Abstract:
A rotational viscometer includes a cylindrical bob attached to a bob axle, a concentric sleeve exterior of the bob, a motor for inducing rotation in the sleeve, a biasing spring attached to the bob axle for resisting axle rotation, and a measurement system comprising an electric field transmitter, an electric field receiver and a rotor extending intermediate the transmitter and receiver. The rotor is attached to the bob axle so that rotation of the bob axle and the rotor presents a measurable deviation of the electrical field received by the electrical field receiver. A processor calculates the angle of displacement of the bob from that sine and cosine of the received electrical field and transmits readable output in the form of a sample viscosity value to a display.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention is generally related to viscometers and more specifically to viscometers employing an inductive displacement sensor to detect the angle of displacement of a bob used to measure viscosity of a tested fluid. 
     Description of the Related Art 
     Viscometers are known to use a variety of configurations to measure rheological properties of a fluid. One frequently employed configuration is a rotational Couette geometry viscometer comprised of a cylindrical bob positioned on a bob axle and a concentric sleeve exterior of the bob suspended from a viscometer housing into a container holding a sample of the fluid to be tested. As the concentric sleeve is rotated at a determined speed, a specified shear rate is exerted on the fluid near the face of the rotor and rotation of the bob is induced. A biasing spring resists rotation of the bob and axle. The resulting deflection of the bob in response to the rotation of the sleeve is an indicator of the viscosity of the fluid intermediate the bob and sleeve. 
     Prior art viscometers include: 
     U.S. Pat. No. 3,751,975 issued to Katsura on Aug. 14, 1973, discloses a pair of magnetic electrical signal generators mounted on opposite ends of the torsion area of a torsion bar. When the torsion bar is rotated with one end submerged in a sample fluid, comparison of the difference between the generated signals provides a direct relationship to the viscosity of the sample fluid. 
     U.S. Pat. No. 4,043,183 issued to Higgs et al. on Aug. 23, 1977, discloses a consistometer for continuously measuring the viscosity of the liquid in a stream. When a reference sensor outside the stream and a detector sensor within the stream are simultaneously spun in relationship to respective stationary sensors, comparison of the difference between the reference signal and the detected signal provides a direct relationship to the viscosity of the liquid in the stream. 
     U.S. Pat. No. 4,175,425 issued to Brookfield on Nov. 27, 1979, discloses a viscometer having a drive cylinder and a driven cylinder attached to a resistance unit, which is linked to a magnetic transducer readout device. The patent states that the inventive structure works with other types of readout devices. 
     U.S. Pat. No. 4,448,061 issued to Brookfield on May 15, 1984, and reexamined on Oct. 9, 1990 and Nov. 21, 1995, discloses a rotational viscometer, which uses a rotor-stator configuration to produce continuous out-feed of electric signals of strengths varying with the viscosity of the liquid being monitored. 
     U.S. Pat. No. 4,484,468 issued to Gau et al. on Nov. 27, 1984, discloses an automatic rotational viscometer comprised of a rotated or torqued sleeve. The sleeve applies rotation to a bob, monitored by an optical encoder, which measures the angular displacement of the bob from the zero azimuth position and continues to be sensed until the angle is stabilized. 
     It would be an improvement to the field to adapt a viscometer with a linear inductive angular displacement sensor to more precisely quantify the amount of force imparted to the bob by the fluid in relationship to the rotation of the bob axle. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the objects of my invention are to provide, among other things, a rotational viscometer that: 
     provides a high degree of accuracy over the operational range; 
     comprises mechanically and electrically simple configuration; 
     is tolerant of variations in environmental conditions; and 
     provides reduced friction forces to the bob and axle. 
     Other objects of my invention will become evident throughout the reading of this application. 
     My invention is a rotational viscometer, which employs an electrical field sensor to measure the induced angle of rotation of a bob by a sample substance. The viscometer includes a generally circular bob attached to a bob axle, a concentric sleeve exterior of the bob, a motor for inducing rotation in the sleeve, a biasing spring attached to the bob axle for resisting axle rotation, and a measurement system comprising an electric field transmitter, an electric field receiver and a rotor extending intermediate the transmitter and receiver. The rotor is attached to the bob axle so that rotation of the bob axle and the rotor results in a measurable deviation of the received electrical field. The processor calculates the angle of displacement of the bob and transmits readable output of a sample characteristic in accordance with determined calculations based on, among other things, the sleeve rotation velocity and the bob displacement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the viscometer of the present invention. 
     FIG. 2 is a detailed partial cross-sectional view of the viscometer. 
     FIG. 3 is an exploded view of a rotary electrical encoder. 
     FIG. 4 is a detailed view of a rotary electrical encoder rotor. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to FIG.  1  and FIG. 2, the viscometer  10  of the present invention is depicted. The viscometer  10  includes a base  11 , upstanding legs  12  and  13 , each supported by base  11 , an upper structure  50  and a moveable stage  15  intermediate base  11  and upper structure  50 . Legs  12  and  13  extend upright to a platform  14  of upper structure  50 . Platform  14  is parallel to the base  11 . Stage  15  is supported on legs  12  and  13  and vertically moveable on legs  12  and  13 . Stage  15  may be fixed at a position on legs  12  and  13  by a locking nut  16 . 
     Upper structure  50  includes a support structure  30  attached to platform  14 . Support structure  30  supports vertical upper sleeve  20  and vertical bob axle  27  in a vertical orientation and normal to stage  15 . Support structure  30  further supports encoder  39  in a fixed position in relation to bob axle  27 . 
     A cylindrical bob  25  is fixedly supported on bob axle  27 . Bob  25  and bob axle  27  are concentrically oriented about a common bob axis  21 . Axle  27  is supported in vertical orientation by upper axle bearings  31  and lower axle bearings  32 . Each of upper axle bearings  31  and lower axle bearings  32  are supported by support structure  30 . 
     Upper sleeve  20  is a hollow, generally cylindrical structure coaxially oriented with bob axle  27 . Upper sleeve  20  is rotatable around axis  21 , and may be described as coaxially concentric to bob axle  27  and bob  25 . Upper sleeve  20  is retained in stable vertical position by upper sleeve bearings  22  and lower sleeve bearings  23 . 
     Upper sleeve  20  extends below platform  14 . A lower sleeve  26  is removably connected to upper sleeve  20 . Connection may be by threading or other suitable means. Lower sleeve  26  is also coaxially concentric with bob axis  21 . 
     A motor  42  and drive belt  40  are provided for rotation of upper sleeve  20  and lower sleeve  26 . In an exemplary embodiment, drive belt  40  contains links  44  that engage splines (not shown) of a motor gear (not shown) and sleeve gear  24 . In the exemplary embodiment, sleeve gear  24  is cylindrical and is fitted around upper sleeve  20  coaxially concentric with axis  21 . The motor  42  is operable at various speeds suitable to impart a desired rotation frequency of upper sleeve  20  and lower sleeve  26 . In the exemplary embodiment, a power converter  52  is provided to convert alternating current power to direct current for supplying power to motor  42 . 
     Referring to FIGS. 1 through 3, electrical assembly  39  is supported by support structure  30  and by encoder cradle  74 . Electrical assembly  39  includes an upper housing  37 , a lower housing  38 , an electrical field transmitter  35 , an electrical field receiver  34  and a rotor  33 . Upper housing  37 , lower housing  38 , electrical field transmitter  35  and electrical field receiver  34  are each positioned in a fixed position in relation to support structure  30  and axle  27 . Rotor  33  is positioned intermediate electrical field transmitter  35  and electrical field receiver  34 . Rotor  33  is attached to axle  27  and revolves with axle  27 . Rotor  33  does not contact either of electrical field transmitter  35  or electrical field receiver  34 . Referring to FIG. 4, rotor  33  includes a rotor hub  71  attached to axle  27 , a rotor outer rim  73  and rotor spokes  72  extending intermediate rotor hub  71  and rotor rim  73 . A suitably structured electrical field receiver  34  is sold by Netzer Precision Motion Sensors Ltd. and is identified as a rotary electric encoder. 
     An electrical connector  60  and connector wiring  62  communicate data received at electrical field receiver  34  to processor  51 . Control wiring  63  connecting processor  51  and motor  42  allow for control of motor  42 . Processor  51  is operationally attached to input interface  55  and to output interface  56 . Such attachment may be by circuit boards and wiring (not shown) known in the art. In an exemplary embodiment, processor  51  includes read only memory and random access memory, allowing processor  51  to control multiple predetermined functions and to control functions determined by operator input. 
     A torsion spring  61  is positioned intermediate electrical assembly  39  and viscometer housing  54 . Spring  61  biases the axle  27  in a determined position and resists rotational movement of axle  27 . Other torsioning devices known in the field may be used, for example axially torsioned wire, metal strips or plastic strips. 
     Referring to FIG.  2  and FIG. 3, extension arm  75  is attached to axle  27  intermediate a lower surface  77  of cradle  74  and an upper surface  78  of support structure  30 . Arm  75  is normal to axis  21  and correspondingly parallel to stage  15  and base  11 . A removable stop  76  extends upwardly from cradle  74  such that arm  75  will engage stop  76  upon rotation of axle  27 . Stop  76  may therefore act as a bar to limit rotation of axle  27  if desired. Upon removal of stop  76  from cradle  74 , rotation of axle  27  will not be limited by stop  76 . An exemplary form of stop  76  comprises a screw insertable in a threaded opening in cradle  74 . 
     In operation, a cup (not shown) containing a sample of fluid to be tested (not shown) is placed on stage  15  and stage  15  is raised to a position where the bob  25  and the lower sleeve  26  are immersed in the sample. Sufficient distance is provided between base  11  and platform  14  to allow a sample container (not shown) to be placed on stage  15  and raised with stage  15  to a proper position in relation to bob  25  and lower sleeve  26 . The specific configuration of bob  25 , lower sleeve  26  and the extent of immersion may be dictated by industry practice or accepted conventions for the types of fluid to be tested. 
     The motor  42  is operable at various speeds in order to induce a specified speed of rotation in upper sleeve  20  and lower sleeve  26 . Such speed is controlled by a motor controller (not shown) known in the art. 
     Rotation of the lower sleeve  26  induces a rotational force in the sample, which rotational force is transmitted to the bob  25  and the spring  61  biasing axle  27 . The extent of rotation of bob  25  in response to rotational force of the sample is a function of, among other things, the viscosity of the sample and the resistance force of the spring  61 . As the spring  61  resistance may be determined within the range of forces applied, the bob  25  angular rotation may comprise an accurate indication of sample viscosity. 
     Rotation of bob  25  results in corresponding rotation of rotor  33 . Rotation of rotor  33  results in measurable distortion of a patterned electrical field generated by electrical field transmitter  35  and received by electrical field receiver  34 . In the exemplary embodiment, such distortion is output to processor  51  as continuously varying voltages proportional to the sine and cosine of the measured angle of angular displacement of axle  27 . In the exemplary embodiment, processor  51  converts such voltages to digital values at a determined integration and conversion rate. 
     As the patterned electrical field is generated over a suitably large area and the rotation of each of the plurality of rotor spokes  72  each generates a distortion in the electrical field, the precision of the resulting measurement is enhanced. Additionally, the lack of contact between the measuring indicator, the rotor  33  and the electrical field transmitter  35  and electrical field receiver  34  reduces error in the resulting measurement and eliminates mechanical variations of heat, environmental moisture and torque on measurement mechanical components. 
     An input interface  55  communicating with processor  51  is provided for entry of instructions to processor  51 . An output display  56  communicating with processor  51  is also provided. The cover  54  is placed on the platform  14  to enclose the apparatus. In the exemplary embodiment, input interface  55  comprises a keyboard, said keyboard including a plurality of keys that define numerical values and a plurality of keys that identify determined functions to be performed through processor  51 . In an exemplary embodiment, processor  51  is operably connected to motor controller (not shown) to operate motor  42  at predetermined speeds. In an exemplary embodiment, processor  51  includes read only memory and random access memory to allow processor to receive operator input, control motor speed, receive input from electrical field receiver  34 , calculate sample properties and transmit to output display  56  sample properties. Processor  51  may further display operational information, such as sleeve rotation speed and angular deflection of the bob. Predetermined function calculations include a calibrate function, a set up function, a sample viscosity, and a sample gel strength. Various functions may be provided for differing types of material, such as drilling mud or cement. 
     In an alternate embodiment, an external processor (not shown), such as a computer, interfaces with processor  51 . In this embodiment, the external processor can communicate entry of-instructions to processor  51 . Additionally, processor  51  can transmit output of sample properties to the external processor. The external processor may directly interface with processor  51  or processor  51  may interface with a network (not shown), such as the Internet, in which the external processor is also interfaced, thereby allowing instructions to and output from processor  51  to be entered and monitored from a location remote of the viscometer  10  through the network. The foregoing disclosure and description of the invention is illustrative and explanatory thereof Various changes in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.