Method and apparatus for forming a reference pressure within a chamber of a capacitance sensor

The present invention relates to a capacitive pressure transducer. More specifically, the present invention relates to improved methods and devices for generating a reference pressure within the chamber of a capacitive pressure transducer assembly.

FIG. 1A shows a cross-sectional view of the conventional capacitive pressure transducer assembly 10 after assembly. FIG. 1B is an exploded view of the upper housing 40, the diaphragm 56, and the lower housing 60 of FIG. 1A. Simply put, the capacitive pressure transducer assembly 10 contains a body that forms an internal cavity. A relatively thin and flexible ceramic diaphragm 56 divides the internal cavity into a first sealed internal chamber 52 and a second sealed internal chamber 54. As described in detail below, the diaphragm 56 is attached so that the diaphragm 56 is curved, moved or deformed according to the pressure difference between the chambers 52 and 54. The transducer assembly 10 provides a parameter that represents the degree of curvature of the diaphragm, thus this parameter indirectly represents the pressure difference between chambers 52, 54. The parameter provided by the transducer assembly 10 representing the pressure difference is the capacitance between the diaphragm 56 and one or more conductors located in the upper housing 40.

The capacitive pressure transducer assembly 10 includes a ceramic upper housing 40 and a ceramic lower housing 60. The upper housing 40 is generally cylindrical when viewed from above, between the upper surface 41, the central lower surface 47, the annular shoulder 42 having the lower surface 42a, and the central lower surface 47 and the annular shoulder 42. It forms an annular channel 43 that is located. The lower surface 42a of the annular shoulder 42 is substantially coplanar with the central lower surface 47. The upper housing further forms an opening (or passage) 48 extending from the upper side to the lower side through the housing 40. The metal conductor 46 is arranged on the center of the lower surface 47.

The diaphragm 56 is generally a circular thin diaphragm having an upper surface 57 and a contralateral lower surface 59. The metal conductor 58 is arranged at the center of the upper surface 57 of the diaphragm 56. The diaphragm 56 and the upper housing 40 are arranged so that the conductor 46 of the upper housing 40 is placed so as to face the conductor 58 of the diaphragm 56. The diaphragm 56 is connected to the upper housing 40 by a high temperature airtight seal (or joint) 70. The seal 70 is located between the lower surface 42a of the annular shoulder 42 of the upper housing 40 and the corresponding annular portion of the surface 57 of the diaphragm 56. Once sealed, the upper housing 40, seal 70 and diaphragm 56 form the reference chamber 52. A reference pressure is generated and maintained within the reference chamber 52. Aperture 48 provides an entrance or entrance path to reference chamber 52.

Generally, the circular lower housing 60 forms a central opening 64 and an upwardly projecting annular shoulder 62 having an upper surface 62a. The upper surface 62a of the shoulder 62 of the lower housing 60 is joined to the corresponding portion of the lower surface 59 of the diaphragm 56 by a hot airtight seal (or joint) 76. The seal 76 can be placed and incorporated in the same manner as the seal 70. Once sealed, the process chamber 54 is formed by the lower housing 60, the seal 76, and the surface 59 of the diaphragm 56.

The pressure pipe 66 having the inlet passage 68 is coupled to the lower housing 60 by a seal, for example, so that the inlet passage 68 is aligned with the opening 64 of the lower housing 60. Therefore, the process chamber 54 is in fluid communication with the external environment through the opening 64 and the inlet passage 68. During operation, the capacitive pressure transducer assembly 10 measures the pressure in this external environment.

Conductors 46, 58 of the capacitive pressure transducer assembly 10 form a parallel plate of the variable capacitor C. As is well known, C = Aε_rε₀/ d, C is the capacitance between the two parallel plates, A is the common area between the parallel plates, ε₀Is the permittivity of the vacuum, ε_rIs the relative permittivity of the material that separates the parallel plates (eg ε in the case of vacuum)_r= 1), d is the axial distance between the parallel plates (that is, the distance between the parallel plates measured along the normal of the parallel plates). Therefore, the capacitance given by capacitor C is a function of the axial distance between conductor 46 and conductor 58. Since the diaphragm 56 moves or bends up and down according to the change in the pressure difference between the chambers 52 and 54, the capacitance given by the capacitor C also changes. At any point in time, the capacitance provided by capacitor C represents the instantaneous pressure difference between chambers 52 and 54. A known electrical circuit (eg, a "tank" circuit characterized by a resonance frequency that is a function of the capacitance given by the capacitor C) is used to measure the capacitance given by the capacitor C and represent the pressure difference. It can generate electrical signals. Conductors 46, 58 can be made of a wide range of conductor materials, such as gold or copper, and can be manufactured by known thin or thick film processes or other known manufacturing methods. When a thin film process is used, the thickness of the conductors 46, 48 may be, for example, about 1 μm.

The diaphragm 56 is often made from aluminium oxide. However, other ceramic materials such as ceramic single crystal oxide materials may be used. Capacitance sensors with ceramic components are disclosed in US Pat. Nos. 5,920,015 and 6,122,976.

As described above, changes in the pressure difference between chambers 52 and 54 cause the diaphragm 56 to bend, thereby changing the gap between conductors 46 and 58. The pressure difference can be measured by measuring the change in the gap. However, the gap can also be affected by factors unrelated to pressure. For example, the gap can be affected by temperature changes. Because the components of the transducer assembly 10 can be made from a wide variety of materials, each with a unique coefficient of thermal expansion, temperature changes in the ambient environment cause the diaphragm 56 to move closer to or away from the conductor 46. there is a possibility. The advantage is that the change in the gap due to the temperature change has different characteristics from the change in the gap due to the change in the pressure difference. It is known that a second conductor (not shown) arranged adjacent to the conductor 46 is included on the lower surface 47 of the upper housing 40 in order to compensate for the change in the gap caused by the change in the ambient temperature. ing. In such an embodiment, the conductors 46 and 58 form a parallel plate of the variable capacitor C1, and the conductor 58 and the second conductor form a parallel plate of the variable capacitor C2. The two capacitors C1 and C2 can be used in a known manner to reduce the sensitivity of the transducer to temperature changes.

The upper housing 40 is a surface parallel to the surface formed by the conductor 58 (ie, diaphragm 56) when the lower surface 47 and any of the conductors placed on it have the same pressure in the chambers 52, 54. Aligned to be placed in. As mentioned above, the capacitance formed by the conductors 46, 58 depends on the gap (ie, the axial distance) that exists between these opposing conductors. Relatively small (eg, 0.0004 inch (10-12 μm)) gaps are partly due to the thickness of the seal 70 and the shape and configuration of the upper housing 40 (eg, the amount by which the lower surface 42a deviates from the plane, ie, if. If there is, it depends on the deviation from the lower surface 47).

In operation, the capacitive pressure transducer assembly 10 is commonly used as an absolute pressure transducer. In this form, the reference chamber 52 has virtually zero pressure, eg 10^-8Exhaust to less than Thor, after which the reference chamber 52 is sealed. The reference pressure then becomes a baseline, from which the pressure in the process chamber 54 is determined. To maintain the reference chamber 52 at virtually zero pressure, the converter assembly 10 includes a tube 80, a cover 82, a holding wire 86, a screen 88 and a getter element 84. As shown in FIGS. 1A and 1B, the screen 88 supports the getter element 84 within the hollow portion of the tube 80, while the holding wire 86 presses and holds the getter element 84 against the screen 88. The hollow portion of the tube 80 is placed above the opening 48 of the upper housing 40, which allows the getter element 84 to communicate fluidly with the reference chamber 52. In addition to supporting the getter element 84, the screen 88 also prevents particles that adversely affect the operation of the diaphragm 56 from passing into the reference chamber 52.

The bottom end of the tube 80 is connected to the upper surface 41 of the upper housing 40 around an opening 48 by a high temperature airtight seal 92. The cover 82, on the other hand, is attached to the upper end of the tube 80 by a cold airtight seal 94. The seals 92, 94 and the seal 70 located between the shoulder 42 of the upper housing 40 and the diaphragm 56 all assist in maintaining the reference pressure generated in the reference chamber 52. The high temperature seal 92 is made of hot glass material, while the low temperature seal 94 is made of low temperature glass material. To form the hot seal 92, a hot glass material is adhered to the bottom edge of the tube 80, the corresponding sealing area of the surface 41, or both. The hot glass material is melted and a force perpendicular to the top surface 41 of the upper housing 40 is applied between the tube 80 and the upper housing 40, after which the hot glass material is cooled (ie solidified) to a high temperature. The airtight seal 92 is formed. The cold seal 94 is similarly formed between the top edge of the tube 80 and the corresponding sealing region of the cover 82. The melting temperature of the hot glass material of the hot seal 92 is higher than the melting temperature of the cold glass material of the cold seal 94. To obtain different melting temperatures, the glass materials of the seals 92, 94 may be composed of different materials or may be of common material in different amounts. The melting temperature of the high temperature seal 92 is higher than the melting temperature of the high temperature seals 70 and 76, and the melting temperature of the high temperature seal 70 and 76 is higher than the melting temperature of the low temperature seal 94.

The getter element 84 is composed of a material that, when activated, acts to effectively absorb any gaseous impurities present in the sealed reference chamber 52. Therefore, when activated, the getter element 84 helps maintain the reference pressure at ultra-high vacuum levels for extended periods of time (eg, 10 years or more).

The ultra-high vacuum pressure, or substantially zero pressure, is a convenient and useful reference pressure, but other reference pressures can be used. After a reference pressure is generated in the chamber 52, a pressure tube 66 can be connected to a fluid source (not shown) to measure the pressure of this fluid. By connecting the pressure tubes 66 in this way, the fluid whose pressure is measured is sent to the process chamber 54 (and the lower surface 59 of the diaphragm 56). The center of the diaphragm 56 moves or curves up and down according to the pressure difference between the chambers 52 and 54, which changes the capacitance of the capacitor C. Since the instantaneous capacitance of capacitor C represents the position of diaphragm 56, the transducer assembly 10 can measure the pressure in chamber 54 relative to the reference pressure generated in chamber 52.

The accuracy of the capacitive pressure transducer assembly 10 depends on the accuracy with which the reference pressure in the reference chamber 52 can be generated and maintained. In other words, if the actual pressure in the reference chamber 52 deviates from the intended and designed reference pressure, the performance of the capacitive pressure transducer assembly 10 will be reduced accordingly.

Each step of generating a reference pressure in the reference chamber 52, activating the getter element 84, and sealing the cover 82 against the tube 80 is generally a capacitive pressure conversion. The last few steps performed when manufacturing the vessel assembly 10. Therefore, the upper housing 40 is connected to the diaphragm 56 with the high temperature seal 70, the lower housing 60 is connected to the diaphragm 56 with the high temperature seal 76, and the pressure tube 66 is connected to the lower housing 60 around the opening 64. Each step of doing and joining the tube 80 (with the screen 88, getter element 84 and holding wire 86) to the surface 41 of the upper housing 40 around the opening 48 with a hot seal 92 is usually It should have already been completed before the reference pressure was generated.

To generate a reference pressure within the reference chamber 52, the reference chamber 52 typically undergoes a burnout and exhaust process, after which the cover 82 is sealed against the tube 80. The reference chamber 52 is "burned out" by heating the inner surfaces that form the reference chamber 52, including the faces of the cover 82, tube 80, and housing 40 that communicate fluidly with the reference chamber 52, and the chamber 52 is , The reference chamber 52 is "exhausted" by suction in an ultra-high vacuum. Burnout heat evaporates contaminants such as volatiles and moisture that may be present on these inner surfaces. On the other hand, the exhaust vacuum sucks the evaporated pollutants and gas from the reference chamber 52 to the outside. Since the cover 82 is not yet sealed in the tube 80, contaminants and gases are drawn out of the reference chamber 52, the opening 48 and the hollow portion of the tube 80. While the burnout and exhaust processes are complete and the vacuum pressure is maintained, the cover 82 is sealed in tube 80 with a cold seal 94 to generate a reference pressure within the reference chamber 52.

2A and 2B show conventional methods and devices used to generate a reference pressure within the reference chamber 52 of the capacitive pressure transducer assembly 10. Figure 2A shows the entire burnout and exhaust process. On the other hand, FIG. 2B shows the entire process in which the cover 82 is sealed on the top edge of the tube 80. The device includes a vacuum enclosure 93 that forms an internal vacuum chamber 95. With reference to FIG. 2A, the cold sealing material 94a is placed on the top edge of the tube 80. The semi-finished transducer assembly 10, i.e. the transducer assembly in which the cover 82 is not yet sealed in the tube 80, is then placed in the vacuum chamber 95. [For clarity, pressure tube 66 has been omitted from Figure 2A, Figure 2B and some of the other drawings thereafter. However, the pressure tube 66 is generally coupled to the lower housing 60 before the assembly is placed in the vacuum chamber 95. ] After the converter assembly 10 is placed in the vacuum chamber 95, the vacuum enclosure 93 is placed in the oven (not shown), the vacuum source (not shown) is coupled to the vacuum chamber 95, and the reference chamber 52 Burnout and exhaust process begins. During the burnout and exhaust process, which can last for more than 20 hours, the transducer assembly 10 is heated to a temperature of about 250 ° C, 10^-8An ultra-high vacuum pressure of about Thor (or less) is generated in the vacuum chamber 95. In FIG. 2A, burnout and exhaust of reference chamber 52 (and opening 48 and tube 80) is indicated by an arrow extending upward from reference chamber 52 through opening 48 and upward through the tip of tube 80. Has been done.

After the burnout and exhaust of the reference chamber 52 is complete, the cover 82 is coupled to the tube 80 by a cold seal 94. The cover 82 is attached to and sealed in the tube 80 without opening the vacuum enclosure 93 to maintain vacuum in the reference chamber 52. Therefore, as seen in FIG. 2A, the cover 82 is attached to the end of the rod 96 that penetrates into the vacuum chamber 95 of the vacuum enclosure 93 before the burnout and exhaust processes are initiated. When the burnout and exhaust process is complete, the rod 96 can be moved to bring the cover 82 into contact with the cold sealing material 94a located at the top of the tube 80.

The cold sealing material 94a forming the cold seal 94 does not melt during the burnout and exhaust processes. That is, the burnout temperature is generally set to be equal to or lower than the melting temperature of the low temperature sealing material 94a. In addition, the burnout and exhaust processes must not damage the seals already formed within the transducer assembly 10 (eg, high temperature seals 70, 76, 92). Therefore, the burnout temperature must not exceed the melting temperature of these seals.

A high temperature movement seal 99 (eg, gasket) is placed on the vacuum housing 93 where the rod 96 penetrates the vacuum housing 93. The high temperature movement seal 99 serves to allow the rod to move freely up and down and at the same time maintain the pressure present in the vacuum chamber 95 of the vacuum housing 93.

Before starting the burnout and exhaust process, the cover 82 is attached to the end of the rod 96 by the cold seal 98. The melting temperature (ie, melting point) of the cold seal 98 is lower than the melting temperature of the cold sealing material 94a and higher than the burnout temperature, so it does not melt during the burnout and exhaust processes. The rod 96 extends through the high temperature motion seal 99 and, along with the cover 82, is aligned with the tube 80 of the transducer assembly 10.

Then, referring to FIG. 2B, after the burnout and exhaust processes are completed, the rod 96 / cover 82 is in contact with the cold sealing material 94a while the pressure in the vacuum chamber 95 is maintained. Can be lowered. The temperature in the vacuum chamber 95 then rises (as instructed by the oven) to melt the cold sealing material 94a. Further, this temperature rise melts the low temperature seal 98 and activates the getter element 84. In order to form the cold airtight seal 94 between the cover 82 and the tube 80, the temperature in the vacuum chamber 95 is lowered until the cold sealing material 94a solidifies. On the other hand, the cold seal 98 is sufficiently melted and the rod 96 is pulled away from the transducer assembly 10. Once the cold seal 94 is formed (and thus the reference pressure in the reference chamber 52 is generated), the temperature in the vacuum chamber 95 drops to ambient temperature, after which the vacuum source is removed and the assembled converter assembly 10 is removed from the vacuum chamber 93.

FIG. 3 shows in more detail the conventional burnout, exhaust and sealing processes of the devices and methods of FIGS. 2A and 2B. In Figure 3, the x-axis of the process flow represents time and the y-axis represents temperature in degrees Celsius. Before starting the burnout and exhaust process, in step A of the process flow, the cover 82 is attached to the rod 96 via the cold seal 98, and the converter assembly 10, the cover 82 and the rod 96 are placed in the vacuum chamber 95. It is placed (Fig. 2A). During steps A B, the temperature inside the vacuum chamber 95 rises to a burnout temperature of 250 ° C and the pressure is 10^-8It drops to the exhaust pressure of Thor. Steps A B are completed in 3 hours. After the burnout temperature and exhaust pressure have been achieved (step B), in steps B C, the reference chamber 52 is burned out and exhausted in 20 hours. Immediately before reaching step C, the rod 96 and cover 82 are lowered to bring the cover 82 into contact with the cold sealing material 94a located on the top edge of the tube 80. When the burnout and exhaust steps are completed (step C), in steps C D, the temperature in the vacuum chamber 95 rises to 475 ° C, which melts the cold sealing material 94a and the cold seal 98. Steps C D last for 3 hours. Then, in steps D E, the vacuum chamber 95 is maintained at 475 ° C for 30 minutes to ensure that the cold sealing material 94a and the cold seal 98 are sufficiently melted. Then, in steps E F, the temperature in the vacuum chamber 95 is lowered to 400 ° C. for 2 hours, which solidifies the low temperature sealing material 94a to form the low temperature airtight seal 94. The cold seal 98 has a melting point of 400 ° C. or less, so the cold seal 98 maintains a molten state during steps E F. Just before reaching step F, rod 96 is lifted away from cover 82 (Figure 2B). Finally, the temperature and pressure in the vacuum chamber 95 are brought to ambient conditions for 4 hours, and in steps F G, the assembled pressure converter assembly 10 is removed from the vacuum chamber 95 of the vacuum enclosure 93. Is done. As shown in Figure 3, the traditional burnout, exhaust and sealing process can be completed in 32 and a half hours.

The methods and devices described above do not necessarily ensure that an accurate reference pressure is generated in the reference chamber 52 of the capacitive pressure transducer assembly 10. For example, in a vacuum enclosure 93 utilizing a rod 96 and a high temperature motion seal 99, 10^-8It is extremely difficult to create and maintain an ultra-high vacuum of toll (or less). The reason for this is that the presence of the high temperature movement seal 99 tends to impair the pressure integrity of the vacuum enclosure 93. Also, accurate control of the position and orientation of the cover 82 and tube 80 during the rod actuation fitting process is difficult and costly. If the cover 82 is not properly aligned or oriented with respect to the tube 80 during the fitting process, the integrity of the cold seal 94 may be compromised or the cold seal 94 may fail altogether. There is also sex.

Therefore, there is a need for methods and equipment to accurately generate the reference pressure in the reference chamber of the capacitive pressure transducer assembly.<patcit num="1"><text>U.S. Pat. No. 5,920,015</text></patcit><patcit num="2"><text>U.S. Pat. No. 6,122,976</text></patcit>

<p> The present invention relates to methods and devices for accurately generating a reference pressure in a reference chamber of a capacitive pressure transducer assembly.</p>

<p> The pressure transducer includes a cover and a housing that forms a reference chamber and an opening. A meltable encapsulant material is placed on at least one of the cover and housing. The device includes a pressure chamber that can rotate between the first and second positions and a guide that can be attached to the transducer near the opening. The guide portion forms an internal space. A cable can be used to rotate the pressure chamber between the first and second positions. Actuator motors and actuator rods can be used alternately to rotate the pressure chamber. A pressure source connected to the pressure chamber creates the desired pressure in the pressure chamber, while a heater (eg, an oven) selectively heats the pressure chamber to a sufficiently high temperature to melt the encapsulating material. Can be done.</p><p> The cover is aligned within the guide space and the guide is attached to the transducer near the opening. The converter, cover and guide are located in the pressure chamber, the pressure chamber rotates to the first position, pressure is generated in the pressure chamber through the pressure source, and the chamber is heated to burn out unwanted material. To do. After a reference pressure is generated in the reference chamber, the pressure chamber rotates to a second position, where gravity causes the cover to move towards an opening in space. The heater then heats the pressure chamber to melt the encapsulating material. Upon cooling, the sealing material forms a seal that seals the reference pressure within the reference chamber of the transducer.</p><p> The device may include a heavy body such as a ball arranged in the space of the guide portion.</p><p> By utilizing a device having a guide and a rotatable pressure chamber, the methods and devices of the present invention can accurately position and orient the cover during the sealing process of the reference chamber. Moreover, the methods and devices of the present invention do not require the use of high temperature exercise seals to maintain pressure in the pressure chamber.</p><p> The various objects, features and advantages of the present invention can be fully understood with reference to the following detailed description of the present invention when considered in conjunction with the following drawings. In the drawings, similar reference numerals identify similar components. The drawings below are for illustration purposes only and are not intended to limit the invention. The scope of rights of the present invention is described in the following claims.</p>

The present invention relates to methods and devices that accurately generate a reference pressure within a reference chamber of a capacitive pressure transducer assembly. The present invention can create an ultra-high vacuum in the vacuum chamber to facilitate the burnout and exhaust process of the converter assembly, and during the reference chamber sealing process, the opening cover is delivered and fitted. Can be controlled. Further, the present invention can maintain an ultra-high vacuum in a vacuum chamber without using a high temperature motion seal.

FIG. 4A shows a side view of an exemplary device 100 configured according to the present invention. FIG. 4B shows a front view of the device 100. The device 100 is composed of a vacuum housing 110 and a support assembly 120. The vacuum housing 110 forms an internal vacuum chamber, which will be described in detail below. A capacitive pressure transducer assembly 10 that is burned out, exhausted and sealed is secured within the internal vacuum chamber of the vacuum enclosure 110. The support assembly 120 supports the vacuum enclosure 110 when the capacitive pressure transducer assembly 10 is burned out, exhausted and sealed, and more specifically, the vacuum enclosure 110 and the capacitive type disposed therein. The pressure transducer assembly 10 and can be rotated while these processing steps are being performed.

The vacuum housing 110 includes a metal lower flange 112 and a metal upper housing 114. The vacuum housing 110 also includes left and right pins 136 coupled to the upper housing 114 and a vacuum port (not shown) connected to one end of the vacuum line 138. The other end of the vacuum line 138 is connected to a vacuum pump (not shown) that sucks ultra-high vacuum. The pins 136 form a rotating shaft 240, which allows the vacuum enclosure 110 to rotate when supported by the supporting assembly 120. Since the vacuum port is located near the left pin 136, that is, near the axis of rotation 240, the vacuum line 138 minimizes movement and curvature as the housing 110 rotates. The vacuum enclosure 110 also includes a cable (or wire) 116 having one end connected to the rear of the lower flange 112. When the vacuum housing 110 is held in the support assembly 120, i.e. by pins 136, the cable 116 is operated to place the vacuum housing 110 diagonally forward and downward (FIGS. 7A and 7B) and rearward. It can be rotated to an upright position (Fig. 8A and Fig. 8B).

The support assembly 120 includes a base 126, left and right support brackets 132, two lower supports 122 and two upper supports 124. The support bracket 132, the lower support 122, and the upper support 124 are all mounted on the surface of the base 126. The base 126 includes an anterior end, a posterior end and opposite lateral ends. As is apparent in FIGS. 4A and 4B, the support bracket 132 is located near the opposing lateral ends of the base 126, and the upper support 124 is near the rear end of the base 126. It is located inside. The lower support 122, on the other hand, is located inside the upper support 124 near the anterior end of the base 126. Each support bracket 132 has a slot (or hole) 134 capable of accommodating the pin 136. Each lower support 122 has a distal end 122a and each upper support 124 has a distal end 124a. The vacuum housing 110 is held in the support assembly 120 by fitting the pins 136 of the upper housing 114 into the slots 134 of the support bracket 132. By grooving and adjusting the slot 134, the pin 136 can be accommodated to facilitate mounting and dismounting of the vacuum housing 110.

After the capacitive pressure transducer assembly 10 is placed in the vacuum enclosure 110 and the vacuum enclosure 110 is held in the support assembly 120, the device 100 is placed in an oven (not shown) and the vacuum line 138 is vacuumed. Connected to the mouth. To operate the cable 116 at a point outside the oven, the opposite end of the cable 116 is routed between the support brackets 132 to exit through an access port provided in the oven. ..

As described in more detail below, when the vacuum enclosure 110 is in the upright position (as shown in FIGS. 4A and 4B), the lower flange 112 of the vacuum enclosure 100 is distal to the upper support 124. Above the edge 124a. However, as the vacuum enclosure 110 rotates forward (as shown in FIGS. 7A and 7B), the upper enclosure 114 is placed on the distal end 122a of the lower support 122.

FIG. 5, which depicts a cross-sectional side view of the vacuum enclosure 110, shows some additional components of device 100 and shows how the capacitive pressure transducer assembly 10 is secured within the vacuum enclosure 110. ing. As is apparent in FIG. 5, the vacuum enclosure 110 also includes a copper sensor support 210 that secures the burnout, exhaust and sealed transducer assembly 10. The transducer assembly 10 can be secured to the sensor support 210 by tightening screws (not shown), or a wide range of other types of fixation suitable for temporarily fastening the transducer assembly 10 to the sensor support 210. By means, it can be fixed to the sensor support 210. The transducer assembly 10 secured to the sensor support 210 typically has a cold sealing material 94a that is placed on the top edge of the tube 80 and the corresponding sealing surface of the cover 82.

The device 100 further includes a cylindrical guide assembly 300, a ball 320 and a copper wool 330. The ball 320 is located in the hollow portion of the guide assembly 300. As described in more detail below, the guide assembly 300 is temporarily coupled to the tube 80 and, along with the balls 320, guides the cover 82 towards the top edge of the tube 80 during the sealing process. The ball 320 is made of a high temperature and high density material such as tungsten carbide or silicon nitride. The copper wool 330 placed between the guide assembly 300 and the upper housing 114 forms a heat transfer path between the upper housing 114, the guide assembly 300 and the transducer assembly 10.

After the transducer assembly 10 is secured within the sensor support 210, the sensor support 210 is coupled to the lower flange 112, fitted with the ball 320, the guide assembly 300 and the copper wool 330, after which the lower flange 112 is on top. It is coupled to the housing 114. After assembly, the lower flange 112 and the upper housing 114 form an internal vacuum chamber 200.

To ensure the airtightness of the vacuum chamber 200, a temporary airtight copper seal is provided between the lower flange 112 and the upper housing 110. A vacuum port (not shown) allows fluid communication between the vacuum line 138 and the vacuum chamber 200. During the burnout, exhaust and sealing steps, the external vacuum pump exhausts the vacuum chamber 200 to ultra-high vacuum pressure through the vacuum line 138 and the vacuum port.

FIG. 6A shows the cylindrical guide assembly 300 in more detail, while FIG. 6B shows a cross section of the guide assembly 300 and how the balls 320 are arranged within the hollow portion of the guide assembly 300. ing. The cylindrical guide assembly 300 forms a hollow cylindrical interior space 316 with a closed distal end 312 and an open proximal end 314. The ball 320 is placed in space 316 of the guide assembly 300 and is free to move in the direction of or away from the distal end 312 and the proximal end 314 of the guide assembly 300, depending on the orientation of the guide assembly 300. To prevent the ball 320 in space 316 from moving excessively laterally (ie, moving perpendicular to the line drawn between the distal end 312 and the proximal end 314), the diameter of the ball 320 is space. It almost matches the diameter dimension of 316. That is, the diameter of the ball 320 is slightly smaller than the diameter of the space 316. In one exemplary embodiment, for example, the ball 320 has a diameter of 0.5000 ± .0001 inches and the space 316 has a diameter of 0.505 ± .002 inches. The diameters of the balls 320 and the space 361 are sized appropriately, taking into account all the thermal expansion effects that occur during the burnout and exhaust process.

The interior space 316 of the guide assembly 300 is also sized to accommodate the cover 82 and tube 80 that are temporarily placed within the space 316. The tube 80 and cover 82 typically have the same radial dimensions. Therefore, the radial dimension of the space 316 is formed to be slightly larger than the radial dimension of the cover 82 and the tube 80.

The cylindrical guide assembly 300 further includes a series of holes 310 arranged radially throughout the guide assembly 300 and a series of tightening screws 318 located near the proximal end of the guide assembly 300. The tightening screw 318 is used to temporarily secure the guide assembly 300 (along with the balls 320 placed therein) to the tube 80 during the burnout, exhaust and sealing steps. The hole 310 serves as a fluid passage between the interior space 316 of the guide assembly 300 and the vacuum chamber 200. Therefore, during the burnout and exhaust steps, i.e., when the cover 82 is not yet sealed in the tube 80, an opening 48 and a hollow portion of the tube 80 and a hole 310 are provided between the reference chamber 52 and the vacuum chamber 200. There is a fluid passage through.

FIG. 7A is a side view showing how the vacuum enclosure 110, guide assembly 300, and ball 320 of device 100 are oriented during the burnout and exhaust process. FIG. 7B shows an enlarged side view showing the orientation and arrangement of the tube 80, the cover 82, the assembly guide 300, and the ball 320 of FIG. 7A more accurately. As described above, prior to fixing the transducer assembly 10 within the sensor support 210, a cold sealing material 94a is placed on the top edge of the tube 80 and the corresponding sealing area of the cover 82. After the transducer assembly 10 is secured within the sensor support 210 and the vacuum chamber 200 is sealed and secured within the support assembly 120, the vacuum enclosure 110 is such that the vacuum enclosure 110 is at the distal end of the lower support 122. Rotate counterclockwise, i.e. forward, until it rests on 122a (as shown in Figure 7A). The position of the distal end 122a is such that when the housing 110 rotates, the ball 320 and the cover 82 located in the internal space 316 of the guide assembly 300 move away from the tube 80 in the direction of the distal end 312 of the guide assembly 300. It is positioned to move. Therefore, sufficient rotation of the vacuum enclosure 110 can ensure that a gap (ie, a fluid passage) between the cover 82 and the tube 80 is present during the burnout and exhaust process. When the transducer assembly 10 is raised to the desired burnout temperature and sucked to create an ultra-high vacuum pressure in the vacuum chamber 200, the transducer assembly 10 burnout and exhaust treatment is initiated. As indicated by the arrows in FIG. 7B, the reference chamber 52 of the converter assembly 10 passes contaminants and gases through the opening 48 (not shown) and the tube 80 and the hole 310 of the guide assembly 300 through the assembly 10. Exhaust by exiting and sucking into the vacuum chamber 200. Contaminants and gases are then further aspirated from the vacuum chamber 300 by an external vacuum pump through the vacuum port and vacuum line 138.

The cable 116 can be operated to rotate the vacuum housing 110 counterclockwise. For example, by applying a load to the vacuum housing 110, when the cable 116 sags, the vacuum housing 110 can be rotated counterclockwise, that is, forward.

At the end of the burnout and exhaust process, the reference pressure in the reference chamber 52 is sealed in the chamber by sealing the cover 82 in the tube 80. FIG. 8A is a side view showing which direction the vacuum housing 110, the guide assembly 300, and the ball 320 of the device 100 are oriented during the cover sealing process. FIG. 8B shows an enlarged side view that more accurately depicts the orientation and placement of the tube 80, cover 82, guide assembly 300, and ball 320 of FIG. 8A. To seal the cover 82 on the tube 80, the vacuum housing 110 of the device 100 rotates clockwise, i.e. to the rear upright position, by pulling the cable 116 attached to the rear of the lower flange 112. (As shown in Figure 8A). Cable guidance (not shown), such as sliding wheels or other types of devices or guides, can be used to facilitate the operation of cable 116. When the vacuum housing 110 is pulled to an upright position, the lower flange 112 of the vacuum housing 110 rests on the distal end 124a of the upper support 124 of the support assembly 120. The upright position does not have to be exactly vertical. Instead, it is convenient to position the distal end 124a of the upper support 124 so that it tilts slightly backwards as the vacuum housing 110 rotates. This reduces the possibility that the vacuum enclosure 110 will inadvertently rotate in the direction of the distal end 122a of the anterior lower support 122 if the cable 116 is loosened.

As the vacuum enclosure 110 rotates to an upright position, gravity causes the ball 320 to move toward the proximal end 314 of the guide assembly 300, which causes the cover 82 to engage the tube 82, and more specifically, the bottom of the cover 82. The cold sealing material 94a placed on the side comes to join with the cold sealing material 94a placed on the upper end of the tube 80. Therefore, when in this position, the weight of the ball 320 and the weight of the cover 82 provide a contact force between the cover 82 and the tube 80 in the contact surface region of the cold sealing material 94a. The temperature in the oven is raised and cold sealed while the ultra-high vacuum is maintained in the vacuum chamber 200 to seal the cover 82 on the tube 80, i.e. to form the cold seal 94. The two layers of material 94a are melted and fused together. This temperature rise also serves to activate the getter element 84 located within the tube 80. After the layers of the low temperature encapsulant material 94a have been sufficiently melted and fused together, the temperature drops below the melting point of the low temperature encapsulant material 94a and upon cooling a cold airtight seal 94 is formed between the cover 82 and the tube 80. (Fig. 8B). When the seal 94 is formed by closing the last fluid passage existing between the reference chamber 52 and the external environment, i.e. the vacuum chamber 200, a reference pressure is generated in the reference chamber 52.

When the seal 94 is formed, the oven and vacuum pump are powered off, the completed converter assembly 10 is removed from the vacuum enclosure 110, and the guide assembly and balls 320 are removed from the converter assembly 10. The device 100 can then be used to process another transducer assembly 10.

Device 100 can be configured to process multiple transducer assemblies 10 at once. Instead of the cable 116, an actuator rod (s) with an actuator motor are advantageously used to control the direction of rotation of the vacuum enclosure 110. Further, the methods and devices described herein relate to a transducer assembly 10 that measures absolute pressure and utilizes a getter element or the like, but using the methods and devices of the present invention, various gauge pressure transducer assemblies. A reference pressure can also be generated in the reference chamber of.

FIG. 9 shows in more detail the burnout, exhaust and sealing processes of the present disclosure. In Figure 9, the x-axis of the process flow represents time and the y-axis represents temperature in degrees Celsius. Prior to the start of the burnout and exhaust steps, in step A of the process flow, the cover 82, ball 320, guide assembly 3000 and pressure transducer assembly 10 are placed in the vacuum chamber 200 of the vacuum enclosure 110, as shown. As shown in 7A and FIG. 7B, the vacuum chamber 110 rotates counterclockwise (forward). During steps A B, the temperature inside the vacuum chamber 200 is raised to a burnout temperature of 250 ° C and the pressure is 10 for 3 hours.^-8It can be lowered to the exhaust pressure of Thor. After the burnout temperature and exhaust pressure have been achieved (step B), the reference chamber 52 is burned out and exhausted in steps B C for 20 hours. Immediately before reaching step C, the vacuum enclosure 100 rotates clockwise (backward) to an upright position, as shown in FIGS. 8A and 8B. When rotated to the upright position, the movement of the ball 320 causes the cover 82 to move in the direction of the tube 80, bringing the two layers of cold sealing material 94a into contact with each other. Upon completion of the burnout and exhaust steps (step C), the temperature in the vacuum chamber 200 is raised to 475 ° C in steps C D, which melts the two layers of cold sealing material 94a. Steps C D last for 3 hours. The vacuum chamber 200 is then maintained at 475 ° C for 30 minutes in steps D E to ensure that the layers of cold encapsulating material 94a are well melted together. Finally, for four and a half hours, the temperature and pressure in the vacuum chamber 200 reached ambient conditions, after which the assembled pressure converter assembly 10 was stepped E G into the vacuum chamber 200 of the vacuum chamber 110. Is removed from.

The burnout of the present disclosure, by removing the intermediate temperature drop portion of the conventional method, where the cold seal 94 must be formed while keeping the cold seal 98 in a molten state (steps E F in FIG. 3). The exhaust and sealing process can be completed in just 31 hours. Therefore, in addition to accurately generating the reference pressure in the reference chamber, the present disclosure also advantageously provides the time required to perform the burnout, exhaust and sealing processes of the pressure transducer assembly 10. It can also be shortened.

Although various embodiments incorporating the teachings of the present invention have been shown and described in detail herein, one of ordinary skill in the art will readily devise many other modified embodiments incorporating these teachings. can do.

<figref num="1A">It is sectional drawing of the conventional capacitance sensor.</figref><figref num="1B">It is a partially enlarged sectional view of the conventional capacitance sensor of FIG. 1A.</figref><figref num="2A">FIG. 5 illustrates conventional methods and equipment used to generate a reference pressure within a reference chamber of a capacitive pressure transducer assembly.</figref><figref num="2B">FIG. 5 illustrates conventional methods and equipment used to generate a reference pressure within a reference chamber of a capacitive pressure transducer assembly.</figref><figref num="3">It is a process flow for generating a reference pressure in a reference chamber of a transducer assembly by the conventional method and apparatus of FIGS. 2A and 2B.</figref><figref num="4A">FIG. 5 is a side view of an apparatus configured by the present invention for generating a reference pressure in a reference chamber of a capacitive pressure transducer assembly.</figref><figref num="4B">It is a front view of the apparatus of FIG. 4A.</figref><figref num="5">It is a partial cross-sectional side view of the device of FIGS. 4A and 4B, showing the internal components of the device, and showing how the pressure transducer assembly is arranged.</figref><figref num="6A">It is a figure which shows the frame assembly constructed by this invention.</figref><figref num="6B">It is sectional drawing of the frame assembly of FIG. 6A.</figref><figref num="7A">It is a figure which shows one step of the exemplary method of generating a reference pressure in a reference chamber of a capacitive pressure transducer assembly by this invention.</figref><figref num="7B">It is an enlarged view further showing how the step of FIG. 7A is executed.</figref><figref num="8A">FIG. 5 illustrates another step in an exemplary method of generating a reference pressure within a reference chamber of a capacitive pressure transducer assembly according to the present invention.</figref><figref num="8B">It is an enlarged view further showing how the step of FIG. 8A is executed.</figref><figref num="9">A process flow for generating a reference pressure in a reference chamber of a transducer assembly by the methods and devices of the present disclosure.</figref>