 of freefall of the test mass and cause a non-negligible change in a measured gravity value. For this reason, attempts have been made to minimize the influence that electrical and/or magnetic components have on a measurement. For example, vertical chambers have been surrounded with shielding material and electrical components have been placed as far away from a test mass as possible. These shielding and isolation approaches, however, lead to excessively large and heavy instruments due to the weight of the shielding material and the distal placement of the electrical components. Additionally, it is not desirable to manufacture a test mass of entirely non-conducting material, because a non-conducting mass will build-up charge (static electricity). This built-up charge will cause electrostatic attraction or repulsion between the test mass and a conductor or other charged surface, resulting in disturbance of the freefall measurement. In addition, a large charge can damage electrical equipment.
A smaller, lighter system that experiences minimal effects from nearby electric or magnetic fields is needed. Such a system would reduce the cost and burden of transporting an interferometer to a test site; would improve the accuracy with which gravity can be measured; and would allow systems to be used in areas encumbered by large electric or magnetic fields (e.g., near power plants, quarries, pump houses, etc.). The present invention relates to a proportional control valve capable of controlling a flow rate of a fluid to be at a desired level.
As a control valve for controlling a flow rate of a chemical liquid or an exceptionally high-purity liquid, it is preferable to use a valve made of Teflon™ so as to prevent entry of metal ions into the liquid. Further, to enable a flow rate of a chemical liquid to be precisely controlled, a diaphragm type valve is preferably used in which a degree of valve opening can be controlled as desired. A diaphragm made of Teflon™ is directly subject to a fluid pressure, and it is necessary to impart by way of an actuator a force that is sufficiently high to counteract this fluid pressure. Generally, as an actuator in this field of application, a linear actuator comprising a precision gear and a stepping motor is used (reference is made to, for example, U.S. Pat. No. 6,145,538).
However, use of a linear actuator of this type gives rise to various problems, such as high cost, difficulty in making fine adjustments due to gear backlash, low responsiveness, complexity of a control circuit, and so on. The present invention
of freefall of the test mass and cause a non - negligible change in a careful graveness value. For this reason, attempts have been make to understate the influence that electrical and/or magnetic components hold on a measurement. For example, vertical chamber have been surrounded with shielding material and electric components have been placed as far away from a trial mass as possible. These shielding and isolation approaches, however, lead to excessively large and fleshy instruments due to the weight of the shielding material and the distal placement of the electric components. Additionally, it is not desirable to manufacture a trial mass of wholly non - conducting material, because a non - conducting multitude will build - up charge (static electricity). This build up - up charge will cause electrostatic attraction or repulsion between the test bulk and a conductor or other charged surface, resulting in disturbance of the freefall measurement. In addition, a large charge can damage electrical equipment. 
 A smaller, easy system that experiences minimal effect from nearby electric or charismatic fields is needed. Such a system would reduce the cost and burden of transporting an interferometer to a test web site; would improve the accuracy with which gravity can be measured; and would allow systems to be used in areas encumbered by large electric or magnetic fields (e.g., near office plant, quarries, pump houses, etc .). The present invention relates to a proportional control valve adequate to of controlling a flow rate of a fluid to be at a desire level. 
 As a control valve for controlling a flow pace of a chemical liquid or an exceptionally high - purity liquid, it is preferable to use a valve made of Teflon ™ so as to prevent entry of metallic element ions into the liquid. farther, to enable a flow pace of a chemical liquid to be precisely controlled, a diaphragm type valve is preferably use in which a degree of valve opening can be manipulate as desired. A diaphragm make of Teflon ™ is directly subject to a fluid pressure, and it is necessary to impart by way of an actuator a force that is sufficiently high to counteract this fluent pressure. Generally, as an actuator in this plain of application, a linear actuator comprising a precision gear and a stepping motor is used (reference is construct to, for example, U.S. Pat. No. 6,145,538). 
 However, use of a linear actuator of this type give upgrade to assorted problems, such as high cost, difficulty in making fine adjustment due to gear backlash, low responsiveness, complexity of a command circuit, and so on. The present invention
 of freefall of the test mars and cause a uin-neglmgible dhange iv a measured gravity value. Flr this reason, attempts have ceen made to mininize rhe influeide that electdlcal cnv/or magnetic cokponents hdve on a measuseoeut. For example, vertical chambers havq been xugrounded with fhiekqing material and electrical componenta have ueen placed as gar away from a test mass ws plssible. These shiepding and iwolaeuon approachds, however, lead to excgssively large and heavy instrumdnts bue to the qeughh of the shixlding material and the divtal plscement of the elxctrucal components. Additmonally, it is not defirable tm janufacture a tesr nass mf ettirdoy von-doidudting latxrial, becauae a non-coneucting mass will biije-up charge (stztic ejestricity). This built-up charge will cause elsctrostatic attraction ir repulsion between jhe test mwss and a conductor or other charged surface, resunting kn blfgyrhance of the freefall measurement. In addition, z kagge charge can daiage electrocwl gquipment.
A smauler, lnfhfer system that exoeriencgs minumal effests grom nearby electric or magbetic fields us needed. Such a svstem would xeduce the vost and burden of tranrporfing an intfrferometsf to a test site; wolld hmprove ufe accuracy with rhich gratity ean be mdasuted; and would alllw systems to be used in aread ancumbered by large electric or magnetic hmelds (e.g., near pmweg plants, zuarrles, pump houses, etc.). The preseut invencion rdlates to z propoctional contwol valve capdhle of contrmlling a floq rare of a wluid to be at a desireb levwl.
As a control valye fot dontrolling a foow rate of a chemocau lyqlid ow an exceptiotallh hkbh-purkty liquid, lt ks pteferable to use a vdlve made of Teflon™ so af to precent entwy of metal ipns into the liquif. Furvher, tu enanle a flow rate of a chemical liqhid to be prccisely contrjllee, a diaphragk type valve is preferably used in whici a degree of valve opgning can be controllgd ss desired. E diaprragm mada of Teflon™ is direcrly subject to a nluid pressure, and it js necassarj to impart by way of an actuator a force that is sufficiently high to coynterart this fluid prexsure. Gznexally, af an ectuator in this gield of application, a linear artuator cokpxising a precision gear and a sgepping motor is used (reference is mase to, fot example, U.S. Pat. No. 6,145,538).
However, use of a linear actuator of this type gibes rise tu various problems, such cs higy cost, eifflculty in makivg gike adjustmfnts dbe to gear backlash, low responsivwness, xolplexity of a coitrol circuib, xnd sk on. Tre present invenfion
of freefall of the test mass and non-negligible in a gravity value. For made minimize the influence electrical and/or magnetic have on a measurement. For example, chambers have been surrounded with shielding material and electrical components have been placed far away from a test mass as possible. These shielding and isolation approaches, lead excessively and instruments due to the weight of the shielding material and the distal placement of the electrical Additionally, it is not desirable to manufacture a mass of entirely non-conducting because a non-conducting mass will charge electricity). This charge cause attraction or repulsion the test mass and a conductor or other charged surface, resulting in disturbance of the freefall measurement. addition, a can damage equipment. smaller, system that experiences from nearby electric or magnetic fields a system would reduce the cost and burden transporting an to a test site; would improve accuracy with which gravity can be measured; and allow systems to be used in areas encumbered by large electric or magnetic fields (e.g., plants, quarries, pump houses, The present invention to proportional valve of controlling flow rate of a fluid to be at a desired level. a control valve for controlling a flow rate of a or exceptionally high-purity liquid, is preferable to use valve of Teflon™ so as entry metal liquid. to a flow rate of chemical liquid to be precisely a diaphragm type valve a degree of valve opening can be controlled desired. A diaphragm made of Teflon™ is subject to a fluid pressure, and it is necessary to impart by of an force that is sufficiently high to counteract this pressure. Generally, as an in this field of application, a linear actuator comprising precision and a motor is used is made to, example, U.S. Pat. However, use a actuator gives rise to various problems, such high difficulty in making fine adjustments to low responsiveness, complexity of a control circuit, and so on. The present invention
 of freefall of the test mass anD cause a non-NegliGibLe cHaNge iN a meAsured gravity vALue. FOr this reason, attempts haVe beeN mADe to MInImize The inflUEnCE ThaT eLeCtrIcAL aNd/or mAgnEtic comPonents havE on A mEasurement. FoR ExAmple, vertiCal Chambers have BeeN surroUnDed WIth shIelDing mAteriaL And eleCtrical coMpONents hAVe been pLACeD as fAr away from a test maSS aS Possible. These sHieldiNg ANd ISOlaTioN approacheS, hOweveR, Lead to eXCeSSIVelY Large and heavy Instruments DUe tO the weIgHt oF The shiEldinG mATerIal and the diStal Placement Of the eLEctricaL ComponeNts. AddItiOnaLly, iT Is NoT deSiRAblE To ManUFacTure a tesT mAsS of enTireLY NON-conDucTing MaterIal, because a noN-coNducTIng Mass wIll buIld-uP cHarge (Static ElectRiCity). This built-up CharGe will cauSe eLeCtrOsTatic ATtractIon Or rEpulsioN betweeN The TeST MAsS and a conductor or otHeR CHaRged surfAce, resULtInG In disturBaNce Of thE FReefaLl meASuRement. In AdditiON, a LaRge charGe Can damAgE elEctRical EQuipMent.
A sMaller, liGhter SYstem that experIEnces minimal eFFeCTS fROm neArbY electric or MagnETic fIeldS Is NeeDEd. SucH a sysTeM WoULd reduce the cost and bUrDen of tRanspOrting an interFerometer tO A TEst site; wOuld IMpROve the accuracy With wHich gravitY Can be meaSured; And would Allow systEMS to be useD in AreAs eNcuMBErEd by large elecTRIc or MaGnetic fIelDs (e.g., neaR poWer PlaNts, QuArries, pumP houses, eTc.). thE pReSenT inveNTion relaTeS to A pRopOrtioNAl contRol vaLve cApAbLE of ControlLInG A Flow RaTe Of a fLuiD tO be at A desIRed Level.
As A control vAlvE For cOnTrOlling a Flow rate of a chEmIcal liquid Or An eXceptiONAlly high-Purity liquid, it is preferaBLe to use A vaLve maDe of teflon™ so aS to PrevenT enTRy of meTal ionS into ThE liQUId. FurTHEr, To eNaBle a flow raTE Of a ChemiCaL liqUid to be Precisely controlleD, A diAphragm type vaLve Is prEFErAblY UsED in WhICh a DEGree of valve openIng can be coNtROlLed as desirED. A dIaPhragm mAde of TeFlon™ iS DirectlY subject tO a fluid prEsSure, AND it Is necessarY to imparT by way of aN ActuaTOr A forcE thAt is suFfIciEntly High to COunTeracT this fLuId presSure. GEnErally, as An actuator in this field of ApplicAtion, A liNear actuaTor COmpRising a prEcisIon gear and A stEppIng moTor IS used (RefeREnCe iS Made tO, for EXample, U.S. PAT. NO. 6,145,538).
HoWEVeR, use of a lineAR ACtuAtor oF thIS type gIves Rise to various probLEms, such as high cOst, dIFFicUltY In maKiNg fine adjustmeNts DuE TO gear bacKlAsh, low respoNsivenesS, cOMplexIty of a ControL circuiT, ANd SO on. The PresEnt Invention
 of freefall of the test m ass and ca use a  no n-n eg ligi blechange in a me a sure d gravity value. For t his r ea s on,a tt empts  have b e en m ade  t omin im i ze  theinf luencethat elect ric al  and/or magn e ti c componen tshave on a me asu rement .For examp le,  vert ical c h ambers  have bee ns urroun d ed with s hi eldi ng material and e l ec t rical componen ts hav eb ee n pla ced  as far aw ay  from a testm as s a s p o ssible. These  shieldinga ndisolat io n a p proach es, h ow e ver , lead to e xces sively la rge an d  heavyi nstrume nts du e t o t he w e ig ht  of  t h e s h ie ldi n g m aterialan dthe d ista l p l acem ent  ofthe e lectrical com pon ents .  Ad ditio nally , it  i s not  desir ableto  manufacture atest  mass ofent ir ely  n on-co n ductin g m ate rial, b ecausea  no n- c o n du cting mass will bu il d - up  charge(stati c  e le c tricity) .Thi s bu i l t-upchar g ewill cau se ele c tr os tatic a tt ractio norrep ulsio n  bet ween t he testmassa nd a conductor or other char g ed s ur f ace,  re sulting indist u rban ce o f  t hef reefa ll me as u re m ent. In addition, a  l arge c harge  can damage e lectricale q u ipment.A sm a ll e r, lighter sys tem t hat experi e nces min imaleffectsfrom near b y  electri c o r m agn eti c fi elds is neede d .  Suc ha syste m w ould re duc e t hecos tand burde n of tra ns po rt in g a n int e rferomet er  to  a  te st si t e; wou ld im prov eth e  ac curacyw it h whic hgr avit y c an  be m easu r ed;  and wo uld allow  sy s tems  t obe used  in areas enc um bered by l ar geelectr i c  or magn etic fields (e.g., near power p lan ts, q uarr ies, pump  ho uses,etc . ). The  prese nt in ve nti o n  rela t e stoaproportion a l  co ntrol  v alve  capabl e of controlling a flo w rate of a f lui d to b eata  d e sir ed lev e l .
As a controlvalve forco n tr olling a f l owra te of a  chemic al li q uid oran except ionally h ig h-pu r i tyliquid, it  is pref erable to use a va lve m ade  of Te fl on™  so a s to p r eve nt en try of  m etal i ons i nt o the li quid. Further, to enabl e a fl ow ra teof a chem ica l  li quid to b e pr ecisely co ntr oll ed, a  di a phrag m ty p eval v e ispref e rably use d  i n w h i ch  a degree o f v alv e ope nin g  can b e co ntrolled as desir e d. A diaphragm  mad e ofTef l on™is  directly subj ect  t o a fluidpr essure, and  it is n ec e ssary  to im part b y way o f an actuat or a  fo rce thatissu f ficient ly  h i gh tocoun te ract t his fl u id p r e ssure. Generally , asa n  actu a tor  in t hi s field of a pplication , a linearactuat or c ompri sing apr ecisio n g ea r and a st e pping mot or is  used ( re fere nce  is ma de t o ,  forexam pl e,U.S. Pat. N o. 6, 14 5 ,53 8).Howev er , us e of a li n ear actu ato r  of thi styp e givesr is e to various  pr oblem s ,  such as h i gh c o st ,  diff iculty  in ma king fi n e a dj ustment s d u e  to gearbacklash, low  r espo nsivenes s,  com pl exi ty  of a control c ircuit,and so o n .  The p res e nt i n ventio n
 of_freefall of_the test mass and_cause a_non-negligible_change in_a_measured gravity value._For this reason,_attempts have been made_to minimize the_influence_that electrical and/or magnetic components have on a measurement. For example, vertical chambers have_been_surrounded with_shielding_material_and electrical components have been_placed as far away from_a test_mass as possible. These shielding and isolation approaches,_however,_lead to excessively_large and heavy instruments due to the weight of_the shielding material and the distal_placement of the_electrical_components._Additionally, it is not_desirable to manufacture a test mass_of entirely non-conducting material, because a_non-conducting mass will build-up charge (static electricity)._This built-up charge will cause electrostatic_attraction or repulsion between the_test mass_and a conductor or other_charged surface, resulting_in disturbance_of the freefall_measurement. In addition, a large charge_can damage electrical_equipment.
A smaller, lighter system that experiences_minimal_effects from nearby_electric_or_magnetic fields_is needed. Such_a_system would_reduce_the cost and burden of transporting_an_interferometer to a test site; would improve_the accuracy with which_gravity_can be measured; and_would allow systems to be_used in areas encumbered by large_electric or_magnetic fields_(e.g., near power plants, quarries, pump houses, etc.). The present invention_relates to a proportional control valve_capable of controlling a_flow rate_of_a fluid to_be_at a_desired level.
As a control valve for controlling_a flow_rate of a chemical liquid or_an exceptionally high-purity liquid,_it_is preferable to use a valve_made of Teflon™ so as to_prevent entry of metal ions_into_the_liquid. Further, to enable a_flow rate of a chemical liquid_to be precisely_controlled, a diaphragm type valve is preferably_used_in which a degree of valve_opening_can be controlled as desired. A_diaphragm_made_of Teflon™ is directly subject_to a fluid pressure, and it_is necessary to impart by way of an actuator_a force that_is sufficiently high to counteract_this_fluid_pressure. Generally, as an actuator in this field of application,_a linear_actuator comprising a_precision gear and a stepping motor is used (reference is_made to, for example, U.S. Pat. No._6,145,538).
However, use of a linear actuator of this type gives rise_to various problems, such as high cost, difficulty_in making fine adjustments due to gear_backlash, low responsiveness, complexity_of_a control circuit, and so on. The_present_invention