GB1599695A

GB1599695A - Mounting device for a filling level measuring means

Info

Publication number: GB1599695A
Application number: GB23514/78A
Authority: GB
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 1977-10-05
Filing date: 1978-05-26
Publication date: 1981-10-07
Also published as: IT7828311A0; DE2744864A1; NL7809634A; JPS5489661A; DE2744864B2; FR2405469A1; IT1100822B; SE7810419L

Description

(54) IMPROVED MOUNTING DEVICE FOR A FILLING LEVEL MEASURING MEANS (71) We, ENDRESS & HAUSER GmbH & Co., a German company of Hauptstrasse 1, 7867 Maulburg, Germany, 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 invention relates to a device for mounting a probe, for a capacitive filling level measurement, in an opening of a container, probe connections leading insulatedly through the opening, the device comprising a screw-in mounting member made of metal which can be screwed into the opening and which has a central opening bounded by a surface diverging conically inwardly of the container, in which central opening is inserted apart connected to the probe and provided with a conical outer surface having an insulating layer thereon, a screw thread connection being provided to compress a spring which forces the conical surfaces together.

Probes for the capacitive measurement of the filling level in a container must be so fixed to the container wall that they are electrically insulated with respect to the container wall and that the electrical connection to the probe is passed outwardly through the container wall in a pressure-tight manner. One known device of the above kind is designed for fixing a rod probe, at the upper end section of which is formed the conical outer surface and which is provided at the end with a screw thread which, together with a screwed on nut, forms the screw thread connection. The screwed-in mounting member matches the shape and dimensions of the particular rod probe. However, the probe used for the capacitive measurement of the filling level can have very different shapes and dimensions.Apart from rod probes in the form of long metal rods of various diameters, which can be partially or com- pletely insulated according to their particular use, cable probes are also used which consist of a metal cable to which is applied an insulating cover. The fixing and lead-in devices used up to now were different from probe to probe according to the particular shape and dimension. This required, on the one hand, the production and storage of a large number of different parts; on the other hand, assembly was made more difficult because each probe had to be assembled and mounted in a different manner.

The object of the invention is the provision of a device of the above kind which, with a very small number of parts, makes possible a more reliable and pressure-tight fixing and leading-in of probes of different constructions and guarantees a perfect insulation.

In accordance with this invention, there is provided a device for mounting a probe within an opening in a container, the probe being for capacitive measurement of the filling level in the container, and for insulatedly leading probe connections through the opening, comprising a metal screw-in mounting member which can be screwed into the opening and which has a central opening bounded by a surface diverging conically in a direction which is inwardly of the container when the mounting member is screwed into said opening of the container, and into which central opening is inserted a metal intermediate member connected to the probe and provided with a conical outer surface having an insulating layer thereon, the intermediate member being provided with an axial bore extending over only a portion of its length, which bore matingly receives an end section of the probe and in which said end section is fixed, an external screw thread being provided on an end section of the intermediate member that projects out of the central opening in the mounting member and a nut being screwed onto the external screw thread so as to compress a spring that urges said conical surfaces together, and an electrical connection for the probe being provided at the upper end of the intermediate member.

With the device according to the invention, only the intermediate member need be made appropriate to the particular constructional form of the probe: all other parts of the device, the number of which is also very low, are the same for all probes. The production and storage of the components is faciliated and made cheaper thereby. For example, the screw-in mounting member which is the most expensive component, can, having regard to the large number of parts, be produced at an acceptable cost in a fine casting of expensive material such as chrome steel. Since, independent of the shape of the probe, mounting always takes place in the same manner, it can even be undertaken by less skilled personnel at the particular assembly location.

Because the axial bore does not pass through the entire length of the intermediate member a very good pressure tightness is achieved because the single connection between the interior of the container and the exterior exists at the conical surfaces forced against one another with the interposition of the insulating layer.

In a preferred form of the invention, the insulating layer is formed by a plastics hose which covers the conical outer surface of the intermediate member and at least that section of the probe adjoining the intermediate member. Preferably, the plastics hose consists of polytetrafluorethylene having a thickness of about 2 mm. The use of a plastics hose provides, on the one hand, a very good electrical insulation and on the other hand, an especially good pressure seal for the leadin at the individual connecting points between the interior and exterior.

Further features and advantages of the invention will become apparent from the following description of embodiments with the aid of the drawings. In the drawings there are shown: Figure 1 a sectional view of a device according to the invention by means of which a partially insulated rod probe is fixed to a container wall, Figure 2 an axial sectional view of the screw-in mounting member of the device of Figure 1, Figure 3 a plan view of the screw-in mounting member of Figure 2, Figure 4 a sectional view of the unit consisting of the rod probe, intermediate member and insulating hose, Figure 5 an axial sectional view of the insulating bush of the device of Figure 1, Figure 6 a plan view of the insulating bush of Figure 5, Figure 7 the device of Figure 1 when used with a completely insulated rod probe and Figure 8 the device according to the invention when used for a cable probe.

Figure 1 shows a capacitive measured value transducer 1 for measuring the level of filling in a container of which only a section is illustrated of the wall of the container 2 forming the upper closure. The measurement of the filling level takes place with the aid of an elongate metallic rod probe 3 which is fixed in an opening 5 in the container wall 2 by means of a fixing and lead-in device 4 and extends downwardly into the container. According to the filling level in the container, the probe 3 is covered by the filling material to a greater or lesser extent so that the capacity between the probe 3 and a counter electrode, which is generally formed by the metal container wall, is variable in accordance with the filling level. Changes in the capacity are sensed with the aid of an electronic circuit which is accommodated in a housing 6 arranged outside the container.

The measuring signals delivered by this circuit are evaluated for indicating the filling level in the container.

Since the probe 3 is electrically connected to the electronic circuit in the housing 6, the device 4 must be so designed that the probe 3 is not only securely fixed to the container wall 2 but that it is also electrically insulated with respect to the container wall 2 and that the electrical connection for the probe passes pressure-tight upwardly through the opening 5.

The fixing and lead-in device 4 includes a screw-in mounting member 7 which is illustrated in Figure 2 in an axial sectional view and in Figure 3 in plan view. The lower part 8 of the screw-in member 7 is cylindrical and is provided with an external screw thread 9.

The upper part 10 is formed as an hexagonal head and has a recess 11 into which three projections 12 extend inwardly arranged at an angle of 120 apart. An upwardly extending short threaded pin 13 is fixed to each of these three projections. A central opening 14 which diverges conically downwards, is arranged in the lower section 8. The upper section of the central opening 14 is cylindrical and is surrounded by an annular collar 15 extending upwardly into the recess 11, so that an annular groove 16 extending around the collar 15 exists at the base of the recess 11.

At the conical peripheral surface of the central opening 14, two slightly inwardly projecting cutting edges 17 are mounted extending around the periphery.

As Figure 1 shows, the screw-in member 7 is screwed into the opening 5 provided with an internal screw thread with the interposition of a sealing ring 18.

The unit 19 illustrated in Figure 4, which in the first place consists of the rod probe 3 and an intermediate member 20, is inserted in the central opening 14 in the screw-in member 7. A fixing section 21 of reduced diameter which is provided at its upper end with a neck 22 is formed at the upper end of the rod probe 3. The intermediate member 20 has an axial bore 23 which fits the diameter of the fixing section 21 and extends from the bottom end over the greater part of the length of the intermediate member, but does not pass through the entire intermediate member. On the outside of the lower half of the intermediate member there is formed an upwardly converging conical section 24 the conical surface of which fits the inner conical surface of the central opening 14 in the screw-in member 7.The conical section 24 changes into a short cylindrical section 25 to which is connected a cylindrical section 26 of somewhat larger diameter so that between the two cylindrical sections 25 and 26 there exists a shoulder 27. The upper end section 28 of the intermediate member, which again has a smaller diameter than the section 26, is provided with an external screw thread. A threaded pin 29 extending upwards axially is mounted on the upper end surface of the intermediate member.

When the fixing section 21 of the rod probe 3 is inserted in the axial bore 23 in the intermediate member 20, the neck 22 is at the level of the cylindrical section 26. Thus, the two parts are rigidly connected to one another in such a manner that the cylindrical section 26 is radially clamped and is forced into the neck 22.

An insulating hose 30 surrounds the lower part of the intermediate member 20, especially the conical section 24 and the attached cylindrical section 25, up to the shoulder 27 as well as the upper portion of the rod probe 3 extending downwards from the intermediate member. Preferably, the insulating hose 30 consists of polytetrafluorethylene with a thickness of about 2 mm.

A slightly outwardly projecting cutting edge 31 extending around the periphery, is mounted substantially in the centre of the conical section 24.

As Figure 1 shows, the unit 19 of Figure 4 is so inserted in the central opening 14 in the screw-in member 7 that the conical surface of the conical section 24 of the intermediate member 20 engages the inner conical surface of the central opening 14 with the interposition of the insulating hose 20. The intermediate member 20 is retained in the central opening 14 by a helical compression spring 33 which is supported on the one hand on the base of the annular groove 16 and on the other hand, through an insulating bush 34, by a lock nut 35 screwed onto the threaded section 28.

The insulating bush 34 which is illustrated in axial section in Figure 5 and in plan view in Figure 6, has a periphery matching the shape of the recess 11 and a cylindrical recess 36 at the lower end, the cross-section of which fits that of the cylindrical section 26 on the intermediate member 20. The recess 26 is surrounded by an annular groove 37 accommodating the spring 33 so that an annular wall 38 of insulating material exists between the recess 36 and the annular groove 37. A recess 39 with an hexagonal cross-section which fits the shape of the lock nut 35 is provided in the upper part of the insulating bush 34. An opening 41 matching the diameter of the threaded section 28 is provided in the partition wall 40 between the recesses 36 and 39.

The housing 6 is mounted on the screw-in member 7. It is retained thereon by a clamping ring 42 which has three bores through which extend the three threaded pins 13 on which are screwed nuts 43.

The described device is assembled in the following manner: first of all, the insulating hose 30 is pushed over the upper end of the rod probe 3 so that the section designed for covering the intermediate member 20 projects beyond the upper end. Then, the intermediate member 20 is pushed over the fixing section 21 by means of its axial bore 23 and in so doing the insulating hose 30 is pushed over the conical section 24 and the attached cylindrical section 25 until it abuts against the shoulder 27. The pushing over is made possible by the extensibility and elasticity of the insulating hose 30. Finally, the cylindrical section 26 is radially clamped and a rigid pressure connection between the rod probe 3 and the intermediate member 20 is produced thereby. The unit 19 of Figure 4 is then ready for insertion.

Next, the unit 19 is assembled with the screw-in member 7. For this purpose, the insulating bush 34 together with the helical compression spring 33 seated in the annular groove 37, in inserted in the recess 11 in the screw-in member 7 and the lock nut 35 is accommodated in the hexagonal recess 39 in the insulating bush 34. The intermediate member 20 of the unit 19 is passed through the central opening 14 in the scrw-in member 7 and the two parts are counter-rotated so that the lock nut 35 is screwed onto the threaded section 28; during this rotation, the screw-in member 7 entrains the insulating bush 34 which in its turn entrains the lock nut 35.

Due to the screwing of the intermediate portion 20 with the lock nut 35, the helical compression spring 33 is increasingly clamped over the insulating bush 34 and the conical section 24 is forced into the conical central opening 14 with an increasing pressure determined by the compression of the spring 33. The mutual rotation of the two parts is perfectly possible due to the selflubricating properties of the insulating hose 30 located between the two conical surfaces.

When the necessary pressure has been reached. the parts take up the position illustrated in Figure 1. The upper end of the insulating hose 30, which projects somewhat beyond the collar 15, is in its turn surrounded by the lower marginal section of the annular wall 38 of the insulating bush 34. Thus, a complete insulation between the screw-in member 7 and the intermediate member 20 exists which is at no point interrupted. The intermediate member 20 is retained in the lower part of the screw-in member 7 by the seating of the conical section 24 in the central opening 14; the insulating hose 30 lying between the conical surfaces produces, on the one hand, the necessary electrical insulation and on the other hand, the pressure-tight connection which is improved still further by the cutting edges 17 and 31 staggered with respect to each other.The part of the intermediate member 20 projecting upwards out of the central opening 14 is supported radially in the recess 36 in the insulating bush 34, which, for its part, is radially supported by means of its peripheral surface in the recess 11 in the screw-in member 7. In this manner, tilting of the unit 19 with respect to the screw-in member is prevented.

The helical compression spring 33 guarantees a uniform pressure for the seating of the intermediate member 20 in the screw-in member 7 and it compensates especially for different heat expansions of the different parts which could change the applied pressure.

After the unit 19 has been assembled together with the screw-in member 7, the entire arrangement can be mounted on the container in such a manner that the screw-in member 7 is screwed into the opening 5 in the container wall 2 with the interposition of the sealing ring 18.

Finally, the housing 6 is fixed to the screwin member 7 and the electrical connection between the probe and the electronic circuit is provided by attaching a connecting lead to the threaded pin 29.

In the embodiment of Figure 1, the insulating hose 30 extends over a certain length downwards beyond the upper part of the rod probe 3 whereby the leakage path between the container wall and the rod probe is extended; on the other hand, the lower part of the rod probe 3 is not insulated.

However, in many cases a completely insulated rod probe is required; the described device is also suitable for such a use without any modification. This is illustrated in Figure 7. All the components, with the exception of the insulating hose 30, are unchanged with respect to the embodiment of Figure 1 and will therefore not be described once again.

The insulating hose 30 is now so long that it covers the entire rod probe 3 and it is closed at the lower end by a closure plug 44 which preferably consists of the same insulating material as the insulating hose 30, thus, in accordance with the preferred embodiment consists of polytetrafluorethylene.

In assembling the device of Figure 7, first of all an insulating hose 30 of the required length is welded at one end to the closure plug 44 and is pushed upwards over the rod probe 3 until the closure plug 44 abuts against the end of the rod probe. The length of the insulating hose must be so calculated for a section to then project beyond the upper end of the rod probe 3 and which is sufficient for covering the intermediate portion 20 up to the shoulder 27.

Further assembly then takes place in the previously described manner.

A particular advantage of the described fixing and lead-in device consists in the fact that it is suitable for probes of very different shapes and dimensions whilst using the same components; all that is required is for the intermediate member to be matched to the particular probe. In Figure 8, this is illustrated by way of example for the case of a cable probe 45 which consists in the usual manner of a metal cable 46 provided with an insulating cover 47.

All parts of the device, with the exception of the intermediate member. are once again unchanged with respect to the embodiment of Figure 1 and will, therefore, not be described further. The intermediate member 48 has the same external shape as the intermediate member 20 of Figures 1 and 4; it only differs therefrom by the fact that the axial bore 49 fits the diameter of the metal cable 46 and that the section 50 designed for pressing in the cable probe is formed at the lower end of the intermediate member.

For assembling the device of Figure 8, a section of the insulating cover 47 corresponding to the length of the axial bore 49 is first of all removed from one end of the cable probe 45 and the section of the metal cable 46 exposed thereby is inserted in the axial bore 49. The forced-in portion 50 is then radially clamped and the intermediate member 48 is rigidly connected to the cable probe 45 thereby. The insulating hose 30 is then pushed downwards -over the intermediate portion 48; the insulating hose 30 is so dimensioned that, after mounting, it still covers a certain length of the cable probe 45.

Further assembly takes place as with the embodiment of Figure 1.

For other forms of capacitive probes, only intermediate member need be provided which have the same external shape and differ from one another by the fact that the axial bore matches the shape and size of the particular probe. All the other parts of the device can remain unchanged. Thereby, storage is simplified and made cheaper and mounting is facilitated because it always takes place in the same manner independently of the shape of the probe.

Instead of the insulating hose 30, a shrinking hose can be used with has initially a larger diameter than the intermediate member 20 and is made to shrink by heating after mounting so that it tightly engages the intermediate member 20 and the adjoining section of the probe.

WHAT WE CLAIM IS: 1. A device for mounting a probe within an opening in a container, the probe being for capacitive measurement of filling level in the container, and for insulatedly leading probe connections through the opening, comprising a metal screw-in mounting member which can be screwed into the opening and which has a central opening bounded by a surface diverging conically in a direction which is inwardly of the container when the mounting member is screwed into said opening of the container, and into which central opening is inserted a metal intermediate member connected to the probe and provided with a conical outer surface having an insulating layer thereon, the intermediate member being provided with an axial bore extending over only a portion of its length, which bore matingly receives an end section of the probe and in which said end section is fixed, an external screw thread being provided on an end section of the intermediate member that projects out of the central opening in the mounting member and a nut being screwed onto the external screw thread so as to compress a spring that urges said conical surfaces together, and an electrical connection for the probe being provided at the upper end of the intermediate member.

2. A device according to claim 1 characterised in that the insulating layer is formed by a plastics hose which covers the conical outer surface of the intermediate member and at least the section of the probe immediately adjacent the intermediate member.

3. A device according to claim 2 characterised in that the plastics hose covers the entire probe and that a closure plug covering the end surface of the probe is applied to the end of the plastics hose remote from the intermediate member.

4. A device according to claim 2 or 3 characterised in that the plastics hose consists of polytetrafluorethylene.

5. A device according to one of claims 2 to 4 characterised in that the plastics hose has a thickness of about 2 mm.

6. A device according to one of claims 2 to 5 characterised in that at least one cutting edge is formed on the conical inner surface of the central opening in the mounting member and/or on the conical outer surface of the intermediate member.

7. A device according to one of the preceding claims characterised in that the end section of the probe introduced into the axial bore in the intermediate member is fixed in the latter by pressing.

8. A device according to one of the preceding claims characterised in that, in the case of an insulated cable probe, the end section provided for fixing is formed by removing the insulation from the metal cable.

9. A device according to one of the preceding claims characterised in that a recess is formed at the end of the mounting member remote from the probe and that an insulating bush is arranged in the recess, which surrounds the end section of the intermediate member extending upwardly out of the central opening and engages, on the one hand, the nut screwed onto the said end section and on the other hand, engages said spring which is supported by the base of the recess.

10. A device according to claim 9 characterised in that the insulating bush has a recess in which a section of the intermediate member not covered by the insulating hose is radially supported and that the insulating bush is radially supported by the peripheral wall of the recess in the mounting member.

11. A device for mounting a probe within an opening in a container, the probe being for capacitive measurement of filling level within the container, said device being substantially as herein described with reference to the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. takes place in the same manner independently of the shape of the probe. Instead of the insulating hose 30, a shrinking hose can be used with has initially a larger diameter than the intermediate member 20 and is made to shrink by heating after mounting so that it tightly engages the intermediate member 20 and the adjoining section of the probe. WHAT WE CLAIM IS:

1. A device for mounting a probe within an opening in a container, the probe being for capacitive measurement of filling level in the container, and for insulatedly leading probe connections through the opening, comprising a metal screw-in mounting member which can be screwed into the opening and which has a central opening bounded by a surface diverging conically in a direction which is inwardly of the container when the mounting member is screwed into said opening of the container, and into which central opening is inserted a metal intermediate member connected to the probe and provided with a conical outer surface having an insulating layer thereon, the intermediate member being provided with an axial bore extending over only a portion of its length, which bore matingly receives an end section of the probe and in which said end section is fixed, an external screw thread being provided on an end section of the intermediate member that projects out of the central opening in the mounting member and a nut being screwed onto the external screw thread so as to compress a spring that urges said conical surfaces together, and an electrical connection for the probe being provided at the upper end of the intermediate member.