WO1992001218A1

WO1992001218A1 - Sensor holder

Info

Publication number: WO1992001218A1
Application number: PCT/GB1991/001143
Authority: WO
Inventors: Timothy Russell; Noel Heary; Michael Sheerin
Original assignee: Amagruss Limited
Priority date: 1990-07-10
Filing date: 1991-07-10
Publication date: 1992-01-23
Also published as: AU8215291A

Abstract

The invention relates to a sensor or electrode holder (1) adapted for use in continuous in-line process measurement applications. The sensor holder has a sleeve (3) for fluid tight insertion in an opening defined by a pipe or vessel through which the medium to be analysed by the sensor (13) flows. The sensor (13) is contained within an electrode cartridge (2) which is capable of fluid tight movement relative to the sleeve (3) between a first operative position and a second inoperative position. In the first operative position, the sensor (13) is exposed to the medium to be analysed contained within the vessel and in the second inoperative position the cartridge (2) is retracted and flow of the medium to be analysed to the sensor (13) is inhibited by a series of O-rings (22, 32, 33, 38, 49, 50) and an end cap (6) on the cartridge (2). The sensor (13) may be removed from the electrode cartridge (2) in the inoperative position without requiring the cessation of the process being monitored.

Description

Sensor Holder

Technical Field

This invention concerns a holder for sensors and the like adapted for use in continuous in-line process measurement applications.

Background Art

Sensor holders are used to support a removable detecting sensor e.g. a pH electrode, an ion-selective electrode, a gas-sensing electrode, a thermometer, a viscometer or a pressure detector, in position in an aperture on a vessel or pipe containing the medium to be analysed, or analyte. Such sensors may be used to detect electrode signals, usually in the form of voltage and current differences, and the signals are usually transmitted to an electronic unit where voltage difference is amplified and the signal transformed into the required units e.g. pH units. Detecting electrodes are usually used for the analysis of fluids, particularly fluids under flow in continuous processes.

In industry, sensors such as electrodes are used in in-line process control e.g. automatic and automated process control and in quality control. In in-line process control the electrode is usually mounted on a vessel or pipe through which the substance to be analysed (the analyte) passes, so as to project inside the vessel or pipe for direct exposure to the analyte.

Electrodes used in in-line situations, together with their holders or mounting devices, require special design. In particular, the mounting device should be simple in design and easy to maintain and should be able to withstand harsh plant environments. To date such devices have proved expensive to manufacture and have been susceptible to leakage and contamination of the analyte. To avoid analyte contamination it has been necessary to interrupt process flows to remove the electrode from its mounting for maintenance operations, such as for inspection, replacement or recalibration.

Caution is required on removal of the electrode where the analyte is at high temperatures or under pressure as the analyte may erupt violently from the aperture in the vessel or pipe in which the electrode holder is mounted. Accordingly, for this reason also flow must be interrupted when removing the electrodes.

Existing devices, therefore, do not allow removal of an in-line process measurement electrode or sensor without interruption to flow. It has been found that this interruption to flow is costly and time consuming.

An object of the present invention is to provide a rugged sensor holder adapted for use in continuous in-line process fluid measurement applications which allows a sensor to be removed from the holder without requiring interruption of the fluid flow.

Disclosureoftheinvention

According to the invention there is provided a sensor holder comprising mounting means adapted for fluid tight mounting in an aperture defined by a vessel or pipe containing the medium to be analysed by the sensor, and sensor holding means characterized in that the sensor holding means is adapted for a fluid tight movement relative to the mounting means between a first operative position in which the sensor located by the sensor holding means is exposed to the said medium to be analysed, and a second inoperative position in which the sensor holding means is retracted into the mounting means allowing the removal of the sensor therefrom, the sensor holder being fluid tight in the second inoperative position following removal of the sensor.

Suitably, the mounting means comprises a tubular sleeve adapted for connection to said vessel or pipe, and the sensor is held within a tubular cartridge which is moveable axially within the tubular sleeve from a first operative position in which the cartridge protrudes outwardly from an end of the sleeve to expose the sensor to a second inoperative position in which the cartridge is withdrawn within the sleeve, sealing means being provided at the outward end of the cartridge to form a fluid tight seal between the cartridge and the sleeve when the cartridge is withdrawn inside the sleeve.

Preferably, the sleeve comprises a threaded mounting collar for threaded engagement with a threaded mounting bush on said vessel or pipe.

Preferably, the electrode cartridge comprises a lower annular head portion, a central tube portion and an upper cartridge head, defined by a lip and a toothed rim and a radial ring projecting from the tube portion below the cartridge head, the upper cartridge head having threads on its internal face to engage complementary threads on the sensor and the head portion having windows through which the medium to be analysed can flow to contact the sensor in the operative position.

Advantageously, the central tube portion comprises a riser thread on its external surface engageable with a complementary thread on the internal surface of the sleeve so that the electrode cartridge is moveable in fluid tight manner relative to the sleeve between the first operative position and the second inoperative position, disengagement of the threads being prevented when the sensor holder is inserted in said vessel or pipe by an abutment member mounted on the electrode cartridge.

Suitably, the abutment member comprises a removable end cap threadingly engageable in the hole of the annular head portion.

Preferably, means are provided to prevent removal of the sensor from the electrode cartridge in the first operative position.

More preferably, the means to prevent removal of the sensor from the electrode cartridge comprises a safety lid for fitting over the sensor having snap fastening means engageable with the cartridge head in the second inoperative position, disengagement of the snap fastening means being prevented by the sleeve in the first operative position so that the sensor may not be removed until the electrode cartridge is in the second inoperative position.

Suitably, the safety lid forms a sliding friction fit with the cartridge head and has an annular top to expose a sensor contact socket, the snap fastening means comprising fingers separated by slots projecting substantially vertically downwards from the annular top and having flanges on the internal face of their lower extremities, the flanges being insertable into a groove defined between the lip and a ring, so that the flanges slide over the cartridge head and snap into the groove.

Preferably, 0-rings are provided between the electrode cartridge and the sleeve; between the sensor element and the electrode cartridge; on the sleeve for contact with the mounting bush; and between the end cap and the cartridge.

Brief Description of the drawings

By way of example only, specific embodiments of the invention in which the sensor is an electrode will now be described with reference to the accompanying drawings, in which,

Figure 1 is a front view of an electrode cartridge component of the electrode holder of the invention;

Figure 2 is a pictorial view of an electrode over which a sheath shown in cross-section is fitted for use in the electrode holder of the invention;

Figure 3 is an exploded view of an electrode holder of the invention in which the electrode is inserted in the electrode cartridge;

Figure 4 is a side view of the electrode holder of Figure 3 in a retracted inoperative position;

Figure 5 is a side view of the electrode holder in its operative position, together with a fragment of a vessel or pipe;

Figure 6 is a cross-section viewed along the line III-III of Figure 5 showing the safety lid in a raised position;

Figure 7 is a longitudinal partial cross-section of an alternative electrode suitable for use with the invention, and

Figure 8 is a longitudinal partial cross-section of an alternative electrode cartridge having 0-rings between it and the end-cap.

Hode(s) For Carrying Out The Invention

As shown in Figures 1 to 6, a sensor or electrode holder 1 according to the invention has three principal components, these being an electrode cartridge 2 which houses an electrode 13, a sleeve 3 which houses the electrode cartridge 2 and in which the electrode cartridge 2 is retractable between a first operative and a second inoperative position, and a safety lid 4 for mounting on the electrode cartridge 2.

The electrode cartridge 2 is mounted within the sleeve 3 and is retractable into and extensible from the sleeve 3. The electrode cartridge 2 (see Fig. 1) is of hollow tubular shape having a lower head portion 30 at the end of a central tube portion 53. At its other end, the central tube portion 53 is provided with a riser thread 27 on its external surface. The riser thread 27 terminates below a ring 54 which projects outwards from the external surface of the tubular electrode cartridge 2.

The head portion 30 is annular having a hole 55 at its lower end and is provided internally with screw threads 5 to which an end cap 6 is screwed. The head portion 30 is also provided with opposing window openings 29, referred to hereinafter as windows, in the tube side - 5 - wall through which fluid can flow through the head portion 30. Two 0-rings 33, 32 are mounted on the head portion 30 above and below the windows 29 respectively.

The end cap 6 has a head portion 47 and a neck portion 48, the neck portion 48 being threaded and being screwed to the complementary threads 5 on the interior of the head portion 30 of the electrode cartridge 2 (see Fig. 3).

At its top end, the diameter of the tubular cartridge 2 is greater than at its lower end to define a cartridge head 62 having a lip 19 at its lower end. The internal surface of the cartridge head 62 is threaded to engage complementary threads 34 on the electrode 13. The safety lid 4 can be fitted over the head 62 to form a friction fit. The lip 19 together with the ring 54 defines a groove 18 which serves to prevent removal of the safety lid 4 from the electrode cartridge 2 as is more fully described below. At its upper rim 15, the head 62 has a plurality of spaced apart upwardly projecting teeth 14.

The electrode cartridge 2 houses an electrode 13 which is shown in detail in Figure 2. The electrode 13 has a tubular portion 36, having a cap 57. The tubular portion 36 is covered by a tubular sheath 37 which is shown in cross-section. The cap 57 is provided with screw threads 34 adjacent its lower rim adjacent the tubular portion 36 and a cylindrical contact socket 58 which projects from its upper surface. The contact socket 58 is provided externally with screw threads 59 to which a cable plug may be screwed. At its lower end, the tubular portion 36 converges to form a pointed electrode tip 60. An electrode wire 31 extends to the electrode tip 60 from the socket 58.

The tubular portion 36 of the electrode 13 is protected by the tubular sheath 37 having an 0-ring 38 at its lower end, adjacent the electrode tip 60. The 0-ring 38 ensures a fluid tight seal betwee- the electrode 13 and a ledge on the internal wall of the electrode cartridge 2. The tubular sheath 37, in addition to protecting the electrode 13, improves the fit of the electrode cartridge 2 and electrode 13. The electrode 13 is housed in the electrode cartridge 2 by inserting the electrode 13 through the head 62 and engaging the external screw threads 34 on the cap 57 of the electrode 13 with the complementary internal screw threads of the cartridge head 62. In this position, the electrode tip 60 is visible through the windows 29 of the head portion 30. The mounting of the electrode 13 within the electrode cartridge 2 is more clearly illustrated having regard to Figure 3 which is an exploded view of the electrode holder of the invention.

Figures 3 to 6 also show the sleeve 3 of the electrode holder in which the electrode cartridge 2 housing the electrode 13 is mounted.

The sleeve 3 is made up of an open ended central tubular portion 61 with a lower tubular wall portion 25, an upper tubular thin-wall portion 46 at its upper end and having an internally threaded mounting collar 20 mounted on the external surface of the sleeve. The mounting collar 20 has screw threads 21 on its interior surface for use in mounting the electrode holder 1 on a mounting bush on a pipeline, tank or other vessel.

The external surface of the sleeve 3 is further provided with 0-rings 22,23 which prevent leakage of fluid from the analyte vessel when the electrode holder 1 is fitted to the vessel. The 0-ring 23 is located between the mounting collar 20 and the lower end of the sleeve 3. The 0-ring 23 forms a tight fit between the wall of the analyte vessel and the electrode holder 1. Leakage of analyte into the electrode holder 1 is therefore prevented.

The 0-ring 22 is positioned above and adjacent the mounting collar 20 so that when the mounting collar 20 is fully engaged by a mounting bush on the analyte vessel, the mounting collar 20 abuts the 0-ring 22 to form a fluid-tight seal. A third 0-ring 24 is positioned immediately beneath the mounting collar 20 on the external surface of the tubular portion 61 to further increase the fluid-tight nature of the device.

The electrode cartridge 2 is held within the sleeve 3 in two ways. Firstly, the electrode cartridge 2 forms a fluid tight fit with the wall portion 25 of the sleeve by virtue of 0-rings 32,33. Secondly, the wall portion 25 is provided internally with screw threads 26 which engage complementary external riser screw threads 27 on the electrode cartridge 2. Therefore, the electrode cartridge 2 cannot be removed from or inserted in the sleeve 3 without a firm pushing or pulling motion and a rotating motion. Accordingly, the risk of accidental removal of the cartridge 2 from the sleeve 3 is somewhat reduced and the screw threads 26,27 therefore form a first safety feature against accidental removal of the electrode 13 from the electrode holder.

The screw threads 26,27 also facilitate the movement of the electrode cartridge 2 between the first operative position and the second inoperative position within the sleeve 3. As shown in Figures 5 and 6, the cartridge 2 projects from the sleeve 3 when in the fully lowered position. The electrode cartridge 2 is lowered into the fully lowered position by turning the electrode cartridge 2 together with the safety lid 4 in a clockwise manner on the threads 26, 27 so that the electrode cartridge 2 emerges from the sleeve 3. The electrode tip 31 is exposed so that fluid passing through the windows 29 may be analysed. In the inoperative or retracted position, the head portion 30 is withdrawn into the sleeve 3 and the cap 6 prevents analyte from entering the electrode holder 1.

In the retracted position (see Figure 4), the 0-ring 32 adjacent the cap 6 also forms a fluid-tight seal between the electrode cartridge 2 and the sleeve 3. The second 0-ring 33 on the head portion 30 maintains the fluid tight nature of the electrode holder 1 when the electrode cartridge 2 is in the extended operative position. In the retracted position the 0-ring 33 also functions as a second fluid-tight seal, in addition to 0-ring 32.

Removal of the electrode 13 from the electrode cartridge 2 requires unscrewing of the electrode which forms a second safety feature against accidental removal of the electrode 13. The electrode 13 may also be removed from the electrode holder by removing the electrode cartridge 2 from the sleeve 3. This is achieved by rotating the electrode cartridge 2 in an anti-clockwise direction on the threads 26, 27. However, complete removal of the cartridge may only be effected when the cap 6 has been removed i.e. when the electrode is not in use. The cap 6 prevents accidental removal of the cartridge 2 in use as its diameter is greater than the lower opening of the sleeve 3.

The third principal component of the invention is the safety lid 4 which is made up of an annular top 8, with an opening 9 from which fingers 10, separated by slots 11, project downwards. The contact socket 58 of the electrode 13 projects through the opening 9. The fingers 10 have shoulders in the form of stops 16 midway along the length of their interior surface.

The fingers 10 are provided with flanges 17 on the internal surface of their lower extremities. The flanges 17 project into the groove 18 provided on the electrode cartridge 2 when the safety lid 4 is securely fitted to the electrode cartridge 2 which is explained more fully below.

The safety lid 4 exhibits a sliding friction fit with the electrode cartridge 2 and is fitted to and removed from the electrode cartridge 2 as follows. A pushing motion is required to force the fingers 10 to flex outwardly over the cartridge head 62. However, where the fingers 10 and teeth 14 are aligned the stops 16 prevent the safety lid 4 from abutting the ring 54. The safety lid 4 is then simply rotated to align the teeth 14 with the slots 11 whereupon the safety lid 4 falls into place and the fingers 10 abut the ring 54.

The construction of the safety lid 4 and electrode cartridge 2 described above ensures that when the safety lid 4 is fitted to the electrode cartridge 2 the fingers 10 are trapped in a recess 45 defined between the tubular wall portion 46 and the cartridge head 62 in the operative position so that it may not be removed. In particular, the flanges 17 ensure that even an appreciable pulling motion will not be sufficient to remove the safety lid 4 as the flanges 17 must overcome the resistance of the lip 19 of the cartridge head 62, and the fingers 10 are prevented from flexing outwardly by the tubular wall portion 46 of the sleeve 3. Accordingly, it is not possible to remove the electrode 13 from the cartridge 2 without first removing the safety lid 4, when the electrode cartridge 2 has been screwed down into its operative position (see Figures 5 and 6).

Therefore, the safety lid 4 forms a third safety feature against accidental removal of the electrode 13 when the electrode holder 1 is in use in an in-line process.

The operation of and use of the electrode holder will now be described in further detail.

Prior to use, the electrode holder 1 is as illustrated in Figure 4 with the head 30 of the cartridge holder 2 in the retracted position within the sleeve 3. The electrode 13 is located within the electrode cartridge 2 with the safety lid 4 fitted over the electrode 13. The cap 6 should be screwed into position on the head 30.

To apply the electrode holder 1 to a pipeline or other analyte-containing vessel 63, the electrode holder 1 is positioned over an aperture 64 in the vessel 63 so that the sleeve 3 projects into the vessel. The electrode holder 1 is secured to the vessel by engaging a mounting bush 65 on the vessel with the mounting collar 20 of the electrode holder 1.

Extension of the head portion 30 is achieved by gripping the safety lid 4 and thus rotating the electrode cartridge 2 relative to the sleeve on the screw threads 26,27 as previously described. The pointed or domed electrode tip 60 is therefore exposed in the windows 29 so that analysis may take place. As the cartridge 2 is screwed down, safety lid 4 rides into recess 45 in sleeve 3, as shown in dashed outline in Figure 5. The recess 45 is seen in Figure 6 where the lid 4 has been removed for clarity.

The 0-rings 23, 24, 32, 33 and 38 ensure fluid-tight seals and prevent analyte from entering the electrode holder 1 and escaping from the vessel or the pipeline through the electrode holder 1. - π -

Fluid-tight seals are particularly important where the analyte may be under high pressure or at a high temperature. In addition, leakage of a stream of analyte at a fitting or connection may lead to contamination of the analyte from outside the pipeline.

Removal of the electrode 13 from the electrode holder 1 may easily be effected while the electrode holder 1 is mounted on a pipeline without interrupting the flow of the process under analysis.

The electrode cartridge 2 is first retracted, by rotating it in an anti-clockwise direction, until the cap 6 abuts the head portion 30. Fluid is therefore prevented from entering the electrode holder 1 while the 0-rings 23, 24, 32, 33 and 38 further ensure the fluid-tight nature of the electrode holder 1.

The safety lid 4 is then removed using a pulling motion so that the flanges 17 overcome the resistance of the lip 19 and the fingers 10 flex outwardly and move over the cartridge head 62. The electrode 13 is then removed from the electrode cartridge 2 using an unscrewing motion. The sheath 37 and 0-ring 38 may then be removed from electrode 13 to effect any maintenance operation necessary, e.g. calibration or repair, to the electrode 13.

The electrode 13 or a replacement electrode may then be refitted with the sheath 37 and 0-ring 38 and replaced in the electrode cartridge 2 using a screwing motion. The electrode cartridge 2 may then be re-extended to expose the head portion 30 and recommence analysis, process flow not having been interrupted.

Figure 7 shows an alternative electrode 13 suitable for use with the invention. The electrode comprises an upper connection portion 12 having screw threads 34 thereon. The tubular portion 36, constructed of a plastics or glass material 36 extends from the connecting portion 12 to form the tip 60 at its end. Analytical measurements are taken at the bulbous tip 60.

The tubular portion contains a polymer matrix 39 which encloses an electrolyte 40. An electrode proper, e.g. a silver wire electrode 41 extends from a terminal within the connection portion 12. A reference electrode 42 is located within the polymer matrix 39 and voltage differences between the electrode 41 and reference electrode 42 are transmitted via a wire 43 to a signal transforming and reading device. As previously described the signal is transformed to units such as pH units. An electrode of this general type is described in European Patent Specification No. 0,247,535A.

The information recorded by the electrode 13 may be displayed on a display unit or may be transmitted to a computer for use in automated or automatic process control. Typically, the electrode signals are transmitted to an electronic unit where voltage differences are amplified and voltage and current outputs may be provided for remote reading and process control. The results may also be sent to a computer or simply used for local alarm and process control.

Figure 8 shows a longitudinal partial cross-section of an alternative form of the electrode cartridge 2 having two 0-rings 49, 50 between it and the end-cap 6. The first 0-ring 49 is mounted on the end-cap 6 in a rebate 51 formed at the upper rim of the neck portion 48 of the end-cap 6. The second 0-ring 50 is also mounted on the end-cap 6 at the base of the neck portion 48 adjacent the head portion 47 of the end-cap 6. The interior of the electrode cartridge 2 is provided with threads as before which are complementary to threads on the neck portion 48 of the end-cap. However, in this embodiment the lower end of the electrode cartridge 2 is indented on its inner surface so that a gripping shoulder 52 is defined. The 0-ring 48 is therefore sandwiched between the gripping shoulder 52 and the rebate 51 of the neck portion 48 when the end-cap 6 is screwed into position in the electrode cartridge 2. In this position the 0-ring 50 is also sandwiched between the head portion 47 of the end-cap 6 and the ends of the electrode cartridge 2. Therefore, the fluid-tight nature of the electrode holder is further increased to prevent any liquid media from gaining access to the interior of the electrode cartridge 2.

Claims

1. A sensor holder (1) comprising mounting means (3) adapted for fluid tight mounting in an aperture defined by a vessel or pipe containing the medium to be analysed by the sensor (13), and sensor holding means (2) characterized in that the sensor holding means (2) is adapted for a fluid tight movement relative to the mounting means between a first operative position in which the sensor (13) located by the sensor holding means (2) is exposed to the said medium to be analysed, and a second inoperative position in which the sensor holding means (2) is retracted into the mounting means (3) allowing the removal of the sensor (13) therefrom, the sensor holder (1) being fluid tight in the second inoperative position following removal of the sensor (13).

2. A sensor holder according to Claim 1, characterized in that the mounting means comprises a tubular sleeve (3) adapted for connection to said vessel or pipe, and the sensor (13) is held within a tubular cartridge (2) which is moveable axially within the tubular sleeve (3) from a first operative position in which the cartridge (2) protrudes outwardly from an end of the.sleeve (3) to expose the sensor (13) to a second inoperative position in which the cartridge (2) is withdrawn within the sleeve (3), sealing means (6, 47, 32, 49, 50) being provided at the outward end of the cartridge (2) to form a fluid tight seal between the cartridge (2) and the sleeve (3) when the cartridge (2) is withdrawn inside the sleeve (3).

3. A sensor holder according to Claim 2, characterized in that the sleeve (3) comprises a threaded mounting collar (20) for threaded engagement with a threaded mounting bush on said vessel or pipe.

4. A sensor holder according to Claim 4 characterized in that the electrode cartridge (2) comprises a lower annular head portion (30), a central tube portion (53) and an upper cartridge head (62), defined by a lip (19) and a toothed rim (15) and a radial ring (54) projecting from the tube portion (53) below the cartridge head (62), the upper cartridge head (62) having threads (35) on its internal face to engage complementary threads (34) on the sensor (13) and the head portion (30) having windows (29) through which the medium to be analysed can flow to contact the sensor (13) in the operative position.

5. A sensor holder as claimed in Claim 4 characterized in that the central tube portion (53) comprises a riser thread (27) on its external surface engageable with a complementary thread (26) on the internal surface of the sleeve (3) so that the electrode cartridge (2) is moveable in fluid tight manner relative to the sleeve (3) between the first operative position and the second inoperative position, disengagement of the threads (26, 27) being prevented when the sensor holder is inserted in said vessel or pipe by an abutment member mounted on the electrode cartridge (2).

6. A sensor holder as claimed in Claim 5 characterized in that the abutment member comprises a removable end cap (6) threadingly engageable in the hole (55) of the annular head portion (30).

7. A sensor holder as claimed in any of the preceding claims characterized in that means are provided to prevent removal of the sensor (13) from the electrode cartridge (2) in the first operative position.

8. A sensor holder as claimed in Claim 7 characterized in that the means to prevent removal of the sensor (13) from the electrode cartridge (2) comprises a safety lid (4) for fitting over the sensor (13) having snap fastening means engageable with the cartridge head (62) in the second inoperative position, disengagement of the snap fastening means being prevented by the sleeve (3) in the first operative position so that the sensor (13) may not be removed until the electrode cartridge (2) is in the second inoperative position.

9. A sensor holder as claimed in Claim 8 characterized in that the safety lid (4) forms a sliding friction fit with the cartridge head (62) and has an annular top (8) to expose a sensor contact socket (58), the snap fastening means comprising fingers (10) separated by slots (11) projecting substantially vertically downwards from the annular top (8) and having flanges (17) on the internal face of their lower extremities, the flanges (17) being insertable into a groove (18) defined between the lip (19) and a ring (54), so that the flanges (17) slide over the cartridge head (62) and snap into the groove (18).

10. A sensor holder according to any of the preceding claims characterized in that 0-rings (22, 32, 38, 49, 50) are provided between the electrode cartridge (2) and the sleeve (3); between the sensor element (13) and the electrode cartridge (2); on the sleeve (3) for contact with the mounting bush; and between the end cap (6) and the cartridge (2).