AT523023A1 - COOLED ULTRASONIC SENSOR - Google Patents

Abstract

A new sensor assembly with an ultrasonic sensor (9) is described. According to one embodiment, the sensor assembly has a carrier block (18, 28) into which the ultrasonic sensor (9) is inserted so that the ultrasonic sensor (9) is thermally coupled to the carrier block (18, 28). The sensor assembly also has fastening means (16) which are designed to fix the carrier block (18, 28) on a hot surface of an object (11) to be examined, as well as thermal insulation (15) which is provided between the carrier block (18, 28) and the hot surface. The thermal insulation (15) has a central opening through which either the ultrasonic sensor (9) or part of a feed path (28a) formed by the carrier block (18, 28) runs.

Description

COOLED ULTRASONIC SENSOR

TECHNICAL AREA

The present description relates to the field of ultrasonic sensors for industrial applications, in particular an ultrasonic sensor with a cooling device,

in order to be able to operate the ultrasonic sensor on hot surfaces.

BACKGROUND

To carry out ultrasonic measurements by means of piezoelectric sensors on hot surfaces (e.g. of plastics processing machines, in the food and steel industries), a number of challenges must be overcome. One problem is, for example, the piezoelectric Curie temperature of the piezoelectric ceramics used. The heating of the piezoceramic above this Curie temperature leads to the loss of the piezoelectric properties due to depolarization. The manufacturers of piezoceramics often recommend / specify that the piezoceramics should not be used above half the Curie temperature. The most frequently used piezoceramics in ultrasonic sensors are based on lead zirconate titanate (PZT). The Curie temperature of PZT is around 350 ° Celsius and the recommended maximum temperature is usually in the range of 150 ° to 200 ° Celsius. For example, there are also single crystals with higher Curie temperatures available (such as quartz, zinc oxide, lithium sulfate and lithium niobate), but these materials have higher Curie temperatures than PZT

significantly lower piezoelectric coefficients.

Another problem that occurs at higher temperatures is the temperature resistance of the cable insulation, the soldered joints and other components of ultrasonic sensors, which can usually cause problems and malfunctions at temperatures above 100 ° Celsius. The temperature resistance of these components is technically possible, but involves considerable effort. Furthermore, the various thermal expansions of the components of an ultrasonic sensor can lead to the destruction of the sensor at higher temperatures (e.g. by loosening connections

connections, breakage of the piezoceramic).

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In addition, the ultrasonic sensor must be acoustically coupled to a hot surface of an object. In the room temperature range, e.g. water, pastes, gels or oils are used here, in particular to compensate for the roughness between the sensor and the surface and to ensure the best possible coupling of the ultrasound into the respective object. At higher temperatures, these coupling agents mentioned above evaporate or dry out and a stable measurement is only possible for a very short period of time. At higher temperatures, the coupling can take place via foils made of, for example, aluminum or gold. However, very high forces are required to attach the ultrasonic sensors to the surface of the object.

press.

In order to be able to work with ultrasonic sensors designed for comparatively low temperatures, delay sections (so-called buffer rods) are arranged between the hot surface of the object to be examined and the ultrasonic sensor, for example. However, only ultrasonic measurements are usually possible over a very short period of time, and the ultrasonic sensor often has to be cooled after the measurement. Another possibility used for longer-lasting measurements is the active cooling of the buffer rods by means of a cooling medium, what

in turn requires a permanent supply of cooling medium.

The inventors have set themselves the task of providing a cooled ultrasonic device which is suitable for a (preferably permanent) coupling of an ultrasonic sensor to metal surfaces with an elevated temperature (e.g. over 100 ° Celsius). It would be desirable to be able to measure signal transit times, signal amplitudes and other acoustic parameters with the help of such a device in pulse or continuous wave operation (e.g. by means of reflection or transmission measurements). Such measurements can enable conclusions to be drawn about the properties of the object (e.g. wall thickness, corrosion, temperature, wear) and / or can also be used to obtain metrological information from a liquid or gaseous medium (e.g. foreign material, density, temperature) that is processed within the object is to obtain and / or information (e.g. wear, positions, speeds) regarding machine elements such as pistons, conveying elements, which are enclosed by the medium

is to determine.

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SUMMARY

The above-mentioned object is achieved by the assembly according to claim 1 and the sensor according to claim 9. Various embodiments and further developments

windings are the subject of the dependent claims.

A sensor assembly with an ultrasonic sensor is described below. According to one embodiment, the sensor assembly has a carrier block into which the ultrasonic sensor is inserted, so that the ultrasonic sensor is thermally coupled to the carrier block. The sensor assembly furthermore has fastening means which are designed to fix the carrier block on a hot surface of an object to be examined, as well as a thermal insulation which is arranged between the carrier block and the hot surface. The thermal insulation has a central opening through which either the ultrasonic sensor or part of a through the carrier block 28

formed pre-run line runs.

As fastening means, screws can be used which are made of plastic, for example polyetheretherketone (PEEK) and which are screwed into the object to be examined. The screws can have screw heads, spring elements being arranged between the screw heads and the carrier block. In one embodiment, a polyvinyl film is arranged as a coupling medium between the ultrasonic sensor and the hot surface or between the feed path and the hot surface. The carrier block can have empty bores and / or ribs on its outside, for example in the form of thread turns. Alternatively, the carrier block can have bores in which thermally conductive rods / pipes (heat pipes), for example made of copper, are arranged, which protrude from the carrier block. The sensor assembly can furthermore have a thermal insulation arranged on the carrier block with openings through which the rods run. Furthermore, the sensor assembly can have a cover which is connected to the carrier block in such a way that the parts of the rods protruding from the carrier block lie within the cover. In one embodiment, the shell is made of thermally insulating material and has at least one inlet and at least one outlet (e.g. several holes),

to allow a flow of a cooling medium within the envelope.

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According to one exemplary embodiment, the ultrasonic sensor has the following: a housing; a piezoelectric element attached to a housing base inside the housing; an acoustic damping material which covers the piezoelectric element inside the housing; a potting compound which covers the acoustically damping material in the interior of the housing; two lines electrically connected to the piezoelectric element, which are surrounded by a high-temperature-resistant insulation, which runs through the acoustically damping material and the potting compound; and a strain relief element which is located in an opening of the housing

is arranged and through which the lines run.

An example of a measuring arrangement comprises an ultrasonic sensor acoustically coupled to a hot surface of an object to be examined and a temperature-resistant film arranged between the hot surface and the ultrasonic sensor,

especially made of polyvinyl.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, exemplary embodiments are explained in more detail with reference to figures. The illustrations are not necessarily true to scale and the exemplary embodiments are not limited to the aspects shown. Rather, emphasis is placed on illustrating the principles on which the exemplary embodiments are based. In the

Pictures shows:

FIG. 1 shows a longitudinal section of an example of an ultrasonic sensor.

Figure 2 illustrates Geweils in a longitudinal section) four different variants

an assembly with an ultrasonic sensor and a mounting device.

Figure 3 illustrates various alternative embodiments in which the

the assembly has a feed line for the ultrasound.

DETAILED DESCRIPTION

1 illustrates in a longitudinal section an example of an ultrasonic sensor 9. This has a, for example, cylindrical housing 1 made of aluminum, for example.

can be made. As an alternative to aluminum, other materials can also be used

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that have similar thermal properties (e.g. coefficient of thermal expansion) and acoustic properties (e.g. speed of sound or the transit time of an ultrasonic pulse through the housing wall with thickness L) and material properties (density) such as aluminum

exhibit nium.

Inside the housing 1 (e.g. on the inside of the front housing wall) a piezoelectric element 2 (piezoceramic, e.g. PZT) is arranged and fastened to the housing wall, e.g. by means of an adhesive 3. Two lines 4a and 4b are electrically connected to the two main surfaces (front and rear) of the piezoelectric element 2. The two lines 4a, 4b are surrounded by high temperature-resistant insulation 5. In the example shown, the line 4a designates the signal line and the line 4b the measurement line. The lines 4a and 4b can, however, also be differential signal lines. On the back of the piezoelectric element 2 there is usually an acoustically damping material 6 which increases the bandwidth of the electroacoustic system (control electronics plus piezoelectric element). In the example shown, the damping material 6 is covered with a high-temperature-resistant potting compound 7, the lines 4a and 4b surrounded by the insulation 5 running through the damping material 6 and the potting compound 7. In this context, “high temperature resistant‘ ”means resistant to temperatures of up to at least 500 ° Celsius. The lines 4a and 4b surrounded by the high-temperature-resistant insulation 5 can be led out of the housing 1 through a strain relief element 8 which is arranged in a housing opening

become.

The ultrasonic sensor 9 shown in Fig. 1 is suitable for use in industrial applications at high temperatures (for example up to 150 ° Celsius. The differences in the coefficient of thermal expansion of the aluminum from which the housing 1 is made, and the commonly used piezoceramics ( such as PZT) are sufficiently small. As a result, the shear forces induced by the different thermal expansion coefficients, which can damage or destroy the piezoelectric element 2, are also acceptably small. The sensor construction according to FIG a good corrosion-resistant and leak-proof sensor, which, due to its design, is suitable for good heat dissipation (away from the piezoelectric element

ment 2).

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In order to maximize the acoustic energy transferred from the piezoelectric element into the object to be examined, which for example consists of steel, the following must

condition must be met

ZaLu AV Zpiezo * ZstaHL- (D)

where Zaiu> Zpriezo and Zsrayr denote the acoustic impedances of the aluminum housing 1, the piezoelectric element 2 or the object to be examined. Equal-

the following must apply to the thickness L of the housing wall in advance: Z = nA / 4,

where n is an integer greater than 0 and A denotes the wavelength of the ultrasound. The acoustic impedances are the product of the speed of sound and the density of the respective material. It is worth mentioning that suitable piezoelectric materials exist whose acoustic impedance Zp; gzo approximately fulfill the condition from equation (1), as a result of which a high degree of transmission of the acoustic energy can be achieved for objects made of steel to be examined. Al suitable piezoelectric materials come into consideration, e.g. 1-3 piezo composites (PZT + polymer), which

have the desired low acoustic impedances of less than 10-10 ° Ns / m *.

The ultrasonic sensor 9 shown in FIG. 1 can be used in the arrangements / systems described below (see FIGS. 2 and 3). Alternatively, other commercially available ultrasonic sensors can also be used (with associated

restrictions regarding the maximum temperature).

Fig. 2 shows in the diagrams (a), (b), (c) and (d) four different variants of an assembly with an ultrasonic sensor 9 and a mounting device,

which can also be designed to cool the ultrasonic sensor 9.

2 (a) illustrates a first example of an assembly / a system with an ultrasonic sensor 9 and a mounting device for mounting the ultrasonic sensor 9 on the (steel) surface of an object 11 to be examined.

the assembly device essentially holds a plate 12 with which the ultrasonic sensor

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9 can be pressed against the surface of the object 11. The necessary contact pressure is provided by tightening the screws 13, which are passed through holes in the plate 12 and screwed into the object 11. The insulated lines 4a and 4b can also be passed through a hole in the plate 12. However, the ultrasonic sensor 9 is not pressed directly against the surface of the object 11, but a coupling material is arranged between the front side of the ultrasonic sensor 9 and the surface. In contrast to conventional applications, a layer 10 made of a ceramic paste or a polyvinyl film, for example, which is suitable for higher temperatures than ceramic paste, can be used as the coupling material. In the example from FIG. 2 (a), the ultrasonic sensor 9 is cooled by the air that the sensor

housing surrounds.

FIG. 2 (b) illustrates a second example of an assembly / a system with an ultrasonic sensor 9 and a mounting device, the assembly from FIG.

2 (b) is suitable for slightly higher temperatures (e.g. 80 ° - 150 ° Celsius) in continuous operation than the previous example. Instead of the plate 12, a support block 18 is provided according to FIG. 2 (b), the outer shape of which can be approximately rotationally symmetrical (but this does not necessarily have to be the case). The carrier block 18 has a central bore in which the ultrasonic sensor 9 is inserted up to a stop (which is formed due to a reduction in the diameter of the central bore). The carrier block 18 can be made of aluminum, copper or some other material with good thermal conductivity. In order to ensure good heat transport between the ultrasonic sensor 9 and the carrier block 18, a heat-conducting paste can be arranged between them. The isolated lines 4a and 5b are in the central bore through the support block 18

passed through.

So that the carrier block 18 can fulfill the function of a heat sink, direct contact between the carrier block 18 and the hot surface of the object to be examined is avoided. In the example shown, an insulating layer 15 for thermal insulation is arranged between the hot surface, which is intended to prevent direct heat transfer from the hot surface to the carrier block by means of heat radiation and to significantly reduce indirect heat transfer by convention. In order to achieve an indirect heat transfer due to the conduction of heat via the screws 16 with which the support block 18 is attached to the hot surface.

prevent the screws 16 from a heat-resistant, but poorly thermally conductive

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capable plastic, for example from PEEK (polyetheretherketone). These measures ensure that the hot surface heats the carrier block 18 as little as possible and consequently the carrier block 18 heats the ultrasonic sensor 9 and the coupling

medium 14 (in this example a polyvinyl film) can cool sufficiently.

The polyvinyl film used as coupling agent 14 can have a thickness in the range of, for example, 20-100 µm. This film thermally and electrically isolates the sensor arrangement 9 from the hot surface of the object 11 to be examined and is able to compensate for unevenness between the end face of the ultrasonic sensor and the hot surface in order to achieve good acoustic coupling. Spring elements 17 (e.g. spiral or disc springs) can be arranged between the heads of the aforementioned plastic screws 16 and the carrier block 18 in order to compensate for different thermal expansions of the carrier block 18 and the plastic (e.g. PEEK) by deforming the spring elements 17. In the present example, the screws 16 are through holes in the support block 18 and the underlying insulating

layer 17 passed through and screwed into object 11.

The carrier block 18 can have structures that improve the dissipation of heat (through thermal radiation and convection) towards the cooler environment. For example, one or more bores 18a can be provided in the carrier block 18, furthermore (cooling) ribs 18b can be arranged on the outside of the carrier block, which ribs can also be formed, for example, by the windings of a thread. The bores 18a and the ribs 18b enlarge the total surface of the support block 18 and thus improve the heat dissipation towards the cooler environment. The bores 18a run within the support block 18 at least partially next to the ultrasonic sensor 9 in the immediate vicinity of this, in order to ensure good heat dissipation.

port to enable.

Figure 2 (c) illustrates a third example of an assembly / system which is suitable for continuous operation at even higher temperatures (e.g. 150 ° -350 ° Celsius) than the previous example. The example from FIG. 2 (c) includes all components of the example from FIG. 2 (b) as well as additional components. For example, in the drilling

stanchions 18a highly thermally conductive rods 19 arranged. The thermally conductive rods 19 can for example consist of copper and in particular as heat pipes (so-called heat

Pipes) be designed. To ensure good heat transfer from the support block 18 to the rods

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19, 19 thermal paste can be placed between the inner surface of the bores 18a and the rods. According to the example shown, a further thermally insulating layer 22 can be arranged on the carrier block 18, which layer has openings through which the rods 19 extend. A heat sink 20 can be attached to those parts of the rods 19 which protrude from the carrier block 19. For this purpose, the heat sink 20 can have bores 20a which are aligned with the bores 18a in the support block 18, so that the rods 19 are arranged partly in the bores 18a in the support block 18 and partly in the bores 20a in the heat sink 20. Thermally conductive paste can also be provided in the bores 20a in order to improve the heat transfer from the rods 19 to the cooling body 20. The mentioned thermal insulation 22 is located between the heat sink 20 and the carrier block 18. The thermally highly conductive rods 19 thermally couple the interior of the carrier block 18 to the heat sink 20. As mentioned, copper with a thermal conductivity of approx. 400 W / (mK) is a suitable one Material for the rods 19. To increase the heat radiation and for the greatest possible heat dissipation to the environment, the carrier block 18 and the

Heat sink 20 colored black, in particular anodized.

In addition, a thermally insulating sleeve 21, which surrounds the cooling body 20, can be placed on the carrier block 18. The thermally insulating sheath 21 can for example consist of high-temperature plastic or ceramic and be fastened to the support block 18, for example by means of a screw connection (see external thread 18b in Fig. 2 (b), the sheath 21 can have a corresponding internal thread). The shell can help to mechanically stabilize the overall system. Instead of the

Other connection techniques can also be used with screw connections.

In the region of the heat sink, the sleeve 21 can have a plurality of bores 21a. These should be so large that the natural convection and thermal radiation allow sufficient heat dissipation to the environment, but the shell 21 offers protection against inadvertent contact with the heat sink 20 in order to avoid injuries. Thus, the components of the assembly and cooling device in the various expansion stages either have a heat-dissipating function and / or structural radio

tion and / or safety-related functions.

If the hot surface of the object 11 has temperatures above 350 ° C

Instead of the cover 21, another cover 23 can be used. An example of this is in

Fig. 2 (d). The shell 23 does not contain any bores 21a for natural convection, but rather an inlet 24 and an outlet 25 for the supply and discharge of a gaseous or liquid cooling medium in order to use the heat sink located within the shell 23.

to cool per 20 by means of forced convection.

If the property to be detected by means of ultrasound is in the near field of the ultrasonic sensor 9, it may be necessary to install a delay line between the object 11 to be examined and the ultrasonic sensor 9, since in the near field interference can make measurements difficult or impossible . In order to establish a lead path between the ultrasonic sensor 9 and the surface of the object 11, the ultrasonic sensor 9 is not arranged in the carrier block at the bottom so that it protrudes from the carrier block (as in Fig. 2 (b) to (d)), but the ultrasonic sensor 9 is arranged within the support block. Examples of systems with an ultrasonic sensor with

running distance are shown in Figs. 3 (a) to (d).

As shown in Fig. 3 (a), the central bore in which the ultrasonic sensor 9 is located is a blind hole, so that the acoustic wave from the ultrasonic sensor 9 to the underside of the carrier block 28 through the metal of the carrier block 28 (e.g. Copper or aluminum) before it is coupled into the object 11. The acoustic path through the metal of the carrier block 28 from the lower side of the ultrasonic sensor to the lower side (contact surface) of the carrier block 28 is referred to as the lead path 28a. A coupling layer 27, which is formed, for example, by a ceramic paste, can be located between the ultrasonic sensor 9 and the carrier block 28. The coupling layer 14 between the contact surface on the underside of the carrier block 28 and the hot surface can, as in the previous examples, be a polyvinyl film or a ceramic paste (application-specific depending on the temperature). In the middle area below the central bore, the carrier block has a projection with a raised contact surface, which is mechanically / acoustically connected to the hot surface via the coupling layer 14. In the outer area, i.e. next to the projection, the thermally insulating layer 15 is arranged between the hot surface and the carrier block 14 (similar to the layer 15 in Fig. 2 (b)). The insulation 15 only has a central opening through which the projection with the contact surface of the carrier block 28 extends. The carrier block 28 is accordingly thermally coupled to the hot surface only via the comparatively small contact area and to the rest

Thermally insulated areas from the hot surface.

Apart from what has been described above, all other components shown in Fig. 3 (a) (screws 16, spring elements 17, holes 18a, ribs / threads 18b) are the same as in Fig. 2 (b) and it reference is made to the description above. The example from FIG. 3 (b) includes, in addition to the components shown in FIG. 3 (a), the copper rods 19, the heat sink 20 (with the bores 20a) and the shell 21 (with the openings 21a), which are designed in the same way are as in the example of Fig. 2 (c). The example from FIG. 3 (c) is essentially the same as the example from FIG. 3 (b), except that the shell 21 has an inlet 24 and an outlet 25 for a cooling medium (and no holes 21a). In this respect, the example from FIG. 3 (c) is constructed similarly to the example from FIG. 2 (d) (apart from the acoustic feed path and the associated

with associated changes in support block 28 compared to support block 18).

In applications in which ultrasound examinations are to be carried out in a fluid inside / or behind a metal structure 29 (eg container wall / housing wall), it can be useful to replace the carrier block 28 from the previous examples with a modified carrier block 32 , which has a cylindrical extension 32a on its longitudinal axis. An example is shown in Fig. 3 (d). The extension 32a is part of the advance path explained above with reference to FIGS. 3 (a) to (c). With the aid of a suitable mechanical structure (e.g. a hexagon 32b) which is mechanically connected to the extension 32a, the lead section can be screwed into a suitable sensor bore 31 with an internal thread 31c in the metal structure 29. As a result, losses and reflections of the acoustic energy at the transition from the carrier block 32 to the hot surface of the metal structure 29 are avoided and the sound

Oil energy is coupled directly into the fluid via the extended flow path.

Claims (10)

PATENT CLAIMS 1. A sensor assembly that includes: an ultrasonic sensor (9), a carrier block (18, 28) into which the ultrasonic sensor (9) is inserted so that the ultrasonic sensor (9) is thermally coupled to the carrier block (18, 28), Fastening means (16) which are designed to fix the carrier block (18, 28) on a hot surface of an object (11) to be examined; a thermal insulation (15) which is arranged between the support block (18, 28) and the hot surface, wherein the thermal insulation (15) has a central opening through which either the ultrasonic sensor (9) or part of a through the Trä - gerblock 28 formed flow path (28a) runs therethrough. 2. The sensor assembly according to claim 1, wherein the fastening means (16) are screws made of plastic, for example se consist of PEEK and which are screwed into the object to be examined (11). 3. The sensor assembly according to claim 2, wherein the screws (16) have screw heads and wherein between the Screw heads and the support block (18, 28) spring elements (17) are arranged. 4. The sensor assembly according to one of claims 1 to 3, wherein between the ultrasonic sensor (9) and the hot surface or between the feed path and the hot surface, a polyvinyl film as the coupling medium (14) is arranged. 5. The sensor assembly according to one of claims 1 to 4, wherein the carrier block (18, 28) has empty bores (18a) and / or wherein the carrier block (18, 28) on its outside ribs (18b), for example in the form of Has thread turns. 6. The sensor assembly according to one of claims 1 to 5, wherein in the carrier block (18, 28) has bores (18a) in which thermally conductive rods (19), for example made of copper, are arranged, which are from the carrier block (18, 28) protrude. 7. The sensor assembly of claim 6, further comprising: a thermal insulation (22) which is arranged on the carrier block (18, 28) and has openings through which the rods (19) extend, and a sheath (21) which is connected to the carrier block (18, 28) in such a way that the parts of the rods (19) protruding from the carrier block (18, 28) inside the sheath (21) lie. 8. The sensor assembly according to claim 7, wherein the sheath (21) is made of thermally insulating material and has at least one inlet (20a, 24) and at least one outlet (20a, 25) to allow a flow of a to enable a cooling medium within the envelope (21). 9. An ultrasonic sensor comprising: a housing (1), a piezoelectric element (2) attached to a housing bottom inside the housing (1), an acoustically damping material (6) which is inside the housing (1) Pilezoelectric element (2) covered, a potting compound (7) which covers the acoustically damping material (6) inside the housing, two lines (4a, 4b) electrically connected to the piezoelectric element (2), which are covered by a high-temperature-resistant insulation ( 5), which runs through the acoustically damping material (6) and the potting compound (7), and a strain relief element (8) which is inserted in an opening in the housing (1) is arranged and through which the lines (4a, 4b) run. 10. A measuring arrangement, which has the following: an ultrasonic sensor (9) according to claim 9 which is acoustically coupled to a hot surface of an object (11) to be examined, and one arranged between the hot surface and the ultrasonic sensor (9) temperature-resistant film (19), in particular made of polyvinyl.