Abstract:
Viscosity or rheology measuring instrument utilizing Hall Effect or like magnetic coupling with parts mounted on driving and driven rotational assemblies.

Description:
[0001]    The present invention claims priority from U.S. provisional application 61/682,980 filed 14 Aug. 2012 and is related to PCT application Ser. No. PCT/US2012/000502 International Filing Date 5 Oct., 2012. The invention relates to viscometers which rely on a linear or angular displacement of driving and driven motions in a fluent medium where viscosity is to be measured. Many such viscometers lack desired base precision and/or are sensitive to axial alignment variations and variation of temperatures. 
     
    
     FIELD AND BACKGROUND OF THE INVENTION 
       [0002]    One of the problems of widely available rotary viscometers is that of temperature drift. For example, the Brookfield Engineering Laboratories, Inc., (BEL) model CAP3000™ cone and plate rotary viscometer with a MSI brand variable inductance transducer has a temperature drift of about −/+2% full scope error over about a −10 to 50° C. range of angular deflection. Coping with axial movement due to e.g. cone tip wear is also an issue in maintaining reliable readings over long durations of instrument use. It is also a need to enable a large angular range for full scale. 
         [0003]    There is also a need for continuous reading of viscosity. For instance, some BEL cone and plate viscometers use an optical time base sensing mechanism for angular air placement giving a limited number of readings per revolution (e.g. two) at 0.01 rpm. 
         [0004]    It is an object of the invention to provide a greater precision in such viscometer. It is a further object to reduce or eliminate problems arising out of axial orientation issues and/or temperature variations. It is a further object to achieve the foregoing with minimal change to configuration of the viscometer and its electrical circuitry and computer interfacing. 
       SUMMARY OF THE INVENTION 
       [0005]    The objects are achieved by a viscometer constructed with a Hall Effect transducer which can be (a) centered axially, (b) mounted a radial distance from the viscometer axis, (c) provided with extra bearing support and (d) other configurations. Other magnetic transducers can also be used to good effect. The transducer should have multiple sensors in a single thermal environment e.g. multiple sensors on a single die monolithic construction preferably also affording capabilities of signal conditioning, A/D conversion, DSP and interface electronics on the same die. 
         [0006]    The magnet and sensor of the Hall Effect transducer are mounted on separate areas of the customary drive shaft and sensing shaft of a rotational viscometer, the latter being suspended from a rotating frame driven by the drive shaft and the sensing shaft being coupled to the drive shaft by one or more torque springs preferably two with each being in spiral form and oppositely coiled. Multiple axially spaced bearings are preferably provided along sensing shaft length and the bearings are mounted from a housing driven by the drive shaft so that there is minimal or no bearing torque drag. A sensing end such as a cone and plate or barrel cylindrical end rotor is installed at the spindle end. 
         [0007]    The electrical signal generated by the Hall Effect transducer, usually a digital signal can be converted to analog using simple low pass filters. The analog signal can be extracted by brush and slip ring means affording continuity of signal extraction and the construction as a whole is usable to extract a wide range signal due to a large range angular relative displacement of the sensing and drive shafts. The signal can be maintained as digital, converted to analog e.g. with pulse width moderation output and low pass filters and converted back to digital. Preferably one or both elements of the Hail Effect transducer (sensor and magnet) are set up on the main axis of a rotary viscometer, but radial offset of one or both is also feasible. Further, the driving shaft and sensing shaft are coupled by one or more spiral coil arrays and more preferably multiple arrays (including one or more served by spindled pairs) to avoid a zero shift at high speed. The instrument and transducer cover a wide range and may have relative angular displacements of up to 300 degrees. This is accomplished by a brush/slip ring form or like means of signal extraction. 
         [0008]    The new viscometer of the invention is exemplified by preferred embodiments described below with references taken in conjunction with the accompanying drawings in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIGS. 1-5  are side views of several embodiments of the invention in which like parts between embodiments have the same reference numbers; 
           [0010]      FIGS. 1-A , and  1 A- 2  (prior art) show schematically a comparison of the viscometer electronics with a Hall Effect transducer or like transducer with state of the art transducer such as the variable inductance MSI transducer cited above; 
           [0011]      FIG. 1B  shows schematically a block diagram of a Hall Effect sensor array to generate differential sine and cosine wave outputs to enable reduced temperature drift; 
           [0012]      FIG. 1C  shows schematically a block diagram of the electronics incorporating a rotary transducer and low pass filter circuits; 
           [0013]      FIG. 1D  shows an optical coupling alternative to brush and slip ring signal extraction; 
           [0014]      FIG. 2  shows another viscometer embodiment  10 . 2  with a coupling  15  connecting two parts of the driving shaft  14 A,  14 B. 
           [0015]      FIG. 3  shows another viscometer with upper and lower half housing configurations as described for  FIG. 2  above but uses the on-axis Hall Effect transducer as in  FIG. 1 . 
           [0016]      FIG. 4  shows a viscometer  10 . 4  similar to  FIG. 3  with a modified sensing shaft assembly  28 A, spindle  26 A, a sensing shaft bearing  30 B′ and single spiral torque spring  32 . 
           [0017]      FIG. 5  shows a viscometer  10 . 5  similar to the viscometer of  FIG. 4  but with dual spiral torque springs as in  FIG. 1 . 
           [0018]      FIGS. 6-13  show test data obtained in implementation of the present invention including performance comparisons with vis-à-vis prior art items; specifically temperature range is shown in  FIG. 6  for the viscometer with Hall Effect transducer; 
           [0019]      FIG. 7  shows linearity within + or −0.1% of full scale range at various temperatures vs. + or −0.25% full scale linearity for the viscometer with MSI transducer; 
           [0020]      FIG. 8  shows error vs. x axis displacement (in range of −0.02 to +0.02 in per inch for the viscometer with Hall Effect transducer vs. for the viscometer with MSI transducer); 
           [0021]      FIG. 9  shows error vs. x axis displacement (in range of −0.02 to +0.02 in per inch for the viscometer with Hall Effect transducer vs. for the viscometer with MSI transducer); 
           [0022]      FIG. 10  shows improvement comparisons for limits on error due to y, z axis deviations; 
           [0023]      FIG. 11  shows improvement comparisons for limits on error due to y, z axis deviations; 
           [0024]      FIG. 12  shows improvement comparisons for limits on error due to y, z axis deviations 
           [0025]      FIG. 13  shows test data obtained in implementation of the present invention including performance comparisons with vis-à-vis prior art items 
           [0026]      FIG. 14  (prior art) shows prior art system error vs. deflection angle performance at various temperatures that may be compared to the performance improvement illustrated in  FIG. 6  for an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]      FIG. 1  shows a viscometer  10 . 1  comprising a motor  12  (preferably a stepper motor with a flywheel mounted on it) coupled to a driving shaft  14 , the drive shaft being mounted from a static frame assembly  16  via a drive housing  18  and drive and sensing shaft bearings,  18 B,  18 C. A frame extension  20  of the driving shaft mounts one component  22 - 1  of a Hall Effect transducer  22  which confronts the other component  22 - 2 . One of them ( 22 - 2 ) can be a dramatically magnetized magnet component and the other ( 22 - 1 ) a magnetic sensor with Hall Effect operation. A sensing shaft  24  suspends a spindle  26  via connector coupling  28  and is held from the frame assembly, via bearings  18 B and  18 C. Two spiral torque springs  32 A and  32 B couple the sensing shaft to the driving shaft for commonly driven rotation but allowing for angular displacement. They are preferably coiled in opposite directions. Various forms of fluid measuring contact means indicated at  34  can be mounted at the spindle lower end. 
         [0028]    Change in viscosity of a measured fluid causes selective angular displacement of the  22 - 1  and  22 - 2  components to produce a signal taken out, via brush and slip ring assembly  36 . A Hall Effect transducer has a voltage output from a magnetic field pickup (typically a semiconductor crystal) that varies with angular displacement in proportion to the strength of the magnetic field. It can be operated in analog or digital modes, the latter being preferred for modern viscometer usage. 
         [0029]      FIGS. 1A and 1B  (Prior Art) compare the general control signal readout showing a general similarity of read-out with low pass filter, analog-digital-converter (ADC) microprocessor, display and computer or both in the present invention, e.g. as in the embodiment of  FIG. 1  with a magnetic sensor or a prior art variable inductance transducer (e.g. MSI) in both instances with brushes and slip rings for signal extraction. Thus it is seen as a significant advantage of the Hall Effect transducer on other like magnetic transducer is that the digital signal can be converted to analog and replace the MSI transducer without any material changes on the electronics design. The same power supply and signal extraction method using brushes and slip rings can be used. The analog signal output range also is compatible with the MSI transducer. 
         [0030]      FIG. 1B  is a more particular block diagram of the Hall Effect transducer&#39;s sensor and with output amplified for sine (sin) and cosine (cos) readings applied to an analog-to-digital converter and through it to a digital signal processor which provides a pulse width modulated (PWM) signal via a PWM driver and a serial digital output via a serial output interlace. A single Hall Effect sensor construction would have large temperature drift and less tolerance to axial/radial misalignment. The monolithic magnetic transducer has multiple Hall Effect sensors around the magnetic sensing center (e.g. eight) to give differential sine and cosine output to give lower temperature drift and higher sensitivity over the whole revolution with higher axial/radial misalignment tolerance. The sensors outputs are digitized by the analog to digital converter on the same die and a Digital Signal Processor (DSP) calculate the angular displacement. The digital result is available in two digital forms, PWM and serial digital output. 
         [0031]      FIG. 1C  shows a block diagram means for converting the transducer pulse width module to an analog output, including low pass filters comprising an R-C circuit, of R 1 , C 1 , R 2 , C 2  constructed to produce a high enough time constant to reduce output ripple but without being sensitive to viscometer electronic circuit impedances thus reducing temperature sensitive drift from leakage currents where the values are typically 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 R1 
                 10,000 
                 ohms 
               
               
                   
                 R2 
                 10,000 
                 ohms 
               
               
                   
                 C1 
                 1  
                 microFarad 
               
               
                   
                 C2 
                 1 
                 microFarad 
               
               
                   
                   
               
             
          
         
       
     
         [0032]      FIG. 1D  shows an optical alternative to brush and slip ring signal extraction with a power supply and DC to AC converter in the stationary section of the Hall Effect transducer and a primary transducer cone coupled via its magnetic field to the moving magnet which has the corresponding secondary coil. This non-contact wireless solution can increase reliability and the life of the viscometer. The DC power is converted to AC to drive the rotary transformer and the AC frequency is selected to maximize efficiency for a given transformer and load impedance. The inducted power on the rotation section is rectified and regulated to drive the magnetic transducer. The digital output from the transducer can be used to drive an optical emitting device and a receiver, on the stationary section, to pick-up the optical signal and feed it to the viscometer electronics. Multiple emitters and/or receivers could be used to eliminate line-of-sight issues. 
         [0033]      FIG. 2  shows another viscometer embodiment  10 . 2  with a coupling  15  connecting two parts of the driving shaft  14 A,  14 B. The drive housing suspended from that shaft has an upper half  20 A and lower half  20 B, divided by an inwardly extending rib support  20 C. The Hall Effect transducer component  22  has a sensor  22 - 1  that is radially displaced from the instrument axis and its cooperating magnet ring  22 - 2 A is on-axis. The sensing shaft  24  is centered by axially spaced bearings  30 A,  30 B acting cooperatively with the frame lower half that has a descending cylindrical section with drive bearings  18 B and holds sensing shaft bearing  30 B. Dual opposite, coiled spiral torque springs  32 A and  32 B are provided. 
         [0034]      FIG. 3  shows another viscometer with upper and lower half housing configurations as described for  FIG. 2  above but uses the on-axis Hall Effect transducer as in  FIG. 1 . 
         [0035]      FIG. 4  shows a viscometer  10 . 4  similar to  FIG. 3  with a modified sensing shaft assembly  28 A, spindle  26 A, a sensing shaft bearing  30 B′ and single spiral torque spring  32 . 
         [0036]      FIG. 5  shows a viscometer  10 . 5  similar to the viscometer of  FIG. 4  but with dual spiral torque springs as in  FIG. 1 . 
         [0037]    The Hall Effect transducer can be, for example, a model AS5045 from Austria MicroSystems (Unterpremestaetten Austria) or a model MLS 90316 from Melexis Technologies SA (Bevaix, Switzerland). Data sheets for these products can be found at the respective websites http://www.ams.com and http://www.melexis.com. See also, published patent application of M. Schrems et al. (assigned to Austriamicrosystem) no. 20110050210 published Mar. 3, 2011 entitled: “Vertical Hall Sensor and Method for Manufacturing a Vertical Hall Sensor”; U.S. Pat. No. 7,259,566 B2 to R. Popovic et al. (assigned to Melexis) for “Magnetic Field Sensor and Method for Operating the Magnetic Field Sensor”, and the published U.S. patent application of C. Schott (Melexis) published Apr. 24, 2012 for “Vertical Hall Sensor.” The disclosures of the above cited items are incorporated in this application by reference as though set out at length herein. One of the Hall Effect sensors described therein (AS5045) was incorporated into conventional Brookfield cone-and-plate and cylinder viscometers, replacing the usual rotary variable inductance differential transformer (MSI model RVIT-Z) of that instrument and in comparative performance tests showed these results:
       (a) an error vs. deflection over a 360° range for the viscometer with Hall Effect transducer vs. 75° full scale range for the same viscometer with MSI transducer, indicating under +0.1% -0.2% of full scale error over a 0° C. to 50° C. temperature range as shown in  FIG. 6  for the viscometer with Hall Effect transducer:   (b) linearity within + or −0.1% of full scale range at various temperatures vs. + or −0.25% lull scale linearity for the viscometer with MSI transducer; ( FIG. 7 )   (c) error vs. x axis displacement (in range of −0.02 to +0.02 in per inch for the viscometer with Hall Effect transducer vs. for the viscometer with MSI transducer) ( FIGS. 8 and 9 ); and   (d) similar improvement comparisons for limits on error due to y, z axis deviations ( FIGS. 10-13 ). The AS5045 sensor pulse width modulation output was used effectively to gain a substantial improvement.       
 
         [0042]    The Hall Effect sensor and a conforming viscometer can operate with the same supply voltage level as existing instruments. The viscometer with the Hall Effect transducer is not sensitive to axial movement between the sensor and magnet over a significant amount of displacement, which is an advantage over other transducer types currently being used in this application. Since these transducers can be designed and internally compensated for temperature variations they are less affected by temperature than many conventional transducers. Also, low rotation speed not available for the viscometer below 5 rpm with the optical time base sensing mechanism is enabled by usage of the Hall Effect transducer down to about 0.01 rpm, with frequent (essentially continuous) readings of angular displacement not dependent on rotation speed. 
         [0043]    The present invention includes use of other forms of large deflection angle accommodation magnetic transducers, in addition to Hall Effect transducers, e.g. rotary variable differential transformer (RVDT), such as the Pickering transducers found in early models of the BEL DV-1 and DV-2 digital viscometers. Also, details of the viscometer could be varied consistent with the present invention known per se, e.g. optical read-out for signal extraction, instead of the brush and slip ring option cited above. 
         [0044]    It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent, with the letter and spirit of the foregoing disclosure and within the scope of this patent.