SENSOR ASSEMBLY

Abstract

A sensor assembly for use in an apparatus comprising at least one moving part and at least one stationary part is provided. The assembly comprises a probe and means for mounting the sensor to a stationary part of the apparatus. The probe comprises a portion of an incomplete circuit which, when completed, produces a signal. In use, when the probe is engaged by a moving part of the apparatus, a signal is produced. A vacuum pump or a compressor pump comprising the sensor and a method for preventing failure of an apparatus are also provided.

Claims

1. A sensor assembly for use in an apparatus comprising at least one moving part and at least one stationary part, the sensor assembly comprising: a probe comprising a portion of an incomplete circuit and configured to form a complete circuit when engaged by the at least one moving part; and a casing configured to sheathe a first portion of the probe such that, in use, a second portion of the probe protrudes from the casing, and wherein the casing comprises a means for mounting the sensor to the stationary part of the apparatus, wherein the assembly is configured to produce a signal when the circuit is completed; and wherein the probe comprises at least two electrodes, wherein one electrode is a positive electrode and one electrode is a negative electrode, wherein the at least two electrodes are separated by an electrically insulating body, and wherein a portion of each electrode is exposed from the electrically insulating body; and wherein at least a part of the exposed portion of each of the electrodes is covered by a sacrificial coating comprising an electrically insulating paint or lacquer such that, in use, when the sacrificial coating is contacted by the moving part of the apparatus, at least part of the coating is removed from each electrode and the circuit is completed.

2. The sensor assembly of claim 1, wherein the assembly is configured to activate a shut-down process of the apparatus when the signal is produced.

3. The sensor assembly of claim 2, wherein the shut-down process is one of a pulsed shut-down or a ramped shutdown process.

4. (canceled)

5. The sensor assembly of claim 41, wherein the assembly further comprises means for adjusting the position of the probe relative to the casing.

6. The sensor assembly of claim 5, wherein the means for adjusting the position of the probe relative to the casing comprises a cam mechanism or a lever mechanism acting on the probe, or an external screw thread which is adapted to operatively engage with the means for adjusting the position of the probe relative to the casing.

7. (canceled)

8. The sensor assembly of claim 71, wherein the portion of each electrode that is exposed from the insulating body is comprised in a portion of the probe protruding from the casing.

9. (canceled)

10. (canceled)

11. The sensor assembly of claim 1 wherein the apparatus is a vacuum pump, and wherein the at least one moving part comprises a rotor and the at least one stationary part comprises a stator.

12. A vacuum pump comprising: a sensor assembly as defined in claim 1; and at least one rotor and at least one stator, wherein the stator comprises at least one internal chamber in which the at least one rotor is rotationally mounted and the sensor is mounted to the stator through a conduit located in the stator such that a portion of the probe protrudes into the internal chamber.

13. A method for preventing failure of an apparatus comprising at least one moving part and at least one stationary part, the method comprising: mounting a sensor assembly as defined in claim 1 to a stationary part of the apparatus; and shutting down operation of the apparatus when the sensor produces the signal.

14. The method of claim 13, wherein shutting down of the apparatus is performed automatically upon production of the signal.

15. The method according to claim 13 wherein the sensor is fitted during manufacture of the apparatus.

16. The method according to claim 13 wherein the sensor is fitted to an existing apparatus.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0051] Preferred features of the present disclosure will now be described, with reference to the accompanying drawings, in which:

[0052] FIG. 1 is a sectional view of a vacuum pump incorporating a sensor assembly according to an embodiment of the present invention;

[0053] FIG. 2 is a detailed view of part of a sensor assembly according to an embodiment of the invention;

[0054] FIG. 3 is a detailed view of an example probe, according to an embodiment of the invention;

[0055] FIG. 4 is a detailed view of an alternative example probe according to a further embodiment of the invention; and

[0056] FIG. 5 is a flow diagram illustrating an example method according to an embodiment of the invention.

DETAILED DESCRIPTION

[0057] FIG. 1 shows a schematic representation of a vacuum pump 10 incorporating a sensor assembly 12 in accordance with an embodiment of the invention. The pump 10 in the illustrated embodiment is a Roots type vacuum pump also referred to as a Roots booster. It will be appreciated that the present invention could be applied to any other type of vacuum pump having parts that move relative to each other. More broadly, the present invention could be applied to other types of pumps or moving apparatus such as compressors.

[0058] The pump 10 comprises at least one moving part and one stationary part. In the illustrated example, the pump comprises two moving parts in the form of rotors 14 (sometimes referred to as impellers) that are mounted to rotate within a stationary stator 16 of the pump 10 that surrounds the two rotors 14. Each rotor 14 comprises a plurality of intermeshing lobes 18 which, in use, come in close proximity to an arcuate internal surface 20 of the stator 16 for at least part of their rotational cycle. The lobes 18 are designed to form an effective seal with the arcuate surface 20 of the stator 16, to drive air that is trapped between adjacent lobes 18 from the inlet port 22 to the outlet port 24 of the pump 10.

[0059] In use, the rotors 14 rotate in opposite direction to one another and do not touch each other or the stator internal surface 20. As such, there is a gap or clearance 26 between the rotors 14 and the stator 16. In many applications, the clearance 26 is desirably between 0.1 and 0.5 mm when the pump 10 is cold. The size of the clearance 26 between the rotor 14 and the stator 16 is important to the function of the pump 10 and must remain above a predetermined size to ensure safe and effective operation of the pump 10. As described above, operational effects may result in a reduction of the clearance 26 below this predetermined size.

[0060] The pump 10 further includes a sensor assembly 12 mounted to the stator 16. The sensor assembly 12 is configured such that, when the clearance 26 between the rotor 14 and the stator 16 is reduced below the predetermined size, the sensor assembly 12 generates a signal. The sensor assembly 12 comprises a sensor circuit 28 configured to generate the signal and a processor 30 configured to receive the signal and generate an output. In embodiments, the processor 30 is configured to generate an output that triggers a shut-down process to cease operation of the pump 10. In embodiments, the shut-down process includes communication with a controller (not shown) for controlling the operation of the pump 10 for performing a controlled shutdown process such a pulsed shut-down process as described in WO 2004/038222 or a ramped shut-down process as known in the art. Alternatively, the output may trigger a cut-off switch for immediate shut-down of the pump 10.

[0061] The sensor assembly comprises a probe 32, which is seated in a bore 34 which extends radially through the side wall of the stator 16 from an external surface 36 to the arcuate internal surface 20 thereof. A portion 38 of the probe 32 extends beyond the arcuate internal surface 20 into an internal cavity 40 of the pump 10 such that an end surface 42 of the probe 32 contacts or engages the rotor 14 when the clearance 26 is below a predetermined value. In embodiments, the predetermined value represents a clearance size at which operation of the pump 10 may be compromised, for example, beyond which the risk of seizure is unacceptable.

[0062] During normal use, when an acceptable size of clearance 26 exists between the rotor 14 and stator 16 exists, the probe 32 and the sensor circuit 28 together form a portion of an incomplete circuit such that no signal is produced by the circuit. However, when the clearance 26 reduces to the predetermined value, i.e. the clearance is too small, the probe 32 is engaged by the rotor 14. Engagement of the probe 32 with the rotor 14 causes the circuit formed by the probe 32 and sensor circuit 28 to be completed and a signal to be produced by the sensor assembly 12.

[0063] FIG. 2 shows an enlarged version of a portion of the sensor assembly 12, according to an embodiment. In the illustrated example, the sensor assembly 12 comprises a probe 32 as described above. The assembly 12 further comprises a casing 50, wherein the casing 50 substantially surrounds or sheathes at least a portion of the probe 32. At a first end 52 of the probe 32, a portion 54 of the probe 32 protrudes from the casing 50 and is configured to, in use, engage with a moving part of an apparatus such as the rotor 14 of a pump 10 described in relation to FIG. 1 above. At a second, opposing end 56 of the probe 32, the probe 32 is configured to connect to a sensor circuit as described above to form an incomplete electric circuit.

[0064] The casing 50 comprises means 58 for mounting the sensor assembly to an apparatus such as the pump stator 16 described above. In the illustrated embodiment, the means 58 comprises an external thread on the casing 50 configured to engage an internal thread of the apparatus such as the bore 34 of the pump 10 of FIG. 1. The casing 50 further comprises means 60 for adjusting the position of the probe 32 relative to the casing 50, in this example, the means for adjusting the position of the probe 32 relative to the casing 50 comprises a thumbwheel 60. The thumbwheel 60 is configured such that manual manipulation of the thumbwheel causes axial movement of the probe in one or two directions relative to the casing 50 to allow the portion 54 of the probe 32 protruding from the casing 50 to be adjusted as required, for example where the predetermined size/value of the clearance needs to be adjusted or tuned. In alternative embodiments, the casing 50 and/or probe 32 may comprise means (not shown) for adjusting both the casing 50 and probe 32 together relative to the apparatus to which it is mounted such that the predetermined value can be adjusted or tuned as required.

[0065] As shown in FIG. 2, the assembly further comprises an O-ring seal 60 which extends around the probe inside the casing 50 and forms a seal between the probe 32 and the casing 50 to reduce or prevent leakage of gas along the probe 32, for example towards the internal cavity 40 of the pump 10.

[0066] In the example shown in FIG. 2, the probe 32 is formed from a single electrode such that, in use, if engaged by an electrically conductive moving component of the apparatus to which the sensor assembly is mounted, an electric circuit to which the probe 32 is connected is completed through the sensor assembly and apparatus, and a signal is output by the circuit.

[0067] With reference to FIG. 3, an alternative probe 132 is shown. In this example, the probe 132 comprises two electrodes 162, 164 extending along the longitudinal length 166 of the probe 132. A first electrode 162 comprises a conductive wire extending generally centrally throughout the length of the probe 132. A second electrode 164 comprises a conductive tube surrounding and substantially concentric with the first electrode 162. The probe 132 further comprises an electrically insulating body 168, which is positioned between the first and second electrodes 162, 164 to electrically isolate the electrodes 162, 164 from each other along the length 166 of the probe 132. In one embodiment, the insulating body 168 comprises an adhesive such as an epoxy resin which can also be used to secure the two electrodes 162, 164 relative to each other.

[0068] At a first end 170 of the probe 132, the electrodes 162, 164 are exposed from the insulating body 168 to define an annular gap 174 between each electrode 162, 164 configured to form a physical break in a circuit of the sensor assembly 12 described above. At a second, opposing end 172 of the probe 132, the electrically conductive electrodes 162, 164 are configured to be coupled to an electric circuit as described above via connections 175 as known in the art. In use, if the gap 174 between the exposed ends of the electrodes 162, 164 is bridged by an electrically conductive component of the apparatus to which the sensor assembly is mounted, the circuit is complete, and a signal is output.

[0069] The probe 132 illustrated in FIG. 3 may be incorporated into a casing as described with respect to FIG. 2 above. In such an embodiment, the casing is preferably formed from an electrically insulating material in order to prevent conductance through the surrounding structure of the assembly and pump.

[0070] The probe 132 further comprises a sacrificial layer 176 at the first end 170. The sacrificial layer 176 extends over the portions of the electrodes which are exposed from the insulating body 168 of the probe 132. The sacrificial layer 176 is configured to be at least partially removed when engaged by a moving component. For example, when used in the arrangement of FIG. 1, the sacrificial layer 176 may be sheared off the end 170 of the probe 132 when engaged by the rotating rotor 14 of the pump 10 to which probe 132, forming part of the sensor assembly 12, is mounted. Removal of the sacrificial layer 176 exposes the ends of the electrodes 162, 164 allowing the rotor 14 to bridge the gap 174 between the electrodes 162, 164 and thereby complete the circuit.

[0071] FIG. 4 illustrates another alternative probe 232 for use in the assembly of the invention. The probe comprises two electrodes 262, 264 each comprising a conductive wire extending along the length 266 of the probe 232. The two electrodes 262, 264 are generally parallel to each other and are parallel but offset from a central axis of the probe 232.

[0072] The probe 232 further comprises an electrically insulating body 268, which surrounds the first and second electrodes 262, 264 to electrically isolate the electrodes 162, 164 from each other along the length 266 of the probe 232 in a similar way to the the insulating body of the embodiment of FIG. 3. The insulating body 268 may be formed from the same materials described above in relation to the insulating body 168 of FIG. 3.

[0073] Referring back to FIG. 4, at a first end 270 of the probe 232, the electrodes 262, 264 are exposed from the insulating body 168 to define a gap 274 between the two electrodes 262, 264 configured to form a physical break in a circuit of the sensor assembly 12 described above. At a second, opposing end 272 of the probe 232, the electrically conductive electrodes 262, 264 are configured to be coupled to an electric circuit as described above via connections 275 as known in the art. In use, if the gap 274 between the exposed ends of the electrodes 262, 264 is bridged by an electrically conductive component of the apparatus to which the sensor assembly is mounted, the circuit is complete, and a signal is output.

[0074] The probe 232 of FIG. 4 further comprises a sacrificial layer 276 at the first end 270. The sacrificial layer 276 extends over the portions of the electrodes which are exposed from the insulating body 268 of the probe 132 in much the same way as described in relation to the probe 132 of FIG. 3. As such, the sacrificial layer 276 is configured to be at least partially removed when engaged by a moving component. For example, when used in the arrangement of FIG. 1, the sacrificial layer 276 may be sheared off the end 270 of the probe 232 when engaged by the rotating rotor 14 of the pump 10 to which probe 232, forming part of the sensor assembly 12, is mounted. Removal of the sacrificial layer 276 exposes the ends of the electrodes 262, 264 allowing the rotor 14 to bridge the gap 274 between the electrodes 262, 264 and thereby complete the circuit.

[0075] The probe 232 illustrated in FIG. 4 may also be incorporated into a casing. However, the casing may not need to be formed from an electrically insulating material as both the electrodes 262, 264 are contained within the electrically insulating body 168. As such, the casing material may be selected from a wider range of materials.

[0076] FIG. 5 is a flow diagram showing an example method for preventing failure of an apparatus comprising at least one moving part and at least one stationary part according to a further embodiment of the invention. The method includes first mounting a sensor assembly to the stationary part of the apparatus at step 301. The sensor assembly used in the exemplary method may have the features of any of the embodiments described above such that it is operable to produce a signal when the sensor detects a minimum clearance exists. The sensor may be mounted such that the sensor may detect when a minimum clearance exists between the moving part and the stationary part. The mounting step may be performed during original manufacture of the apparatus or may be ‘retro-fit’ on an existing pump after original manufacture.

[0077] The method further comprises a step 302 of shutting down operation of the apparatus when the sensor produces a signal. The signal, as described above, is indicative of a minimum clearance between the stationary part and moving part. The shutting down operation may be performed automatically upon generation of the signal by an associated control system or the signal may alert an operator of the apparatus to manually perform the shut-down.

[0078] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0079] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.