DE8802130U1 - Temperature sensor - Google Patents

Description

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Temperature sensor

The innovation relates to a temperature sensor of the type mentioned in the generic term of protection claim 1.

t [Jj The installation of a liquid temperature measuring device

Temperature sensor in a pipe system intended for the transport of thermal energy by means of a liquid (e.g.

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nsiiAieioiaui/ tsi.iijj.yi. iiaun \*n&mdash;ca u·» a pipe section that is closed on one side and extends into the pipe system. The closed end of the pipe section, which is surrounded by the liquid from the outside, separates a temperature sensor chamber from the liquid. This arrangement allows the temperature sensor to be replaced at any time without disrupting the liquid transport. The temperature sensor in the temperature sensor chamber has a cylindrical protective housing and is secured against accidental removal from the pipe section by means of a screw connection.

The housing of the temperature sensor protects a mechanically sensitive measuring element whose electrical conductivity changes as a function of the temperature and prevents, for example, the thin connecting wires from being torn off. The measuring element must not come into direct contact with the flowing liquid, as is the case with gaseous media (EP 190 858), due to the risk of destruction by mechanical forces or corrosion by the medium.

The temperature of the liquid is transferred to the measuring element by means of heat conduction through the wall of the pipe section and the protective housing.

Such an arrangement of the temperature sensor causes a systematic measurement error, which is caused by the dissipation of the heat flow via the cylindrical housing and the connection cable. Another disadvantage is a

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Slow response of the measuring element to temperature changes due to poor thermal contact between the measuring element and the liquid.

For temperature measurement, a thin platinum metal layer applied to a flat or cylindrical ceramic carrier is also advantageously used as a measuring element. Such measuring elements are described in the documents EP 63 264, DE-OS 36 03 and Db=CS 36 03 7S5. These measuring elements are considerably more robust than the measuring elements made of fine wires. However, any bending forces acting on the ceramic carrier must be kept away, as they cause additional measuring errors.

The innovation is based on the task of creating a temperature sensor that reacts quickly and has the smallest possible measurement error, which allows the temperature of a liquid to be measured with high measurement accuracy, can be installed in a pipe system and can be manufactured cost-effectively.

This problem is solved by the characterizing features of claim 1.

In the following, examples of the innovation are explained in more detail using the drawings.

Show it

Fig. 1: a longitudinal section through a temperature sensor,

Fig. 2: a design of a simple holder of a measuring element and the power supply line,

Fig. 3: a longitudinal section through a temperature sensor with a plastic injection-molded carrier of the measuring element and the power supply line,

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Pig, 4: a longitudinal section through a temperature sensor with a two-tone design of a carrier of the measuring element and the power supply and

Fig. 5: a cross-section through a temperature sensor according to Figure 4 in the area of the measuring element.

In Figure 1, a cup-shaped housing 1 of an air flow sensor encloses a measuring element 2. The measuring element 2 is arranged in the housing 1 directly above a base piece 3. The base piece 3 seals the housing 1 at one end against a surrounding liquid 4, the temperature of which is to be measured. Near the other end of the housing 1, the housing wall bulges out in steps and forms a circular collar 5. The collar 5 on the housing 1 is advantageously produced by compression.

A sealing ring 6 of circular or rectangular cross-section is pushed from the base piece 3 to the collar 5 onto the housing 1.

A connecting cable 7 is led out of the open end of the housing 1 and is secured against being torn out by pressing at least one groove 8 into the wall of the housing 1 between the collar 5 and the exit point of the connecting cable 7 from the housing 1. The connecting cable 7 connects the measuring element 2 to an evaluation point not shown here.

The connecting cable 7 is preferably a two-core stranded cable with an eleven-core shield around both plastic-insulated cores 7' and with an extruded outer sheath. Of course, the plastic used for the connecting cable 7 must be selected according to the operating temperature of the temperature sensor.

The housing 1 is with the base piece 3 first from the outside through

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a flange 9 is inserted into a pipe ft/β tem that conducts the liquid 4. A hexagon head screw 12 pushed over the housing 1 from the cable outlet side and screwed into an internal thread 10 of a wall 11 of the pipe system presses the collar 5 and the sealing ring 6 onto the flange 9 to seal the pipe system. The hexagon head screw 12 is only cut open by a quarter in Figure 1 in order to highlight the screw 12 more clearly.

In contrast to the arrangement known from CH-PS 647 867, the arrangement described above only has the housing 1 of the temperature sensor. The temperature sensor therefore seals the pipe system directly, i.e. the temperature sensor can only be replaced after at least one detachable part of the pipe system has been emptied.

Of course, other sealing and fastening methods of the temperature sensor to the pipe system, as are usual in the installation industry, are also conceivable, for example by directly screwing the collar 5 to the flange 9 using four or more screws.

The temperature-sensitive measuring element 2 is a resistance element with a large temperature coefficient and preferably consists of a thin platinum metal layer 14 applied to a, for example, cylindrical or flat, ceramic carrier 13. However, a coil made of a wound, thin platinum wire can also be used as the measuring element 2. In the case of a flat ceramic carrier 13 in the shape of an elongated rectangle, the two connecting wires 15 are preferably arranged on one of the two narrow sides.

Since mechanical forces acting on the measuring element 2 distort the measured value and make the adjustment of the measuring element 2 more difficult, a holder is provided which

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Messelenrent 2 absorbs and protects without any force.

Figure 2 shows a first embodiment of a holder for the measuring element 2.

A plate 16, which is preferably punched from a dimensionally stable insulating material of 0.5 to 1.6 mm thickness, such as epoxy material reinforced with glass fibers, has a width adapted to the clear width of the housing 1 (Figure 1). In the plate 16 (Figure 2) a recess 17 is provided at one end which is large enough to accommodate the measuring element 2 lying in the same plane as the plate 16 , so that the measuring element 2 can fit in it without touching the edges . Symmetrically arranged recesses 18 at the other end of the plate 16 serve to anchor a strain relief 19 made, for example, from a plastic or sheet metal strip, which fixes the two insulated wires 7' of the connecting cable 7, which are fed, for example, on the same side of the plate 16, in the longitudinal axis of the plate 16.

Each conductor 20 of the wires 7* is led to a support point 21 of the plate 16 and is brought into contact there with one of the two connecting wires 15, e.g. by means of soldering. In Figure 2, for example, two support points 21 connected by means of a conductor track 22 are provided for each supply line, one for the conductor 20 and one for the connecting wire 15 .

During assembly, the flat ceramic carrier 13 is inserted into the recess 17 of the plate 16 without the edges of the recess 17 and the ceramic carrier 13 touching. The ceramic carrier 13 is then connected to the plate 16 on the two long sides in the area of the connecting wires 15 using a quick-drying adhesive 23. By pressing on the strain relief 19, the plate 16 is connected to the

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Connecting cable 7 is firmly connected. The plate 16 is inserted into the housing 1 (Figure 1) with the measuring element 2 first and is pushed into the housing 1 up to the base stack 3 using the connecting cable 7.

The plate 16 protects the ceramic carrier from mechanical stress. Contact between the measuring element 2 and the inner wall of the housing 1 and thus the occurrence of parasitic currents that distort the measurement result is prevented with this arrangement.

Other known mountings, in which the measuring element 2 and the plate 16 form a right angle, require a precaution to prevent these parasitic currents. Such a precaution hinders the temperature equalization between the measuring element 2 and the housing 1 and therefore leads to incorrect measurements.

The electrical connections between the conductors 20 (Figure 2) and the connecting wires 15 are made, for example, by means of soldering processes at the support points 21 connected by conductor tracks 22.

Figure 3 shows a longitudinal section of another advantageous embodiment of a holder that enables easy installation of the measuring element 2 by means of a cylindrical carrier 24 molded from plastic. It is divided into a connection part 25 and a measuring chamber part 26. In one embodiment of the carrier 24, the length is 32 mm, the diameter is 5 mm and the measuring chamber length is 12 mm. The carrier 24 is molded from polyphonylene sulfide, for example.

The connection part 25 is characterized by two connection chambers 27 embedded next to each other in the upper half cylinder and two parallel longitudinal guides 2Θ for the wires 7' in the lower half cylinder. The longitudinal guides 28 run parallel to the axis

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of the carrier 24 from the connecting cable 7 to a central partition 29. The two longitudinal guides 28 advantageously have holding grooves for the wires T. In front of the partition 29, at the end of each longitudinal guide 28, a hole 30 adapted to the diameter of the wires 7 ¹ leads through the bottom of a connection chamber. Each connection chamber 27 takes up approximately four fifths of the length of the connection part 25 from the partition 29.

The measuring chamber part in the housing 1 facing the base piece 3 is penetrated by a chamber 31 for receiving the measuring element 2. Two preferably narrow webs 32 connect longitudinal walls 33 of the chamber 31 to increase the stability of the carrier 24 and serve as supports for the measuring element 2 stored in the upper half of the chamber 31. The chamber 31 is wide enough that the boiler element 2 rests on the two webs 32 without touching the long sides 33. The long walls lead from the partition wall 29 to a cylindrical end piece 34 facing the base piece 3. Only the elements 29 and 34 delimit the chamber 31, i.e. the chamber 31 is open above and below the measuring element 2 against the inner wall of the housing, so that the sensitive platinum metal layer ?4 is directly opposite the inner wall of the housing 1 without covers that prevent temperature equalization. A nose 35 molded onto the end piece projects about 2 mm into the chamber 31 above the ceramic carrier 13 and prevents the ceramic carrier 13 from lifting off and thus unwanted contact between the measuring element 2 and the housing 1. Drops of an adhesive for fixing the measuring element 2 in the chamber 31, preferably on the two long sides of the ceramic carrier in the area of the connecting wires 15, can also be used advantageously together with or instead of the nose 35.

During assembly, a wire 7 with the conductor 20 stripped to a width of about 5 mm is pushed through each of the two holes 30 into the connection chamber 27. Each of the two connection wires 15 of the

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Measuring element 2 is inserted into a leadthrough 36 of the partition wall 29 and connected to a conductor 20. The end of the wires 7 ¹ that is pushed through is bent onto the bottom of the connection chamber 27 and at the same time the wires T are inserted into the longitudinal guides 28 so that each wire 7' encloses the material of the carrier 24 located between the bottom of the connection chamber 27 and the bottom of the longitudinal guide 28 in a U-shape. A plastic band 37 surrounds the connection part in the area of the connection chambers and holds the U-shaped wires T in the connection chambers 27 and in the longitudinal guides ZL . The plastic band 37 insulates the two connection points of the connecting wire 15 with the conductor 20 against the housing 1 and at the same time fulfills the function of the strain relief 19. The remaining fifth of the connection part 25, the partition 29 and the end piece 34 have a diameter approximately 0.1 mm larger than the other points of the carrier 24 so that the plastic band 37 does not make it difficult to insert the completed carrier 24 into the housing 1.

For better illustration, Figure 3 shows the longitudinal section through the carrier 24 in the plane parallel to the carrier axis, which contains the conductor 20.

Figure 4 shows another embodiment of a carrier 24 made of injection-molded plastic .

The connection part 25 contains two connection chambers 27 and a tab 38 for fastening the strain relief 19. The connection wires 15 of the measuring element 2 are guided through one of the two feedthroughs 36 inserted into the partition 29, e.g. by means of adhesive, into each of the two connection chambers 27.

The tab 38 is designed, e.g. with notches, so that the wires 7* are clamped immovably to the carrier 24 by means of the strain relief 19 which encompasses the tab 38.

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The connection points 41 such as the conductors 20 and the connecting wires IS are relieved of the tensile forces acting on the conductors 20 outside the bushings 36.

After the connection points 41 have been created, the connection chambers 27 are closed, for example, by means of an insulating plastic band 37. The connection cable 7 leads axially away from the carrier 24.

Figure 5 shows a cross section through the housing 1 in the area of the measuring chamber part 26. The two longitudinal walls 33 of the chamber 31 have a guide groove 40. The guide grooves hold the measuring element 2 laterally in the predetermined position. They are to be dimensioned such that oils do not exert any forces on the ceramic carrier 13 over the entire range of the application temperature. The connecting wires 15 are guided into the connection chambers 27 through the passages 36, which are tightly sealed, e.g. by means of adhesive 23.

The measuring element is pushed through the end piece 34 (Figure 4) into the guide grooves 40. An end plate 39 prevents the measuring element 2 from slipping out by means of a pin. Other methods or devices for fixing the measuring element 2 in the preferred position without force, e.g. melting or gluing the entrance to the guide grooves 40, are conceivable.

During assembly, the equipped carrier 24 is inserted into the housing 1 with the measuring element 2 first. Shortly before the partition wall 29 is inserted into the housing 1, it is advantageous to fill the volume of the chamber 31 on both sides of the measuring element 2 with a thermal paste 42 that ensures good thermal contact between the inner wall of the housing 1 and the measuring element 2. This allows the temperature sensor to respond more quickly to temperature changes in the liquid 4. The carrier is then inserted into the housing 1 up to the base piece 3 using the connecting cable 7.

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When pushed in, the partition wall 29 seals the volume of the chamber 31 against the connection piece 25 and advantageously has a groove on the circumference which holds a Gununi sealing ring 43 inserted between the inner wall of the housing 1 and the partition wall 29. This measure prevents the thermal paste 42 from leaking out.

But other measures, such as introducing a suitable casting compound in the area between the connecting cable 7 and the connecting part 25 (Figure 3), also achieve the same purpose.

The open end of the housing 1 (Figure 1) is closed by rolling, whereby at least one groove 8 is created and the inner wall of the housing clamps the connecting cable 7 in the area of the groove β over the entire circumference. The three grooves 8 pressed into the housing 1 in one embodiment reliably prevent the connecting cable from being torn out.

A grommet 44 is pushed onto the housing 1 as a cable kink protection immediately behind the hexagon head screw 12 from the exit point of the connecting cable 7. The grommet 44 covers at least one groove 8 and preferably protrudes 10 cm beyond the housing 1. The grommet 42 advantageously reduces a heat flow in the wall of the housing 1 that distorts the measurement and thus reduces a measurement error of the temperature sensor. A shrink tube can advantageously be used for the grommet 44, but other grommets 44, e.g. made of rubber, are conceivable.

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Claims (9)

PROTECTIVE FRUITS 1. Temperature sensor with a temperature-sensitive measuring element (2) which, when installed, is screwed sealingly onto a flange (9) in a wall (11) of a pipe system containing a liquid (4) to be transported and one end of its housing (1) is immersed in this liquid (4) through the flange (9), characterized in that the housing (1) is closed at the other end by means of a connecting cable (7) pressed into the housing (1) by means of grooves (8) and that the measuring element (2) is mounted free from bending forces inside the end of the housing (1) which can be immersed in the liquid (4). 2. Temperature sensor according to claim 1, characterized in that the exit point of the connecting cable (7) is protected by means of a heat-insulating grommet (44). 3. Temperature sensor according to claim 1 or 2, characterized in that the measuring element (2) is a platinum metal layer (14) applied to a flat ceramic carrier (13). 4. Temperature sensor according to claim 3, characterized in that the measuring element (2) is held in a recess (17) of a plate (16) and in the plane of the plate (16), that the plate (16) has support points (21) for connecting wires (15) and conductors (20) and an anchor for a strain relief (19) of the conductors (20). 5. Temperature sensor according to claim 3, characterized in that a carrier (24) consisting of a connection part (25) and a measuring chamber part (26) is injection-molded from plastic and that connection channels (27) for a connection point (41) between a conductor (20) and a connection wire (15) are covered with a plastic band (37). PA 2383 DEg 26.01.88 &bull; Il Il Il # ·* ·· · &bull; IIIIII · · 4 · * &bull; 1*111 * * « · I illlll· · » * &diams; · Il M I I «**l ··· ·« «· 6. Temperature sensor according to claim 5, characterized in that the ceramic carrier (13) is mounted on webs (32) in the chamber (31) and that U-shaped bent wires (7 ¹ ) of the connecting cable (7) guided through holes (30) and secured by means of the plastic band (37) form a strain relief (19) for the connecting cable (7). 7. Temperature sensor according to claim 5, characterized in that the ceramic carrier (13) is held by means of guide grooves (40) in longitudinal walls (33) of the chamber (31) and that the carrier (24) has a tab (38) for anchoring the strain relief (19) for the wires (7'). 8. Temperature sensor according to claim 5, 6 or 7, characterized in that the carrier (24) has a partition wall (29) with sealed passages (36) and that the partition wall (29) carries a rubber ring (43) embedded in a groove on the circumference. 9. Temperature sensor according to one of the preceding claims, characterized in that the measuring element (2) is thermally contacted with the inner wall of the housing (1) by means of a thermal paste (42). PA2383 &bull;&igr; · j