Balance with housing capable of being vacuumized

Abstract

The invention relates to a balance (10) comprising: an evacuable housing (12) having a bottom (121), a side wall (122) and a top (123); and a weighing device (14) arranged in the housing (12), the weighing device having a weight carrier (142), a weighing system (141) and a weighing sensor, the weighing system (141) having a base fixed relative to the housing and a load receptacle connected to the weight carrier (142), the load receptacle is coupled in a vertically movable manner to the base via a steering gear assembly hinged to the base, and in a force-transmitting manner to the load cell fixed relative to the base via a lever assembly. The invention is characterized in that a vertical column (124) protrudes upward from the center of the bottom (121) of the housing (12), on the free end of which a base of the weighing system (141) is fixed.

Description

Technical Field

[0001] The present invention relates to a balance, comprising:

[0002] A vacuumable housing having a bottom, side walls and a top, and

[0003] A weighing device is arranged in the housing, the weighing device having a weighing object carrier, a weighing system and a weighing sensor,

[0004] The weighing system comprises a base fixed relative to a housing and a load receiver connected to a weighing object carrier, wherein the load receiver is coupled to the base in a vertically movable manner via a steering gear assembly hinged on the base, and is coupled to a weighing sensor fixed relative to the base in a force-transmitting manner via a rod assembly on the other hand. Background Art

[0005] Precision balances, for example, precision balances used as so-called mass comparators for comparative weight measurement for calibration or verification purposes are well known to those skilled in the art. The tolerable measurement uncertainty for such precision balances is extremely low and strictly standardized (for example, according to OIML R111.1). In order to reduce this measurement uncertainty accordingly, it is necessary to completely suppress potential external interference parameters as much as possible. One of the interference parameters is the density of the air surrounding the test weight, because each weight block is subject to a buoyancy force that reacts against the gravity of the weight related to the density of its surrounding air. Therefore, it is known that weight measurements that should meet the highest precision standards are performed under vacuum conditions. For this reason, the actual weighing device (and of course the weight block to be weighed with it) is arranged in an airtight housing that is evacuated before measurement. Therefore, the influence of the above-mentioned lift can be completely eliminated.

[0006] However, evacuating the housing is associated with additional problems. Depending on the degree of evacuation, i.e., the negative pressure in the housing relative to the balance environment, considerable forces act on the housing, which can lead to mechanical stresses and distortions, which in turn can be transmitted to delicate elements of the weighing system of the actual weighing device, which are fastened to the housing with their base. Additional measurement uncertainties can therefore arise as a result.

[0007] In the context of this specification, a measuring system is understood to be a complex mechanism consisting of rods and deflectors, by means of which a load holder, into which the weight of the test weight is introduced during the weighing process, is coupled on the one hand to a base fixed relative to the housing of the weighing system in a vertically displaceable manner and on the other hand to a load cell fixed relative to the base. In precision balances, which usually work according to the electromagnetic compensation principle (EMK balances), the load cells mentioned are typically moving coil assemblies, wherein the coil current required to compensate for the deflection caused by the weight acting on the load holder is used as a measure of the weight that has an effect. The specific nature of the load cell is not relevant in the context of the present invention. However, in any case, such weighing systems and their longitudinally extending, extremely delicate and partially folded rod assemblies, deflector assemblies and articulated assemblies are extremely susceptible to mechanical stresses and distortions.

[0008] An additional problem associated with evacuating the housing is the temperature drop associated with the reduction in gas pressure. This temperature drop may cause changes in the dimensions in the weighing system due to thermal expansion, which in turn may produce further measurement uncertainties. Summary of the invention

[0009] The object of the present invention is to improve a balance having an evacuable housing in such a way that the described measurement uncertainty associated with evacuation is reduced.

[0010] This object is achieved in conjunction with the features of the preamble of claim 1 in that a vertical column projects upward from the center of the bottom of the housing, to the free end of which the base of the weighing system is fastened.

[0011] Preferred embodiments of the invention are the subject matter of the dependent claims.

[0012] Conventionally, the fixed connection of the weighing system relative to the housing is achieved in such a way that the base of the weighing system is directly fixed to the bottom surface of the housing. The present invention is different from this. Instead, the connection is carried out indirectly by means of a stable column that protrudes upward from the center of the housing bottom. The distortion of the housing bottom (in particular, the distortion is manifested as a bending) is deflected into a purely vertical movement by means of the column. Therefore, the weighing system whose base is fixed to the top of the column is also only subject to vertical displacements that act the same for all its components. In this respect, internal stresses in the weighing system that could lead to the above-mentioned measurement uncertainties are eliminated. The person skilled in the art recognizes that it is not important whether the (plate-shaped) base of the weighing system is directly fixed to the top of the column or whether the free end of the column carries a platform that protrudes beyond the outer periphery of the column and on which the base of the weighing system is fixed. What is decisive is to reduce the (indirect) contact of the base of the weighing system with the housing bottom to a minimum area preset by the cross section of the column, within which stresses in the horizontal plane are not transmitted, but only harmless vertical movements are transmitted.

[0013] This solution works particularly well when the bottom of the housing is designed in the shape of a disk and is surrounded by a side wall in an annular manner. This rotational symmetry of the bottom ensures that the camber caused by the negative pressure only leads to a vertical rise of the column (and thus the weighing system) and excludes any lateral tilting.

[0014] A solution directed to the same aspect provides that the bottom and the side walls of the housing are constructed in one piece from a consistent material. In particular, the bottom and the side walls of the housing can be rotationally symmetrically machined from a material block, in particular a metal block, preferably by means of milling, drilling and / or electro-erosion. Alternatively, however, additive manufacturing techniques are also conceivable. In any case, the aim of this solution is that any deformations that occur during evacuation will become rotationally symmetrical, so that these deformations are generally deflected into a purely vertical movement of the column according to the invention.

[0015] However, since it is impossible to produce the weighing system rotationally symmetrically, it is inherently associated with unavoidable asymmetries. Therefore, in a preferred embodiment of the invention, it is provided that the weighing system protrudes beyond the outer periphery of the column at least in the area of ​​the load container and, if present, also beyond the edge of the support plate that carries the weighing system, and that the weighing object carrier, which is constructed as a pendulum weighing pan, is suspended and articulated on the load container below the load container. In other words, the actual weighing device is therefore constructed according to the concept of a bottom pan balance. Thus, in the case of a suitable articulated coupling of the weighing object carrier to the load container, it can be ensured that the weight to be measured is always accurately vertically introduced into the load container. In addition, this solution provides for optimal utilization of the free space generated by the column according to the invention in the housing below the weighing system, which free space is thus transformed into a weighing space.

[0016] In precision balances with evacuable housings, the replacement of test weights with restoration of ventilation and re-evacuation is always accompanied by a significant time consumption. It is therefore known that a test weight chamber with an automatic load changer is provided within the evacuable housing, which allows a plurality of test weights from the chamber to be weighed in sequence without having to restore ventilation and re-evacuate the housing during this period. In the context of the present invention, it is considered particularly advantageous in this respect that a rotating table with a test weight chamber arranged concentrically with the column is supported on the column in a rotatable manner. The rotating table can have a plurality of locations for storing test weights distributed on its periphery. In order to load the weighing object carrier, the test weight currently to be weighed can be rotated to the weighing object carrier and transferred from the chamber to the weighing object carrier by means of a suitably constructed load transfer device. This transfer can be achieved in particular by vertical adjustment of the rotating table and / or an element arranged on the rotating table. The specific design structure of this load transfer device is irrelevant in the context of the present invention. However, it will be appreciated by a person skilled in the art that, in the context of precise measurements, any movement or mobility should be minimized and therefore the distances and gaps should be dimensioned as small as possible, so that changes in the relative height position between the weighing object carrier and the rotating table will be disadvantageous due to distortions of the housing. However, due to the invention and its improvements described here, these problems need not be feared. As explained at the outset, according to the invention, all distortions of the housing are deflected into vertical movements of the column. Therefore, the rotating table supported on the column itself rises or falls with the column and therefore its relative height position relative to the weighing system fixed on the top of the same column or the weighing object carrier connected to the weighing system fixedly at a relative height does not change at all.

[0017] However, from the perspective of the actual design structure, it may be equally or even more advantageous to support the turntable on the outside, that is, on the inner wall of the housing, although this may lead to a vertical relative movement of the turntable and the weighing object carrier when the housing is evacuated; however, a stable support of the turntable radially further outward is significantly easier to achieve in terms of design structure than radially further inward, that is, on a column. Therefore, the person skilled in the art must weigh the suboptimalities of the actual implementation against each other in individual cases.

[0018] It is generally considered advantageous to minimize the space of the housing to be evacuated as much as possible. Therefore, in a particularly preferred embodiment of the invention, it is provided that the side walls of the housing do not extend upwardly beyond the column or at least extend upwardly beyond the column at a height less than that of the weighing system, and the weighing system is assembled into a corresponding recess at the top of the housing. In other words, the rotational symmetry of the housing, which is described above as being preferred, is interrupted in a targeted manner in the region of the housing top. However, this is harmless. In this region, due to the non-rotationally symmetrical shape of the weighing system itself, there is already a symmetry interruption anyway, so that the asymmetry of the housing top is only matched to this symmetry interruption. In addition, the housing top does not come into contact with the weighing system, so that any distortion of the top that may occur will not have a negative impact on the weighing system and thus on the measurement result.

[0019] As already mentioned above, the housing, which is preferably made of metal, is designed with thick walls in its particularly preferred embodiment. This serves not only to maximize the mechanical stability, but also to maximize the thermal capacity and thermal conductivity of the housing, which in turn leads to a reduction in temperature differences within the housing when evacuating the housing. Therefore, after evacuating the housing, the stable temperature required for the measurement will be reached more quickly than in a thin-walled housing. Accordingly, a series of measurements can be carried out more quickly in succession.

[0020] The surface of the housing is preferably unpainted and polished. This prevents evaporation of the pigment in a vacuum inside the housing and thus prevents corresponding contamination of the test weight. In this way, the reflectivity can be maximized outside the housing, so that electromagnetic radiation acting on the housing from the outside causes less or slower temperature changes inside the housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Further details and advantages of the invention are obtained from the following detailed description and the accompanying drawings.

[0022] in:

[0023] Figure 1 A schematic diagram of a balance according to the invention is shown. DETAILED DESCRIPTION

[0024] Figure 1 A balance 10 according to the invention is shown in a highly schematic diagram. The balance 10 shown comprises an evacuable housing 12 and a weighing device 14 arranged in the housing 12. In the embodiment shown, the balance 10 is fastened via feet 16 to a vibration-isolating base 18. The specific type of fastening of the balance 10 to the base 18 and the manner of its vibration isolation are not important in the context of the present invention.

[0025] The housing 12 is essentially formed by a bottom 121, which can be designed in particular in the form of a disk. Around the edge of the bottom 121, a side wall 122 is raised in an annular manner, which in the embodiment shown is connected to the bottom 121 in one piece and with the same material. The housing 12 is provided with a top 123 designed as a removable cover, which can be fixed in a gas-tight manner on the free edge of the side wall 122. In this way, a cavity surrounded by walls is generated on all sides, which cavity can also be called a weighing space 124.

[0026] The weighing space 124 can be evacuated via evacuation means (not shown). A person skilled in the art will understand that absolute evacuation is impossible in practice and therefore recognizes that evacuation here means generating a significant negative pressure in the weighing space relative to the housing surroundings.

[0027] According to the invention, in the center of the bottom 121, a vertical column 125 protrudes into the weighing space 124. In the embodiment shown, the column 125 is designed integrally with the bottom 121 and of the same material.

[0028] A support plate 126 is fixed to the top of the column 125 , ie to its free end, which supports the column 125 on one side beyond the outer circumference and into the weighing space 124 .

[0029] A weighing system 141 of the weighing device 14, in particular a base of the weighing system, is fixed to the carrier plate 126. A weighing object carrier 142, which is designed as a pendulum weighing pan, is articulated to a load container (not shown separately) of the weighing system 141. In the embodiment shown, the articulated coupling of the weighing object carrier 142 at the load container passes through a recess in the carrier plate 126. The weighing object carrier 142 is suspended in a freely swinging manner next to the column 125 in the weighing space 124. A test weight 20 is shown on the weighing pan of the weighing object carrier 124.

[0030] The negative pressure generated by the evacuation of the weighing space 124 generates a significant force acting on the wall of the housing 12. Figure 1 As shown in the figure by the dashed lines to a significantly exaggerated degree, these forces can lead to temporary elastic deformations of the housing wall. In particular, in the area of ​​the disk-shaped bottom 121, this deformation is realized essentially as a rotationally symmetrical arch. This leads to an inconsistent distribution of elevations and inclinations over the entire bottom (these elevations and inclinations lead to distortions of the weighing system fixed to the bottom in a planar manner). However, in the center of the bottom 121, the arch only acts as a vertical elevation. As a result, the column 125 arranged in the center of the bottom 121 moves in a purely vertical direction. As a result, the weighing device 14 fixed to the column 125 also moves purely vertically. This vertical movement is Figure 1This vertical movement involves the entire weighing device 14, including the weighing system 141 of the weighing device, the weighing object carrier 124 of the weighing device (and the test weight 20), and the weighing device in the vertical direction. Figure 1 Therefore, in the case of evacuation, all these elements will not perform relative movements with respect to each other, so that the deformation of the housing 12 caused by evacuation will not have any influence on the measurement result of the weighing device 14.

[0031] In the embodiment shown, in order to minimize the volume of the weighing space, the side wall 122 does not extend beyond the upper edge of the weighing system 141. Instead, the top 123 of the housing 12 has a recess 127 corresponding to the shape of the weighing system 141 in the area of ​​the weighing system 141, into which the weighing system 141 extends without contact.

[0032] Of course, the embodiments discussed in the detailed description and shown in the drawings represent only illustrative examples of the invention. In view of the present disclosure, a wide range of variation possibilities are provided to the skilled person. In particular, the skilled person may arrange other components within the weighing space 124. In particular, a test weight compartment, for example in the form of a rotating table supported on a column 125, and an automated load changing device may be arranged within the weighing space 124. However, for the sake of clarity, Figure 1 These elements are not shown.

[0033] Reference numerals list

[0034] 10 Balance

[0035] 12 Shell

[0036] 121 bottom

[0037] 122 side wall

[0038] 123 Top

[0039] 124 weighing space

[0040] 125 columns

[0041] 126 Loading plate

[0042] 127 recess

[0043] 14Weighing equipment

[0044] 141 weighing system

[0045] 142 weighing object carrier

[0046] 16 feet

[0047] 18 Base

[0048] 20 test weights

Claims

1. A balance (10), comprising: A vacuum-capable housing (12) having a bottom (121), a side wall (122) and a top (123), and A weighing device (14) is arranged in the housing (12), the weighing device having a weighing object carrier (142), a weighing system (141) and a weighing sensor, The weighing system (141) comprises a base fixed relative to a housing and a load container connected to the weighing object carrier (142); the load container is coupled to the base via a steering gear assembly hinged on the base in a vertically movable manner, and is coupled to a weighing sensor fixed relative to the base via a rod assembly in a force-transmitting manner. It is characterized in that a vertical column (124) extends upward from the center of the bottom (121) of the housing (12), and the base of the weighing system (141) is fixed on the free end of the column.

2. The balance (10) according to claim 1, It is characterized in that The bottom (121) of the housing (12) is configured in a disk shape and is surrounded in an annular manner by the side wall (122).

3. A balance (10) according to any one of the preceding claims, It is characterized in that The bottom (121) and the side wall (122) of the housing (12) are constructed in one piece with the same material.

4. A balance (10) according to any one of the preceding claims, It is characterized in that The free end of the column (125) carries a bearing plate (126) extending beyond the outer periphery of the column, and the base of the weighing system (141) is fixed to the bearing plate.

5. A balance (10) according to any one of the preceding claims, It is characterized in that The weighing system (141) protrudes beyond the outer periphery of the column (125) and, if present, also beyond the edge of the carrying plate (126) at least in the area of ​​the load container, and a weighing object carrier (142) designed as a pendulum weighing pan is articulated on the load container in a suspended manner below the load container.

6. The balance (10) according to claim 5, It is characterized in that A rotating table with a test weight compartment arranged concentrically with the column is supported on the column (125) in a rotatable manner.

7. A balance (10) according to any one of the preceding claims, It is characterized in that The side wall (122) of the housing (12) does not extend upward beyond the column (125) or at least extends upward beyond the column at a height less than that of the weighing system (141), and the weighing system (141) is assembled into a corresponding recess (127) of the top (123) of the housing (12).

8. A balance (10) according to any one of the preceding claims, It is characterized in that The housing (12) is made of a preferably thick-walled material and has unpainted, polished surfaces on the outside and inside.

Images