Vacuum pump lubricant condition monitoring

Abstract

An oil container 10 for use in a vacuum pump, with a lubricant reservoir (14, fig.2), within the cartridge body 12. Within the reservoir there is at least one lubricant receiving and / or retaining medi

Description

FIELD OF INVENTION The present invention relates to a lubricant cartridge for use in a vacuum pump and a vacuum pump comprising a lubricant cartridge. BACKGROUND Common vacuum pumps comprise a housing having an inlet and an outlet; at least one rotor comprising one or more rotor elements; at least one stator; a motorfor driving rotation of the rotor and at least two bearings for supporting the rotor. During operation, gas is conveyed from the inlet to the outlet by rotation of the rotor elements. More specifically, gas may be conveyed by momentum transfer as gas molecules collide with the rotor elements, such is the case for a turbomolecular vacuum pump for example. Alternatively, gas may be conveyed by positive displacement of a working volume defined by the rotor and / or stator, such is the case for rotary vane pumps for example. The bearings may be magnetic bearings and / or mechanical bearings. Typically, at least one bearing is a mechanical bearing, such as a ball bearing. Mechanical bearings must be lubricated during operation to reduce frictional effects and ensure smooth running of the pump. Lubrication is commonly provided in the form of an oil. Overtime, such oils deteriorate and become contaminated, which can ultimately lead to bearing failure. As a result, pumps are typically serviced at scheduled intervals to allow for assessment of the oil and bearing conditions and performance of maintenance where necessary. Certain vacuum pumps, such as rotary vane pumps and the like, may also use oils for sealing working volumes within the pump, to prevent leakage and improve pumping efficiency. Deterioration and contamination of the oil over time may affect the pumping efficiency of the vacuum pump. These oils may be the same oils used to lubricate the bearings within the pump, hence monitoring their condition is important to support proper operation of the vacuum pump. Scheduling services at fixed intervals does not account for potential contamination, deterioration or quality issues associated with the oil, which could affect the service life of the bearing, and where applicable, sealing within the pump. For example, the rate of contamination and deterioration of the oil may vary depending on the application environment and exposure to certain gases or vapours. Scheduling services at fixed intervals could therefore lead to unexpected failure due to late servicing. This may result in high repair and replacement costs alongside great inconvenience for the user. Alternatively, scheduling services at fixed intervals could give rise to premature or unnecessary servicing. This may also result in lost time and costs for the user. Preventing unplanned product failures and reducing warranty claims is therefore of high importance. Bearing conditions may be monitored by measurement of the thermal signature of the pump, vibration signature of the pump and / or lubricant conditions. Monitoring of the lubricant conditions provides for earlier indication of bearing failure, however known means of lubricant monitoring are often complex, costly and unsuitable for use in vacuum pumps. It is an object of the present invention to provide a vacuum pump with means for varied service intervals based on real-time oil condition monitoring. The present invention aims to advantageously allow for early capture of potential problems which could result in bearingfailure, whilst also overcoming the problems associated with both fixed service intervals and existing oil monitoring methods. SUMMARY OF THE INVENTION in a first, aspect, the present invention provides a lubricant cartridge for use in a vacuum pump. The lubricant cartridge comprises a cartridge body defining a lubricant reservoir; at least one lubricant receiving and / or retaining medium arranged within the lubricant reservoir; wherein said at least one lubricant receiving and / or retaining medium contains an embedded electrode arrangement; and wherein said electrode arrangement is connectable to a controller for detecting changes in an electrical parameter of lubricant within the lubricant reservoir. Lubricants, such as oils, are inherently non-conductive, however through use their electrical properties vary due to deterioration and contamination. More specifically, the presence of metallic and non-metallic wear debris from the bearing, chemical degradation and quantity of the oil may alter the presence of ions and particles resulting in changes to the lubricant’s dielectric constant, conductivity, inductance and / or complex impedance. Since the electrodes are embedded within the lubricant receiving and / or retaining medium, lubricant retained by this medium can act as a dielectric for the electrode arrangement. As the lubricant condition changes during use of the vacuum pump, the ionic mobility and conductivity of the dielectric changes, resulting in changes in the electrical parameters measured across the electrode arrangement. Such changes in electrical parameters may therefore provide an indication of the condition of the lubricant and / or bearing at an early stage before changes may be observed otherwise, for example in the thermal or vibration signature of the pump or during scheduled maintenance of the pump. The present invention therefore provides a lubricant cartridge adapted for monitoring the condition of lubricant within a vacuum pump. This advantageously allows for real-time monitoring of lubricant conditions, which in turn supports varied service intervals. As a result, premature bearing failure, due to late scheduling of services, and unnecessary servicing is avoided, reducing lost time and costs. Embedding the electrode arrangement within the lubricant receiving and / or retaining medium ensures that, the electrode arrangement is always in close contact with the lubricant, whilst also providing for a compact assembly. in a preferred embodiment, the electrode arrangement comprises at least a first electrode and a second electrode arranged about the first electrode. The first electrode and the second electrode may comprise ring electrodes. Preferably the first electrode comprises an inner ring and a plurality of arms extending outwardly from the inner ring. The second electrode preferably comprises an outer ring and a plurality of arms extending inwardly from the outer ring. Preferably each arm of the plurality of arms extends radially from the respective inner and outer rings. it is advantageous that the electrodes have as large an active surface area as possible and are closely spaced to maximise capacitance and minimise resistance, for enhanced precision and reliability. The use of arms extending from the rings acts to increase the surface area of the electrodes whilst also minimising impeded oil flow through the lubricant receiving and / or retaining medium. The electrodes are preferably arranged in such a way that the arms of the first electrode are in close proximity to the arms of the second electrode and more preferably, each of the arms of the first electrode faces a respective arm of the second electrode. More preferably, at least one of the arms of the first electrode comprises a plurality of rods extending outwardly, preferably perpendicularly, therefrom. Similarly, at least one of the arms of the second electrode preferably comprises a plurality of rods extending outwardly, preferably perpendicularly, therefrom. The plurality of rods further increases the surface area of the electrodes and minimises impedance of oil flow through the lubricant receiving and / or retaining medium. Each rod of the plurality of rods may comprise a tip for piercing the lubricant receiving and / or retaining medium. This improves ease of assembly and insertion of the electrodes into the lubricant receiving and / or retaining medium, which in turn reduces the time and costs associated with manufacture and assembly of the lubricant cartridge. It should beappreciated that the order of assembly may vary, for example the electrodes may be introduced into the lubricant reservoir before the lubricant receiving and / or retaining medium or alternatively the lubricant receiving and / or retaining medium may be introduced into the lubricant reservoir followed by the electrodes. The electrode arrangement is preferably formed from a suitable material that is not reactive with the lubricant, such as but not. limited to copper or aluminium. It should be appreciated that the lubricant cartridge may comprise more than one lubricant receiving and / or retaining medium. This advantageously allows for additional elements to be introduced between lubricant receiving and / or retaining media. For example, a wicking element, such as a felt finger, may be arranged between a first receiving and / or retaining medium and a second receiving and / or retaining medium, fortransporting lubricant to a bearing. The electrode arrangement may span across each lubricant receiving and / or retaining medium. Alternatively, each additional medium may comprise its own electrode arrangement. For example, the lubricant cartridge may comprise two such media each comprising an electrode arrangement as previously described. Incorporation of separate electrode arrangements within each lubricant receiving and / or retaining medium is particularly advantageous where electrode geometries are not optimised for reduced impedance of lubricant, such is the case for ring electrodes. Movement of the lubricant through the wicking element maybe impeded by the inclusion of such electrodes, hence it may be advantageous that the electrode arrangement does not interfere with the wicking element. In a preferred embodiment, the lubricant cartridge contains a temperature sensor. Preferably the temperature sensor is located within theoil reservoirand more preferably the temperature sensor is embedded within the lubricant receiving and / or retaining medium. The temperature sensor may be a low-cost temperature sensor, such as but not limited to a thermistor. The electrical properties of the lubricant, and thus the measured parameters, depend not only on the concentration of impurities but also on the ionic mobility. Ionic mobility is temperature dependent, hence inclusion of a temperature sensor within the lubricant cartridge allows for derivation of temperature compensated values of the measured electrical parameters, improving accuracy of the lubricant monitoring. Additionally, since lubricant temperature increases with increased friction in the bearing, the measured temperature may also provide further indication of the bearing conditions. The temperature sensor may be used to replace or complement traditional thermal management sensing techniques present in existing vacuum pumps. The lubricant receiving and / or retaining medium may be a lubricant absorbing element for storing lubricant. Additionally, or alternatively, the lubricant receiving and / or retaining medium may be a filter. Preferably the lubricant receiving and / or retaining medium is made from a fibrous material, a foam material, a sponge material or the like. More preferably, the lubricant receiving and / or retaining medium is a felt material. In a further aspect, the lubricant cartridge preferably forms part of a control system, which includes a controller connected to the electrode arrangement and configured to detect, changes to an electrical parameter of the lubricant within the cartridge. Preferably, an AC voltage source is connected across the electrode arrangement to avoid polarisation of the ions over time, which could give rise to inaccurate determination of the lubricant and / or bearing conditions. Preferably, at least one electrode of the electrode arrangement is grounded and more preferably at least one electrode of the electrode arrangement is connected to a common ground with the cartridge body, which forms an additional electrode. Where a temperature sensor is included in the lubricant cartridge, the temperature sensor is preferably connected to the controller and the controller is preferably configured to derive temperature compensated values of the measured electrical parameter. Preferably, the measured electrical parameter includes at least one of capacitance, conductivity, inductance and / or complex impedance of the lubricant, A preferred example of a simple and low cost approach to measure capacitance is via a capacitive bridge circuit. Impedance may be measured via a divider circuit that gives rise to direct measurement of the change of the real component of the impedance as a change in the ratio of the amplitude of the sensing voltage and the reference voltage. It should be appreciated that alternative approaches to measure the electrical parameters are known and may be used. Further information on lubricant condition may also be derived by monitoring the phase difference between the sensing voltage and the reference voltage which will vary with the change in the imaginary component of the impedance. Monitoring the phase difference between the real and imaginary impedance can be useful to discriminate between metallic wear and non-metallic wear of the bearing, since changes in conductivity occur only due to the presence of metallic particulates within the lubricant. The controller is preferably configured to emit a warning when a threshold condition is satisfied. The threshold condition may be when at least one measured electrical parameter and / or temperature compensated value reaches, exceeds or decreases below a threshold value. Alternatively, the threshold condition may be when the rate of change of at least one measured electrical parameter and / or temperature compensated value reaches, exceeds or decreases below a threshold value. The warning may take the form of an error message, a light and / or an audible alarm or the like. The warning may also take the form of a wireless signal emitted from the controller to an external device, including but not limited to a handheld PDA or mobile device for example. In use, when the threshold condition is satisfied the warning signal indicates to the user that the condition of the lubricant and / or bearing has deteriorated and thus a scheduled service may be required, to allowfor detailed inspection and preventative maintenance. As previously described, this advantageously provides for varied service intervals based on real-time lubricant condition monitoring. Services can therefore be scheduled before bearing failure and / or significant deterioration of the lubricant, without the need for unnecessary precautionary services. This in turn can significantly reduce service downtime throughout the life of the vacuum pump, reduce costs associated with servicing and risks associated with unexpected failure and / or reductions in pumping performance between servicing. The present invention also provides a vacuum pump comprising; a housing having an inlet and an outlet; at least one rotor arranged within the housing; at least two bearings for supporting the rotor; a lubricant cartridge comprising a cartridge body defining a lubricant reservoir, a lubricant receiving and / or retaining medium located within the lubricant reservoir and an electrode arrangement embedded within the lubricant receiving and / or retaining medium; and a controller connected to the electrode arrangement and configured to detect changes in an electrical parameter of the lubricant. The lubricant cartridge may include any or all the features of the lubricant cartridge as aforementioned. The lubricant cartridge may be inserted into a recess of the vacuum pump housing. Preferably, the lubricant cartridge is releasably connected within the vacuum pump to allow for easy replacement during servicing, thereby reducing service times. Incorporation of the electrode arrangement within the lubricant cartridge may therefore provide for a low-cost and easily replaceable method for lubricant monitoring. In use, lubricant is transported from the lubricant reservoir to the bearings and / or the working space, via the lubricant receiving and / or retaining medium. Transportation of the lubricant may be driven by a wicking element, such as a felt finger or a feeding Une and / or by a lubricant feed element, such as an oil feed nut, oil flinger, or the like located at the end of the rotor. The electrode arrangement is connected to the vacuum pump controller. The oil cartridge may further comprise a temperature sensor which may be located within the oil reservoir and which is preferably located within the lubricant receiving and / or retaining medium. The temperature sensor is preferably connected to the vacuum pump controller, which may be configured to derive temperature compensated values of the measured electrical parameter. Electrochemical monitoring may be incorporated into the vacuum pump controller via a capacitance to digital convertor device or dedicated measurement technique, for example a capacitance bridge. This eliminates the need for an additional controller, which may act to increase the cost and size of the system. The control system may include any or all the features described above such that, in use, the controller emits a warning when a threshold condition is satisfied to indicate to the user that the condition of the lubricant and / or bearing has deteriorated and thus a scheduled service may be required. It should be appreciated that the proposed method of lubricant monitoring may be used in combination with existing methods of lubricant and / or bearing monitoring, such as vibrational measurement. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: FIG 1 illustrates an exploded view of an embodiment of the lubricant cartridge. FIG 2 illustrates a cross sectional view of the lubricant cartridge of FIG 1. FiG 3a illustrates an alternative embodiment of an electrode arrangement of the lubricant cartridge. FiG 3b illustrates the first electrode of the electrode arrangement of FIG 3a. FIG 3c illustrates the second electrode of the electrode arrangement of FIG 3a. Figure 4a illustrates an alternative embodiment of the electrode arrangement. FIG 4b illustrates the first electrode of the electrode arrangement of FIG 4a. FIG 4c illustrates the second electrode of the electrode arrangement of FIG 4a. FIG 5 illustrates the lubricant cartridge comprising the electrode arrangement of FIG 4a. FIG 6 illustrates a cross section through a portion of a vacuum pump comprising the lubricant cartridge. DETAILED DESCRIPTION OF THE DRAWINGS FIG 1 illustrates an exploded view of an embodiment of a lubricant cartridge 10. The lubricant cartridge 10 comprises a cartridge body 12 which defines a lubricant reservoir 14. Within the lubricant reservoir 14 are two lubricant receiving and / or retaining media 16. It should be appreciated that the lubricant cartridge 10 may include any number of lubricant receiving and / or retaining media 16, which may be configured to store and / or filter lubricant. An electrode arrangement 18 is embedded within each of the lubricant receiving and / or retaining media 16. The electrode arrangement 18 comprises a first electrode 20 and a second electrode 30 arranged about the first electrode 20. Preferably the second electrode 30 is arranged concentrically about the first electrode 20, as shown. In this embodiment both the first electrode 20 and the second electrode 30 are ring electrodes. The electrode arrangement 18 is configured to be connected to a controller (not shown) configured to detect changes in an electrical parameter of the lubricant. The oil cartridge 10 also comprises a wicking element 40, in the form of a finger felt, and two plain felt discs 42 located between the two lubricant receiving and / or retaining media 16. The wicking element 40 functions to transport the lubricant from the lubricant receiving and / or retaining media 16 to the rotor and / or bearing (not shown). The cartridge body 12 may be secured within a vacuum pump by conventional fastening means, such as bolts. O-rings 13 may be positioned about the sealing surfaces to maintain a leak tight seal. FIG 2 illustrates a cross-section of the lubricant cartridge 10, which comprises the same features as the lubricant cartridge 10 of FIG 1 and further comprises a temperature sensor 50. The temperature sensor 50 is located within the lubricant reservoir 14, preferably within at least one lubricant receiving and / or retaining medium 16, as shown. In use, the electrodes 20, 30 and the temperature sensor 50 are connected to a controller configured for monitoring the conditions of the lubricant contained within the lubricant reservoir 14. Specifically, changes in an electrical parameter of the lubricant are measured across the electrodes 20, 30 and the temperature of the lubricant is measured by the temperature sensor 50. The controller is preferably configured to derive temperature compensated values of the measured electrical parameter of the lubricant. FIG 3a illustrates an alternative embodiment of an electrode arrangement 18', in which the surface area of the electrode arrangement 18’ is increase for improved accuracy and precision of the measured electrical parameters of the lubricant. The electrode arrangement 18’ comprises a first electrode 20’ and a second electrode 30’ arranged about the first electrode 20’. Preferably the second electrode 30’ is arranged concentrically about the first electrode 20’, as shown. The geometry of the first electrode 20’ and second electrode 30’ are described with reference to FIG 3b and FIG 3c respectively. The first electrode 20’ comprises an inner ring 22 and a plurality of arms 24 extending outwardly from the inner ring 22. The arms 24 are preferably equispaced about the outer circumference of the inner ring 22 of the first electrode 20’. The second electrode 30’comprises an outer ring 32 and a plurality of arms 34 extending inwardly from the outer ring 32. The arms 34 are preferably equispaced about the inner circumference of the outer ring 32 of the second electrode 30’. Preferably the number of arms 24 of the first electrode 20’ is equal to the number of arms 34 of the second electrode 30’. For example, in this embodiment, each electrode 20’, 30’ comprises a total of four sets of arms 24, 34, however, it should be appreciated that any number of arms may be provided on each electrode. This advantageously ensures that each arm 24 of the first electrode 20’ is positioned in-between two arms 34 of the second electrode 30’ and vice versa. This allows for the electrical parameters of the lubricant to be measured between each arm 24, 34, increasing the accuracy and precision of the measurement whilst minimising impedance of lubricant flow around the electrode arrangement 18’. The arms 24, 34 also allow for the first electrode 20’ and second electrode 30’ to be arranged in close proximity to one another, further increasing the accuracy and precision of the measured electrical parameters. FIG 4a illustrates an alternative electrode arrangement 18”, in which the surface area of each electrode is further increased and impedance of the lubricant flow around the first electrode 20” and second electrode 30” is further minimised. The second electrode 30” is arranged about the first electrode 20” and preferably such that the second electrode 30” is arrange concentrically about the first electrode 20”. FIGs 4b and 4c illustrate the first electrode 20” and second electrode 30” of FIG 4a respectively. The first electrode 20" comprises an inner ring 22' and a plurality of arms 24’ extending outwardly from the inner ring 22’. Preferably, each arm of the plurality of arms 24’ extends radially from one end of the inner ring 22’ as shown. The second electrode 30” comprises an outer ring 32’ and a plurality of arms 34’ extending inwardly from the outer ring 32’. Preferably, each arm of the plurality of arms 34’ extends radially from one end of the outer ring 32’, as shown. Each arm of the plurality of arms 24’, 34’ further comprise a plurality of rods 26, 36 extending outwardly. A total of five rods per arm are shown, however each arm may comprise any number of rods. Preferably each arm 24’, 34’ comprise the same number of rods 26, 36. Preferably each rod 26 is connected to each arm 24’ along a common plane A and each rod 36 is connected to each arm 34’ along a common plane B, Preferably, the rods 26, 36 are equispaced along the length of each arm 24’, 34’ and extend in the same direction relative to the arm 24’, 34’. Each rod 26, 36 may comprise a tip 28, 38 for piercing the lubricant receiving and / or retaining medium upon assembly of the lubricant cartridge. Further, the first electrode 20” and the second electrode 30” each comprise a connecting element 29, 39 respectively, extending through the cartridge body (not shown) and being connectable to an AC voltage source. As illustrated in FIG 4a, the rods 26 connected to the arm 24’ of the first electrode 20” and the rods 36 connected to the arm 34’ of the second electrode 30” are arranged in close proximity. Preferable planes A and B are substantially parallel. FIG 5 illustrates the lubricant cartridge 10’ comprising the electrode arrangement 18” of FIGs 4a-c. The lubricant cartridge 10’ comprises a cartridge body 12’which defines a lubricant reservoir 14’. The lubricant reservoir 14’contains a lubricant receiving and / or retain!ng medium, not shown, in which the first electrode 20” and second electrode 30” are embedded. Figure 6 illustrates a portion of a vacuum pump 100 comprising the lubricant cartridge 10’ of FIG 5. The vacuum pump 100 comprises a rotor shaft 110 and a roller bearing 120 for supporting rotation of the rotor shaft 110. The rotor shaft 110 comprises a lubricant feed element 130, in the form of a conical oil feed nut, for transporting lubricant to the roller bearing 120. As shown, the lubricant feed element is tapered to allow transport of lubricant. The roller bearing 120 is located within a bearing housing 125. The roller bearing 120 is positioned between a first end portion of the rotor shaft 110 and the bearing housing 125. The bearing housing 125 may be integral with the vacuum pump housing (not shown) or a component fitted to the vacuum pump housing. The lubricant cartridge 10’ is inserted into a recess of the bearing housing 125. Preferably, the lubricant cartridge is releasably connected within the bearing housing 125 or the vacuum pump housing (not shown) to allow for easy replacement during servicing, thereby reducing service times. In use, the roller bearing 120 is supplied with lubricant from the lubricant cartridge 10', to form a load-carrying film that reduces friction and wear. The lubricant from the lubricant reservoir 14’ is transported to the lubricant feed element 130 via the one or more wicking elements 40’. From the lubricant feed element 130 the lubricant is then transported to the roller bearing 120, as indicated by the arrows in FIG 6. Lubricant that has passed through the roller bearing 120 returns to the lubricant reservoir 14’of the oil cartridge 10’via one or more lubricant return channels 140. The lubricant within the oil reservoir 14’ is stored within the one or more lubricant receiving and / or retaining medium (not shown). The electrode arrangement 18” of FIG 4a is embedded within the one or more lubricant receiving and / or retaining media. This ensures that the electrodes 20”, 30” are in contact with the lubricant to ensure accurate and reliable lubricant monitoring. The electrodes 20”, 30” are connected to an AC voltage source and a controller (not shown) via their respective connecting element 29, 39, The controller is preferably the pump controller, which is configured to measure an electrical parameter of the lubricant. The pump controller may be configured for electrochemical monitoring via incorporation of a capacitance to digital convertor device or dedicated measurement technique, for example a capacitance bridge. At least one of the electrodes 20”, 30” is grounded, preferably via connection to a common ground with the cartridge body 12’, which forms an additional electrode. The controller may also be configured to emit a warning signal when the measured electrical parameter and / or the rate of change of the electrical parameter of the lubricant reaches, exceeds or decreases below a threshold value. This indicated to the user that a service should be scheduled. REFERENCE NUMERALS 10,10’ lubricant cartridge 12, 12’ cartridge body 13 o-ring 14, 14’ lubricant reservoir 16 lubricant receiving and / or retaining medium 5 18, 18’, 18” electrode arrangement 20, 20’, 20” first electrode 22, 22’ inner ring 24, 24’ arm 26 rod 10 28 tip 29 connecting element 30, 30’, 30” second electrode 32, 32’ outer ring 34, 34’ arm 15 36 rod 38 tip 39 connecting element 40, 40’ wicking element 42 plain felt disc 20 50 temperature sensor 100 vacuum pump 110 rotor shaft 120 roller bearing 125 bearing housing 25 130 lubricant feed element 140 lubricant return channels

Claims

1. A. lubricant cartridge for use in a vacuum pump comprising:a cartridge body defining a lubricant reservoir;at least one lubricant receiving and / or retaining medium located within the lubricant reservoir; whereinsaid at least one lubricant receiving and / or retaining medium contains an embedded electrode arrangement; and, wherein the electrode arrangement is connectable to a controller for detecting changes in an electrical parameter of lubricant within the lubricant reservoir.

2. The lubricant cartridge of claim 1, wherein the electrode arrangement comprises at least a first electrode and a second electrode arranged about the first electrode.

3. The lubricant cartridge of claim 2, wherein the first electrode and the second electrode are ring electrodes.

4. The lubricant cartridge of claim 2 or 3, wherein the first electrode comprises an inner ring and a plurality of arms extending outwardly from the inner ring.

5. The lubricant cartridge of any of claims 2 to 4, wherein the second electrode comprises an outer ring and a plurality of arms extending inwardly from the outer ring.

6. The lubricant cartridge of claim 4 or 5, wherein at least one of the arms comprises a plurality of rods extending outwardly therefrom.

7. The lubricant cartridge of claim 6, wherein each rod of the plurality of rods comprises a tip for piercing the lubricant receiving and / or retaining medium.

8. The lubricant cartridge of any preceding claim, comprising a temperature sensor.

9. The lubricant cartridge of claim 8, wherein the temperature sensor is embedded within the at least one lubricant receiving and / or retaining medium.

10. The lubricant cartridge of any preceding claim, wherein the at least one receiving and / or retaining medium is a lubricant absorbent element for retaining lubricant within the reservoir.

11. The lubricant cartridge of any of claims 1 to 9, wherein the at least one receiving and / or retaining medium is a lubricant filter.

12. A combination of:the lubricant cartridge of any preceding claim, anda controller connected to the electrode arrangement and configured to detect changes to an electrical parameter of the lubricant.

13. The combination of claim 12, when dependant from claim 8, wherein the temperature sensor is connected to the controller, which is configured to derive temperature compensated values of said electrical parameter.

14. The combination of claim 12 or 13, wherein the electrical parameter is one of relative 5 permittivity, conductivity, inductance and / or complex impedance of the lubricant.

15. The combination of any of claims 12 to 14, wherein the controller is configured to emit a warning signal when the electrical parameter and / or the rate of change of the electrical parameter reaches, exceeds or decreases below a threshold value.

16. A vacuum pump comprising;10 a housing having an inlet and an outlet;at least one rotor arranged within the housing;at least two bearings for supporting the rotor;a lubricant cartridge comprising a cartridge body defining a lubricant reservoir, and at leastone lubricant receiving and / or retaining medium located within the lubricant reservoir, 15 wherein said at least one lubricant receiving and / or retaining medium contains an embedded electrode arrangement; anda controller connected to the electrode arrangement and configured to detect changes in an electrical parameter of the lubricant.15

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