GB1574107A

GB1574107A - Thermometer assembly

Info

Publication number: GB1574107A
Application number: GB2260578A
Authority: GB
Original assignee: Rosemount Engineering Co Ltd
Current assignee: Emerson Process Management Ltd
Priority date: 1978-05-25
Filing date: 1978-05-25
Publication date: 1980-09-03
Also published as: DE7914727U1

Description

(54) IMPROVED THERMOMETER ASSEMBLY (71) We, ROSEMOUNT ENGINEERING COMPANY LIMITED, a British Company, of Durban Road, Bognor Regis, Sussex PO22 9QX, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to thermometer assemblies of the type having an electrical temperature sensing element, e.g. resistance thermometers, thermistors, and thermocouples.

It is usual for such thermometer assemblies to be formed with a tubular probe which is closed at one end. The sensing element of the assembly is located in the probe at the closed end and lead out wires extend from the element along inside the probe emerging at the other end. At this other end there is normally fixed to the probe a termination head by which the assembly can be fixed in an operational location and which also carries terminals to which the lead out wires are connected.

The thermometer assembly can then be connected to a utilisation circuit by means of these terminals. Thermometer assemblies of this kind will be referred to hereinafter as assemblies of the type described.

Commonly such thermometer assemblies have a terminal head which is made primarily of an insulating ceramic material.

This ceramic material is usually bolted to a metal plate which is itself brazed or welded to the end of the probe.

According to one aspect of the present invention, a thermometer assembly of the type described has a termination head comprising a block of electrically insulating plastics material and electrical terminals, each terminal comprising a threaded bore in the block, a non-circular metal base plate having a screw threaded hole therethrough registering with the bore in the block, and a terminal screw threaded in both the hole in the base plate and the bore in the block, the base plate being located in a complementary formation of the block so that the base plate cannot turn relative to the block when the terminal screw is screwed into or out of the block, and the base plate being electrically connected to a respective lead out wire from the sensor element of the assembly.Such an arrangement provides a much simpler termination head for thermometer assemblies which can-be made very much more cheaply than the types commonly used hitherto.

In a preferred embodiment, each base plate is rectangular and is located between integrally formed parallel flanges upstanding from a surface of the block. Preferably, each such base plate has a tag portion extending from one edge, and said respective lead out wire is connected to said tag portion.

In a particularly convenient embodi- ment, each tag portion extends towards an edge of the block and the block is cut away under the tag portion to allow access to the tag portion for the electrodes of a resistance welding machine for connecting said respective lead out wire to the portion. By employing this construction, the lead out wires can be resistance welded to the respective tag portions.

Normally, each terminal includes a washer between the base plate and the head of the screw. Wires from a utilisation circuit can then be connected to the terminal by clamping them between the washer and the base plate -by tightening the screw. In the arrangement with rectangular base plates, it is convenient for the washers to be also rectangular and located between the upstanding flanges of the block so that the washers also are preven- ted from turning as the screws are screwed tight.

In a preferred arrangement, the probe of the thermometer assembly is force fitted in a hole in the block. A resilient metal clip may be located between the probe and the inside of a hole in the block and grip the probe and the block. In this way the probe can be connected to the block easily and securely without the need for extensive tools.

In the preferred embodiment, the block is moulded from nylon filled with glass fibres. This material has proved to be sufficiently strong, yet resilient.

According to another aspect of the present invention, a method of making a thermometer assembly of the type described includes the steps of forming the termination head of a block of electrically insulating plastics material and providing electrical terminals thereon by, for each terminal, locating a non-circular metal base plate having a hole therethrough in a complementary formation of the block, so that the base plate cannot turn relative to the block, and with its hole registering with a bore provided in the block, then tapping an internal screw thread in both the hole in the base plate and the bore in the block and screwing a terminal screw into said thread so that the base plate is held in place on the block by the screw, and subsequently electrically connecting the lead out wires from the sensor element of the assembly to respective base plates.Preferably, each said terminal screw is self tapping and the internal thread is formed as the screw is screwed in.

An example of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a perspective view from slightly above and one side of a complete thermometer assembly embodying the present invention, Figure 2 is an elevation from another side of the assembly of Figure 1, Figure 3 is a plan view of the assembly from above, Figure 4 is an underneath plan view of the assembly, Figure 5 is an exploded perspective view from underneath illustrating how the probe is fastened to the terminal head of the assembly, and Figure 6 is a scrap section taken along line 6-6 of Figure 3 and illustrating a terminal of the assembly.

Referring to the drawings, a thermometer assembly comPrises an elongate tubular probe 10 which has a closed end 11. A temperature sensor (not shown) is contained in the probe adjacent the closed end. Various such sensors are known including resistance thermometer sensors, thermocouples and thermistor devices.

Electrical lead out wires extend from the sensor inside the probe emerging at the other end thereof. Fastened at this other end of the probe 10 there is a termination head 12. As shown in the drawings, this termination head has a generally circular shape and is orientated in a plane perpendicular to the axis of the probe with the probe extending symmetrically from the centre of the head 12. The head is provided with a plurality of terminals, indicated generally at 13, which will be described in more detail later. In this example, there are four such terminals which are suitable for a "four wire connection" to the sensor in the probe. The lead out wires from the sensor emerging from the end of the probe are connected to the terminals so that the thermometer assembly can be readily connected in a utilisation circuit.

The head 12 also serves to mount the assembly in an operational location and for this purpose there are two spring loaded bolts 14. These bolts 14 are of a kind well known in this art.

The termination head 12 comprises a block 15 moulded from glass fibre filled nylon. As can be seen best in Figure 3, the block has, from above a generally cruciform appearance with one of the terminals 13 provided in each arm of the cross. The block 15 is moulded with the arms of the cross thicker in the axial direction of the probe 10. The upper surface 16 of each arm is formed in the shape of a rectangular section channel with parallel flanges 17 and 18 along each of the edges of the arm. Between these flanges 17 and 18 there is located a base plate 19. The base plate 19 is of generally rectangular cross-section and fixed between the flanges 17 and 18 so that it cannot rotate in its own plane. A threaded hole 20 extends through the base plate 19 and registers with a similarly threaded bore 21 extending into the material of the block 15. In the assembled article, a screw 22 is screwed in both the hole 20 and the bore 21. The screw is shown removed in Figure 6 for clarity. Because of the threads in both the hole 20 in the base plate and the bore 21 in the block, and because the base plate 19 is prevented from rotating by the flanges 17 and 18, the screw 22 effectively holds the base plate 19 securely in position against the surface 16 of the block.

Further, the base plate 19 is continuously retained in position even as the screw 22 is screwed in and out of the bore 21, provided at least a portion of the screw 22 remains engaged in the thread of the bore 21.

In a very convenient way of manufacturing the assembly, a self tapping screw is used for the screw 22 and the threads in the hole 20 and in the bore 21 are provided simultaneously simply by screwing home the self tapping screw 22. A rectangular washer 23 is provided between the base plate 19 and the screw 22 and is prevented also from rotating by the flanges 17 and 18. When the thermometer assembly is to be connected in an external circuit, wires of the external circuit can easily be connected by placing them between the base plate 19 and the washer 23 and then tightening the screw 22.

Each of the base plates 19 is provided with an integral tag 24 extending from one of its edges. The tag 24 extends through a gap in the flange 18 on one side of the base plate. As can be seen best in Figure 3, the tag 24 of each base plate 19 extends outwards towards an edge of the block 15.

Further, on the far side of the flange 18 from the main part of the base plate 19, the block 15 is cut away so that both the upper and lower surfaces of the end of the tag 24 are accessible.

Lead out wires from the sensor element at the end 11 of the probe 10 emerge from the open end of the probe 10 through a bore provided through the centre of the block 15 of the termination head. These wires are shown emerging at 25 and 26 in Figure 3. The open end of the bore through the block 15 is sealed off with a drop 27 of silicone rubber. After emerging from the bore in the block 15 the wires are separated into pairs 25 and 26 as shown and the wires of each pair are passed on opposite sides of separating posts 28 and 29. The pairs of wires are then fed through gaps 30 and 31 between adjacent flanges 18 and to the tags 24 of respective terminals.As can be seen in Figure 3, the disposition of the tags 24 and the shape of the block 15 provide sufficient access to the tags 24 to enable the electrodes of a resistance welding machine to be brought to bear on opposite sides of the tags 24 so that the lead out wires can be resistance welded to the tags.

Considering now Figure 5, there is shown an exploded view from underneath the block 15 illustrating the method of fastening the block to the probe 10. As can be seen in the Figure, the block 15 has a bore 32 extending through its centre.

This bore is made with a diameter slightly greater than the external diameter of the tube of the probe 10. A resilient metal clip 33 is fitted over the open end of the probe 10 and this end with the clip 33 is then forced into the bore 32. The clip 33 is so shaped that it penetrates with the end of the probe 10 into the bore 32 slightly deforming the inner surface of the bore.

When forced fully home, barblike formations on the outer surfaces of the clip 33 engage in the bore 32 preventing the clip 33 from being withdrawn. At the same time, the clip 33 is compressed by the bore 32 onto the probe 10 so as to grip it firmly.

In this way, the probe 10 is firmly secured on the bore 32. The bore 32 is stepped to a reduced diameter part way through the thickness of the head to provide an annular shoulder against which the end of the tube of the probe 10 can abut, so that the tube cannot be forced right through the head.

WHAT WE CLAIM IS: - 1. A thermometer assembly of the type described, having a termination head comprising a block of electrically insulating plastics material and electrical terminals, each terminal comprising a threaded bore in the block, a non-circular metal base plate having a screw-threaded hole therethrough registering with the bore in the block, and a terminal screw threaded in both the hole in the base plate and the bore in the block, the base plate being located in a complementary formation of the block so that the base plate cannot turn relative to the block when the terminal screw is screwed into or out of the block, and the base plate being electrically connected to a respective lead-out wire from the sensor element of the assembly.

2. A thermometer assembly as claimed in claim 1, wherein each base plate is rectangular and is located between integrally formed parallel flanges upstanding from a surface of the block.

3. A thermometer assembly as claimed in claim 2, wherein each base plate has a tag portion extending from one edge, and said respective lead-out wire is connected to said tag portion.

4. A thermometer assembly as claimed in claim 3, wherein each tag portion extends towards an edge of the block and the block is cut away under the tag portion to allow access to the tag portion for the electrodes of a resistance welding machine for connecting said respective lead-out wire to the tag portion.

5. A thermometer assembly as claimed in claim 4 wherein the lead-out wires are resistance welded to the respective tag portions.

6. A thermometer assembly as claimed in any preceding claim wherein said terminal includes a washer between the base plate and the head of the screw.

7. A thermometer assembly as claimed in any of claims 2 to 5, wherein each terminal includes a rectangular washer between the base plate and the head of the screw and located also between the upstand

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In a very convenient way of manufacturing the assembly, a self tapping screw is used for the screw 22 and the threads in the hole 20 and in the bore 21 are provided simultaneously simply by screwing home the self tapping screw 22. A rectangular washer 23 is provided between the base plate 19 and the screw 22 and is prevented also from rotating by the flanges 17 and 18. When the thermometer assembly is to be connected in an external circuit, wires of the external circuit can easily be connected by placing them between the base plate 19 and the washer 23 and then tightening the screw 22. Each of the base plates 19 is provided with an integral tag 24 extending from one of its edges. The tag 24 extends through a gap in the flange 18 on one side of the base plate. As can be seen best in Figure 3, the tag 24 of each base plate 19 extends outwards towards an edge of the block 15. Further, on the far side of the flange 18 from the main part of the base plate 19, the block 15 is cut away so that both the upper and lower surfaces of the end of the tag 24 are accessible. Lead out wires from the sensor element at the end 11 of the probe 10 emerge from the open end of the probe 10 through a bore provided through the centre of the block 15 of the termination head. These wires are shown emerging at 25 and 26 in Figure 3. The open end of the bore through the block 15 is sealed off with a drop 27 of silicone rubber. After emerging from the bore in the block 15 the wires are separated into pairs 25 and 26 as shown and the wires of each pair are passed on opposite sides of separating posts 28 and 29. The pairs of wires are then fed through gaps 30 and 31 between adjacent flanges 18 and to the tags 24 of respective terminals.As can be seen in Figure 3, the disposition of the tags 24 and the shape of the block 15 provide sufficient access to the tags 24 to enable the electrodes of a resistance welding machine to be brought to bear on opposite sides of the tags 24 so that the lead out wires can be resistance welded to the tags. Considering now Figure 5, there is shown an exploded view from underneath the block 15 illustrating the method of fastening the block to the probe 10. As can be seen in the Figure, the block 15 has a bore 32 extending through its centre. This bore is made with a diameter slightly greater than the external diameter of the tube of the probe 10. A resilient metal clip 33 is fitted over the open end of the probe 10 and this end with the clip 33 is then forced into the bore 32. The clip 33 is so shaped that it penetrates with the end of the probe 10 into the bore 32 slightly deforming the inner surface of the bore. When forced fully home, barblike formations on the outer surfaces of the clip 33 engage in the bore 32 preventing the clip 33 from being withdrawn. At the same time, the clip 33 is compressed by the bore 32 onto the probe 10 so as to grip it firmly. In this way, the probe 10 is firmly secured on the bore 32. The bore 32 is stepped to a reduced diameter part way through the thickness of the head to provide an annular shoulder against which the end of the tube of the probe 10 can abut, so that the tube cannot be forced right through the head. WHAT WE CLAIM IS: -

1. A thermometer assembly of the type described, having a termination head comprising a block of electrically insulating plastics material and electrical terminals, each terminal comprising a threaded bore in the block, a non-circular metal base plate having a screw-threaded hole therethrough registering with the bore in the block, and a terminal screw threaded in both the hole in the base plate and the bore in the block, the base plate being located in a complementary formation of the block so that the base plate cannot turn relative to the block when the terminal screw is screwed into or out of the block, and the base plate being electrically connected to a respective lead-out wire from the sensor element of the assembly.

ing flanges of the block to prevent the washer turning relative to the base plate.

8. A thermometer assembly as claimed in any preceding claim wherein the probe of the assembly is force fitted in a hole in the block.

9. A thermometer assembly as claimed in claim 8 wherein a resilient metal clip is located between the probe and the inside of the hole m the block and grips the probe and the block.

10. A thermometer assembly as claimed in any preceding claim wherein the block is made of nylon.

11. A thermometer assembly as claimed in claim 10 wherein the nylon is filled with glass fibres.

12. A thermometer assembly as claimed in any preceding claim wherein the block is moulded.

13. A thermometer assembly as claimed in any preceding claim wherein the terminal screws are self-tapping screws.

14. A method of making a thermometer assembly of the type described including the steps of forming the termination head of a block of electrically insulating plastics material and providing electrical terminals thereon by, for each terminal, locating a non-circular metal base plate having a hole therethrough in a complementary formation of the block, so that the base plate cannot turn relative to the block, and with its hole registering with a bore provided in the block, then tapping an internal screw thread in both the hole in the base plate and the bore in the block and screwing a terminal screw into said thread so that the base plate is held in place on the block by the screw, and subsequently electrically connecting the leadout wires from the sensor element of the assembly to respective base plates.

15. A method as claimed in claim 14, wherein each said terminal screw is selftapping and the internal thread is formed as the screw is screwed in.

16. A thermometer assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. A method of making a thermometer assembly substantially as hereinbefore described with reference to the accompanying drawings.