Sensor Having a Housing

Abstract

In an embodiment a sensor includes a sensor element, a connecting element configured for electrical connection and a housing located on the sensor element, wherein the housing comprises a housing material with cured liquid silicone rubber (LSR) as a main component.

Claims

1.-12. (canceled)

13. A sensor comprising: a sensor element; a connecting element configured for electrical connection; and a housing located on the sensor element, wherein the housing comprises a housing material with cured liquid silicone rubber (LSR) as a main component.

14. The sensor of claim 13, wherein the sensor element comprises a temperature-sensitive member.

15. The sensor of claim 14, wherein the temperature-sensitive member comprises a thermistor material.

16. The sensor of claim 13, wherein the connecting element comprises an electrical wire.

17. The sensor of claim 13, wherein the connecting element comprises a lead frame.

18. The sensor of claim 13, wherein the housing material has a thermal conductivity of 0.2-0.3 W/(m K) at 100° C.

19. The sensor of claim 13, wherein the housing material has a coefficient of thermal expansion of 2×10.sup.−4-4×10.sup.−4 K.

20. The sensor of claim 13, wherein the housing material has a hardness of 10-90 Shore A.

21. The sensor of claim 13, wherein the housing material has a dielectric strength of 20 kV/mm or more.

22. The sensor of claim 13, wherein the housing is arranged on a part of the connecting element.

23. The sensor of claim 13, wherein the housing is applied by injection molding.

24. The sensor of claim 23, wherein the housing is applied by liquid injection molding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In the following, further exemplary embodiments of the invention are described in detail by reference to figures. However, the invention is not limited to these embodiments. In the figures, similar elements, elements of the same kind and identically acting elements may be provided with the same reference signs.

[0063] FIG. 1 shows a first embodiment of the sensor with a cuboid housing and a connecting element;

[0064] FIG. 2 shows a sectional view of the first embodiment wherein leads of the sensor element are soldered to wires of the connecting element;

[0065] FIG. 3 shows the first embodiment in another perspective view;

[0066] FIG. 4 shows a second embodiment of the sensor with a two-part cylindrical housing and a connecting element; and

[0067] FIG. 5 shows a sectional view of the second embodiment wherein leads of the sensor element are crimped with wires of the connecting element.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0068] The sensor 1 in FIGS. 1 to 3 comprises a sensor element 2 comprising a temperature-sensitive member 21 and a pair of leads 22. The pair of leads 22 for electrical connection is arranged between the temperature-sensitive member 21 and a connecting element.

[0069] The whole sensor element 2 is covered by a one-part and tight and impermeable housing 8, fully encapsulating the sensor element 2. In the present embodiment the housing 8 has a cuboid shape. The shape and structure of the housing 8 can be modified according to the application of the sensor.

[0070] The temperature-sensitive member 21 is arranged at a first end of the sensor element 2 designated as sensor head 3 inside the housing 8.

[0071] The temperature-sensitive member 21 consists of a thermistor material. In the first embodiment the thermistor material has a negative thermal coefficient. In another embodiment the thermistor material may have a positive thermal coefficient.

[0072] The leads 22 consist of an electrically conductible material such as nickel, copper, silver, a similar conductive metal or one of their alloys. The leads 22 are fixed to the temperature-sensitive member 21 at a side opposite to the sensor head 3. The leads 22 are directed away from the sensor head 3.

[0073] The sensor element of the first embodiment has a cylindrical shape and a diameter of ≤2.4 mm.

[0074] The sensor 1 of the first embodiment is used for temperature measurements. Possible applications are, for example, temperature measurements of chemical fluids or solid surfaces. The sensor 1 is designed for temperature measurements in an extended measuring range from −40° C. up to 250° C.

[0075] Therefore the sensor head 3 on the first end of the sensor housing 8 is in contact with a surface to be measured.

[0076] The heat of the medium 4 is quickly conducted to the temperature-sensitive member through the thin housing 8 at the sensor head 3.

[0077] At a second end 5 of the sensor housing 8 two insulated wires 6 are fixed to the leads of the sensor element 2 as an electric connecting element. The wires 6 are fixed to the leads by solder 62. The part of the wires 6 which is in contact with the leads 22 is not insulated. The insulation of the remaining wires consists of a silicone material.

[0078] In the present embodiment the second end 5 is the side of the housing 8 with the largest distance to the sensor head 3.

[0079] Only a part of the insulated wires 6 is shown in the figure. Further portions of the insulated wires 6 are not shown in the figure. At the end of the insulated wires 6 not shown in the figures a plug may be fixed to connect the insulated wires 6 with electric circuitry.

[0080] In the shown embodiment a portion 7 of the insulated wires 6, adjacent to the sensor element 2, the solder connection 62 and the sensor element 2 are covered by the housing 8.

[0081] The housing 8 comprises liquid silicone rubber (LSR) as the main component. The housing is applied onto the sensor by injection molding. The molded housing 8 consists of only one layer whose inner surface adapts smoothly and tightly to the shape of the sensor element 2. Therefore the housing 8 fits closely with the sensor element 2. The outer surface of the housing is formed by a mold.

[0082] The housing material may comprise further components. LSR being the main component, the ratio of LSR in the housing material is at least 50 wt %. Additionally, the housing material comprises additives and filler materials. Possible filler materials are oxide ceramics, which contain oxides of silicon and/or aluminium. Further, nitrides such as AlN and BN or carbides such as SiC may be used as filler materials.

[0083] Such filler materials can influence several properties of the housing material like its tensile strength, hardness, dielectric strength, thermal elongation and thermal conductivity.

[0084] Besides, coloring agents can be added to colorize the transparent LSR material.

[0085] However, the housing material consists of one single homogeneous layer, wherein the added agents are homogenously dispersed in the LSR phase.

[0086] The housing material of the first embodiment is applied onto the sensor 1 by liquid injection molding. Due to the low viscosity of the liquid educts, a low housing wall thickness at the sensor head 3 ≥0.2 mm can be achieved. The low housing wall thickness shortens the response time of the sensor.

[0087] Furthermore, the housing material has strong hydrophobic properties and thus provides good protection for the electric components against water and humidity.

[0088] The possible elongation before breaking of the chosen housing material is more than 100%. The elongation is defined as the possible elastic deformation of a component relative to its original length. Due to its tightness and elasticity, the housing provides strong mechanical protection, especially in shock absorption.

[0089] Furthermore LSR shows a high chemical resistance. Therefore it is suitable to protect the sensor during temperature measurements in aggressive chemical mediums.

[0090] The viscosity of the uncured LSR depends on the respective application and ranges between 50,000 and 500,000 [mPa s]. The viscosity decreases during the molding process due to the shear thinning behaviour of the LSR material.

[0091] The uncured LSR is a mixture of liquid components comprising a component A and a component B. The component A comprises polysiloxane with organic substituents and a platinum catalyst. The component B comprises also polysiloxane with organic substituents and a cross-linker.

[0092] The components A and B may comprise the same type of polysiloxane with the same organic groups or different types of polysiloxane with different organic groups. The organic substituents may be methyl, vinyl, phenyl or similar substituents.

[0093] By exposure to UV-radiation or heating, a cross-linking reaction of the polysiloxane is triggered. The cross-linking reaction converts the liquid mixture to a solid housing material.

[0094] The cured LSR has the following properties: The thermal conductivity of LSR without an additive at 100° C. is typically between 0.2 and 0.5 W/(m K). The coefficient of thermal expansion is approximately 2×10.sup.−4-4×10.sup.−4 K. The compression set typically amounts to 5 to 25%. The hardness typically amounts to 10 to 90 Shore A. The dielectric strength according to DIN IEC 243-2 is 20 kV/mm or more.

[0095] FIG. 3 shows the first embodiment of the sensor 1 from a different perspective. The elements that have been described above are not be described again.

[0096] In the first embodiment the insulated wires 6 each consist of a single wire. In another embodiment the wires 6 are stranded wires.

[0097] In a further embodiment the sensor element may be contacted by more than two insulated wires.

[0098] In yet a further embodiment the sensor comprises two or more sensor elements covered by the same or several housings.

[0099] FIGS. 4 and 5 show a second embodiment of the sensor 1. Basically, the second embodiment is similar to the first embodiment of the sensor 1.

[0100] Different to the first embodiment, here the sensor housing 8 is shaped as a two-part cylinder. The part 9 of the cylinder at the second end's side 5 has a higher diameter than the part 10 at the first end's side 3.

[0101] Therefore, the part 9 at the second end's side 5 can accommodate a crimped connection 62 between the wires 6 and the leads 22. A portion of the wires 6 which is in contact with the leads is not insulated. The leads are arranged at the second end's side 5 of the temperature-sensitive member 21 and are directed away from the sensor's head 3.

[0102] The sensor element 2, the crimped connection 62 and a portion 7 of the wires 6 are covered by the housing 8.

[0103] A fluid medium 4 to be measured is at least in contact with the thinner part 10 of the sensor housing 8 comprising the sensor head 3. The thin wall thickness at the thinner part 10 of the housing 8 allows a short response time for temperature measurements. In another embodiment, the whole housing 8 and the insulated wires 6 are in contact with the medium to be measured 4.

[0104] In a forth embodiment, not shown in the figures, the connecting element for electrical connection is a lead frame instead of wires.

[0105] Although the invention has been illustrated and described in detail by means of the preferred embodiment examples, the present invention is not restricted by the disclosed examples and other variations may be derived by the skilled person without exceeding the scope of protection of the invention.