FG5 Absolute Gravimeter
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1. s Manual for more information it is also the interface between the user and the dropping chamber The controller can be operated in two modes OSC and DROP The operator controls the status of these modes and the dropper triggering with the RESET switch and the TRIGGER switch In DROP mode a single trigger causes the controller to drive the motor to lift the cart and test mass to a specified height An additional trigger then initiates the drop sequence the cart pulls away with an acceleration greater than g and then tracks the test mass maintaining a specified separation distance during free fall and finally softly catches the test mass at the bottom If a TTL pulse is entered into EXT TRIG this will also cause a lift and a separate pulse will cause the drop These are normally supplied by the computer during data acquisition To exit DROP mode press RESET The controller is now insensitive to triggers OSC oscillation mode is used to slowly raise and lower the cart the object is never in freefall to create slow and constant interference fringes The magnitude of this fringe signal is used for system alignment purposes To initiate OSC mode first make sure the dropper is un travel locked and the press OSC You should see the position LEDs on the front of the SIM indicate a slow movement of the cart To stop OSC mode press the TRIGGER button at any time The cart will automatically stop at the bottom of the next oscillation cycle A2. three spherical feet or balls that fit and orient it to vees in the cart The drive mechanism is a support structure inside the dropping chamber on which the cart drag free chamber travels up and down and is driven by a DC servo motor The cart is attached to a belt that is driven up and down by a shaft attached to the motor The motor is located outside of the chamber is connected to the shaft via a ferrofluidic feedthrough this device allows the vacuum to be maintained inside the chamber while a shaft rotates through the wall The motor also turns an optical shaft encoder that Fy Fg5 Absolute Gravimeter provides accurate information to the dropper controller on the position and velocity of the pulley At the beginning of a drop the cart accelerates downwards with an acceleration greater than g allowing the test mass to begin freefall Once a certain separation typically about 3 mm between the cart and the test mass is reached the cart slowsdown and then tracks the test mass maintaining a constant separation of a few millimeters Finally at the bottom of the drop the cart gently catches the test mass and decelerates to a stop The tracking during the drop is accomplished by a sophisticated servo system that works as follows By keeping track of the cart position using a shaft encoder on the belt drive pulley and using the interferometer fringes to establish the object position the distance between the cart and the
3. estar siempre del siguiente modo e Meter Select 1F e Gain 1 e Time Constant 1 Body Temp Mode TEMP e Meter BIAS Bias Voltage Colocar en 0 V meter e Dejar calentar al menos dos horas o hasta que la temperatura se haya estabilizado antes de comenzar las observaciones Montaje del instrumento Colocar la base orientando la burbuja en la direcci n N S aye Fg5 Absolute Gravimeter Nivelar la base utilizando las 3 patas Medir la altura de referencia inferior utilizando la regla microm trica Limpiar bien la base y colocar encima el superspring con el bot n de bloqueo mirando al lado del nivel esf rico Fijarlo con las 3 sujeciones Nivelar los niveles del superspring Quitar la tapita Colocar encima el interfer metro y poner el l ser al lado La fibra ptica queda en la direcci n N S encima de la burbuja El ocular queda perpendicular a la direcci n N S Fyarlo con las 4 sujeciones Apretar en diagonal 18 Fg5 Absolute Gravimeter Quitar la tapita Volver a nivelar la base Montar las patas de la segunda base Apretarlas bien Colocar la segunda base sin los pies encima del interfer metro El agujero debe quedar mirando al lado del nivel esf rico Colocar la camara de ca da encima de la segunda base La bomba i nica queda en la direcci n del anteojo Fyarlo con las 3 sujeciones Desbloquear el Travel Lock de la c ma
4. mass can be derived During freefall this separation 1s maintained at a constant distance by using a servo motor drive system to control the cart inside the Dropping Chamber Because there is essentially no relative motion between the test mass and the drag free chamber the effects of residual air drag are eliminated Guide Rods Glass Sphere Linear Detector Top Drag Free Chamber Cover Cart Corner Cube Test Mass Bottom Drag Free Chamber Cover fig 10 Cart drag free chamber 3 2 The service ring The Service Ring is at the base of the Dropping Chamber It provides connections and mounting for the following e A bellows type vacuum valve for the initial evacuation of the vacuum system e A Ferrofluidic rotary vacuum feedthrough which connects the motor shaft to the cart drive mechanism e A servo motor rotary shaft encoder assembly which moves the cart and senses its position e An ion pump mounted on a 2 Conflat flange which maintains the vacuum once the chamber has been evacuated by the roughing pump e Spare 2 Conflat and Mini Conflat flanges are blanked off and can be used for additional vacuum accessories Fe5 Absolute Gravimeter Electrical Vacuum Valve Control lon Pump Feed Thru Thermocouple Gauge fig 11 FG5 service ring 3 3 The dropper controller The dropper controller is the servo circuit that controls the motor that drives the cart Located in the SIM please the SIM User
5. FGS Absolute Gravimeter Jos Manuel Serna Pedro Vaquero Sergio Sainz Maza Marta Calvo B Cordoba Javier Lopez Carmen Lopez J A L pez Fernandez INFORME TECNICO IT OAN 2012 01 Contents Contents QU e estic EE EE i E ake uae Eu I Li EAN o dl l Ze FOJ PANCIPIESOLOPErAnO edat AR 3 3 Hardware components and function e ze eeee ee es 5 Saka Toedroppne chamba E E E A EEE 5 Jaz RARE A 8 3 35 Ihedfopperconirolier a Reni 9 5A IM OM a OOO aia 10 e SUDEP AE 11 d MASEL SV STEIN retail ae alos 12 e E DE RR EE 13 De SPECIFICANO 15 0 e e ec ptt encetat bth ole 15 la Rebel 16 Appendix About the installation procedure Spanish 17 l Contents Fg5 Absolute Gravimeter 1 Gravimetry laboratory The CDT Yebes Gravimetry Laboratory hosts some of the most accurate state of the art gravimeters in the world Specially designed to host gravimeters given the delicacy of these instruments and their high sensitivity presents a very controlled thermal behavior double chamber with air conditioning system in the external one and structural behavior isolated concrete pillars We offer this laboratory for future RICAGs regional AG comparisons up to 6 instruments fig 1 Gravimetry laboratory Instrumentation GWR OSG Superconducting Gravimeter is permanently installed in the laboratory fig 2 Observatory Superconductin
6. anel delante Power on girar Ilave a la derecha Winters MODEL 10 r ias ji MAN 1 Meter Select 1F 2 Servo Control AUTO 3 Servo Control e 4 GAIN 1 5 TIME CONSTANT 1 6 BODY TEMP MODE TEMP DI Fe5 Absolute Gravimeter Cable fotodiodo TH APO MOTOR ENODER DROPPER E Cable TTL Cable del reloj ran nel F maan L1 Lis ei is ter Lee L DORIA ve PAR E Ch a rep H Ei dd 1 dE I fera sza Je fe lis DAL Fg5 Absolute Gravimeter Cable de la temperatura Ze Bn nio rie E e pl Kaz SS Cables del ordenador Cable del SS KE Fe5 Absolute Gravimeter _26
7. d 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 measurement and provides system servo control Each component is discussed in detail below Vacuum Chamber Free Falling Drag Free Corner Cube Chamber Drive lon Pump Motor Photo Detector Laser Light Interferometer Support Springs Mai Internal Reference ot Corner Cube Spring Servo Coil fig 7 FGS subsystems 3 1 The dropping chamber The Dropping Chamber is an evacuated chamber which contains a drag free cart which in turn houses the test mass corner cube Next figure shows a schematic A drive mechanism 1s used to drop track and catch the test mass inside the drag free cart Laser light passes through a window in the bottom of the Dropping Chamber to the corner cube inside the test mass and is then reflected back down through the window to the interferometer Fe5 Absolute Gravimeter Belt Tension Adjustment Top Flange Top Pulley Assembly Viewing Port Top Drag Free Chamber Cover Cart Drag Free Chamber Test Mass Bottom Drag Free Chamber Cover Guide Rods Drive Belt Helical Shaft Coupler Ferrofluidic Feedthrough Helical Shaft Coupler Bottom Pulley Servo Mator Assembly L Travel Lock I Shaf
8. d without the loop reductions and drift a Fg5 Absolute Gravimeter corrections normally required when using relative instrumentation With the FG5 the absolute gravity value is determined and reported immediately Figure 6 shows how gravity is measured with an FGS A test body containing a corner cube retro reflector is dropped from the top of the dropping chamber The laser light is split to reflect off the falling corner cube and a fixed corner cube which serves as a reference The mass accelerates to the bottom of the chamber and the raw fringe signal is detected by the photodiode as the dropped object falls The optical fringes in the raw fringe signal are timed to create calibrated time and distance pairs The lower part of the figure demonstrates the increase in the fringe signal frequency as the test body accelerates Test Object Fixed Reference j paa i A ZA FY YA Raw Fringe Sigal f Nf NN 7 i i i Y i i J Di Ti Di T D Ti fig 6 Direct measurement of Absolute g Fg5 Absolute Gravimeter 3 Hardware components and function The FG5 System consists of a Dropping or Vacuum Chamber Interferometer Base Superspring Laser System Controller and Electronics The test mass is allowed to free fall inside the evacuated Dropping Chamber The Interferometer Base or IB is used to monitor the position of the freely falling test mass The Superspring is an active long period isolation device use
9. del conector TRIG OUT Conector TRIG tarjeta del ordenador Cable del bar metro Channel 4 del Patch Panel Panel de suministro de potencia BARO OUT Cable BNC Channel 3 del Patch Panel OUTPUT del Laser Controller Cable BNC Channel 1 del Patch Panel SPHERE OUT del Superspring Controller Cable BNC Channel 2 del Patch Panel METER MONITOR del panel suministrador de potencia de la bomba t nica Sensor de temperatura en el Channel 0 Sensor sobre la base del tripode Cable de senal del Dropper Lemo blanco Cable codificador conector Lemo azul A la transmisi n del motor Cable de potencia del motor Lemo naranja Transmision del motor Cable de potencia del fotodiodo Lemo verde Conector POWER del interfer metro Y Comprobar que el interruptor COIL del SS Controller est apagado conectar Cable del Superspring Lemo amarillo El otro extremo se conecta al superspring justo antes de desbloquearlo Comprobar que los cables de power control del SS est n bien conectados Lo mismo con los cables de power control del DROPPER T w k SS e w y we I d i a e eo i Fe A m in ap Ko rrm HL e Fe5 Absolute Gravimeter Cables camara vacio Cable de energia Fe5 Absolute Gravimeter Cables laser Para empezar a calentar el laser es el que tarda mas en alcanzas su temperatura 2 o 3 horas Panel trasero AC on DC on En unos min se enciende la luz roja P
10. eam is reflected back up out of the Superspring and into the interferometer base where it reflects off Mirror 1 or the pick off mirror passes through the translator plate twiddler reflects off Mirror 2 and is recombined with the reference beam at Beamsplitter 2 fig 13 Interferometer diagram 10 Fg5 Absolute Gravimeter This interferometer is of the Mach Zender type with a fixed reference arm and a variable test arm During a drop the motion of the test mass affects the path length of the test beam The interference fringes which result from the recombination of the test beam and the reference beam provide an accurate measure of the motion of the test mass relative to the mass suspended on the Superspring The two beams are recombined at Beamsplitter 2 and then split again One set is focused by a lens to strike the detector APD The interference fringes are converted to an Analog signal and a Transistor Transistor Logic TTL signal which is transmitted to the time interval analyzer card in the system controller The other recombined beam set travels horizontally until it reaches the attenuator plate rattler This beam is split yet again and reflects between the beamsplitter coating and the uncoated side of the attenuator plate Three beams of decreasing intensity emerge from the coated side The first and brightest of these beams travels horizontally into the fringe viewer The second and third b
11. eams are deflected vertically by a mirror A flag in front of the mirror blocks the second beam allowing the third dimmest beam to exit the interferometer where it is reflected off Mirror 3 and enters the collimating telescope 329 Superspring The Superspring 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 The mainspring 1s contained in a support housing also supported by springs that is actively servo controlled to track the Superspring mass at the end of the mainspring The result is a long period 30 60 second or 16 30 mHz spring mass system that isolates against ground motions occurring at a higher frequency than its own enhanced natural frequency This insures that any change in the length of the test beam is due only to the acceleration of the dropped object Window Top Flange en gt PESA LI ag Compensating HF ver Le Focus Lever Focus Motor Main Spring Support Springs Mans Corner Cuba Sphera Emitter Service Ring 1 L i Leve Detector Bottom Flange Linear Aclu lor fig 14 Superspring schematic Fg5 Absolute Gravimeter 3 6 Laser system The FG5 employs a stabilized helium neon laser Winters Electro Optics Model 100 iodine stabilized laser to provide an accurate and stable wavelength used in the interferometric measureme
12. g Gravimeter Besides the following instrumentation is available not always installed in the Gravimetry laboratory because they participate in different measurement projects FG5 absolute gravimeter A10 absolute gravimeter L amp R LaCoste and Romberg relative gravimeter gPhone Scintrex Fg5 Absolute Gravimeter fig 3 Gravimeters FG5 A10 and Scintrex Auxiliary instrumentation Seismometers GNSS stations H maser for clock measurement calibration Maintenance stuff CDT Yebes participate in the international organizations projects related with Gravimetry Science GGP AGrav ECAG ICAG fig 4 GWR OSG and FGS installed in Yebes Fg5 Absolute Gravimeter D FGS principles of operation A ballistic absolute gravimeter works by dropping an object in a vacuum and measuring the time it takes to fall a specified distance Galileo recognized that the acceleration of a freely falling body is independent of its mass and legend has it that he demonstrated this by dropping objects of different weight from the leaning tower of Pisa though this may be apocryphal Newton s theory of gravitation also required that the acceleration of a falling body in an external gravity field did not depend on its size shape or mass Thus measuring the acceleration of a freely falling object 1s equivalent to measuring gravity This freefall acceleration is given the special symbol g to remind us that gravity is re
13. installation procedure Spanish Pasos previos Elegir localizacion y buscar el Norte Buscar 3 puntos cercanos de red AC para la caja de electronica el controlador de la bomba y el multimetro Fluke Situar la caja de electronica aproximadamente a m del punto de localizacion e Comprobar que los voltajes de suministro son los correctos e Comprobar el funcionamiento correcto de la bomba 1 nica Los siguientes interruptores deben estar apagados e Main AC power trasera e Main DC power trasera e Laser Main AC power y HV power la llave e Si la bomba i nica est manteniendo el vac o del Dropper con la bater a del controlador de la bomba desconectar el controlador los tres interruptores AC BAT y HV de derecha a izquierda enchufarle a la red AC y volver a conectarlo los tres interruptores de izquierda a derecha e Situar el l ser en el suelo aproximadamente a 1 m del punto de localizaci n Situar la fibra ptica en lugar seguro e Conectar el cable de Main AC power trasera a la red Si utilizamos UPS Conectar UPS a red y el cable de Main AC power a la UPS e Encender los interruptores Main AC y DC power trasera e Conectar los dos cables que van al L ser y encender el L ser para que alcance cuanto antes su equilibrio t rmico Encender el interruptor Main AC Power del l ser y la llave para HV e Seleccionar el pico de l ser normalmente el E e Colocar Servo Control en AUTO Los dem s controles deben
14. itical for the gravity measurement and should not need to be adjusted Finally because the laser light is polarized it is necessary to rotate the output of the fiber about its axis so as to evenly split the laser power between the test and reference beams horizontally polarized light 1s transmitted more efficiently into the reference beam while more vertically polarized light is transmitted in the test beam the nominal position is thus at about 45 Again this adjustment is performed at the factory and should not need to be changed by the user 12 Fg5 Absolute Gravimeter 4 FGS Setup For more detailed description please consult references Place electronics box approximately 1 m from measurement location Check line voltage settings especially for WEO laser Check that ion pump is powered on and operating correctly Connect to reliable AC power source Make sure the FG5 Power Supply AC amp DC power is off Make sure the WEO Controller switches AC and HV are set to OFF Turn FGS Power Supply AC power on Place laser on stable surface connect cables to WEO controller turn on WEO controller and enable HV The laser should emit laser light within a min
15. lternatively you can press DROP and this will place the controller in DROP mode at the bottom of the next oscillation cycle Take care not to hit the RESET button directly as this will immediately and roughly drop the test mass and cause excessive wear on the balls and vees Fg5 Absolute Gravimeter 3 4 Interferometer Mirror 3 Fiber Collimating Assembly Beam Splitter 1 Beamsplitter 2 Rattler Mirror 1 Twiddler fig 12 Schematic of FGS interferometer The optical fiber directs the laser light from the laser head to the interferometer base At the input of the interferometer a lens collimates the light from the optical fiber It 1s then directed to Beamsplitter 1 where it is split into the test beam and the reference beam The reference beam 1s split again at Beamsplitter 2 and travels to the Avalanche Photo Diode APD and the fringe viewer Note that the path length of the reference beam remains constant The test beam is reflected vertically at beamsplitter 1 and passes through a compensator plate and a window in the bottom of the Dropping Chamber It is then reflected back down by the corner cube in the test mass The test beam returns through the window the compensator plate and passes down through the interferometer base to the Superspring The test beam passes through the top window of the Superspring chamber to the corner cube in the Superspring mass From here the test b
16. nt system This laser is a primary standard for the definition of the meter at the Bureau International des Poids et Measures BIPM in Sevres France It is a highly stabilized frequency standard trivially converted to a distance standard in a vacuum having an absolute frequency accuracy of 1 part in 10 50 kHz All models of lasers need to be warmed up and reach thermal equilibrium before gravity data are acquired As a rule of thumb it is best to power on the laser the night before measurements if possible At a minimum the lasers should be one at least 1 4 hours for good results Again regardless of the laser model the light is always linearly polarized and reaches the interferometer via a single mode polarization maintaining fiber optic cable The fiber polarization is set to match that of the laser light at the factory under normal operations it is never necessary to adjust the rotation at the input of the fiber The light enters the fiber optic cable via a 5 ax1s mount that focuses the light down to a diameter of a few microns This adjustment is also done at the factory and is extremely sensitive The laser light exits the fiber and diffracts at a well defined angle to avoid back reflections A collimating assembly is attached to the output of the fiber and 1s adjusted such that the final beam 1s well collimated at approximately 8 mm Again note that this collimation adjustment is performed at the factory is extremely sensitive cr
17. on has calmed down enable Superspring Servo Check and adjust if necessary beam verticality Use Twiddler and lower mirror to maximize fringe signal check with oscilloscope and OSC mode Check and adjust if necessary beam verticality again Place dropper in DROP mode Verify that Rubidium clock has stabilized RUB POWER light 1s steady ON Turn on Magma Box if necessary KE Fg5 Absolute Gravimeter Turn on laptop PC power Turn computer power ON and set up software Enter the total reference height and check all other parameters Take data Tear Down Back up data if applicable and turn computer power OFF Travel lock Dropper Turn DC Power Off Turn off laser HV and AC power Turn AC Power off Travel lock Superspring Disconnect all cables but get power to ion pump and generally leave fiber optic connected between laser and IB Unless shipping overseas keep ion pump powered ON Remove dropper double check it is travel locked Remove dropper tripod and disassemble Remove IB from Superspring and place it and laser in shipping box Remove Superspring double check it is travel locked Pack Superspring tripod 14 Fg5 Absolute Gravimeter 5 Specifications TOTAL SHIPPING WEIGHT 150 kg in 6 containers ome vorei oo srnce agent NOMINAL POWER REQUIREMENT 50W PERFORMANCE SPECIFICATIONS 2
18. pGal observed agreement between FGs instruments 15 pGal sqrt Hz at a quiet site PRECISION eg 1 uGal in 3 75 minutes or 0 1 uGal in 6 25 hours OPERATING TEMPERATURE RANGE 20 C to 30 C 6 Applications MFG5 APPLICATIONS GEOPHYSICAL RESEARCH PRECISION MEASUREMENTS A Complementary verification of e Pressure transducer and load displacements measured with cell calibration GPS and VLBI Redefinition of the kilogram Volcanic magma flow monitoring in the SI system of units Postglacial rebound studies Big G determinations and i i equivalence principle e Uplift of subduction studies Calibration of superconducting D ESZEMBEN of other high precision relative Long period tidal monitoring gravity meters and earth inelasticity modeli e INERTIAL NAVIGATION ENVIRONMENTAL MONITORING Gravity reference station Water table monitoring in deep determinations and or multiple aquifers Relative gravity network Nuclear waste management control points and cleanup Establishing geodetic tie points Global sea level studies for for gravity networks global warming Defining the geoid EXPLORATION AND RESOURCE MANAGEMENT Oil exploration Mineral exploration 15 Fg5 Absolute Gravimeter gi References 1 FGSManual2007 pdf 2 FGSPowerPoint pdf 3 FG5 brochure pdf 4 FG5 211 2010 Service Report pdf 5 workshop2010materialFG5 doc 16 Fg5 Absolute Gravimeter Appendix About the
19. ra de caida Subir y bajar el carrito manualmente con una llave allen 19 Fg5 Absolute Gravimeter Al transportar la c mara de caida si la bomba i nica est manteniendo el vac o del Dropper con la bateria del controlador de la bomba hay que desconectarlo de derecha a izq enchufarle a la red AC y volver a conectarlo de izq a dcha Comenzar a conectar los cables Dejar el cable del SS sin conectar se conectar al final Conectar el l ser para que empiece a calentarse es lo que m s tarda en alcanzar la temperatura Poner los pies bajo las patas y las almohadillas azules bajo los pies Una vez que los pies toquen las bolas blancas de nylon de las patas elevar cada uno 1 vuelta y media en sentido contrario a las agujas del reloj Comprobar que est n separadas las 2 partes pasando un papel fino Volver a nivelar en caso de ser necesario Medir la altura de referencia superior metiendo la regla por la hendidura 20 Fg5 Absolute Gravimeter Conexion de los cables Listado de conexiones Y Ordenador Comprobar que el interruptor de potencia esta apagado Cable de potencia del ordenador Panel de suministro de potencia Cables cintas grises trasera del Match Panel Conectores del ordenador anal gico arriba digital abajo Cable BNC del conector TTL del interter metro Conector FRINGES de la tarjeta del orden Cable BNC del conector 10 MHz Conector CLK tarjeta del ordenador Cable BNC
20. sponsible The FGS represents the latest generation of ballistic absolute gravimeters and is based on technology developed over the last forty years by Dr James Faller of the National Institute of Standards and Technology NIST and his colleagues fig 5 FGS installed at Yebes The FGS absolute gravimeter is a high precision high accuracy transportable instrument that measures the vertical acceleration of gravity The operation of the FG5 is simple in concept A test mass 1s dropped vertically by a mechanical device inside a vacuum chamber and then allowed to fall a distance of about 20 cm A laser interferometer is used to determine the position of the test mass as a function of time during its freefall The acceleration of the test mass is calculated directly from the measured trajectory The interferometer generates an optical interference fringe each time the test mass falls the wavelength of the laser light These fringes are counted and timed with an atomic clock to obtain precise time and distance pairs A least squares fit to these data are used to determine the value of g This method of measuring gravity is absolute because the determination is purely metrological and relies solely 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 accurate time scale The value of gravity obtained with the FGS can be use
21. t Encoder lon Pump Bottom Flange fig 8 FGS dropping chamber front view Fe5 Absolute Gravimeter Ben Tension J A i d Can Drag ree Chamber Ak URLA e ez d Adjutimest Tag Poley Ace Tap Ovag Free k Chamber Correr G Linear Bear pi a ALI i i Bottom Dreg Fa i Chamber Cover Drive Sell i Guido Rods A Service Ring dy 3 E Li ik I mme s KN Get ylity T 5 _ Bohom Flange fig 9 FGS dropping chamber side view The drag free cart is used to lift drop and catch the test mass The term drag free refers to the fact that though the chamber 1s evacuated there are still some residual air molecules The cart effectively pushes these molecules out of the way of the test mass which is falling inside the cart In addition to reducing drag the cart also reduces magnetic and electrostatic forces on the test mass The test mass contains a retro reflective corner cube surrounded by a support structure which is 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 center When in contact with the cart the test mass is supported by
22. ute or SO Place Superspring tripod at measurement location Orient the line from the center of the tripod to the bull s eye level along a North South axis Use tripod feet to center the bull s eye level Measure and record the lower reference height Place and lock Superspring in tripod with travel lock oriented towards bull s eye level Level the Superspring tripod to the Superspring bubble levels Remove Superspring dust cap Place IB on top of Superspring with fiber optic oriented towards bull s eye level Assemble dropping chamber tripod Place dropping chamber tripod onto IB with the small hole in the tripod oriented towards the bull s eye level Remove dust cap from IB Place dropping chamber into dropping chamber tripod with the ion pump oriented towards the beam blocker side of the IB Place the dropping chamber tripod feet under the tripod and adjust them until they are just touching the legs of the dropping chamber tripod Turning each foot one turn counter clockwise one turn at a time lift the dropping chamber two total turns Fine tune the level of the dropping chamber If necessary fine tune the level of the Superspring Measure and record the upper reference height Un travel lock the dropping chamber Verify DC power is OFF Connect the cables from the electronics to Superspring IB and dropping chamber Un travel lock the Superspring Turn on DC power If necessary Zero the Superspring When spring moti
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