RU2295091C1 - Explosion-proof thermocouple and its body - Google Patents

Abstract

FIELD: thermocouples for stove gas burners.

SUBSTANCE: proposed thermocouple has hot junction on upper part of small mass and part in form of truncated cone which has flame receiving wall of preset axial length and deflection angle adaptable to shape of flame for reduction of temperature gradient between flame receiving wall and hot junction. Outer sleeve is connected with tubular base of larger diameter for cold junction by means of tubular base.

EFFECT: quick switching-off of drive after extinguishing of flame.

7 cl, 5 dwg

Description

Application area

The present invention relates to a safe thermocouple for detecting extinction of flame, where the design of the tubular body of the thermocouple is designed for a gas burner stove to quickly turn on the valve.

State of the art

Safety thermocouples are used to detect the presence or absence of a flame when installing in the immediate vicinity of a gas burner, a stove equipped with a burner with radially arranged flame outlets. This type of thermocouple is equipped with a temperature sensor. One of the tongues of flame collides with the surface of the sensor, generating an electromotive force (emf), which feeds the actuator of the safety valve, keeping it open. After the flame goes out, the electromagnetic valve closes under the action of the spring force when the emf as a result of cooling, it generates drops below a threshold value specific to the value of the electromagnetic valve. Response time and emf threshold the valves obtained to lock and unlock the actuator depend on the type of valve used and the range of performance values. The position of the thermocouple in relation to the flame is chosen to maintain a balance between the two necessary values of the lock and unlock times, since a faster response to heating causes an increase in the unlock time during cooling. EP-597157-A, EP-552135-A, GB-2249383-A and FR-2062094-A contain examples of thermocouples of known construction mounted on a hotplate.

Figure 2 presents the thermocouple design, which corresponds to the prototype adapted for the burner plate "BU". The thermocouple 20 is located with its vertical axis "A" on the support "SP" in the burner. The flame emitted by the BU burner is regulated between a flame of two sizes of different calorific value: a large flame of maximum power "F1" and a small flame of minimum power "F2". The thermocouple sensor 21-22 is located at a certain horizontal distance "E" from the burner "BU" and at a certain vertical height "H" from the support "SP", adjustable in relation to the output of the flame so that as soon as the flame goes out, thermocouple 20 stopped heating with residual heat from the burner body.

In accordance with the prototype (figure 2), the thermocouple 20 is made of an outer tubular sleeve 21-23 of a thermoelectric alloy, such as Ni-Cr, a low heat conductor, which serves as the outer conductor of the thermocouple. The hard conductor 25 of another alloy, which serves as the inner conductor of the thermocouple, is directed into the sleeve 21-23 of the transmitting housing. The thermocouple sensor 21-22 contains the upper end part 21 of a smaller diameter, pressed-stamped at one end of the thermoelectric rod 25 and then welded to its upper part. A work junction "HJ1" made in this way is in thermal contact with the metal surface of the sensor 21-22 heated by the flame. As a result of stamping the sleeve 23, the flame receiving head at the end of the sleeve 23 also comprises a transition portion in the form of a truncated cone 22 of intermediate diameter.

The base 24 of the transmitting housing (FIG. 2) contains a tube of a larger diameter than the sleeve 23 of brass, a good electrical and heat conductor, and is telescopically connected to the sleeve 23 and welded to it, forming a “free junction” CJ2. The tubular base 23-24 has a constant inner diameter that fits snugly against the inner insulating sleeve 26 of the inner conductor 25. The insulating sleeve begins behind the conical portion 22 and continues below the "SP" support. In the tubular base 24, the end of the inner rod 25 is welded to another semi-rigid copper rod 25 'for electrically connecting the free junction "CJ1" of the thermocouple. The free junction CJ1-CJ2 is located at the height of the thermocouple support device “SP” at the end provided with support device 27. At the lower end, the tubular body 23-24 is provided with a support edge or protrusion 27 for fixing the thermocouple and its vertical positioning on the support “SP” connected with a burner.

Examples of thermocouples of the above construction are given in US-3332803, US-3556864, US-4021268, FR-2696531-A3, EP-1215473 and JP 07031087, Rinnai Corp (release date 09/03/96), which have an adapter or connector for attaching a thermocouple to the support for adjusting the position E, H of the sensor with respect to the flame F1. The sensor 21-22 is surrounded by a large flame "F1", and the junction HJ1 is heated to approximately 500 ° C to generate a nominal emf value, when the user changes the power of the burner BU, a small flame F2 does not reach the surface of the sensor 21-22.

In the prototype (FIG. 2), the construction of thermocouple 20 has two “working junctions” that are axially separated from each other, as described in EP-607099-A2, where the emf generated by the secondary junction HJ2 is electrically opposed emf generated by the primary junction HJ1, to increase the response speed during cooling and reduce the unlock interval. The end portion 21 of the thermocouple sensor 20 has a diameter of approximately 2 mm, the outer sleeve 23 of the housing has a diameter of approximately 3.3 mm, and the tubular base 24 of the housing has a diameter of approximately 6 mm. The length of the end portion 21 of the sensor is approximately 4.5 mm, the angle of inclination alpha-1 (α1) of the region of the truncated cone 22 with respect to the vertical axis “A” of the thermocouple is approximately 13 degrees or less.

Due to the small diameter and length of the sensor 21-22, the latter is an almost vertical flame receiving wall far from the flame opening. Approaching the position “E” of the thermocouple 20 to adapt to the flame of two sizes F1 and F2 would cause excessive heating of the sensor 21-22, which negatively affects the life of the thermocouple or glows the wall of the sensor 21-22 to a temperature above 650 ° C. Changing the “H” position of the sensor 21-22 to adapt the surface of the truncated sensor cone 22 to a small flame can cause a drop in temperature at the joint HJ1, in particular during initial heating, subsequently lengthening the valve unlocking time.

When the flame of the burner F1 goes out, the cooling time to the unlock threshold Vde depends not only on the rate of heat dissipation from the sensor 21-22 through the housing 23-24, but also on the temperature reached in the metal wall of the sensor 21-22 due to the reflection of the flame F1.

4 and 5, dashed lines are used to represent typical EMF curves 28L and 28S. (mV) / t (s), corresponding to the response of the thermocouple 20 of the prototype (FIG. 2), heated by a large flame F1 or a small flame F2, respectively, and a typical cooling curve 28C after extinction of the tribe. The maximum threshold value "unlock valve" Ve of the actuators of some safety valves SV in the total volume is approximately 2.5 mV under load, so the initial time "t1'-t0" of flame F1 is approximately 4 seconds (figure 4), and the threshold value Vde in the same actuator for "unlocking the valve" and turning off the valve is 2.2 mV, slightly less due to the hysteresis "ΔVde", so that after extinguishing a large flame F1 at the time "te" (Fig. 5), the valve is turned off and closed "SV" occurs after a temporary The interval "t3'-te" is approximately 20 seconds. However, due to the variation in the performance of the solenoid valve actuator SV, some devices have a Vde-min release threshold of approximately 1 mV under load. As a result, the cooling interval "t3'-te" to unlock the actuator SV, the minimum value of which Vde increases to 40 seconds (figure 4).

The next problem arises when the thermocouple 20 of the prototype (FIG. 2) is heated by a large flame F1, which generates a high emf value (mV), as in curve 28L in figure 4, and the user changes the gas flow rate of the burner BU to a minimum, while continuing to cook on a fine flame F2. Part of the sensor in the form of a truncated cone 22 is not achieved by a small flame F2 due to the small angle alpha-1 (α1) = 10-13 degrees of the heat-receiving wall 22, and also due to the significant length of the upper end part 21, which mainly forms the heat-receiving surface of the sensor. For this reason, in the case of an SV valve actuator that has a high unlock threshold Vde, for example Vde = 2.2 mV, the thermocouple 20 does not generate enough to maintain an emf. the above Vde value, and the cooking process is interrupted involuntarily. In Fig. 4, the response of the emf (mV) of the thermocouple 20 from the current time “ts” of switching from the large flame F1 to the small F2 is represented by curve 28S. Now the temperature of the junction HJ1 drops, emf (mV) after the cooling interval gradually generates a fall of "ts-t2" below the maximum threshold value Vde = 2.2 mV, and the valve actuator SV shuts off, stopping the cooking process when it is not required by the user.

Description of the invention

The object of the invention is the design of a thermocouple supplying a safety solenoid valve and designed for a gas burner for cooking, the above design of a thermocouple containing a thermosensitive head provided with an inclined metal wall exposed to the flame of the burner, and a tubular base equipped with positioning means on the burner to ensure quick response when heating and cooling a thermocouple, including heating a thermocouple head with a small flame it corresponds to the minimum burner power output.

Compared with the known thermocouple, the design of the thermocouple in accordance with the invention provides a faster response time when generating a high emf value (mV) Ve from ignition without metal head wall protecting the working junction from overheating. This is achieved by increasing the area of the metal wall of the sensor, covered by both large and small flame warmers. During cooling, the thermocouple of the invention also provides a shorter valve shutdown response time due to the minimum length and weight of the sensor and, as a result, the low thermal resistance from the working junction to the tubular base to cool the working junction when the flame goes out.

By upgrading the design of the flame receiving head, the thermocouple design of the invention also provides reliability when generating a high emf value (mV) in conditions when the user reduces the flame to continue the cooking process with less power. Thermocouple generated emf (mV) exceeds the threshold value Vde for unlocking the electromagnetic drive, thereby preventing unwanted interruption of the cooking process with any drive devices.

The thermocouple sensor of the invention is designed with a working junction enclosed in the final part of the head of large and small diameter in order to reduce its thermal mass without compromising the service life of the thermocouple, while the part of the head in the form of a truncated cone is designed with a conical metal wall having such an angle of inclination α1, which is more open in the direction of the flame than in previously known thermocouples to provide a wider area of flame coverage, while the above conical wall surface also iblizhaetsya the end of the flame thus, in particular, it is achieved that, at least the upper part of a small flame.

An object of the invention is to reduce the temperature gradient between the metal wall in the form of a truncated cone and junction HJ1, as a result of which the working junction reaches a temperature of about 500 ° C without the flame receiving metal wall of red color accompanying overheating, by reducing the thermal resistance between the wall in the form of a truncated cone and a tubular base of well-conducting material, forming a free junction, which dissipates the heat transmitted by the heated wall of the head. This goal is achieved by overlapping a tubular heat sink base on a sleeve of thermoelectric material, a segment of a greater length than the segment of the sleeve, open and exposed to air.

An additional advantage of this sensor design is that the inner junction rod is inserted into the part of the head in the form of a truncated cone with sufficient clearance to prevent the risk of a short circuit between both thermoelectric conductors.

Description of drawings

Figure 1 is a view of a thermocouple in accordance with the invention mounted on a cooking zone.

Figure 2 is a view of a thermocouple prototype.

Figure 3 is a longitudinal view of a thermocouple in accordance with the invention of figure 1.

Figure 4 is a graph of the emf (mV) / time generated by the thermocouple in figure 3 when it is heated.

5 is a graph of the emf (mV) / time generated by the thermocouple in figures 1, 3 when it cools.

Detailed Description of the Invention

According to figures 1 and 3, the design of explosion-proof thermocouple 10 is designed for a burner plate "BU" with radially arranged flame outlets in the direction opposite to the Central axis "A" of the tubular body of the thermocouple 11-14. The thermocouple 10 is mounted on the support of the burner "SP" in a vertical position relative to the axis A, located at a predetermined distance "E" from the output of the flame of the burner, and at a height of "H" from the annular protrusion of the support 17 in the burner. The clearance "E" is determined by a sufficient distance from the burner so that the thermocouple is no longer heated by its residual heat. The height "H" or the total length of the thermocouple, about 30 mm, is determined so that the sensor faces the flame outlet F1 and F2.

The thermocouple 10 is adapted to heat the JJ1 junction with a large flame F1 or a small flame F2 from the burner (FIG. 1), which is reflected by the surface or covers the surface of the thermocouple head 11-12, causing emf generation (mV) (FIG. 4) from the ignition timing t0 (FIG. 4). The safety valve "SV" is powered by an emf (mV) generated by the thermocouple, keeping the solenoid valve actuator SV on.

In accordance with figure 1 and figure 3, the heat-receiving head 11-12 contains the upper end 11 and part in the form of a truncated cone 12 with a surface exposed to a small flame F2, and facing the exit of the flame. The part in the form of a truncated cone 12 with an angle of α-2 (α2) relative to the axis “A” exposes its entire surface to the action of a small flame F2 in accordance with the shape of a small flame F2, the final part of which is usually ascending.

The sensitive end portion 11 of the thermocouple head has a small length L1 and a small diameter "d" in order to reduce its weight to the minimum possible. The inner core of the thermoelectric conductor 15 is selected as thin as possible in order to reduce the mass of the upper end 11 of the thermocouple without compromising the service life. The connection of the two thermoelectric "conductors" 11 and 15 of the pair forms the primary working junction HJ1.

In the embodiment of the thermocouple 10 (FIG. 3), the length L1 of the end part 11 is less than 2 mm, preferably between 1 mm and 1.5 mm, which is necessary for the press fit of the inner rod 15. The diameter "d" of the end part 11 is less than 2 mm, preferably less than 1.5 mm. The angle α-2 (α2) of the deviation from the conical wall 12 is between 15-30 degrees, preferably 20 degrees. Wall W1 has a thickness of about 0.25 mm, the least possible for resistance to wear and cracking under the influence of thermal stresses. The length of the L2 part in the form of a truncated cone is determined by the typical size of the final part of the small flame F2, where L2 = from 2.5 mm to 3.5 mm. The diameter D1 of the sleeve is determined, starting from the diameter "d" of the end part 11 of the head and after fitting the part of the head 12 in the form of a truncated cone using the aforementioned deflection angle alpha-2 (α2) and the above length L2 intended for the end part of the flame F2.

The transmitting housing 13-14 of the thermocouple 10 contains a cylindrical sleeve 13 of thermoelectric alloy having a diameter D1 and a length of "L3 + L3 '", and a tubular base 14, which is a good heat conductor, length L4 of about 20 mm It is telescopically connected to the sleeve 13 and then welded to it to form a second free junction CJ2, its diameter D2 is about 6 mm, its wall thickness W2 is about 1.5 mm, sufficient to dissipate the heat transferred from the head 11-12. The tubular body 13-14 has a constant inner diameter, suitable for the inner insulating sleeve 16 for the inner conductor 15.

A portion of the sleeve 13 with a length L3 of about 6 mm remains exposed to air, while a second portion with a length L3 ′ greater than L3 is blocked by the tubular base 14. The thermal resistance between the head 11-12 and the tubular base of the conductor 14 is thereby reduced . With this, the quick cooling of the working junction HJ1 of the thermocouple is successfully achieved after the flame is extinguished by increasing heat dissipation from the hot head 11, 12 using a large area of thermal contact between the sleeve 13 and the tubular base 14. This minimum thermal resistance in the heat dissipation channel further reduces temperature gradient between the receiving flame (F1, F2) wall 12 and the generating emf we join HJ1, whereby at the working joint HJ1 a sufficiently high temperature is reached, about 500 ° C, without the need for excessive heating of the wall 12.

The small thermal mass of the end portion 11 enclosing the junction HJ1, after ignition of the heating pad, is first quickly heated by the thermal conductivity of the wall in the form of a truncated cone 12, which receives a flame, in particular a small flame F2. As a result, the EMF curve is quickly achieved. 18L, shown in FIG. 4, necessary to activate the valve actuator SV, above the threshold value “Ve” blocking its valves.

In accordance with FIGS. 4 and 5, the thermocouple 10 shown in FIG. 1 is an example of two working junctions, a primary HJ1 and a secondary HJ2, axially spaced, which have opposite emf values. The secondary working junction HJ2 is placed under the exposed segment L3 of the thermoelectric sleeve and, thus, the emf generated by it significantly lower than the primary junction of HJ1. Difference in emf between them is the resulting output emf thermocouples 10 represented by curves 18L, 18S, and 18C in FIG. The dashed line 28S of the known thermocouple 20 (FIG. 2) is shown in the same graph in FIG. 4. Part of its head in the form of a truncated cone 22 is not achieved by a small flame F2 due to the significant length of the end part 21 and the small angle alpha-1 (α1) = 10-13 degrees of the exposed wall 22.

The primary JJ1 junction should be quickly heated by the F1 tribe and also cooled rapidly after extinction (Fig. 4). The heating of the secondary junction HJ2 must be delayed relative to the primary junction HJ1 during the initial period "t1-t0" until the electromagnetic drive is locked to achieve rapid growth of the resulting emf 18L above the maximum threshold value Ve = 2.5 mV. The cooling of the JJ2 junction should also be delayed with respect to the JJ1 junction during the final “t3-te” drive enable period to quickly drop the 18S curve of the resulting emf. below the minimum drive enable threshold Vde = 1 mV.

For this, the secondary junction of HJ2 is located at a distance of, for example, 14 mm from the junction of HJ1. The cable of the inner conductor 15 'is welded to the thermoelectric wire 19 of the secondary junction HJ2, forming a free junction CJ1, at a large distance, for example 13 mm in height, from the secondary junction HJ2. Following the heating curve 18L in FIG. 4, the initial time period “t1-t0” for heating with flame F1 is only 2.5 seconds for the maximum value of the “blocking” of the drive Ve, Ve = 2.5 mV under load. Following the cooling curve 18C in FIG. 5, the time interval “t3-te” after the large flame F1 has been extinguished is only 10-17 seconds according to the threshold “unlock” Vde between Vde = 2.2 mV and Vde = 1 mV, which is much lower than the previously known thermocouple 20, where, following curve 28C in FIG. 5, “t3'-te = 20-40 seconds.

Next, the thermocouple 10 is heated during cooking by a small flame F2 from the time “ts” of the flame change, curve 18S in FIG. 4, representing the generated emf (mV). The safety valve SV remains on and the cooking process is not interrupted, because, despite the reduction of the flame F2, the value 18S of the generated emf remains higher than the entire “RVde” scatter interval (FIG. 5) when generating an unlock value between 2.2 mV and 1 mV.

The design features of the thermocouple 10, designed for both flame F1 and flame F2 of the stove burner, in accordance with the invention can also be applied to a thermocouple with one working junction НJ1, located at the end 11 of the head, instead of a design with two opposite working junctions НJ1 and HJ2 , which is depicted in the drawings.

Claims (7)

1. Explosion-proof thermocouple designed for a gas burner stove (BU) with radially arranged outputs giving both a large flame (F1) and a small flame (F2), with a sensor (11, 12) and a cylindrical transmission housing (13, 14) made at least with a metal sleeve (11-14) of total length (H) and an internal thermoelectric rod (15) and containing at least one working junction (HJ1, HJ2) welded to the upper end part (11 ) of the sensor, where the large (F1) and small (F2) flames are directed towards the sensor (11, 12) in the direction opposite to the axis (A) of the thermo ares for generating emf (mV) (18L, 18S, 18C), required to supply a safety gas valve (SV) equipped with an electromagnetic actuator, which has a certain threshold value Ve for blocking the valve during heating of the thermocouple and a certain threshold value Vde to enable and disable the valve during cooling, and the thermocouple (10) contains a tubular base (14) of a conductive alloy welded to the sleeve (13) of the housing, forming a free junction (CJ2), and means (17) for supporting and positioning the thermocouple on the burner (BU) so that dates the nozzle (11-12) was at a certain distance (E) from the output of the flame (F1, F2) on the burner, characterized in that the sensor (11, 12) receiving the flame of the burner (F1, F2) is made using the above end part (11) containing a working junction (HJ1) in the form of a tip of a given length "L1" and a diameter "d" significantly smaller than the diameter "D1" of the above thermoelectric sleeve (13), and a part in the form of a truncated cone (12) in thermal connection with the working junction (HJ1), having a wall for receiving a flame (F1, F2), deflected towards the latter, with the angle of inclination of alpha-2 (α2) with respect to the axis (A) of the thermocouple, given the length L2 in the axial direction and the same diameter D1 as that of the thermoelectric sleeve (13), the above geometric dimensions L1, L2, d, D1 and The alpha-2 (α2) of the sensor (11, 12) is adapted to the shape of a small flame (F2) to cover the area of the inclined wall (12), and the length L2 and diameter D1 are much larger than the same dimensions of the upper end part (11) containing the working junction (HJ1), as a result of which the temperature gradient between the above wall (12) receiving the flame, and the working junction (HJ1) low. 2. A thermocouple according to claim 1, characterized in that the aforementioned part in the form of a truncated cone (12) is formed by a wall with an angle of deviation of alpha-2 (α2) of more than 15 °, and the length L1 of the end part (11) of the head is less than 2 mm. 3. A thermocouple according to claim 1, characterized in that the aforementioned part in the form of a truncated cone (12) is formed by a wall with an angle of deviation of alpha-2 (α2) between 15-30 ° and an axial length between 2.5 and 3.5 mm. 4. A thermocouple according to claim 1, characterized in that the aforementioned part in the form of a truncated cone (12) is formed by the aforementioned angle of deviation of alpha-2 (α2) between 15-30 °, the diameter of the thermoelectric sleeve is about 4 mm and the diameter "d" of the end part (1) heads less than 2.5 mm. 5. Thermocouple according to claim 1, characterized in that the transmitting housing (13, 14) of the thermocouple is made using an external sleeve (13) of a thermoelectric alloy and a tubular base (14) of a heat-conducting alloy connected to the sleeve (13) with formation of a free junction (CJ2), and means of support and positioning (17) of the thermocouple on the burner (SP), adjusted so that the sensor (11, 12) is facing the output of the flame (F1, F2) and located at a given distance (E ) from it, as a result of which a small flame (F2) reaches the above receiving wall (12), partially made in the form of a truncated cone, deviating by an angle alpha-2 (α2) between 15 and 30 ° to heat the above working junction (HJ1). 6. A thermocouple according to claim 1, characterized in that the transmitting housing (13, 14) of the thermocouple is made using an external sleeve (13) common with the sensor from a thermoelectric alloy of a given constant diameter D1, to which a tubular base (14) is telescopically connected from a heat-conducting alloy, forming a free junction (CJ2) with a thermoelectric sleeve (13) so that the first segment of the sleeve (13) of a certain length L3 after the sensor (11-12) is open and exposed to ambient air, and the second segment of the sleeve ( 13) of the same or greater length L3 'than open The lived-in segment L3 is covered by the above-mentioned tubular base (14) to achieve low thermal resistance for heat dissipation from the sensor (11, 12) through the tubular base (14), as a result of which the valve actuator (SV) is disconnected after the burner flame has extinguished (F1, F2) occurs over a short period of time (t3-te). 7. A thermocouple according to claim 1, characterized in that the diameter "d" of the end part (11) of the sensor, which contains the above working junction (HJ1), is made less than 2.5 mm in size, the aforementioned angle α-2 (α2) of the truncated cone (12) is selected in the range of 15-30 °, the transmitting housing (13, 14) of the thermocouple is made using an external sleeve (13), common with the sensor, from a thermoelectric alloy of constant diameter D1 of about 4 mm, to which the tubular base is telescopically connected (14 ) from a well-conducting heat alloy, forming a free junction (CJ2) with a sleeve (13) so that the first open The finished segment of the sleeve (13) of length L3 after the sensor (11, 12) is exposed to ambient air, and the second segment of the sleeve (13) of the same or greater length L3 'than the open segment L3 is covered by the above tubular base (14) to achieve a low thermal resistance for heat dissipation from the sensor (11, 12) through the tubular base (14), the secondary working junction (HJ2) is welded to the above inner thermoelectric rod (15) with the second inner segment of the conductor (19) from another alloy and is located below the above open segment L3 of the thermoelectric sleeve (13) and has an electric polarity opposite to the primary working junction (HJ1), and the resulting value of the emf (18L, 18S) between both working junctions (HJ1, HJ2) is greater than the threshold value Vde in order to keep the valve actuator (SV) switched on when there is a flame (F1, F2), as a result of which the valve actuator (SV) is switched off after the flame has extinguished ( F1, F2) occurs after a short period of time (t3-te).

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