Abstract:
The present invention relates to a new piezoelectric quartz level sensor mainly applied in the attitude stabilized and control system of the aircraft, robot, vehicle, ship, oil drilling platform, construction, industrial automation equipment, radar, and satellite, comprising a sensitive element, signal processing circuit, base, outer case and socket. The piezoelectric quartz level sensor transfers the deflection angle of the object to the force exerted on two symmetrical mounted round piezoelectric quartz wafers, and then utilizing the prominent force sensitivity of the piezoelectric quartz, the level attitude parameter of an objected can be detected through the frequency variation due to the force exerted on the two piezoelectric quartz wafers. Therefore, the present invention can satisfy the demand of high stability and resolution, low non-linear degree, quick start time, wide measuring range and operating temperature, good ability to resist shock, and digital output.

Description:
BACKGROUND OF THE PRESENT INVENTION 
   1. Field of Invention 
   The present invention relates to a new piezoelectric quartz level sensor mainly applied in the attitude stabilized and control system of the aircraft, robot, vehicle, ship, oil drilling platform, construction, industrial automation equipment, radar, and satellite, comprising a sensitive element, signal processing circuit, base, outer case and socket. 
   2. Description of Related Arts 
   The level sensor utilizing the prominent strength sensitivity property of the piezoelectric quartz exists. The measurement range of the piezoelectric quartz tilt measuring device from Japanese Tokyo Denpa C., LTD is 5.7°, the accuracy is 0.12°, it can us used for 3000 times, and the operating temperature is from −10° C. to 50° C., mainly used for measuring the tilt angle of the construction and bridge. Sundstrand Data Control Company from USA designs a two-axis and three-axis tilt measurement device composed of QA-1300 quartz flexible accelerometer has a accuracy of 0.23°, mainly used for oil distilling. However, these piezoelectric quartz level sensors have drawbacks of low stability and resolution, long time start time, lower ability to resist shock, therefore, they can not satisfy the demand of high stability and resolution, good ability to resist shock, and quick start time. 
   SUMMARY OF THE PRESENT INVENTION 
   A main object of the present invention is to provide a piezoelectric quartz level sensor of high stability and resolution, good ability to resist shock, and quick start time. 
   Accordingly, in order to accomplish the above object, the present invention adopts two symmetrical mounted round piezoelectric quartz wafers, transfer the deflection angle φ of the object to be measured to the force F exerted on two symmetrical mounted round piezoelectric quartz wafers. Utilizing the prominent force sensitivity of the piezoelectric quartz, the level attitude parameter of an objected can be detected through the frequency variation due to the force exerted on the two piezoelectric quartz wafers. As shown in  FIG. 1 , when the piezoelectric quartz wafer is stressed in the radial direction, such as ΔF 1 , the resonant frequency f changes to f+Δf 1 ; when the piezoelectric quartz wafer is pulled in the radial direction, such as ΔF 2 , the resonant frequency f changes to f−Δf 2 , so the corresponding force variation ΔF 1  and ΔF 2  can be determined through detecting the frequency variation of the resonator. Therefore, when a tilt angle is inputted to the piezoelectric quartz level sensor, transfer the attitude corresponding to the tilt angle to a radial force exerting on the two symmetrical mounted round piezoelectric quartz wafers, and then the resonant frequency of one of the two symmetrical mounted round piezoelectric quartz wafers exerted a radial force increases to f+Δf 1 , while the other decreases to f−Δf 2 , so that the input tilt angle can be determined by detecting the frequency differential Δf=(f+Δf 1 )−(f−Δf 2 )=Δf 1 +Δf 2  of the two symmetrical mounted round piezoelectric quartz wafers. 
   The  FIG. 2  illustrates the schematic view of the new piezoelectric quartz level sensor. When the level sensor deflects an angle φ, the relationship between the frequency differential Δf and φ can be determined through the pressure force variation of the two piezoelectric quartz resonator: 
   
     
       
         
           
             
               
                 
                   
                     
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         f 
                       
                       = 
                       
                         2 
                         ⁢ 
                         
                           
                             K 
                             f 
                           
                           · 
                           
                             
                               f 
                               2 
                             
                             
                               D 
                               · 
                               n 
                             
                           
                           · 
                           
                             b 
                             c 
                           
                           · 
                           m 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           g 
                           ⁡ 
                           
                             ( 
                             
                               
                                 sin 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 ϕ 
                               
                               - 
                               
                                 sin 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   ϕ 
                                   0 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       = 
                       
                         
                           K 
                           ϕ 
                         
                         · 
                         
                           ( 
                           
                             
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               ϕ 
                             
                             - 
                             
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 ϕ 
                                 0 
                               
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
             
             
               
                 ( 
                 1 
                 ) 
               
             
           
         
       
     
   
   In this formula, 
             K   ϕ     =     2   ⁢       K   f     ·       f   2       D   ·   n       ·       b   c     .               
mg is a proportional coefficient related to the sensitive element of the level sensor, K f  is the Ratajski coefficient of the quartz resonator, D is the cross section width for passing Δf, and n is the resonant coefficient. From the formula (1) the tilt angle can be determined by detecting the frequency variation Δf of the quartz resonator.
 
   The measurement range and resolution are two basic technical parameters of the sensor. It seems that the measurement range and resolution have no relationship, but actually relate to each other. On a given condition, one improves on the cost of the other. Therefore, the ratio of the measurement range and resolution K, as an index, can reflect the performance of the sensor. The inventor finds the relationship between the index K and the sensor: 
   
     
       
         
           
             
               
                 K 
                 = 
                 
                   
                     
                       
                         
                           
                             2 
                           
                           ⁢ 
                           β 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             T 
                             m 
                           
                           ⁢ 
                           
                             DN 
                             0 
                           
                         
                         
                           η 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             nf 
                             0 
                             2 
                           
                         
                       
                       · 
                       
                         K 
                         f 
                       
                     
                     ⁢ 
                     
                       
                         nf 
                         0 
                         2 
                       
                       D 
                     
                   
                   = 
                   
                     
                       
                         2 
                       
                       ⁢ 
                       β 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         K 
                         f 
                       
                       ⁢ 
                       
                         N 
                         0 
                       
                       ⁢ 
                       
                         T 
                         m 
                       
                     
                     η 
                   
                 
               
             
             
               
                 ( 
                 2 
                 ) 
               
             
           
         
       
     
   
   In this formula, F 0  is the base frequency of the quartz resonator, n is harmonic time, K f  is the Ratajski coefficient of the quartz resonator, T m  is the breaking limit force of the quartz resonator, β is the safety factor that is smaller than 1, N 0  is the frequency constant of the quartz resonator, η is the frequency stability of the quartz resonator, and D is the stress surface width of the quartz resonator. 
   The formula (2) reflects the relationship between the sensor performance index K and the quartz resonator structure parameter. Given the quartz resonator structure parameter, the K that the sensor can achieve can be calculated; or calculate the quartz resonator structure parameter according to the sensor performance index, so as to design a quartz resonator that can satisfy the demand. 
   The piezoelectric quartz level sensor of the present invention comprises a sensitive element, a first signal processing circuit, a second signal processing circuit, a base, an outer case and a socket. The base and the outer case are attached closely to form a cavity. The sensitive element and signal processing circuit are mounted on the base. The power and signal processed come in and out by a lead-in wire through the socket. 
   The sensitive element is composed of two round piezoelectric quartz wafers mounted on both sides of a center axial line of a column between the top plate and the bottom plate, and the two round piezoelectric quartz wafers are positioned between the top plate and the bottom plate, and fastened on the base by a pallet. A sensitive block presses on the top plate. A sealed cavity cover covers on the base through a sealed gasket, and is connected to the base by bolt to form a sealed cavity. Two round piezoelectric quartz wafers have three preferred embodiments, vertical parallel structure, level parallel structure, or inclined structure. A piezoelectric quartz wafers signal output connector and a vacuum pump are weld on the base. 
   The piezoelectric quartz level sensor further comprises an overload protective unit in the sensitive unit. The overload protective unit for the axial direction comprises an elastic element of the sensitive block, a shock absorber between the bottom plate and the pallet, and an adjustable axial retaining bolt on the column upside of the sensitive block. The overload protective unit for the transverse and longitudinal direction comprises an overload protective retaining frame and four adjustable axial retaining bolts around the column of the sensitive block. In the present invention, the sensitive block can be preferably embodied as four structures, as shown in  FIG. 8 , the sensitive block can be single-screw structure, double-screw structure, a structure with two side holes, or a structure with three holes. 
   The two-dimensional piezoelectric quartz level sensor of the present invention further provides a double layer shock absorber on the upside and downside of the sensitive element. The first layer shock absorber comprises a lower locating shock absorber added on the downside of the sensitive element, and an upper locating shock absorber added on the upside of the sensitive element, wherein the lower locating shock absorber is mounted on the frame base, and the upper locating shock absorber is mounted beneath the frame cover. The mounting frame comprise a frame base, a frame cover  41  and four frame columns, which are resembled by a bolt. The sensitive element  3 , signal processing circuit and, and fixing board is suspended in the mounting frame through the lower locating shock absorber and the upper locating shock absorber to form a first shock absorber protective structure. The second layer shock absorber comprises a lower shock absorber provided between the inner side of the base and the frame base, and an upper shock absorber provide between the inner side of the top plate of the outer case and the frame cover, wherein the lower shock absorber and the upper shock absorber are fixedly suspended in the sealed cavity composed of base and the outer case, so that the whole mounting frame forms the second layer shock absorber protective structure. 
   The sealed cavity of the sensitive element of the one-dimensional piezoelectric quartz level sensor comprises a base, a sealed cavity cover and a sealed gasket. The sealed cavity is sealed by a zigzag structure or a wedge structure. 
   The piezoelectric quartz level sensor transfers the deflection angle of the object to the force exerted on two symmetrical mounted round piezoelectric quartz wafers, and then utilizing the prominent force sensitivity of the piezoelectric quartz, the level attitude parameter of an objected can be detected through the frequency variation due to the force exerted on the two piezoelectric quartz wafers. Therefore, the present invention can satisfy the demand of high stability and resolution, low non-linear degree, quick start time, wide measuring range and operating temperature, good ability to resist shock, and digital output. 
   These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of frequency variation when stressed in the radial direction according to a preferred embodiment of the present invention, wherein (a) is the schematic diagram of frequency variation when pressed, and (b) is the schematic diagram of frequency variation when pulled. 
       FIG. 2  is a schematic diagram of the new piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 3  is a schematic diagram of the one-dimensional piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 4  is a sectional view of the one-dimensional piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 5  is a perspective view of three mounting structures of the two piezoelectric quartz wafers of the sensitive elements according to the above preferred embodiment of the present invention, wherein (a) illustrates the vertical parallel structure, (b) illustrates the level parallel structure, and (c) illustrates the inclined structure. 
       FIG. 6  is a perspective view of a sensitive block of the piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 7  is a perspective view of an overload protective retaining frame of the piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 8  is a perspective view of four structures of the sensitive block of the piezoelectric quartz level sensor according to the above preferred embodiment of the present invention, wherein (a) is a single-spiral structure, (b) is a double-spiral structure, and (c) is a structure with two side holes, and (d) is a structure with three holes. 
       FIG. 9  is a sectional view of a vacuum sealed cavity of the sensitive element of the piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 10  is a sectional view of a sealed cavity of the sensitive element of the piezoelectric quartz level sensor according to the above preferred embodiment of the present invention, wherein (a) is a zigzag structure, and (b) is a wedge structure. 
       FIG. 11  is a sectional view of a two-dimensional piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 12  is a perspective view of a double shock absorber of the two-dimensional piezoelectric quartz level sensor according to the above preferred embodiment of the present invention. 
       FIG. 13  is a perspective view of an upper locating shock absorber and lower locating shock absorber of the two-dimensional piezoelectric quartz level sensor according to the above preferred embodiment of the present invention, wherein (a) is the upper locating shock absorber, and (b) is the lower locating shock absorber. 
       FIG. 14  is a perspective view of an upper shock absorber and lower shock absorber of the two-dimensional piezoelectric quartz level sensor according to the above preferred embodiment of the present invention, wherein (a) is the upper shock absorber, and (b) is the lower shock absorber. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention, a new piezoelectric quartz level sensor, has two embodiments of one-dimensional and two-dimensional structures. As shown in  FIG. 3 , the one-dimensional piezoelectric quartz level sensor comprises a sensitive element  3 , a first signal processing circuit  4 , a second signal processing circuit  5 , a bottom base frame  1 , an outer case  2  and a socket  10 .  FIG. 4  is a sectional view of a one-dimensional piezoelectric quartz level sensor. The base  1  and the outer case  2  are attached closely to form a cavity. The one-dimensional piezoelectric quartz level sensor further comprises a shock pad  11  provided between the sensitive element  3  and the bottom base frame  1 . The power and signal come in and out by a lead-in wire  9  through the socket  10 . The sensitive element  3  is composed of two round piezoelectric quartz wafers  23  mounted on both sides of a center axial line of a column between the top plate  22  and the bottom plate  24 , and the two round piezoelectric quartz wafers  23  are positioned between the top plate  22  and the bottom plate  24 , and fastened on the base  13  by a pallet  16 . A sensitive block  21  presses on the top plate  22 . A sealed cavity cover  15  covers on the base  13  through a sealed gasket  14 , and is connected to the base by bolt  25  to form a sealed cavity. The base  13  comprises a first vacuum connector  29   a , a second vacuum connector  29   b , and a vacuum pump  31 . Two round piezoelectric quartz wafers have three preferred embodiments, as shown in  FIG. 5 , vertical parallel structure, level parallel structure, or inclined structure. In the vertical parallel structure, two round piezoelectric quartz wafers  23   b   1  and  23   b   2  mounted between the top plate  22   b  and bottom plate  24   b  in a level parallel manner. In the level parallel structure, two round piezoelectric quartz wafers  23   c   1  and  23   c   2  mounted between the top plate  22   c  and bottom plate  24   c  in a symmetrical inclined manner. 
   In the three above preferred mounting structures, the lead-in wire  28   a  and  28   b  of two piezoelectric quartz wafers are connected with the excitation circuits through vacuum connector  29   a  and  29   b  respectively forming an oscillating circuit. When the objected to be tested changes its attitude, the two round piezoelectric quartz wafers outputs in a differential frequency manner, so as to detect the inclined angle of an object. 
   As shown in  FIG. 4 , the one-dimensional piezoelectric quartz level sensor further comprises an overload protective unit for the axial, transverse, longitudinal direction of the piezoelectric quartz wafer  23  provided in the sensitive unit  3 . The overload protective unit for the axial direction comprises an elastic element of the sensitive block  21 , a shock absorber  32  between the bottom plate  24  and the pallet  16 , and an adjustable axial retaining bolt  19  on the column upside of the sensitive block  21 . The overload protective unit for the transverse and longitudinal direction comprises an overload protective retaining frame  17  and four adjustable axial retaining bolts  18   a ,  18   b ,  18   c , and  18   d  around the column of the sensitive block  21 . 
   In the sensitive block structure, as shown in  FIG. 6 , the column is a main body of the sensitive block, and the elastic element is a part of the shock absorbing system, which makes the sensor have a self-correction feature. As shown in  FIG. 6 , d and D is the inner and outer diameter of the elastic element respectively, h 2 −h 1  is the height of the elastic element, and point C is the mass center of the sensitive block. In the present invention, the sensitive block can be preferably embodied as four structures, as shown in  FIG. 8 , the sensitive block  21  can be single-screw structure comprising three column segments with different diameter, comprising a mass body  21   a  as a main body of the sensitive block  21 , an elastic body  21   b  for buffering, and a bolt segment  21   c  for mounting on the top plate wherein the mass body  21   a  is on the upside segment of the sensitive block  21  with larger diameter, the elastic body  21   b  is on the center segment of the sensitive block  21 , and the bolt segment  21   c  is on the downside segment of the sensitive block  21 . The elastic body  21   b  is single-screw spring structure. The sensitive block  21  can be double-screw structure comprising three column segments with different diameter, comprising a mass body  21   d  as a main body of the sensitive block  21 , an elastic body  21   e  for buffering, and a bolt segment  21   f  for mounting on the top plate wherein the mass body  21   d  is on the upside segment of the sensitive block  21  with larger diameter, the elastic body  21   e  is on the center segment of the sensitive block  21 , and the bolt segment  21   f  is on the downside segment of the sensitive block  21 . The elastic body  21   e  is double-screw spring structure. The sensitive block  21  can be a structure with two side holes, comprising three column segments with different diameter, comprising a mass body  21   m  as a main body of the sensitive block  21 , an elastic body  21   n  for buffering, and a bolt segment  21   s  for mounting on the top plate wherein the mass body  21   m  is on the upside segment of the sensitive block  21  with larger diameter, the elastic body  21   n  is on the center segment of the sensitive block  21 , and the bolt segment  21   s  is on the downside segment of the sensitive block  21 . The elastic body  21   n  is a structure with two side holes. 
   The sensitive block  21  can be a structure with three holes, comprising three column segments with different diameter, comprising a mass body  21   x  as a main body of the sensitive block  21 , an elastic body  21   y  for buffering, and a bolt segment  21   z  for mounting on the top plate wherein the mass body  21   x  is on the upside segment of the sensitive block  21  with larger diameter, the elastic body  21   y  is on the center segment of the sensitive block  21 , and the bolt segment  21   z  is on the downside segment of the sensitive block  21 . The elastic body  21   x  is a structure with three holes. 
   As shown in  FIG. 7 , the overload protective retaining frame  17  is round barrel shape with through-caved work. The inner and outer diameter of the barrel shape frame is d′ and D′ respectively. Four transverse retaining bolt holes corresponding to the adjustable retaining bolts  18   a ,  18   b ,  18   c ,  18   d  and an axial retaining bolt  19  are on the upper end and top of the barrel shape frame. The retaining frame has fastening bolt  26   a  and  26   b  on the bottom. Four transverse retaining bolt holes have a distance L 2  from the bottom of the frame. The length of d, D, h 1 , h 2  of the sensitive block and the position of C, and the matched retaining frame d′, D′ and L 2  value determine the measuring scale, the capability of resisting vibration and shock, and the capability of resisting overload. 
   When a strong shock and a high overload are exerted to the piezoelectric quartz level sensor, the shock pad of the sensitive element  11  shown in  FIG. 3  and the shock absorber  32  of the pallet, the elastic column of the sensitive block  21 , the overload protective frame  17  and the adjustable retaining bolts  18   a ,  18   b ,  18   c ,  18   d  around it, the retaining protective structure composed of axial retaining bolt  19  for absorbing shock and protecting overload can improve the environmental adaptive capacity of the sensor. 
   As shown in  FIG. 9  the sealed cavity of the sensitive element of the one-dimensional piezoelectric quartz level sensor comprises a base, a sealed cavity cover and a sealed gasket. The sealed cavity is sealed by a zigzag structure or a wedge structure as shown in  FIG. 10 . The base  13  and the sealed cavity cover  15  have a sealed locating ring  42   a  and  42   b  respectively for locating the sealed gasket. Press the annular zigzag edge  43   a  or wedge edge  44   a  of the base  13  into the sealed gasket  14  by a resembling clip to seal the cavity, and fasten it by a bolt  25 . The sealed cavity improves the working environment of the quartz wafer resonator, so as to improve the frequency stability of the quartz wafer resonator. The main performance index of the one-dimensional piezoelectric quartz level sensor of the present invention is shown in table 1. 
   
     
       
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               the main performance index of the different embodiments of the one-dimensional 
             
             
               piezoelectric quartz level sensor of the present invention 
             
           
        
         
             
                 
                 
                 
                 
               Nonlinear 
                 
                 
             
             
                 
               Measurement 
                 
               Responsive 
               degree 
               Stability 
             
             
               Embodiment 
               range 
               resolution 
               time(ms) 
               (% FS) 
               (1/min) 
               Output form 
             
             
                 
             
             
               Embodiment 1 
               0.0001°-50° 
               0.001° 
               &lt;50 
               &lt;0.1 
               1 × 10 −9   
               Digital output 
             
             
               Embodiment 2 
               0.0001°-50° 
               0.001° 
               &lt;50 
               &lt;0.1 
               1 × 10 −9   
               Digital output 
             
             
                 
             
           
        
       
     
   
   The two-dimensional piezoelectric quartz level sensor of the present invention comprises a sensitive element  3 , a first signal processing circuit  4 , a second signal processing circuit  5 , a bottom base frame  1 , an outer case  2  and a socket  10 . As shown in  FIG. 11 , the bottom base frame  1  and the outer case  2  are attached closely to form a cavity. The sensitive element  3  is fixed on the fixing board  34 . The signal processing circuit  4  and  5  is mounted on the bottom base frame  1 . The power and signal come in and out by a lead-in wire  9  through the port  36  of the SR232. 
   The two-dimensional piezoelectric quartz level sensor of the present invention further provides a double layer shock absorber on the upside and downside of the sensitive element  3 . As shown in  FIGS. 11 and 12 , the first layer shock absorber comprises a lower locating shock absorber  33  added on the downside of the sensitive element  3 , and an upper locating shock absorber  35  added on the upside of the sensitive element  3 , wherein the lower locating shock absorber  33  is mounted on the frame base  38 , and the upper locating shock absorber  35  is mounted beneath the frame cover  41 . The mounting frame comprise a frame base  38 , a frame cover  41  and four frame columns  39 , which are resembled by a bolt. The sensitive element  3 , signal processing circuit  4  and  5 , and fixing board  34  is suspended in the mounting frame through the lower locating shock absorber  33  and the upper locating shock absorber  35  to form a first shock absorber protective structure. The second layer shock absorber comprises a lower shock absorber  37  provided between the inner side of the bottom base frame  1  and the frame base  38 , and an upper shock absorber  40  provide between the inner side of the top plate of the outer case  2  and the frame cover  41 , wherein the lower shock absorber  37  and the upper shock absorber  40  are fixedly suspended in the sealed cavity composed of bottom base frame  1  and the outer case  2 , so that the whole mounting frame forms the second layer shock absorber protective structure. 
   The lower locating shock absorber  33 , the upper locating shock absorber  35 , the lower shock absorber  37  and the upper shock absorber  40  are made of silicon rubber, whose structures is shown in  FIG. 13  and  FIG. 14 . 
   When a strong shock and a high overload are exerted to the piezoelectric quartz level sensor, the shock absorber and overload protective retaining structure composed of shock absorber and overload protective retaining device of sensitive element  3 , the lower locating shock absorber  33 , the upper locating shock absorber  35 , the lower shock absorber  37  and the upper shock absorber  40  improves the capability of resisting shock of the sensor. 
   When a tilt angle is inputted, the two-dimensional piezoelectric quartz level sensor can sense the inputted tilt angle in both of the X-axial and Y-axial direction. The shock resisting capability of the two-dimensional piezoelectric quartz level sensor is up to 10000 g, the measurement scale is 0.0001°-50°. The main performance index of the two-dimensional piezoelectric quartz level sensor of different embodiments of the present invention is shown in table 2. 
   
     
       
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               the main performance index of the different embodiments of the two-dimensional 
             
             
               piezoelectric quartz level sensor of the present invention 
             
           
        
         
             
                 
                 
                 
                 
               Nonlinear 
                 
                 
             
             
                 
               Measurement 
                 
               Responsive 
               degree 
               Stability 
             
             
               Embodiment 
               range 
               resolution 
               time(ms) 
               (% FS) 
               (1/min) 
               Output form 
             
             
                 
             
           
        
         
             
               Embodiment 1 
               0.0001°-50° 
               0.001° 
               &lt;50 
               &lt;0.1 
               1 × 10 −9   
               Digital output 
             
             
               Embodiment 2 
               0.0001°-50° 
               0.001° 
               &lt;50 
               &lt;0.1 
               1 × 10 −9   
               D/A output 
             
             
               Embodiment 2 
               0.0001°-50° 
               0.001° 
               &lt;50 
               &lt;0.05 
               1 × 10 −9   
               D/A output 
             
             
                 
             
           
        
       
     
   
   One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting. 
   It will thus be seen that the objects of the present invention have been fully and effectively accomplished. It embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.