Pressure sensing device for rheometers

Abstract

A rheometer for measuring flow properties of a flowable material includes a substantially smooth measuring surface having a plurality of pressure sensors at spaced locations therein to measure pressure exerted against the measuring surface at the locations of the pressure sensors, and a rotatable surface spaced a distance from the substantially smooth measuring surface to form a sample receiving space therebetween for receiving a sample of material for which flow properties are to be measured. The substantially smooth surface may include monolithically integrated miniature pressure sensors which do not interfere with the substantially smooth surface. Pressure sensing diaphragms formed by the smooth surface deflect in response to local pressures against the surface to enable the measurement of unperturbed local pressures of materials sheared between the surfaces. The pressure sensors are sufficiently small that measured pressures are considered to be significantly local properties compared to the size of the measuring surface.

1 . A rheometer for measuring flow properties of a flowable material, comprising: 
 a stationary, substantially smooth measuring surface having a plurality of pressure sensors at spaced locations therein to measure pressure exerted against the stationary, substantially smooth measuring surface at the locations of the pressure sensors; and    a rotatable surface spaced a distance from the stationary, substantially smooth measuring surface and the locations of the pressure sensors therein to form a sample receiving space therebetween for receiving a sample of material for which flow properties are to be measured.    
   
   
       2 . A rheometer for measuring flow properties of a flowable material according to  claim 1 , wherein the distance between the stationary, substantially smooth measuring surface and the rotatable surface is adjustable.  
   
   
       3 . A rheometer for measuring flow properties of a flowable material according to  claim 2 , additionally including a proximity sensor in the stationary, substantially smooth measuring surface to measure the distance between the stationary, substantially smooth measuring surface and the rotatable surface.  
   
   
       4 . A rheometer for measuring flow properties of a flowable material according to  claim 3 , wherein the rotating surface is cone shape and is arranged with the point of the cone directed toward the stationary, substantially smooth measuring surface.  
   
   
       5 . A rheometer for measuring flow properties of a flowable material according to  claim 4 , wherein the proximity sensor is aligned with the point of the cone.  
   
   
       6 . A rheometer for measuring flow properties of a flowable material according to  claim 5 , wherein the stationary, substantially smooth measuring surface is circular.  
   
   
       7 . A rheometer for measuring flow properties of a flowable material according to  claim 6 , wherein the proximity sensor is in the center of the circular stationary, substantially smooth measuring surface.  
   
   
       8 . A rheometer for measuring flow properties of a flowable material according to  claim 7 , wherein the proximity sensor is a capacitive type sensor.  
   
   
       9 . A rheometer for measuring flow properties of a flowable material according to  claim 1 , additionally including a proximity sensor in the stationary, substantially smooth measuring surface to measure the distance between the stationary, substantially smooth measuring surface and the rotatable surface.  
   
   
       10 . A rheometer for measuring flow properties of a flowable material according to  claim 1 , wherein the rotating surface is cone shape and is arranged with the point of the cone directed toward the stationary, substantially smooth measuring surface.  
   
   
       11 . A rheometer for measuring flow properties of a flowable material according to  claim 1 , wherein the stationary, substantially smooth measuring surface is circular.  
   
   
       12 . A rheometer for measuring flow properties of a flowable material according to  claim 1 , additionally including a temperature sensor in the stationary, substantially smooth measuring surface to measure the temperature of the sample material.  
   
   
       13 . A rheometer for measuring flow properties of a flowable material, comprising: 
 a plate having a substantially smooth measuring surface against which a flowable material can act;    a plurality of cavities in the plate under the measuring surface;    deformable portions of the measuring surface of the plate extending over each of the plurality of cavities and resiliently deformable into the cavities in response to pressure applied to the deformable portions of the measuring surface;    a single sensor in each of the plurality of cavities, each sensor cooperable with the deformable portion of the measuring surface extending over that cavity to sense the deformation of such deformable portion and provide a signal indicative of a single deformation sensed, the deformation of the deformable portions being indicative of the pressure applied to such deformable portions and of the flow properties of the flowable material; and    a rotatable surface spaced a distance from the substantially smooth measuring surface and the locations of the pressure sensors therein to form a sample receiving space therebetween for receiving a sample of material for which flow properties are to be measured.    
   
   
       14 . A plate having a plurality of pressure sensors according to  claim 13 , wherein the substantially smooth measuring surface is formed by a wafer secured to a substrate.  
   
   
       15 . A plate having a plurality of pressure sensors according to  claim 14 , wherein the cavities are created by wells formed in the wafer, the wells resulting in thin portions of the wafer that extend over the wells and form the deformable portions of the measuring surface.  
   
   
       15 . A plate having a plurality of pressure sensors according to  claim 14 , wherein the cavities are created by wells formed in the substrate, wherein portions of the wafer extend over the wells in the substrate, the portions of the wafer which extend over the wells forming the deformable portions of the measuring surface.  
   
   
       17 . A plate having a plurality of pressure sensors according to  claim 14 , additionally including a spacer positioned between the wafer and the substrate, wherein the cavities are created by openings extending through the spacer, wherein portions of the wafer extend over the openings in the spacer, the portions of the wafer which extend over the openings in the spacer forming the deformable portions of the measuring surface.  
   
   
       18 . A rheometer for measuring flow properties of a flowable material according to  claim 13 , wherein the distance between the substantially smooth measuring surface and the rotatable surface is adjustable.  
   
   
       19 . A rheometer for measuring flow properties of a flowable material according to  claim 13 , additionally including a proximity sensor in the plate to measure the distance between the substantially smooth measuring surface and the rotatable surface.  
   
   
       20 . A rheometer for measuring flow properties of a flowable material according to  claim 19 , wherein the proximity sensor includes two capacitive plates arranged perpendicularly to the substantially smooth surface to form a capacitive proximity sensor.