Abstract:
Disclosed herein is a calibration apparatus for vacuum gauge having a combined use for an 1 Torr level, a 10 Torr level, and a 100 Torr level vacuum gauge. According to the present invention, there is provided a calibration apparatus for vacuum gauge, in which a standard pressure gauge  140, 142  is installed within a pressure vessel  120  for calibrating a monitoring pressure gauge  560,  the apparatus comprising: a balance mounting shaft  134  installed vertically within the pressure vessel  120  and provided with a plurality of balance mounting bases  138  spaced apart from one another at predetermined intervals along an axial direction, and the standard pressure gauge  140, 142  being connected to lower portion of the balance mounting shaft; a plural sets of balances mounted between the respective balance mounting bases  138,  each of which is composed of a plurality of balances; means for elevating each balance of the plural sets of the balances from the balance mounting base  138  separately or mounting the balance on the balance mounting base  138;  and means for controlling the operation of the elevating means according to commands received from the outside.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a calibration apparatus for vacuum gauge, and more in particular, to a calibration apparatus for vacuum gauge, which can be used not only for an 1 Torr level vacuum gauge, a 10 Torr level vacuum gauge, but also for a 100 Torr level vacuum gauge also.  
         [0003]     2. Background of the Related Art  
         [0004]     Recently, researches and developments about measurement of small pressure have been performed vigorously due to developments in environmental industries and process industries. In general, the measurement of small pressure refers to the measurement of pressures falling in a range below several thousands of Pa, that is, it refers to the measurement of pressures falling in the range from one-several hundredths to one-several thousandths of the atmospheric pressure, in view of the fact that the atmospheric pressure is about 100 kPa (100,000 Pa).  
         [0005]     A measuring gauge for small pressure using mercury or oil has been developed or is under international development. The vacuum gauge for measuring small pressures can be divided into 1 Torr type vacuum gauge, 10 Torr type vacuum gauge, and 100 Torr type vacuum gauge depending on the commercial applications, and such vacuum gauge occupies 95% of all vacuum gauges.  
         [0006]     Meanwhile, a laser interference type or an ultrasonic interference type mercury pressure gauge has been employed in calibration of such vacuum gauge for measuring small pressures. However, in general such reference pressure gauge has not been employed in general calibration body and test body due to its complexity of device and aversion for mercury. Accordingly, up to date, after any one vacuum gauge has been calibrated, a next vacuum gauge is calibrated with help of the previous calibrated vacuum gauge. However, such method increases uncertainty of the gauge, and decrease calibration efficiency because continuous periodical calibration (for instance, every six month) for reference gauge is necessarily in demand.  
         [0007]     In addition, according to the recent technologies developed until now, the vacuum gauge for 10 Torr level vacuum has been calibrated by the calibration apparatus of 10 Torr type vacuum gauge, and the vacuum gauge for 100 Torr level vacuum has been calibrated by the calibration apparatus of 100 Torr type vacuum gauge respectively. Difficulties arising from the measurement and calibration have been increased, as the pressure to be measured becomes lower (for instance, 1 Torr).  
         [0008]      FIG. 1  is a view for showing whole systematic construction of a calibration apparatus applicable to the present invention and to the conventional art. As shown in  FIG. 1 , the conventional calibration system for vacuum gauge may comprise a calibration apparatus for vacuum gauge  100 , a gas supply device, a monitoring pressure gauge  560 , and a gas discharge device.  
         [0009]     The gas supply device comprises a gas supply valve  542 , a volume variable valve  544 , and a first vacuum pump  550 , and the like for supplying predetermined pressure via a gas supply pipe  540  to a piston which will be described below. Especially, the first vacuum pump  550  includes a trap  552  for blocking back-streaming of oil vapor in addition to a pump valve  554  as rotary type pump is employed for it. Also, a portion of the gas supply pipe  540  is branched to be connected to the monitoring pressure gauge  560 .  
         [0010]     The gas discharge device operates to form a vacuum inside the calibration apparatus  100  of the vacuum gauge, and includes a second vacuum pump  580 , a trap  582  and a blocking valve  584  having identical construction. Also, a needle valve  574  and a vent valve  572  are connected to one end of a gas discharge pipe  570 .  
         [0011]     Hereinafter, conventional art of the calibration apparatus for vacuum gauge shown in  FIG. 1  will be described.  FIG. 2  is a view for showing schematic construction of the conventional calibration apparatus  10  for vacuum gauge. As shown in  FIG. 2 , a pressure vessel  20  is sealed from the outside, and is provided with a piston  40  and a cylinder  42  constituting a force balance type pressure gauge within it. Also, the weight sets  30  are arranged above the piston  40 , and a lower portion of the piston  40  is connected to the gas supply pipe  540 .  
         [0012]     In such calibration apparatus  10  for vacuum gauge, equilibrium state can be achieved by supplying gas via the gas supply pipe  540  after loading all the weight sets  30  on the piston  40 . The piston  40  is maintained at a raised state after it has been come up by means of the equilibrium of upper and lower forces.  
         [0013]     In this state, the monitoring pressure gauge  560  can be calibrated by determining whether the indicated value of the monitoring pressure gauge  560  conforms to the measured pressure value Pi based on following formula (1): 
 
 P   i   =F/A+P   r   (1) 
 
         [0014]     Here, P i  represents measured pressure value, F represents total downward force obtained by adding the mass of the piston  40  and that of the tare weight, A represents cross-sectional area of the piston  40 , and P r  represents reference pressure inside the pressure vessel  20 .  
         [0015]     The reference pressure P r  is the pressure formed around the piston, and becomes to be vacuum at the time of measuring the absolute pressure and becomes to be atmospheric pressure at the time of measuring the gauge pressure. The reference pressure P r  is maintained at vacuum or atmospheric pressure and is regarded as a predetermined value during the measurement. However, as F represents gravitational load obtained by adding the mass of the piston and that of the weight sets in formula (1), it always has a minimum value exceeding the mass of the piston. Accordingly, with regard to the measured pressure P i , minimum pressure (normally, several kPa) exists, which corresponds to the minimum value described above, and therefore, it is impossible to measure pressures below the above pressure.  
         [0016]     A method for variable residual pressure, which is denoted by following formula (2), is suggested as a substitute for the above described measuring method, in which it is possible to cope with the change of the load due to change of the weight sets by maintaining the pressure P m  below the piston to be uniform and varying the reference pressure P r ′ around the piston: 
 
 P   m   =F/A+P   r ′  (2) 
 
         [0017]     Here, P m  represents the pressure monitored below the piston, F represents the gravitational load obtained by adding the mass of the piston and that of the weight sets, A represents cross-sectional area of the piston, and P r ′ represents variable reference pressure around the piston.  
         [0018]     However, such method has not also been employed in practical, because it is difficult to change the weights located within a vacuum chamber effectively without breaking such low pressure as it is under the vacuum or reference pressure. Furthermore, calibration of the vacuum gauge is difficult and is not economical, because respective vacuum gauges such as 1 Torr type, 10 Torr type and 100 Torr type vacuum gauge should be calibrated by means of respective calibration apparatus for the vacuum gauge.  
       SUMMARY OF THE INVENTION  
       [0019]     Accordingly, the present invention has been made to overcome above-mentioned problems arising from conventional technologies, and the object of the present invention is to provide a calibration apparatus for vacuum gauge, which is capable of measuring small pressure precisely, and calibrating several types of vacuum gauge such as 1 Torr type, 10 Torr type, and 100 Torr type vacuum gauge in an identical calibration apparatus.  
         [0020]     To accomplish the above objects of the present invention, there is provided a calibration apparatus for vacuum gauge having a combined use for an 1 Torr level, a 10 Torr level, and a 100 Torr level vacuum gauge, in which a standard pressure gauge  140 ,  142  is installed within a pressure vessel  120  for calibrating a vacuum gauge, the apparatus including:  
         [0021]     A shaft, connected to motor, installed vertically within the pressure vessel and provided with a plurality of weight-set mounting bases spaced apart from one another at predetermined intervals along an axial direction, the balance mounting shaft being connected at a lower portion thereof to the standard pressure gauge;  
         [0022]     a plural sets of balances mounted between the respective balance mounting bases, and each of which being composed of a plurality of balances;  
         [0023]     means for elevating each balance of the plural sets of the balances from the balance mounting base separately or mounting the balance on the balance mounting base; and  
         [0024]     means for controlling the operation of the elevating means according to commands received from the outside.  
         [0025]     According to the present invention, the balance mounting bases  138  can be five, and the balance sets can also be five.  
         [0026]     Also, according to the present invention, the balance sets can be five, and the first set of balance  210  is composed of three balances having respective masses of 1 g, 9 g and 90 g, the second set of balance  220  is composed of three balances having respective masses of 2 g, 18 g, and 180 g, the third set of balance  230  is composed of three balances having respective masses of 4 g, 36 g, and 360 g, the fourth set of balance  240  is composed of three balances having respective masses of 8 g, 72 g, and 720 g, and the fifth set of balance  250  is composed of three balances having respective masses of 3.332 g, 29.990 g, and 299.902 g.  
         [0027]     Furthermore, according to the present invention, the elevating means comprises a servo motor  112  installed at the outside of the pressure vessel;  
         [0028]     a rotary motion feed through  114  respectively connected at one side to the servo motor  112  for transferring the rotation force to the inside of the pressure vessel  120 ;  
         [0029]     a lead screw  128  connected vertically and mounted rotatably to the other side of the rotary motion feed through  114  respectively;  
         [0030]     a transporting shaft  129  mounted in parallel with the lead screw  128  in such a fashion as to be spaced apart from the lead screw at a predetermined interval;  
         [0031]     a transporting head  130  connected in common to the lead screw  128  and the transporting shaft  129  to move upwardly and downwardly according to the rotation of the lead screw  128 ; and  
         [0032]     a plurality of arms  132  installed around the balance mounting shaft to extend from the transporting head  130  to the sets of balances for elevating the balances selectively.  
         [0033]     In addition, the balance mounting shaft  134  is installed at center of the pressure vessel  120 , and the lead screw  128  and the transporting shaft  129  are installed around the balance mounting shaft  134  at equal intervals.  
         [0034]     Furthermore, the three balances of the respective sets of balance  210 ,  220 ,  230 ,  240 , and  250  are preferably arranged in a descending order with regard to the gravity direction depending on respective masses. Also, the three balances of the respective sets of balance  210 ,  220 ,  230 ,  240 , and  250  can be arranged in a descending order with regard to the gravity direction depending on respective diameters.  
         [0035]     According to the present invention, the servo motor  112  comprises a step motor, and a brushless DC servo motor.  
         [0036]     Also, the calibration apparatus can further comprises means for detecting the lowest and the highest elevation amount of the elevating means, detected signals of the detecting means are transmitted to the control means, and the control means can operate to stop the elevating means or actuate it continuously in response to the detected signals.  
         [0037]     Meanwhile, the detecting means can be composed of a first limit switch  148  installed at the highest elevation height; a second limit switch  150  installed at the lowest elevation height; and an indicator  146  capable of reciprocating between the first and second limit switches  148 ,  150  in cooperation with the operation of the elevating means.  
         [0038]     In addition, the standard pressure gauge can be composed of a cylinder  142  fixed within the pressure vessel and connected at one end to gas supply means; and a piston  140  a piston which is installed at the inside of the cylinder in such a fashion as to move upwardly and downwardly, and on which a balance is located. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0040]      FIG. 1  is a view for showing whole systematic construction of a calibration apparatus for vacuum gauge applicable to the present invention and to the conventional art;  
         [0041]      FIG. 2  is a schematic view for showing construction of the conventional calibration apparatus for vacuum gauge;  
         [0042]      FIG. 3  is a schematic view for showing a calibration apparatus for vacuum gauge of the present invention having a combined use for an 1 Torr type, a 10 Torr type, and a 100 Torr type vacuum gauge;  
         [0043]      FIG. 4  is a planar view for showing the calibration apparatus for vacuum gauge shown in  FIG. 3 ;  FIG. 5  is a view for showing only a set of balance and a balance elevation device constituting the calibration apparatus shown in  FIG. 3 ;  
         [0044]      FIG. 6   a  is a schematic side cross-sectional view for showing the first set of balance  210  and a transporting head  130   a  shown in  FIG. 5 , when the load of the balance is not applied to a balance mounting base  138 ;  
         [0045]      FIG. 6   b  is a side cross-sectional view similar to  FIG. 6   a , when a balance  215  having a mass of 1 g is lowered to the balance mounting base  138 ;  
         [0046]      FIG. 6   c  is a side cross-sectional view similar to  FIG. 6   a , when a balance  215  having a mass of 1 g and a balance  213  having a mass of 9 g are lowered to the balance mounting base  138  to thereby apply total 10 g gravity load;  
         [0047]      FIG. 6   d  is a side cross-sectional view similar to  FIG. 6   a , when a balance  215  having a mass of 1 g, a balance  213  having a mass of 9 g, and a balance  211  having a mass of 90 g are lowered to the balance mounting base  138  to thereby apply total 100 g gravity load;  
         [0048]      FIG. 7  is a graphic view for showing processes of arranging balances sequentially on the mounting base, pressurizing the reference pressure gauge, and then reducing the pressure so as to calibrate a vacuum gauge of a particular level;  
         [0049]      FIG. 8   a  is a side cross-sectional view for showing a initial preparing step for calibrating respective vacuum gauges including an 1 Torr level, a 10 Torr level, and a 100 Torr level vacuum gauge, wherein every set of balance  210 ,  220 ,  230 ,  240 , and  250  is arranged on the corresponding balance mounting base  138 ;  
         [0050]      FIG. 8   b  is a side cross-sectional view for showing a calibration step of an 1 Torr level vacuum gauge, wherein a balance  225  having a mass of 2 g, a balance  245  having a mass of 8 g, a balance  255  having a mass of 3.332 g are arranged on the corresponding balance mounting bases to thereby apply load on the standard pressure gauge  140 ,  142 ;  
         [0051]      FIG. 8   c  a side cross-sectional view for showing a calibration step of a 10 Torr level vacuum gauge, wherein a balance  225  having a mass of 2 g, a balance  223  having a mass of 18 g, a balance  245  having a mass of 8 g, a balance  243  having a mass of 72 g, a balance  255  having a mass of 3.332 g, and a balance  253  having a mass of 29.990 g are arranged on the corresponding balance mounting bases to thereby apply load on the standard pressure gauge  140 ,  142 ;  
         [0052]      FIG. 8   d  is a side cross-sectional view for showing a calibration step of a 100 Torr level vacuum gauge, wherein a balance  255  having a mass of 3.332 g, a balance  245  having a mass of 8 g, a balance  253  having a mass of 29.990 g, a balance  243  having a mass of 72 g, a balance  221  having a mass of 180 g, a balance  225  having a mass of 2 g, a balance  223  having a mass of 18 g, a balance  251  having a mass of 299.902 g, and a balance  241  having a mass of 720 g are arranged on the corresponding balance mounting bases to thereby apply load on the standard pressure gauge  140 ,  142 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0053]     Preferred embodiments of the calibration apparatus for vacuum gauge and the calibration method for vacuum gauge using same of the present invention will now be described in detail in connection with the appended drawings below.  
         [0054]     In the appended drawings and detailed description of the present invention, the same element, although depicted in different drawings, will be designated by the same reference numeral or character. In  FIG. 1 , schematic description about the whole systematic construction of the calibration apparatus for vacuum gauge applicable to the present invention has been done as described above.  
         [0055]     Hereinafter, detailed inside construction of the calibration apparatus for vacuum gauge shown in  FIG. 1  will now be described below. First of all,  FIG. 3  is a schematic view for showing a calibration apparatus  100  for vacuum gauge of the present invention having a combined use for an 1 Torr type, a 10 Torr type, and a 100 Torr type vacuum gauge, and  FIG. 4  is a planar view for showing the calibration apparatus for vacuum gauge shown in  FIG. 3 . As shown in  FIG. 3  and  FIG. 4 , The calibration apparatus  100  for vacuum gauge generally comprises a cylindrical pressure vessel  120 , five step motors  112  installed above the pressure vessel  120 , and a base  144  supporting the pressure vessel  120 .  
         [0056]     The five step motors  112  are composed of the first, second, third, fourth, and fifth step motor  112   a,    112   b,    112   c,    112   d,  and  112   e,  installed at equal intervals above the pressure vessel  120 . In the step motor  112 , a rotation shaft (not shown) is projected to both ends thereof. Accordingly, one end of the rotation shaft transfers rotation force via a rotary motion feed through  114  to the inside of the pressure vessel  120 , and the other end of the rotation shaft transforms rotation movement into linear movement to thereby move an indicator  146  upwardly and downwardly.  
         [0057]     The indicator  146  can reciprocate between the highest point and the lowest point according to the rotation of the motor, and the first limit switch  148  and the second limit switch  150  are installed at the respective highest and lowest points. The limit switches  148 ,  150  are made of a photo-sensor, and the indicator  146  senses the present position by penetrating or blocking lights as it passes by the photo-sensor.  
         [0058]     The rotary motion feed through  114  is a mechanical part transferring rotation force to the inside of the pressure vessel  120  concurrently with maintaining vacuum state within the pressure vessel  120 . The detailed construction of the rotary motion feed through  114  is well known to those skilled in the relevant art to which the present invention pertains, so detailed description of it will be abridged. The rotary motion feed through  114  is installed at respective five step motors  112 , and a lead screw  128  is connected via a coupling to an end of the rotary motion feed through. Therefore, the first rotary motion feed through  114   a  and the first lead screw  128   a  are connected to the first step motor  112   a,  and the second rotary motion feed through  114   b  and the second lead screw  128   b  are connected to the second step motor  112   b.  In  FIG. 3 , only two step motors  112   a ,  112   b  and two lead screws  128   a ,  128   b  have been shown for supporting the understand of the construction of the present invention.  
         [0059]     Also, five transporting shafts  129  are arranged to be parallel with and near the respective lead screw  128  so as to make the transporting heads  130  to move linearly according to the rotation of the lead screw  128 . Every transporting head  130  is connected to the respective lead screw  128 , so one transporting head  130  is connected to the lead screw  128  and the transporting shaft  129  concurrently. Actually, the transporting heads  130  are arranged around the balance along a spiral trace.  
         [0060]     The balance mounting shaft  134  having a desired height is located at center of the pressure vessel  120 , and is provided with cylinder/piston type standard pressure gauge  140 ,  142 . In the above described balance mounting shaft  134 , five balance mounting bases  138 , which project slightly in a longitudinal direction, are provided along an axial direction. Such balance mounting base  138  transfers the load of the balance to the standard pressure gauge  140 ,  142  when the balance has been lowered along the balance mounting shaft and is mounted on it.  
         [0061]     The balance has been inserted into the balance mounting shaft  134 , and is located between the respective balance mounting bases  138 .  
         [0062]     If it is to be more concretely described, the balance is composed of five sets of balances  210 - 250  as follows. The first set of balance  210  is composed of three balances having respective masses of 1 g, 9 g and 90 g, the second set of balance  220  is composed of three balances having respective masses of 2 g, 18 g, and 180 g, the third set of balance  230  is composed of three balances having respective masses of 4 g, 36 g, and 360 g, the fourth set of balance  240  is composed of three balances having respective masses of 8 g, 72 g, and 720 g, and the fifth set of balance  250  is composed of three balances having respective masses of 3.332 g, 29.990 g, and 299.902 g. This is listed in Table 1.  
         [0063]     Further, a lift arm  132  is fixed to the transporting head  130  at one end so that it can move upwardly and downwardly along with the movement of the transporting head  130 . The other end of the lift arm  132  is a free end and supports a lower portion of the balance. Concrete construction of the lift arm  132  will be described next time.  
                                                         TABLE 1                           First balance   Second balance   Third balance       balance set   (upper balance)   (mid balance)   (lower balance)                                First set   90   g   9   g   1   g       Second set   180   g   18   g   2   g       Third set   360   g   36   g   4   g       Fourth set   720   g   72   g   8   g       Fifth set   299.902   g   29.990   g   3.332   g                  
 
         [0064]     The cylindrical pressure vessel  120  is made of metal, and four openings (the first opening  122   a,  the second opening  122   b,  the third opening  124   a,  and the fourth opening  124   b ) are formed at mid region of the vessel. These openings  122 ,  124  are formed to maintain vacuum within the pressure vessel  120  or to supply particular gas. The inside of the openings can be seen by naked eyes because they are closed by transparent window.  
         [0065]      FIG. 5  is a view for showing only a set of balance and a balance elevation device constituting the calibration apparatus shown in  FIG. 3 . As shown in  FIG. 5 , the first set of balance  210  is composed of three balances such as a balance  215  having a mass of 1 g, a balance  213  having a mass of 9 g and a balance  211  having a mass of 90 g, the second set of balance  220  is composed of three balances such as a balance  225  having a mass of 2 g, a balance  223  having a mass of 18 g, and a balance  221  having a mass of 180 g, the third set of balance  230  is composed of three balances such as a balance  235  having a mass of 4 g, a balance  233  having a mass of 36 g, and a balance  231  having a mass of 360 g, the fourth set of balance  240  is composed of three balances such as a balance  245  having a mass of 8 g, a balance  243  having a mass of 72 g, and a balance  241  having a mass of 720 g, and the fifth set of balance  250  is composed of three balances such as a balance  255  having a mass of 3.332 g, a balance  253  having a mass of 29.990 g, and a balance  251  having a mass of 299.902 g.  
         [0066]     As described above, each set of balances  210 ,  220 ,  230 ,  240 , and  250  is composed of three balances. Each balance is formed to be disk shape, and it has a different diameter depending on its weight. Accordingly, any of the three balances from each set of balance can be mounted by means of the lift arm  132  depends on its difference of height.  
         [0067]     In  FIG. 5 , only one lead screw  128  with five transporting heads  130  is shown, however, the five lead screws  128   a ,  128   b ,  128   c ,  128   d , and  128   e  are configured to surround the balance mounting shaft  134  and each transporting head  130  is connected to each lead screw  128  along the spiral trace.  
         [0068]      FIG. 6   a  is a schematic side cross-sectional view for showing the first set of balance  210  and a transporting head  130   a  among the plural sets of balance shown in  FIG. 5 , when load of the balance is not applied to a balance mounting base  138 . As shown in  FIG. 6   a , an upper surface of the balance  215  having a mass of 1 g is configured to overlap with a lower surface of the balance  213  having a mass of 9 g, and an upper surface of the balance  213  having a mass of 9 g is configured to overlap with a lower surface of the balance  211  having a mass of 90 g.  
         [0069]     Furthermore, a lifter  160  is fixed to free end of the lift arm  132 . A through hole for the balance mounting base  138  is formed at center of the lifter  160  having a circular disk shape. Three circular step portions are formed at the circumferential edge of the lifter  160  in radial direction, and each step portion has a height enough to contact with corresponding lower surface of the balances  215 ,  213 , and  211  having respective masses of 1 g, 10 g, and 100 g.  
         [0070]     Accordingly, as shown in  FIG. 6   a , when the transporting head  130   a  is moved upwardly to lift the arm  132  and the lifter  160 , the balance  215  having a mass of 1 g, the balance  213  having a mass of 9 g, and the balance  211  having a mass of 90 g are lifted upwardly by the lifter  160  at the same time. Of course, instead of a bolt, various fixing means such as adhesives and the like can be used to fix the lifter  160  to the lift arm  132 .  
         [0071]      FIG. 6   b  is a side cross-sectional view similar to  FIG. 6   a , when a balance  215  having a mass of 1 g is lowered to the balance mounting base  138 . As shown in  FIG. 6   b , when the first transporting head  130   a  is lowered by the rotation of the first lead screw  128   a , the lift arm  130  and the lifter  160  move in the downward direction integrally. In this instance, the lowering height is preferable to be so high as to mount the single balance  215  having a mass of 1 g on the balance mounting base  138 . That is, in a state shown in  FIG. 6   b , gravity load of 1 g is applied to the standard pressure gauge  140 ,  142 .  
         [0072]      FIG. 6   c  is a side cross-sectional view similar to  FIG. 6   a , when only the balance  215  having a mass of 1 g and the balance  213  having a mass of 9 g are lowered to the balance mounting base  138  so that total 10 g gravity load is applied. As shown in  FIG. 6   c , when the first lead screw  128   a  is additionally rotated to thereby lower the first transporting head  130   a , the lift arm  132  and the lifter  160  are lowered integrally in addition. In this instance, the lowering height is preferable to be so high as to mount the balance  215  having a mass of 1 g and the balance  213  having a mass of 9 g on the balance mounting base  138 . That is, in a state shown in  FIG. 6   c , as the balance having a mass of 1 g and the balance  213  having a mass of 9 g are located in contact with each other and are mounted on the balance mounting base  138 , so total gravity load of 10 g is applied to the standard pressure gauge  140 ,  142 , however, the balance  211  having a mass of 90 g is supported by the lifter  160 .  
         [0073]      FIG. 6   d  is a side cross-sectional view similar to  FIG. 6   a , when the balance  215  having a mass of 1 g, the balance  213  having a mass of 9 g, and the balance  211  having a mass of 90 g are lowered to the balance mounting base  138  so that total 100 g gravity load is applied. As shown in  FIG. 6   d , when the first lead screw  128   a  is additionally rotated to thereby lower the first transporting head  130   a , the lift arm  132  and the lifter  160  are lowered integrally in addition. In this instance, the lowering height is preferable to be so high as to mount all the balance  215  having a mass of 1 g, the balance  213  having a mass of 9 g and the balance  211  having a mass of 90 g on the balance mounting base  138 . That is, in a state shown in  FIG. 6   d , as the balance having a mass of 1 g, the balance  213  having a mass of 9 g and the balance  211  having a mass of 90 g are located in contact with each other and are mounted on the balance mounting base  138 , so total gravity load of 100 g is applied to the standard pressure gauge  140 ,  142 , however, the load of the balance is not applied on the lifter  160 .  
         [0074]     As shown in  FIG. 6   a  to  FIG. 6   d , the first transporting head  130   a  reaches at a highest position shown in  FIG. 6   a  and reaches at a lowest position shown in  FIG. 6   d  by the rotation of the first lead screw  128   a.    
         [0075]     Such highest and lowest positions are also shown in an opposite side (upper rotation shaft on the basis of  FIG. 3 ) of the first step motor  112   a  proportionally. Accordingly, the first limit switch  148  is installed at the highest position, and the second limit switch  150  is installed at the lowest position. As a result, during an initialization process of the position of the each transporting head at the beginning of the operation, the indicator  146  passes the highest position, that is the first limit switch  148 , or the lowest position, that is, the second limit switch  150  so that the present position can be set accurately as a reference position.  
         [0076]     While the elevating operation of the first set of balance  210  has been described with regard to the accompanying  FIG. 6   a  to  FIG. 6   d , however, such structure is identical with all of the second, third, fourth, and the fifth sets of balances  220 ,  230 ,  240 , and  250 , and such operation can be performed in same way.  
         [0077]     Hereinafter, the balance combinations for respective vacuum level in the calibration apparatus for vacuum gauge having a combined use for an 1 Torr level, a 10 Torr level, and a 100 Torr level vacuum gauge according to the present invention will be described below.  
         [0078]     First of all, balance combinations for calibrating the 1 Torr level vacuum gauge will be described. In view of the pressure transformation, 1 Torr corresponds to 133.32 Pa, so that balance combinations for 10 Pa, 20 Pa, 30 Pa, . . . 120 Pa, 133.32 Pa are required to calibrate the 1 Torr level vacuum gauge. Balance combinations for such pressure stages are listed in Table 2.  
                                 TABLE 2                       Pressure   Balance combination                                10   Pa   1 g       20   Pa   2 g       30   Pa   1 g + 2 g       40   Pa   4 g       50   Pa   1 g + 4 g       60   Pa   2 g + 4 g       70   Pa   1 g + 2 g + 4 g       80   Pa   8 g       90   Pa   1 g + 8 g       100   Pa   2 g + 8 g       110   Pa   1 g + 2 g + 8 g       120   Pa   4 g + 8 g       130   Pa   1 g + 4 g + 8 g       133.32   Pa (=1 Torr)   2 g + 8 g + 3.332 g       140   Pa   2 g + 4 g + 8 g       150   Pa   1 g + 2 g + 4 g + 8 g       160   Pa   1 g + 2 g + 4 g + 9 g                  
 
         [0079]     As can be seen from Table 2, it is possible to change pressures from 0 Pa to 160 Pa in stage by appropriately combining prepared balances so as to calibrate the 1 Torr level vacuum gauge, it is also possible to calibrate a pressure of 1 Torr (133.32 Pa) accurately.  
         [0080]     It is necessary to monitor the difference between the pressure values of the standard pressure gauges  140 ,  142  and the vacuum gauge (not shown) to be calibrated with increasing the pressures in an ascending order such as from 10 Pa, 20 Pa, 30 Pa, . . . 120 Pa, 133.32 Pa, 140 Pa, 150 Pa, to 160 Pa in stage, and then decreasing the pressures in a descending order such as from 160 Pa, 150 Pa, 140 Pa, 133.32 Pa, 120 Pa, . . . , 30 Pa, 20 Pa, 10 Pa, to 0 Pa so as to calibrate the 1 Torr level vacuum gauge.  
         [0081]      FIG. 7  is a graphic view for showing processes of arranging balances sequentially on the mounting base, pressurizing the standard pressure gauge, and then reducing the pressure so as to calibrate the vacuum gauge of a particular level. In  FIG. 7 , a horizontal axis denotes for time (sec), and a vertical axis denotes for pressure Pa applied by the balance. Balance combinations for calibrating the 10 Torr level vacuum gauge will be described below. In view of the pressure transformation, 10 Torr corresponds to 1333.2 Pa, so that balance combinations for 100 Pa, 200 Pa, 300 Pa, . . . , 1200 Pa, 1333.2 Pa are required to calibrate the 10 Torr level vacuum gauge. Balance combinations for such pressure stages are listed in Table 3.  
                                 TABLE 3                       Pressure   Balance combination                                100   Pa   1 g + 9 g       200   Pa   2 g + 18 g       300   Pa   1 g + 2 g + 9 g + 18 g       400   Pa   4 g + 36 g       500   Pa   1 g + 4 g + 9 g + 36 g       600   Pa   2 g + 4 g + 18 g + 36 g       700   Pa   1 g + 2 g + 4 g + 9 g + 18 g + 36 g       800   Pa   8 g + 72 g       900   Pa   90 g       1000   Pa   1 g + 9 g + 90 g       1100   Pa   2 g + 18 g + 90 g       1200   Pa   1 g + 2 g + 9 g + 18 g + 90 g       1300   Pa   4 g + 36 g + 90 g       1333.2   Pa (=1 Torr)   1 g + 3.332 g + 9 g + 29.990 g + 90 g       1400   Pa   1 g + 4 g + 9 g + 36 g + 90 g       1500   Pa   2 g + 4 g + 18 g + 36 g + 90 g       1600   Pa   1 g + 2 g + 4 g + 9 g + 18 g + 36 g + 90 g                    
         [0082]     As can be seen from Table 3, it is possible to change pressures from 10 Pa to 1600 Pa in stage by appropriately combining prepared balances so as to calibrate the 10 Torr level vacuum gauge, it is also possible to calibrate a pressure of 10 Torr (1333.2 Pa) accurately. The reason why pressures for respective stages as shown in Table 3 are required is identical with that of calibrating the 1 Torr level vacuum gauge.  
         [0083]     Balance combinations for calibrating the 100 Torr level vacuum gauge will be described below. In view of the pressure transformation, 100 Torr corresponds to 13332.24 Pa, so that balance combinations for 1000 Pa, 2000 Pa, 3000 Pa, . . . , 12000 Pa, 13332.24 Pa are required to calibrate the 100 Torr level vacuum gauge. Balance combinations for such pressure stages are listed in Table 4.  
         [0084]     As can be seen from Table 4, it is possible to change pressures from 0 Pa to 14000 Pa in stage by appropriately combining prepared balances so as to calibrate the 100 Torr level vacuum gauge, it is also possible to calibrate a pressure of 100 Torr (13332.24 Pa) accurately. The reason why pressures for respective stages as shown in Table 4 are required is identical with that of calibrating the 1 Torr level vacuum gauge.  
                                 TABLE 4                       Pressure   Balance combination                                1000   Pa   1 g + 9 g + 90 g       2000   Pa   2 g + 18 g + 180 g       3000   Pa   1 g + 2 g + 9 g + 18 g + 90 g + 180 g       4000   Pa   4 g + 36 g + 360 g       5000   Pa   1 g + 4 g + 9 g + 36 g + 90 g + 360 g       6000   Pa   2 g + 4 g + 18 g + 36 g + 180 g + 360 g       7000   Pa   1 g + 2 g + 4 g + 9 g + 18 g + 36 g + 90 g +               180 g + 360 g       8000   Pa   8 g + 72 g + 720 g       9000   Pa   180 g + 720 g       10000   Pa   8 g + 72 g + 180 g + 720 g       11000   Pa   2 g + 18 g + 360 g + 720 g       12000   Pa   1 g + 2 g + 9 g + 18 g + 90 g + 360 g + 720 g       13000   Pa   4 g + 36 g + 180 g + 360 g + 720 g       13332.24   Pa (=1 Torr)   3.332 g + 8 g + 29.990 g + 72 g + 180 g +               299.902 g + 720 g       14000   Pa   1 g + 2 g + 4 g + 8 g + 9 g + 18 g + 36 g +               72 g + 90 g + 180 g + 360 g + 720 g                  
 
         [0085]     An actual calibrating method for vacuum gauge using the combination of balances and construction of the present invention will now be described below.  
         [0086]      FIG. 8   a  is a side cross-sectional view for showing an initial preparing step for calibrating respective vacuum gauges including an 1 Torr level, a 10 Torr level, and a 100 Torr level vacuum gauge, wherein every set of balance  210 ,  220 ,  230 ,  240 , and  250  is arranged on the corresponding balance mounting base  138 . Accordingly, a load of the balance has not been transferred to the standard pressure gauge.  
         [0087]      FIG. 8   b  shows a calibration step of an 1 Torr level vacuum gauge. The balance combination for applying 1 Torr (=133.32 Pa) is 2 g+8 g+3.332 g, as can be seen in Table 2. Accordingly, as shown in  FIG. 8   b,  a balance  225  having a mass of 2 g, a balance  245  having a mass of 8 g, and a balance  255  having a mass of 3.332 g are arranged on the corresponding balance mounting bases  138 , and remaining balances are maintained to be spaced from the balance mounting bases  138  by means of the lift arm  132 .  
         [0088]      FIG. 8   c  shows a calibration step of a 10 Torr level vacuum gauge. The balance combination for applying 10 Torr (=1333.2 Pa) is 1 g+3.332 g+9 g+29.990 g+90 g, as can be seen in Table 3. Accordingly, as shown in  FIG. 8   c,  a balance  215  having a mass of 1 g, a balance  213  having a mass of 9 g, a balance  211  having a mass of 90 g, a balance  255  having a mass of 3.332 g, and a balance  253  having a mass of 29.990 g are arranged on the corresponding balance mounting bases  138 , and remaining balances are maintained to be spaced from the balance mounting bases  138  by means of the lift arm  132 .  
         [0089]      FIG. 8   d  shows a calibration step of a 100 Torr level vacuum gauge. The balance combination for applying 100 Torr (=13332.24 Pa) is 3.332 g+8 g+29.990 g+72 g+180 g+299.902 g+720 g, as can be seen in Table 4. Accordingly, as shown in  FIG. 8   d,  a balance  255  having a mass of 3.332 g, a balance  245  having a mass of 8 g, a balance  253  having a mass of 29.990 g, a balance  243  having a mass of 72 g, a balance  221  having a mass of 180 g, a balance  251  having a mass of 299.902 g, and a balance  241  having a mass of 720 g are arranged on the corresponding balance mounting bases  138 , and remaining balances are maintained to be spaced from the balance mounting bases  138  by means of the lift arm  132 .  
         [0090]     In the description of the present invention, the rotating lead screw and the fixed transporting shaft are employed to elevate the transporting head and the lift arm upwardly and downwardly. However, this is only illustrative, and they can be elevated upwardly and downwardly by transforming the rotation force of the motor into linear elevation operation by means of employing a linear motor, a cam with cam shaft, a rack and pinion, and various link devices, and the like. Such mechanical transformations should be construed to be pertained to the scope of the present invention.  
         [0091]     Furthermore, it has been described that the calibration apparatus of the present invention can be used for an 1 Torr level vacuum gauge, a 10 Torr level vacuum gauge, and a 100 Torr level vacuum gauge concurrently. However, as is well known to those skilled in the relevant art, any of the pressure level to be calibrated can be omitted. For instance, the calibration apparatus can be modified to be used only in calibrating an 1 Torr level vacuum gauge and a 10 Torr level vacuum gauge by adjusting the mass and the number of the balances, and it can be also modified to be used only in calibrating a 10 Torr level vacuum gauge and a 100 Torr level vacuum gauge. Of course, such modifications will be pertained to the scope of the present invention.  
         [0092]     In addition, the transporting heads can be installed between the lead screws, and two transporting heads can be connected to one transporting shaft at different heights by providing three transporting heads. In this case, they will not interfere with each other because the transporting heads reciprocate at different positions.  
         [0093]     As described above, according to the calibration apparatus for vacuum gauge having combined use for an 1 Torr level, a 10 Torr level, and a 100 Torr level vacuum gauge of the present invention, it is possible to measure small pressures precisely, and calibrate the 1 Torr level, a 10 Torr level, and a 100 Torr level vacuum gauge by means of a calibration apparatus.  
         [0094]     Accordingly, it is possible to reduce calibration cost, and decrease required calibration time. It is also possible to calibrate various pressure levels of vacuum gauges quickly as the economic efficiency and effectiveness have been improved.  
         [0095]     Furthermore, it is possible to detect hysteresis and the like by applying identical pressure under an identical condition. Accordingly, repeating reproduction property is excellent.  
         [0096]     In addition, the calibration apparatus for vacuum gauge of the present invention can be installed on a table because its compact appearance. Accordingly, it is possible to calibrate the vacuum gauge with very high degree of precision and occupation of small space. For instance, the pressure gauge using Hg has been uneconomical in installment, operation and measurement owing to its large size.  
         [0097]     Although the present invention has been described in connection with the above described preferred embodiments, it should be understood that various modifications, additions and substitutions can be made by those skilled in the art without departing from the scope and spirit of the present invention disclosed in the accompanying claims.