Method And Apparatus For Monitoring Abrasion

Abstract

Scroll pump comprising a first scroll having a first scroll wall 11 extending from a first scroll base; and a second scroll having a second scroll wall 7 extending from a second scroll base towards th

Description

TECHNICAL FIELD The present disclosure relates to a method and apparatus for monitoring abrasion. The method and apparatus are suitable for monitoring abrasion of a seal in a pump. The method and apparatus have particular application in monitoring abrasion of a seal in a scroll pump. Aspects of the invention relate to a scroll pump, a method of monitoring a seal in a scroll pump; and a seal for a scroll pump. BACKGROUND Scroll pumps comprise a fixed scroll and an orbiting scroll which, in use, follows an orbiting path. The fixed scroll and the orbiting scroll have respective scroll walls. A seal is provided for sealing against the opposing scroll plate (or base) to provide a seal to minimise internal leakage of the pumped gas, thereby improving performance. The seal is typically in the form of a tip seal situated on the distal end of the scroll wall, protruding above the scroll wall so that it can engage the opposing face of the meshed scroll. Contact between the seal and scroll counter-face maintains pumping performance by reducing or preventing leakage over the scroll wall. As the pump operates the seal slowly wears and eventually requires replacement to ensure performance is maintained. Replacement intervals for the tip seal is typically based on a run time of the scroll pump. The replacement interval is defined to ensure that the performance of the scroll pump is maintained. In certain pumping applications, the rate of abrasion of the tip seal may be relatively low meaning that a longer service interval could have been implemented without adversely affecting performance. In other pumping applications, the tip seal may experience a higher rate of abrasion and a short service interval may have been appropriate to maintain performance. Understanding the seal wear, and hence if a replacement is required, requires physically dismantling the pump and inspecting the seal. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a scroll pump, a method of monitoring a seal in a scroll pump; and a seal as claimed in the appended claims. According to an aspect of the present invention there is provided a scroll pump comprising: a first scroll having a first scroll wall extending from a first scroll base; a second scroll having a second scroll wall extending from a second scroll base towards the first scroll base; a seal disposed on the second scroll for cooperating with the first scroll to form a seal; at least one target associated with the seal, the at least one target being movable towards the first scroll base along a longitudinal axis as the seal is abraded; and at least one sensor for detecting the at least one target, the at least one sensor being configured to output a sensor signal providing an indication of a separation distance between the at least one target and the at least one sensor. In use, the seal may be abraded. In particular a front face of the seal may be abraded due to surface friction. For example, the seal may be abraded due to surface friction with the first scroll base. The abrasion at the front face may reduce the width (or thickness) of the seal. The seal may be moveable relative to the second scroll to help maintain the seal. The seal may be moveable towards the first scroll wall along the longitudinal axis to maintain the seal. The at least one target is moveable with the seal. The at least one target is displaced along the longitudinal axis as the width of the seal decreases. The displacement of the at least one target reduces the separation distance between the at least one target and the at least one sensor. The separation distance can be used to monitor the abrasion and determine when abrasion of the seal is greater than a threshold value. The threshold value may be predefined to indicate that the seal should be replaced. The seal can be replaced (or a replacement scheduled) in dependence on a determination that the separation distance is less than or equal to a separation distance threshold. The seal may be a tip seal. The tip seal may be disposed on the second scroll wall. The tip seal may cooperate with the first scroll base to form the seal. Alternatively, the seal may be a channel seal. The channel seal may be disposed on the second scroll base. The channel seal may cooperate with the first scroll wall to form the seal. The first scroll may be one of a fixed scroll and an orbiting scroll; and the second scroll may be the other of the fixed scroll and the orbiting scroll. The first scroll may be a fixed scroll; and the second scroll may be an orbiting scroll. The first scroll wall may be in the form of a fixed scroll wall; and the first scroll base may be a fixed scroll base. The second scroll wall may be in the form of an orbiting scroll wall; and the second scroll base may be an orbiting scroll base. The seal may be disposed on the orbiting scroll. At least in certain embodiments, the at least one target may be disposed on the orbiting scroll and the at least one sensor may be disposed on the fixed scroll. Alternatively, the first scroll may be an orbiting scroll; and the second scroll may be a fixed scroll. The first scroll wall may be in the form of an orbiting scroll wall; and the first scroll base may be an orbiting scroll base. The second scroll wall may be in the form of a fixed scroll wall; and the second scroll base may be a fixed scroll base. The seal may be disposed on the fixed scroll. At least in certain embodiments, the at least one target may be disposed on the fixed scroll and the at least one sensor may be disposed on the orbiting scroll. A second seal may be disposed on the first scroll for cooperating with the second scroll to form a second seal. At least one second target may be associated with the second seal, the at least one second target may be movable towards the second scroll along a longitudinal axis as the second seal is abraded. At least one second sensor may be provided for detecting the at least one second target. The at least one second sensor may be configured to output a second sensor signal providing an indication of a separation distance between the at least one second target and the at least one second sensor. The at least one second sensor may be provided on the second scroll. The second seal may be a second tip seal. The second tip seal may be disposed on the first scroll wall. The second tip seal may cooperate with the second scroll base to form the second seal. Alternatively, the second seal may be a second channel seal. The second channel seal may be disposed on the first scroll base. The second channel seal may cooperate with the second scroll wall to form the second seal. A first seal may be disposed on the fixed scroll wall and a second seal may be disposed on the orbiting scroll wall. At least one first target may be associated with the first seal and at least one second target may be associated with the second seal. At least one first sensor may be provided for detecting the at least one first target. The at least one first sensor may be disposed on the orbiting scroll. The at least one first sensor may be configured to output a first sensor signal providing an indication of a separation distance between the at least one first target and the at least one first sensor. At least one second sensor may be provided for detecting the at least one second target. The at least one second sensor may be disposed on the fixed scroll. The at least one second sensor may be configured to output a second sensor signal providing an indication of a separation distance between the at least one second target and the at least one second sensor. The scroll pump may comprise a control unit configured to monitor the seal. The control unit may comprise at least one processor. The at least one processor may be configured to: receive a sensor signal from the at least one sensor, the sensor signal providing an indication of the separation distance between the at least one target and the at least one sensor. The at least one processor may be configured to process the sensor signal to determine that the separation distance between the at least one target and the at least one sensor is less than a separation distance threshold. The at least one processor may output a notification signal in dependence on a determination that the separation distance is less than or equal to a separation distance threshold. The separation distance represents a distance between the at least one target and the at least one sensor. In use, the separation distance between the at least one target and the at least one sensor varies as the orbiting scroll follows an orbiting path. The processing of the sensor signal may determine that the separation distance is less than the separation distance threshold for at least a portion of the orbiting path followed by the orbiting scroll. The separation distance may be less than the separation distance threshold while the at least one target is closest to the at least one sensor, for example when they are aligned with each other the longitudinal axis. The sensor signal may be processed to determine that a smallest separation distance between the at least one target and the at least one sensor is less than the separation distance threshold. The sensor signal may be inversely proportional to the separation distance. The magnitude of the sensor signal may increase as the separation distance decreases. The processing of the sensor signal may comprise determining a peak magnitude of the sensor signal. The determination that the separation distance is less than the separation distance threshold may comprise determining that the peak magnitude is greater than or equal to a peak magnitude threshold. The separation distance may be determined in dependence on the sensor signal. The at least one processor may determine a discrete value for the separation distance. The processing of the sensor signal may comprises determining the separation distance in dependence on the sensor signal; and comparing the determined separation distance to the separation distance threshold. The separation distance may be determined along the longitudinal axis. The at least one processor may be configured to determine a smallest (minimum) value of the separation distance. The smallest value may be determined in dependence on a peak magnitude of the sensor signal. The peak magnitude typically corresponds to the sensor signal output by the at least one sensor when the orbiting scroll is in a first orbital position in which the distance between the at least one target and the at least one sensor is smallest. The at least one sensor and the at least one target may be aligned with each other along the longitudinal axis when the orbiting scroll is in the first orbital position. Alternatively, the at least one sensor and the at least one target may comprise a radial offset and / or a circumferential offset when the orbiting scroll is in the first orbital position. The at least one processor may be configured to determine a distance between the at least one target and the at least one sensor along the longitudinal axis in dependence on a smallest (minimum) value of the separation distance. At least in certain embodiments, the at least one target and the at least one sensor may be aligned with each other along a longitudinal sensing axis during at least part of an operating cycle, for example when the orbiting scroll is in a first orbital position. In these embodiments, the separation distance between the at least one target and the at least one sensor along the longitudinal axis may be determined directly from the sensor signal. For example, the distance along the longitudinal axis may correspond to a smallest (minimum) value of the separation distance between the at least one target and the at least one sensor. In embodiments in which a radial offset and / or a circumferential offset is maintained between the at least one target and the at least one sensor throughout the operating cycle, the at least one processor may be configured to determine the distance along the longitudinal axis in dependence on the sensor signal and a predefined geometric relationship between the at least one target and the at least one sensor. For example, the distance along the longitudinal axis may be determined in dependence on a minimum value of the separation distance and geometric data defining the radial offset and / or the circumferential offset between the at least one target and the at least one sensor. Alternatively, the at least one processor may be configured to determine a separation distance along an oblique axis. A separation distance threshold may be defined to take account of the radial offset and / or the circumferential offset between the at least one target and the at least one sensor. The at least one processor may be configured to inhibit operation of the scroll pump in dependence on a determination that the separation distance is outside an operating range. The at least one processor may be configured to determine that the separation distance is within a predetermined operating range. Operation of the scroll pump may be inhibited if the separation distance is determined to be outside the operating range. The at least one processor may be configured to inhibit operation of the scroll pump if the smallest (minimum) separation distance is less than a lower operating threshold and / or that the smallest (minimum) separation distance is greater than an upper operating threshold. The lower operating threshold and / or the upper operating threshold may define the operating range for the scroll pump. The lower operating threshold may define a minimum separation distance for operation of the scroll pump. The processor may output a control signal to inhibit operation of the scroll pump in dependence on a determination that the smallest (minimum) separation distance is less than or equal to the lower operating threshold and / or that the smallest (minimum) separation distance is greater than the upper operating threshold. A warning or notification signal may be output to provide a user notification. Alternatively, or in addition, the at least one processor may be configured to inhibit operation of the scroll pump in dependence on a determination that the at least one target is absent. The at least one processor may be configured to control operation of the scroll pump in dependence on a determination that the at least one target is present or absent. The at least one processor may be configured to enable operation of the scroll pump in dependence on a determination that the at least one target is present (i.e., that the at least one target is detected). The at least one processor may be configured to inhibit operation of the scroll pump in dependence on a determination that the at least one target is absent (i.e., that the at least one target is not detected). The processor may process the sensor signal to determine the presence or absence of the at least one target. The processor may output a control signal to inhibit operation of the scroll pump in dependence on a determination that the at least one target is absent. A warning or notification signal may be output, for example to notify a user of the issue. The at least one processor may be configured to monitor a rate of change of the separation distance between the at least one target and the at least one sensor along the longitudinal axis. The at least one processor may estimate a time period for replacing the seal in dependence on the determined rate of change of the separation distance. The notification signal may comprise the estimated time period. The at least one processor may monitor and / or predict an abrasion rate of the seal. The at least one processor may predict when the seal will require replacement. This may facilitate advance scheduling of maintenance or servicing of the scroll pump to replace the seal. The at least one sensor may comprise a Hall effect sensor. The at least one target may comprise a ferrous target or a magnetic target. Other types of sensor may be used. The at least one sensor may comprise an inductive sensor. The inductive sensor may be configured to detect a target in the form of a ferrous or magnetic target. Alternatively, the at least one sensor may comprise a variable reluctance sensor. The variable reluctance sensor may be configured to detect a target in the form of a ferrous or magnetic target. The at least one target may be fastened to the seal. The seal typically comprises a front face and a rear face. The at least one target may be fastened to the rear face of the seal. Alternatively, the at least one target may be at least partially embedded in the seal. The at least one target may be partially or completed encapsulated in the seal. The seal may be overmoulded around the at least one target. The seal is disposed on the second scroll wall and, in use, cooperates with the first scroll base to form a seal. The at least one sensor may be disposed on the first scroll. The at least one target may be disposed on the second scroll. The at least one target and the at least one sensor may be aligned with each other along a longitudinal sensing axis when the orbiting scroll is in a first orbital position. The separation distance is smallest when in the orbiting scroll is in the first orbital position. According to a further aspect of the present invention there is provided a method of monitoring a seal in a scroll pump, wherein the scroll pump comprises: a first scroll having a first scroll wall extending from a first scroll base; a second scroll having a second scroll wall extending from a second scroll base towards the first scroll base; a seal disposed on the second scroll for cooperating with the first scroll base to form a seal; at least one target associated with the seal, the at least one target being movable towards the first scroll along a longitudinal axis as the seal is abraded; and at least one sensor for detecting the at least one target, the at least one sensor being configured to output a sensor signal providing an indication of a separation distance between the at least one target and the at least one sensor; wherein the method comprises: receiving a sensor signal from the at least one sensor, the sensor signal providing an indication of a separation distance between the at least one target and the at least one sensor; determining that the separation distance between the at least one target and the at least one sensor is less than a separation distance threshold; and generating a notification in dependence on a determination that the separation distance is less than or equal to a separation distance threshold. The method may comprise inhibiting operation of the scroll pump in dependence on one or more of the following: a determination that the separation distance is outside an operating range; and a determination that the at least one target is absent. According to a further unclaimed aspect there is provided a seal assembly for a scroll pump, the seal assembly comprising: a sealing member for mounting to a scroll wall; and at least one target for detection by a sensor; wherein the at least one target is coupled to the sealing member. The at least one target may be fastened to the sealing member. The sealing member may comprise a front face and a rear face. The at least one target may be fastened to the rear face of the sealing member. The at least one target may be at least partially embedded in the sealing member. The at least one target may be partially or completed encapsulated in the sealing member. The sealing member may be over-moulded around the at least one target. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of a scroll pump incorporating a sensor and a target for monitoring abrasion of a tip seal; Figure 2 shows a plan view of an orbiting scroll of the scroll pump shown in Figure 1; Figure 3 shows a tip seal provided on a distal end of the orbiting scroll wall of the orbiting scroll shown in Figure 2; Figure 4A shows a sectional view through the orbiting scroll illustrating the target in a first longitudinal position; Figure 4B shows a sectional view through the orbiting scroll illustrating the target in a second longitudinal position; Figure 5 shows the position of the sensor in the fixed scroll of the scroll pump; Figure 6 shows a variant of the tip seal in which the target is embedded into the tip seal; Figure 7A illustrates a first sensor signal from the sensor in a time domain; Figure 7B illustrates the first sensor signal in a frequency domain; Figure 8A illustrates a second sensor signal from the sensor in a time domain; Figure 8B illustrates the second sensor signal in a frequency domain; and Figure 9 is a block diagram illustrating operation of a controller for the scroll pump. DETAILED DESCRIPTION A scroll pump 1 in accordance with an embodiment of the present invention is described herein with reference to Figures 1 to 3. The scroll pump 1 in the present embodiment is a scroll vacuum pump. The scroll pump 1 may, for example, be used in industrial and high vacuum processes. The scroll pump 1 is described herein with reference to a longitudinal axis X. References herein to a component or feature extending longitudinally or in a longitudinal direction are to be understood as referring to a direction which is at least substantially coincident with or parallel to the longitudinal axis X. References herein to a component or feature extending radially or in a radial direction are to be understood as referring to a direction which is at least substantially perpendicular to the longitudinal axis X. As shown in Figure 1, the scroll pump 1 comprises an orbiting scroll 3 and a fixed scroll 5 disposed in a housing 6. The orbiting scroll 3 and the fixed scroll 5 are configured to cooperate with each other. The orbiting scroll 3 has an orbiting scroll wall 7 extending longitudinally from an orbiting scroll base 9 towards the fixed scroll 5. The orbiting scroll base 9 is generally in the form of a plate or a disc; and has a front face 9a and a rear face 9b. The orbiting scroll wall 7 extends from the front face 9a of the orbiting scroll base 9. The fixed scroll 5 is fixed to the extent that it does not rotate or follow an orbiting path (i.e., the fixed scroll 5 is a nonorbiting scroll). However, the fixed scroll 5 may be translatable in at least one direction, for example along the longitudinal axis X. The fixed scroll 5 has a fixed scroll wall 11 extending longitudinally from a fixed scroll base 13 towards the orbiting scroll base 9. The fixed scroll base 13 has a front face 13a and a back face 13b. The front face 13a of the fixed scroll base 13 opposes the front face 9a of the orbiting scroll base 9. The fixed scroll wall 11 extends from the front face 13a of the fixed scroll base 13. The orbiting scroll 3 and the fixed scroll 5 cooperate with each other to form a seal. In particular, the orbiting scroll wall 7 cooperates with the fixed scroll base 13; and the fixed scroll wall 11 cooperates with the orbiting scroll base 9. The orbiting scroll wall 7 comprises a tip seal 20 for sealing against the fixed scroll base 13 to form a seal. The tip seal 20 comprises a sealing member 21 having a front face 21a and a rear face 21b. In use, the front face 21a of the sealing member 21 cooperates with the fixed scroll base 13 to form a seal. The fixed scroll wall 11 may optionally have a (second) tip seal for sealing against the orbiting scroll base 9 to provide a second seal. The scroll pump 1 comprises a drive shaft 15 and an electric motor 16. The motor 16 is configured to rotate the drive shaft 15. The drive shaft 15 comprises a concentric shaft portion 17 and an eccentric shaft portion 19. The orbiting scroll 3 is fixedly mounted to the drive shaft 15. In particular, the orbiting scroll 3 is fixedly mounted to the eccentric shaft portion 19 of the drive shaft 15. The rotation of the eccentric shaft portion 19 imparts an orbiting motion to the orbiting scroll 3 relative to the fixed scroll 5. The relative motion of the orbiting scroll 3 and the fixed scroll 5 pumps fluid from an inlet disposed in a radially outer position to an outlet disposed at a radially inner position. The drive shaft 15 is supported for rotation by first and second bearings 22, 23. The first and second bearings 22, 23 each comprise a single row bearing. A third bearing 24 supports the orbiting scroll 3. The third bearing 24 in the present embodiment comprises a double row bearing. The first and second bearings 22, 23 constrain the drive shaft 15 to rotate about a rotational axis coincident with the longitudinal axis X. Axial displacement of the drive shaft 15 causes the orbiting scroll 3 (which is mounted on the drive shaft 15) to be displaced relative to the fixed scroll 5. The scroll pump 1 is configured to reduce any such axial movement of the drive shaft 15. The scroll pump 1 in the present embodiment comprises an axial spring 25 to apply an axial force F1 to the concentric shaft portion 17 of the drive shaft 15. The orbiting scroll 3 follows an orbiting path having a centre of orbit. The fixed scroll 5 has a geometric centre which is aligned with the longitudinal axis X of the scroll pump 1 (which corresponds to the rotational axis of the drive shaft 15). When the orbiting scroll 3 and the fixed scroll 5 are aligned with each other, the centre of orbit of the orbiting scroll 3 and the geometric centre of the fixed scroll 5 are aligned with each other. The centre of orbit and the geometric centre are at least substantially coincident with the longitudinal axis X. The orbiting scroll 3 is shown in Figures 2 and 3. The tip seal 20 is disposed on the orbiting scroll wall 7. The tip seal 20 is disposed on the orbiting scroll wall 7 distal from the front face 9a of the orbiting scroll base 9. The tip seal 20 forms a spiral when viewed in a plane perpendicular to the longitudinal axis X. The tip seal 20 extends at least substantially along a length of the orbiting scroll wall 7. The tip seal 20 protrudes beyond the end of the orbiting scroll wall 7 in a longitudinal direction (parallel to the longitudinal axis X). The tip seal 20 is removably mounted to the orbiting scroll wall 7 to facilitate replacement. The tip seal 20 is mounted so as to constrain radial movement and / or rotational movement (about the longitudinal axis X) relative to the orbiting scroll wall 7. However, the tip seal 20 is movable in a longitudinal direction relative to the orbiting scroll wall 7. In use, the front face 21a of the sealing member 21 is abraded due to the relative movement of the orbiting scroll 3 and the fixed scroll 5. The longitudinal movement of the tip seal 20 helps to ensure a seal is maintained when the front face 21a of the sealing member 21 is abraded. A cross-section through the orbiting scroll wall 7 is shown in Figures 4A and 4B. The tip seal 20 is illustrated as being spaced apart from the fixed scroll base 13 for clarity. It will be understood that the tip seal 20 cooperates with the fixed scroll base 13 to form a seal. As shown in Figures 4A and 4B, the tip seal 20 is mounted in a channel 30 formed in the orbiting scroll wall 7. The channel 30 is formed in a distal (outer) edge 31 of the orbiting scroll wall 7. The channel 30 extends at least substantially along a length of the orbiting scroll wall 7. The rear face 21b of the sealing member 21 is disposed in the channel 30. The front face 21a of the sealing member 21 is configured to cooperate with the front face 13a of the fixed scroll base 13 to form a seal. In use, the tip seal 20 is biased towards the fixed scroll base 13 due to the gas pressure in the channel 30. A biasing means may optionally be provided to bias the tip seal 20 towards the fixed scroll base 13. The biasing means may comprise a resilient insert (not shown) located in the channel 30. The resilient insert may, for example, comprise a compressible member disposed in the channel 30. In use, the front face 21a of the sealing member 21 contacts the front face 13a of the fixed scroll base 13. The orbital movement of the orbiting scroll wall 7 relative to the fixed scroll 5 causes the front face 21a of the sealing member 21 to be abraded by surface friction. The abrasion of the front face 21a reduces the thickness of the sealing member 21. As described herein, the tip seal 20 is movable relative to the orbiting scroll wall 7 in a longitudinal direction to compensate for abrasion of the front face 21a. In use, the longitudinal movement of the tip seal 20 at least partially compensates for any reduction in thickness of the sealing member 21 due to abrasion. The biasing means is operative to bias the tip seal 20 towards the fixed scroll base 13. When there is a relatively small amount of abrasion, the tip seal 20 has a first depth d1 (as shown in Figure 4A). When there is a relatively large amount of abrasion, the tip seal 20 has a second depth d2 (as shown in Figure 4B). The first depth d1 is greater than the second depth d2 (d1>d2). The tip seal 20 is replaced periodically to maintain the seal between the orbiting scroll wall 7 and the fixed scroll base 13. The tip seal 20 is formed of Polytetrafluoroethylene (PTFE), but other materials may be used. The tip seal 20 is machined to the required shape. In a variant, the tip seal 20 may be moulded. The scroll pump 1 in the present embodiment is configured to monitor an extent of the abrasion (wear) of the tip seal 20. In particular, the abrasion of the sealing member 21 is monitored. The abrasion of the front face 21a of the sealing member 21 reduces the thickness of the sealing member 21 in the longitudinal direction. The tip seal 20 is moveable in the longitudinal direction to compensate for abrasion (wear) of the front face 21a. The front face 21a continues to cooperate with the fixed scroll 5 to maintain a seal. The scroll pump 1 comprises at least one sensor 35A to provide an indication of a thickness of the tip seal 20 (in the longitudinal direction). The at least one sensor 35A in the present embodiment is in the form of a Hall effect sensor 35A (also known as a Hall sensor). The Hall effect sensor 35A is operative to detect the presence and magnitude of a magnetic field using the Hall effect. As shown in Figures 4A and 4B, the Hall effect sensor 35A in the present embodiment is mounted to the fixed scroll wall 11 of the fixed scroll 5. As shown in Figure 5, the Hall effect sensor 35A is mounted to the back face 13b of the fixed scroll base 13 in the present embodiment. In a variant, the Hall effect sensor 35A could be mounted to the front face 13a of the fixed scroll base 13 or in an aperture formed therein. The operation of the Hall effect sensor 35A is described herein with reference to a longitudinal sensing axis X1 extending parallel to the longitudinal axis X and extending through the Hall effect sensor 35A. At least one target 37A is associated with the sealing member 21 to enable an extent of the abrasion of the tip seal 20 to be monitored. In the present embodiment, the at least one target 37A is incorporated into the tip seal 20. The sealing member 21 and the at least one target 37A are configured to undergo displacement together. In particular, the sealing member 21 and the at least one target 37A are configured to be displaced in a longitudinal direction as the front face 21a is abraded. The at least one target 37A is coupled to the tip seal 20 and, in use, is displaced in the longitudinal direction as the front face 21a is abraded resulting in a reduction in the depth d of the sealing member 21. The at least one target 37A is configured to be detected by the Hall effect sensor 35A. In use, the extent of the abrasion of the tip seal 20 is monitored by sensing a proximity of the at least one target 37A to the Hall effect sensor 35A. The or each target 37A in the present embodiment comprises or is composed of a ferrous material. The or each target 37A may, for example, be formed of iron or steel. In a variant, the or each target 37A may be in the form of a permanent magnet. The or each target 37A may comprise a coating applied to the sealing member 21, for example applied to the rear face 21b of the sealing member 21. The coating may comprise a ferrous material, for example in the form of a powder or granules. A biasing means may optionally be provided to bias the at least on target 37A towards the fixed scroll base 13. The biasing means may comprise a resilient insert (not shown), such as a compressible member, which is disposed behind the or each target 37A. The at least one target 37A is spaced apart from the front face 21a of the sealing member 21. Thus, the at least one target 37A does not interrupt the seal formed between the front face 21a and the fixed scroll base 9. The at least one target 37A may be inset into the tip seal 20 or at least partially embedded therein. Alternatively, the at least one target 37A may be disposed on the rear face 21b of the sealing member 21. The at least one target 37A in the present embodiment is in the form of a single target 37A. The target 37A is disposed on an underside of the sealing member 21. As shown in Figures 4A and 4B, the target 37A is fastened to the rear face 21b of the sealing member 21, for example using an adhesive or mechanical fastener. The target 37A in the present embodiment is mounted in an aperture (labelled as aperture 39 in the variant illustrated in Figure 6) formed in the back face 21b of the sealing member 21. The aperture 39 is in the form of a channel elongated in a lengthwise direction. The target 37A is in the form of an elongated strip target 37A extending at least partway along the length of the sealing member 21. The elongated form of the target 37A increases the effective target area. An adhesive or mechanical fastener may be provided to secure the target 37A to the tip seal 20. In a variant, the target 37A may be biased against the rear face 21b of the sealing member 21. For example, a spring member may be provided to bias the target 37A against the rear face 21b of the sealing member 21. In a variant, the target 37A may be integrated into the sealing member 21 to form a tip seal 20 having a unitary structure. For example, the sealing member 21 may be over-moulded around the at least one target 37A. The or each target 37A may be embedded in the sealing member 21. A variant of the tip seal 20 is illustrated in Figure 6. The at least one target 37A in this variant is over-moulded into an underside of the sealing member 21. The target 37A in the present embodiment is at least substantially aligned with the Hall effect sensor 35A along the longitudinal sensing axis X1 when the orbiting scroll 3 is in a first orbital position (illustrated in Figures 4A and 4B). A smallest separation distance AX1 between the target 37A and the Hall effect sensor 35A corresponds to the separation distance AX1 along the longitudinal sensing axis X1 when the target 37A and the Hall effect sensor 35A are aligned. In a variant, the target 37A and the Hall effect sensor 35A may not align with each other along the longitudinal sensing axis X1 (irrespective of the orbital position of the orbiting scroll 3). The target 37A and the Hall effect sensor 35A may be offset from each other in a radial direction and / or a circumferential direction. Any such radial and / or circumferential offset may be accounted for when assessing an extent of the abrasion of the sealing member 21. A separation distance threshold may be defined to take account of the offset between the Hall effect sensor 35A and the target 37A. Alternatively, a known radial and / or circumferential offset may be used to determine the longitudinal separation distance AX1 in dependence on the peak magnitude of the sensor signal SG1. The peak magnitude represents a largest instantaneous value of the sensor signal SG1. A plurality of the targets 37A may be provided, for example spaced apart from each other along a length of the sealing member 21. The plurality of targets 37A may be separated from each other in a radial direction (from a geometric centre of the orbiting scroll 3) and / or a circumferential direction. The scroll pump 1 may comprise a plurality of the Hall effect sensors 35A to monitor the position of respective targets 37A. The plurality of Hall effect sensors 35A may each be associated with a respective one of the plurality of targets 37A. The Hall effect sensor 35A outputs a sensor signal SG1. The sensor signal SG1 is an electrical signal which provides an indication of a separation distance AX1 distance (i.e., a spacing or a gap) between the Hall effect sensor 35A and the target 37A. The magnitude of the sensor signal SG1 is directly proportional to the proximity of the at least one target 37A. The Hall effect sensor 35A is operable to determine the proximity of the at least one target 37A as the orbiting scroll 3 moves relative to the fixed scroll 5. The separation distance AX1 distance between the Hall effect sensor 35A and the target 37A varies as a result of the orbiting motion of the orbiting scroll 3. The cyclical variations of the sensor signal SG1 correspond to the orbital motion of the orbiting scroll 3. The peak magnitude of the sensor signal SG1 occurs when the separation distance AX1 between the Hall effect sensor 35A and the target 37A is smallest. In the present embodiment, this corresponds to the Hall effect sensor 35A and the target 37A being aligned with each other along the longitudinal sensing axis X1. Thus, the peak magnitude of the sensor signal SG1 provides an indication of the separation distance △X1 between the Hall effect sensor 35A and the target 37A along the longitudinal sensing axis X1. The sensor signal SG1 is an electrical signal. In the present embodiment, the sensor signal SG1 represents a voltage in the Hall effect sensor 35A. A first example of the sensor signal SG1 is illustrated in a time domain in Figure 7A; and in a frequency domain in Figure 7B. The first example of the sensor signal SG1 is indicative of the signal received for a tip seal 20 having little or no abrasion, for example a new tip seal 20 (as shown in Figure 4A). A second example of the sensor signal SG1 is illustrated in a time domain in Figure 8A and in a frequency domain in Figure 8B. The second example of the sensor signal SG1 is indicative of the signal received for a tip seal 20 having a large amount of abrasion, for example a worn or abraded tip seal 20 (as shown in Figure 4B). The distance between the Hall effect sensor 35A and the target 37A decreases as the front face 21a is abraded and the tip seal 20 is displaced towards the fixed scroll base 13. There is a corresponding movement of the target 37A towards the Hall effect sensor 35A. The magnitude of the sensor signal SG1 output from the Hall effect sensor 35A increases as the separation distance AX1 distance between the Hall effect sensor 35A and the target 37A decreases. The separation distance AX1 distance provides an indication of the longitudinal position of the rear face 21b of the sealing member 21. Thus, the sensor signal SG1 can be processed to determine the extent of the abrasion of the front face 21a of the sealing member 21. A controller 100 is provided for monitoring the abrasion of the tip seal 20. In particular, the controller 100 is configured to monitor wear of the sealing member 21 due to abrasion of the front face 21a. The controller 100 is illustrated in Figure 1. The controller 100 may be integrated into the scroll pump 1 or may be separate from the scroll pump 1. The controller 100 comprises a processing means 101 and a memory means 103. The processing means 101 comprises at least one electrical processor 101 having at least one electrical input 105 and at least one electrical output 107. The memory means 103 comprises one or more memory device 103. A set of computational instructions is stored on the memory device 103. When executed, the computational instructions cause the electrical processor 101 to perform the method(s) described herein. The at least one electrical input 105 is configured to receive the sensor signal SG1 from the Hall effect sensor 35A. The controller 100 is described herein as having a single electrical processor 101, but this is merely illustrative. The processor 101 is configured to process the sensor signal SG1 to determine a proximity of the at least one target 37A in relation to the Hall effect sensor 35A. The peak magnitude of the sensor signal SG1 is indicative of a smallest separation distance AX1 between the at least one target 37A and the Hall effect sensor 35A along the longitudinal sensing axis X1. In the present embodiment, the processor 101 is configured to convert the first signal SG1 from the time domain (shown in Figures 7A and 8A) to the frequency domain (shown in Figures 7B and 8B). The processor 101 may, for example, apply a Fourier transform the first signal SG1 from the time domain to the frequency domain. The processor 101 is configured to process the sensor signal SG1 to determine a smallest separation distance AX1 between the Hall effect sensor 35A and the at least one target 37A. In the present embodiment, the smallest separation distance AX1 corresponds to the separation distance AX1 along the longitudinal sensing axis X1. It will be understood that the conversion of the first signal SG1 to the frequency domain is optional. The controller 100 may be configured to monitor a peak magnitude of the first signal SG1 in the time domain. The abrasion of the front face 21a of the sealing member 21 is inversely proportional to the separation distance AX1 between the Hall effect sensor 35A and the target 37A in the longitudinal direction. By monitoring the separation distance AX1 between the Hall effect sensor 35A and the target 37A, the processor 101 can indirectly determine an extent of the wear of the tip seal 20. The processor 101 is configured to generate a notification signal SG2 to indicate that the tip seal 20 should be replaced in dependence on a determination that the separation distance AX1 between the Hall effect sensor 35A and the target 37A is less than or equal to a separation distance threshold. The notification signal SG2 is generated in dependence on the sensor signal SG1 from the Hall effect sensor 35A. The processor 101 may, for example, determine that the peak magnitude SG1(MAX) of the sensor signal SG1 is greater than or equal to a peak magnitude threshold TH2 (as illustrated in Figures 7B and 8B, by way of example). The peak magnitude threshold may be predefined, for example to correspond to a sensor signal at a defined separation. Alternatively, or in addition, the processor 101 may perform statistical analysis on the sensor signal SG1, for example to determine an average, mean or root mean square (RMS) of the sensor signal SG1. The notification signal SG2 may be generated in dependence on the statistical analysis of the sensor signal SG1. The electrical output 107 is configured to output the notification signal SG2 to indicate that the tip seal 20 should be replaced. The processor 101 may determine a time period (or service window) for replacing the tip seal 20. The time period for replacing the tip seal 20 may be predefined, for example a predefined time period after determining that the distance between the Hall effect sensor 35A and the target 37A is less than or equal to the separation distance threshold. Alternatively, the time period for replacing the tip seal 20 may be determined dynamically, for example in dependence on an estimated rate of abrasion. By estimating the rate of abrasion of the sealing member 21, the processor 101 may predict when a replacement of the tip seal 20 is appropriate. This may facilitate scheduling of a service to replace the tip seal 20. The servicing may be pre-planned, for example to be combined with servicing other components or instruments in the scroll pump 1. The processor 101 may be configured to log data indicative of a rate of abrasion of the sealing member 21 and one or more operating parameter of the scroll pump 1. The one or more operating parameter may comprise one or more of temperature, power, cycles, pressure, etc. By monitoring the one or more operating parameter, a determination may be made of which factor(s) are material to abrasion of the sealing member 21. By way of example, a correlation between scroll temperature and abrasion observed over time, may provide an indication that increased cooling is appropriate to control or reduce abrasion of the sealing member 21. The changes in control strategy may be applied to the scroll pump 1 or may logged for development of the scroll pump 1. This may help to reduce abrasion of the sealing member 21. The operation of the scroll pump 1 will now be described. The orbiting scroll 3 follows an orbiting path relative to the fixed scroll 5. The tip seal 20 cooperates with the fixed scroll base 13 to form a seal. The front face 21a of the sealing member 21 is abraded due to surface friction and the tip seal 20 is advanced in a longitudinal direction (relative to the orbiting scroll base 9) to maintain the seal. The displacement of the tip seal 20 results in a corresponding displacement of the target 37A towards the fixed scroll 5, as illustrated in Figure 4B. The Hall effect sensor 35A detects the target 37A as the orbiting scroll 3 travels relative to the fixed scroll 5. The Hall effect sensor 35A outputs the sensor signal SG1 which is indicative of the proximity of the target 37A. As shown in Figures 7A and 8A, the sensor signal SG1 varies as the orbiting scroll 3 orbits relative to the fixed scroll 5. The peak magnitude of the sensor signal SG1 is indicative of the smallest separation distance AX1 between the Hall effect sensor 35A and the target 37A. In the present embodiment, the smallest separation distance AX1 corresponds to a separation distance AX1 along the longitudinal sensing axis X1 (when the Hall effect sensor 35A and the target 37A are aligned with each other). The tip seal 20 is displaced towards the fixed scroll 5 as the front face 21a is abraded which results in a corresponding displacement of the target 37A in a longitudinal direction. The processor 101 is configured to monitor the longitudinal separation distance AX1 and to output notification signal SG2 in dependence on a determination that the smallest separation distance AX1 between the Hall effect sensor 35A and the target 37A is less than the separation distance threshold. The separation distance threshold is defined to correspond to a predetermined amount of abrasion of the sealing member 21. A block diagram 200 is shown in Figure 9 to illustrate the operation of the processor 101. The processor 101 is activated (BLOCK 205). The processor 101 receives the sensor signal SG1 from the Hall effect sensor 35A (BLOCK 210). The processor 101 processes the sensor signal SG1 to determine a smallest separation distance AX1 between the Hall effect sensor 35A and the target 37A (BLOCK 215). The determined smallest separation distance AX1 is compared to a separation distance threshold TH1 (BLOCK 220). If the determined smallest separation distance AX1 is greater than the separation distance threshold, the processor 101 continues to monitor the sensor signal SG1 (BLOCK 210). If the determined smallest separation distance △X1 is less than or equal to the separation distance threshold, the processor 101 outputs the notification signal SG2 to indicate that the tip seal 20 should be replaced (BLOCK 225). The processor 101 may optionally determine a time period to schedule replacement of the tip seal 20, for example in dependence on a determined rate of abrasion. The process ends (BLOCK 230). The processor 101 may optionally be configured to inhibit operation of the scroll pump 1 in dependence on the sensor signal SG1. The processor 101 may inhibit operation of the scroll pump 1 in dependence on a determination that the smallest separation distance AX1 is less than a lower operating threshold and / or that the smallest separation distance AX1 greater than an upper operating threshold. The lower operating threshold and / or the upper operating threshold may define an operating range for the scroll pump 1. The lower operating threshold may define a minimum separation distance for operation of the scroll pump 1. A determination that the smallest separation distance AX1 is less than the lower operating threshold may indicate excessive wear of the sealing member 21. In dependence on a determination that the separation distance AX1 is less than or equal to the lower operating threshold, the processor 101 may prevent operation of the scroll pump 1. The upper operating threshold may define a maximum separation distance for operation of the scroll pump 1. In dependence on a determination that the separation distance AX1 is greater than or equal to the upper operating threshold, the processor 101 may prevent operation of the scroll pump 1. A determination that the smallest separation distance AX1 is greater than the upper operating threshold may indicate that the tip seal 20 has not been fitted correctly. For example, this may indicate that the tip seal 20 is not aligned correctly in the channel 30 or has not been inserted correctly. The processor 101 may be configured to output a control signal to inhibit operation of the scroll pump 1. A warning or notification signal may be output, for example to notify a user of the issue. Alternatively, or in addition, the processor 101 may be configured to control operation of the scroll pump 1 in dependence on a determination that the at least one target 37A is present or absent. The processor 101 may be configured to enable operation of the scroll pump 1 in dependence on a determination that the at least one target 37A is present (i.e., that the at least one target 37A is detected). The processor 101 may be configured to inhibit operation of the scroll pump 1 in dependence on a determination that the at least one target 37A is absent (i.e., that the at least one target 37A is not detected). The processor 101 may process the sensor signal SG1 to determine the presence or absence of the at least one target 37A. A determination that the at least one target 37A is absent may indicate that the tip seal 20 has not been fitted correctly or that an incorrect tip seal 20 (or a non-genuine tip seal) has been fitted. The processor 101 may be configured to output a control signal to inhibit operation of the scroll pump 1. A warning or notification signal may be output, for example to notify a user of the issue. The present invention has been described with particular reference to the at least one target 37A associated with the tip seal 20 disposed on the orbiting scroll wall 7. Alternatively, or in addition, at least one second target 37B may be associated with a second tip seal 40 (shown in Figure 1) disposed on the fixed scroll wall 11. The second tip seal 40 is provided on the fixed scroll wall 11. The second tip seal 40 comprises a second sealing member 41 which, in use, cooperates with the orbiting scroll base 9 to form a second seal. At least one second sensor 35B may be provided for detecting the at least one second target 37B. The at least one second sensor 35B may be provided on the orbiting scroll 3. The at least one second target 37B and the at least one second sensor 35B may be configured to monitor abrasion of the second tip seal 40. The at least one second target 37B may be movable towards the orbiting scroll base 9 as the second tip seal 40 is abraded. The at least one second sensor 35B may be configured to output a second sensor signal providing an indication of a separation distance AX1 between the at least one second target 37B and the at least one second sensor 35B. The second sensor signal may be processed in accordance with the method(s) described herein in relation to the first sensor signal SG1. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. The present invention has been described with particular reference to a scroll pump 1 having one or more tip seal 20. Alternatively, or in addition, the scroll pump 1 may comprise one or more channel seal for cooperating with a respective scroll wall to form a seal. The one or more channel seal may be disposed on the orbiting scroll base 9 for cooperating with the fixed scroll wall 11; and / or disposed on the fixed scroll base 13 for cooperating the of the orbiting scroll wall 7. The at least one target 37A may be associated with the channel seal. The at least one sensor 35 may be provided to monitor a longitudinal position of the at least one target 37A to provide an indication of the abrasion of the channel seal. The operation of the processor 101 and the corresponding method are substantially unchanged from the embodiment described herein. Rather than make an absolute determination of a separation distance AX1 between the Hall effect sensor 35A and the target 37A, the processor 101 may determine a relative change in the separation distance AX1 between the Hall effect sensor 35A and the target 37A. The processor 101 may output the notification signal SG2 in dependence on a determination that the peak magnitude of the sensor signal SG1 has increased by a predetermined proportion. For example, the processor 101 may output the notification signal SG2 in dependence on a current (instantaneous) peak magnitude which is a predetermined proportion greater than the peak magnitude when the tip seal 20 was new. The scroll pump 1 has been described herein with reference to a Hall effect sensor 35A and a target 37A. It will be understood that other types of sensor may be used. For example, the scroll pump 1 may comprise an inductive sensor 35A. The inductive sensor 35A may be configured to detect a target 37A comprising or consisting of a ferrous target. The target 37A may be magnetised or non-magnetised. The sensor 35A, 35B may comprise a variable reluctance sensor 35A, 35B. The variable reluctance sensor 35A, 35B is a type of inductive sensor which is passive. The variable reluctance sensor 35A, 35B may be configured to detect a target 37A, 37B. The target 37A, 37B may comprise a ferrous or magnetic target. In a further variant, the at least one sensor 35A, 35B and the at least one target 37A, 37B may both be associated with either the orbiting scroll 3 or the fixed scroll 5. The at least one sensor 35A, 35B may be mounted behind the at least one target 37A, 37B in the orbiting scroll wall 7 or the fixed scroll wall 11. For example, the at least one sensor 35A, 35B and the at least one target 37A, 37B may both be mounted in the orbiting scroll wall 7 or the fixed scroll wall 11. As the sealing member 21, 41 is abraded, the seal 20, 40 may be displaced in the longitudinal direction X away from the at least one sensor 35A, 35B. In use, the at least one sensor 35A, 35B may directly measure a longitudinal displacement of the seal 20, 40 as the sealing member 21, 41 is abraded. The abrasion (wear) of the seal 20, 40 can be measured in 5 dependence on the signal received from the at least one sensor 35A, 35B. Reference Numerals SCROLL PUMP 1 ORBITING SCROLL 3 FIXED SCROLL 5 HOUSING 6 ORBITING SCROLL WALL 7 ORBITING SCROLL BASE 9 FRONT FACE 9a REAR FACE 9b FIXED SCROLL WALL 11 FIXED SCROLL BASE 13 DRIVE SHAFT 15 MOTOR 16 CONCENTRIC SHAFT PORTION 17 ECCENTRIC SHAFT PORTION 19 TIP SEAL 20 SEALING MEMBER 21 FIRST BEARING 22 SECOND BEARING 23 THIRD BEARING 24 AXIAL SPRING 25 CHANNEL 30 DISTAL OUTER EDGE 31 MEANS 33 SENSOR 35A, 35B TARGET 37A, 37B APERTURE 39 HALL EFFECT SENSOR 45 CONTROLLER 100 PROCESSOR 101 MEMORY DEVICE 103 ONE ELECTRICAL INPUT 105 ELECTRICAL OUTPUT 107 10 BLOCK DIAGRAM (200) START 205 RECEIVE SENSOR SIGNAL (SG1) 210 DETERMINE SEPARATION DISTANCE (AX1) 215 COMPARE SEPARATION DISTANCE (AX1) TO THRESHOLD VALUE 220 OUTPUT NOTIFICATION SIGNAL (SG2) TO REPLACE TIP SEAL 225 END 230

Claims

1. A scroll pump (1) comprising:a first scroll (3, 5) having a first scroll wall (7, 11) extending from a first scroll base (9, 13);a second scroll (3, 5) having a second scroll wall (7, 11) extending from a second scroll base (9, 13) towards the first scroll base (9, 13);a seal (20, 40) disposed on the second scroll (3, 5) for cooperating with the first scroll (3, 5) to form a seal;at least one target (37A, 37B) associated with the seal (20, 40), the at least one target (37A, 37B) being movable towards the first scroll (3, 5) along a longitudinal axis (X) as the seal (20, 40) is abraded; andat least one sensor (35A, 35B) for detecting the at least one target (37A, 37B), the at least one sensor (35A, 35B) being configured to output a sensor signal (SG1) providing an indication of a separation distance (AX1) between the at least one target (37A, 37B) and the at least one sensor (35A, 35B).

2. A scroll pump (1) as claimed in claim 1 comprising a control unit (100) configured to monitor the seal (20, 40), the control unit (100) comprising at least one processor (101); wherein the at least one processor (101) is configured to:receive the sensor signal (SG1) from the at least one sensor (35A, 35B), the sensor signal (SG1) providing an indication of the separation distance (AX1) between the at least one target (37A, 37B) and the at least one sensor (35A, 35B);process the sensor signal (SG1) to determine that the separation distance (AX1) between the at least one target (37A, 37B) and the at least one sensor (35A, 35B) is less than a separation distance threshold (TH1); andoutput a notification signal (SG2) in dependence on a determination that the separation distance (AX1) is less than or equal to a separation distance threshold (TH1).

3. A scroll pump (1) as claimed in claim 2, wherein processing the sensor signal (SG1) comprises determining a peak magnitude of the sensor signal (SG1); the determination that the separation distance (AX1) is less than the separation distance threshold (TH1) comprising determining that the peak magnitude is greater than or equal to a peak magnitude threshold (TH2).

4. A scroll pump (1) as claimed in claim 2 or claim 3, wherein processing the sensor signal (SG1) comprises determining the separation distance (AX1) in dependence on the sensor signal (SG1); and comparing the determined separation distance (AX1) to the separation distance threshold (TH1).

5. A scroll pump (1) as claimed in claim 4, wherein the at least one processor is configured to determine a smallest value of the separation distance (AX1).

6. A scroll pump (1) as claimed in any one of claims 2 to 5, wherein the at least one processor (101) is configured to inhibit operation of the scroll pump (1) in dependence on:a determination that the separation distance (AX1) is outside an operating range; and / ora determination that the at least one target (37A, 37B) is absent.

7. A scroll pump (1) as claimed in any one of claims 2 to 6, wherein the at least one processor is configured to:monitor a rate of change of the separation distance (AX1) between the at least one target (37A, 37B) and the at least one sensor (35A, 35B); andestimate an operating time period for replacing the seal (20, 40) in dependence on the determined rate of change of the separation distance (AX1);wherein the notification signal (SG2) comprises the estimated operating time period.

8. A scroll pump (1) as claimed in any one of the preceding claims, wherein the at least one sensor (35A, 35B) comprises a Hall effect sensor (35A, 35B); and the at least one target (37A, 37B) comprises a ferrous or magnetic target (37A, 37B).

9. A scroll pump (1) as claimed in any one of claims 1 to 7, wherein the at least one sensor (35A, 35B) comprises an inductive sensor or a variable reluctance sensor; and the at least one target (37A, 37B) comprises a ferrous or magnetic target (37A, 37B).

10. A scroll pump (1) as claimed in any one of the preceding claims, wherein the at least one target (37A, 37B) is fastened to the seal (20, 40).

11. A scroll pump (1) as claimed in claim 10, wherein the seal (20, 40) comprises a front face and a rear face; wherein the at least one target (37A, 37B) is fastened to the rear face of the seal (20, 40).

12. A scroll pump (1) as claimed in claim 10 or claim 11, wherein the at least one target (37A, 37B) is at least partially embedded in the seal (20, 40).

13. A scroll pump (1) as claimed in any one of the preceding claims, wherein the at least 5 one sensor (35A, 35B) is disposed on the first scroll (3, 5).

14. A scroll pump (1) as claimed in any one of the preceding claims, wherein the first scroll (3, 5) is one of an orbiting scroll (3) and a fixed scroll (5); and the second scroll (3,5) is the other of the orbiting scroll (3) and the fixed scroll (5).1015. A scroll pump (1) as claimed in any one of the preceding claims comprising a second seal (20, 40) disposed on the first scroll (3, 5) for cooperating with the second scroll (3, 5) to form a second seal; wherein at least one second target (37A, 37B) is associated with the second seal (20, 40), the at least one second target (37A, 37B) being movable towards the 15 second scroll (3, 5) along a longitudinal axis as the second seal (20, 40) is abraded; and at least one second sensor (35A, 35B) for detecting the at least one second target (37A, 37B).

16. A scroll pump (1) as claimed in any one of the preceding claims, wherein the at least one target (37A, 37B) and the at least one sensor (35A, 35B) are aligned with each other along 20 a longitudinal sensing axis (X1) when the orbiting scroll is in a first orbital position.

17. A method of monitoring a seal (20, 40) in a scroll pump (1), wherein the scroll pump(1) comprises:a first scroll (3, 5) having a first scroll wall (7, 11) extending from a first scroll base (9, 25 13);a second scroll (3, 5) having a second scroll wall (7, 11) extending from a second scroll base (7, 11) towards the first scroll base (9, 13);a seal (20, 40) disposed on the second scroll (3, 5) for cooperating with the first scroll (3, 5) to form a seal;30 at least one target (37A, 37B) associated with the seal (20, 40), the at least one target(37A, 37B) being movable towards the first scroll (3, 5) along a longitudinal axis (X) as the seal (20, 40) is abraded; andat least one sensor (35A, 35B) for detecting the at least one target (37A, 37B), the at least one sensor (35A, 35B) being configured to output a sensor signal (SG1) providing an 35 indication of a separation distance (AX1) between the at least one target (37A, 37B) and theat least one sensor (35A, 35B);wherein the method comprises:receiving a sensor signal (SG1) from the at least one sensor (35A, 35B), the sensor signal (SG1) providing an indication of a separation distance (AX1) between the at least one target (37A, 37B) and the at least one sensor (35A, 35B);determining that the separation distance (AX1) between the at least one target5 (37A, 37B) and the at least one sensor (35A, 35B) is less than a separation distancethreshold (TH1); andgenerating a notification in dependence on a determination that the separation distance (AX1) is less than or equal to a separation distance threshold (TH1).10

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