Temperature-resistant fill level measurement device

Abstract

The present disclosure relates to a radar-based fill-level measurement device for measuring a fill level of a fill substance located in a container. Besides a housing, the device includes an antenna and a housing neck, which is arranged between the housing and the antenna, wherein the housing neck has between the housing and the antenna a predefined thermal resistance, and at least one electronics module partially arranged in the housing neck. The thermal resistance of the housing neck is dimensioned in such a manner to be low, such that, at a temperature in the container of at least 200° C., the temperature at the electronics module is limited to, at most, 80° C. Thus, a high resolution and temperature-resistant and simultaneously compact, fill-level measurement device is provided for high radar frequencies of, for example, 79 GHz.

Claims

1. A radar-based fill-level measurement device for measuring a fill level of a fill substance located in a container, comprising: a housing; an antenna that is embodied in such a manner and arranged on the container, in order to transmit electromagnetic waves in the direction of the fill substance and to receive electromagnetic waves reflected in the container; a housing neck embodied of a thermally conductive material and arranged between the housing and the antenna and thermally coupled with the housing and the antenna, wherein the housing neck has between the housing and the antenna a predefined thermal resistance of less than 15 Kelvin per watt; and an electronics module arranged partially in the housing neck, wherein the thermal resistance of the housing neck is so dimensioned that, at a temperature in the container of 200° C., a temperature at the electronics module amounts to, at most, 85° C.

2. The fill-level measurement device as claimed in claim 1, wherein the thermally conductive material is stainless steel, aluminum, or copper.

3. The fill-level measurement device as claimed in claim 1, wherein the housing neck has a round cross section.

4. The fill-level measurement device as claimed in claim 3, wherein the housing neck is manufactured of stainless steel, and the housing neck has an average minimum wall thickness of 4 mm.

5. The fill-level measurement device as claimed in claim 4, wherein the housing neck has a maximum average outer diameter of 80 mm.

6. The fill-level measurement device as claimed in claim 4, wherein the housing neck has a maximum length of 140 mm.

7. The fill-level measurement device as claimed in claim 1, wherein the housing neck has an inner surface with a thermally insulating layer of polyphenylene sulfide.

8. The fill-level measurement device as claimed in claim 1, wherein the antenna and/or the housing are/is connected with the housing neck via at least one releasable connection.

9. The fill-level measurement device as claimed in claim 8, wherein a heat conductive paste is provided on the at least one releasable connection.

10. The fill-level measurement device as claimed in claim 1, further comprising: a thermally insulating element arranged in the housing neck between the electronics module and the antenna.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

(2) FIG. 1 shows a schematic view of a fill-level measurement device of the present disclosure mounted on a container,

(3) FIG. 2 shows a detailed representation of a fill-level measurement device of the present disclosure, and

(4) FIG. 3 shows a graph of temperature of the electronic component as a function of temperature in the container.

DETAILED DESCRIPTION

(5) For an improved understanding of the invention, FIG. 1 shows an arrangement of a radar-based fill-level measurement device 1 of the invention on a container 2. Located in the interior of the container 2 is a fill substance 3, whose fill level L is to be determined.

(6) For determining fill level L, the fill-level measurement device 1 is mounted on the container 2 above the fill substance 3 at, with reference to the container floor, a known installed height h, which, depending on container size, can be more than 30 m high. For this, the fill-level measurement device 1 is arranged in such a manner by means of a flange connection on the top of the container 2 that it transmits electromagnetic waves T.sub.HF, which are produced by an electronics module 131, via an antenna 12 in the direction of the fill substance 3. This can occur using the FMCW- or pulse travel time methods, for example, at a frequency of 79 GHz or higher.

(7) After reflection on the fill substance surface, fill-level measurement device 1 receives the reflected electromagnetic waves R.sub.HF back via the antenna 12. In such case, the travel time measured by the fill-level measurement device 1 between transmitting and receiving the high frequency electromagnetic waves T.sub.HF, R.sub.HF depends on the distance a to the fill substance surface. The subsequent calculating of the fill level L from the travel time, or the distance a, for the fill substance surface is done by the fill-level measurement device 3 using its installed height h: L=h−a. The calculation is done by a corresponding device electronics 111 of the field device 1. Device electronics 111 is contained within a housing 11.

(8) The fill-level measurement device 3 of the invention can, such as shown in FIG. 1, be connected via the device electronics 111 by means of a bus system, for instance, a “PROFIBUS”, “HART” or “wireless HART” bus system, to a superordinated unit 4, for example, a process control system. In this way, on the one hand, information concerning the fill level L can be sent to the process control system, in order, in given cases, to control in- or outgoing flows to or from the container 2. It is, however, also possible to communicate information concerning the operating state of the fill-level measurement device 1.

(9) Arranged within the antenna 12 is a process seal 121, for example, made of a chemically inert plastic, in order to seal the fill-level measurement device 1 fluid-tightly from the interior of the container 2. Besides the necessity of a fluid seal, it is, however, additionally, necessary to protect the fill-level measurement device 1 against temperature influences from the interior of the container 2.

(10) Depending on application, a temperature T.sub.C of up to 200° C. and higher can reign in the interior of the container 2, for example, due to a chemical reaction occurring in the fill substance 3 at the moment. Since the electronic components 111, 131 of the field device 1 are designed, as a rule, however, only for a temperature T.sub.E up to about 80° C., the field device 1 includes for protecting the electronic components against thermal loading a housing neck 13, which is arranged between the antenna 12 and the housing 11.

(11) For achieving a best possible resolution in the case of the fill level measurement, the electronics module 131 for the high frequency signal production must be arranged near the antenna 12. The reason for this is that the in-coupling of the electromagnetic waves T.sub.HF into the antenna 12 in the case of high transmitting/receiving frequencies, for example, 79 GHz, is very loss burdened as distance increases. Therefore, the electronics module 131 is not arranged in the more remote housing 11, but, instead, in the housing neck 13 located nearer to the antenna 12. In order nevertheless to protect the electronics module 131 against possible thermal loading from the interior of the container 2, the housing neck 13 has, according to the invention, a thermal resistance R.sub.th,N sufficiently small that at a temperature of at least 200° C. in the container 2 (especially at the site of the antenna 12) the temperature T.sub.E of the electronic component 131 rises at most to 80° C.

(12) A detailed sectional view of the fill-level measurement device 1 of the invention is shown in FIG. 2. In this representation, the variables influencing thermal resistance R.sub.th,N are more exactly evident: besides the material, of which the housing neck 13 is manufactured, these are, above all, the geometric dimensions of the housing neck 13: the length I.sub.N, the outer diameter D.sub.N as well as the wall thickness d.sub.N of the housing neck 13 (in the shown representation, the housing neck 13 has, for instance, a round cross section).

(13) How, for example, a change of the wall thickness d.sub.N affects thermal resistance R.sub.th,N of the housing neck 13 is evident from the graph of FIG. 3: at a temperature of 200° C. in the container 2 and an increase of the wall thickness d.sub.N from 2 mm to 5.6 mm (this corresponds to reducing thermal resistance R.sub.th,N from about 19.04 Kelvin/watt to about 7.13 Kelvin/watt, when the other dimensions remain unchanged at D.sub.N=80 mm, I.sub.N=140 mm,

(14) ${\lambda }_N=15\frac{W}{\mathrm{mK}})$
the temperature T.sub.E at the electronics module 131 lessens from about 83° C. to about 63° C., which then represents an uncritical temperature for the electronics module 131. These simulation values are based on the assumption that the housing neck 13 in the case of a wall thickness d.sub.N of 5.6 mm for thermal decoupling of the electronics module 131 has additionally a 1 mm thick, thermally insulating insert 132 of PPS on the inner surface of the housing neck 13 (see FIG. 2). As shown in FIG. 2, it would, for this purpose, moreover, be an option to arrange in the housing neck 13 a thermally insulating element 135 (for example, a correspondingly embodied ceramic having a high thermal resistance) between the electronic component 131 and the antenna 12.

(15) The graph of FIG. 3 additionally shows that the lessening of thermal resistance R.sub.th,N is accompanied by a slight increase of the temperature at the device electronics 111 in the housing 11. In the sense of the invention, this can, however, be tolerated, since the temperature of the device electronics 111 is still significantly below 80° C. Rather, according to the invention, it is effected that also the electronic component 131 located in the housing neck 13 is thermally decoupled from the container 2 in such a manner that, even at a temperature of 200° C. in the container 2, the temperature T.sub.E at the electronic component 131 in the housing neck 13 remains below 80° C.