DE10131591C1 - Method and device for determining the height of phase interfaces in melt containers - Google Patents

Abstract

In order to determine the level of the surface (8) of the melted substance or the level ("H") of a melted glass material (7) in containers (1) having a bottom (2) and an upper bottom surface (3), an ultrasonic transmitter (11) and an ultrasonic receiver (12) are used, in glass melting installations, and the reflection signals from the surface of the melted substance (8) are evaluated. To this end, (a) at least one coupling element (9, 10) is guided through the bottom (2), and the upper side (9a, 10a) of said coupling element is arranged below the surface (8) of the melted glass material (7), at least essentially flush with the upper bottom surface (3); b) at least one ultrasonic element from the group consisting of the ultrasonic emitter (11), ultrasonic receiver (12) and transmitter-receiver unit is arranged on the lower side of the at least one coupling element (9, 10); and c) the level ("H") is determined from the difference in the propagation times of the sound waves between the ultrasonic emitter (11), the ultrasonic receiver (12) or the emitter-receiver unit, deducting the propagation times in the at least one coupling element. The level can be regulated by regulating the supply quantity of filling material, by means of a regulating device (17), in a melted substance vat which is connected upstream from the melted substance container (1), according to the quantity removed from the melted substance container (1).

Description

The invention relates to a method for determining the altitude of Phase interfaces in melt tanks with a bottom and one upper floor surface in glass melting plants using a Ultrasonic transmitter and an ultrasonic receiver and by Auswer reflection signals at these phase interfaces.

The glass level measurement and control is - besides influencing Temperature profiles in the longitudinal direction and in several vertical cross sectional profiles of a glass channel - for fully automatic glass processing an essential prerequisite for an even and trouble-free free production. Changes in the glass level call above all different ones Item weights emerge, so that the balance between glass removal and batch insert is constantly maintained.

Basics of ultrasound technology, the transmitter and receiver, the Frequencies, sound propagation and various uses in the "Encyclopedia of Natural Sciences and Technology", 1981, dual castles Verlag, Weinheim, pages 4718 and 4719.  

It is known from US-A-4 194 077 and US-A-4 302 623 that Layer thickness of feed material (batch, aggregates, cullet), the floating in a melting pan on a glass melt, by two to determine different measuring methods, namely once from above by ultrasonic signals, the reflections of which at the phase boundary furnace atmosphere / material to be loaded, and secondly from below by measuring the hydrostatic pressure of the glass melt using a bubbler and a pressure sensor. From the difference of the measured values the layer thickness is then calculated. Since both measuring methods with measuring errors with different causes are considerable inaccuracies. Especially the level measurement by the gas pressure in bubblers, as also described in US-A-3,200,971 very imprecise due to the considerable influence of the glass viscosity.

From US-A-4 345 106 it is known to fill a glass melt ze in a melting tank from above by ultrasonic signals to determine different frequencies and by phase shift and frequency modulation towards the position of the melt level conclude. Since the ultrasound signals are the feed material must penetrate, which is not homogeneous and considerable scatter caused by sound waves, this measuring method is also not sufficiently precise.

The problems of "signal noise" due to US reflections on the waiters Areas of loose fill are measured by Dr. Berrie u. a. in the article "Non-contact level measurements in the glass-making industry ", published in International Glass Review, Spring / Summer 1996, pages 75 to 79, described in detail.

Through the essay by Faber u. a. "Application of ultrasonic measuring techniques in industrial glass melting ", published in Glastech. Ber. 64 (1991), No. 5, pages 117 to 122, it is known by means of from above in the Glass melt immersed transmitter and receiver following melt parameters to determine: a) The presence of bubbles, b) Glass flow gen and c) the corrosion of refractory material. The level measurement  is not specified.

Measurements from above, and this includes the well-known opti measurements by infrared and laser beams, radioactive radiation gene and mechanical scanning, but are always with the disadvantage connected that the superstructure of the melt container (melting tank, Work tub and feeder or forehearth) with appropriate through breaks must be provided in which evaporated and condensed again Settled glass components. The breakthroughs or openings can negatively affect both the melting and the measuring process sen.

In Fröhler's book "Glass and Glass Products", information leaflet 50, 1996, published by J. Agst Moers, pages 276/277, are shown in a table dene measuring methods for glass level measurement in feeders each other compared, including the scanning with a Pt electrode, the electrical resistance measurement, the pneumatic probe and the radioisotopic measurement. There too the need for Openings in the dining ceiling and purging air indicated.

Similar limiting comments are also in the glass tech. Ber. Glass Sci. Technol. 73 C2 (2000), pages 111 to 123, in the chapter "Sensors for Glass Melting Processes" by Faber u. a. to find. There concludes on page 119 that the application of acoustic Sensors is still limited because of the interpretation of the acoustic Reflections from molten glass is quite complex, and that such Ultrasonic measurements only local information about the glass melt (Defects, speed) or via the refractory material (wall thickness) deliver.

With lateral ultrasonic measuring methods for the determination of the remaining wall glass channels also deal with the "HVG Communication No. 1801" by Fleischmann u. a. dated 01.08.1993 and "HVG Communication No. 1875" on a lecture by Fleischmann on June 5th, 1996 on the occasion of the 70th DGG Glass Technology Conference in Cottbus. However, it is not about  the level measurement.

From DE 198 47 318 C1 it is also known through the bottom of Glass melting tubs introduce heating electrodes at their lower ends are provided with transmitters and receivers for ultrasonic signals. However, this is intended to determine the remaining length of the electrodes is decisive for the heating output. By signal-dependent feeding the heating output of the electrodes should be adjusted to constant values become. However, this is also not a level measurement.

The invention is based on the object of a method of the genus described at the beginning, with which it is possible to the level or the altitude of the melt level above the upper bottom surface of a melt container exclusively by Determine ultrasound signals and their measurement processing, without recesses and / or in the superstructure of the melt container Breakthroughs should be provided.

The object is achieved in the above-mentioned method according to the invention in that the level of a glass melt in the melt container is determined by

• a) at least one coupling element through the bottom thereof leads and its top below the melt level of the Glass melt at least essentially flush in the top Arranges floor space,
• b) at least on the underside of the at least one coupling element at least one ultrasound element from the group of ultrasound transmitters, Arranges ultrasound receiver and transmitter-receiver unit, and
• c) from the transit time difference of the sound waves between ultrasound the, ultrasonic receiver or transmitter-receiver unit under Deduction of the transit times in the at least one coupling element determines the level.

The object is completely achieved by the invention, namely the level or the height of the melt level above half of the upper bottom surface of a melt container exclusively through ultrasonic signals and their metrological processing determine without exception in the superstructure of the melt container gene and / or breakthroughs should be provided.

It also has the following other advantages: It is a simple mechanical structure for direct Measurement of the level, so that a corresponding device too to replace other devices and to retrofit existing ones Melt containers can be used, one or more times at almost any point on the tank bottom of melting tanks, Work tubs and feeders or forehearths. It depends on the measurement principle, only one or two openings in the floor are required to achieve this Coupling element or the coupling elements with the glass melt in To touch. Movable parts are no more necessary than dangerous radiation sources that require approval, such as radioactive Substances. The measurement accuracy is amazingly high. So can For example, level differences of just 0.1 to 0.3 mm are corrected become. Known systems such as Piezo crystals are used.

Avoiding breakthroughs in the superstructure or in the furnace ceiling avoids the impairment of the glass melt and the temperature and viscosity distribution in the glass melt due to undesired gas leaks and / or air ingress and thus process disturbances. Further condensation of vaporized glass components and solid accumulations on the measuring devices avoided. Finally be also undesirable interactions with necessarily existing ones Heating or cooling devices in the upper furnace and / or in the ceiling of the Avoid melt container.  

In the course of further refinements of the method according to the invention, it is particularly advantageous if, either individually or in combination:

• - Separated from each other in the bottom of the melt container, vertically and arranges two coupling elements parallel to each other and that a coupling element on its underside with an ultrasound transmitter and the other coupling element on its underside an ultrasound receiver,
• - In the bottom of the melt container, a vertical coupling arranges element that has a transmitter emp catcher unit for ultrasonic signals is provided,
• - The ultrasonic transmitter with a data processing device a pulse train for the generation of ultrasonic signals strikes and the portions of the reflected at the phase interfaces Ultrasound signals by means of the data processing device analy based and obtains signals for the fill level, and / or if you
• - The actual value signals for the level and setpoint signals for the Filling level of a control arrangement is activated and by means of the rule arranging the balance between the supply and removal amounts of glass melt in and out of the melt container adjusts specified values, especially if you use the Control arrangement the amount of feed material in a Melting tank upstream melting tank according to the The withdrawal quantity regulates from the melt container.

Further advantageous refinements of the method according to the invention result from the other procedural claims.  

The invention also relates to a device for determining the heights location of phase interfaces in melt tanks with a bottom and using an upper floor surface in glass melting plants an ultrasonic transmitter and an ultrasonic receiver and through Evaluation of reflection signals at these phase interfaces.

To achieve the same object, such a device according to the invention is characterized in that for determining the level of a glass melt in the melt container

• a) at least one coupling element through the bottom thereof is guided, the top of which is below the melt level Glass melt at least essentially flush in the top Floor area is arranged,
• b) at least on the underside of the at least one coupling element at least one ultrasound element from the group of ultrasound transmitters, Ultrasonic receiver and transmitter-receiver unit is arranged and if
• c) a data processing device is provided, by means of which Transit time difference of the sound waves between ultrasound transmitter, Ultra sound receiver or transmitter-receiver unit minus the Runtimes in the at least one coupling element the level is determinable.

In the course of further refinements of the device according to the invention, it is particularly advantageous if - either individually or in combination -:

• - Separated from each other in the bottom of the melt container, vertically and two coupling elements are arranged parallel to one another, one of which has a coupling element on its underside with a Ultrasonic transmitter and the other coupling element on it Underside is provided with an ultrasound receiver,  
• - In the bottom of the melt container, a vertical coupling element is arranged, the underside with a transmitter Receiver unit for ultrasonic signals is provided,
• - The coupling elements made of at least one material from the Group of ceramic materials, refractories with low thermal conductivity, metals and composites exist, and / or if
• - The coupling elements are provided with a cooling device.

Two exemplary embodiments of the subject matter of the invention and their mode of operation are explained in more detail below with reference to FIGS. 1 to 3.

Show it:

Fig exemplary implementation. 1 a highly abstracted vertical section through a first off, receivers are arranged separately from each other in the ultrasonic transmitter and,

Fig. 2 is a vertical section through a second embodiment analogous to FIG. 1, but in which ultrasonic transmitter and receiver are structurally combined, and

Fig. 3 shows the envelope of oscillator diagrams of the receiver at two different surface conditions of the glass melt (top and bottom), and the difference from these graphs (center).

In Fig. 1 is a cross section through a melt container 1, which is a feeder channel and a forehearth in this case. This has a floor 2 with an upper, horizontal and flat floor surface 3 and two side walls 4 and 5 and a ceiling 6 . These components are made of refractory materials. Thermal insulation, outer jacket, frame parts and heating and cooling devices are omitted for the sake of simplicity. The melt container 1 is filled with a glass melt 7 , which reaches up to a melt level 8 , the height of which is an amount "H" above the bottom surface 3 , which characterizes the fill level.

Two coupling elements 9 and 10 are passed through the bottom 2 in the vertical direction, the flat upper sides 9 a and 10 a thereof being in one plane with the bottom surface 3 and being touched by the glass melt 7 . The coupling elements 9 and 10 carry at their lower ends an ultrasonic transmitter 11 or an ultrasonic receiver 12 , hereinafter only called "transmitter" and "receiver" for short.

Transmitter 11 and receiver 12 are connected via lines 13 and 14 of a data processing device 15 , which - not particularly Darge - contains a control unit, a signal processor and a microcomputer. The control unit controls the delivery of the pulses to the transmitter 11 . The receiver 12 passes the received pulse train to the data processing device 15 . Their output signals are applied via a line 16 to a control arrangement 17 for the fill level. Inputs and outputs for setpoints and control signals are not shown. For example, the Chargiereinrich device of a melting tank can be controlled or regulated by the control arrangement 17 in order to maintain the balance between the supply of glass raw materials and the removal of glass melt. For data processing device 15 generally includes an input keyboard 15 a, a display device 15 b, and a printer 15 c for signal recording. The input keyboard can be dispensed with if programmed accordingly.

Since the glass melt 7, depending on the type of glass, can have temperatures of 900 ° C. to approx. 1,600 ° C. and the transmitter and receiver, for which piezo crystals can be used, only hold temperatures of less than 350 ° C., the coupling elements 9 and 10 consist of a ceramic material or a refractory material with low thermal conductivity, a metal or composite material and have a corresponding length. Possibly. they can also be provided with cooling devices, not shown.

The coupling element 9 emits ultrasound waves via its top 9 a, a part of which is reflected on the melt surface 8 to the top 10 a of the coupling element 10 , which is indicated by the arrows 18 . Each coupling element is in direct contact with the glass melt on the one hand and the transmitter and receiver on the other.

The data processing device 15 emits a sequence of ultrasonic pulses via the transmitter 11 , which runs through the coupling element 9 of the transmitter 11 and through the glass melt 7 to the melting mirror 8 and from there back to the coupling element 10 and to the receiver 12 (arrows 18 ). Reflections occur at the material or phase interfaces passed through the transmitter / coupling element, coupling element / glass melt, glass melt / furnace atmosphere (melting mirror) and back, glass melt / coupling element, coupling element / receiver, which are registered by the receiver as staggered pulse sequences. The data processing device 15 extracts the transit time signal for the melt surface (the melt level 8 ) and thus the entire pulse transit time from this pulse sequence. The total impulse running time t _imp is made up of the running times of the individual sections:

t _imp = t _k1 + 2 × t _glass + t _k2 (1), where

t _k1 = pulse transit time in the coupling element of the transmitter,
t _k2 = pulse _{transit time} in the coupling _{element of} the receiver and
t _glass = pulse transit time in the glass melt.

The determination of the level of the glass melt through the Datenverarbei processing device 15 can be determined by various methods, wherein the data processing means 15 performs the selection bar of the pulse trains and det hide my reflections at the coupling elements and the entire pulse transit time t _imp determined.

The following procedures have been successfully tested:

• a) The speeds of sound for all materials are known:
  If the speeds of sound and the lengths of the coupling elements and thus the pulse duration are known, the pulse duration in the glass melt can be calculated on the basis of the total pulse duration and the path length in the glass melt can be determined if the speed of sound in the glass is known:
  t _glass = 0.5 × (t _imp - t _k1 - t _k2 ), (2) where
  S _glass = v _glass × t _glass and
  S _glass = path length in the glass melt and
  v _Glass = speed of sound in the glass melt.
• b) The speeds of sound are only known for the coupling elements:
  If the speeds of sound and the lengths of the coupling elements are known, the pulse duration in the glass melt can be calculated based on the total pulse duration:
  
  t _glass = 0.5 × (t _imp - t _k1 - t _k2 ). (3)
  Using a parameterization cycle by defined raising and lowering the fill level of the glass melt, the change in the pulse transit time Δt _imp can be measured and from this the change in the pulse transit time in the glass melt Δt _glass can be determined and the sound speed - v _glass - can be calculated. The device can be parameterized using the now known speed of sound in the glass melt - v _glass :
  v _glass = ΔS _glass / Δt _glass (4).
• c) The speeds of sound in the materials are not known:
  The change in the pulse transit time Δt _imp can be measured on the basis of a parameterization cycle by defined raising and lowering of the fill level of the glass melt. Since the lengths of the coupling elements are constant, their pulse transit times are also constant. This means that the change in the pulse transit time is due to the change in the pulse transit time in the glass melt:
  Δt _imp = Δt _glass (5).
  With a known pulse transit time in the glass melt Δt _glass , the speed of sound - v _glass - is calculated. The device can be parameterized using the now known speed of sound in the glass melt - v _glass .

The data processing device 15 selects the pulse transit time in the glass melt t _glass from the entire pulse train. With a known pulse running time in the glass melt, the fill level "H" of the glass melt can be calculated with a known sound velocity v _glass or determined with a parameterization cycle if the speed of sound is unknown, as described above.

In Fig. 2 are for the same parts or parts with the same function the same reference numerals used. In this case, the transmitter and receiver are connected to a transmitter-receiver unit 19 with an equally vertically arranged coupling element 21 , which also has a flat and horizontal upper side 21 a, which is flush with the upper floor surface 3 . Ultrasonic waves are now emitted from this upper side 21 a and return to it, which is indicated by the vertical parallel arrows 20 .

Fig. 3 shows the envelopes S1 and S2 of the oscillator diagrams of the receiver with two different surface states and the difference from these diagrams (envelopes S3). To a certain extent, these envelopes outline the amplitudes of the vibrations. These are the envelopes of ultrasonic pulses, which were recorded with an oscillograph after appropriate amplification.

The receiver signal resulted from longitudinal, transverse and surface waves. The time of arrival of the signals from the melt level 8 can be clearly recognized and evaluated from the transit time interval corresponding to H '. Similar evaluations can be obtained from a phase comparison of the pulse sequences. The data processing device is programmed using appropriate software, taking into account the above calculation bases. The display and measurement accuracy was between about 0.1 and 0.3 mm mirror difference.

LIST OF REFERENCE NUMBERS

1

melt container

2

ground

3

floor area

4

Side wall

5

Side wall

6

blanket

7

molten glass

8th

melt surface

9

coupling element

9

a top

10

coupling element

10

a top

11

ultrasonic transmitter

12

ultrasonic receiver

13

management

14

management

15

Data processing device

15

a input keyboard

15

b display device

15

c printer

16

management

17

regulating arrangement

18

arrows

19

Transceiver unit

20

arrows

21

coupling element

21

a top
"H" measure of level
"H '" Measure of level
S1 envelopes
S2 envelopes
S3 envelopes

Claims (17)

1. A method for determining the height of phase interfaces in melt containers ( 1 ) with a bottom ( 2 ) and an upper bottom surface ( 3 ) in glass melting systems using an ultrasonic transmitter ( 11 ) and an ultrasonic receiver ( 12 ) and by evaluating reflection signals surfaces of this phase boundary, characterized in that the level ("H") of a glass melt ( 7 ) in the melt container ( 1 ) is determined in that

• a) through the bottom ( 2 ) of at least one coupling element ( 9 , 10 , 21 ) and the top ( 9 a, 10 a, 21 a) below the melt level ( 8 ) of the glass melt ( 7 ) at least substantially flush in the upper Arranges floor surface ( 3 ),
• b) arranges at least one ultrasound element from the group of ultrasound transmitters ( 11 ), ultrasound receiver ( 12 ) and transmitter-receiver unit ( 19 ) on the underside of the at least one coupling element ( 9 , 10 , 21 ), and
• c) from the transit time difference of the sound waves between the ultrasonic transmitter ( 11 ), ultrasonic receiver ( 12 ) or transceiver unit ( 19 ), deducting the transit times in the at least one coupling element ( 9 , 10 , 21 ), the fill level ("H" ) certainly.

2. The method according to claim 1, characterized in that in the bottom ( 2 ) of the melt container ( 1 ) separated from each other, perpendicular and parallel to each other, two coupling elements ( 9 , 10 ) and the one coupling element ( 9 ) on its underside with a Ultrasound transmitter ( 11 ) and the other coupling element ( 10 ) on its underside with an ultrasound receiver ( 12 ). 3. The method according to claim 1, characterized in that one arranges a vertical coupling element ( 21 ) in the bottom ( 2 ) of the melt container ( 1 ), which is provided on its underside with a transmitter-receiver unit ( 19 ) for ultrasonic signals. 4. The method according to claim 1, characterized in that the ultrasonic transmitter ( 11 ) via a data processing device ( 15 ) with a pulse train for the generation of ultrasonic signals and the reflected at the phase interfaces portions of the ultrasonic signals by means of the Datenververarbeitungeinrich device ( 15 ) analyzed and from it signals for the level ("H") wins. 5. The method according to claim 4, characterized in that one connects the actual value signals for the fill level ("H") and setpoint signals for the fill level ("H") of a control arrangement ( 17 ) and by means of the control arrangement ( 17 ) the balance between regulates the supply and withdrawal quantities of molten glass in and out of the melt container ( 1 ) to predetermined values. 6. The method according to claim 5, characterized in that by means of the control arrangement ( 17 ) regulates the feed quantity of charging material into a melting tank ( 1 ) upstream of the melting tank in accordance with the amount withdrawn from the melting tank ( 1 ). 7. The method according to claim 1, characterized in that one selects the material for the coupling elements ( 9 , 10 , 21 ) and their length in such a way that the temperature of the temperature of the glass melt at the top ( 9 a, 10 a , 21 a) the coupling elements ( 9 , 10 , 21 ) at the lower ends of the coupling elements ( 9 , 10 , 21 ) is lowered to a temperature which corresponds at most to the maximum permissible operating temperature of the ultrasonic elements ( 11 , 12 , 19 ). 8. The method according to claim 7, characterized in that cooling the coupling elements ( 9 , 10 , 21 ). 9. The method according to claim 4, characterized in that

• a) the data processing device ( 15 ) is designed in such a way that it emits a sequence of ultrasonic pulses through the respective coupling element ( 9 , 21 ) and through the transmitter ( 11 ) or the transmitter-receiver unit ( 19 ) the glass melt ( 7 ) runs to the melt mirror ( 8 ) and from there back to the coupling element ( 10 , 21 ) and to the receiver ( 12 ) or to the transmitter-receiver unit ( 19 ),
• b) the reflections occurring at the material or phase interfaces passed through transmitter / coupling element, coupling element / glass melt, glass melt / furnace atmosphere (melting mirror) and back through glass melt / coupling element, coupling element / receiver are registered as temporally staggered pulse sequences by the receiver,
• c) the data processing device ( 15 ) extracts the transit time signal for the melt level ( 8 ) and thus the entire pulse transit time from the pulse train, the total pulse transit time t _{imp being} composed of the transit times of the individual sections as follows:
  t _imp = t _k1 + 2 × t _glass + t _k2 , where
  t _k1 = pulse transit time in the coupling element of the transmitter,
  t _k2 = pulse _{transit time} in the coupling _{element of} the receiver and
  t _glass = pulse transit time in the glass melt.

10. The method according to claim 1, characterized in that at known sound velocities and pulse transit times for all materials and with known lengths of the coupling elements ( 9 , 10 , 21 ), the pulse transit time and the path length (s) in the glass melt are determined as follows on the basis of the total pulse transit time become:
t _glass = 0.5 × (t _imp - t _k1 - t _k2 ), where
S _glass = v _glass × t _glass and
S _glass = path length in the glass melt and
v _Glass = speed of sound in the glass melt. 11. The method according to claim 1, characterized in that at known sound velocities and lengths only for the coupling elements based on the total pulse transit time, the pulse transit time in the glass melt is calculated:
t _glass = 0.5 × (t _imp - t _k1 - t _k2 ),
whereby the change in the pulse transit time Δt _{imp is} measured on the basis of a parameterization cycle by defined raising and lowering of the fill level of the glass melt and the change in the pulse transit time in the glass melt Δt _{glass is} determined and the speed of sound - v _glass - is calculated and the device is calculated using the now known speed of sound in the glass melt - v _glass - is parameterized as follows:
v _glass = ΔS _glass / Δt _glass . 12. The method according to claim 1, characterized in that at unknown sound velocities in the materials and constant lengths and pulse durations of the coupling elements ( 9 , 10 , 21 ) measured by means of a parameterization cycle by defined raising and lowering the fill level of the glass melt, the change in the pulse duration Δt _imp The change in the pulse transit time is due to the change in the pulse transit time in the glass melt as follows:
Δt _imp = Δt _glass ,
and wherein with a known pulse transit time in the glass melt Δt _glass, the speed of sound - v _glass - in the glass melt is calculated and the device is parameterized by means of the now known speed of sound in the glass melt - v _glass . 13. Device for determining the altitude of phase boundary surfaces in melt containers ( 1 ) with a bottom ( 2 ) and an upper bottom surface ( 3 ) in glass melting systems using an ultrasonic transmitter ( 11 ) and an ultrasonic receiver ( 12 ) and by evaluating reflection signals at these phase interfaces, characterized in that for determining the fill level ("H") of a glass melt ( 7 ) in the melt container ( 1 )

• a) through the bottom ( 2 ) at least one coupling element ( 9 , 10 , 21 ) is passed, the top ( 9 a, 10 a, 21 a) below the melt level ( 8 ) of the glass melt ( 7 ) at least substantially flush in the upper floor surface ( 3 ) is arranged,
• b) at least one ultrasonic element from the group of ultrasonic transmitters ( 11 ), ultrasonic receiver ( 12 ) and transmitter-receiver unit ( 19 ) is arranged on the underside of the at least one coupling element ( 9 , 10 , 21 ), and that
• c) a data processing device ( 15 ) is provided, by means of which the transit time difference of the sound waves between ultrasound transmitter ( 11 ), ultrasound receiver ( 12 ) or transceiver unit ( 19 ) is deducted from the transit times in the at least one coupling element ( 9 , 10 , 21 ) the fill level ("H") can be determined.

14. The apparatus according to claim 13, characterized in that in the bottom ( 2 ) of the melt container ( 1 ) separated from each other, perpendicular and parallel to each other two coupling elements ( 9 , 10 ) are arranged, of which one coupling element ( 9 ) on its underside is provided with an ultrasonic transmitter ( 11 ) and the other coupling element ( 10 ) on its underside with an ultrasonic receiver ( 12 ). 15. The apparatus according to claim 13, characterized in that in the bottom ( 2 ) of the melt container ( 1 ) a vertical coupling element ( 21 ) is arranged, which is provided on its underside with a transmitter-receiver unit ( 19 ) for ultrasonic signals. 16. The apparatus according to claim 13, characterized in that the coupling elements ( 9 , 10 , 21 ) made of at least one material from the group of ceramic materials, the refractory materials with low thermal conductivity, the metals and the composite materials. 17. The apparatus according to claim 16, characterized in that the coupling elements ( 9 , 10 , 21 ) are provided with a cooling device.