Abstract:
Viscometer ( 80 ) with a rotor ( 51 ) rotatable by a coupling magnet ( 34 ) and a driving magnet ( 38 ) to shear a tested fluid thus imparting torque to a bob ( 30 ) mounted on a bob shaft ( 24 ) supported via a pair of bob shaft bearings. A spiral spring ( 70 ) restricts the rotation of bob shaft ( 24 ). Magnetometer ( 10 ) measures the angular position of a top magnet ( 72 ) connected to the top of bob shaft ( 24 ). This angular position information is further converted to the viscosity of the tested fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a division of a utility patent application “High Pressure Viscometer with Chamber Preventing Sample Contamination”, filed Oct. 24, 2005. 
   BACKGROUND 
   1. Field of Invention 
   The present invention relates to a low maintenance high pressure viscometer. 
   2. Description of Prior Art 
   In connection with the drilling of oil and gas wells, drilling fluid is commonly used to drive drill bit and bring sand and stone cuttings back to ground surface. Viscosity property of drilling fluid is critical in the drilling process. A drilling fluid with excessive viscosity would make it difficult to pump it down to bore hole, while a drilling fluid with insufficient viscosity would make it difficult to carry sand and stone cuttings back to ground surface. The viscosity property of a drilling fluid varies significantly with the change of temperature and pressure. Thus a viscometer capable of closely simulating down-hole conditions with low maintenance is of great interest. Down-hole conditions are typically from room temperature and pressure up to 40,000 psi and 600° F. 
   A few types of arrangements have been applied to measure the viscosity of liquids under high temperature and high pressure conditions. In U.S. Pat. No. 3,435,666, a helical spring is attached to the inside bob through a bob shaft while driving the outer cylinder. The shear force applied on the bob is proportional to the torque applied by the liquid, which is also measured by a strain gauge torque transducer. One of the drawbacks of this design is that packing  41  is required to dynamically seal the rotating tube  32 . Due to the nature of the dynamical seal, it has difficulty to seal above 2,000 psi. Thus any test conditions above 2,000 psi in pressure will be difficult to achieve. In U.S. Pat. No. 4,633,708, a sealed container within a high pressure vessel is used for testing rheologically evolutive materials. One of the drawbacks of this design is that seal  12  is used to separate the test sample from outside pressurizing fluid. Measurement error due to the friction between seal  12  and shaft  14  is inevitably added. For very thick test samples such as cement this error is possibly tolerable. However, a typical drilling fluid under high temperature and pressure conditions has a typical viscosity of 10 cP to 30 cP when shear rate is around 500 l/s. This friction-induced error is too high to provide meaningful results. In U.S. Pat. No. 4,466,276, an open top slurry cup within a high pressure vessel is used to measure cement consistency. One of the drawbacks of this design is that due to the wide-open top of the slurry cup, the sample can mix with pressurization fluid easily, which leads to inaccurate results. In model 75 viscometer manufactured by Fann Instrument Company, a pair of v-shape jewel bearings is used to support a complicated bob assembly whose rotational movement is restricted by a helical spring. One of the drawbacks of this design is that the jewel bearings are fragile, easy to break, prone to wear and expensive to replace. Another drawback of this design is that helical spring assembly is generally much more complicated and spacious comparing to spiral spring assembly. 
   It is an object of this invention to provide a high pressure viscometer wherein viscosity is determined under conditions closely simulating down-hole conditions. 
   It is another object of this invention to provide a high pressure viscometer that eliminates measurement errors due to seal frictions. 
   It is another object of this invention to provide a viscometer that requires substantially less maintenance work yet meets industry standards of accuracy, reliability, durability, dependability, and ease of cleaning. 
   SUMMARY 
   A viscometer in accord with the present invention conveniently comprises a pressure vessel inside which a rotor is suspended and a magnetic coupling for rotating the rotor. Suspended within the rotor is a bob capable of angular motion about the longitudinal axis of the rotor. The device is constructed so that the bob and the rotor are immersed within the liquid, the viscosity of which is to be determined. The bob is suspended within the pressure vessel by a pair of low friction ball bearings and bob shaft. A spiral spring permits limited angular motion of the bob shaft. A magnet is secured on top of the bob shaft. A magnetometer located on the top of the pressure vessel senses the rotation of the magnet. 
   The apparatus and method of the present invention provide a way to measure the shear stress property of fluid under shear condition. 

   
     DRAWING FIGURES 
     Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with accompanying drawing in which: 
       FIG. 1  is a cross-section view of a preferred embodiment of the invention; 
       FIG. 2  is an alternative embodiment with jewel bearings and conical support; 
       FIG. 3  is another alternative embodiment with jewel bearings and three-piece pressure vessel configuration. 
   

   REFERENCE NUMERALS IN DRAWINGS 
   
       
         10  magnetometer 
         10 A magnetometer 
         10 B magnetometer 
         12  inlet 
         12 A inlet 
         12 B inlet 
         13 A top jewel bearing 
         13 B top jewel bearing 
         14  set screw 
         14 A set screw 
         14 B set screw 
         15 A top sleeve 
         15 B top sleeve 
         16  spring holder 
         16 A spring holder 
         16 B spring holder 
         18  bob shaft bearing 
         19  small gap 
         19 A small gap 
         19 B small gap 
         20  bearing spacer 
         21  sample injection hole 
         21 A sample injection hole 
         21 B sample injection hole 
         22  bob shaft bearing 
         23  small gap 
         23 A small gap 
         23 B small gap 
         24  bob shaft 
         24 A bob shaft 
         24 B bob shaft 
         25  small gap 
         25 A small gap 
         25 B small gap 
         26  o-ring 
         26 A o-ring 
         26 B o-ring 
         27  small gap 
         28  set screw 
         28 A set screw 
         28 B set screw 
         29  screw thread 
         30  bob 
         30 A bob 
         30 B bob 
         31  rotor inside cap 
         31 A rotor inside cap 
         31 B rotor inside cap 
         32  support bearing 
         32 A support bearing 
         32 B support bearing 
         33  rotor bottom 
         33 A rotor bottom 
         33 B rotor bottom 
         34  coupling magnet 
         34 A coupling magnet 
         34 B coupling magnet 
         35  cell wall 
         35 A cell wall 
         35 B cell wall 
         36  magnet holder 
         36 A magnet holder 
         36 B magnet holder 
         38  driving magnet 
         38 A driving magnet 
         38 B driving magnet 
         39  thermal couple 
         39 A thermal couple 
         39 B thermal couple 
         40  magnet mount 
         40 A magnet mount 
         40 B magnet mount 
         41  straight bore 
         41 A straight bore 
         41 B straight bore 
         42  bearing 
         42 A bearing 
         42 B bearing 
         43  conical surface 
         43 A conical surface 
         43 B conical surface 
         44  bearing 
         44 A bearing 
         44 B bearing 
         45  chamber 
         46  lock nut 
         46 A lock nut 
         46 B lock nut 
         47  cell bottom 
         47 A cell bottom 
         47 B cell bottom 
         48  bushing 
         48 A bushing 
         48 B bushing 
         49  chamber 
         49 A chamber 
         49 B chamber 
         50  screw 
         50 A screw 
         50 B screw 
         51  rotor 
         51 A rotor 
         51 B rotor 
         52  heater 
         52 A heater 
         52 B heater 
         53  rotor inside wall 
         53 A rotor inside wall 
         53 B rotor inside wall 
         54  pivot 
         54 A pivot 
         54 B pivot 
         55  fin 
         55 A fin 
         55 B fin 
         56  rotor outside wall 
         56 A rotor outside wall 
         56 B rotor outside wall 
         57 A bottom jewel bearing 
         58  o-ring 
         58 A o-ring 
         59  conical surface 
         59 A conical surface 
         60  anti mixer 
         60 A anti mixer 
         60 B anti mixer 
         61  venting hole 
         61 A venting hole 
         62  cell body 
         62 A cell body 
         62 B cell body 
         63  screw thread 
         63 A screw thread 
         63 B screw thread 
         64  snap ring 
         66  bearing holder 
         66 A bearing holder 
         66 B cell coupling 
         67  flat 
         67 A flat 
         67 B flat 
         68  snap ring 
         70  spiral spring 
         70 A spiral spring 
         70 B spiral spring 
         72  top magnet 
         72 A top magnet 
         72 B top magnet 
         74  outlet 
         74 A outlet 
         74 B outlet 
         76  cell cap 
         76 A cell cap 
         76 B cell cap 
         78  thread 
         80  viscometer 
         80 A viscometer 
         80 B viscometer 
         82  anti mixer bottom fin 
         82 A anti mixer bottom fin 
         82 B anti mixer bottom fin 
         84  anti mixer middle fin 
         84 A anti mixer middle fin 
         84 B anti mixer middle fin 
         86  anti mixer top fin 
         86 A anti mixer top fin 
         86 B anti mixer top fin 
         88  bob vent 
         90 A needle pin 
         90 B needle pin 
     
  
   DESCRIPTION 
   FIG.  1 —Preferred Embodiment 
     FIG. 1  is a cross-section view of a viscometer  80  with a cell body  62  and a cell cap  76 . Cell body  62  is detachable from cell cap  76  via a screw thread  63 . An o-ring  26  assures against the escape of fluid through screw thread  63 . Inside of cell body  62  and below screw thread  63  is a conical surface  59  with reduced diameter, below which a cylindrical cell wall  35  extends downward to a cell bottom  47 . A tapered hole with a conical surface  43  and a straight bore  41  is located in the center of cell bottom  47 . A pivot  54 , which is secured to cell bottom  47  by a lock nut  46  through a thread  78 , is seated into said tapered hole on conical surface  43 . Lock nut  46  is tightened to provide initial seal on conical surface  41  between cell bottom  47  and pivot  54 . A thermal couple  39  is inserted into the center of pivot  54 . Radially outward of the outer surface of pivot  54  is a bushing  48 . Bushing  48  is made of Rulon, Teflon or equivalent plastics. A magnet holder  36  and a coupling magnet  34  are positioned radially outward of bushing  48 . A screw  50  secures magnet holder  36  and coupling magnet  34  to the bottom of a rotor  51 . Rotor  51  consists of a cylindrical rotor outside wall  56 , a disc shape rotor bottom  33 , a hollow cylindrical rotor inside wall  53  and a rotor inside cap  31 . A fin  55  extruded on the outer surface of rotor outside wall  56  provides better agitation of sample during measurement. A support bearing  32  provides vertical support of the assembly of rotor  51 , magnet holder  36  and coupling magnet  34 , which can rotate freely on the same central axis of pivot  54 . 
   A bearing holder  66  consists of a conical section and two different outside diameter sections. The outer surface of the conical section of bearing holder  66  mates inside conical surface  59  of cell body  62 . An o-ring  58  provides liquid-tight seal on conical surface  59 . A bob shaft  24  passes through the center of bearing holder  66  and rotationally supported by a bob shaft bearing  18 , a bob shaft bearing  22 , a bearing spacer  20 , a snap ring  68  and a snap ring  64 . An anti-mixer  60  is attached on bob shaft  24  by a set screw  28 . Anti mixer  60  consists of an anti mixer bottom fin  82 , an anti mixer middle fin  84 , an anti mixer top fin  86  and a cylindrical shell that connects these three fins together. Bearing holder  66  has various inside diameter bore sections so that a small gap  23 , a small gap  25  and a small gap  27  are formed between the outside diameter of those anti mixer fins and those inside bore sections of bearing holder  66 . Furthermore, a chamber  45  is formed between anti mixer top fin  86  and anti mixer middle fin  84  and a chamber  49  is formed between anti mixer middle fin  84  and anti mixer bottom fin  82 . A bob  30  is crewed on the bottom of bob shaft  24  via a screw thread  29 . A bob vent  88  is provide along the axial direction of bob  30  connecting the inside vacancy of bob  30  to its top. 
   A machined flat  67  is provided on the top of bearing holder  66 . Mating and resting on flat  67  is a spring holder  16 . A spiral spring  70  is placed in the center of spring holder  16  so that the outside lead of spiral spring  70  is fixed to the inside counter bore of spring holder  16  and the inside lead of spiral spring  70  is fixed to bob shaft  24  with any conventional means. A horseshoe type top magnet  72  is fixed to the top of bob shaft  24  with a set screw  14 . Additionally, a sample injection hole  21  channels from the top of bearing holder  66  to chamber  45 . A venting hole  61  connects outer surface of bearing holder  66  to a small gap  19  between bob shaft  240 D and bearing holder  66  ID. 
   An inlet  12  and an outlet  74  provide ports for applying and releasing pressure. A magnetometer  10  located on the top of cell cap  76  can measure the rotational displacement of top magnet  72 . 
   A magnet mount  40  is rotationally supported on the outside of cell body  62  by a bearing  42  and a bearing  44 . Magnet mount  40  can be rotated by any conventionally means such as gear box or motor. A pair of driving magnet  38  is mounted on magnet mount  40  at considerably the same level where coupling magnet  34  is mounted inside of the cell body  62 . 
   OPERATION 
   FIG.  1 —Preferred Embodiment 
   Pivot  54  is secured to cell body  62  by lock nut  46  and can be cleaned together with cell body  62 . During installation, screw  50  holds magnet holder  36 , coupling magnet  34  and rotor  51  together. Bushing  48  is pushed into the bottom of magnet holder  36 . This said subassembly is dropped into cell body  62  and rotationally supported by pivot  54 . Test sample is poured into cell body  62  so that sample surface just submerges the top of rotor  51 . 
   Holding bob shaft  24  in hand, install bob shaft bearing  18 , bearing spacer  20 , bob shaft bearing  22 , snap ring  68  and snap ring  64  onto bob shaft  24 . Then vertically insert this subassembly into bearing holder  66 . Next install spring holder  16  and spiral spring  70  onto the top of bearing holder  66 . Top magnet  72  is secured to the top of bob shaft  24  thereafter. Slide anti mixer  60  onto bob shaft  24  from bottom of bob shaft  24  and secure it at the position as shown in  FIG. 1  with set screw  28 . Bob  30  is finally screwed onto bob shaft  24  bottom via screw thread  29 . Install o-ring  58  onto the outer surface of bearing holder  66 . Then vertically push this bob shaft holder assembly down into cell body  62  slowly. 
   During pushing down this bob shaft holder assembly, air trapped inside of bob  30  is vented through bob vent  88 . Bob  30  also expels the sample fluid causing sample fluid level to rise. This expelled volume is stopped by o-ring  58  and can only cause sample fluid level to rise inside of bearing holder  66 . Consequently, chamber  49  is partially or totally filled with sample fluid after bearing holder assembly is total seated down engaging with cell body  62  on conical surface  59 . A syringe is used to inject additional sample fluid through sample injection hole  21  to bring sample fluid level up so that sample fluid would totally fill up chamber  49  and chamber  45 . Finally screw down cell cap  76  with o-ring  26  in place. Pump pressurization fluid from inlet  12  until all air inside of pressure vessel is expelled out through outlet  74 . Sample testing pressure can be raised by pumping more pressurization fluid into pressure vessel or releasing some pressurization fluid from pressure vessel. 
   It is very important to have rotor  51  and bob  30  concentrically aligned. Conical surface  59  is machined with high precision to ensure bob  30  is concentrically aligned with rotor  51 . This conical surface  59  also significantly simplifies the installation process since no addition adjustment or screw turning is required to ensure the good concentricity between rotor  51  and bob  30 . 
   A motor or gearbox drives magnet mount  40  to rotate carrying driving magnet  38 . A heater  52  heats up cell body  62  while thermal couple  39  provides temperature feedback for temperature control. Due to the magnetic coupling between driving magnet  38  and coupling magnet  34 , rotor  51  rotates at the same revolving speed as magnet mount  40  does. Because the viscosity of tested sample, a torque is generated on bob  30  causing it to rotate. Because of spiral spring  70 , the rotation angle of bob shaft  24  is roughly proportional to the torque applied on bob  30 . Magnetometer  10  picks up the rotation angle of top magnet  72  which rotates with bob shaft  24 . The rotation angle in turn can be used to calculate the viscosity of tested sample. 
   One of the drawbacks of most liquid pressurized viscometers is the mixing between tested sample and pressurization fluid. If a seal is provided between pressurization fluid and tested sample, the seal will induce friction error causing inaccurate measurement. If pressurization fluid is allowed to contact tested sample directly, pressurization fluid will mix with tested sample because of stirring and compressibility of tested sample. 
   In current invention, when pressurization fluid is applied, the sample fluid level is pushed down due to the compressibility of tested sample. Thus initial sample fluid inside of chamber  45  goes down to chamber  49  through small gap  25 , and some of the initial sample fluid inside of chamber  49  goes down to the lower measurement zone through small gap  27 . However, chamber  45  and chamber  49  are large enough so that at maximum rated pressure, chamber  49  is still at least half filled with sample fluid. This ensures the accuracy of the measurement because measurement zone below anti mixer bottom fin  82  is always totally filled with sample fluid. 
   Additionally, because anti mixer bottom fin  82  separates lower measurement zone and chamber  49 , fluid inside of chamber  49  is relatively static. Thus no stirring could cause the mixing between pressurization fluid and tested sample if the interface between pressurization fluid and tested sample is inside of chamber  49 . 
   The pressurization fluid should be chosen carefully. This pressurization fluid should not spontaneously dissolve into or mix with the tested sample, and should have a specific gravity lower than the specific gravity of the sample. Pressurization fluid communicates pressure with sample fluid through venting hole  61  and small gap  23  while keeping bob shaft bearing  18  and bob shaft bearing  22  submerged. Because pressurization fluid is generally a clean, nonabrasive liquid, this ensures bob shaft bearing  18  and bob shaft bearing  22  rotate freely and have long working life span. If conventional type of bearings, such as roller bearing, ball bearing and spherical bearing, are used in a comparative viscometer without mechanism preventing sample mixing with pressurization fluid, those bearings will quickly stop working properly, normally with excessive drag, because tested sample is normally filled with a lot of fine solid contents. 
   DESCRIPTION 
   FIG.  2 —An Alternative Embodiment with Jewel Bearings and Conical Support 
     FIG. 2  is a cross-section view of a viscometer  80 A with a cell body  62 A and a cell cap  76 A. Cell body  62 A is detachable from cell cap  76 A via a screw thread  63 A. An o-ring  26 A assures against escape of fluid through screw thread  63 A. Inside of cell body  62 A and below screw thread  63 A is a conical surface  59 A with reduced diameter, below which a cylindrical cell wall  35 A extends downward to a cell bottom  47 A. A tapered hole with a conical surface  43 A and a straight bore  41 A is located in the center of cell bottom  47 A. A pivot  54 A, which is secured to cell bottom  47 A by a lock nut  46 A through a thread  78 A, is seated into said tapered hole on conical surface  43 A. Lock nut  46 A is tightened to provide initial seal on conical surface  41 A between cell bottom  47 A and pivot  54 A. A thermal couple  39 A is inserted into the center of pivot  54 A. Radially outward of the outer surface of pivot  54 A is a bushing  48 A. Bushing  48 A is made of Rulon, Teflon or equivalent plastics. A magnet holder  36 A and a coupling magnet  34 A are positioned radially outward of bushing  48 A. A screw  50 A secures magnet holder  36 A and coupling magnet  34 A to the bottom of a rotor  51 A. Rotor  51 A consists of a cylindrical rotor outside wall  56 A, a disc shape rotor bottom  33 A, a hollow cylindrical rotor inside wall  53 A and a rotor inside cap  31 A. A fin  55 A extruded on the outer surface of rotor outside wall  56 A provides better agitation of sample during measurement. A support bearing  32 A provides vertical support of the assembly of rotor  51 A, magnet holder  36 A and coupling magnet  34 A, which can rotate freely on the same central axis of pivot  54 A. 
   A bearing holder  66 A consists of a conical section and two different outside diameter sections. The outer surface of the conical section of bearing holder  66 A mates inside conical surface  59 A of cell body  62 A. An o-ring  58 A provides liquid-tight seal on conical surface  59 A. A bob shaft  24 A passes through the center of bearing holder  66 A while not in contact with its inside bore directly. A machined flat  67 A is provided on the top of bearing holder  66 A. Mating and resting on flat  67 A is a spring holder  16 A. A spiral spring  70 A is placed in the center of spring holder  16 A so that the outside lead of spiral spring  70 A is fixed to the inside counter bore of spring holder  16 A and the inside lead of spiral spring  70 A is fixed to bob shaft  24 A with any conventional means. 
   A needle pin  90 A has its lower portion fixed on the top of pivot  54 A. Resting on the top of needle pin  90 A is a bottom jewel bearing  57 A secured to the bottom of bob shaft  24 A. Resting on top of spring holder  16 A is a top sleeve  15 A, on which a top jewel bearing  13 A is mounted. The tip of bob shaft  24  is in contact with top jewel bearing  13 A. Thus bob shaft  24  is rotationally supported by bottom jewel bearing  57 A and top jewel bearing  13 A. Also secured to the bottom of bob shaft  24 A is a bob  30 A. 
   A horseshoe type top magnet  72 A is also fixed to the top of bob shaft  24 A with a set screw  14 A. 
   An anti-mixer  60 A is attached on bob shaft  24 A by a set screw  28 A. Anti mixer  60 A consists of an anti mixer bottom fin  82 A, an anti mixer middle fin  84 A, an anti mixer top fin  86 A and a cylindrical shell that connects these three fins together. Bearing holder  66 A has various inside diameter bore sections so that a small gap  23 A, a small gap  25 A and a small gap  27 A are formed between the outside diameter of those anti mixer fins and those inside bore sections of bearing holder  66 A. Furthermore, a chamber  45 A is formed between anti mixer top fin  86 A and anti mixer middle fin  84 A and a chamber  49 A is formed between anti mixer middle fin  84 A and anti mixer bottom fin  82 A. 
   Additionally, a sample injection hole  21 A channels from the top of bearing holder  66 A to chamber  45 A. A venting hole  61 A connects outer surface of bearing holder  66 A to a small gap  19 A between bob shaft  24 A OD and bearing holder  66 A ID. 
   An inlet  12 A and an outlet  74 A provide ports for applying and releasing pressure. A magnetometer  10 A located on the top of cell cap  76 A can measure the rotational displacement of top magnet  72 A. 
   A magnet mount  40 A is rotationally supported on the outside of cell body  62 A by a bearing  42 A and a bearing  44 A. Magnet mount  40 A can be rotated by any conventionally means such as gear box or motor. A pair of driving magnet  38 A is mounted on magnet mount  40 A at considerably the same level where coupling magnet  34 A is mounted inside of the cell body  62 A. 
   OPERATION 
   FIG.  2 —An Alternative Embodiment with Jewel Bearings and Conical Support 
   Pivot  54 A is left on cell body  62 A secured by lock nut  46 A between tests and can be cleaned together with cell body  62 A. During installation, screw  50 A holds magnet holder  36 A, coupling magnet  34 A and rotor  51 A together. Bushing  48 A is pushed into the bottom of magnet holder  36 A. This said subassembly is dropped into cell body  62 A and rotationally supported by pivot  54 A. Test sample is poured into cell body  62 A so that sample surface just submerges the top of rotor  51 A. 
   Insert bob shaft  24 A into bearing holder  66 A. Next install spring holder  16 A and spiral spring  70 A onto the top of bearing holder  66 A. Top magnet  72 A is secured to the top of bob shaft  24 A thereafter. Slide anti mixer  60 A onto bob shaft  24 A from bottom of bob shaft  24 A and secure it at the position as shown in  FIG. 2  with set screw  28 A. Bob  30 A is finally screwed onto bob shaft  24 A bottom via screw thread  29 A. Install o-ring  58 A onto the outer surface of bearing holder  66 A. Then vertically push this bob shaft holder assembly down into cell body  62 A slowly. 
   During pushing down this bob shaft holder assembly, bob  30 A expels the sample fluid causing sample fluid level to rise. This expelled volume is stopped by o-ring  58 A and can only cause sample fluid level to rise inside of bearing holder  66 A. Consequently, chamber  49 A is partially or totally filled with sample fluid after bearing holder assembly is total seated down engaging with cell body  62 A on conical surface  59 A. A syringe is used to inject additional sample fluid through small injection hole  21 A to bring sample fluid level up so that sample fluid would totally fill up chamber  49 A and chamber  45 A. Then place top sleeve  15 A on top of spring holder  16 A so that bob shaft  24 A is centered by top jewel bearing  13 A. Finally screw down cell cap  76 A with o-ring  26 A in place. Pump pressurization fluid from inlet  12 A until all air inside of pressure vessel is expelled out through outlet  74 A. Sample testing pressure can be raised by pumping more pressurization fluid into pressure vessel or releasing some pressurization fluid from pressure vessel. 
   A motor or gearbox drives magnet mount  40 A to rotate carrying driving magnet  38 A. A heater  52 A heats up cell body  62 A while thermal couple  39 A provides temperature feedback for temperature control. Due to the magnetic coupling between driving magnet  38 A and coupling magnet  34 A, rotor  51 A rotates at the same revolving speed as magnet mount  40 A does. Because the viscosity of tested sample, a torque is generated on bob  30 A causing it to rotate. Because of spiral spring  70 A, the rotation angle of bob shaft  24 A is roughly proportional to the torque applied on bob  30 A. Magnetometer  10 A picks up the rotation angle of top magnet  72 A which rotates with bob shaft  24 A. The rotation angle in turn can be used to calculate the viscosity of tested sample. 
   In this embodiment, when pressurization fluid is applied, the sample fluid level is pushed down due to the compressibility of tested sample. Thus initial sample fluid inside of chamber  45 A goes down to chamber  49 A through small gap  25 A, and some of the initial sample fluid inside of chamber  49 A goes down to the lower measurement zone through small gap  27 A. However, chamber  45 A and chamber  49 A are large enough so that at maximum rated pressure, chamber  49 A is still at least half filled with sample fluid. This ensures the accuracy of the measurement because measurement zone below anti mixer bottom fin  82 A is always totally filled with sample fluid. 
   DESCRIPTION 
   FIG.  3 —An Alternative Embodiment with Jewel Bearings and Three-Piece Pressure Vessel Configuration 
     FIG. 3  is a cross-section view of a viscometer  80 B with a cell body  62 B, a cell coupling  66 B and a cell cap  76 B. Cell body  62 B is detachable from cell coupling  66 B via a screw thread  63 B and cell cap  76 B is screwed on top of cell coupling  66 B. An o-ring  26 B assures against escape of fluid through screw thread  63 B. Inside of cell body  62  and below screw thread  63  is a conical surface  59 B with reduced diameter, below which a cylindrical cell wall  35 B extends downward to a cell bottom  47 B. A tapered hole with a conical surface  43 B and a straight bore  41 B is located in the center of cell bottom  47 B. A pivot  54 B, which is secured to cell bottom  47 B by a lock nut  46 B through a thread  78 B, is seated into said tapered hole on conical surface  43 B. Lock nut  46 B is tightened to provide initial seal on conical surface  41 B between cell bottom  47 B and pivot  54 B. A thermal couple  39 B is inserted into the center of pivot  54 B. Radially outward of the outer surface of pivot  54 B is a bushing  48 B. Bushing  48 B is made of Rulon, Teflon or equivalent plastics. A magnet holder  36 B and a coupling magnet  34 B are radially positioned outward of bushing  48 B. A screw  50 B secures magnet holder  36 B and coupling magnet  34 B to the bottom of a rotor  51 B. Rotor  51 B consists of a cylindrical rotor outside wall  56 B, a disc shape rotor bottom  33 B, a hollow cylindrical rotor inside wall  53 B and a rotor inside cap  31 B. A fin  55 B extruded on the outer surface of rotor outside wall  56 B provides better agitation of sample during measurement. A support bearing  32 B provides vertical support of the assembly of rotor  51 B, magnet holder  36 B and coupling magnet  34 B, which can rotate freely on the same central axis of pivot  54 B. 
   A bob shaft  24 B passes through the center of cell coupling  66 B while not in contact with its inside bore directly. A machined flat  67 B is provided on the top of cell coupling  66 B. Mating and resting on flat  67 B is a spring holder  16 B. A spiral spring  70 B is placed in the center of spring holder  16 B so that the outside lead of spiral spring  70 B is fixed to the inside counter bore of spring holder  16 B and the inside lead of spiral spring  70 B is fixed to bob shaft  24 B with any conventional means. 
   A needle pin  90 B has its lower portion fixed on the top of pivot  54 B. Resting on the top of needle pin  90 B is a bottom jewel bearing  57 B secured to the bottom of bob shaft  24 B. Resting on top of spring holder  16 B is a top sleeve  15 B, on which a top jewel bearing  13 B is mounted. The tip of bob shaft  24  is in contact with top jewel bearing  13 B. Thus bob shaft  24 B is rotationally supported by bottom jewel bearing  57 B and top jewel bearing  13 B. Also secured to the bottom of bob shaft  24 B is a bob  30 B. 
   A horseshoe type top magnet  72 B is also fixed to the top of bob shaft  24 B with a set screw  14 B. 
   An anti-mixer  60 B is attached on bob shaft  24 B by a set screw  28 B. Anti mixer  60 B consists of an anti mixer bottom fin  82 B, an anti mixer middle fin  84 B, an anti mixer top fin  86 B and a cylindrical shell that connects these three fins together. Cell coupling  66 B has various inside diameter bore sections so that a small gap  23 B, a small gap  25 B and a small gap  27 B are formed between the outside diameter of those anti mixer fins and those inside bore sections of cell coupling  66 B. Furthermore, a chamber  45 B is formed between anti mixer top fin  86 B and anti mixer middle fin  84 B and a chamber  49 B is formed between anti mixer middle fin  84 B and anti mixer bottom fin  82 B. 
   Additionally, a sample injection hole  21 B channels from the top of cell coupling  66 B to chamber  45 B. 
   An inlet  12 B and an outlet  74 B provide ports for applying and releasing pressure. A magnetometer  10 B located on the top of cell cap  76 B can measure the rotational displacement of top magnet  72 B. 
   A magnet mount  40 B is rotationally supported on the outside of cell body  62 B by a bearing  42 B and a bearing  44 B. Magnet mount  40 B can be rotated by any conventionally means such as gear box or motor. A pair of driving magnet  38 B is mounted on magnet mount  40 B at considerably the same level where coupling magnet  34 B is mounted inside of the cell body  62 B. 
   OPERATION 
   FIG.  3 —An Alternative Embodiment with Jewel Bearings and Three-Piece Pressure Vessel Configuration 
   Pivot  54 B is left on cell body  62 B secured by lock nut  46 B between tests and can be cleaned together with cell body  62 B. During installation, screw  50 B holds magnet holder  36 B, coupling magnet  34 B and rotor  51 B together. Bushing  48 B is pushed into the bottom of magnet holder  36 B. This said subassembly is dropped into cell body  62 B and rotationally supported by pivot  54 B. Test sample is poured into cell body  62 B so that sample surface just submerges the top of rotor  51 B. 
   Secure anti mixer  60 B to bob shaft  24 B by tightening set screw  28 B. Insert bob shaft  24 B into cell coupling  66 B from bottom. Next install spring holder  16 B and spiral spring  70 B onto the top of cell coupling  66 B. Top magnet  72 B is secured to the top of bob shaft  24 B thereafter. Bob  30 B is screwed onto bob shaft  24 B bottom via screw thread  29 B thereafter. Then vertically screw on cell body  62 B to cell coupling  66 B. 
   During screwing on cell body  62 B, bob  30 B expels the sample fluid causing sample fluid level to rise. A syringe is used to inject additional sample fluid through small injection hole  21 B to bring sample fluid level up so that sample fluid would totally fill up chamber  49 B and chamber  45 B. Then place top sleeve  15 B on top of spring holder  16 B so that bob shaft  24 B is centered by top jewel bearing  13 B. Finally screw down cell cap  76 B onto cell coupling  66 B. Pump pressurization fluid from inlet  12 B. Sample testing pressure can be raised by pumping more pressurization fluid into pressure vessel through inlet  12  or releasing some pressurization fluid from pressure vessel through  74 B outlet. 
   A motor or gearbox drives magnet mount  40 B to rotate carrying driving magnet  38 B. A heater  52 B heats up cell body  62 B while thermal couple  39 B provides temperature feedback for temperature control. Due to the magnetic coupling between driving magnet  38 B and coupling magnet  34 B, rotor  51 B rotates at the same revolving speed as magnet mount  40 B does. Because the viscosity of tested sample, a torque is generated on bob  30 B causing it to rotate. Because of spiral spring  70 B, the rotation angle of bob shaft  24 B is roughly proportional to the torque applied on bob  30 B. Magnetometer  10 B picks up the rotation angle of top magnet  72 B which rotates with bob shaft  24 B. The rotation angle in turn can be used to calculate the viscosity of tested sample. 
   In this embodiment, when pressurization fluid is applied, the sample fluid level is pushed down due to the compressibility of tested sample. Thus initial sample fluid inside of chamber  45 B goes down to chamber  49 B through small gap  25 B, and some of the initial sample fluid inside of chamber  49 B goes down to the lower measurement zone through small gap  27 B. However, chamber  45 B and chamber  49 B are large enough so that at maximum rated pressure, chamber  49 B is still at least half filled with sample fluid. This ensures the accuracy of the measurement because measurement zone below anti mixer bottom fin  82 B is always totally filled with sample fluid. 
   RAMIFICATIONS 
   It is not necessary to have both chamber  45  and chamber  49 . With just chamber  45  or chamber  49  and its sufficient volume, pressurization fluid and test sample can still be separated well. 
   Anti mixer  60  does not have to be designed as shown in  FIG. 1 . Anti mixer top fin  86 , anti mixer middle fin  84  and anti mixer bottom fin  82  can be removed. Then just add fins to the inside of bearing holder  66  as long as either chamber  45  or chamber  49  is still formed and communicates pressure from top to bottom in substantially reduced opening. As a matter of fact, anti mixer  60  could be totally eliminated if chamber  45  or chamber  49  is bored out of bearing holder  66  inside while the reduced inside diameter sections of bearing holder  66  do not directly rub on bob shaft  24 . 
   Bob  30  does not have to be cylindrical shape. It could be a blade, frame or any geometry shape. 
   Bob shaft bearing  18  and bob shaft bearing  22  could be combined as one needle bearing or equivalent bearing with low friction. 
   Rotor  51  does not have to be driven with a magnetic coupling across cell body  62 . Rotor  51  could be driven to rotate with any means such as directly driven at the bottom of the cell body with dynamic seal, etc. 
   Spiral spring  70  could be helical spring or other types of equivalent resilient mechanism. 
   There are many other ways to measure the angular displacement of bob shaft  24 . For example, in preferred embodiment viscometer  80 , top magnet  72  and magnetometer  10  can be replaced with a pair of concentrically mounted electrical stator and rotor to measure the rotation of bob shaft  24 . Additionally, top magnet  72  and magnetometer  10  can be replaced with an encoder to measure the rotation of bob shaft  24 . A potentiometer and a brush attached to bob shaft  24  could measure the rotation as well. 
   Alternatively, a metal arm or wiper which rotates with bob shaft  10 , and a wire-wound conductance transducer which is mounted directly or indirectly on bearing holder  66  or cell cap  76 , can also be used to measure the rotation of bob shaft  24  by measuring the conductance change in the wire-wound coil. 
   Viscometer  80  can also be reduced to much simpler construction for non-pressurized viscometer applications. It can be accomplished by removing sealing related components, such as all o-rings etc. In non-pressurized application, sample cups can have open bottoms, and the lower part of sample cups can be immersed into a liquid—the liquid&#39;s viscosity to be measured. 
   CONCLUSION, AND SCOPE 
   Accordingly, the reader will see that this invention can be used to construct a high pressure viscometer with accurate measurement easily. The simple configuration enables simple operation procedure and low maintenance. 
   OBJECTS AND ADVANTAGES 
   From the description above, a number of advantages of my viscometer become evident:
         (a) Due to conventional low friction ball bearings design, current invention substantially reduces operation cost comparing to jewel bearing designs. It had been unsuccessful to use conventional ball bearings in liquid pressurized high pressure viscometer because any fine solids in tested sample would cause low friction ball bearings to fail. Also because ball bearings are much durable than jewel bearings, maintenance task is reduced significantly.   (b) Totally eliminate the measurement error because of sample mixing with pressurization fluid in a comparative viscometer.   (c) Very conveniently isolate all electrical component from pressurized zone thus reducing maintenance work.   (d) Very compact design by using small size spiral spring.   (e) Extremely simple installation and disassembly procedures due to conical bearing holder design while maintaining high concentricity between bob and rotor.
 
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.