INSTRUMENT FOR GRAVIMETRIC MOISTURE DETERMINATION WITH GLASS SHIELD

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is entitled to benefit of a right of priority under 35 USC §119 from European patent application 11183598.9, filed 30 Sep. 2011, the content of which is incorporated by reference as if fully recited herein.

TECHNICAL FIELD

The disclosed embodiments relate to a measuring instrument for the gravimetric determination of moisture content, particularly an instrument in which a glass shield protects a sample heating means.

BACKGROUND

The moisture content of a sample is determined by drying the sample and by manually determining its weight before and after the drying process. Due to the laborious procedures involved, this method is very expensive and error-prone.

Under certain conditions, the weight loss can also be determined during the drying process. For a given sample, the measured value for the weight decreases as a function of the temperature, the elapsed drying time, and the parameters of the testing compartment, according to a weight/time graph which asymptotically approaches the dry weight of the sample. The graph for the sample under examination can be determined through comparison experiments and expressed mathematically in the form of an approximation formula. Based on the available electronic capabilities, an appropriately equipped measuring instrument for the gravimetric determination of moisture content is able to calculate the moisture content of a sample from the measured parameters of the graph and the drying time and to indicate the moisture content on a display unit. With this method, it is no longer necessary for the material under test to be completely dried out, because sufficient information is obtained by determining the coordinates of two measurement points in the weight/time diagram.

As mentioned above, the change in the weight of a sample is essentially a function of the temperature, the elapsed drying time, and the parameters of the testing compartment. The instruments that are commercially available at this time are limited in their accuracy primarily because of the demanding requirements which have to be met by the testing compartment.

Normally, the sample is spread in a thin layer onto a flat sample receiver, for example a sample tray. The tray is arranged inside the gravimetric moisture determination instrument, extending preferably in a horizontal plane and parallel to the plane of the sample-heating means, in order to achieve a uniform heating of the sample.

Devices that are used as sample-heating means include a variety of radiation sources such as radiant heaters, microwave generators, halogen- and quartz lamps. As could be established by experiments, one of the main causes for the inaccuracy in the determination of measurement values in existing gravimetric moisture-determination instruments lies in the nature of the radiation sources being used and in their arrangement in the testing compartment.

A measuring instrument of the aforementioned kind for the gravimetric determination of moisture content is described in the European Patent EP 0 611 956 B1. In this instrument, the loading of the weighing pan occurs outside of the gravimetric moisture-determination instrument. To load and unload the sample, the balance which is arranged on a drawer-like carriage is slid out of the instrument housing. As a radiation source, a ring-shaped halogen lamp is being used which, in the operating state of the apparatus, is arranged above the sample receiver. Examples of further design configurations are published in EP 1850 110 A1. For example, a measuring instrument is disclosed which is opened up for loading through a horizontal swivel movement of a part of the housing. In a further embodiment, a part of the housing is swiveled in the vertical direction. Likewise, the measuring instruments disclosed in U.S. Pat. No. 7,851,712 B2 are opened for loading by vertically swiveling a part of the housing.

To protect the heating means, a glass shield can be arranged between the sample and the sample-heating means. This glass shield tends to get dirty. In the measuring instruments of the known state of the art, the glass shield can be accessed only with difficulty and is therefore rarely cleaned, which can cause errors in the results of the measurements.

It is therefore an object to provide a measuring instrument for gravimetric moisture determination which can be cleaned easily.

SUMMARY

This task is solved by an embodiment of the measuring instrument for gravimetric moisture determination as defined in the appended claims.

The measuring instrument for gravimetric moisture determination comprises a housing and a weighing device arranged inside the housing. The weighing device has a load receiver onto which a sample can be placed. The housing has a stationary housing part and a movable housing part. The movable housing part can occupy positions for measuring and for servicing, respectively, wherein in the measuring position, the stationary housing part and the movable housing part form an essentially enclosed testing compartment around the load receiver, and wherein in said testing compartment a heating means is arranged for the heating of a sample that can be placed on the load receiver. In the servicing position, the stationary housing part and the movable housing part are spaced apart from each other in such a way that the heating means is accessible for servicing. In the measuring position, a glass shield is arranged between the sample-heating means and the sample. The glass shield is arranged on the movable housing part and removable without the use of tools. Thus, the glass shield can easily be taken out and cleaned. The user or the service technician will need less time for this process and will therefore perform it more frequently.

The term “testing compartment” means a space which is enclosed by the housing of the measuring instrument and which can be opened and closed in order to bring in or take out a sample. Arranged inside the testing compartment are a sample receiver and a means for heating the sample. The sample receiver is connected to a gravimetric measuring instrument.

The term “housing part” in the present context is meant to include the elements of the instrument that are attached to it. Typically, the sample-heating means is arranged in the movable housing part while the weighing device, the sample receiver and the electronic module are arranged in the stationary housing part.

The measuring instrument can occupy a loading position where the stationary housing part and the movable housing part are spaced apart from each other in such a way that a sample can be put on the load receiver. By means of a position-shifting device, the movable housing part can be brought from the measuring position into the loading position. In the measuring position as well as in the loading position or in the servicing position, the movable housing part is located above the stationary housing part.

Advantageously, in the servicing position, the heating means and consequently also the glass shield are oriented essentially in a vertical position. As a result, the heating means is facing towards the user and is more easily accessible.

In one embodiment, the glass shield is connected to the movable housing part by means of a connection that can be released without tools. For servicing, the glass shield can simply be pulled out of the movable housing part.

In a further possible embodiment, the glass shield is connected to the movable housing part by means of components that can likewise be released without tools. These components can, for example, hold the glass shield clamped in a predefined position. It is also possible that the glass shield and the components are connected to each other by way of a spring and groove connection. The spring and groove connection can be released manually without the use of tools.

It is also possible to use holders. The holders can also serve to hold the glass shield in a defined position. In a possible embodiment, the glass shield can be held in a defined position between an upper holder and a lower holder, wherein at least one of the holders can be removed without tools. In this configuration, the upper holder is arranged on the side facing towards the sample-heating means. The lower holder is arranged on the side facing towards the sample receiver. The glass shield is held in place between the upper and the lower holder. Either the upper or the lower holder is removable without the use of tools. To uninstall the glass shield, the holder that is removable without a tool needs to be taken out. Subsequently, the glass shield can be removed without the need for a tool.

The glass shield as well as the upper and the lower holder can be slid into the movable housing part and positioned and held in their place by means of guide tracks that are arranged on the movable housing part. In the measuring position and/or loading position the guide tracks have an essentially horizontal orientation. In the servicing position, the guide tracks are oriented essentially in a vertical direction.

The holder that is removable without tools and/or the glass shield can be pulled in a controlled direction out of the movable housing part by means of at least one guide track. The guide track makes it easier for the user to remove or to install the glass shield and/or the holder that is removable without tools.

In the servicing position the guide track is oriented vertically. This makes it possible for the user to remove the glass shield and/or the holder that is removable without tools from the movable housing part through an upward-directed movement. Furthermore, the user has the holder, the glass shield and the sample-heating means directly in his view. This arrangement makes it easier for the user to take out the glass shield.

The removal of the glass shield and the holder is additionally facilitated by a service opening in the movable housing part. The service opening allows the glass shield and/or a holder to be taken out. Ideally, the service opening is arranged in the extension of the path of the guide track. This arrangement makes it possible to pull the glass shield and/or the holder out of the movable housing part through the service opening in a track-guided move.

The service opening is open in the servicing position, but closed in the measuring position and the loading position. In the measuring position and the loading position, the service opening is closed by a portion of the movable housing part. Accordingly, the opening does not exist when measuring or loading takes place. Thus, no contaminants can enter through the service opening into the measuring instrument during measuring and loading.

In a preferred embodiment, at least a part of an interior draft shield is arranged around the sample-heating means and the glass shield. A part of the interior draft shield serves as the upper holder for holding the glass shield in place. Thus, no additional holder is necessary for the glass shield. The interior draft shield is arranged on the movable housing part.

The measuring instrument further includes a light-screening barrier by means of which the direction of the heat radiation falling on the sample can be influenced. This light-screening barrier can serve simultaneously as the lower holder of the glass shield. The light-screening barrier is arranged on the movable housing part and can be taken out without using tools.

The sample-heating means can include for example a heater plate, a heating foil, a broadband light source, a monochromatic light source, a heat radiator, a heating coil, a Peltier element, or a microwave generator.

In an advantageous embodiment, the measuring instrument includes an electrical contact means with a first part and a second part. The first part of the electrical contact means is connected to the stationary housing part, and the second part of the electrical contact means is connected to the movable housing part. In the measurement position, an electrical connection exists by way of the first and the second part of the electrical contact means. In the loading position, the electrical connection between the first and the second part of the electrical contact means is interrupted.

Ideally, only the stationary housing part is directly connected to the electric grid, while the movable part is supplied with electricity only through the electrical contact means. This arrangement serves to ensure that the movable housing part receives electricity only while the instrument is in measuring position. In the loading position and in the servicing position, there is no voltage applied to the movable housing part. Consequently, the sample-heating means is not supplied with current during loading and servicing, and the danger of burn injuries to the user is reduced.

Ideally, the weighing device is arranged in the stationary housing part. In a preferred embodiment, the weighing device is arranged in a weighing compartment. The weighing compartment and the testing compartment are separated from each other by at least one vertical separating wall, wherein the latter has at least one passage opening through which a connecting member extends which serves to connect the weighing device to the sample receiver that is arranged in the testing compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

Details of the disclosed embodiments of the measuring instrument may be learned from the description of the embodiment illustrated in the drawings, wherein

FIG. 1, in a sectional view, shows a schematic representation of a measuring instrument in measuring position;

FIG. 2, in a sectional view, shows a schematic representation of the measuring instrument of FIG. 1 in loading position;

FIG. 3
a is a schematic representation of a further measuring instrument with a temperature sensor, wherein the latter is in measuring position;

FIG. 3
b is a schematic representation of the measuring instrument of FIG. 3a, wherein the temperature sensor is in the loading position;

FIG. 4 shows a perspective view of the measuring instrument in measuring position;

FIG. 5 shows the measuring instrument of FIG. 4 in loading position;

FIG. 6 shows the measuring instrument of FIG. 4 in servicing position;

FIG. 7 shows the measuring instrument of FIG. 6 in servicing position with partially removed glass shield and draft protector; and

FIG. 8 shows the movable housing part of the measuring instrument of FIG. 7 in servicing position without glass shield.

DETAILED DESCRIPTION

FIGS. 1 and 2 represent schematic, sectional views of a measuring instrument 10 in measuring position (FIG. 1) and in loading position (FIG. 2). The measuring instrument 10 has a housing 20 in which a testing compartment 30 is arranged. The housing 20 is subdivided into a movable housing part 22 and a stationary housing part 21. When the instrument is in use, the stationary housing part 21 is standing on a solid support surface. The movable housing part 22 is attached to the stationary housing part. To the rear, i.e. on the side of the testing compartment 30 that faces away from the user, a weighing device 40 is arranged in the stationary housing part 21. The movable housing part 22 is constrained on the stationary housing part 22 by means of a translatory-motion guide 24. The translatory-motion guide 24 is configured so that the movable housing part 22 maintains an essentially constant orientation during its movement from the measuring position into the loading position. In other words, during its movement the movable housing part 22 remains essentially parallel to the stationary housing part 21. The stationary housing part 21, which is configured as a hollow body, contains a weighing cell 43 and at least one electronic module 90 which are connected to each other by transfer means 52. The electronic module 90 includes at least one signal-processing module (not shown in detail) and in some cases also a controller- and/or regulator module. The weighing cell 43 has at least one stationary portion 41 and a load-receiving portion 42. State-of-the-art types of weighing cells include for example elastic deformation bodies carrying strain gauges, weighing cells that operate according to the principle of electromagnetic force compensation, weighing cells with oscillating strings, capacitative weighing sensors and the like. The stationary portion 41 of the weighing cell 43 is solidly connected to the stationary housing part 21. Arranged on the load-receiving portion 42 is a connecting member 47 through which a sample receiver 60 is connected to the load receiving portion 42 of the weighing cell 43. As shown in the drawing, a sample tray 61 with a sample 62 can be set on the sample receiver 60. If the sample receiver 60 is suitably configured, the sample 62 can of course also be put directly on the sample receiver 60.

The measuring instrument 10 as shown in FIG. 1 is in measuring position which means that the sample receiver 60 and the sample tray 61 sitting on it are inside the testing compartment 30. The stationary housing part 21 and the movable housing part 22 form an essentially enclosed testing compartment 30 surrounding the sample receiver 60. A heating means 70 is arranged essentially parallel to the plane of the sample receiver 60, so as to obtain as homogeneous a heat distribution as possible at least on the surface of the sample 62. It is also possible to arrange an additional heating means in the testing compartment 30 below the sample receiver 60 in order to expose the underside of the sample 62 to radiation. However, it is not absolutely necessary to arrange the heating means 70 parallel to the plane of the sample receiver 60. Depending on the sample 62 and on the measurement that is to be performed, it may also be advantageous to arrange the heating means 70 at an oblique angle to the sample receiver 60.

To allow the moisture given off by the sample 62 to escape from the testing department 30, the housing 20 has outlet vents 27 arranged at an appropriate location of the movable housing part 22, preferably above the heating means 70. To generate sufficient air circulation inside the testing compartment 30, there should further be air vent openings provided at appropriate locations.

The measuring instrument 10 in FIG. 1 is shown in measuring position. The stationary housing part 21 and the movable housing part 22 form an essentially enclosed testing compartment 30. The latter is essentially delimited at the top by the movable housing part 22 and at the bottom by the stationary housing part 21. The heating means 70 is arranged in the movable housing part 22. Ideally, the heating means 70 is mechanically connected to the movable housing part 22 through releasable plug-in connections. Thus, the heating means 70 can be uninstalled without much effort for cleaning or repair. Furthermore, with the use of plug-in connections the user of the measuring instrument 10 is able to select from different heating means with different functional characteristics. This enables the user to match the conditions inside the testing compartment to a specific sample 62.

The measuring instrument 10 includes an electronic module 90 which is arranged in the stationary housing part 21. The electronic module 90 has a variety of controller/regulator devices. Among others, the electronic module 90 also includes a controller/regulator device for the control and regulation of the heating means 70. A temperature sensor 80 which is illustrated schematically in the drawing serves to measure the temperature of the sample 62 and to deliver to the controller/regulator device 35 the information required for the regulation of the heating means 70. The controller/regulator device 35 is further connected to the weighing device 40, specifically to the electronic module 90, by means of at least one transfer means 52. The transfer means 52 serves for the transmission of electrical and/or electronic signals. As a result, the controller/regulator device 35 can receive signals from the electronic module 90. The measuring instrument 10 is supplied with power by means of an electrical connection 88. The electrical power connection 88 is arranged on the stationary housing part 21. Preferably, the electrical current is delivered only by way of the stationary housing part 21. Thus, the user or the service technician is not subjected to the risk of receiving an electric shock in the course of a servicing operation.

The controller/regulator device 35 and the temperature sensor 80 are connected to each other through a transfer means 51. Furthermore, the controller/regulator device 35 and the sample-heating means 70 are connected to each other through a further transfer means 53. The transfer means 51, 53 serve to transmit electrical and electronic signals between the respective apparatus components. During the measurement process, the temperature in the testing compartment 30 is measured by means of the temperature sensor 80. The temperature signal generated by means of the temperature sensor 80 is transmitted by way of the transfer means 51 to the controller/regulator device 35. For the controller/regulator device 35 the temperature signal is an input signal based on which the sample-heating means 70 is controlled. In the measurement position, the temperature sensor 80 is located between the sample receiver 60 and the sample-heating means 70. This arrangement makes it possible to obtain the temperature value that is relevant for the measurement. The temperature sensor could also be placed at a different location. However, the temperature values that are thereby obtained are less accurate in representing the heat level in the testing compartment. The temperature sensor 80 is arranged on a rod 81 which is fastened to the stationary housing part 21. The rod 81 is essentially rigid, with a first end and a second end. Arranged at the first end is the temperature sensor 80, while the second end is connected to the stationary housing part 21. Due to the fact that the second end is connected to the stationary housing part 21, the operation of the temperature sensor 80 does not require an electrical and/or electronic connection from the stationary housing part 21 to the movable housing part 22.

The transfer means 51 is arranged at or inside the rod 81. The rod 81 can be swivel on a fulcrum pivot 82. The fulcrum pivot 82 is at the second end of the rod 81 and has a substantially horizontal pivot axis 83.

The rod 81 and the fulcrum pivot 83 are arranged so that during the change from the measuring position to the loading position, the temperature sensor 80 moves along a circular path in a vertical plane. Arrangements are also possible where the circular path lies in a different, i.e. non-vertical plane. For example, the axis of the fulcrum pivot can be given an essentially vertical orientation, so that the temperature sensor 80 is constrained to a circular path in a horizontal plane during the change from the measuring position to the loading position.

In the measuring position, the rod 81 is force-biased by the spring tension of a spring element 84. When the movable housing part 22 is brought from the measuring position into the loading position, the rod 81 moves away from the sample receiver 60 under the elastic force of the pre-tensioned spring element 84. In the loading position, the temperature sensor 80 and the rod 81 are therefore not obstructing the access to the sample receiver 60, which facilitates the loading of the measuring instrument. Ideally, the spring element 84 is constituted by a torsion spring wherein the torque axis coincides with the axis of the fulcrum pivot 83. Of course, other spring elements could also be used, such as for example compression spring elements. In any case, the spring element needs to be arranged so that it is elastically biased in the measuring position while being unstressed or less biased in the loading position.

As the sample-heating means 70 is arranged in the movable housing part 22 and the controller- and regulator device 35 is arranged in the stationary housing part 21, the transfer means 53 has to transmit electrical and/or electronic signals from the stationary housing part 22 to the movable housing part 21. This can be accomplished for example with a flexible cable. However, due to the position shifts of the movable housing part 21, this cable would be subjected to bending cycles and therefore susceptible to wear.

This problem can be circumvented by using an electrical contact means with a first part 86 and a second part 87, wherein the first part 86 is connected to the movable housing part 22 and the second part 87 is connected to the stationary housing part 21. Under this concept, the first and the second part of the electrical contact means 86, 87 are arranged so that in the measuring position the first and second part 86, 87 form an electrical connection, and that in the loading position the electrical connection is interrupted. It is a significant advantage of this arrangement that in the loading position the sample-heating means 70 is not supplied with electricity. Ideally, the electronics for the control are arranged exclusively in the stationary housing part 22. The control of the sample-heating means 70 takes place only by way of the first and second electrical contact means 86, 87. Therefore, no connection is needed for the transmission of control signals to the movable housing part 21. This is a further reason for arranging the temperature sensor 80 on the stationary housing part 21. If the temperature sensor 80 were arranged on the movable housing part 22, it would be necessary to transmit signals between the stationary housing part 21 and the movable housing part 22. As a further advantage of the measuring instrument 10, the temperature can also be measured and registered in the loading position by means of the temperature sensor 80. Thus, it is for example possible to measure the ambient temperature during the loading process.

The electrical contact means 86, 87 include a plug-in connection where one of the two parts of the electrical contact means 86 is configured as a plug and the other part as a socket that cooperates with the plug. The direction of insertion of the plug connection is essentially vertical.

In FIG. 2 the measuring instrument 10 of FIG. 1 is shown in loading position. By means of a translatory-motion guide 24, the movable housing part 22 can be moved away from the stationary housing part 21, whereby the measuring instrument 10 is brought from the measuring position into the loading position. In this change of position, the movable housing part 22 undergoes in essence a purely translatory displacement. In the loading position the movable housing part 22 is located above the stationary housing part 21 and above the weighing device 40. The sample-heating means 70 in this position is located between the movable housing part 22 and the stationary housing part 21. This prevents accidental touching of the sample-heating means 70 which may be very hot.

In the change to the loading position, the temperature sensor 80 is moved upward and laterally away from the sample receiver 60. Thus, the temperature sensor 80 will not interfere with the loading of the sample receiver 60.

In the loading position, the electrical contact means 86, 87 is interrupted. There is no electricity flowing from the stationary housing part 21 to the movable housing part 22. Since the movable housing part 22 does not have a power connection of its own, no electric current is entering the movable housing part 22 in the loading position.

FIGS. 3
a and 3b illustrate a further measuring instrument 110 in a schematic representation. FIG. 3a shows the measuring instrument 110 in the measuring position, and FIG. 3b shows the same measuring instrument 110 in the loading position.

The measuring instrument 110 has a housing 120 with a stationary housing part 121 and a movable housing part 122.

When the instrument is in measuring position, the stationary housing part 121 and the movable housing part 122 together form an essentially enclosed testing compartment 130, in which the sample receiver 160 is located. Arranged above the sample receiver 160 is a sample-heating means 170. The sample-heating means 170 is solidly connected to the movable housing part 122. A temperature sensor 180 is arranged on a rod 181. The rod 181 has a first and a second end. Attached to the first end is the temperature sensor 180, while the second end is pivotally connected to the stationary housing part 121. In the measuring position of the instrument, the temperature sensor 180 is located above the load receiver 160 and underneath the sample-heating means 170. In loading position, the temperature sensor 180 is located essentially off to the side of the load receiver 160. This is accomplished with a design where the rod 181 is rigid and is connected to the stationary housing part 121 by means of a fulcrum pivot 182. Ideally, the axis 183 of the fulcrum pivot 182 is oriented horizontally. In measuring position, the rod 181 can be spring-biased by the elastic force of a spring element. When the movable part 122 is moved from the measuring position into the loading position, the rod 181 moves upwards and laterally in a circular arc under the biasing force of the spring element. In the measurement position, the spring element is preferably held in a pre-tensioned state by the movable housing part 122.

To obtain the most stable measurement results possible, there can be an interior draft shield arranged inside the testing compartment (see FIGS. 6-8). This interior draft shield is arranged so that it surrounds the sample receiver 160 and the sample-heating means 170, delimiting a nearly enclosed section of space. The interior draft shield can include an upper part 174 and a lower part 165. The upper part 174 is arranged on the movable housing part 122. The upper part 174 of the interior draft shield forms a cylindrical interior space which is open towards the sample receiver. Arranged inside this cylindrical interior space is the sample-heating means. The upper part of the interior draft shield can consist of a cylindrical circumference wall alone. However, it is advantageous if the cylinder has an upper end wall which is horizontally oriented in the measuring and in the loading position of the instrument. This end wall is preferably arranged above the sample-heating means 170. Ideally, the side of the end wall that faces towards the sample-heating means 170 is heat-reflecting. Consequently, a part of the heat that is being generated is reflected by the interior draft shield and used to heat the sample which is located on the sample receiver 160. The lower part 165 of the interior draft shield is arranged on the stationary housing part 121. The lower part 165 of the interior draft shield forms a cylindrical interior space which is open towards the sample-heating means 170. Arranged in this cylindrical interior space is the sample receiver 160. In measuring position, the interior space of the upper part 174 of the interior draft shield and the interior space of the lower part 165 of the interior draft shield form a chamber in which the sample-heating means 170 and the sample receiver 160 are located. The upper as well as the lower part of the interior draft shield 165, 174 can be made of one piece of material or assembled from several sections.

FIGS. 4, 5, 6, 7 and 8 illustrate an embodiment of the measuring instrument 210 in different positions. The measuring instrument 210 has all of the components that have already been covered in the description of the schematic drawings of FIGS. 1 and 2.

FIG. 4 shows the measuring instrument 210 in measuring position. As the housing 220 is closed in the measuring position, most of the components cannot be seen. The housing 220 has a stationary housing part 221 and a movable housing part 222. In measuring position, the stationary housing part 221 and the movable housing part 222 form an essentially enclosed testing compartment. The movable housing part 222 has outlet vent openings 227 which allow gases to escape from the testing compartment inside the housing 220 into the ambient atmosphere. Advantageously, in the measurement position of the instrument the outlet vent openings 227 are located on the topside of the movable housing part 222. Especially advantageous is an arrangement of the outlet vent openings 227 above the sample-heating means 170 which is likewise arranged inside the housing 220.

FIG. 5 shows the measuring instrument 210 of FIG. 4 in loading position. The movable housing part 222 has been brought from the measuring position into the loading position by a translatory movement. To enable this translatory movement, the movable housing part 222 is connected to the stationary housing part 221 by a translatory-motion guide 224. The translatory-motion guide 224 has two essentially parallel pivoting legs whose orientation defines the direction of the translatory movement of the movable housing part 222.

The stationary housing part 221 is of an elongated shape. The weighing device is largely enclosed by the stationary housing part 221. Only a sample receiver 260 which is connected to the weighing device protrudes laterally from the stationary housing part 221. Containers of various shapes such as sample trays, crucibles and the like can be put on the sample receiver 260. The stationary housing part 221 includes a portion that is located to the side of the sample receiver 260 that faces away from the user. Advantageously, in this portion the weighing device is arranged. In loading position, the movable housing part 222 is located above the stationary housing part 221, ideally above the portion that is located to the side of the sample receiver 260.

The movable temperature sensor 280 is arranged on a pivotally mounted rod 281. As described in the schematic representation of FIGS. 3a and 3b, the rod 281 is connected to the stationary housing part by means of a fulcrum pivot. The axis of the fulcrum pivot is likewise oriented horizontally, and the rod 281 is likewise elastically biased in the measuring position by means of a spring force. In the measuring position, the temperature sensor 280 is located between the sample-heating means 270 and the sample receiver 260. In the loading position, the temperature sensor 280 and the rod 281 are removed sideways and upward from the sample receiver 260. This makes it possible to load a sample on the measuring instrument 210 without the temperature sensor 280 standing in the way of the user.

The sample-heating means 270 is arranged in the movable housing part 222. During the measurement, the sample-heating means 270 becomes hot and thereby heats the sample which is arranged below the heating means on the sample receiver 260. An electric current is required for the heating. The stationary housing part 221 is therefore equipped with a power connector 288 which is arranged on the backside of the measuring instrument 210. The movable housing part does not have a power connection of its own. The electric current therefore has to be transmitted from the stationary housing part 221 to the movable housing part 222. This is accomplished with an electrical contact means which has a first part 286 and a second part 287. The first part 286 of the electrical contact means is connected to the stationary housing part 221, while the second part of the electrical contact means is connected to the movable housing part 222. The two parts 286, 287 of the electrical contact means are arranged so that in measuring position an electrical contact exists from one to the other and the sample-heating means 270 is supplied with electrical current. In the loading position, there is no contact through the electrical contact means 286, 287. The electrical contact is established automatically by the movement of the movable housing part 222. A pivotable, concentric plug connection of the kind used in water heaters has proven particularly suitable as electrical contact means. The pivotable, concentric plug connection is particularly robust and reliable in closing and opening an electrical contact. However, other configurations are likewise conceivable. Particularly suitable are plug/socket connections.

With this arrangement, an electrical connection exists in the measuring position by way of the first and second part of the electrical contact means 286, 287, while the connection between the first and second part of the electrical contact means 286, 287 is interrupted in the loading position. In the loading position, the heating means is therefore not under power and the risk of injury is therefore reduced. The second part of the electrical contact means 286 is covered up in FIG. 5 by the movable housing part 222 and is therefore not visible.

To reduce air turbulence in the testing compartment, an interior draft shield 265, 274 which surrounds the sample receiver 260 can be arranged inside the testing compartment. This draft shield 265, 274 is preferably designed so that it conforms to the outside contour of the sample tray and/or the outside contour of the sample-heating means 270. As the sample trays being used are normally round, it suggests itself to use an interior draft shield 265, 274 with a round contour shape. The interior draft shield can include an upper part 274 and a lower part 265. The upper part 274 is arranged on the movable housing part 222. The upper part 274 of the interior draft shield encloses a cylindrical interior space which is open towards the sample receiver. Arranged inside this cylindrical interior space is the sample-heating means 270. The upper part of the interior draft shield can consist of a cylindrical circumference wall. It is advantageous if the cylinder also has at least a partial boundary surface above the sample receiver, preferably a cylinder end wall. This surface is arranged preferably above the sample-heating means 270. Ideally, the side of the end wall that faces towards the sample-heating means 270 is heat-reflecting. Consequently, a part of the heat that is being generated is reflected by the interior draft shield and used to heat the sample which is located on the sample receiver 260. In addition, the end wall can have openings, so that gases can escape into the outside atmosphere from the testing compartment through the openings in the end wall and outlet vent openings 227 in the housing 220. However, it is also possible that the end surface has no openings.

The lower part 265 of the interior draft shield is arranged on the stationary housing part 221. The lower part 265 of the interior draft shield forms a cylindrical interior space which is open towards the sample-heating means 270. Arranged in this cylindrical interior space is the sample receiver 260. In measuring position, the interior space of the upper part 274 of the interior draft shield and the interior space of the lower part 265 of the interior draft shield form a chamber in which the sample-heating means 270 and the sample receiver 260 are located. The upper as well as the lower part of the interior draft shield 265, 274 can be made of one piece of material or assembled from several sections.

To set a sample tray in place in the testing compartment, it is possible to use a sample tray holder 266. The sample tray holder 266 has a handle 267 and seating surfaces 268 for the sample tray. During the transfer of the sample tray, the rim of the latter rests on the seating surfaces 268. During the measurement, the sample tray rests only on the sample receiver 260 and the sample tray holder 266 does not touch the sample tray. In particular, the weight of the sample tray holder 266 is not received by the weighing device.

In FIG. 6 the inventive measuring instrument 210 of FIGS. 4 and 5 is shown in servicing position. To arrive at the servicing position, a portion of the movable housing part 222 has been swiveled about an essentially horizontal pivot axis 225 from the loading position into the servicing position. The sample-heating means 270 is arranged in the pivoting portion of the movable housing part 222 and is swiveled together with the pivoting portion of the movable housing part 222 during the change into the servicing position. As a result, the components in the movable housing part 222 are easily accessible for servicing. Arranged in the upper housing part 222 is the sample-heating means 270. During the measurement process, the sample-heating means 270 is protected by a glass shield 272. Surrounding the sample-heating means 270 is the upper part 274 of the interior draft shield.

To give a clearer view of the position and configuration of the sample-heating means 270, of the glass shield 272 and of the interior draft shield 274, the measuring instrument 220 is shown in FIG. 7 with the upper part 274 of the interior draft shield partially removed, and in FIG. 8 the movable housing part 222 is shown without glass shield 272.

Arranged on the cylinder end surface of the interior draft shield 274 is a reflecting surface which serves to reflect the heat radiation generated by the sample-heating means 270. The reflection can also be achieved with a suitable reflective material of the cylinder end surface or a reflective coating of the cylinder end surface. An essentially circular light-screening barrier 273 serves to concentrate the heat rays generated by the sample-heating means 270.

In servicing position, the sample-heating means 270 is oriented vertically. At least a portion of the upper part 274 of the interior draft shield is attached to the movable housing part 222 by means of a plug-in connection, wherein the plug-in direction is essentially vertical in the servicing position. The glass shield 272 is clamped between the light-screening barrier 273 and a portion of the upper part 274 of the interior draft shield 274. To remove the glass shield, only a part of the interior draft shield 274 needs to be pulled out of the plug-in connection. Subsequently, the glass shield can be removed simply by pulling it out, without using a tool. The easy removal of the glass shield 272 is of particular advantage, because it facilitates the taking-out and cleaning of the glass shield 272 which is prone to get dirty.

The glass shield 272 and/or a portion of the upper part 274 of the interior draft shield can be pulled out of the movable housing part in a controlled direction by means of a guide track 275. In the servicing position, the guide track 275 has an essentially vertical orientation.

The removal of the glass shield 272 is additionally facilitated by a service opening 223. The service opening 223 is an access opening in the movable housing part 222 which is open only in the servicing position but not in the measuring position or in the loading position. An inadvertent touching of the sample-heating means is thereby prevented, which reduces the risk of burn injuries. The service opening is realized with a two-part configuration of the movable housing part. According to this concept, the two parts of the movable housing part are designed so that in the move to the servicing position a portion of the movable housing part does not participate in the swivel movement. This non-swiveled portion clears the access to the service opening in the swiveled portion of the movable housing part.

The width of the service opening 223 is advantageously equal to or larger than the width of the glass shield 272. This allows the glass shield to be removed easily. The service opening 223 is arranged at a right angle to the plug-in direction of the upper part of the interior draft shield 274 and in the extension of the path of the guide track 275. As a result of this arrangement, the glass shield 272 can easily be pulled out of the service opening 223.

The upper part of the interior draft shield 274 can be composed of several components. Advantageously, the portion that faces towards the service opening 223 can be removed without tools. This requires the service opening 223 to be wider than the upper part of the interior draft shield 274.

The sample-heating means 270 can be attached to the movable housing part 222 in a variety of ways. For example, the sample-heating means 270 could be fastened to the movable housing part 222 by means of screws or with a plug-in connector. If a plug-in connector is used, the sample-heating means 270 can easily be pulled out for servicing. Ideally, this plug-in connection could be designed so that the plug insertion is directed essentially perpendicular to the plane of the service opening 223.

The sample-heating means 270, the light-screening barrier 273, the glass shield 272 and the upper part of the interior draft shield 274 have openings which, together with the outlet vent openings 227 allow the vapors and/or volatile substances escaping from a sample to be vented into the outside atmosphere. The openings are therefore arranged so as to ensure the direct venting of gases that escape from the sample. It is of advantage if these openings provide a direct line of vision to the sample that is located on the sample receiver 260, whereby a visual inspection of the measurement process is made possible.

In place of the interior draft shield 274 and the light-screening barrier 273, one could use other suitable attachment devices to hold the glass shield 272 in place.

Since the glass shield 272 is easy to take out, it can be cleaned more easily and quickly by the user or the service technician. Ideally, the glass shield 272 is made so that it can be cleaned in a conventional washing machine without damage.

The embodiments presented herein show, partially in schematic form, measuring instruments for the gravimetric determination of moisture content with different properties and features. For clarity's sake, the different properties and features have been presented in different examples of embodiments, but it is also possible to realize some, several, or all of the described features and properties in one and the same measuring instrument.

INSTRUMENT FOR GRAVIMETRIC MOISTURE DETERMINATION WITH GLASS SHIELD

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CPC

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