Sensor device for measuring the mass flow rate of liquid hot melt adhesives

Abstract

To provide a sensor device for measuring a mass flow rate of a liquid hot-melt adhesive having a modularized and reversibly connectable configuration.SOLUTION: A sensor device comprises: a component having a flow path of a hot-melt adhesive; a first temperature measuring device; a second temperature measuring device; a heater for heating the second temperature measuring device; and a control unit for controlling the heater and measuring a mass flow rate. The first temperature measuring device and the second temperature measuring device are attached to a sensor block. The sensor block is removably connected to a sensor support. The sensor support is removably closed by a closing element on the opposite side of the sensor block. Each of the first temperature measuring device and the second temperature measuring device is planar and flat in a direction of flow of the hot-melt adhesive. The first temperature measuring device and the second temperature measuring device are arranged parallel to each other in the flow path. The sensor support is removably connected to the component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention relates to a sensor device for measuring the mass flow rate of a liquid hot melt adhesive, the sensor device comprising a flow path for the hot melt adhesive, a first temperature measuring device arranged in a first position of the flow path for measuring the temperature of the hot melt adhesive in the first position of the flow path, a second temperature measuring device arranged in a second position of the flow path, and a heater assigned to the second temperature measuring device and for heating the second temperature measuring device, the second temperature measuring device being used to measure a second temperature of the heated second temperature measuring device, a control unit for controlling the heater and for measuring the mass flow rate being arranged and configured to control the temperature of the second temperature measuring device to a value, to determine the heating power for heating the second temperature measuring device and to measure the mass flow rate in the flow path.

[0002] The invention further relates to an applicator for dispensing a hot melt adhesive as well as to an application system for a liquid hot melt adhesive, which application system comprises a melter for providing the liquid hot melt adhesive, a heated applicator for dispensing the hot melt adhesive, a heated conveying device for conveying the hot melt adhesive from the melter to the applicator and a control system for adapting in particular the conveying rate of the hot melt adhesive. [Background technology]

[0003] Systems of this kind, application devices and sensor devices for measuring the mass flow rate of liquids such as hot melt adhesives are known from the prior art. Such sensor devices use the principle of convective anemometry and do not require direct intervention in the mass flow rate by means of moving mechanical parts. This measurement principle requires that a temperature measuring device is heated above the temperature of the hot melt adhesive, which is detected by a second temperature measuring device. Depending on the flow rate of the hot melt adhesive surrounding the heated temperature measuring device, a certain amount of heat is released into the surrounding flowing fluid. By means of a control device, the temperature of the heated temperature measuring device is controlled to be a fixed positive value above the temperature of the surrounding hot melt adhesive. The required heating power and the associated energy consumption are a measure for the flow rate and therefore for the mass flow rate of the liquid. A description of the measurement principle can be found in non-patent document 1.

[0004] According to the prior art, the two temperature measuring devices are arranged along an axis passing through the flow passage, offset by 90° from each other, and the sensor is constructed as a rod-shaped element. A drawback of the prior art is that the area of ​​the sensor creates additional flow resistance to the mass flow rate, which negatively affects the pump power required to deliver a certain amount of hot melt adhesive and causes pressure losses in the system. Furthermore, the placement of these sensors can cause swirls in the hot melt adhesive, which can cause uneven liquid flow, especially in the area near the discharge nozzle, which can have a detrimental effect on the application quality of the hot melt adhesive on the substrate or workpiece. Furthermore, the swirls can limit the accuracy of the measurement results obtained. In addition, these sensors are difficult to maintain as a unit and cannot be easily removed from the housing for replacement. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Schoenteich, B., Fischer, F.: "Precise mass flow measurement in highly viscous adhesives - virtually no pressure loss": ifs report of the Institute for Joining and Welding Technology, Braunschweig University of Technology, No. 1 / 2013, pp. 10-13. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a sensor device for measuring the mass flow rate of liquid hot melt adhesives, which substantially avoids or reduces the disadvantages of the prior art and, in particular, has little influence on the flow, is simple to manufacture and position, and achieves high measurement accuracy. [Means for solving the problem]

[0007] According to one aspect of the present invention, a sensor device for measuring the mass flow rate of a liquid hot melt adhesive is provided, comprising a flow path for a hot melt adhesive, a first temperature measuring device arranged at a first position of the flow path for measuring the temperature of the hot melt adhesive at the first position of the flow path, a second temperature measuring device arranged at a second position of the flow path, and a heater assigned to the second temperature measuring device and for heating the second temperature measuring device, the second temperature measuring device being used to measure a second temperature at the heated second temperature measuring device, and a control unit used for controlling the heater and measuring the mass flow rate is configured and provided to control the temperature of the second temperature measuring device to one value, determine the heating output for heating the second temperature measuring device, and measure the mass flow rate in the flow path.

[0008] According to a further aspect of the invention there is provided an application device and system comprising such a sensor device. [Brief description of the drawings]

[0009] [Figure 1]1 is a cross-sectional view of a hot melt adhesive application system equipped with a sensor device in a first embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of a partial cross section of the hot melt adhesive application system according to FIG. 1; [Diagram 3] FIG. 13 is a perspective view of a sensor device mounted within a housing in an alternative embodiment. [Figure 4] FIG. 13 is a cross-sectional view of a sensor device and housing in an alternative embodiment, taken along a cross section perpendicular to the flow direction of the hot melt adhesive. [Diagram 5] 2 is a cross-sectional view of the sensor device and housing according to FIG. 1 in a cross section in the flow direction of the hot melt adhesive. [Figure 6] FIG. 13 is a perspective view of a sensor support in an alternative embodiment. [Figure 7] FIG. 2 is a cross-sectional view of a sensor support taken along a cross section perpendicular to a predetermined flow direction of the hot melt adhesive. [Figure 8] FIG. 2 is a cross-sectional view of a sensor support taken along a section parallel to a predetermined flow direction of the hot melt adhesive. [Figure 9] FIG. 1 is a diagram of a liquid hot melt adhesive applicator and a sensor device attached thereto. [Figure 10] FIG. 2 is a control circuit diagram for measuring mass flow rate. [Figure 11] This is a liquid hot melt adhesive application system. [Figure 12] FIG. 13 is a diagram of an alternative embodiment of a sensor device mounted within a housing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] According to one aspect of the invention, the invention is based on the idea that the first and second temperature measuring devices are arranged substantially parallel to each other in the flow path. In this specification, the expression "substantially parallel" means that the first and second temperature measuring devices are oriented exactly parallel, including deviations from the exactly parallel orientation of up to ±20°. Such orientation and shaping of the sensors not only reduces the flow resistance induced by the measuring devices, but also reduces the occurrence of eddies in the mass flow. This allows for improved measurement accuracy compared to the prior art. Furthermore, such a structure allows for advantageous grouping and modularization of the components, which in this respect also contributes to the cost advantages of a modular and grouped construction of the sensor device. Furthermore, this also allows for positioning the measuring devices at different locations in the liquid hot melt adhesive application system.

[0011] According to another aspect or preferred embodiment of the invention, the first and second temperature measuring devices are arranged substantially on the same side of the flow path. Advantageously, this arrangement also achieves improved measurement accuracy and reduced flow resistance. This also supports an advantageous grouping of components.

[0012] According to a preferred embodiment, the first and second temperature measuring devices each have a sensor, which is equipped with a resistance thermometer. Furthermore, according to an aspect of the invention, at least one of the temperature measuring devices is equipped with a heater, in particular a heatable resistor, and the first and second temperature measuring devices are each equipped with a sensor having a ceramic material and a passivation glass. This type of structure allows for an advantageous functional integration to be achieved, allowing the creation of a flow-free sensor geometry, which contributes, among other things, to a reduction in resistance.

[0013] According to a preferred development, the first and second temperature measuring devices have a sensor carrier, on which the sensors are arranged. This allows, according to one aspect of the invention, a modularization of the sensor device and at the same time simplifies the removal of the sensor units for easy maintenance. Overall, this allows for cost savings compared to the prior art.

[0014] Preferably, the first temperature measuring device, the second temperature measuring device and the sensor support are accommodated in a housing, which defines the flow path, and which is preferably heatable by at least one electric heating cartridge and / or is equipped with a housing temperature sensor, whereby the special importance of maintaining an approximately constant preferred processing temperature during hot melt adhesive application is taken into account.

[0015] Preferably the sensor support is fixed to the housing by screws, self-aligning bayonet connectors, press fit or adhesive etc. Depending on the intended use of the sensor device either a simple reversible connection of the components or a non-reversible connection with high security against unintentional removal of components over the life of the product is possible.

[0016] Furthermore, according to a preferred embodiment, the sensor carrier is mounted in the application device, in particular in the application nozzle. This allows the advantage of a reduction in components, since the application device already provides a housing part for the integration of the sensor device. Furthermore, such a positioning is also suitable for further increasing the measurement accuracy with respect to the mass flow rate of the application device. Since the distance between the sensor and the application device is small, the flow velocities in two adjacent areas can be considered to be approximately the same.

[0017] Furthermore, according to a preferred embodiment, it is proposed that the sensor carrier is mounted in the hose connection, which makes it possible to advantageously mount the measuring device in the mass flow of the hot melt adhesive, for example, in the area of ​​the application nozzle, if the construction space is limited or if the flow rate of the hot melt adhesive at the hose connection is important.

[0018] Furthermore, the sensor support is preferably configured as an at least partially hollow body, preferably as a tube, and / or the side of the tube facing away from the sensor is at least partially closed by a closure element, which is preferably connected to the sensor support by a screw connection, and / or preferably on the side of the tube facing away from the closure element, a sensor block is fixed to the sensor support, the upper side of the sensor support being configured in such a way that the sensors of the first and second temperature measuring devices can be at least partially inserted into the sensor block, the sensor block, the sensor support and the closure element being configured in such a way that the wires for the sensors can pass through them. Such a construction saves material compared to a solidly configured sensor support and at the same time simplifies maintenance and installation operations. Furthermore, electrical lines or cables can also be guided through the housing without problems.

[0019] Preferably, the sensor block is connected to the sensor carrier by a frictional and / or positive locking connection, and the sensor block and / or the sensor carrier are at least partially filled with a filler, in particular a heat-resistant synthetic resin. The positive locking not only provides a sealing effect that prevents the hot melt adhesive from migrating into the sensor housing, but also achieves a more reliable fixing of the components. The at least partial filling, on the one hand, fixes the sensor and the cable in place, and on the other hand, protects against undesired conductive connections due to the insulating properties of the resin.

[0020] According to preferred developments, the sensor block is connected to the sensor support by means of screws, by means of self-aligning bayonet connectors, by means of a press fit or by gluing. Again, such connecting elements allow a reversible or irreversible connection of components depending on the application.

[0021] Furthermore, the sensor block and / or the sensor support are preferably made of plastic, preferably of heat-resistant plastic, particularly preferably of polyetheretherketone (PEEK), which provides the advantages of the invention, namely reduced weight, limited thermal and electrical conduction, good processability and durability.

[0022] Another preferred alternative embodiment is characterized in that the control unit is equipped with an input unit for control parameters, a PID controller, at least one analog / digital converter and at least one digital / analog converter, and as the control parameter a constant temperature difference to be maintained between the temperature of the second temperature measuring device and the temperature of the first temperature measuring device is used, in particular a temperature difference of 5 to 50 K, preferably 10 to 15 K. In one aspect of the invention, the control unit allows a fast and stable control of the heating unit in order to ensure a constant temperature difference between the temperature measuring devices, in particular by using a PID controller. Furthermore, the aforementioned temperature difference spread allows a further improvement in the measurement quality and at the same time a minimal intervention in the temperature field of the hot melt adhesive.

[0023] Furthermore, the application system for the liquid hot melt adhesive is equipped with the following components: a melting device for providing the liquid hot melt adhesive, a heated application device for dispensing the hot melt adhesive, a heated conveying device for conveying the hot melt adhesive from the melting device to the application device, a control system for adapting in particular the conveying rate of the hot melt adhesive and a sensor device for measuring the mass flow rate of the hot melt adhesive, whereby the advantage according to the invention is obtained of utilizing the high measuring quality of the sensor device according to the invention, which ensures that the conveying rate of the hot melt adhesive matches the desired target value with high accuracy. EXAMPLES

[0024] A preferred embodiment of the present invention will be described below with reference to the drawings. A hot melt adhesive application system according to a first embodiment shown in Figures 1 and 2 includes a conveying device 2 for conveying a molten hot melt adhesive 4 (only a reference number here) from a melting device 76 (not shown in Figure 1, see Figure 11) to an application device 6, a melting device 76 (not shown here) (Figure 11), the application device 6, and a sensor device 12 for measuring the mass flow rate of the liquid hot melt adhesive.

[0025] The applicator 6 is equipped with a nozzle assembly 8 for dispensing hot melt adhesive 4 onto a substrate or workpiece (not shown). The applicator 6 comprises, in a manner known per se, a housing 7, flow passages formed therein, valve assemblies and connections for introducing fluid, a control device for controlling the applicator, and other components.

[0026] The sensor device 12 is in this embodiment arranged between the application device 6 and the transport device 2 and comprises a housing 10 which contains and defines the flow path 5. The housing 10 is fitted with connecting members 18a and 18b which allow a reversible connection with the application device 6 and the transport device 2.

[0027] On the process side, the hot melt adhesive 4 passes through a housing 10 in the direction of the arrow 9 .

[0028] For heating purposes, the housing 10 is equipped with a heating cartridge 14, which allows the housing 10 to be maintained at an optimum temperature for processing the hot melt adhesive 4. A housing temperature sensor (not directly shown) in a corresponding housing bore 16 is used to monitor the temperature of the housing 10.

[0029] A sensor arrangement 12 for measuring the mass flow rate of the liquid hot melt adhesive 4 is arranged partially in the flow passage 5 of the housing 10. The sensor arrangement 12 comprises a sensor carrier 20, a first temperature measuring device 24 and a second temperature measuring device 28. Furthermore, the sensor arrangement is also equipped with a sensor block 22 and a closing element 26.

[0030] A first temperature measuring device 24 and a second temperature measuring device 28 are fixed on this sensor block 22. They partially protrude into the flow channel 5 and are thus arranged so that they come into contact with the hot melt adhesive 4 flowing therethrough during operation. The first temperature measuring device 24 and the second temperature measuring device 28 are arranged side by side and parallel to one another. The sensor block 22 is screwed to the sensor support 20 and is at least partially closed by a closing element 26 on the side facing the sensor block 22. The sensor block 22 and the sensor support are preferably made of plastic, preferably of a heat-resistant plastic, particularly preferably of polyetheretherketone (PEEK).

[0031] As shown in FIG. 3, each temperature measuring device 24 and 28 is equipped with a sensor, preferably formed as a resistance thermometer 30. At least one of the temperature measuring devices 24 or 28 is equipped with a heatable resistor 32 as a further sensor. In a preferred embodiment, the first temperature measuring device 24 and the second temperature measuring device 28 are equipped with a combined heating / temperature measuring sensor 33 of identical construction. However, a heatable resistor is preferably used only for the second temperature measuring device 28. As a result, the first temperature measuring device 24 is used only for temperature measurement, whereas the second temperature measuring device 28 is used to measure temperatures higher than the hot melt adhesive 4, which are achieved by the heatable resistor 32. The sensor may also be constructed with a ceramic material and a passivation glass.

[0032] As can be seen from Figures 3 and 4, the closure element 26 is fixed to the sensor support 20 by means of two screws 29a and 29b. In the alternative embodiment according to Figure 4, furthermore, various cables 34 are guided at least partially through the sensor support 20. For the fastening and electrical insulation of the cables or wires, the sensor block 22 and the sensor support 20 are partially filled with a synthetic resin 36.

[0033] 4 and 5, the housing 10 is provided with a cylindrical housing bore 38 with an internal thread 40. The sensor support 20 is provided with a corresponding external thread 39, allowing a form-fitting of the components.

[0034] Another alternative embodiment of the sensor support 20 is shown in Figure 6. Here, the sensor support 20 does not have an external thread and is connected to a corresponding part of the housing 10, for example by a crimp connection.

[0035] 7 and 8, the sensor support 20 is provided with an internal thread 42 on its inner side opposite the closure element 26. In this embodiment, the sensor block 22 including the sensors 24 and 28 is provided with an external thread 43, by means of which it is screwed into the sensor support 20.

[0036] An alternative arrangement in which the sensor device 12 is mounted directly in an application device 45 for dispensing the hot melt adhesive 4 is within the scope of another embodiment of FIG.

[0037] The applicator 45 comprises a base body 47 in which a pipe line 44 for supplying the hot melt adhesive 4 is arranged. A filter 46 for filtering the hot melt adhesive 4 is in fluid connection with the pipe line 44. Below the filter 46, based on the orientation of the applicator 45 in FIG. 9, there is a distribution channel 48, which is used to distribute the hot melt adhesive 4 in the applicator 45 perpendicularly to the cross section of FIG. 9. The base body 47 of the applicator 45 is equipped with a cylindrical bore 49, into which the sensor device 12 in the base body 47 is attached by press-fit or by means of screws, adhesive or a bayonet connector. The first temperature measuring device 24 and the second temperature measuring device 28 thus protrude into the distribution channel 48 in a manner that does not impede the flow.

[0038] The base body 47 is further fitted with a valve 50 for controlling the mass flow rate of the hot melt adhesive. A channel 52 extends from the valve 50. The channel 52 merges into a slot nozzle 58 formed by nozzle elements 54 and 56. The nozzle elements 54 and 56 are fixed to the base body 47 of the applicator 45 by means of a clamping device 60. To accommodate electrical components, the applicator 47 is further equipped with a receiving device 62.

[0039] On the process side, the hot melt adhesive 4 thus reaches the applicator 45 via the pipe line 44. It then passes through a filter 46 before reaching a distribution channel 48, which distributes the hot melt adhesive 4 perpendicularly to the cross section in the applicator 45. The hot melt adhesive 4 leaves the distribution channel 48 via a valve 50 and a channel 52 into a slot nozzle 58, where it is fed to a substrate, not shown.

[0040] The control unit 63, shown in the block circuit diagram as a preferred embodiment in Fig. 10, comprises a unit 64 for defining control parameters 65, additional elements 72 and 74, a PID controller 66, a digital / analog converter 68 and two analog / digital converters 70a, 70b. The control unit further uses a first temperature measuring device 24 comprising at least a resistance thermometer 30 and a second temperature measuring device 28 comprising a resistance thermometer 30 and a heatable resistor 32. The sensors 30 and 32 of the temperature measuring devices 24 and 28 are mounted in the mass flow of the hot melt adhesive, as already explained.

[0041] The role of the controller 66 is to keep the control parameter 65 constant and to keep constant the desired difference between the temperature of the surrounding hot melt adhesive 4 and the higher temperature of the second temperature measuring device 28. For this purpose, the heating output of the heatable resistor 32 is appropriately controlled, with both the temperature value of the first temperature measuring device 24 for the surrounding hot melt adhesive 4 and the temperature value of the second temperature measuring device 28 being fed back to the controller 66. Converters 68 and 70a and 70b convert the digital signals into analog signals and vice versa. The power consumed by the heatable resistor 32 is a measure for the mass flow rate of the hot melt adhesive.

[0042] The sensor device 12 is preferably part of a system 75 for applying the hot melt adhesive 4, as shown in Fig. 11. The application system 75 includes a melting device 76 for conveying and melting the hot melt adhesive 4. Furthermore, the sensor device 12 is used to measure the mass flow rate and is located anywhere between the melting device and the application device, or inside the application device, as shown in Fig. 10. Furthermore, the system 75 is equipped with the application device 6 as well as a control system 78 and a conveying device 2.

[0043] The hot melt adhesive 4 is conveyed to the application device 6 by the conveying device 2. The sensor device 12 is configured to measure the mass flow rate of the hot melt adhesive. Information about the detected mass flow rate is sent to the control system 78 and is used to control the conveying device in the melting device 76.

[0044] 12 shows an alternative embodiment of the sensor arrangement 12, in which a first temperature measuring device 24 and a second temperature measuring device 28 are arranged one behind the other in the flow direction 9 (with respect to the flow direction 9) in the flow channel 5. In this embodiment, this is achieved by correspondingly arranging the first temperature measuring device 24 and the second temperature measuring device 28 in the sensor block 22. For the description of the other components, reference is made to the corresponding embodiment in relation to FIG. 3, where identical components are provided with the same reference numerals. [Explanation of symbols]

[0045] 2. Conveyor 4. Hot melt adhesives 5 Flow Path 6 Coating equipment 7. Housing 8 Nozzle Assembly 9 Flow Direction 10. Housing 12 Sensor device 14 Heating Cartridge 16 Housing temperature sensor in the corresponding housing bore 18a, b Connection members 20 Sensor support 22 Sensor block 24 First temperature measuring device 26 Closing element 28 Second Temperature Measuring Instrument 29a, b screws 30 resistance thermometer 32 Heatable resistor 33 Combined heating / temperature measurement sensor 34 Cable 36 Synthetic Resins 38 Housing bore 39 External thread 40 Internal thread 42 Internal thread 43 External thread 44 Pipeline 45 Coating Equipment 46 Filter 47 Base body 48 Distribution Channels 49 Recess (bore) 50 Valve 52 Channels 54, 56 Nozzle element 58 Slot Nozzle 60 Clamping device 62 Containment Device 63 Control Unit 64 Control parameter input unit 65 Control parameters 66 PID Controller 68 Digital to Analog Converter 70a,b Analog / Digital Converter 72, 74 Additional elements 75 Hot melt adhesive application system 76 Melting Equipment 78 Control Systems

Claims

1. A sensor device (12) for measuring the mass flow rate of a liquid hot melt adhesive (4), comprising: a member having a flow passage (5) configured to receive the hot melt adhesive (4); a first temperature measuring device (24) arranged at the first position of the flow path (5) and configured to measure the temperature of the hot melt adhesive (4) at the first position of the flow path (5); a second temperature measuring device (28) disposed at a second position of the flow path (5); a heater (32) assigned to the second temperature measuring device (28) and configured to heat the second temperature measuring device (28); a control unit (63) configured to control the heater (32) and to measure the mass flow rate; the second temperature measuring device (28) is configured to measure a second temperature at the second temperature measuring device (28); the control unit (63) is configured to determine a heating power for heating the second temperature measuring device (28) by adjusting the temperature of the second temperature measuring device (28) to a certain value and to calculate the mass flow rate in the flow path (5); The sensor device (12) comprises a sensor block (22), the first temperature measuring device (24) and the second temperature measuring device (28) are mounted on the sensor block (22), the sensor block is removably connected to a sensor support (20), the sensor support is removably at least partially closed by a closing element (26) on the side opposite the sensor block, the first temperature measuring device (24) and the second temperature measuring device (28) are each planar and flat along the direction of flow of the hot melt adhesive, the first temperature measuring device (24) and the second temperature measuring device (28) are arranged substantially parallel to each other in the flow path (5), and the sensor support is removably connected to the member.

2. 2. The sensor device (12) according to claim 1, characterized in that the first temperature measuring device (24) and the second temperature measuring device (28) each have a sensor (33), the sensor being equipped with a resistance thermometer (30).

3. 3. The sensor device (12) according to claim 1 or 2, characterized in that the first temperature measuring device (24) and the second temperature measuring device (28) have a sensor (33) having a ceramic material and a passivation glass.

4. The sensor device (12) according to any one of claims 1 to 3, characterized in that the member includes a housing, the first temperature measuring device (24), the second temperature measuring device (28) and the sensor support (20) are accommodated in the housing (10), and the housing (10) defines the flow path (5).

5. 5. The sensor device (12) according to claim 4, characterized in that the housing (10) is configured to be heated by at least one electric heating cartridge (14) and / or is equipped with a housing temperature sensor (16), the sensor support (20) has an internal thread (42) opposite the closure element (26), and the sensor block (22) has an external thread (43) which screws into the sensor support.

6. 6. The sensor device (12) according to claim 4 or 5, characterized in that the sensor support (20) is arranged in a housing bore (38) of the housing (10), and the sensor support is fixed to the housing (10) by means of screws, a self-aligning bayonet connector or a press fit.

7. The sensor device (12) according to any one of claims 1 to 3, characterized in that the member comprises an application device or an application nozzle, and the sensor support (20) is removably connected to the application device (45) or the application nozzle and inserted therein.

8. 4. The sensor device (12) according to claim 2 or 3, characterized in that the sensor support (20) is configured as an at least partially hollow body or tube, the closure element is connected to the sensor support (20) by a screw connection (29a, 29b), the sensor block (22) is configured such that the sensors (33) of the first temperature measuring device (24) and the second temperature measuring device (28) are at least partially inserted into the sensor block (22), and the sensor block (22), the sensor support (20) and the closure element (26) are configured so that wires (34) for the sensors (33) can pass through them.

9. 9. The sensor device (12) according to claim 1, characterized in that the sensor block (22) is connected to the sensor support (20) by frictional engagement or form-fitting, and the sensor block (22) and / or the sensor support (20) are at least partially filled with a filler or a heat-resistant synthetic resin (36).

10. 10. The sensor device (12) according to any one of claims 1 to 9, characterized in that the sensor block (22) is connected to the sensor support (20) by means of screws, by means of a self-aligning bayonet connector or by means of a press fit.

11. The sensor device (12) according to any one of claims 1 to 10, characterized in that the sensor block (22) and / or the sensor support (20) are made from plastic, heat-resistant plastic or polyetheretherketone (PEEK).

12. The sensor device (12) according to any one of claims 1 to 11, characterized in that the control unit (63) is equipped with an input unit (65) for control parameters (64), a PID controller (66), at least one analog / digital converter (70a, 70b) and at least one digital / analog converter (68), and a constant temperature difference to be maintained between the temperature of the second temperature measuring device (28) and the temperature of the first temperature measuring device (24), a temperature difference of 5 to 50 K or a temperature difference of 10 to 15 K is used as the control parameter.

13. An application device (45) for dispensing the hot melt adhesive, comprising the sensor device (12) according to any one of claims 1 to 12, for measuring the mass flow rate of the hot melt adhesive.

14. a melting device (76) configured to provide a liquid hot melt adhesive (4); a heated application device (45) configured to dispense the liquid hot melt adhesive (4); a heated conveying device (2) configured to convey the liquid hot melt adhesive (4) from the melting device (76) to the heated applicator (45); a control system (78) configured to regulate the delivery rate of the liquid hot melt adhesive (4); A liquid hot melt adhesive application system (75) comprising: a sensor device (12) according to any one of claims 1 to 12, for measuring a mass flow rate of the liquid hot melt adhesive.

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