Abstract:
An apparatus and method for measuring the horizontal position uses a gas bubble in a bubble level. The gas bubble is in a cylindrical sealed housing that is partially filled with liquid. At least two light-emitting devices are used to illuminate the gas bubble and an inner bottom surface of the bubble level. A corresponding number of receiving devices are used to receive the light that is either reflected by the inner bottom surface or is reflected and refracted by the gas bubble. The amount of light received is translated into an electrical signal and is sent to a processing unit to calculate the position of the gas bubble. The light-emitting devices and the receiving devices are disposed in an alternating manner at the periphery of the cylindrical sealed housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is entitled to benefit of a right of priority under 35 USC §119 from Chinese Patent Application 201410389066.4, filed on 8 Aug. 2014, the content of which is incorporated by reference as if fully recited herein. 
       TECHNICAL FIELD 
       [0002]    The invention relates to an apparatus and method for measuring the position of a gas bubble in a bubble level, and an apparatus containing a bubble level, and more particularly, to an apparatus and method for measuring the position of a gas bubble in a bubble level in the field of weighing instrument. 
       BACKGROUND 
       [0003]    Many instruments and equipments can work properly only when they are put horizontally, such as electronic balances (i.e., weighing instruments) operating based on gravitation. There are errors when a balance is inclined. The more inclination the balance has, the larger the errors are. To maintain a certain level of precision, the balances must be kept within a certain horizontal range. Therefore, each of the balances is equipped with a bubble level and adjustable feet comprising height adjustment screws. Bubble levels comprise a sealed housing that is partially filled with liquid and contains a gas or air bubble. The upper part of the housing comprises a transparent window. The inside wall of the transparent window is a curved surface with a large radius. The gas bubble is located in the center of the bubble level when the device is aligned horizontally. The position of the gas bubble will move towards an upper direction when the device is inclined and not aligned horizontally. Users may observe the air bubble position, which indicated the inclined status of the electronic balance via the transparent window above the housing. Users may change the level status by adjusting the height of the adjustable feet by rotating the adjustment screw threads while observing the position of the gas bubble in the electronic balance until the gas bubble is located in the center of the bubble level. 
         [0004]    Usually there is a marking circle on the transparent window of the bubble level. The level status is out of an acceptance range when the edge of the gas bubble exceeds the marking circle, and the weighing error will be too large, and the result will be unreliable. As a result, users have to position the gas bubble back into the marking circle, and preferably back to the center, by adjusting the level status. 
         [0005]    It is well-known that three points can determine a plane. Therefore, a device that requires adjustment of the level status, such as an electronic balance, normally has three supporting points (i.e., three feet). One of the three feet is fixed, while the other two feet are adjustable. However, to those users who are less experienced, it is very difficult to adjust the level status by adjusting the height of those two feet based on the position of the gas bubble. Due to the triangle shape caused by the three feet, when the height of one foot is adjusted, the gas bubble moves in a diagonal direction. It is very inconvenient for the users. 
         [0006]    Thus, an apparatus for automatically adjusting the level by motor control is contemplated. Or it is contemplated to send out an alarm as the gas bubble exceeds the marking circle so that the users may be prompted to roll the two adjustable feet to adjust the level status according to the position of the gas bubble. It is also contemplated to correct the weighing results according to the relationship between the incline status and weighing errors, and make the weighing results more precise by correcting the weighing results. Due to these and other reasons, it is desired to obtain the electronic data (value) of the level status (inclining status). A motor control system can determine how to adjust the mechanism only if it received the electronic signal or data of the level status. Patent CN100362326C discloses how to use electronic tilt sensor for alarming, amending the following weight, starting automatic calibration, and start the leveling guide, etc. 
         [0007]    There are various methods and apparatuses for measuring the level status in the prior art. 
         [0008]    Patent CN202204509U discloses a gas bubble electric-potential-type level sensor. Each electrode receives a different electric potential when the gas bubble is in different positions. The position of the gas bubble can be deferred from different electric potentials of electrodes. However, the liquid filled in the sealed housing must be conductive, and the electrodes also have to be inserted into the bubble level. It makes the manufacturing process very complex and is costly. The electrodes obstruct the visibility of the air bubble and interfere with users&#39; observations. 
         [0009]    Patent CN1645070A, i.e., US7325321 B2, discloses a method and apparatus for aligning an electronic balance. An inclination sensor is a gas-bubble-type level. A light-emitter emits light downwards from the top of a bubble level. There are at least three receiving devices installed below the bubble level. However, the light-emitter installed on the top influence the users&#39; observations of the gas bubble to a certain extent. 
         [0010]    Patent DE3234372A1 discloses a balance with an electronic inclination sensor. This electronic inclination sensor is a gas-bubble-type level. A light emitter emits the light upwards from the bottom of a bubble level. Receiving device(s) is installed at the upper of the bubble level, and severely interferes with users&#39; observations of the gas bubble. 
         [0011]    Patent JP58033114 discloses an apparatus with a gas bubble level. It is equipped with a lighting cell on one side and a plurality of optical sensors on the other side. This apparatus has a transparent cube. The lighting cell is installed on one side of the cube, while the plurality of optical sensors are installed on the other side of the cube. Due to the cubic structure, this apparatus is not suitable for 2-D level status. 
       SUMMARY 
       [0012]    In order to address the above-identified drawback in the prior art, this invention provides an apparatus and method for measuring the position of a gas bubble in a bubble level and an apparatus containing a bubble level that ensures unobstructed visibility and allows users clear view to the gas bubble and its position while measuring the level status of the bubble level in an electronic or photo-electric manner. 
         [0013]    According to an aspect of the present invention, it provides an apparatus for measuring the position of a gas bubble in a bubble level. The bubble level comprises a cylindrical shaped sealed housing. The cylindrical shaped sealed housing is partially filled with liquid and contains said gas bubble. The apparatus comprises at least two light-emitting devices and at least two light receiving devices. The light emitted from each light-emitting device illuminates the gas bubble and an inner bottom surface of the bubble level. The inner bottom surface is part of the sealed housing. In operating position the bottom surface is mainly aligned horizontally. In an advantageous embodiment the bottom surface is mainly a flat plane. However other shapes of the bottom surface are possible, e.g. a cone shape surface. On the top surface of the cylindrical shaped sealed housing a window is located. The window comprises a transparent material which allows the user to observe the location of the gas bubble and visual checking of the correct alignment of the apparatus. In operating position the window is mainly aligned horizontally. A cylindrical shaped side wall of the cylindrical shaped sealed housing encircles the bottom surface and the window. The bubble and the liquid are located between the bottom surface and the window. In operating position the cylindrical shaped side wall is mainly aligned vertically. The cylindrical shaped side wall and the bottom surface are arranged orthogonally to each other. 
         [0014]    Each receiving device receives the light that is reflected by the inner bottom surface of the bubble level and reflected and refracted by the gas bubble and converts it into electrical signals. The electrical signals are processed for calculating the position of the gas bubble, wherein, each of the at least two light-emitting devices and each of the at least two receiving devices is alternately arranged at the periphery of the cylindrical shaped sealed housing. That is, the said light-emitting devices and the said receiving devices are arranged on a circle which is concentric with the cylindrical shaped sealed housing. Advantageously in operating position the circle is located in a mainly horizontally oriented plane. 
         [0015]    According to an aspect of the present invention, the apparatus further comprises a light distributor. The light distributor obstructs partial light emitted from the light-emitting devices so that it would not illuminate an adjacent receiving device, allows the light emitted from the light-emitting devices directly illuminate on and around said gas bubble as much as possible, and allows the receiving devices receive the light on the surface of or around the gas bubble as much as possible. 
         [0016]    According to an aspect of the present invention, the circular sidewall of the housing is transparent. 
         [0017]    According to an aspect of the present invention, the circular sidewall of the housing is opaque. Each of the at least two light-emitting devices and each of the at least two receiving devices is alternately arranged at the periphery above the cylindrical shaped sealed housing. Ideally all the light-emitting devices and all the receiving devices are located on a circle in one horizontally aligned plane. 
         [0018]    According to an aspect of the present invention, the apparatus comprises at least one of: two light-emitting devices and two receiving devices; three light-emitting devices and three receiving devices; four light-emitting devices and four receiving devices; five light-emitting devices and five receiving devices; or six light-emitting devices and six receiving devices. 
         [0019]    According to an aspect of the present invention, the light-emitting devices and the receiving devices both are approximately uniformly-spaced. 
         [0020]    According to an aspect of the present invention, the signal from each receiving device is recorded upon the illumination of each light-emitting device, M*N number of signals Uij are derived after each of the light-emitting devices having been illuminated once, where i=1 to M, j=1 to N, M is the number of light-emitting devices, N is the number of light receiving devices, the signals Uij are used to calculate the position of the gas bubble. Preferably the light-emitting devices emit light subsequently, which means one after the other light-emitting device is emitting light. That is the light-emitting devices do not emit light at the same time. The advantage of this approach is that the light emitted by a single light-emitting unit causes a signal at each light receiving device. Consequently each emitted light signal causes N light receiving signals and the signals can put into connection with each light emitting device. Hence, the calculation of the position of the bubble is based on more information, which leads to better results, or an accurate result can be achieved with less receiving devices. 
         [0021]    According to an aspect of the present invention, a reference position of the gas bubble is defined, the signal U 0 ij of each receiving device when the gas bubble locates at the reference position is recorded, the differences between signals Uij and U 0 ij are used to calculate the position of the gas bubble, where i=1 to M, j=1 to N. 
         [0022]    According to an aspect of the present invention, each light-emitting device is a light-emitting diode. Each light-emitting device emits light by lighting in successive pulses. 
         [0023]    According to an aspect of the present invention, the light is visible light or infrared light. 
         [0024]    According to an aspect of the present invention, each receiving device is a photodiode or a photo-triode or a called phototransistor. 
         [0025]    The present invention also provides an apparatus comprising the inventive bubble level. 
         [0026]    The present invention also provides a method for measuring the position of a gas bubble in a bubble level. The bubble level comprises a cylindrical shaped sealed housing. The sealed housing is partially filled with liquid and contains the gas bubble. The method comprises: alternately arranging at least two light-emitting devices and at least two receiving devices at the periphery of the cylindrical shaped sealed housing; recording the signal from each receiving device upon the illumination of each light-emitting device, and deriving M*N number of signals Uij after each of the light-emitting devices having been illuminated once, where i=1 to M, j=1 to N, M is the number of light-emitting devices, N is the number of receiving devices; and calculating the position of said gas bubble with the signals Uij. 
         [0027]    According to an aspect of the present invention, the method further comprises: defining a reference position of the gas bubble, and recording the signal U 0 ij of each receiving device when the gas bubble locates at the reference position; and calculating the position of said gas bubble with the differences between signals Uij and U 0 ij, where i=1 to M, j=1 to N. The electrical signals are processed for calculating the position of the gas bubble. 
         [0028]    The above general description and following detailed description of the present invention are exemplary and illustrative, and are intended to provide further explanations for the present invention as recited in the claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]    The accompanying drawings are included to provide a further understanding of the present invention, and are included and formed as a part of the present application. Embodiments of the present invention are illustrated in accompanied drawings and are used to explain the principles of the present invention together with this description. In the drawings: 
           [0030]      FIG. 1(   a ) shows a perspective view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a first embodiment of the present invention; 
           [0031]      FIG. 1(   b ) shows a side sectional view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a first embodiment of the present invention; 
           [0032]      FIG. 1(   c ) shows a perspective view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a second embodiment of the present invention; 
           [0033]      FIG. 2  shows a perspective view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a third embodiment of the present invention; 
           [0034]      FIG. 3  shows a perspective view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a fourth embodiment of the present invention; 
           [0035]      FIG. 4  shows a perspective view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a fifth embodiment of the present invention; 
           [0036]      FIG. 5(   a ) shows a side sectional view an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus that has a light distributor equipped according to embodiments of the present invention; 
           [0037]      FIG. 5(   b ) shows a lateral sectional view of the light shielding effects of the light distributor according to embodiments of the present invention; and 
           [0038]      FIG. 6  shows the connection diagram between the apparatus for measuring the position of a gas bubble in a bubble level and related circuits according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Embodiments of the present invention will now be described in detail in connection with the accompanied drawings. 
         [0040]    The present invention provides an apparatus for measuring the position of a gas bubble in a bubble level. The bubble level comprises a cylindrical shaped sealed housing. The sealed housing is partially filled with liquid and contains the gas bubble. The apparatus comprises: at least two light-emitting devices and at least two receiving devices. The light emitted from each light-emitting device illuminates the gas bubble and an inner bottom surface of the bubble level. Each receiving device receives the light that is reflected by the inner bottom surface of the bubble level and reflected and refracted by the gas bubble and converts it into electrical signals. The electrical signals are processed for calculating the position of the gas bubble. 
         [0041]    When the circumcircle of the housing is transparent, each of the at least two light-emitting devices and each of the at least two receiving devices is alternately located at the circumcircle of the cylindrical seal housing. 
         [0042]    When the circumcircle of the housing is opaque, each of the at least two light-emitting devices and each of the at least two receiving devices is alternately located at the periphery of the upper location of the cylindrical sealed housing. 
         [0043]    The benefit of said at least two light-emitting devices and at least two receiving devices being alternately located at the periphery is that the best observation window (above the center) is left to users while the position of the gas bubble is merely measured around the housing. Therefore, there are very few signals that can be derived if there is only one light-emitting device or only one receiving device. Thus, the performance is very poor and the apparatus is unpractical. By having at least two light-emitting devices and at least two receiving devices evenly and alternately located, and in combination with reasonable algorithms (e.g., Least Square Method), better result can be derived. Normally, the more devices are used, the higher precision and better sensitivity on all directions could be derived, as well as the better performance. 
         [0044]      FIG. 1(   a ) shows a perspective view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a first embodiment of the present invention.  FIG. 1(   b ) shows a side sectional view of an apparatus for measuring the position of a gas bubble in a bubble level and a bubble level containing the apparatus according to a first embodiment of the present invention. According to the first embodiment of the present invention, an apparatus  100  for measuring the position of a gas bubble in a bubble level is provided. The bubble level comprises a cylindrical shaped sealed housing  102 , which is partially filled with liquid  104  and contains a gas bubble  106 . The apparatus  100  comprises two light-emitting devices D 1 , D 2 , and two receiving devices Q 1 , Q 2 . The light emitted from each light-emitting device D 1 , D 2  illuminates the gas bubble  106  and the inner bottom surface  112  of the bubble level. Each receiving device Q 1 , Q 2  receives the light that is reflected by the inner bottom surface  112  of the bubble level and reflected and refracted by the gas bubble  106  and converts it into electrical signals. The electrical signals are processed for calculating the position of said gas bubble  106 . 
         [0045]    In another embodiment, the circular side wall  114  of the housing  102  is opaque. Each of the two light-emitting devices D 1 , D 2  and each of the two receiving devices Q 1 , Q 2  is alternately located above the cylindrical shaped sealed housing  102 . As shown in the  FIG. 1(   a ), in the clockwise direction, there are receiving device Q 1 , light-emitting device D 1 , receiving device Q 2 , and light-emitting device D 2 . Meanwhile, users can clearly observe the gas bubble  106  and its position at the center via a transparent window  108  above the housing  102  of the bubble level. 
         [0046]    In one embodiment, the circular side wall  114  of said housing  102  is transparent. Each of the two light-emitting devices D 1 , D 2  and each of the two receiving devices Q 1 , Q 2  is alternately located at the periphery of the cylindrically shaped sealed housing  102  (not shown in the figure), for example in the clockwise direction, there are receiving device Q 1 , light-emitting device D 1 , receiving device Q 2 , and light-emitting device D 2  in turn. The light-emitting devices D 1 , D 2  and the receiving devices Q 1 , Q 2  must have be well positioned and mainly direct to the gas bubble  106  and its vicinity. 
         [0047]    The two light-emitting devices D 1 , D 2  and the two receiving devices Q 1 , Q 2  can be distributed equidistantly over the circumference of the cylindrically shaped sealed housing. Hence the two light-emitting devices D 1 , D 2  and the two receiving devices Q 1 , Q 2  are located alternately by 90 degree. Four photo-electric signals (or values after AD conversion) may be derived when the gas bubble  106  locates at a certain position. In other words, when the first light-emitting device D 1  is lighted, two photo-electric signals (or values) U 11  and U 12  could be derived. When the second light-emitting device D 2  is lighted, another two photo-electric signals (or values) U 21  and U 22  could be derived. When the air bubble  106  is located at a different position, these four photo-electric signals or values, which could be recorded in advance, are different. During further usage, the four signals or values recorded in advance may be matched based on four photo-electric signals or values measured in real-time so as to obtain the current position of the gas bubble  106 . Or, it could be used to determine whether the gas bubble  106  exceeds a marking circle  110 . The four photo-electric signals or values may also be recorded in advance when the gas bubble  106  is located at a different position. Then, a common mathematical modeling method may be used to establish an empirical formula of the relationship between the four photo-electric signals and gas bubble position (X, Y) or the four photo-electric signals and the distance (R) between the gas bubble  106  and the center of the bubble level. During later usage, according to the four measured photo-electric signals, the current position (X, Y) of the gas bubble  106  could be obtained, or whether the gas bubble  106  exceeds the marking circle  110  may be determined. 
         [0048]    For example, the value Uij is derived, where i=1, 2; j=1, 2, 
         [0000]        X=Kx 11* U 11+ Kx 12* U 12+ Kx 21* U 21+ Kx 22* U 22 
         [0000]        Y=Ky 11* U 11+ Ky 12* U 12+ Ky 21* U 21+ Ky 22* U 22 
         [0000]    Or, signal value U 0 ij could be measured and recorded in advance when the gas bubble  106  locates at a reference position, for example in the center of the bubble level. The difference between the signal value Uij measured in real-time and the signal value U 0 ij which is recorded in advance when the gas bubble  106  locates at the center is used to calculate the position of the gas bubble  106 . In this way, the accuracy could be increased and the impact of temperature drift could be reduced. 
         [0000]        X=Kx 11*( U 11− U 011)+ Kx 12*( U 12− U 012)+ Kx 21*( U 21− U 021)+ Kx 22*( U 22− U 022)
 
         [0000]        Y=Ky 11*( U 11− U 011)+ Ky 12*( U 12− U 012)+ Ky 21*( U 21− U 021)+ Ky 22*( U 22− U 022)
 
         [0000]        R=SQRT ( X*X+Y*Y ) 
         [0049]    where: 
         [0050]    U 0 ij are the four voltage values which are recorded in advance when the gas bubble  106  locates at the center, i=1, 2, j=1, 2. 
         [0051]    Kxij (i=1,2; j=1,2) means that Uij changes 1/Kxij volt when the position of the gas bubble  106  moves 1 mm in the X axis direction. Kyij (i=1,2; j=1,2) means that Uij changes 1/Kyij volt when the position of the gas bubble  106  moves 1 mm in the Y axis direction. Both of them could be derived by experiments and methods such as Least Square Method. 
         [0052]    Due to the symmetrical arrangement of all the light emitting and light receiving devices around the bubble level, (i.e., D 1  and D 2  locate at symmetric positions while Q 1  and Q 2  locate at symmetric positions), and due to Q 1  and Q 2  are the same type of device to have similar performance while D 1  and D 2  are the same type of device to have similar performance, the following results can be obtained always: 
         [0000]      Kx11˜=−Kx22
 
         [0000]      Kx12˜=−Kx21
 
         [0000]      Ky11˜=−Ky22
 
         [0000]      Ky12˜=−Ky21
 
         [0000]    so: 
         [0000]        X=Kx 1*( U 11− U 011− U 22+ U 022))+ Kx 2*( U 12− U 012− U 21+ U 021)
 
         [0000]        Y=Ky 1*( U 11− U 011− U 22+ U 022))+ Ky 2*( U 12 −U 012 −U 21+ U 021)
 
         [0053]    Since the same type of devices has similar temperature drifts, U 11 -U 22  allows the temperature drifts of the two devices counteract with each other. So do U 12 -U 21 . Therefore, the method of the present invention could obtain stable results. 
         [0054]    In an embodiment, each light-emitting device is an LED, which emits light by being lighted in turn by pulse. 
         [0055]    In an embodiment, the light is visible light or infrared light. The advantage of visible light lies in that it can illuminate the bubble level while measuring the position of the gas bubble in a photo-electric manner so that users can clearly observe. The disadvantage of visible light lies in that it is vulnerable to ambient light and has higher power consumption and cost. The infrared light, which would not interfere with user&#39;s sight, is commonly used. Infrared light is less impacted by ambient light and has lower power consumption and cost. 
         [0056]    In an embodiment, each receiving device is a Photo-diode or a Photo-triode. The sensitivity of Photo-triodes is high, and its followed circuit is simple. 
         [0057]    In an embodiment, one light-emitting device and one receiving device could be assembled into one device. At least two such assembled devices are evenly disposed at the periphery of the bubble level. 
         [0058]      FIG. 1(   c ) shows a perspective view of an apparatus  100 ′ for measuring the position of a gas bubble in a bubble level according to a second embodiment of the present invention. The only difference between  FIG. 1(   c ) and  FIG. 1(   a ) is that photo-diodes PD 1  and PD 2  in  FIG. 1(   c ) are used to replace the photo-triodes (phototransistors) Q 1  and Q 2  as receiving devices. The advantages of using photo-diodes are quick response and good linearity. The remaining devices and their configurations and calculation method of  FIG. 1(   c ) are the same to those of  FIG. 1(   a ), and thus are not redundantly described herein. 
         [0059]      FIG. 2  shows a perspective view of an apparatus  200  for measuring the position of a gas bubble in a bubble level according to a third embodiment of the present invention. 
         [0060]    The apparatus  200  comprises four light-emitting devices D 1 -D 4  and four receiving devices Q 1 -Q 4 . 
         [0061]    Usually, the light-emitting devices D 1 -D 4  are lighted by pulse so that their transient luminous intensity is much bigger than the ambient light intensity. Hence better signals could be obtained. Meanwhile, since there are a plurality of light-emitting devices D 1 -D 4 , these light-emitting devices D 1 -D 4  should be lighted in turn to obtain high resolution. For example, for four light-emitting devices and four receiving devices, sixteen signals could be obtained if the light-emitting devices are lighted in turn. On the contrary, if the four light-emitting devices are lighted at the same time, only four signals could be obtained. As a result, the resolution and precision would be much worse. While the circuit is simple and calculation workload is less, the later disposition could only be applied in low requirement situations. 
         [0062]    It is preferred that the four light-emitting devices D 1 -D 4  and the four receiving devices Q 1 -Q 4  are alternately and equidistantly located whereby the angle between two adjacent devices is 45 degree. The light-emitting devices and all the receiving devices are located in the same horizontally aligned plane. Sixteen photoelectric signals (or data values after A/D conversion) can be obtained when the gas bubble  106  locates at a certain position. The sixteen original photo-electric signals when the gas bubble  106  locates at different positions (such as 65 positions, R=0, and R=1, 2, 3, 4 mm, within 0 to 360 degree spaced by a 22.5 degree interval) may be recorded in advance. During later usage, the newly measured sixteen photo-electric signals are compared with the original sixteen signals (such as in 65 positions) recorded in advance to calculate the current position of the gas bubble  106  or to determine whether the gas bubble  106  exceeds the marking circle  110 . Alternatively, the sixteen photo-electric signals when the gas bubble  106  locates at different positions may be recorded in advance and then a common mathematical modeling method (for example Least Square Method) may be used to build an empirical formula to give the relationship between the sixteen photo-electric signals and the gas bubble position (X, Y), or the distance (R) from the sixteen photo-electric signals and the gas bubble  106  to the center of the bubble level. During later usage, according to the newly measured  16  photo-electric signals Uij, the gas bubble  106  position (X, Y) could be directly calculated, or it may be determined whether the gas bubble  106  exceeds the marking circle  110 . Two data values (X, Y) or just one data value (R) is obtained from the calculation of sixteen data values, resulting in strong anti-interference ability, high precision, good reliability, and even sensitivity in each direction. Also due to the symmetrical dispositions of D 1 -D 4  and Q 1 -Q 4  at the circumcircle of bubble level, Uij and U(i+2)(j+2) (i=1,2, j=1,2) usually change reversely when the position of the gas bubble  106  changes. Uij and U(i+2)(j−2) (i=1,2, j=3,4) usually change reversely as well. 
         [0063]    Then 
         [0000]        Kxij˜=−Kx ( i+ 2)( j+ 2), (i=1,2, j=1,2) 
         [0000]        Kxij˜=−Kx ( i+ 2)( j− 2), (i=1,2, j=3,4) 
         [0000]    and 
         [0000]        Kyij˜=−Ky ( i+ 2)( j+ 2), (i=1,2, j=1,2) 
         [0000]        Kyij˜=−Ky ( i+ 2)( j− 2), (i=1,2, j=3,4) 
         [0064]    So the temperature drifts in the apparatus are counteracted eventually. As more data values are calculated, the useful signals are strengthened while temperature drifts are counteracted. The result becomes more stable. The precision becomes higher. 
         [0065]    While not shown in figures, another embodiment in which three light-emitting devices and three receiving devices are disposed alternately and equidistantly located at the circumcircle of the bubble level whereby the angle between two adjacent devices is 60 degrees. Nine photo-electric signals (or data after A/D conversion) could be obtained when the gas bubble  106  locates at a certain position. The problem is that the mathematical modeling will be a little more complex for the reason that the spacing angle is 60 degree instead of 90 degree which cannot coincide with both X-axis and Y-axis. 
         [0066]    In another embodiment, five light-emitting devices and five receiving devices being alternately and equidistantly disposed at the circumcircle of the bubble level. Twenty-five photo-electric signals (or data after A/D conversion) could be obtained when the gas bubble  106  locates at a certain position. The precision is even higher except that the mathematical modeling will be more complex and the cost is also higher. 
         [0067]    In another embodiment, six light-emitting devices and six receiving devices being alternately and equidistantly disposed at the circumcircle of the bubble level. 36 photo-electric signals (or data after A/D conversion) could be obtained when the gas bubble  106  locates at a certain position. The precision is even higher, especially for a bubble level with a larger diameter, except that the mathematical modeling will be more complex and the cost is also higher. 
         [0068]      FIG. 3  shows a perspective view of an apparatus  300  for measuring the position of a gas bubble in a bubble level according to a fourth embodiment of the present invention. As shown in  FIG. 3 , if the precision requirement is not very high, three light-emitting devices and four receiving devices being alternately and mostly equidistantly spaced whereby the angle between two adjacent devices is mostly 45 degrees. However, there is no light-emitting device in one 45 degree position. In other words, it is preferred that the plurality of light-emitting devices and receiving devices are alternately disposed as evenly as possible, but it is not entirely necessary. Compared to the previous embodiment, the calculation method will be more complex. But for a person skilled in the art, it can be contemplated with reference to the previous disclosure of the present invention. 
         [0069]      FIG. 4  shows a perspective view of an apparatus  400  for measuring the position of a gas bubble in a bubble level according to a fifth embodiment of the present invention. The difference between  FIG. 4  and  FIG. 3  lies in that in  FIG. 4 , a visible light emitting device LED 1  was placed in the 45 degree position which is left empty in  FIG. 3 . This visible light emitting device LED 1  is used to illuminate the gas bubble  106  or for alarming. Meanwhile, the visible light emitting device LED 1  is not used in measuring the position of the gas bubble  106 . The remaining devices and their settings and calculation methods of  FIG. 4  are all the same to those of  FIG. 3 , and thus are not redundantly described herein. 
         [0070]      FIG. 5(   a ) shows a side sectional view of an apparatus  500  for measuring the position of a gas bubble in a bubble level that has a light distributor  501  equipped according to embodiments of the present invention.  FIG. 5(   b ) shows a lateral sectional view of the light shielding effects of the light distributor  501  according to embodiments of the present invention. 
         [0071]    The light distributor  501  is used to shield useless light and direct light to the gas bubble  106  and its vicinity. Users still can clearly see the gas bubble  106  and its position via the transparent window  108  on the top of the bubble level. 
         [0072]    The light distributor  501  not only obstructs by the ledge part  504  partial light emitted from the light-emitting devices to prevent the light from directly radiating the adjacent receiving devices, but also leave out a light path (i.e., light guiding gap  506 ) to allow light emitted from said light-emitting devices  508  directly illuminate on and around the gas bubble  106  as much as possible, and to allow the light receiving devices  508  receive the light from the surface of or around the gas bubble  106  as much as possible. In the  FIG. 5(   a ),  508  can represent either the light-emitting devices or the light receiving devices if it turns 45 degree. The light emitting and light receiving devices are placed alternately on the periphery of the window  108 . This light distributor  501  can also comprise a shield element  502 , which shields the impact from ambient light. The shield element  502  can be a circular shaped tube which is at least partially encloses the cylindrical shaped sealed housing  102 . Advantageously the upper end of the sealed housing  102  is enclosed by the shield element  502 . Ideally the shield element  502  is opaque or comprises a material with reduced light transmission properties. Ideally the ledges  504  are molded on the inner surface of the shield element  502 . Between two neighboring ledges  504  a light guiding gap  506  is located. The light guiding gaps  506  and the ledges are arranged concentric with respect to the center of the cylindrical housing  102 . 
         [0073]    The light distributor  501  can optimize light path, increase performance and reduce the impact from disturbing light while strengthening useful signals. Then stable results with high precision are obtained. To install the light-emitting devices and receiving devices in a convenient manner, small light-emitting devices and receiving devices with larger scattering angle (such as ±70 degree) could be installed horizontally and the light axis is directed downward towards the inner bottom surface  112 . Then light distributor  501  can shield useless light while the light guiding gap  506  allows useful light pass through (by utilizing the feature of larger scattering angle). Thus a very good result can be obtained. Those small light-emitting devices or receiving devices with larger scattering angle and forward light axis are common in the market, so the cost is very low. Please note, in  FIG. 5(   a ),  508  can represent either the light-emitting devices or the light receiving devices if it turns 45 degree. The present invention requires a very small additional height of the bubble level, which wouldn&#39;t interfere with users&#39; observation of the position of the gas bubble  106 . This is another advantage of the present invention. 
         [0074]    However, the light distributor  501  is not necessary if the performance requirement is not so high or the light-emitting devices  508  and receiving devices  508  themselves have good directivity which exactly direct to the position of the gas bubble  106 . 
         [0075]    In theory, it is preferred that the light axis of the light-emitting devices and receiving devices is downward but deviates 45 degrees toward the gas bubble  106 . But those types of devices are rare in the market. Or they have to be customized, which result in high cost. 
         [0076]      FIG. 6  shows the connection diagram between the apparatus for measuring the position of a gas bubble in a bubble level and related circuits according to embodiments of the present invention. As shown in  FIG. 6 , controlling signals to light-emitting devices D 1 -DM are sent by MCU  602  (or CPU, or some other devices). The signals arrive at the switch driving circuit Id to light the light-emitting devices D 1  to DM in turn. Various conditioning circuits  604  can be inserted between each of the receiving devices Q 1  and the analog to digital convertor AD, for example, filtering circuit and amplifier, etc. These are common for those ordinarily skilled in the art. MCU  602  utilizes the result from the analog to digital convertor AD to calculate the deviation position (X, Y) of the gas bubble, or the distance (R) between the position of the gas bubble and the center of the bubble level. The result is used for level status display, inclination alarming, feedback input of level controlling system, or weighting result correction, start the leveling guide, etc. 
         [0077]    The present invention relates to an apparatus and method for measuring the position of a gas bubble in a bubble level and a bubble level comprising the apparatus. The present invention is used for inclination alarming of a balance or gas bubble position display (which can be used to instruct users to conveniently adjust the balance to its level status), feedback input of level controlling system, or weighting result correction, etc. Meanwhile, it ensures users can clearly observe the gas bubble and its position of a physical bubble level. It brings excellent user experiences and convenient application. The apparatus has simple construction, low cost, reliable result, and high precision. 
         [0078]    Those skilled in the art may readily understand that the above exemplary embodiments of the present invention can have various modifications and variations without departing from the spirit and scope of the present invention. Therefore, the present invention is intended to cover the modifications and variations that fall within the scope as recited in the claims and its equivalents.