the cart to drive into the bottom or top of the dropping chamber and burn out the motor. 4.5.2.Analog Servo The analog servo has three different sections. They are: Cart-position, Cart- velocity, and Sphere-position. The cart servos use the rotary shaft encoder as a position/velocity sensor.

  • Page 97: Cart Velocity

    Adjustment and Maintenance 4.5.2.2.Cart Velocity The servo takes the cart position derivative. A velocity lead trimpot on the PC-board adds phase margin which tends to speed up or damp the servo in the velocity mode. Servos that measure position and control velocity tend to have a slow exponential response without this precaution.

  • Page 98: Active Sphere Servo

    Adjustment and Maintenance 4.5.2.4.Active Sphere Servo The sphere signal is added with an offset called height and another offset called hover height. The height offset is always added to provide a tracking difference between the cart and the test mass during free-fall. The hover height is switched in by the EPROM and gives an overall reduced offset which makes the cart track the test mass very close to the rest position.

  • Page 99: Superspring Connections

    Adjustment and Maintenance 4.5.3.1.SUPERSPRING CONNECTIONS Name TYPE Destination Name Front Panel: SPHERE OUT BNC16 COIL OUT Back Panel: COMP OUT NOISE INJECT Table 4-5 Superspring Connections The preamplifier relays the signal to the Superspring controller, which controls a motor. The motor drives a lever system that raises and lowers the mass and mainspring.

  • Page 100: Motor Drive Selection

    Adjustment and Maintenance The LED driver supplies a constant current to drive the LED in the Superspring can. This current can be adjusted internally using the potentiometer (pot). The sphere signal buffer buffers the signal from the Superspring can so it can be routed to different parts of the board.

  • Page 101: Remote

    Adjustment and Maintenance 4.5.3.2.4.REMOTE The Superspring can be made to zero using an external TTL signal. 4.5.3.2.5.MANUAL In manual mode, the spring motor is controlled by the potentiometer (pot) on the front panel. A setting greater than 5 will move the spring up less than 5 will lower the spring.

  • Page 102: Maintenance Schedule

    Adjustment and Maintenance 4.5.4.Maintenance Schedule To keep the instrument at its optimum performance level proper maintenance procedures should be periodically performed. 4.5.4.1.Annually Inspect, 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.

  • Page 103: Troubleshooting

    5.1. The FG5 System The FG5 absolute gravimeter is an extremely sensitive instrument which must be set up and operated with the utmost care to achieve optimum results. It is especially important to maintain a system check log during set up and observation.
  • Page 104 Troubleshooting...
  • Page 105 Troubleshooting Problem Solution Dropping chamber will not drop Travel lock engaged Controller not initiated Current at portable ion pump power increases Ferrofluidic rotary feedthrough needs to after each drop. be replaced. Vacuum level (ion pump current) consistently This can be caused by a small leak in the high.

  • Page 106: Interferometer And Laser

    Troubleshooting connection. Check that the cart voltage changes as you manually lift the mass (using a hex wrench). Very bad sound during drop Sphere signal is not present because of the cable is not connected or a there is a bad cable/connector.
  • Page 107 Troubleshooting adjusted. Iodine cell needs rotation adjustment to maximize beam. Laser tube needs to be replaced. WEO laser will not lock Ambient temperature too high (30C) Laser not warmed up Laser sweep turned on Incorrect toroid voltage setting Large systematic signal in the least-squares Interferometer base and dropper tripod residual plot.
  • Page 108 Troubleshooting instrument, or optical feedback) Large residual amplitude Check parameter file, do not fit past point Bad cables, especially PIO ribbon cable Bad grounding of fringe signal 10nm residual frequency swept Wrong laser type selected Incorrect laser modulation frequency entered in the fg5param.dat file No fringes at all No power to APD.

  • Page 109: Superspring

    Troubleshooting 5.2.3.SUPERSPRING A Superspring problem usually results in gravity data with a large drop-to- drop scatter. A chart recorder is very helpful in monitoring the status of the Superspring. A two channel recorder can monitor both sphere and coil output. However, if a one channel recorder is used, it is best to monitor coil output.
  • Page 110 Troubleshooting detector. The Superspring is still locked. Spring damps suddenly after Spring is off level, check bubble unlocking. levels for proper level. Spring is out of range and is hitting upper or lower physical limit of the spring. Horizontal flexure ( delta rod )has been damaged and needs replacement.

  • Page 111: System Controller

    Troubleshooting 5.2.4.SYSTEM CONTROLLER Since the system controller performs real time gravity computations/corrections, records data, and initiates the dropping sequence, a failure of this component results in a catastrophic system failure. Table 5-4 gives a list of problems and possible solutions for the system controller. The primary source of all problems encountered with the controller units have been with poor cable connections or the computer to docking station connection and lock in.

  • Page 112: Electronics

    5.2.5.ELECTRONICS The system electronics consists of the timing system, controllers for primary subsystems, and power supplies for most components in the FG5. Some of the electronic subsystems are manufactured by Micro-g Solutions, while others are “off-the-shelf” components from other commercial vendors.
  • Page 113 Troubleshooting Beam verticality is off Beam is not collimated High rotation/translation of test mass Wrong laser lock or the laser hopped a peak. Sinusoidally varying gravity value Rubidium standard is warming up or will not lock. VCXO trim may need adjustment. Large noise (often looks like a Poor system grounding.

  • Page 114: Environmental Sensors Package

    Troubleshooting 5.2.6.ENVIRONMENTAL SENSORS PACKAGE The environmental sensors package is an optional system for the FG5. Therefore, if there is a major failure, it is possible to continue observations. Occasionally, the operator can obtain temperature and pressure data from an alternate source. If the pressure data is accurate enough ( ± 1 mb or better), local barometric pressure attraction corrections accurate to better than one µGal can still be computed and applied during post processing.

  • Page 115: Rotation Monitor

    Troubleshooting 5.2.7.ROTATION MONITOR The rotation monitor is an optional system for the FG5, so it is possible to operate the FG5 without it. The rotation monitor is a diagnostic tool which is used to determine if there is excessive rotation of the test mass about a horizontal axis (i.e.

  • Page 116: Gravity Site Selection

    5.3.4.TEMPERATURE STABILITY Although the FG5 will operate properly over a wide temperature range, it is important to have a site with good temperature stability to minimize possible problems with temperature sensitive components (e.g. laser and Superspring).
  • Page 117 Troubleshooting 5-15...

  • Page 118: Ac Power

    Troubleshooting 5.4. AC POWER Problems with AC power are not uncommon, especially in remote field environments. Make sure that ground is available before plugging in system. It is 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...

  • Page 119: Switching The Ac Power

    Appendix A Switching the AC Power 6. SWITCHING THE AC POWER Switching between 100-115VAC and 220-240 VAC NOTE: Check the manuals for each component to determine the proper fuse for the line voltage being used. 6.1. LASER 6.1.1.WEO Model 100 Laser Possible voltage selection positions (50-60Hz): 100, 115, 220, and 240 1.

  • Page 120: Main Power Supply

    Appendix A Switching the AC Power Stanford Research Systems SR 620 Time Interval Counter Possible voltage selection positions (50-60Hz): 100, 115, 220, and 240 1. Remove AC plug 2. Remove card selector with a paper clip or needle nose pliers. 3.

  • Page 121: Computer

    AC power cord. Some models (such as the IBM ThinkPad) use a universal power supply, so switching is not required. Please check the computer manual supplied with the FG5 for complete details. 6.6. Docking Station Select the proper line voltage (115 or 230 VAC) using the red switch located at the rear of the docking station.
  • Page 122 Appendix A Switching the AC Power 1. To switch input power settings, make sure power cables are not connected to the turbo pump, then remove the access panel at the rear of the motor and use Table 6-1 to set for the proper input voltage. High Voltage (220-240 VAC) Low Voltage (100-115 VAC) Connector...

  • Page 123: Pumping/Baking The Chamber

    7.1. Choosing the Pumping Method A 70 l/s turbo pumping station (turbo pump, backing pump, and controller/power supply) is currently included with each FG5, and is used to evacuate the dropping chamber when necessary. It is possible to use a turbo pump as small as 40 l/s, if necessary, with good results.

  • Page 124: Connecting The Turbo Pump To The Dropping Chamber

    Appendix B Pumping/Baking the Chamber 7.2. Connecting the Turbo Pump to the Dropping Chamber Remove the turbo pump from its shipping case and make sure it is set for the proper AC line voltage (see appendix A). Place the lid of the turbo pump case on the floor near the dropping chamber and interferometer.

  • Page 125: Heating The Chamber

    Appendix B Pumping/Baking the Chamber The turbo-pump should reach normal operational speed in a few minutes. If the pump indicates a high load for an extended period it indicates that there is a leak in the system. While the turbo-pump is pumping down the system it is very important that the AC power is not interrupted.

  • Page 126: Starting The Ion Pump

    Appendix B Pumping/Baking the Chamber Turn off the heat tapes and allow the turbo pump to continue pumping the chamber for at least 4 hours. Make sure that the test-mass remains locked until the chamber is completely cool. When the chamber has returned to ambient temperature, remove the heat tapes and reinstall the ion pump magnet package.

  • Page 127: The Rotation Monitor

    Appendix C The Rotation Monitor 8. THE ROTATION MONITOR 8.1. INSTALLATION Remove two opposing M6x25 screws holding the test chamber top flange. Attach the attitude monitor to the top flange using two M6x35 screws. There should be no washers underneath the screws holding the top lid or the rotation monitor will not set flat.

  • Page 128: The Data Logging System

    Appendix C The Rotation Monitor Verify that there is good sensitivity to motion of beam using mirror mount #3. Sometimes an extra reflection from the glass viewport will interfere with the measurement. Any extraneous reflections can be blocked with a piece of paper or tape.

  • Page 129: Checklists And Logs

    9. Checklists and Logs It is helpful to use checklists to assure that critical tasks associated with operation of the FG5 are done correctly. Logs are strongly recommended so the operators can easily record the status of the system and document any information (e.g.

  • Page 130: Switching The Ac Power

    Appendix D Checklists and Logs 9.1. Switching the AC Power Switching the AC voltage checklist Determine and use proper fuse for each component. WEO 100 Laser: Use drum in power entry module. Remove drum from power entry module before rotating. AL-1 Laser: Use card in power entry module.
  • Page 131 Appendix D Checklists and Logs...

  • Page 132: Fg5 Setup

    Appendix D Checklists and Logs 9.2. FG5 Setup FG5 SETUP CHECKLIST Unpack and assemble interferometer. Position interferometer over reference mark. Orient so laser is in the north-south direction, if possible Set up electronics case and remove covers. Check AC line voltage. Connect main AC power cable.
  • Page 133 Appendix D Checklists and Logs Rough level interferometer using bubble levels on tripod tray. Place tripod feet under tripod until they just contact nylon ball on tripod legs. Raise dropper above interferometer (1 turn for each foot). Make sure interferometer and dropper do not touch. Check levels on tripod tray and center, if necessary.
  • Page 134 Appendix D Checklists and Logs Connect three cables to the dropping chamber: Vacuum feedthrough (white Lemo), motor cable (orange Lemo), shaft encoder (blue Lemo). Connect BNC from temperature probe on tripod tray to BNC 16 1H. Connect Superspring cable. Connect APD power (green Lemo). Connect BNC fringe signal to interferometer TTL port and front panel of Scaler/Counter.
  • Page 135 Verify 1f signal of the WEO and put these values in the FG5param.dat file. Make sure that the time constant is set to 1f. Reconnect BNC from WEO 1f signal to BNC16 4H channel. Set up the software to run correctly at the site. Table 9-2 FG5 Setup...

  • Page 136: Dropping Chamber Pump Down And Bake-Out

    Checklists and Logs 9.3. Dropping Chamber Pump Down and Bake-Out FG5 PUMP DOWN AND BAKE-OUT Set turbo pump for proper line voltage (see appendix A). Place turbo pump on case lid and connect pump to dropper with flexible stainless steel tube.

  • Page 137: Dropping Chamber Maintenance

    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 Removing Dropping Chamber Cover Checklist...

  • Page 138: Replacing Dropping Chamber Cover

    Appendix D Checklists and Logs Unlock valve locking ring and slowly open valve. Vent with dry nitrogen, if possible Remove top flange. Loosen snubber lock nuts and screws. Remove chamber cover from service ring. Keep bottom flange clean and protect O-ring surface. Table 9-4 Removing Dropper Cover 9.4.2.Replacing Dropping Chamber Cover...

  • Page 139: Replacing Drive Belt

    Appendix D Checklists and Logs After installing dropper, adjust level bubbles on tripod tray. Table 9-5 Replacing Dropper Cover 9.4.3.Replacing Drive Belt Replacing Drive 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.
  • Page 140 Appendix D Checklists and Logs Table 9-6 Replacing Drive Belt 9-12...

  • Page 141: Adjust Belt Tension

    Appendix D Checklists and Logs 9.4.4.Adjust Belt Tension Adjusting Belt Tension Checklist Tighten belt adjustment screw until belt is straight. Tension belt by tightening adjustment screw three turns (until tension spring is just short of coil bind). or tension belt using torque wrench.

  • Page 142: Replacing V-Plate

    Appendix D Checklists and Logs Remove Conflat mounting screws. Remove Conflat (with feedthrough attached). Remove Helical coupling from feedthrough. Unscrew feedthrough from Conflat flange. Lubricate O-ring on new feedthrough. 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...
  • Page 143 Appendix D Checklists and Logs Remove top drag-free cover from cart and pull out of the way (do not detach 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.

  • Page 144: Replacing The Linear Bearings

    Appendix D Checklists and Logs 9.4.7.Replacing the Linear Bearings Replacing Linear Bearings Checklist Remove dropping chamber cover. Remove drive belt. Remove top rod ring. Remove upper bumper stop assembly. Remove ribbon cable wires and clamp from cart. Lift cart off guide rods. Remove two retaining rings for each linear bearing (wind off end of bearing).
  • Page 145 Appendix D Checklists and Logs Table 9-10 Replace Linear Bearings 9-17...

  • Page 146: Replacing Shaft Bearings (Drive Pulley)

    Appendix D Checklists and Logs 9.4.8.Replacing Shaft Bearings (Drive Pulley) Replacing Shaft Bearings (Drive Pulley) Checklist Remove dropping chamber cover. Remove drive belt. Disconnect Helical coupling between pulley shaft and Ferrofluidic feedthrough. Remove screws holding bottom rod ring to bottom flange. Rotate guide rod structure so shaft clears service ring.

  • Page 147: Replacing Shaft Bearings (Top Pulley)

    Appendix D Checklists and Logs Push bearings out of yoke. Make sure new bearings are cleaned and lubricated with Krytox LVP low vacuum grease. Reassemble in reverse order (make sure bowed snap ring is oriented correctly and fully seated in groove). Table 9-11 Shaft Bearings- Drive Pulley 9.4.9.Replacing Shaft Bearings (Top Pulley)

  • Page 148: Replacing Rotary Shaft Encoder

    Appendix D Checklists and Logs Remove retaining ring from other end of shaft. Remove pulley from bearing mounting yoke. Push bearings out of yoke. Make sure new bearings are cleaned and lubricated with Krytox LVP low vacuum grease. Reassemble in reverse order (make sure bowed snap ring is oriented correctly and fully seated in groove).
  • Page 149 Appendix D Checklists and Logs Table 9-13 Replace Shaft Encoder 9-21...

  • Page 150: Interferometer Alignment

    Appendix D Checklists and Logs 9.5. Interferometer Alignment Interferometer Alignment Checklist Adjust mirrors 1 and 2 (use alignment pinholes in spatial filter). Adjust optical isolator, if necessary. Reinsert 25.4 mm lens in spatial filter (curved surface toward input beam). Reinsert 128 mm collimating lens in spatial filter. Adjust collimating lens position by minimizing spot in telescope.

  • Page 151: Superspring Maintenance

    Appendix D Checklists and Logs 9.6. Superspring Maintenance 9.6.1.Removing Superspring Cover Removing Superspring Cover Checklist Remove Superspring cover (including top flange) from service ring. Do 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.

  • Page 152: Removing Service Ring

    Appendix D Checklists and Logs 9.6.3.Removing Service Ring Removing Service Ring Checklist Unplug in-line connector (on electrical feedthrough) closest to bulkhead. Remove 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.
  • Page 153 Appendix D Checklists and Logs Remove travel lock fork from main rod. Unhook support springs 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.

  • Page 154: Replacing Flexures

    Appendix D Checklists and Logs 9.6.5.Replacing Flexures Replacing Flexures Checklist Remove Superspring cover. Put dust cover over top main tube. Remove service ring. 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.
  • Page 155 Appendix D Checklists and Logs Remove emitter-detector block (including test mass, spring, and flexure). Note orientation of emitter-detector block. Wear plastic gloves when handling test mass. Remove spring from test mass (count number of spring turns holding upper anchor to main spring). Put lower lock nut on new flexure assembly.

  • Page 156: Assembling Superspring

    Appendix D Checklists and Logs Screw on top nut (to center of coarse adjustment tool). Remove pulling tool. Align beam holes in top lever and test mass. Table 9-19 Replacing Superspring Flexures 9.6.6.Assembling Superspring Assembling Superspring Checklist Replace emitter-detector block in original orientation (below lever pivots).
  • Page 157 Appendix D Checklists and Logs Check movement of center tube (so it doesn’t rub). Remove cable tie and foam or rubber shim. Recheck center tube for free movement. Make sure test mass is centered in cage and wires do not rub. Replace spring assembly in service ring (don’t tighten screws).

  • Page 158: Replacing Focus Lever Motor

    Appendix D Checklists and Logs Connect Superspring controller to Superspring. Drive zero-positioning motor (ZPM) until sphere voltage is zero. Measure gap between two levers near ZPM. Adjust coarse adjustment screw so motor will be in center of travel position (6 ± 0.5 mm gap between lever arms). Make sure sphere voltage goes +/- to assure true center position.

  • Page 159: Adjusting Micro-Switches

    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 Packing the FG5 Checklist Unplug cables from electronics rack and components. Store ion pump, GPIB, and PIO cables in electronics case.
  • Page 160 Appendix D Checklists and Logs Unplug power cords and printer cable from system controller and printer. Store in system controller case. Close system controller lid and place controller/docking station in system controller case. Close case and secure latches. Unplug all BNC and power cables from rotation monitor (if used). Store in rotation monitor case.
  • Page 161 Appendix D Checklists and Logs Place brass tripod feet in Superspring case, and blue pads in dropper case. Close dropping chamber case and secure latches. Engage Superspring travel lock. Remove Superspring from interferometer and insert top plug. Place Superspring in Superspring case. Remove telescope assembly from interferometer base.
  • Page 162 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: Index

    Aneroid Wafer Assembly......2-20, 4-24 Adjusting Micro Switches......9-27 Annual Maintenance ......... 4-42 Assembling Superspring ......9-24 APD ..............2-9 FG5 Setup ............9-3 Circuit ............4-26 Interferometer Alignment......9-18 Focusing the Beam ........4-17 Packing the FG5........... 9-27 Function ............2-17 Pump Down and Bake-Out ......
  • Page 164 Switching AC Power ........6-3 Features............1-2 Drive Belt History ............1-1 Replacing............4-2 Optional Systems ......... 2-21 Drive Mechanism ..........2-2 Setting Up ............3-1 FG5 Software ............ 2-16 Function............2-6 FG5 System............2-1 Driver LED ..............4-40 FG5COMND.DAT File Editing ............3-18 Drop Function............2-7...
  • Page 165 Index Linear Actuator ..........2-19 Linear Bearings Hardware Lubrication............. 4-6 Optional ............2-16 Micro-g Modifications ........4-6 Required ............2-16 Replacement........... 4-5 Linear Detector...........2-4, 2-19 Lubrication Linear Bearings..........4-6 O-Ring ............4-4 Installing Rotation Monitor......... 8-1 Pulley Bearings ..........4-7 Interference Fringe..........
  • Page 166 Reference Height Servo Motor/Drive Belt System......2-4 Measuring.............3-10 Setting Bubble Levels Removal Tripod ............4-14 Dropping Chamber Cover ......4-1 Setting Up The FG5 ..........3-1 Service Ring ..........4-18 Setup Replacement Dropper Controller........3-18 Coil...............4-19 Dropping Chamber Tripod......3-4 Drive Belt ............4-2 Electronics Case ..........
  • Page 167 Releasing ............. 3-13 Switching AC Power AL-1 Laser............. 6-1 Docking Station ..........6-3 Universal Time Interval Counter FG5 System ........... 6-1 Function ............2-18 Ion Pump Power Supply ........ 6-2 UTIC..............4-31 IOtech ADC 16 ..........6-3 Function ..........2-8, 2-18 Rear Mains Power Rack ........
  • Page 168 Index Replacement ..........4-4 Vacuum Valve .............2-6 Valve Vacuum ............2-6 WEO 100 Laser ..........2-9 Velocity Setup .............. 3-4 Cart...............4-37 Shutting Down ..........3-20 Venting the Dropping Chamber......4-1 Switching AC Power ........6-1 Vertical Adjustment Window Test Beam............3-9 Comparator ..........4-40 Vertical Alignment Dropping Chamber ........4-13 Verticality...

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