EP1303169A1 - Temperature sensor with a sensing element and its application - Google Patents

Abstract

Temperature sensor with a sensor element for insertion in the zone between a cooker radiative heater and ceramic hob unit. The sensor element (3) comprises a temperature dependent electrical resistance with a resistance layer comprising a metal from the platinum group of metals. <??>The invention also relates to use of the inventive sensor in a control circuit for an electric cooker with a radiative heat source and a glass-ceramic cooking plate.

Description

The invention relates to a temperature sensor with at least one sensor element which a protective housing made of heat-resistant ceramic is at least partially surrounded, wherein the sensor element provided with connecting lines in the area of one end of the Protective housing is arranged, while the connecting cables over the other protective housing end are led outside. The invention further relates to its use.

DE 27 38 926 A1 describes a protective tube for a thermocouple for continuous measurement the temperature of molten steel known to have an inner ceramic tube with a closed end, which contains the thermocouple, further by an outer quartz tube arranged above the inner ceramic tube is closed to the outside, an annular one between the two concentrically arranged tubes Space is formed by a heat insulating formed in the annular space Interlayer is insulated. The inner ceramic tube is preferably made of aluminum oxide, Beryllium oxide and / or magnesium oxide. However, it is also possible to use metal carbide Use material for the inner ceramic tube.

Due to a relatively high heat resistance up to temperatures of 2000 ° C the structure of the protective tube proves to be relatively complex, as it is, for example hardly usable in household appliances, where cheap pricing is usually required should be.

Furthermore, EP 0 288 915 B2 describes an electric radiant heater for heating a plate, in particular a glass-ceramic hot plate known, in which on an insulating body electrical heating resistors are arranged at a distance from the plate and at which a rod-shaped temperature sensor of a temperature protection switch between the insulating body and the plate through the heating zone of the radiant heater defining the central area projects; there is at least one cam-like with a small extension in the longitudinal direction of the temperature sensor and this in the central area of the heating zone assigned spacer for maintaining a minimum distance between the insulating body or the resistors arranged thereon and the temperature sensor or the plate as well as to protect against bulging of the insulating body and to stiffen the radiant heater is used. The spacer is in the unheated area of the heating zone arranged and as an upward projection of the insulating body in one piece with the Insulated body formed, the temperature sensor formed with a metallic outer tube is largely rigidly mounted at the respective end and on a switch head of the Temperature protection switch is clamped relatively firmly.

The object of the invention is to measure the temperature in radiant heaters, such as those under ceramic hobs are used to carry out, the commonly used electromechanical Rod expansion switch replaced by a resistance temperature sensor shall be. The temperature range to be measured should be between -40 to + 750 ° C. Farther should be a relatively simple cable connection via flat connector, the attachment the temperature sensor should be extremely inexpensive.

The object is achieved in that a temperature-dependent sensor element electrical measuring resistor is provided with a resistance layer, which at least has a metal from the platinum metal group.

An essential feature of the invention is the fact that the connecting lines are led to the outside via the other protective housing end, designed as plug contacts are.

Advantageous embodiments of the device according to the invention are in claims 2 to 9 specified.

In an advantageous embodiment of the invention, the heat-resistant ceramic of the protective housing has cordierite; however, it is also possible to use steatite as the heat-resistant ceramic of the protective housing. The protective housing is provided with a connection block for connecting the connection lines (18) with connection contacts.
The measuring resistor is advantageously fixed as a sensor element by means of a ceramic encapsulation in the end region of the protective housing; however, it is also possible to cover the measuring resistor as a sensor element in the receiving end region of the protective housing by means of a housing cover. In addition, the sensor element can be fixed both by potting and by a housing cover.

The protective housing can be an elongated housing which is open at the top, which is advantageously covered with a lid.

The object is achieved for use by claims 10 and 11.

The temperature sensor is used to form a controlled variable in a control loop, the at least one radiant heater acting thermally on the temperature sensor having.

The temperature sensor is advantageously used as a resistance thermometer in the range between a radiant heater and a hotplate, in particular glass-ceramic hotplate an electric cooker.

It proves to be advantageous that the ceramic as a protective housing or as a protective tube is not more oxidized and therefore does not become black, such as a metallic protective tube; the thermal coupling always remains the same.

The ceramic as a protective housing or as a protective tube also serves as an insulator and reduced the insulation distance to be maintained between the glass-ceramic plate and the heating coils Not. There are clear work steps, such as insertion, bending and twisting, whereby an easy production or a simple automation of the production is given is. The main assembly direction is vertical.

Another advantage is the relatively small number of components; so are several functions integrated in one component; the housing serves as a protective tube, as a connection block and for conductor insulation. The flange advantageously positions the housing and fastened the mica lid.

The temperature sensor according to the invention is used essentially for temperature measurement a radiant heater, using the maximum temperature at 750 ° C is. Furthermore, there is the possibility of flame monitoring or monitoring of exhaust gas stoves or also hot air arrangements possible.

In the following the subject matter of the invention is shown in FIGS. 1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b and 5 and 6a, 6b and 6c explained in more detail.

Figures 1a and 1b each show a temperature sensor in a radiator housing Serving tin pot of an electric cooker, the sensor with a surrounding Ceramic housing is guided through a side wall of the tin pot; according to Figure 1b Sensor attached to the tin pot with a separate metal flange. In Figure 1a is the metal flange saved. The tin pot has a recess to accommodate the ceramic housing.

Furthermore, FIGS. 2a and 2b each show the ceramic housing according to FIGS. 1a and 1b with the temperature sensor, which integrates the connection block, protective tube and insulator.

Figures 3a and 3b show a cross section through the ceramic housing, the electrical Conductors to the measuring element are recognizable.

The connection contacts bent downward can be seen from FIGS. 4a and 4b, Secure stops against slipping.

Figure 5 shows the electrical conductor together with the stops against slipping and the connection contact, whereby the bending line can also be seen.

FIGS. 6a and 6b each show the metal flange together with metal flags, with FIG 6a corresponds to a side view corresponding to FIG. 3a, while FIG. 6b corresponds to a longitudinal section with 90 ° rotation.

FIG. 6c shows a top view of the metal flange, the perspective corresponding to FIG. 1b.

According to Figure 1a is a trough-shaped ceramic housing as a protective housing 1 of a sensor element 3 provided, the protective housing 1 through the side wall of a tin pot trained radiant heater housing 15 in the inner region 19 between radiant heater 11th and a glass ceramic plate 13 serving as an outer cover is sufficient. That by means of a The cover 7, which can be closed, has a protective housing 1 in the area of its housing 19 directed towards the inner area Measuring tip as the end region 20, the sensor element 3 for temperature measurement, which is connected to the in the protective tube-like part of the Protective housing 1 arranged electrical conductor 4 (only partially recognizable) connectable is. The sensor element 3 is in the area of the end region 20 of the protective housing 1 by means of a ceramic Potting 10 fixed. An execution without potting 10 is also possible; doing so the end region 20 designed as a hollow mold is covered with a cover made of mica 7, so that the sensor element cannot fall out. It is also possible to have one already sensor element 3 fixed by potting 10 additionally through an attached cover Protect mica 7 against contact.

On its side facing away from the end region (tip) 20 of the protective housing 1, the Housing two slots for connection contacts 2, which by bending or twisting are fixed along a bending line, which can be seen below with reference to FIGS. 4a and 4b becomes.

The heat-resistant ceramic of the protective housing 1 is preferably made of cordierite or made of steatite. So that the mica cover 7 before assembly and bending of the metal flags 16 is not lost, it is secured to the housing with potting or adhesive 17.

A variant of FIG. 1a is shown in FIG. 1b, with an additional, perpendicular to Metal flange 5 bent at the top to improve the stability in the area of the connection contacts 2 is provided. Then it is not necessary to fix the cover 7 with potting, since the flags 6 hold the lid in the housing.

The heating coils 14 shown in cross section are also shown in FIGS. 1a and 1b of radiant heater 11 recognizable.

According to FIGS. 2a and 2b, that which can optionally be closed by means of a cover made of mica can be closed trough-shaped ceramic housing 1 recognizable from above. In the area of its measuring tip or in the end region 20, the ceramic housing 1 has the sensor element 3 for temperature measurement on, which via connection conductor 18 each with one of the pairs Elongated electrical conductor 4 connected in the rod-shaped part of the protective housing 1 is.

Between the two conductors 4 there is a for separating or isolating the electrical conductors 4 provided middle web 8 made of electrically insulating material. The elongated electrical Conductors 4 open into the connection area on their side opposite the measuring element 3 with the stops 12 and the actual connection contact 2, which is based on Figure 5 can be seen. Furthermore, FIG. 2a shows the partially broken view Radiant heater 11 can be seen, which is in a tin pot shown here in fragments 15 is located and secured with flags 16, the protective housing 1 of the sensor.

2b, the one already described with reference to FIG. 1b is also partially dashed here metal flange 5 shown for stable mounting of the ceramic protective housing 1, which after applying a cover (not visible here) to the ceramic protective housing 1 is attached as a metal flange 5 and by turning two metal flags 6 is secured in its position. Conductors and contacts consist of a temperature-resistant Material, e.g. Stainless steel or inconel. The sensor element 3 is optionally with the already described ceramic encapsulation 10 glued into the measuring tip as the end area, or a cover 7 made of a mica plate is inserted into the ceramic housing in such a way that the entire interior structure is covered.

Figure 3a shows a cross section through the ceramic protective housing 1 according to Figures 1a and 2a with the electrical conductors 4 located therein, with a part of the fragmentary in the background Radiator housing 15 shown with metal flags located at the top 16 is recognizable. In this embodiment, the metal flags serve to fasten the sensor element. With reference number 17 is the potting or adhesive for the lid - as already explained with reference to Figure 1 a.

Figure 3b also shows a cross section through the ceramic protective housing 1, however in the background the metal flange 5 already described with reference to FIGS. 1b and 2b is recognizable, the upper edge of which is now provided with the metal flags 6. Also in this one Embodiment, the metal flags are used to attach the sensor.

FIG. 4a shows a side view of the connection contacts 2 already known from FIG. 1a, which are bent downwards along a bending line 9 and for connection to a temperature control electronics serve. The radiator housing 15 is shown in fragments. The Stops 12 are intended to prevent slipping when building up the sensor arrangement.

FIG. 4b shows an arrangement corresponding to FIG. 4a, but this is used for a device with a metal flange 5 according to FIGS. 1b, 2b and 3b. They are here too downward angled connection contacts 2 recognizable, being on the upper edge of metal flange 5 are the metal flags 6.

According to FIG. 5, one of the two conductors leading to the sensor element (not recognizable here) is 4 shown in a top view, the connection contact 2 along the bending line 9 according to should be turned down. The tongue-shaped stops 12 projecting laterally in each case should prevent slipping during construction. The conductor 4 is either as shown with Stops 12 and connection contact 2 connected or conceivable as a separate part that is welded on must become; Conductor 4 can also be formed as a component of the sensor element be, but then the connection conductors would be omitted.

The sheet metal flags 6 secure according to the following figures 6a, 6b, 6c by their protrusion up to and beyond the mica cover also the optionally attachable cover. The design of the metal flange 5 can be varied depending on the application. With a suitable flange the sensor or the ceramic protective housing can also be used for other high-temperature measurements in the range up to 750 ° C. The flange 5 shown is, for example fixed with two screws to the bottom of the radiant heater 11 (Figure 1b).

However, it is also possible to dispense with the separate flange and the ceramic housing in a correspondingly shaped recess in the tin pot or radiant heater housing 15 of the Directly use radiant heaters and analogously as in the case of sheet metal flange 5 with flags 16 to fix. In such a case, the optional cover in the protective housing with ceramic Potted glued so that it is not lost before installation in the radiant heater housing goes.

Claims (11)

Temperature sensor with at least one sensor element which is at least partially surrounded by a protective housing made of heat-resistant ceramic, the sensor element provided with connecting lines being arranged in the region of one end of the protective housing, while the connecting lines are directed outwards via the other protective housing end are characterized, characterized in that a temperature-dependent electrical measuring resistor is provided as a sensor element (3) with a resistance layer which has at least one metal from the platinum metal group. Temperature sensor according to claim 1, characterized in that the heat-resistant ceramic of the protective housing (1) has cordierite. Temperature sensor according to claim 1 or 2, characterized in that the heat-resistant ceramic of the protective housing (1) has steatite. Temperature sensor according to one of claims 1 to 3, characterized in that the protective housing (1) is provided at its end facing away from the sensor element (3) with a connection block for connecting the electrical conductors (4) with connection contacts. Temperature sensor according to Claim 4, characterized in that the electrical conductors (4) are designed as plug contacts in the region of the connection block. Temperature sensor according to one of claims 1 to 5, characterized in that the measuring resistor is fixed as a sensor element (3) by means of a ceramic encapsulation (10) in the end region (20) of the protective housing (1). Temperature sensor (measuring resistor) according to one of Claims 1 to 6, characterized in that the end region (20) of the protective housing, which receives the measuring resistor as a sensor element (1), is covered by a housing cover (7). Temperature sensor according to one of claims 1 to 7, characterized in that the protective housing is stretched and is open at the top. Temperature sensor according to claim 8, characterized in that the protective housing is covered with a cover. Use of a temperature sensor according to one of claims 1 to 9, for formation a controlled variable in a control loop that has at least one on the temperature sensor thermally acting radiant heater. Use of a temperature sensor according to claim 10 as a resistance thermometer in Area between a radiant heater and a hotplate, especially a glass-ceramic hotplate an electric cooker.

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