GB2147737A

GB2147737A - A thermocouple device

Info

Publication number: GB2147737A
Application number: GB08420511A
Authority: GB
Inventors: Karl Hehl
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-08-24
Filing date: 1984-08-13
Publication date: 1985-05-15
Also published as: DE3330491C2; IT8404855A0; IT1180283B; IT8404855A1; GB2147737B; GB8420511D0; NL8402450A; DE3330491A1; CH666355A5; FR2551208B1; FR2551208A1

Abstract

The ends of the wires (13a', 13b'), which serve as a thermo pair of a thermocouple, are enclosed by a heat-resistant sleeve (16), and are fused to form a mixed metal body (13m).This mixed metal body (13m) is axially pressed into a recess (21) provided in a heat-conducting plate member (17). The heat-conducting plate member (17) protrudes beyond the end of the sleeve (16) and the end face of said plate member (17) is in thermal contact with a metallic heat-conducting housing (18) which axially holds together the sleeve (16) and the heat-conducting plate (17). This provides good pre-requisites for achieving economic mass-production with a high measuring accuracy and a high speed of reaction. <IMAGE>

Description

SPECIFICATION A thermocouple device The present invention relates to a thermocouple device which comprises two wires of a different materials with said wires being accommodated, in a tension-relieving manner, in a protective sleeve and being electro-conductively connected to each other at one end (measuring point or hot junction) to form a theremocouple, and a sleeve formed from heat-resistant material surrounding the said wires at least in the region of the measuring point; said device including the other end (cold junction) of the wires forming the thermocouple being connectable to a voltage measuring instrument, and a metallic heat-conducting plate member axially supported on the protective sleeve, the ends of the wires being embedded in said plate member which protrudes beyond the end of the heat-resistant sleeve the end of said plate member being in thermal contact with a metallic heat-conducting housing which axially holds together the heat-resistant sleeve and the heat-conducting plate member.

In a known thermocouple device of the abovedescribed type (US PS 2 517 033), the exposed and cleaned ends of the wires enclosed by the sleeve are embedded in a solder or any other suitable metal alloy and, in consequence, are electrically joined together. To some extent, a sleeve which is covered at the bottom by a mica plate serves as a casting mould during casting of the molten solder or the alloy. At its lower end, the cast which is rotationally symmetrical body of soldering metal, has a radial flange. It is suitable, therefore, for serving as a heat-conducting plate in the system. A thermocouple device results therefrom which has a high measuring accuracy and a high speed of reaction. However, the casting process which is necessary is detrimental to economic mass-production.

The present invention seeks to develop a thermocouple device of the above-described type so that, in terms of its measuring accuracy and speed of reaction, it meets all the requirements appertaining to practical purposes without the need for a considerable amount of additional technical outlay.

According to the present invention there is provided a thermocouple device comprises two wires of different materials with said wires being acommodated in a tension-relieving manner, in a protective sleeve and being electro-conductively connected to each other at one end (measuring point or hot junction) to form a thermocouple, and a sleeve formed from heat-resistant material surrounding said wires at least in the region of the measuring point; the other end (cold junction) of the wires forming the thermocouple being connectable to a voltage measuring instrument, and a metallic heat-conducting plate member axially supported on the protective sleeve, the ends of the wires being embedded in said plate member which protrudes beyond the end of the heat-resistant sleeve, the end face of said plate member being in thermal contact with a metallic heat-conducting housing which axially holds together the heat-resistant sleeve and the heat-conducting plate member, characterised in that a mixed metal body, formed by fusing the two wires is axially pressed into a concentric recess provided in the heat-conducting plate member, in a form-fitting manner.

To increase the measuring accuracy even further, any disturbing electrical potentials may be kept remote from the measuring point, without any appreciable detrimental effect upon the conduction of heat between the object and the measuring point, when an electrically insulating plate, preferably a mica plate of high thermal permeability, is insertable between the end face of the heat-conducting plate and the cup-shaped heat-conducting housing.

Because selection is possible according to particular requirements, mass-production costs can be reduced because the mica plate is only inserted if needed; that is to say, it is only inserted for customers who demand a maximum degree of measuring accuracy.

Mass-production is considerably rationalised when the structural unit I including heat-conducting plate member with centering neck portion, the mixed metal body and the wires I is embedded in a moulded part which integrally constitutes the heat-resistant and protective sleeves, and which has been formed in an injection moulded process from a heat-resistant, high-polymer material, by inserting the unit into the injection moulding die.

The pre-requisite for achieving a simple manufacturing method as created, as a result thereof, whereby the heat-conducting plate member, which encloses the mixed metal body, is embedded in the protective sleeve formed by injection-moulding, and a cold-formed flange of the heat-conducting housing engages behind said formed sleeve portion.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial sectional view of a thermocouple device illustrated inserted in a recess in a plasticising cylinder of a plastics material injection moulding machine; Figure 2 is an enlarged fragmentary view of a portion of the thermocouple device shown in longitudinal section and a connecting plug; Figure 3 illustrates a protective sleeve of the thermocouple device before it has been deformed; Figure 4 illustrates a ceramic sleeve forming a sleeve; Figure 5 illustrates a heat-conducting plate member; Figure 6 illustrates a mica plate of the thermocouple device; and Figure 7 illustrates the heat-conducting housing of the thermocouple device before it has been deformed.

In the embodiment which is illustrated in the drawings, the thermo pair of the thermocouple device is formed by two wires 13a' and 13b' which are accommodated in a tension-relieving manner, in a protective sleeve 15 and are formed from iron and constantan. These wires are fused together at one end (the hot junction or measuring point) to form a thermal junction and surrounded by a heatresistant ceramic sleeve 16 in the region of the measuring point. The voltage measuring instrument is connected to the other ends (cold junction) of the wires 13a' and 13b' as a comparing point.At the measuring point, a mixed metal portion or body 13m I formed by fusing the wires 13a' and 13b' and thereby mixing the metals I is embedded in a metallic heat-conducting plate member 17 in a form-fitting manner, and said plate member 17 is machined from aluminium or from a berylium/ copper alloy. The fusion of the wires is effected in a rare or inert gas atmosphere by means of an electric arc; that is to say, with the exclusion of oxygen. This means that any oxidation or scaling is effectively eliminated. A mixed metal body is produced which has a high degree of mixing and is substantially shaped like an ellipsoid.

The heat-conducting plate member 17 is axially supported on ceramic heat resistant sleeve 16 and protrudes beyond the end of said sleeve 16. The end face of the heat-conducting plate member 17 is in thermal contact with a heat-conducting housing 18 which axially holds together the heat-conducting plate member 17 and the sleeve 16. The radially symmetrical heat-conducting plate member 17 is disposed in a portion of sleeve 16 of greater inside diameter a-a and is centred on an internal annular shoulder 16a of the ceramic sleeve 16. The annular shoulder 16a extends perpendicularly to the axis of symmetry of the thermocouple device and the rear end of the shoulder 16a seals an annular chamber 22a which is defined externally by the internal surface of the ceramic sleeve 16 and internally by the periphery of the heat-conducting plate member 17.The mixed metal body 13m is substantially shaped like an ellipsoid and is pressed into a concentric, conical recess provided in the heat-conducting plate member 17, thereby forming two annular contact faces y and z. The mixed metal body 13m is held in the recess 21 by means of a constricted portion 17a' of a hollow centering neck portion 17a located at the rear of the heat-conducting plate member 17. An additional constricted portion 17a" of the centering neck portion 17a grips the encased wires 13a and 13b for the purposes of relieving tension. In addition, the protective casing 13 of the thermo pair of the thermocouple device is enclosed in a tensionrelieving manner by a constricted portion 15b' of the protective sleeve 15. All of the constricted portions 17a', 17a" and 15b' are produced by coldforming the centering sleeve 17a and the protective sleeve 15, respectively.As a result, the rear portion 15b of the protective sleeve has a relatively thin wall.

The diameter of the heat-conducting plate member 17 is preferably at least three times greater than the maximum diameter of the mixed metal body 13m but is smaller than the maximum inside diameter a-a of the ceramic sleeve 16. This ensures intensive conduction of heat between the object to be measured, i.e. the plasticising cylinder, for example, and the measuring point.

A plate 20, of an electrically insulating material preferably a mica plate of high thermal permeability, is insertable, if required, between the end face of the heat-conducting plate member 17 and the cup-shaped heat-conducting housing 18, and said plate 20 protrudes radially all round the flat end face of the heat-conducting plate member 17.

When the mica plate is inserted, disturbing electrical potentials emanating from the object to be measured can be screened from the measuring point to achieve maximum accuracy of measurement.

As is apparent from Figure 1, the flat end face S of the cup-shaped heat-conducting housing 18 abuts against the object 10 due to the bias of a coil spring 12 which surrounds the pair of thermocouples, one end of said coil spring 12 abutting against internal flange 18a of the heat-conducting housing 18, and the other end of said coil spring 12 abutting against a connecting plug 14. The initial tension of the coil spring 12 determines the abutment pressure of the end face S and is adjustable by means of a hollow threaded member 11 whose external threaded portion 11a is in threaded engagement with the object 10 and whose internal threaded portion is in threaded engagement with the coil spring 12.The threaded member extends into receiving bore 19 which is provided for receiving the object 10 and has engagement plugs or pins 11a, and said threaded member extends into a hexagonal portion 11b at its rear end.

A modified structure of the thermocouple element (not shown) differs from the embodiment illustrated in the drawing as follows: Instead of providing heat resistant sleeve 16, which is formed, for example, from ceramic material, and a protective sleeve 15, there is a moulded part which is made from a heat-resistant, high-polymer material by an injection moulding process; said moulded part having the same external diameter as the sleeve 16 in the portion of the measuring point and additionally having the same shape as the protective sleeve 15.

This moulded part has embedded therein the unit formed from the heat-conducting plate member 17 with centering neck portion 17a, the mixed metal body 13m and the wires 13a' and 13b'. During the injection moulding process, embedding is effected in the cavity of an injection moulding die.

At the rear end of the measuring point, the radially symmetrical moulded part has an external annular shoulder which corresponds to the external flange 15a of the protective sleeve 15 in the embodiment shown in the drawing. The internal flange 18a of the cold-formed heat- conducting housing 18 engages behind said annular shoulder. The end portion of the protective casing 13 of the thermo pair is embedded in a rear potion of the moulded part; said portion protruding from the heat-conducting housing 18. In this modified embodiment which has just been described it is therefore not necessary for a protective sleeve 15 and a sleeve 16 to be assembled separately.

The additional alternative possibility of inserting the mica plate and attaching the heat-conducting housing 18 is achieved in accordance with the manufacturing method used for the embodiment shown in the drawing; this is because the heatconducting plate member 17, which is embedded in the moulded part, protrudes with its end face beyond the moulded part in the same manner as is shown in connection with the embodiment illustrated in the drawing.

The wires 13a' 13b of the thermocouple device are connectable at the "cold junction" in known manner by plug 14 to a voltage measuring instrument (not shown).

Claims

1. A thermocouple device comprises two wires (13a', 13b') of different materials with said wires (13a', 13b') being accommodated, a tension-relieving manner, in a protective sleeve (15) and being electro-conductively connected to each other at one end (measuring point or hot junction) to form a thermocouple, and a sleeve (16) formed from heat-resistant material surrounding said wires (13a', 13b') at least in the region of the measuring point; the other end (cold junction) of the wires forming the thermocouple being connectable to a voltage measuring instrument, and a metallic heatconducting plate member (17) axially supported on the protective sleeve (15), the ends of the wires (13a', 13b') being embedded in said plate member (17) which protrudes beyond the end of the heatresistant sleeve (16), the end face of said plate member (17) being in thermal contact with a metallic heat-conducting housing (18) which axially holds together the heat-resistant sleeve (16) and the heat-conducting plate member (17), characterised in that a mixed metal body (13m), formed by fusing the two wires (13a', 13b'), is axially pressed into a concentric recess (21) provided in the heatconducting plate member (17), in a form-fitting manner.

2. A thermocouple device as claimed in claim 1, in which the mixed metal body (13m) is substantially shaped like an ellipsoid and is pressed into a conical recess (21) provided in the heat-conducting plate member (17), which plate member (17) is centred on an internal annular shoulder (16a) of the heat-resistant sleeve (16), thereby forming two annular contact faces (y,z).

3. A thermocouple device as claimed in claim 1 or 2, in which the mixed metal body (13m) is held in the recess (21) by means of a constricted portion (17a') of a hollow centering neck portion (17a) located at the rear of the heat- conducting plate member (17); an additional constricted portion (17a") enclosing the encased wires (13a, 13b) in a tension-relieving manner.

4. A thermocouple device as claimed in any of claims 1 to 3, in which the diameter of the heatconducting plate member (17) is at least three times greater than the maximum diameter of the maximum diameter of the mixed metal body (13m) but is smaller than the inside diameter (a-a) of the shaped sleeve (16)

5. A thermocouple device as claimed in any of claims 1 to 4, in which an electrically insulating plate (20), preferably a mica plate of high thermal permeability, is inserted between the end face of the heat-conducting plate member (17) and the cup-shaped heat-conducting housing; (18); said plate (20) protruding radially all round the flat end face of the heat-conducting plate member (17).

6. A thermocouple device as claimed in any of claims 1 to 5, in which when secured in its position of use, the flat end face (S) of the heat-conducting housing (18) abuts against the object (10) to be measured under the action of a coil spring (12) which surrounds the thermo pair one end of said coil spring (12) abutting against an internal flange (18a) of the heat-conducting housing (18), and the other end of said coil spring (12) abutting against the plug (14), and in which the initial axial tension of the coil spring (12) is adjustable by means of a hollow threaded member (11) whose external thread (1 lea') is in threaded engagement with the object (10) and whose internal thread is in threaded engagement with the coil spring (12).

7. A thermocouple device as claimed in any of claims 1 to 6, in which the heat-resistant sleeve (16) is a ceramic sleeve which supports, at its rear end, a coaxial protective sleeve (15) and an inwardly extending flange (18a) of the heat-conducting housing (18) engages therebehind, and the protective sleeve (15) encloses in a tension-relieving manner the protective casing (13) of the wires of the thermocouple in the region of a constricted portion (15b').

8. A thermocouple device as claimed in any of claims 1 to 6, in which the structural unit including heat-conducting plate (17) with centering neck portion (17a), the mixed metal body (13m) and the wires (13a', 13b') - is embedded in the protective sleeve, which has been formed in an injection moulding process from a heat-resistant, high-polymer material, by inserting the unit into the injection moulding die.

9. A thermocouple device as claimed in claim 8, in which the protective sleeve has an annular shoulder at the rear end of the measuring point and the internal flange (18a) of the heat-conducting housing (18) engages behind said annular shoulder, and in which the end portion of the protective casing (13) of the encased wires (13a, 13b) is embedded in the sleeve.

10. A thermocouple device substantially as herein described and illustrated with reference to the accompanying drawings.