FILL LEVEL MEASUREMENT DEVICE

Abstract

The disclosure relates to a radar-based, fill level measurement device for determining a fill level of a fill substance located in a container. The fill level measurement device includes a high frequency unit for producing high frequency signals and for determining fill level based on received high frequency signals. A hollow conductor is provided for transmitting or receiving high frequency signals. The hollow conductor is subdivided into a first portion facing the high frequency unit, and a second portion faceable toward the fill substance, wherein an insulation transparent for the high frequency signals separates the first portion fluidically from the second portion. A first hollow space is connected fluidically with the second portion and the first hollow space is arranged relative to the second portion behind the insulation. Thus condensate formation on the insulation is prevented, so that the functioning of fill level measurement device is not degraded.

Claims

1.-8. (canceled)

9. A fill level measurement device for determining a fill level of a fill substance located in a container, comprising a high frequency unit, which is designed to produce or process high frequency signals for determining fill level, a hollow conductor, which is coupled to the high frequency unit for transmitting the high frequency signals to the fill substance or for receiving high frequency signals reflected on the fill substance, wherein the hollow conductor is subdivided into: a first portion facing the high frequency unit, and a second portion faceable toward the fill substance; and an insulation transparent for the high frequency signals and separating the first portion fluidically from the second portion, wherein a first hollow space, which is connected fluidically with the second portion, wherein the first hollow space is arranged relative to the second portion behind the insulation.

10. The fill level measuring device of claim 9, wherein a second hollow space, which is connected fluidically with the second portion, wherein the second hollow space is arranged relative to the second portion in front of the insulation.

11. The fill level measuring device of claim 9, wherein the high frequency unit is designed to produce the high frequency signals with frequencies greater than 75 GHz.

12. The fill level measuring device of claim 9, wherein thermal resistance of the hollow conductor between the insulation and the first hollow space is sized in such a manner that at a temperature in the container of at least 180° C. the temperature difference down to the temperature in the first hollow space is at least 30° C.

13. The fill level measuring device of claim 9, wherein a screw thread connects the first hollow space fluidically with the second portion.

14. The fill level measuring device of claim 9, including a process isolation, which blocks an end region of the second portion faceable toward the fill substance.

15. The fill level measuring device of claim 14, wherein a fluidic seal is arranged between the process isolation and the end region of the second portion, especially a fluidic seal composed of at least two sealing rings.

16. The fill level measuring device of claim 15, wherein the first hollow space is designed in such a manner as a function of the permeability coefficient of the fluidic seal that the volume of the hollow space is dimensioned with at least 1.2 cm.sup.3 per a permeability coefficient of the seal of 10.sup.−12 kg/(s*bar).

Description

[0020] The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

[0021] FIG. 1 an arrangement, in principle, of a fill level measurement device of the invention mounted on a container,

[0022] FIG. 2 a schematic view of the components of the fill level measurement device of the invention, and

[0023] FIG. 3 a detail view of the essential components of the fill level measurement device.

[0024] In order to provide a basic understanding of the invention, shows FIG. 1 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.

[0025] For determining the fill level L, the fill level measurement device 1 is mounted on the container 2 above the fill substance 3 at a previously known, installed height h relative to the container floor. Depending on container size, it can be even greater than 100 m. The fill level measurement device 1 is so arranged on the top of the container 2 that it can transmit high frequency signals S.sub.HF toward the fill substance 3. That can occur using the FMCW method or the pulse travel time method, for example, at a frequency of 79 GHz or higher.

[0026] After reflection on the fill substance surface, the fill level measurement device 1 receives the reflected high frequency signals R.sub.HF, wherein the travel time measured by the fill level measurement device 1 between transmitting and receiving the high frequency signals S.sub.HF, R.sub.HF depends on the distance d to the fill substance surface. The subsequent calculation of the fill level L from the travel time, or the distance d, to the fill substance surface is done by the fill level measurement device 3 using its installed height h:

L=h−d

[0027] The fill level measurement device 1 of the invention can, such as shown in FIG. 1, be connected 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, or a decentral database. In this way, on the one hand, information concerning the fill level L can be transmitted, in order, in given cases, to control in- or outgoing flows to or from the container 2. Also information concerning the operating state of the fill level measurement device 1 can be communicated.

[0028] Depending on application, a temperature T.sub.C of up to 200° C., or even more, and/or a positive pressure of a number of bar can reign in the interior of the container 2, for example, due to a chemical reaction, which the fill substance 3 momentarily undergoes in the container 2. Moreover, in given cases, corrosive fill substances 3 can, because of bubble formation or overfilling, come into direct contact with the fill level measurement device 1. These influences can degrade the functioning of the fill level measurement device 1. Besides the limited temperature stability of the electronic components of the fill level measurement device 1, especially condensate formation can be experienced in the fill level measurement device 1.

[0029] Shown in cross sectional view in FIG. 2 are components of the fill level measurement device 1 critical in this connection: [0030] A high frequency unit 10 serves for producing the high frequency signals S.sub.HF to be transmitted and for processing the reflected high frequency signals R.sub.HF. The high frequency unit 10 includes the functional blocks required for the particular functional principle: In the case of implementing the FMCW method, the high frequency signal S.sub.HF can be produced by means of a PLL (“phase locked loop”); the received high frequency signal R.sub.HF can be mixed with the instantaneously transmitted high frequency signal S.sub.HF, such that the distance d, and fill level L, can be ascertained from the difference frequency of the mixed signals. A correspondingly designed evaluation block can ascertain the difference frequency, for example, by means of an FFT (“Fast Fourier Transformation”) of the mixed signal. [0031] A hollow conductor 11, in the case of which at least its inner wall is electrically conductive to the signal line, is connected to the high frequency unit 10, in order to out-couple the high frequency signal S.sub.HF into the container 2 and to couple the high frequency signals R.sub.HF reflected in the container 2 back into the high frequency unit 10. In the case of the example of an embodiment shown in FIG. 2, the opening of the hollow conductor 11 directed toward the fill substance 3 is conically expanded, whereby a corresponding antenna is embodied. [0032] A process isolation 15 of a material (for example, PMMA, PTFE or PC) transparent for the high frequency signals S.sub.HF, R.sub.HF seals the antenna, and the hollow conductor 11, from the fill substance 3, in order to prevent penetration of the fill substance 3 into the hollow conductor 11.

[0033] FIG. 3 shows an enlarged detail A of the fill level measurement device 1 of FIG. 2. As can be seen from such a detail view, the hollow conductor 11 is sealed in the region of the antenna toward the process isolation 15 supplementally by two external sealing rings 16, since the process isolation 15 can, in given cases, not have the required accuracy of fit with the antenna. The pressure resistance of the fill level measurement device 1 is essentially achieved by an insulation 12 in the interior of the hollow conductor 11. The insulation 12 is in the illustrated example of an embodiment disc shaped and can, depending on the positive pressure to be expected, have a thickness between 200 μm and 5 mm. Ideally, the thickness equals the half wavelength of the high frequency signal S.sub.HF, R.sub.HF. Also, the insulation 12 is transparent for the high frequency signals S.sub.HF, R.sub.HF, thus, transmissive. Therefore, the material of the insulation 12 can be, for example, a glass.

[0034] Insulation 12 divides the hollow conductor 11 into a first portion 11a facing toward the high frequency unit 10 and a second portion 11b, which during operation faces toward the fill substance 3. Insulation 12 seals the two portions 11a,b fluid-tightly from one another. In such case, the hollow conductor 11 is so designed in the illustrated example of an embodiment that the second portion 11b forms a holder for the first portion 11a. In this regard, the first portion 11a has an external thread, while the second portion 11b has a corresponding internal thread, so that the first portion 11a of the hollow conductor 11 can be screwed via the resulting screw thread 14 into the second portion 11b forming the holder. Insulation 12 can, accordingly, such as shown in FIG. 3, be mounted on the first portion 11a, for example, by means of welding, before the screwing in.

[0035] Depending on material, the sealing rings 16 have only finitely small gas-permeability coefficients in the order of magnitude of 10.sup.−12 kg/(s*bar). As a result, in spite of the sealing rings 16, and in spite of the process isolation 15, with rising duration of operation, gases, such as gaseous portions of the fill substance 3, can diffuse into the second portion 11b of the hollow conductor 11. In order that, nevertheless, no condensation, for example, water condensation, occurs on the insulation 12, the fill level measurement device 1 of the invention includes a first hollow space 13. Such is arranged relative to the second portion 11b at a distance a behind the insulation 12, thus, in the region of the first portion 11a. In such case, the hollow space 13 is arranged in the illustrated embodiment rotationally symmetrically around the hollow conductor 11. In principle, a rotationally symmetric design of the first hollow space is, however, not obligatory within the scope of the invention. As can be seen in FIG. 3, the hollow space 13 is fluidically connected with the second portion 11b via the screw thread 14, so that a gas transport or pressure equalization can take place therethrough.

[0036] This has the result that, at high temperatures T.sub.C in the container 2, condensation takes place not on the insulation 12, but in the first hollow space 13, since the first hollow space 13 is arranged relative to insulation 12, according to the invention, further removed from the fill substance 3.

[0037] Accordingly, condensation formation on the insulation 12 can be avoided by lessening the thermal resistance R.sub.th,H of the hollow conductor 11 between the insulation 12 and the first hollow space 13, wherein

[00001]$R_{\mathrm{th},G}=\frac{1}{{\lambda }_H}*\frac{a}{A_H}$

[0038] In such case, λ.sub.H is the thermal conductivity of the utilized hollow conductor-material with the units, W/(m*K). Stainless steel as potential material for the hollow conductor 11 has, for example, a thermal conductivity λ.sub.H of 15 W/(m*K).

[0039] A.sub.H is the cross sectional area of the hollow conductor 11 in the region between the insulation 12 and the first hollow space 13. The cross sectional area A.sub.H is in the case of rotationally symmetric design of the hollow conductor 11

[00002]$A_H=\frac{\pi }{4}\left(D_o^2-D_i^2\right)$

[0040] In such case, is D.sub.o the outer diameter and D.sub.i the inner diameter of the hollow conductor 11. In the case of square design of the hollow conductor 11, the cross sectional area A.sub.H is alternatively

A.sub.H=D.sub.a.sup.2−D.sub.i.sup.2

[0041] In such case, D.sub.o and D.sub.i are, respectively, the outer and inner edge lengths of the cuboid shaped hollow conductor 11.

[0042] A sufficient safety against condensate formation on the insulation 11 is provided, when thermal resistance R.sub.th,H is structurally is so established that at a temperature T.sub.C in the container 2 of at least 180° C. the temperature difference down to the temperature in the first hollow space 13 amounts to at least 30° C. The volume of the first hollow space 13 is preferably sized as a function of the permeability coefficients of the sealing rings 16, in order to prevent condensate formation on the insulation 12. A sufficient dimensioning rule is that the volume of the hollow space 13 should be at least 1.2 cm.sup.3 per permeability coefficient of the seal of 10.sup.−12 kg/(s*bar). In such case, taken into consideration is that the permeability coefficient of the sealing rings 16, in given cases, depends on the temperature T.sub.C in the container 2.

[0043] The fill level measurement device 1 shown in FIG. 3 includes an optional extension of the invention in the form of a second hollow space 17. In contrast with the first hollow space 13, the second hollow space 17 is located relative to the second portion 11b of the hollow conductor 11 in front of the insulation 12. In this way, the risk of condensate formation on the insulation 12 is supplementally reduced, since by the additional, second hollow space the pressure rise in the total hollow space is slowed and the pressure necessary for condensate formation is achieved later.

[0044] This extension can make sense, for example, when the first hollow space 13 for structural or manufacturing reasons cannot be dimensioned sufficiently large according to the above mentioned volume specification, or when the thermal resistance R.sub.th,H of the hollow conductor 11, for example, cannot, in turn, for structural reasons be reduced to the above described maximum value.

LIST OF REFERENCE CHARACTERS

[0045] 1 fill level measurement device [0046] 2 container [0047] 3 fill substance [0048] 4 superordinated unit [0049] 10 high frequency unit [0050] 11 hollow conductor [0051] 11a first hollow conductor portion [0052] 11b second hollow conductor portion [0053] 12 insulation [0054] 13 first hollow space [0055] 14 screw thread [0056] 15 process isolation [0057] 16 sealing ring [0058] 17 second hollow space [0059] A.sub.H cross sectional area of the hollow conductor [0060] a distance between the second hollow conductor portion and the hollow space [0061] D.sub.o outer diameter, or edge length, of the hollow conductor [0062] D.sub.i inner diameter, or edge length, of the hollow conductor [0063] d distance of the fill level measurement device to the fill substance [0064] h installed height of the fill level measurement device [0065] L fill level [0066] S.sub.HF, R.sub.HF high frequency signals [0067] R.sub.th,H thermal resistance of the hollow conductor [0068] T.sub.C temperature in the container interior [0069] λ.sub.H thermal conductivity