Aerosol provision system with liquid amount estimation

Abstract

A device for an aerosol provision system comprises a controller configured to: obtain a power level value indicating a level of power applied to a vaporiser of the aerosol provision system during a puff taken by a user, the vaporiser configured to generate aerosol by vaporising liquid from a reservoir of the aerosol provision system; obtain a puff duration value indicating a duration of the puff; determine a mass of aerosol generated by the vaporiser during the puff using the power level value and the puff duration value; and estimate an amount of liquid in the reservoir after the puff by using the determined mass of aerosol and a known amount of liquid in the reservoir prior to the puff.

Description

[0001] AEROSOL PROVISION SYSTEM WITH LIQUID AMOUNT ESTIMATION Technical Field

[0002] The present disclosure relates to a device for an aerosol provision system configured to estimate an amount of liquid in a reservoir of the aerosol provision system, an aerosol provision comprising such a device, and a method for estimating a liquid amount in an aerosol provision system.

[0003] Background

[0004] Aerosol provision systems which deliver aerosol for inhalation by a user are known, and include e-cigarettes and other electronic nicotine delivery systems that deliver nicotine in the aerosol. In some systems, the aerosol is generated by vaporising liquid to form a vapour, which is entrained in a flow of air drawn through the system as a user inhales or “puffs” on a mouthpiece of the system. Vaporisation is often produced by heating the liquid with an electrically powered heater comprising one or more heating elements; these and similar arrangements can be referred to as a vaporiser. The liquid is stored in a tank or reservoir of the system, and delivered to the vaporiser at a suitable rate in order to be vaporised. For example, this may be achieved by a porous wick which establishes a liquid flow path between the interior of the reservoir and the heater.

[0005] The user can continue to use the aerosol provision system for as long as there is liquid available in the reservoir. When the liquid has been consumed, no more aerosol can be generated and, depending on the design of the system, the user has to replace the whole system, replace the reservoir with a new full reservoir, replace a cartridge part of the system that includes the reservoir and possibly the vaporiser with a new cartridge having a full reservoir, or refill the reservoir with more liquid from a separate store. It is useful if the user is able to monitor the consumption of the liquid, for example to keep track of their usage of the aerosol provision system, and also to be aware when the reservoir is becoming empty so that preparation can be made for any of the above actions for obtaining a new supply of liquid. A range of options have been suggested for this, including a reservoir with a transparent wall through which the user can directly observe the amount of remaining liquid, and a variety of sensors that are configured to measure or detect the level of liquid in the reservoir. These approaches require particular features of or directly associated with the reservoir, however, which may need to be replaced together with the reservoir in systems having a replaceable cartridge.

[0006] Approaches for determining an amount of liquid in the reservoir of an aerosol provision system therefore of interest.

[0007] Summary

[0008] According to a first aspect of some embodiments described herein, there is provided a device for an aerosol provision system comprising: a controller configured to: obtain a power level value indicating a level of power applied to a vaporiser of the aerosol provision system during a puff taken by a user, the vaporiser configured to generate aerosol by vaporising liquid from a reservoir of the aerosol provision system; obtain a puff duration value indicating a duration of the puff; determine a mass of aerosol generated by the vaporiser during the puff using the power level value and the puff duration value; and estimate an amount of liquid in the reservoir after the puff by using the determined mass of aerosol and a known amount of liquid in the reservoir prior to the puff.

[0009] According to a second aspect of some embodiments described herein, there is provided an aerosol provision system comprising a device according to the first aspect.

[0010] According to a third aspect of some embodiments described herein, there is provided a method for estimating a liquid amount in an aerosol provision system, the method comprising: obtaining a power level value indicating a level of power applied to a vaporiser of the aerosol provision system during a puff taken by a user, the vaporiser configured to generate aerosol by vaporising liquid from a reservoir of the aerosol provision system; obtaining a puff duration value indicating a duration of the puff; determining a mass of aerosol generated by the vaporiser during the puff using the power level value and the puff duration value; and estimating an amount of liquid in the reservoir after the puff by using the determined mass of aerosol and a known amount of liquid in the reservoir prior to the puff.

[0011] These and further aspects of the certain embodiments are set out in the appended independent and dependent claims. It will be appreciated that features of the dependent claims may be combined with each other and features of the independent claims in combinations other than those explicitly set out in the claims. Furthermore, the approach described herein is not restricted to specific embodiments such as set out below, but includes and contemplates any appropriate combinations of features presented herein. For example, an aerosol provision system, an aerosol provision system device, and a method may be provided in accordance with approaches described herein which includes any one or more of the various features described below as appropriate.

[0012] Brief Description of the Drawings

[0013] Various embodiments of the invention will now be described in detail by way of example only with reference to the following drawings in which:

[0014] Figure 1 shows a simplified schematic longitudinal cross-section through an example aerosol provision system to which aspects of the disclosure can be applied;

[0015] Figure 2 shows a graph of aerosol collected mass measurements against puff duration for a range of vaporiser power levels collected from a population of aerosol provision systems with a same type of vaporiser;

[0016] Figure 3 shows the graph of Figure 2 with linear best fit lines added for each vaporiser power level; Figure 4 shows the graph of Figure 2 with nonlinear best fit lines added for each vaporiser power level;

[0017] Figure 5 shows a simplified longitudinal cross-section through an aerosol provision system configured according to examples of an aspect of the present disclosure;

[0018] Figure 6 shows a simplified schematic graph of aerosol mass against puff parameters with lines for three different liquid types and with offset values indicated for adjusting the line for one liquid to the other liquid types;

[0019] Figure 7 shows a highly schematic representation of a first example of representations that can be shown on an indicator of an aerosol provision system to indicate liquid amount in a reservoir to a user;

[0020] Figure 8 shows a highly schematic representation of a second example of representations that can be shown on an indicator of an aerosol provision system to indicate liquid amount to a user; and

[0021] Figure 9 shows a flow chart of steps in an example method for estimating liquid amount in an aerosol provision system according to an aspect of the present disclosure.

[0022] Detailed Description

[0023] Aspects and features of certain examples and embodiments are discussed I described herein. Some aspects and features of certain examples and embodiments may be implemented conventionally and these are not discussed I described in detail in the interests of brevity. It will thus be appreciated that aspects and features of apparatus and method discussed herein which are not described in detail may be implemented in accordance with any conventional techniques for implementing such aspects and features.

[0024] As described above, the present disclosure relates to electronic aerosol or vapour provision systems, such as e-cigarettes. Throughout the following description the terms “e- cigarette” and “electronic cigarette” may sometimes be used; however, it will be appreciated these terms may be used interchangeably with aerosol (vapour) provision system or device. The systems are intended to generate an inhalable aerosol by vaporisation of an aerosolforming substrate in the form of a liquid or gel which may or may not contain nicotine. Additionally, hybrid systems may comprise a liquid or gel substrate plus a solid substrate which is also heated. The solid substrate may be for example tobacco or other non-tobacco products, which may or may not contain nicotine. The term “aerosolisable substrate material” as used herein is intended to refer to substrate materials which can form an aerosol, either through the application of heat or some other means. The term “aerosol” may be used interchangeably with “vapour”.

[0025] As used herein, the term “component” is used to refer to a part, section, unit, module, assembly or similar of an electronic cigarette or similar device that incorporates several smaller parts or elements, possibly within an exterior housing or wall. An electronic cigarette may be formed or built from one or more such components, and the components may be removably or separably connectable to one another, or may be permanently joined together during manufacture to define the whole electronic cigarette. For example, a system may comprise (at least) two components separably connectable to one another and configured, for example, as an aerosolisable substrate material carrying component holding liquid or another aerosolisable substrate material (a cartridge, cartomiser or consumable, or simply “pod”), and a control unit or device (“device”) component having a controller for controlling operation of the aerosol provision system, and a battery for providing electrical power to operate an element for generating vapour from the substrate material. For the sake of providing a concrete example, in the present disclosure, a cartridge or cartomiser (cartridge component or consumable) is described as an example of the aerosolisable substrate material carrying portion or component in which the aerosolisable substrate material is a liquid or a gel held in a reservoir or tank (storage area), but the disclosure is not limited in this regard and is applicable to any configuration of aerosol provision system having a liquid reservoir. A cartridge component may include more or fewer parts than those included in the examples. This is true also of the device component.

[0026] The present disclosure is particularly relevant to aerosol provision systems and components thereof that utilise aerosolisable substrate material in the form of a liquid or a gel which is held in a reservoir, tank, container or other receptacle comprised in the system. In such systems an arrangement for delivering the substrate material from the reservoir for the purpose of providing it for vapour I aerosol generation is included. The terms “liquid”, “gel”, “fluid”, “source liquid”, “source gel”, “source fluid” and the like may be used interchangeably with “aerosolisable substrate material” and “substrate material” to refer to aerosolisable substrate material that has a form capable of being stored and delivered in accordance with examples of the present disclosure.

[0027] Figure 1 is a highly schematic diagram (not to scale) of a generic example aerosol / vapour provision system such as an e-cigarette 10, presented for the purpose of showing the relationship between the various parts of a typical system and explaining the general principles of operation. The e-cigarette 10 has a generally elongate shape in this example, extending along a longitudinal axis indicated by a dashed line, and comprises two main components, namely a control or power component, section or unit (device component) 20, and a cartridge component, assembly or section 30 (sometimes referred to as a cartomiser or clearomiser) carrying aerosolisable substrate material and operating as a vapourgenerating component.

[0028] The cartridge component 30 includes a reservoir 3 containing a source liquid or other aerosolisable substrate material comprising a formulation such as liquid or gel from which an aerosol is to be generated, for example containing nicotine. As an example, the source liquid may comprise around 1 to 3% nicotine and 50% glycerol, with the remainder comprising roughly equal measures of water and propylene glycol, and possibly also comprising other components, such as flavourings. Nicotine-free source liquid may also be used, such as to deliver flavouring. A solid substrate (not illustrated), such as a portion of tobacco or other flavour element through which vapour generated from the liquid is passed, may also be included. The reservoir 3 has the form of a storage tank, being a container or receptacle in which source liquid can be stored such that the liquid is free to move and flow within the confines of the tank. For a consumable cartridge component 30, the reservoir 3 may be sealed after filling during manufacture so as to be disposable after the source liquid is consumed, otherwise, it may have an inlet port or other opening through which new source liquid can be added by the user. The cartridge component 30 also comprises an electrically powered heating element or heater 4 located externally of the reservoir tank 3 for generating the aerosol by vaporisation of the source liquid by heating. Note that in other examples, source liquid may be generated by an alternative powered means such as a vibrating mesh. More generally, the powered means that vaporise the liquid may be referred to as a vapour generating element or vaporiser. A liquid transfer or delivery arrangement (liquid transport element) such as a wick or other porous element 6 may be provided to deliver source liquid from the reservoir 3 to the heater 4 or other vapour generator. A wick 6 may have one or more parts located inside the reservoir 3, or otherwise be in fluid communication with the liquid in the reservoir 3, so as to be able to absorb source liquid and transfer it by wicking or capillary action to other parts of the wick 6 that are adjacent or in contact with the heater 4. This liquid is thereby heated and vaporised, to be replaced by new source liquid from the reservoir for transfer to the heater 4 by the wick 6. The wick may be thought of as a bridge, path or conduit between the reservoir 3 and the heater 4 that delivers or transfers liquid from the reservoir to the heater. Terms including conduit, liquid conduit, liquid transfer path, liquid delivery path, liquid transfer mechanism or element, and liquid delivery mechanism or element may all be used interchangeably herein to refer to a wick or corresponding component or structure.

[0029] A heater and wick (or similar) combination is sometimes referred to as an atomiser or atomiser assembly 7, and the reservoir 3 with its source liquid plus the atomiser 7 may be collectively referred to as an aerosol source. Other terminology may include a liquid delivery assembly or a liquid transfer assembly, where in the present context these terms may be used interchangeably to refer to a vapour-generating element (vapour generator) plus a wicking or similar component or structure (liquid transport element) that delivers or transfers liquid obtained from a reservoir to the vapour generator for vapour I aerosol generation. Various designs are possible, in which the parts may be differently arranged compared with the highly schematic representation of Figure 1. For example, the wick 6 may be an entirely separate element from the heater 4, or the heater 4 may be configured to be porous and able to perform at least part of the wicking function directly (a conductive mesh, such as a metallic mesh, for example). In an electrical or electronic device, the vapour generating element may be an electrical heating element that operates by ohmic / resistive (Joule) heating or by inductive heating. In general, therefore, an atomiser can be considered as one or more elements that implement the functionality of a vapour-generating or vaporising element able to generate vapour from source liquid delivered to it, and a liquid transport or delivery element able to deliver or transport liquid from a reservoir or similar liquid store to the vapour generator by a wicking action I capillary force. An atomiser is typically housed in a cartridge component of an aerosol generating system. In some designs, liquid may be dispensed from a reservoir directly onto a vapour generator with no need for a distinct wicking or capillary element. Embodiments of the disclosure are applicable to all and any such configurations which are consistent with the examples and description herein.

[0030] Returning to Figure 1 , the cartridge component 30 also includes a mouthpiece or mouthpiece portion 35 having an opening or aerosol outlet through which a user may inhale the aerosol generated by the atomiser 7. A single inhalation, during which the user obtains an amount of aerosol, will be referred to herein as a “puff”. In other designs, a mouthpiece may be provided as a separate component which may be permanently or separably connectable to the cartridge component 30.

[0031] The power component or control unit or, simply, device or device component 20 includes a cell or battery 5 (referred to hereinafter as a battery, and which may be rechargeable) to provide power for electrical components of the e-cigarette 10, in particular to operate the vaporiser such as the heater 4. Additionally, there is a controller 28 such as a printed circuit board and / or other electronics or circuitry for generally controlling the e- cigarette. The control electronics / circuitry 28 operates the heater 4 using power from the battery 5 when vapour is required, for example in response to a signal from an air pressure sensor or air flow sensor (“puff sensor”, not shown) that detects an inhalation on the system 10 during which air enters through one or more air inlets 26 in the wall of the device component 20. When the heater 4 is operated, the heater 4 vaporises source liquid delivered from the reservoir 3 by the liquid delivery element 6 to generate the aerosol, and this is then inhaled by a user through the opening in the mouthpiece 35. The aerosol is carried from the aerosol source to the mouthpiece 35 along one or more air flow channels (not shown in Figure 1) that connect the air inlet(s) 26 to the aerosol source to the aerosol outlet when a user inhales on the mouthpiece 35. Since in this example the air inlets 26 to the system are located in the device component 20, the cartridge component 30 has its own air inlet(s) in air flow communication with the device component 20 so that air drawn in through the device component air inlet(s) 26 can reach the interior of the cartridge component 30, and the atomiser 7. In other designs, air inlets may be located in the outer wall of the cartridge component 30 so that air enters directly into the cartridge component 30 instead of arriving there via the device component 20.

[0032] The device component (control unit) 20 and the cartridge component (cartomiser, consumable) 30 are, in this example, separate connectable parts detachable from and reattachable to one another by movement in a direction parallel to the longitudinal axis, as indicated by the double-headed arrows in Figure 1. Each component 20, 30 has a connecting portion 21 , 31 at an end facing towards the corresponding end of the other component, and the components 20, 30 are joined together when the aerosol provision system 10 is ready for use or in use by cooperating engagement elements at the connecting portions 21 , 31 (for example, a screw or bayonet fitting, or a push-fit, snap-fit or magnetic connection) which provide mechanical and in the present case electrical connectivity between the device component 20 and the cartridge component 30. Electrical connectivity is required if the heater

[0033] 4 operates by ohmic heating, or where a vibrating mesh vapour generator or other electrically powered vaporiser is used, so that current can be passed through the heater 4 or otherwise supplied to the vaporiser, and / or to any other electrically powered parts in the cartridge component 30, when these parts in the cartridge component 30 are connected to the battery

[0034] 5 in the device component 20. In systems that use inductive heating, electrical connectivity for vapour generation can be omitted if no vapour generating parts requiring electrical power are located in the cartridge component 30, although electrical power may still need to be supplied to other electrical parts in the cartridge component. For inductive heating, an inductive work coil can be housed in the device component 20 and supplied with power from the battery 5, and the cartridge component 30 and the device component 20 shaped so that when they are connected, there is an appropriate exposure of the heater 4 to flux generated by the coil for the purpose of generating current flow in the material of the heater 4. For all non-inductively powered parts, the connecting portions 21 , 31 include electrical contacts to complete electrical circuits between the powered parts and the battery 5 when the cartridge component 30 and the device component 20 are connected together. Also, apertures for air flow from the device component 20 to the cartridge component 30 are included at the connecting portions 21 , 31 of the two components 20, 30 in designs having one or more air inlets 26 in the outer wall(s) of the device component 20. The connecting portions 21 , 31 therefore provide an interface between the cartridge component 30 and the device component 20. The Figure 1 design is merely an example arrangement, and the various parts and features may be differently distributed between the device component 20 and the cartridge component 30, and other undepicted elements may be included. The two components 20, 30 may connect together end-to-end in a longitudinal configuration as in Figure 1 , or in a different configuration such as a parallel, side-by-side arrangement. The system may or may not be generally cylindrical and / or have a generally longitudinal shape. Either or both components 20, 30 may be intended to be disposed of and replaced when exhausted (the reservoir 3 is empty or the battery 5 is flat, for example), or be intended for multiple uses enabled by actions such as refilling the reservoir 3, replacing the reservoir independently of the cartridge component 30, and recharging the battery 5. In other examples, the aerosol provision system 10 may be unitary, in that the parts of the device component 20 and the cartridge component 30 are comprised in a single housing and cannot be separated. Embodiments and examples of the present disclosure are applicable to any of these configurations and other configurations of which the skilled person will be aware.

[0035] During operation of an aerosol provision system, an amount of aerosol is generated during a puff on the system, the aerosol being delivered to the user via the mouthpiece for inhalation. The aerosol is generated by vaporisation of liquid taken from the reservoir, so the amount of aerosol in a puff corresponds to an amount of liquid vaporised to produce the puff, and as puffs continue, the liquid is consumed and the amount of liquid remaining in the reservoir reduces. In particular, a mass of the aerosol in a puff is related to the mass of the liquid used to generate the aerosol of that puff. It is proposed herein to use the relationship between aerosol amount generation and liquid consumption to estimate a remaining amount of liquid in the reservoir. By determining the mass of aerosol in one or more puffs, the remaining amount of liquid in the reservoir may be estimated by subtraction of the mass of aerosol that has been generated from a mass of liquid in the reservoir at a previous time, such as the total liquid mass in the reservoir when full if the total accumulated aerosol mass is tracked, or the liquid mass in the reservoir before a particular puff if the aerosol mass of that puff is determined. Mass is a convenient metric to use for this procedure, but other metrics might also be used, such as volume, or a relationship between one metric for aerosol amount and another metric for liquid amount.

[0036] Since the generated aerosol is delivered internally to the user via inhalation, it is not feasible to directly measure the amount of aerosol in an actual real life puff when the user uses the aerosol provision system. However, the amount of aerosol which is generated during a puff depends on operating parameters of the aerosol provision system which can be measured. For example, more aerosol is generated in a longer puff than in a shorter puff, so aerosol amount depends on puff duration. A higher amount of power delivered to the vaporiser during the puff can also increase the amount of aerosol, for example by heating a heating element of the vaporiser to a higher temperature, so aerosol amount depends on vaporiser operating power level. Factors such as these can be readily measured during operation of an aerosol provision system, and the controller may be configured to use measured or otherwise ascertained values for these factors to determine an amount of aerosol in a puff using a predetermined relationship between these factors and aerosol amount. From this, a corresponding decrease in the amount of liquid in the reservoir can be determined, allowing a remaining amount of liquid to be estimated. This can then be reported or indicated to the user. The user can then be aware of their liquid consumption, and prepare for replacement or refilling of the reservoir as it approaches an empty state.

[0037] It is contemplated that any technique for determining aerosol amount in a manner that allows the amount of generated aerosol to be subtracted from the amount of liquid in the reservoir in a meaningful way may be used. As noted above, mass is a useful metric for this purpose. If mass is used, an approach proposed herein for determination of the mass of aerosol generated in a puff is to use a metric designated as aerosol collected mass (ACM).

[0038] The ACM may characteristically refer to a mass of aerosol collected, in laboratory or test conditions, externally from the aerosol provision system during one or more puffs of the device. The ACM may be determined for a given aerosol provision system under certain operating conditions by collecting aerosol in a laboratory aerosol analyser I puff analyser during one or more puffs carried out under controlled conditions of airflow (for example, of airflow duration and airflow rate profile) by the aerosol analyser. The aerosol for a known number of one or more puffs is collected, for example on a fibrous pad, or otherwise condensed out of the aerosol I vapour phase for analysis, and then weighed to determine its mass. The mass of aerosol generated in a puff by a known aerosol generating system operating with known values of operational parameters of the aerosol generating system is thereby determined.

[0039] Using this approach, the aerosol mass for a puff under various operating conditions can be ascertained from one particular example of the aerosol generating system. However, users in the future will be using other aerosol generating systems, which may not function identically to the tested aerosol generating system even if all the systems are of the same design. It is known that there can be considerable system-to-system variation that affects aerosol generation, arising from factors including manufacturing variation and user puff techniques, so that no two systems, even when of intended exactly identical design, will perform exactly identically and generate exactly the same amount of aerosol in a puff under identical operating conditions. In order to obtain meaningful ACM data which can employed for the purpose proposed herein of estimating liquid amount in a reservoir, it is proposed to collect ACM data from populations of aerosol provision systems of the same design or type, in particular having vaporisers of the same type, and use this data to empirically derive a relationship between aerosol mass per puff and values of operating parameters of the aerosol provision systems that can be applied, to determine aerosol mass per puff, in aerosol provision systems of the same type which are later supplied to users. The use of data from a population allows an averaging effect across system-to-system variations, and it has been found that the resulting relationship provides a result which is accurate enough to enable reservoir liquid amount estimation at an accuracy level which is useful to users. Another source of potential error may be noted, in that the collected mass of aerosol may differ from the mass of liquid which was vaporised, since some aerosol may condense in or on parts of the aerosol delivery system or the aerosol analyser or otherwise be diverted and not collected for weighing. Nevertheless, it has been found that this does not affect the measured data significantly enough to undermine the usability of the ascertained relationship for the purpose of estimated reservoir liquid amount, and may be ignored.

[0040] As with averaging techniques in general, the accuracy of the determined relationship between aerosol mass generated and values of the aerosol provision system operating parameters which is ascertained from ACM data obtained empirically as described above can be improved by increasing the size of the population of aerosol provision systems of the same type or with the same vaporiser type from which the data is collected. Hence, it is suggested that as large a population as possible is used, within limits set by factors such as time, cost, and the number of vaporisers and / or systems which are available for the purpose. For example, a population comprising about 20 or about 50 or about 100 individual vaporisers or aerosol provision systems (where individual vaporisers, for example included within individual cartridges which are used in turn with the same device or a smaller number of devices to make complete aerosol provision systems) of the same type may be used to obtain a body of ACM data. Larger or smaller populations are not excluded, however.

[0041] It is recognised that many factors affect the amount of aerosol which is comprised within a single puff made on an aerosol provision system of a particular type and design. These include tolerances in part manufacturing and assembly, ambient pressure, humidity, ambient temperature, the temperature of the liquid, properties of the liquid, the strength of the puff (air flow rate through the system and past the vaporiser), puff duration, recent puff history, power level applied to the vaporiser, actual operating power of the vaporiser including electrical tolerances, and efficiency of the vaporiser. If account were to be taken of all the variables when attempting to determine the amount or mass of aerosol in any given puff, the determination would become very laborious. Moreover, some of the factors are not straightforward to measure or account for. Other factors have been determined by experiment to not have a significant effect, so may be ignored without detriment to the estimation. These include the temperature of the liquid, the airflow rate during a puff, and the time between puffs.

[0042] Accordingly, it is proposed herein to concentrate on a small number of readily measurable and verifiable parameters. In a first example, it has been found that sufficient accuracy to enable meaningful reservoir liquid amount reporting to a user can be obtained by considering the level of electrical power applied to the vaporiser (which will typically be a heater, but as noted above, may not be), and the duration of the puff. These two parameters are typically straightforward to ascertain within an aerosol provision system. In some very simple systems, the power supply (battery) delivers only a fixed power level to the vaporiser, so that a single power level value can be provided to the controller of the aerosol provision system for use in liquid amount estimation. More sophisticated aerosol provision systems allow the user to set the power level, perhaps by selection of one power level from a quantity of available power levels, or by adjustment within an available continuous power level range. The selected power regime may correspond to a constant power level over a puff or to a profile of varying power level over a puff. The controller is configured to control the battery to supply the selected power level to the vaporiser, so that the controller has access to the value of the power level which is used for any given puff.

[0043] Regarding puff duration, some aerosol provision systems are “puff activated” and include a so-called puff detector or puff sensor, which is a sensor configured to detect when a user inhales on the system. Such sensors detect changes in air flow or air pressure, and are typically used to activate the aerosol provision system for operation. When an inhalation is detected, the sensor sends a signal to the controller, which responds by controlling the supply of power to the vaporiser so that vapour is generated, and stops the supply of power at the end of the puff, when the sensor detects that inhalation has ceased. In such an arrangement, the controller may be provided with a clock configured to time the length of the puff, so that the controller can thereby obtain a value of the duration of the puff. Other aerosol provision systems are activated by a user operated control element on the aerosol provision system, such as a switch or a button, by which the user indicates that aerosol generation is required, in response to which the controller controls the power to be supplied to the vaporiser. For example, the user may press a button at the same time as inhaling on the aerosol provision system, so that the vaporiser is powered for the duration of the button press. In such a system, a puff sensor may be provided for the sole purpose of allowing puff duration to be measured, as described above, rather than for activating aerosol generation. Alternatively, the operation of the user control element may be used as a proxy for puff duration, if it is assumed that the user will operate the user control element to obtain aerosol for approximately the duration of their puff. Hence, a clock may be provided which is configured to time the period between the start and stop of the user control operation, for example, the duration for which a button is pressed, or the time elapsed between a switch being turned on and then off. This time period can then be taken by the controller as a value for the duration of the puff.

[0044] Therefore, in order to obtain empirical data from which an appropriate equation relating aerosol mass to power level and puff duration, measurements of ACM can be made for a range of different known power level values and known puff duration values, using a population of aerosol provision systems of the same design and / or having a same design of vaporiser. The equation can then be obtained by fitting a function or functions to the empirical data. Figure 2 shows a graph of empirical data obtained in this way from a population of aerosol provision systems of the same type, in that a population of pods or cartridges of the same design, each having an electrically powered vaporiser in the form of an electrical heating element and a reservoir of aerosolisable liquid, were used together with one or more different devices to form the population of aerosol provision systems. The graph indicates puff duration in seconds on the x-axis, and ACM per puff in milligrams on the y-axis. Each data point represents an amount of aerosol, as the ACM, per puff averaged over 25 puffs, measured in laboratory conditions. A selection of different power level values were used for each puff duration value, as indicated. It can be seen that for each power level value and puff duration value combination, the data points cluster together but do show some variation, arising from the pod-to-pod or system-to-system variation discussed below. It is this variation that the proposed approach aims to address, by suggesting an implementation that turns variable experimental data obtained from a specific population of aerosol provision systems into a workable algorithm applicable to a wider group of the same type of aerosol provision system when used in real world conditions.

[0045] Figure 3 shows the graph of Figure 2, with best fit linear functions also shown, for each power level value. Hence a group of best fit lines is obtained, each relating ACM to puff duration value, for each power level value. The functions describing these lines can be then be combined in order to obtain an equation that relates both power level value and puff duration value to ACM. If the ACM is taken as corresponding to the actual mass of aerosol in a puff, M in milligrams, and purely as an example, the equation may have the following form:

[0046] M = A - Bt - CP + DtP where A, B, C and D are constants, t is the puff duration value in seconds and P is the power level value in watts. As an illustration, for one particular aerosol provision system type, values for the constants were determined to be A = 0.760722, B = 1.150802, C = 0.432436 and D = 0.622964. The skilled person will understand that different values for the constants, and indeed a different form for the equation, may be determined from other empirical data and other mathematical techniques.

[0047] Two sources of error can be identified when using an equation of this type, obtained by linear fitting to empirical data. There is a systematic error arising from the mathematical approach taken to derive a single equation from a spread of data points. The value of the aerosol mass predicted using the equation may fall relatively far from the mean of the empirical data, so that a calculated aerosol mass may not accurately reflect the actual aerosol mass in a real puff. This may be found to be worse in some operating regions, for example in the box 40 in Figure 3 for the illustrated empirical data, and at shorter puff durations, as shown in the magnified inset 42. These issues may to some extent be addressed by collecting empirical data from a larger population of aerosol provision systems, to improve the accuracy of the function fitting. There is also the random pod-to-pod or system-to-system error mentioned above, arising from manufacturing and operational differences and variations between vaporisers, reservoirs and overall aerosol provision systems. Even if the best-fit line is very accurate so that the equation can perfectly predict the mean value for the aerosol mass at a puff-duration and power level combination, there will be variation around the mean which is unpredictable so that in a real life situation the calculated aerosol mass will likely differ from the actual aerosol mass in an actual puff. Nevertheless, it has been found that the proposed approach is still sufficiently accurate to enable useful estimation of remaining liquid amount that can be reported to the user is a meaningful way.

[0048] While linear fitting to empirical data is straightforward to achieve, and may provide a relatively simple equation that can be efficiently computed to calculate aerosol mass during use of an aerosol provision system, more complex fitting may be applied to the empirical data in some other examples, by fitting a nonlinear function to the data. This can improve accuracy of the determined aerosol mass. Any nonlinear mathematical function may be chosen to best fit a curve to the empirical data; the skilled person will understand how to achieve this with reference to the nature of the data obtained from the laboratory measurements. Examples of suitable functions include, but are not limited to, a quadratic or cubic polynomial function, or a polynomial function of higher order, a spline function, or a piece-wise linear function.

[0049] Figure 4 again shows the graph of Figure 2, and differs from Figure 3 in that best fit nonlinear functions are shown fitted to the data for each power level value. As before, the functions describing the best fit lines can be then be combined in order to obtain a single equation that relates both power level value and puff duration value to ACM. Again, this equation can be used to calculate aerosol mass in a puff from the power level value and duration of the puff. A comparison of Figure 4 with Figure 3 shows that the systematic error is reduced compared to the linear fitting, and is much closer to zero since the predicted value, indicated by the line, is much closer to the mean of the measured data. The unpredictable pod-to-pod variation remains, but on average the overall error should be lower than when linear fitting is used. Improvement is particular significant at lower puff durations, as indicated by the magnified inset 44. To improve this further, more empirical data could be collected for shorter puff durations, for example, for other puff duration values near to one second, such as at and / or between 0.5 seconds and 1 .5 seconds.

[0050] Hence, an equation that relates aerosol mass of a puff to the power level value at the vaporiser used to generate the aerosol in the puff, and the value of the duration of the puff, can be obtained from empirical data measured in laboratory conditions. This equation can be provided to the controller of an aerosol provision system, and stored in memory of the controller (or memory accessible by the controller). The controller is configured to obtain a value of the power level and a value of the puff duration during puffs taken on the aerosol provision system, as described above. When the user takes a puff on the aerosol provision system, the controller obtains the power level value and the puff duration value, and uses these values, with the equation, to determine a mass of the aerosol contained in the puff that has been taken. The controller is further configured to use the determined mass of aerosol to estimate an amount of liquid in the reservoir of the aerosol provision system.

[0051] Broadly, the estimation is achieved using the determined mass of aerosol in the puff and a known amount of liquid in the reservoir prior to the puff. This may be implemented in a variety of ways, in which the controller obtains or is provided with a value for the total capacity of the reservoir, being the amount of liquid contained in the reservoir when it is full, before any puffs have been taken. In some configurations, the pod or reservoir may not be replaceable, and the controller is provided during manufacture with a value for the total capacity of the reservoir. This may or may not be a mass; it could alternatively be a volume, which the controller is configured to convert to a mass, for example. In configurations in which the pod or reservoir can be replaced, it may be that only reservoirs of a single capacity are provided by the manufacturer, so that the value of this capacity is provided to the controller during manufacture, and the controller is configured to recognise when a new pod or reservoir is fitted, so that the amount of liquid in the reservoir at that time can be assumed to be equal to the pre-provided value for the total capacity.

[0052] In more complex arrangements, the controller may be configured to obtain an expected amount of liquid in the reservoir when the reservoir or pod is newly fitted to the aerosol provision system, or newly filled, that is, a value for the total liquid capacity of reservoir when it is full. It is known to provide reservoirs and / or pods / cartridges with identifying elements which can be read by a controller when the reservoir or pod is coupled to the device of the aerosol provision system in order to obtain identification information about the reservoir / pod. In the current context, this information may include or otherwise indicate a value of the reservoir’s total liquid capacity. The identification information may include items of data or information about the pod or reservoir, or may give a simple identification of the pod / reservoir from which the controller is able to ascertain the data or information, for example from a store of such data or information for different pods / reservoirs held in the controller or accessible by the controller from elsewhere. Examples of identifying elements include resistors, capacitors, chips or other electrical or electronic components in circuitry in the pod that can be electrically detected or interrogated by the controller, bar codes, QR codes or other indicia that can be optically read or otherwise sensed by a sensor or detector operated by the controller, and shaped features that engage with complementary features in or on the device, where the controller can sense the engagement. Other examples are not excluded. Where a refillable reservoir is provided, a refilling action may be detected, and reported to the controller, which can assume that after refilling the reservoir contains a liquid amount matching its total liquid capacity. Once the controller has obtained the total liquid capacity for the full reservoir, the amount of liquid consumed from the reservoir by conversion to aerosol in a puff can be determined per puff using the equation, and deducted from the known total liquid capacity in the reservoir to estimate the amount of liquid remaining in the reservoir. The controller may store the new, reduced amount of liquid, and deduct the aerosol amount in the next puff from that amount, and so on. In other words, the controller keeps track of the amount of aerosol in the reservoir as it depletes after each puff, and subtracts the aerosol amount of the each puff from the reservoir aerosol amount immediately prior to the puff. Alternatively, the controller may accumulate the total amount of aerosol generated by adding the aerosol amount in each puff to the amount in the previous puffs, and subtract the total aerosol amount from the original reservoir total liquid capacity when an estimate of the remaining liquid amount in the reservoir is required.

[0053] The estimate of the liquid amount in the reservoir may be stored by the controller and used internally by processes of the aerosol provision system, and / or it may be indicated or reported to the user. An example of a process may be automatic ordering of a replacement pod when the reservoir approaches depletion, if the aerosol provision system is configured to communication with a remote server or with a personal electronic device of the user such as a mobile phone. Indicating to the user may be done regularly or periodically, or on demand when the user operates a user control of the aerosol provision system to request an indication, or only when the reservoir is approaching an empty state (the remaining liquid amount falls below a predetermined threshold, for example) in order to warn the user that the supply of liquid is about to run out.

[0054] The controller may be configured to store the equation, and directly use the equation to determine the mass of aerosol in a puff by utilising the obtained values of power level and puff duration in the equation. This approach requires computation by the processor for each puff, but has a low storage requirement since only the equation needs storing. It can also give a relatively accurate determination of the aerosol amount for each puff, since the equation returns a value for the aerosol amount for any value of puff duration and power level; the equation performs an extrapolation between the selected discrete values of puff duration and power level for which the empirical data was collected, which may not correspond to the puff duration value and / or of the power level value for an actual puff.

[0055] In other examples, the controller may store a look-up table that stores, for multiple combinations of puff duration value and power level value, a corresponding value for the mass of aerosol in a puff with that combination of puff duration and power level. The controller is configured, when a puff takes places, to retrieve, from the look-up table, an aerosol mass value corresponding to the values of power level and puff duration that the controller has obtained for that puff. The look-up table therefore maps values of power level and values of puff duration to values of aerosol mass. The provision of a look-up table reduces computation by the controller, since there is no need to calculate a value for the equation for each puff, but has an increased storage requirement since a look-up table will be larger than the equation. Also, accuracy may be reduced, since the look-up table can comprise only a limited selection of possible values for the puff duration and the power level. In actuality, the puff duration, and possibly also the power level (depending on power selection implementation in the aerosol provision system) may take any value which may not correspond directly to a value in the lookup table. The controller therefore may therefore allocate an obtained value to the nearest value recorded in the look-up table, or it may always round up or round down the obtained value to the next recorded value. Alternatively, the look-up table may be configured to contain ranges of values of puff duration and / or power level, where the ranges map onto single values for aerosol mass. The look-up table may be populated using the equation to determine values for aerosol mass per puff for a selection of different power levels and puff durations, which may or may not correspond to the values for power level and puff duration used to collect the original empirical data.

[0056] Figure 5 shows a highly simplified schematic representation of an example of an aerosol provision system with a device configured to implement remaining liquid amount estimation as described herein. The aerosol provision system 10 is similar to the example shown in Figure 1 , and comprises a device component 20 and a cartridge or pod component 30. The system 10 may be unitary, or the pod component 30 may be replaceable. As before, the pod component 30 comprises a reservoir 3 for storing aerosolisable liquid, and having a total liquid capacity when full of liquid. The pod component 30 also comprises a vaporiser 4 for vaporising liquid from the reservoir in order to generate aerosol for delivery to the user during a puff. Also as before, the device component comprises a battery 5 for supplying electrical power to the vaporiser 4, and a controller 28 for controlling the supply of power from the battery 5 to the vaporiser 4. The controller 28 comprises a processor 22 for performing operations and actions such as controlling the supply of power, and estimating remaining liquid amount in the reservoir 3 as described herein. The controller 28 has a memory 23, in which is stored an equation for determining the aerosol amount in a puff, or a look-up table derived from the equation, as described above. The controller 28 also has a clock 24 for timing puff duration, either via a puff detector 32 or via detection of user operation of a button or other user operable control 27 to activate the vaporiser, again as described above. The pod component 30 may include an identifying element from which the controller may obtain a value for the reservoir’s total liquid capacity, again as described above. Finally, the aerosol provision system 10 may be provided with an indicator 29 such as a visual display on or in an outer housing or wall of the aerosol provision system 10, and operable by the controller 28 to display as indication of an estimated remaining liquid amount in the reservoir 3. Examples of indicators are described further below. Note that some parts of the aerosol provision system may be located differently from the Figure 5 example, for example within the other of the pod component and the device component.

[0057] The above examples have utilised vaporiser power level and puff duration as variable operating parameters that are taken into account to determine the amount of aerosol in a puff. As already mentioned, a variety of factors can affect the amount of aerosol in a puff, some of which can be considered as more or less difficult to account for or considered as more or less significant in their effect. In other examples disclosed here, the type of liquid in the reservoir, from which the aerosol is generated, is also taken into account. It has been determined that liquid type can have a relatively significant effect on the amount of aerosol generated in a puff, and it may be accounted for relatively straightforwardly, thereby improving accuracy of the remaining liquid amount estimation. The term “liquid type” is intended to acknowledge that liquid aerosol forming substrate that is vaporised to generate aerosol for delivery by an aerosol provision system is available in many different compositions. Liquids of different nicotine strength and different flavour are readily available, for example, and may be composed of different ingredients and differing proportions of ingredients, which may affect the rate and temperature at which the liquid vaporises. Hence, puffs at equal power and of equal duration carried out on the same aerosol provision system using different liquids may tend to contain different masses of aerosol. Hence, the use of a single equation to determine aerosol mass per puff without regard to the liquid type may produce varying accuracy of estimation of the remaining liquid amount.

[0058] It may be that a particular aerosol provision system is configured to only be used with a single liquid type. For example, the aerosol provision system may be of a design in which the pod or the reservoir cannot be replaced, or the reservoir cannot be refilled. In such a case, there is no need to take account of the type of liquid in estimating the remaining liquid amount in the reservoir. All that is required is that the empirical data from which the equation used by the controller for determining aerosol amount in a puff is collected using the same type of liquid as is contained in the reservoir, or alternatively a type of liquid with the same or similar vaporisation characteristics as the liquid type contained in the reservoir so that the equation is applicable and give sufficiently accurate results. In the current context, therefore, liquid of a particular type is considered to have vaporisation characteristics or behaviour different from liquid of another type.

[0059] Other aerosol provision systems are configured to allow the user to consume different liquid types, however, either by replacement of the pod or the reservoir with a pod or reservoir that may contain a different liquid type, or by refilling of the reservoir with a different liquid type. In such arrangements, it is useful if the controller is additionally able to take account of the liquid type when determining the mass of aerosol in a puff. Hence, in some examples, the controller may be configured to obtain an indication of the liquid type in the reservoir, and to determine the mass of aerosol using the indicated liquid type in addition to the power level value and the puff duration.

[0060] The liquid type may be indicated to the controller in any convenient manner. For example, the pod or reservoir may include an identifying element such as described above in the context of enabling the controller to ascertain the total liquid capacity of the reservoir. In the context of liquid type indication, the information or indication carried by the identifying element may include an indication of the liquid type, or enable the controller to access the liquid type from the identity of the pod / reservoir. Hence, the controller reads or detects an identifying element in or on the reservoir or the pod to obtain an indication of the liquid type. In other examples, the controller may be configured to more directly detect the liquid type, via one or more sensors or detectors able to detect a property or characteristic of the liquid. An optical detector may detect colour or opacity of the liquid for example, which may correspond to a liquid type. The liquid may contain an ingredient or additive that can be detected and which indicates liquid type, for example by fluorescing or having a particular reflective characteristic.

[0061] In order to account for the possibility of different liquid types in the reservoir, the empirical ACM data can be collected for two or more different liquids, in addition to different power levels and puff durations. An option is to derive a single equation from best fits lines or curves fitted to all the data, as described above, but since the liquid type is not a numerical value, this is not straightforward since numerical values would need to be attributed to each liquid type, reflecting their different vaporisation characteristics and the effect of this on aerosol generation, in order to incorporate liquid type as a parameter into the equation. Other approaches are therefore proposed.

[0062] In a first example, a separate equation is derived from ACM collected for each type of liquid. Hence, two or more equations are derived, and each equation is provided to the controller and stored against or otherwise labelled with its corresponding liquid type. The controller obtains an indication of the type of liquid in the reservoir as described above, and thereafter uses the appropriate equation for the indicated liquid type to estimate the remaining liquid amount, until the liquid amount in the reservoir is exhausted. When the reservoir is replaced or refilled, the controller obtains an indication of the liquid type now in the reservoir, and proceeds accordingly with the appropriate equation.

[0063] In other examples, a single equation is stored by the controller, together with offset values corresponding to different liquid types, and the controller is configured to apply an appropriate offset value to the result of the equation, corresponding to the indicated liquid type. An offset value compensates the mass of aerosol determined from the equation for the type of liquid which has been vaporised. An offset value may have the form of a percentage increase or decrease to be applied to the result of the equation, or an absolute value of an increase or a decrease, for example. Offset values can be determined by deriving an equation for each liquid type from the ACM empirical data, selecting one of the equations (perhaps that for a most commonly used liquid type) and assessing how much the function for each equation deviates from that for the selected equation. An offset value can then be applied by the controller to the result of the selected equation to adjust the result to or towards the result that would be calculated using the equation for the relevant liquid, when the liquid type differs from the liquid type of the selected equation. Several alternative approaches are proposed for the use of offsets.

[0064] In a first alternative, a single offset value is determined for each liquid type. This is a simple approach that assumes that the effect of a different liquid type on vaporisation is consistent across all power levels and puff durations, and the result of the equation can be adjusted upwards or downwards by a fixed amount or fixed percentage to compensate for the effects of that liquid. This is advantageous in that storage requirements for storing the offsets in the controller’s memory are low, but this may be at the expense of accuracy if the differences in vaporisation characteristics between liquids are not well represented by a fixed adjustment.

[0065] Figure 6 shows a simplified graphical representation of example equations with offsets. A line representing the equation for each of three liquids X, Y and Z, as a plot of aerosol mass against puff parameters (puff duration and power level). Liquid X produces a certain amount of aerosol in a puff. The equation for liquid X is stored in the controller. Liquid Y produces a lesser amount of aerosol per puff, and this can be calculated by applying an offset ‘a’ to the aerosol mass calculated using the equation for liquid X, where ‘a’ has a negative value, or is a percentage less than 100%, so that the calculated aerosol mass is reduced. Liquid Z produces a greater amount of aerosol per puff, and this can be calculated by applying an offset ‘b’ to the aerosol mass calculated using the equation for liquid X, where ‘b’ has a positive value, or is a percentage greater than 100%, so that the calculated aerosol mass is increased. The controller uses the indicated liquid type to select the appropriate offset to apply to the equation, where, when the liquid type is liquid X, an offset of zero is applied or the offsetting step is omitted.

[0066] In a second alternative, it is recognised that a single offset value for each liquid type may not accurately reflect the changes in aerosol mass produced by the vaporisation characteristics of different liquids, since the changes may not be constant or in constant proportion across all puff parameters. For example, there may be variation across the power level regime available in the aerosol provision system. Accordingly, in this example, an offset value is determined for each of several power level values, for every liquid type for which the empirical data has been collected. The offsets may have the form of absolute or percentage values, to adjust the equation result upwards or downwards, as before. All these offset values are stored in the controller, labelled with or stored against their corresponding liquid type and power level value, together with a single equation for calculating aerosol mass from power level value and puff duration, which has been determined from the empirical data for one liquid type. The controller obtains an indication of the liquid type, calculates the equation when a puff occurs to determine the aerosol mass in that puff, using the puff duration and power level values for the puff, and adjusts the result of the equation using the offset value for the indicated liquid type and the puff’s power level. This may be particularly applicable in aerosol provision systems in which a number of fixed power level settings are available for selection by the user (rather than power level selection from a continuous range), so that offsets can be derived at each of the fixed power levels, for improved accuracy. Use of this approach is not precluded for systems with a continuous power level range, however, or for systems that offer power level settings different from or in addition to the power level values that can be selected by the user. The controller may be configured to select the offset corresponding to the power level value which is closest to the power level value of the puff, or the power level reached by always rounding up or always rounding down the power level value of the puff, for example. This alternative requires more storage in the controller memory for the offset values, but can provide improved accuracy in determining the aerosol mass in a puff.

[0067] In a third alternative, offset values are employed in conjunction with the puff duration. Two or more puff durations are specified, and an offset value is determined from each of the specified puff durations, for every liquid type for which the empirical data has been collected. Again, the offsets may have the form of absolute or percentage values, to adjust the equation result upwards or downwards. The offset values are stored in the controller, labelled with or stored against their corresponding liquid type and puff duration, together with a single equation for calculating aerosol mass from power level and puff duration which has been determined from the empirical data for one liquid type, as before. The controller obtains an indication of the liquid type and calculates the equation when a puff occurs to determine aerosol mass in that puff, using the puff duration and power level values for the puff. However, since puff duration can vary on a continuous scale and depends entirely on the user’s behaviour for that particular puff, it is unlikely that the actual puff duration will match any of the specified puff durations for which offset values have been provided. Therefore, in order to obtain an offset value to adjust the result of the equation, the controller retrieves a pair of the offset values stored for the indicated liquid type, where the actual puff duration value lies between the two puff values of the offset values. The controller then interpolates between the pair of retrieved offset values to obtain an offset value corresponding to the actual puff duration. For example, if there is a stored offset value for a puff of one second duration and a stored offset value for a puff of three seconds duration, an interpolated offset value for use with an actual puff of two seconds duration would be the average of the offset values for one and three seconds durations. Any mathematical interpolation technique may be employed, however. Then, the controller applies the interpolated offset value to the aerosol mass calculated from the stored equation, in order to adjust for the liquid type, and thereby determines the aerosol mass for the puff. The storage requirements for the controller’s memory for this approach will depend on the number of specified puff durations for which offset values are determined, where accuracy can be increased by specifying more puff durations, with closer spacings, to obtain more offset values, at the cost of increased storage needs.

[0068] The approaches described above that use offset values for particular power levels or for particular puff durations to adjust for liquid type could be modified or combined. For example, interpolation between offset values for two power level values could be used in a case where a puff has a power level value that does not match any of the power level values for which an offset value is stored. Offset values could be obtained and stored for a plurality of puff duration values, to increase the chance that an actual puff duration matches a puff duration value having an offset, and in the event of no match, the controller could select the offset value for the puff duration which is closest to the actual puff duration value, or always round up or round down to the next or previous puff duration to select the offset value.

[0069] The use of a look-up table has been described above, mapping power level values and puff duration values to aerosol mass, that is derived from the equation and used by the controller to determine the aerosol mass of a puff as an alternative to calculating the result of the equation for each puff. This concept can be extended to manage the situation of different liquid types, by constructing and storing a look-up table from the equation obtained from the empirical data for each liquid type. The stored look-up tables are labelled with or stored with reference to the relevant liquid type. The controller then retrieves the aerosol mass amount corresponding to the obtained puff duration and power level values from the look-up table for the indicated liquid type.

[0070] It may occur that the controller is not able to obtain an indication of the type of liquid in the reservoir. For example, the type of liquid may not match any of the liquid types which the controller is configured to handle and therefore be unknown or unidentifiable to the controller. The identifying element in the pod or reservoir that is intended to indicate liquid type to the controller may be faulty, missing or otherwise unreadable or undetectable by the controller. In such a case, the controller may be configured not to perform estimation of the remaining liquid level amount, to avoid indicating inaccurate liquid consumption information to the user. Alternatively, and more usefully, the controller may be configured to default to using the equation, or offsets, or look-up table corresponding to a pre-specified one of the liquid types, for example a liquid type that is the most “average” out of the liquid types known to the controller (for example having an intermediate vaporisation characteristic or behaviour, such as liquid X in Figure 6). This liquid type may be considered most likely to be similar to the unknown liquid type, so that the determined aerosol mass result may be more accurate.

[0071] As noted above, the aerosol provision device may comprise an indicator, for indicating to the user of the aerosol provision device an amount of liquid in the reservoir. The controller is then configured to operate the indicator to indicate the estimated amount of liquid in the reservoir, using the estimation obtained based on the determined mass of aerosol in puffs as described above. The indicator may be configured to provide a visual indication to the user, such as comprising one or more lights (such as light emitting diodes) which can be illuminated, or a display screen to show numbers, letters or symbols. Since the information to be indicated to the user is an amount of liquid present or remaining in a reservoir which has a capacity of a certain liquid amount when it is full, the indicator may be configured to indicate the estimated amount of liquid in the reservoir as a remaining proportion of the total liquid capacity, for example “50%”, “0.5”, “1 / 2”, “half” or an equivalent symbol when half of the original total liquid capacity has been used and half remains in the reservoir, or “25%”, 0.25”, “1 / 4” or “quarter” or any equivalent symbol when three quarters of the original total liquid capacity has been used and one quarter remains in the reservoir.

[0072] The indicator could be updated after every puff to report each small decrement in the remaining amount of liquid to the user, for example by showing the remaining amount as a percentage figure. However, this level of detail and resolution may not be particularly valued by a user, and reporting in large steps of decreasing amount, at a lower resolution can be more helpful and easier to understand. This approach may be easier to represent by symbolic, non-numeric indication as well. Also, having larger steps or ranges of the remaining proportion of the liquid to indicate to the user can shield the user from inaccuracies inherent in the estimation, such as the systemic and random errors described above. It becomes possible to indicate estimated remaining amounts within a range around the reservoir being half-full simply as “half-full”, for example, which by most users will be considered sufficiently detailed and useful.

[0073] Accordingly, while the controller may calculate the aerosol mass in every puff, and may make an estimation of the amount of liquid in the reservoir by deducting the puff mass after each puff (as an alternative to periodically deducting an accumulated puff mass after several puffs, such after each two puffs or five puffs or ten puffs, for example) , it is not necessary in all examples to indicate this change to the user after each puff. Rather, in some examples it is proposed to update the indication of the amount of liquid in the reservoir only periodically, when the estimated remaining amount falls below predefined threshold levels. Decreases between the threshold levels will not be specifically indicated in this case. This can be understood as the total liquid capacity of the reservoir, that is, the amount of liquid the reservoir holds when full, being divided into N ranges (where N is an integer) of remaining proportion of the total liquid capacity, and the indicator being configured to indicate or represent each of the N ranges, and being operable by the controller to indicate or represent at any given time which of the N ranges the remaining amount of liquid in the reservoir falls into at that time.

[0074] A relatively small number of ranges may be used, again to reduce the resolution of the liquid amount indication presented to the user. For example, five or fewer ranges may be used, i.e. N < 5. Also, the N ranges may be selected to be of unequal size. In other words, at least one of the N ranges may be a larger proportion of the total liquid capacity than at least one other of the N ranges. Equal size ranges may alternatively be used, but unequal ranges may aid in shielding the user from inherent inaccuracies in the estimation. For example, if the inaccuracies are considered larger when the reservoir is closer to full, or closer to empty, a larger range may be assigned to fuller proportions or emptier proportions. Also, the user may be more interested to know that the reservoir is becoming empty, compared to depletion when the reservoir is near full, so a smaller range might be useful for emptier proportions, to in effect increase the resolution of the indication as the reservoir empties.

[0075] As an example, assume N = 5. For each of the ranges 1 to 5, the indicator shows a different indication or representation to the user. If the total reservoir capacity is designated as a liquid amount F, range 1 may correspond to liquid amounts between F and f where f < F, and f is a threshold between range 1 and range 2. When the estimated liquid amount is F or less than F, but higher than f, the indicator is operated to show the representation for range 1. Range 2 corresponds to liquid amounts between f and f’ where f’ < f and f’ is a threshold between range 2 and range 3. When the estimated liquid amount falls below f, the controller operates the indicator to show the representation for range 2. Range 3 corresponds to liquid amounts between f’ and f” where f” < f’ and f” is a threshold between range 3 and range 4. When the estimated liquid amount falls below f’, the controller operates the indicator to show the representation for range 3. Range 4 corresponds to liquid amounts between f” and f’” where f’” < f” and f’” is a threshold between range 4 and range 5. When the estimated liquid amount falls below f”, the controller operates the indicator to show the representation for range 4. Range 5 corresponds to liquid amounts between f’” and 0, and when the estimated liquid amount falls below f’”, the controller operates the indicator to show the representation for range 5.

[0076] In this example, the representation for range 1 may be a representation that the reservoir is full, and the representation for range 5 may be a representation that the reservoir is empty.

[0077] Purely as an example, the thresholds between the ranges, if defined as percentages of the total reservoir capacity F (100%), when N = 5, may be selected such that f = 75%, f’ = 60%, f” = 37.5% and f” = 12.5%. Hence range 1 covers a 25% proportion of the total reservoir capacity (100% to 75%), range 2 covers a 15% proportion of the total reservoir capacity (75% to 60%), range 3 covers a 22.5% proportion of the total reservoir capacity (37.5% to 60%), range 4 covers a 25% range of the total reservoir capacity (12.5% to 37.5%) and range 5 covers a 12.5% capacity (0% to 12.5%). Hence, the ranges are of different sizes, as mentioned above. The range sizes can be chosen to accommodate inaccuracies in the estimation.

[0078] Figure 7 shows a schematic representation of a first example of indications that may be shown by the indicator, for N = 5, in other words, the indicator is configured to show five different indications or representations, one for each of the five ranges. In this example, which is in no way limiting, the representations have the form of adjacent blocks or bars 50 (which can be displayed on an LCD screen, for example), each representation having a different number of bars, and the number of bars decreasing from four to zero from range R1 to range R5. This form of indication is similar to representations of decreasing battery power commonly displayed on electronic consumer devices, so will be familiar and well-understood by the user. Note that while the use of four bars, which are equally sized, suggests to the user remaining liquid levels of 100%, 75%, 50%, 25% and 0%, it is not necessary that the thresholds between the ranges which trigger the chance from one representation to the next (as described above) match these values. For example, they may have the values given in the preceding paragraph. This can further shield the user from the errors inherent in the approach, arising from the use an equation derived from empirical data collected from systems that have inherent system-to- system variation that cannot be accounted for.

[0079] In another example N = 4, so that the total reservoir capacity is divided into four ranges. Purely as an example, the thresholds between the ranges in such a case may be selected to be 60%, 37.5% and 12.5% so that range 1 covers estimated liquid amounts between 100% and 60%, range 2 covers estimated liquid amounts between 60% and 37.5%, range 3 covers estimated liquid amounts between 37.5% and 12.5% and range 4 covers estimated liquid amounts between 12.5% and 0%. Again, therefore, the ranges are of unequal size.

[0080] Figure 8 shows a schematic representation of a second example of indications that may be shown by the indicator, for N=4, in other words the indicator is configured to show four different indications or representations, one for each of the four ranges. In this example, which is in no way limiting, the representations have the form of the illumination of one or more lights, such as LEDs, where a different colour and / or sequence and / or brightness of illumination is used for each range. This can also be implemented by the display of coloured symbols on a screen. In Figure 8 different shading is employed to represent different colours. For example, a “traffic light” system may be used, in which a green light or symbol is shown for an estimated liquid amount in range R1 (suggesting “full” to the user), an amber or yellow light or symbol is shown for an estimated liquid amount in range R2, a red light or symbol is shown for an estimated liquid amount in range R3, and a flashing red light is shown for an estimated liquid amount in range R4 (suggesting “empty” or “near empty” to the user).

[0081] Many other forms of representations that may be displayed by the indicator will be apparent to the skilled person, and the disclosure is not limited to the above examples. Visual non-numeric indicators are considered useful as being easily and widely understood, but the estimated remaining liquid may be indicated numerically if preferred.

[0082] As remarked above with regard to Figures 3 and 4, errors in determination of the aerosol mass in a puff from the equation may be more significant in some operating regimes of aerosol provision system. In particular, accuracy may be lower for short puff durations and at low power levels. Accordingly, in some examples it is proposed to not report an estimated liquid amount in the reservoir if puffing enters such a regime. For example, the controller may be configured not to operate the indicator if the obtained puff duration value is below a predetermined threshold, where the threshold is selected to correspond to a puff duration below which the determination of aerosol mass is deemed to be inaccurate, where inaccuracy can be assessed appropriately for a particular system having regard to the quality of fitting of the function to the empirical data. Similarly, and alternatively or additionally, the controller maybe configured not to operate the indicator is the obtained power level value is below a predetermined threshold, where the threshold is selected to correspond to a power level below which the determination of aerosol mass is deemed to be inaccurate. If the below-threshold regime is used long term, for example if the user chooses to run the aerosol provision system always at a very low power level setting, the indicator may be continuously not operated, until an above-threshold regime is used. If a below-threshold regime is brief, for example if the user randomly takes a short puff, the controller might be configured not to perform the determination of aerosol mass and estimation of the reservoir liquid amount, so that the short puff is disregarded during tracking the consumption of liquid out of the reservoir. Alternatively, a predetermined fixed aerosol mass value, based on a likely aerosol mass in a short or low power puff, might be provided in the controller for use in such circumstances, in place of a determined aerosol mass value.

[0083] Figure 9 shows a flow chart of steps in a method for estimating a liquid amount in an aerosol provision system, generally in line with features of the preceding disclosure. The method may be performed by a controller comprised within an aerosol provision system, such as within a device component of an aerosol provision system that can be coupled to a cartridge or pod component to form the complete aerosol provision system. A first step S1 is optional, and comprises obtaining an indication of a liquid type of a liquid in a reservoir of the aerosol provision system. As discussed above, taking account of liquid type when estimating liquid amounts can improve accuracy, but this step may be omitted, such as for simplicity, or in cases where the liquid type in the reservoir is already known, and / or cannot be changed. In a second step S2, a power level value is obtained, being a level of power which is applied a vaporiser of the aerosol provision system during a puff taken by a user of the aerosol provision system. The vaporiser operates under the supply of electrical power to generate aerosol for the puff by vaporising liquid from the reservoir. In a third step S3 (noting that steps S2 and S3 may be reversed in order or carried out simultaneously), a puff duration value is obtained, being a duration of the puff for which the power at the obtained power level value has been applied to the vaporiser. Once the power level value and the puff duration value have been obtained, the method proceeds to step S4, in which a mass of aerosol in the puff is determined using the power level value and the puff duration value. If an indication of the type of liquid in the reservoir has been obtained in step S1 , the liquid type indication is also used in the determination. The mass of aerosol may be determined using an equation relating power level and puff duration to mass of aerosol which is a function fitted to empirical data from measurements of mass of aerosol generated during puffs of known puff duration value at known power level value previously made on a population of aerosol provision systems, or cartridges for aerosol provision systems, and having a same type of vaporiser as the aerosol provision system in which the method is being carried out.

[0084] Once the mass of aerosol in the puff has been determined, the method proceeds to step S5, in which an estimation is made of an amount of liquid in the reservoir, using the determined mass of aerosol and a known amount of liquid that was in the reservoir prior to the puff. Optionally in step S6, an indication can be provided to the user of the aerosol provision system of the estimated amount of liquid in the reservoir. In some examples, the indication may usefully be an indication of the remaining proportion of a total liquid capacity of the reservoir, being the amount of liquid in the reservoir when it is full. In some examples, the indication may be a visual non-numeric indication.

[0085] In conclusion, in order to address various issues and advance the art, this disclosure shows by way of illustration various embodiments in which the claimed invention(s) may be practiced. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and / or exclusive. They are presented only to assist in understanding and to teach the claimed invention(s). It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope of the claims. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. other than those specifically described herein. The disclosure may include other inventions not presently claimed, but which may be claimed in future.

Claims

Claims1. A device for an aerosol provision system comprising: a controller configured to: obtain a power level value indicating a level of power applied to a vaporiser of the aerosol provision system during a puff taken by a user, the vaporiser configured to generate aerosol by vaporising liquid from a reservoir of the aerosol provision system; obtain a puff duration value indicating a duration of the puff; determine a mass of aerosol generated by the vaporiser during the puff using the power level value and the puff duration value; and estimate an amount of liquid in the reservoir after the puff by using the determined mass of aerosol and a known amount of liquid in the reservoir prior to the puff.

2. A device according to claim 1 , wherein the controller is further configured to obtain an indication of a liquid type of the liquid in the reservoir, and determine the mass of aerosol using the indicated liquid type in addition to the power level value and the puff duration value.

3. A device according to claim 1 or claim 2, wherein the controller is configured to determine the mass of aerosol using an equation relating power level and puff duration to mass of aerosol, the equation being obtained by fitting to empirical data from measurements of mass of aerosol generated during puffs with known puff duration value and known power level value made on a population of aerosol provision systems or cartridges therefor with a same type of vaporiser as the aerosol provision system.

4. A device according to claim 3, wherein the equation is by linear fitting to the empirical data.

5. A device according to claim 3, wherein the equation is obtained by nonlinear fitting to the empirical data.

6. A device according to any one of claims 3 to 5, wherein the controller stores the equation, and is configured to determine the mass of aerosol for the puff by calculating the mass of aerosol using the equation.

7. A device according to claim 6 when dependent on claim 2, wherein the controller stores one or more additional equations, each equation obtained by fitting to empirical datafrom measurements made using a different liquid type, and the controller is configured to use the equation corresponding to the indicated liquid type.

8. A device according to claim 6 when dependent on claim 2, wherein the controller stores offset values for the equation, each offset value compensating the equation for a different liquid type, and the controller is configured to compensate the mass of aerosol determined from the equation using the offset value corresponding to the indicated liquid type.

9. A device according to claim 6 when dependent on claim 2, wherein the controller stores offset values for the equation, the offset values comprising an offset value for each of a set of power levels for each of different liquid types, and the controller is configured to compensate the mass of aerosol determined from the equation using the offset value corresponding to the obtained power level value and the indicated liquid type.

10. A device according to claim 6 when dependent on claim 2, wherein the controller stores offset values for the equation, the offset values comprising an offset value for two or more puff durations for each of different liquid types, and the controller is configured to select a pair of offset values corresponding to the indicated liquid type, interpolate between the offset values to obtained an interpolated offset value corresponding to the obtained puff duration, and compensate the mass of aerosol determined from the equation using the interpolated offset value.

11. A device according to any one of claims 3 to 5, wherein the controller stores a lookup table constructed using the equation which maps power level values or ranges of power level ranges and puff duration values or ranges of puff duration values to mass of aerosol values, and is configured to determine the mass of aerosol for a puff using the look-up table.

12. A device according to claim 11 when dependent on claim 2, wherein the controller stores one or more additional look-up tables, each look-up table constructed using the equation when fitted to empirical data from measurements made using a different liquid type, and the controller is configured to determine the mass of aerosol for a puff using the look-up table corresponding to the indicated liquid type.

13. A device according to any preceding claim, further comprising an indicator for indicating to the user an amount of liquid in the reservoir, wherein the controller is configured to operate the indicator to indicate the estimated amount of liquid in the reservoir.

14. A device according to claim 13, wherein the indicator is configured to indicate the estimated amount of liquid in the reservoir as a remaining proportion of a total liquid capacity of the reservoir.

15. A device according to claim 14, wherein the total liquid capacity of the reservoir is divided into N ranges of remaining proportion of the total liquid capacity, the indicator is configured to indicate each of the N ranges, and the controller is configured to operate the indicator to indicate the range into which the estimated amount of liquid in the reservoir falls.

16. A device according to claim 15, wherein the N ranges are of unequal size.

17. A device according to claim 15 or claim 16, where N is five or less.

18. A device according to any one of claims 13 to 17, wherein the indicator is configured to provide a visual non-numeric indication.

19. A device according to any one of claims 13 to 18, wherein the controller is further configured to not operate the indicator in the event that the obtained power level value is below a predetermined threshold, where the threshold corresponds to a power level below which the determination of the mass of aerosol is deemed inaccurate, and / or in the event that the obtained puff duration value is below a predetermined threshold, where the threshold corresponds to a puff duration below which the determination of the mass of aerosol is deemed inaccurate.

20. An aerosol provision system comprising a device according to any one of claims 1 to 19.

21. A method for estimating a liquid amount in an aerosol provision system, the method comprising: obtaining a power level value indicating a level of power applied to a vaporiser of the aerosol provision system during a puff taken by a user, the vaporiser configured to generate aerosol by vaporising liquid from a reservoir of the aerosol provision system; obtaining a puff duration value indicating a duration of the puff; determining a mass of aerosol generated by the vaporiser during the puff using the power level value and the puff duration value; andestimating an amount of liquid in the reservoir after the puff by using the determined mass of aerosol and a known amount of liquid in the reservoir prior to the puff.

22. A method according to claim 21 , further comprising obtaining an indication of a liquid type of the liquid in the reservoir, and determining the mass of aerosol using the indicated liquid type in addition to the power level value and the puff duration value.

23. A method according to claim 21 or claim 22, wherein the mass of aerosol is determined using an equation relating power level and puff duration to mass of aerosol, the equation being a function fitted to empirical data from measurements of mass of aerosol generated during puffs with known puff duration value and known power level value made on a population of aerosol provision systems or cartridges therefor with a same type of vaporiser as the aerosol provision system.

24. A method according to any one of claims 21 to 23, further comprising providing an indication to the user of the estimated amount of liquid in the reservoir, as a remaining proportion of a total liquid capacity of the reservoir.

25. A method according to claim 24, wherein the indication is a visual non-numeric indication.

Images