HK1069256B - Temperature sensor - Google Patents

Description

The invention relates to a temperature sensor as defined in claim 1.

Such a temperature sensor is described, for example, in EP 0 141 923 B. This well-known solution has a circular rib in the radiator pot, protruding from the bottom of the pot, separating two separately controllable heating coils.

The tube of the temperature sensor extends over both heating coils, but this contains a three-part rod, the middle part of which extends only over the area of the central heating coil.

In the reverse design, where the coefficient of expansion of the middle part of the rod is greater than that of the surrounding tube, the outer parts of the rod shall have a coefficient of expansion no greater than that of the surrounding tube, but preferably smaller.

This action results in the outer parts of the rod, located in the areas of the outer heater, extending to the same or greater extent than the surrounding tube, thereby overcompensating the influence of the switchable heater and the temperature sensor essentially detects the temperature in the central area of the pot and thus the temperature in the area of the inner heater.

The above document also describes a solution in which the tube is also formed into three parts, with the parts of the tube essentially overlapping with those of the bar. The middle section of the tube has a greater coefficient of thermal expansion than the outer sections of the tube and the outer parts of the bar have a greater coefficient of thermal expansion than the middle section of the bar. The outer sections, or parts of the tube and bar, are arranged in the area of the external heating rotor.

In these solutions, despite compensation for the influence of the external heating coil, the switch point of the temperature sensor is shifted, due to the fact that heat from the radiator's boiler inevitably passes through the heat sink and radiation into the heating chamber, which also causes the switch housing to expand according to its coefficient of thermal expansion and thus affect the switch point.

In the case of conventional radiant heater temperature sensors with a continuous rod held in a tube connected to the case of a switch and extending into the case of the switch, a very noticeable drop in the response temperature occurs when the case of the switch, which is usually made of steatite and is located outside the radiant heater's furnace, heats up. This requires the response temperature of the sensor to be raised accordingly, which results in the actual response temperature being greatly exceeded in a relatively cold case of the switch.

The purpose of the invention is to avoid this disadvantage and to propose a temperature sensor of the type mentioned at the outset, which avoids a greater exceedance of the desired response temperature in cold switch cases.

According to the invention, this is achieved by the characteristics of claim 1 for a temperature sensor of the type mentioned at the beginning.

These measures allow the extension of the switch housing to be taken into account and to avoid the shifting of the switch point to a large extent or entirely due to the thermal extension of its housing.

Another problem is that the heat generated in a heating boiler which absorbs a heating spindle passes through the wall of the boiler into the heating chamber of a boiler which absorbs that boiler and heats itself. In particular, when several radiant heating elements are placed in a boiler room, the result is relatively high temperatures in the heating chamber when the boiler is running at full load and all the radiant heating elements are in operation. However, for safety reasons, the heating chamber temperature or the wall temperature of a boiler which is in a relationship with it must not exceed a certain value.

The characteristics of claim 2 now mean that in a multiple-heater and thus radiant heater, the switching of the individual temperature sensors is controllable when switching the individual heater switches in succession, by selecting the coefficients of expansion of the part of the switch rod and the switch housing that fits into the switch housing. The proposed selection criteria for the coefficients of expansion of the switch switch allow only partial compensation of the effect of heat retention of the switch housing and thus at higher heater room temperatures to a lower temperature, thus avoiding a significant increase in the temperature of the heater and thus the temperature of the heater room.

The advantage of claim 3 is that the effect of the heat exchanger on the switch housing can be virtually fully compensated, making the radiator control essentially independent of the temperature in the heating chamber in which the radiator is located.

The advantage of claim 4 is that the choice of a suitable heat absorption coefficient can influence the response time of the switch's temperature sensor, which can also influence the switching time of the associated switch, thus allowing the boiling performance of the corresponding radiant heater to be optimized.

The characteristics of claims 5 and 6 allow the heat absorption coefficient of the two parts of the rod to be easily adjusted.

In order to optimise the boiling performance of a radiant heater according to the invention, it is particularly advantageous to provide for the features of claim 7.

The invention is described in more detail by reference to the accompanying drawings, which show the embodiments. Fig. 1 shows a heating chamber of a cooking oven with a radiant heater in a vertical section,Fig. 2 a view of the radiant heater as shown in Fig. 1 and Fig. 3 shows a larger scale temperature sensor according to the invention.

The reference 1 designates a radiant heater comprising a pot 2 containing a heating coil 3 in a spiral position, embedded in a bed matrix 4. The radiant heater 1 is placed below a plate 5 of metal, glass, ceramic or other materials, with the cooking surface 6 on its top. Between the cooking surface 6 and the heating coil 3 there is a temperature sensor 7 connected to a switch 18 which is not connected to the latter. The temperature sensor is easily guided through holes in the essentially cylindrical wall of the radiant heater 1, or 2 on top of it.

The temperature sensor 7 is therefore exposed to the temperature below the cooking surface 6 in the radiation chamber between the cooking surface 6 or the plate 5 supporting it and the heating coil 3 and can thus detect this temperature.

The design of the temperature sensor 7 is shown in Figure 3.

Essentially, the temperature sensor 7 consists of an outer tube 8 made of a material with a relatively high coefficient of thermal expansion, such as a metal, especially steel, a two-part rod 9 inside it, both parts of which are designated L1 and L2, and a switch 10 contained in a housing 18, at the movable switch contact 11 which is tensioned against its open position, the rod 9 is connected to its part L2 which extends into the housing 10 of the switch 8.

The one end of tube 8 which may have any cross-section is closed, which may also be done by means of an adjustable support (not shown) for bar 9 or its part L1. In the built-in condition of the temperature sensor 7, part L1 of bar 9 extends over the area of radiant heater 1 over which the heater 3 extends. The second part L2 of bar 9 is located in the area of the wall of the pot 2, which is made of a poorly conductive material, is located in the area of this wall on the front side of the L1 part of the bar and extends into the housing 10 of switch 18, which is located outside the radiant heater 1 but contains a heater, which is not located near the radiant heater, which is exposed to the temperature of the heater 10 in the heating chamber.

The tube 8 of the temperature sensor 7 is firmly connected to the housing 10 of the switch 18.

When heating coil 3 is switched on, the temperature sensor is exposed to the radiation from the heating coil or to the temperature in radiation heater 1 between heating coil 3 and plate 5. This causes the tube 8, which has a significantly higher coefficient of thermal expansion than the L1 part of the rod 9, to expand more than the L1 part, thus reducing the pressure on the moving contact 11. When the corresponding temperature is reached, the contact 11 is able to move into its opening position due to its pre-voltage and to interrupt the current circuit of the heating coil 3.

As heat from the radiator chamber 1 passes through the wall of its pot 2, the radiator chamber and hence the housing 10 are also heated, which also expands according to its coefficient of thermal expansion, causing a corresponding shift of the fixed contacts 12 of the switch relative to the end of the tube 8 and thus a shift of the switch point of the switch 18.

To avoid this or to limit this effect to a tolerable extent, the L2 part of bar 9 extending into the housing 10 of switch 18 has a coefficient of thermal expansion which, in combination with its axial extension, gives a product selected depending on the product from the coefficient of thermal expansion of the housing 10 and its extension towards bar 9 from the wall of the pot 2 to the end of the holders of the fixed contacts 12 attached to it.

If these products are chosen equally, the result is a substantially complete compensation of the heat expansion of the housing 10 and thus a substantially complete compensation of the effect of the heating of the housing 10 due to the heat diffusing through the wall of the pot 2.

If, on the other hand, these products are chosen so that the product of the coefficient of thermal expansion of the part 12 of the rod 9 extending into the housing 10 is less than the product of the coefficient of thermal expansion and extension of the housing between its end facing the pot 2 of the radiator 1 and the supports of its fixed contacts 12 in the axial direction of the rod 9, the switch point 18 will be shifted towards too low temperatures as the content increases in heating, provided that the downward moving contact 11 of the switch 18 opens towards the tube 8.

In principle, a different configuration of the movable contact 11 is also possible, i.e. it can be pre-tensioned in the direction of its closed position, in which case the L1 rod has a greater coefficient of thermal expansion than the tube 8 and the products mentioned above must be chosen in reverse in order to achieve the same effect in the sense of a kinematic reversal.

An imperfect compensation of the effect of the heating of the housing 10 as above may be desirable to ensure that, when the temperature of the housing rises, which also implies a rise in the heating chamber of the stove, which in turn results in an increase in the wall temperature of the stove, which reduces the energy supplied to the radiator and thus to the heating chamber, due to the switch 18 being turned off at lower temperatures in the radiator 1.

Furthermore, the two parts L1, L2 of the rod 9 have different heat absorption coefficients, with the L2 part of the rod 9 preferably having a lower heat absorption coefficient.

This ensures that the switching temperature when the heater is switched on, i.e. when the radiant heater is cold, is higher than the switching temperature when the heater is in the temperature equilibrium state. This results in an over-swinging behaviour of the temperature sensor when the heater is switched on in the cold state. This allows the cooking performance to be optimized, which means that a higher glazing temperature is available when the heater is switched on in the cold state, thus reducing the time until the cooking temperature is reached.

The heat absorption coefficients can be adjusted by different colours, different surface designs, e.g. by applying profiles or different surface roughness, etc., or by different metal alloys, e.g. Al2O3.

Claims (7)

1. A temperature sensor (7) for a radiant element (1), especially a cooking stove, which radiant element (1) is formed substantially by a heating spiral placed in a pot (2) and which element (1) is arranged in a heating chamber which is covered upwardly by a glass ceramic plate or a steel plate (5) comprising a cooking surface (6), with the temperature sensor (7) comprising a tube (8) which extends through the cavity of the pot (2) substantially parallel to the plate (5) covering the same, which penetrates at least one thermally insulating wall of the pot (2) and whose one end is joined to a housing (10) of a switch (18) comprising at least one movable switching contact (11) cooperating with fixed contacts (12) held in the housing, and an at least bipartite rod (9) is held with its one end in the interior of said tube (8) which is sealed off at its second end, which rod (9) extends into the housing (10) of the switch (18) and actuates the switching contact (11), with the tube (8) and the at least bipartite rod (9) having different coefficients of thermal expansion, characterized in that the part (L2) of the rod (9) extending into the housing (10) of the switch (18) ends outside of the cavity of the pot (2) and the product of the coefficient of thermal expansion of the part (L2) of the rod (9) projecting into the housing (10) of the switch (18) and its axial extension is chosen depending on the product of the coefficient of thermal expansion of the housing (10) of the switch (18) and its extension progressing in the direction of the rod (9) up to the fixing devices of the fixed contacts (12) of the switch (18) in such a way that a displacement of the switching point of the switch is prevented substantially or entirely as a result of the thermal expansion of the switch housing.
2. A temperature sensor according to claim 1, characterized in that the product of the coefficient of thermal expansion of the part (L2) of the rod (9) projecting into the housing (10) of the switch (18) and its axial extension is smaller than the product of the coefficient of thermal expansion of the housing (10) of the switch (18) and the extension of the housing (10) in the direction of the rod (9) up to the fixing devices of the fixed contacts (12).
3. A temperature sensor according to claim 1, characterized in that the product of coefficient of thermal expansion of the housing (10) of the switch (18) and the extension of the housing (10) in the direction of the rod (9) up_to the fixing devices of the fixed contacts (12) and the product of the coefficient of thermal expansion of the part (L2) of the rod (9) projecting into the housing (10) of the switch (18) and its axial extension are substantially equal, with the housing (10) and the part (L2) of the rod (9) projecting into the same are preferably made of the same material and the extension of said part (L2) of the rod (9) is substantially equal to the extension of the housing (10) in the axial direction of the rod (9) up to the fixing devices of the fixed contacts (12).
4. A temperature sensor according to one of the claims 1 to 3, characterized in that the two parts (L1, L2) of the rod (9) have a different heat absorption coefficient ε.
5. A temperature sensor according to claim 4, characterized in that the adjustment of the heat absorption coefficient occurs by configuration of the surfaces, e.g. by coloring, and/or measures influencing the size of the surface such as profiling of the cross section or setting the roughness of the surface.
6. A temperature sensor according to claim 4 or 5, characterized in that the adjustment of the heat absorption coefficient occurs by metal additions such as Al₂O₃.
7. A temperature sensor according to one of the claims 4 to 6, characterized in that the heat absorption coefficient of the part (L2) of the rod (9) which extends into the housing (10) of the switch (18) is adjusted to the respective coefficient of the housing (10).