DEVICE FOR LONG-TERM TEMPERATURE MEASUREMENT OF TEMPERATURES ABOVE 200 °C

Description

Technical field

[0001] The invention relates to a device for long-term temperature measurement of temperatures above 200 °C, comprising a transponder and an antenna connected to the transponder via a coaxial cable, wherein the antenna connection of the transponder is connected to the inner conductor of the coaxial cable and its outer conductor to the ground potential of the transponder. State of the art

[0002] Particularly in connection with food prepared in an oven, radio-interceptable devices for long-term temperature measurement of temperatures above 200 °C are known (EP 1985983 A2). These devices can, for example, be designed as a measuring probe with a handle that can be inserted into the food. Such devices have a transponder and an antenna connected to the transponder via a coaxial cable. The antenna connection of the transponder is connected to the inner conductor of the coaxial cable, and its outer conductor is connected to the ground potential of the transponder. For a particularly compact design, the antenna is designed as a shortened monopole arranged in a housing that forms the handle. However, a disadvantage of this design is that the shortened monopole antenna has a very low intrinsic impedance, which leads to limited power transmission between the antenna and the transponder.Against this background, in order to enable not only improved power transmission between the transponder and the antenna, but also stable radio transmission conditions, the antenna features an additional loading coil for impedance matching. Furthermore, the choice of materials, the dimensions, and the electrical and thermomechanical properties of the numerous individual components must be carefully considered beforehand, and the individual components must be precisely matched to one another. US 2012 / 188133 A1 discloses an insertion probe for measuring the core temperature of food. The probe has a SAW temperature sensor (635, Fig. 6) connected to a coaxial cable (605, Fig. 6). The end of the cable not connected to the sensor forms a loop antenna (615, Fig. 6). Description of the invention

[0003] The invention is therefore based on the objective of designing a device of the type described above in such a way that improved transmission conditions are made possible cost-effectively with low component requirements and design effort, without requiring complex coordination of the components to each other.

[0004] The invention solves the stated problem by forming a loop antenna with the self-supporting coaxial cable, the inner conductor of which is connected to ground potential at the end opposite the transponder. Due to these features, initially only the self-supporting coaxial cable and the transponder connected to it are required to obtain a mechanically and thermally robust device in a particularly simple manner. Preferably, the loop antenna is formed from the self-supporting coaxial cable by shaping the coaxial cable into a loop and connecting the inner conductor to ground potential at the end of the coaxial cable opposite the transponder. For the purposes of the invention, a self-supporting coaxial cable is understood to be a coaxial cable that, due to its inherent dimensional stability, can bear its own weight and the weight of the transponder without deformation.Advantageously, the coaxial cable is so stable that deformation during normal measurement use is ruled out. In addition to the inner and outer conductors, the coaxial cable typically also has a dielectric between them. This effectively shields the circuit running through the inner conductor from external interference fields, without impairing the transmission quality of the loop antenna. Furthermore, because the inner conductor of the loop antenna is connected to ground potential at the end of the coaxial cable opposite the transponder, the resulting galvanic short circuit provides the additional benefit of electrostatic discharge protection, without requiring any additional components or measures.For the purposes of this invention, a connection to ground potential is understood to mean any direct or indirect electrical connection to the ground terminal of the transponder. If the transponder has a symmetrical signal connection for the antenna, then, for the purposes of this invention, one of the two signal connections is considered the antenna connection and the other the ground connection, whereby the specific assignment is irrelevant. The self-supporting coaxial cable can, for example, be a semi-rigid or semi-flexible coaxial cable. The transponder can, in principle, include an acoustic surface wave sensor as a sensor unit. Preferably, the transponder has an acoustic surface wave sensor housed in a metallic transponder package, for example, a TO-25 or TO-39 package. The transponder package can be connected to the ground terminal of the transponder.

[0005] Particularly favorable conditions arise when the coaxial cable has an exposed metal sheath as the outer conductor. This eliminates the need for additional sheathing or insulation materials surrounding the outer conductor, such as those based on high-temperature-resistant plastics, thus opening up a wider range of applications due to improved food compatibility. Consequently, not only is the need for shielding of the coaxial cable, which negatively impacts transmission performance, avoided, but manufacturing costs can also be further reduced.

[0006] To further improve the mechanical stability and heat resistance of the device, thus achieving a particularly durable construction, it is recommended that the transponder be connected to the coaxial cable via an adapter without soldering. The preferably metallic adapter enables both mechanical and electrical coupling of the transponder to the coaxial cable, thereby stiffening the connection area between the transponder and the coaxial cable. The solder-free connection is preferably achieved by welding or screwing. This creates a highly conductive connection that, unlike soldered connections, is also particularly robust against high temperatures well above 200 °C, as well as against mechanical shocks and vibrations. In principle, it may be provided that, for mechanical stabilization and improved sealing, some or all welded connections or...Screw connections are sealed and reinforced by applying a stabilizer based on a glass solder or a high-temperature resistant adhesive.

[0007] Particularly simple manufacturing conditions arise when the inner conductor at the end of the coaxial cable opposite the transponder is welded to the outer conductor as ground potential. In the simplest case, the coaxial cable is bent to form the loop antenna, and to close the loop, the inner conductor at the free end of the coaxial cable is welded to the outer conductor in the area of ​​the forming antenna base. This connection point between the inner conductor in the area of ​​the antenna base and the outer conductor can also be sealed and reinforced by applying a stabilizer based on glass solder or a high-temperature adhesive.

[0008] Another advantageous design can be achieved if the inner conductor on the end of the coaxial cable opposite the transponder is connected to the transponder's ground terminal, preferably via the adapter. This measure allows the device to be built particularly compactly because the coaxial cable and the transponder together form a closed loop without any protruding components.

[0009] In order to improve the transmission characteristics, particularly in this context, it is proposed that the coaxial cable, acting as a loop antenna, forms a closed loop, preferably a ring, with the transponder.

[0010] In the context of long-term temperature measurements of cooked food, it is recommended that the coaxial cable serve as a feed line for the transponder and a loop antenna spaced apart from the transponder. This allows the transponder to be easily inserted into the food and, for example, record its core temperature, while the transmission performance of the device is not affected by the food due to the spaced loop antenna.

[0011] Particularly favorable transmission conditions result when the loop diameter of the loop antenna corresponds to an integer multiple of the transponder's wavelength. Preferably, the loop diameter is adapted to the wavelength range in which the transponder is read, so that the characteristic impedance already enables reliable transmission without additional adjustments.

[0012] To ensure a long service life, especially in the presence of water vapor, it is proposed that the outer conductor of the coaxial cable be heat-treated. This measure passivates the outer conductor, which is predominantly made of copper, thus significantly reducing its tendency to oxidize, even when repeatedly exposed to a water vapor atmosphere at temperatures above 200 °C for extended periods. For the passivation of typical coaxial cables, for example, they are heat-treated in two successive steps, each lasting 15–30 minutes at 250 °C in ordinary air, after which any leaking dielectric fluid is removed.

[0013] To achieve improved sealing and thus better protection against aggressive external influences, such as water vapor, despite simplified manufacturing conditions, it is recommended that the transponder be inserted into the receiving chamber of a protective sleeve. Preferably, the metallic protective sleeve is welded to the outer conductor of the coaxial cable, resulting in a reliable seal even without additional sealing elements. The protective sleeve can be connected to the transponder's ground terminal. Alternatively, the protective sleeve can also establish a connection between the transponder's ground terminal and the outer conductor of the coaxial cable. If the transponder is connected to the coaxial conductor via an adapter without soldering, both the transponder and the adapter can be inserted into the receiving chamber of the protective sleeve. Brief description of the invention

[0014] The invention is illustrated in the drawing as an example. It shows Fig. 1 a schematic representation of a device according to the invention in a first embodiment, Fig. 2 one of the Fig. 1 Fig. 3 shows a detailed view of the transponder and the adapter on a larger scale, Fig. 3 shows a schematic representation of a device according to the invention in a further embodiment, and Fig. 4 shows one of the Fig. 3 A corresponding detailed view of the transponder and adapter on a larger scale. Ways to implement the invention

[0015] A device according to the invention for long-term temperature measurement of temperatures above 200 °C comprises a transponder 1. The antenna connection 2 of the transponder is connected to the inner conductor 3 of a self-supporting coaxial cable 4, whereas the outer conductor 5 of the coaxial cable 4 is connected to the ground potential of the transponder 1 via a metallic adapter 6. The schematically indicated connection points 7, 8 are preferably designed as welded connections. The adapter 6 enables both mechanical and electrical coupling of the transponder 1 to the coaxial cable 4, thus stiffening the connection area between the transponder 1 and the coaxial cable 4.

[0016] The self-supporting coaxial cable 4 also forms a feed line for the transponder 1 and a loop antenna 9 spaced apart from the transponder 1. The inner conductor 3 is welded to the outer conductor 5 as ground potential at the end of the coaxial cable 4 opposite the transponder 1, as indicated by the connection point 10 at the antenna base. The connection point can be additionally sealed and reinforced with a stabilizer (not shown), e.g., based on glass solder or a high-temperature adhesive. For improved protection of the transponder 1 from, for example, water vapor, a protective sleeve 11 can be provided, which surrounds the transponder 1 and, if applicable, also the adapter 6, as shown in Figs. 1 and 2 is illustrated.

[0017] Figs. 3 and 4Figure 1 shows a further embodiment of a device according to the invention. In this embodiment, the coaxial cable 4, acting as a loop antenna 9, forms a closed loop in the shape of a ring with the transponder 1. The inner conductor 3 is connected to the ground terminal 12 of the transponder 1 at the end of the coaxial cable 4 opposite the transponder 1. This connection point is further sealed and reinforced by a stabilizer 13 for mechanical stabilization and improved sealing; this stabilizer can be, for example, a glass solder or a high-temperature-resistant adhesive. The transponder 1 can have a metallic transponder housing, for example, a TO-25 or TO-39 package, which is connected to the ground terminal 12 of the transponder 1. It can also be provided that the adapter 6 encloses the transponder 1 for additional protection.

Claims

1. Device for long-term temperature measurement of temperatures above 200 °C, comprising a transponder (1) and an antenna connected to the transponder (1) via a coaxial transmission line (4), wherein the antenna connection (2) of the transponder (1) is connected to the inner conductor (3) of the coaxial transmission line (4) and its outer conductor (5) is connected to the ground potential of the transponder (1), wherein the self-supporting coaxial transmission line (4) forms a loop antenna (9), the inner conductor (3) of the loop antenna (9) being connected, at its end opposite the transponder (1), to the ground potential.

2. Device according to claim 1, characterised in that the coaxial transmission line (4) comprises an exposed metal sheath as outer conductor (5).

3. Device according to claim 1 or 2, characterised in that the transponder (1) is connected to the coaxial transmission line (4) in a soft-solder-free manner via an adapter (6).

4. Device according to any one of claims 1 to 3, characterised in that the inner conductor (3), at the end of the coaxial transmission line (4) opposite the transponder (1), is welded to the outer conductor (5), which forms the ground potential.

5. Device according to any one of claims 1 to 3, characterised in that the inner conductor (3), at the end of the coaxial transmission line (4) opposite the transponder (1), is connected to the ground terminal (12) of the transponder (1).

6. Device according to any one of claims 1 to 5, characterised in that the coaxial transmission line (4) together with the transponder (1) forms a closed loop.

7. Device according to any one of claims 1 to 5, characterised in that the coaxial transmission line (4) forms a supply line for the transponder (1) and a loop antenna (9) spaced apart from the transponder (1).

8. Device according to any one of claims 1 to 7, characterised in that the loop diameter of the loop antenna (9) corresponds to an integer multiple of the wavelength of the transponder (1).

9. Device according to any one of claims 1 to 8, characterised in that the outer conductor (5) of the coaxial transmission line (4) is heat-treated.

10. Device according to any one of the preceding claims, characterised in that the transponder (1) is inserted into the receiving chamber of a protective sleeve (11).