阅读说明：本技术 加热器管理 (Heater management ) 是由 S·比拉特 于 2016-03-21 设计创作，主要内容包括：公开了加热器管理。一种电操作的气溶胶生成系统包含检测不利条件(如干燥加热器或未经授权的加热器类型)的构件。系统包含有包含用于加热气溶胶形成基质的至少一个加热元件的电加热器(30)、电源(14)和连接到电加热器并连接到电源并且包含存储器的电路(16),该电路(16)被配置成当加热器(30)的初始电阻(R1)与相对于初始电阻的电阻变化(R2-R1)之间的比率大于存储于存储器中的最大阈值或小于最小阈值时确定不利条件,并且在存在不利条件的情况下控制向电加热器(30)供应的电力或向使用者提供指示。系统具有不需要预存储的最大电阻值的益处,并且因此该系统能够使用不同加热器并且适应因制造公差所致的电阻变化。(Heater management is disclosed. An electrically operated aerosol-generating system includes means to detect an adverse condition, such as a dry heater or an unauthorized heater type. The system comprises an electric heater (30) comprising at least one heating element for heating the aerosol-forming substrate, a power supply (14), and an electrical circuit (16) connected to the electric heater and to the power supply and comprising a memory, the electrical circuit (16) being configured to determine an adverse condition when a ratio between an initial resistance (R1) of the heater (30) and a change in resistance (R2-R1) from the initial resistance is greater than a maximum threshold value or less than a minimum threshold value stored in the memory, and to control the power supplied to the electric heater (30) or provide an indication to a user in the presence of an adverse condition. The system has the benefit that it does not require a pre-stored maximum resistance value and therefore the system is able to use different heaters and accommodate resistance variations due to manufacturing tolerances.)

1. An electrically operated aerosol-generating system comprising:

an electric heater comprising at least one heating element for heating the aerosol-forming substrate;

a power source; and

circuitry for use in an electrically operated aerosol-generating device, the circuitry being connected, in use, to an electric heater for heating an aerosol-forming substrate and to a power supply, the circuitry comprising a memory and being configured to measure an initial resistance or rate of initial change of resistance of the heater within a predetermined period of time after power is supplied to the heater, to compare the initial resistance or rate of initial change of resistance of the heater with a range of acceptable values, and if the initial resistance or rate of initial change of resistance is outside the range of acceptable values, to prevent power from being supplied to the electric heater or to provide an indication until the heater or the aerosol-forming substrate is replaced.

2. An electrically operated aerosol-generating system according to claim 1, wherein the electrical circuit is configured to measure the initial resistance or initial rate of change of resistance using a lower power to supply power to the heater to heat the aerosol-forming substrate in a separate routine.

3. An electrically operated aerosol-generating system according to claim 1 or 2, wherein the system comprises a device and a removable cartridge, wherein the power source and the electrical circuit are in the device and the electric heater is in the removable cartridge, and wherein the cartridge comprises a liquid aerosol-forming substrate.

4. An electrically operated aerosol-generating system according to any preceding claim, wherein, in use, the aerosol-forming substrate is in contact with the heating element.

5. An electrically operated aerosol-generating system according to any preceding claim, wherein the predetermined period of time is between 50ms and 200ms, preferably between 50ms and 150ms, and more preferably about 100 ms.

6. An electrically operated aerosol-generating system according to any preceding claim, wherein if the initial resistance or initial rate of change of resistance is within the range of acceptable values, the circuit is configured to determine that an acceptable heater is present when the ratio between the initial resistance of the heater and the change in resistance relative to the initial resistance is less than a maximum threshold stored in the memory or greater than a minimum threshold stored in the memory, and to control the power supplied to the electric heater based on whether an acceptable heater is present or to provide an indication in the absence of an acceptable heater.

7. An electrically operated aerosol-generating system according to claim 6, wherein the electrical circuit is configured to determine that an acceptable heater is present within the first second of supplying power to the heater.

8. An electrically operated aerosol-generating system according to any preceding claim, wherein the system is an electrically heated smoking system.

9. A heater assembly, comprising:

an electric heater comprising at least one heating element; and

circuitry for use in an electrically operated aerosol-generating device, the circuitry being connected, in use, to an electric heater for heating an aerosol-forming substrate and to a power supply, the circuitry comprising a memory and being configured to measure an initial resistance or rate of initial change of resistance of the heater within a predetermined period of time after power is supplied to the heater, to compare the initial resistance or rate of initial change of resistance of the heater with a range of acceptable values, and if the initial resistance or rate of initial change of resistance is outside the range of acceptable values, to prevent power from being supplied to the electric heater or to provide an indication until the heater or the aerosol-forming substrate is replaced.

10. A heater assembly according to claim 9, wherein the electrical circuit is configured to measure the initial resistance or initial rate of change of resistance using a lower power to supply power to the heater to heat the aerosol-forming substrate in a separate routine.

11. An electrically operated aerosol-generating device comprising:

a power source; and

a circuit connected to the power supply and comprising a memory, the circuit being configured to be connected to an electric heater in use and configured to measure an initial resistance or rate of initial change of resistance of the heater within a predetermined period of time after power is supplied to the heater, compare the initial resistance or rate of initial change of resistance of the heater to a range of acceptable values, and prevent power supply or provide an indication to the electric heater until the heater or aerosol-forming substrate is replaced if the initial resistance or rate of initial change of resistance is outside the range of acceptable values.

12. An electrically operated aerosol-generating device according to claim 11, wherein the electrical circuit is configured to measure the initial resistance or initial rate of change of resistance using a lower power to supply power to the heater to heat the aerosol-forming substrate in a separate routine.

13. A method of detecting an incompatible or damaged heater in an electrically operated aerosol-generating system, the system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the method comprising:

measuring an initial resistance or rate of initial change of resistance of the heater over a predetermined period of time after power is supplied to the heater, comparing the initial resistance or rate of initial change of resistance of the heater with a range of acceptable values, and if the initial resistance or rate of initial change of resistance is outside the range of acceptable values, preventing power from being supplied to the electric heater or providing an indication until the heater or the aerosol-forming substrate is replaced,

wherein the step of measuring the initial resistance or initial rate of change of resistance is performed as a separate routine using lower power to supply power to the heater to heat the aerosol-forming substrate.

14. A method according to claim 13, further comprising detecting when a heater or aerosol-forming substrate is inserted into the system.

15. A method according to claim 14, wherein the step of measuring the initial resistance or initial rate of change of resistance is performed immediately after insertion of a heater or aerosol-forming substrate into the system is detected.

Technical Field

The invention relates to heater management. Particular examples disclosed relate to heater management in an electrically heated aerosol-generating system. Aspects of the invention are directed to an electrically heated aerosol-generating system and a method for operating an electrically heated aerosol-generating system. Some examples described relate to a system that can detect an abnormal change in resistance of a heater element, which can indicate an adverse condition at the heater element. The adverse condition may, for example, indicate a level of depletion of the aerosol-forming substrate in the system. In some of the examples described, the system may be effective with heater elements having different resistances. In other examples, the detected resistance signature may be used to determine or select how the system may be operated. Some aspects and features of the present invention have particular application to electrically heated smoking systems.

Background

WO2012/085203 discloses an electrically heated smoking system comprising a liquid storage portion for storing a liquid aerosol-forming substrate; an electric heater comprising at least one heating element for heating the liquid aerosol-forming substrate; and circuitry configured to determine a depletion of liquid aerosol-forming substrate based on a correlation between the power applied to the heating element and the resulting change in temperature of the heating element. In particular, the circuit is configured to calculate a rate of temperature rise of the heating element, wherein a higher rate of temperature rise indicates that a wick conveying the liquid aerosol-forming substrate to the heater is dry. The system compares the rate of temperature rise to a threshold value stored in memory during manufacturing. If the rate of temperature rise exceeds a threshold, the system may stop supplying power to the heater.

The system of WO2012/085203 may use the resistance of the heater element to calculate the temperature of the heating element, which has the advantage that no dedicated temperature sensor is required. However, the system still needs to store a threshold value that depends on the resistance of the heater element, and thus optimize the heater element for a particular resistance or range of resistances.

However, it may be desirable to allow the system to operate with different heaters. Typically in a system of the type described in WO2012/085203, the heater is provided in a disposable cartridge together with a supply of liquid aerosol-forming substrate. The heater elements in different cartridges may have different resistances. This may be the result of manufacturing tolerances in the same type of cartridge or because different cartridge designs are available in the system to provide different user experiences. The system of WO2012/085203 is optimised for heaters of known specific resistance to be used in the system, which heaters are determined at the time of manufacture of the system.

It would be desirable to have an alternative system for determining the degree of drying out of a heater or other adverse condition at a heater in an electrical smoking system, and particularly in a system that can operate with different heaters.

In an electrically heated aerosol-generating system having a permanent device portion and a consumable portion containing an aerosol-forming substrate, it would also be desirable to be able to readily determine whether the consumable portion is a "genuine" consumable or a consumable deemed compatible with the device by the manufacturer of the device. This is true both in systems where the heater is part of a consumable and in systems where the heater is part of a permanent installation.

Disclosure of Invention

In a first aspect, there is provided an electrically operated aerosol-generating system comprising:

an electric heater comprising at least one heating element for heating an aerosol-forming substrate;

a power source; and

a circuit connected to the electric heater and to the power source and including a memory, the circuit configured to determine an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold or less than a minimum threshold stored in the memory or when the ratio reaches a threshold stored in the memory outside of an expected period of time, and to control power supplied to the electric heater based on whether an adverse condition exists or to provide an indication based on whether an adverse condition exists.

The phrase "when the ratio reaches a threshold stored in the memory outside of an expected period of time" shall expressly encompass the case when the ratio reaches the threshold earlier than the expected period of time and the case when the ratio reaches the threshold later than the expected period of time or does not reach the threshold at all.

One disadvantage in aerosol-generating systems or aerosol-generating devices is the shortage or depletion of the aerosol-forming substrate at the heater. In general, the less aerosol-forming substrate delivered to the heater for vaporisation, the higher the temperature of the heating element for a given power applied. For a given power, the release or how the release of the temperature of the heating element during a heating cycle varies over a plurality of heating cycles may be used to detect whether there is depletion of the amount of aerosol-forming substrate at the heater, and in particular whether there is insufficient aerosol-forming substrate at the heater.

Another disadvantage is the presence of counterfeit or incompatible heaters or damaged heaters in systems with replicable or disposable heaters. If the heater element resistance rises faster or slower than expected for a given power applied, it may be because the heater is counterfeit and has different electrical characteristics than the true heater, or it may be because the heater is damaged to some extent. In either case, the circuit may be configured to prevent the supply of power to the heater.

Another disadvantage is the presence of counterfeit, incompatible or old or damaged aerosol-forming substrates in the system. If the heater element resistance rises faster or slower than expected for a given power applied, it may be because the aerosol-forming substrate is counterfeit or old and therefore has a higher or lower moisture content than expected. For example, if a solid aerosol-forming substrate is used, it may dry out if it is extremely old or has been subjected to improper storage. If the substrate is drier than expected, then less energy will be used for vaporization than expected and the heater temperature will rise faster. This will result in an unexpected change in the resistance of the heater element.

By using a certain ratio of initial resistance to subsequent resistance, the system does not need to determine the actual temperature of the heating element or to have any pre-stored knowledge about the resistance of the heating element at a given temperature. This allows different approved heaters to be used in the system and allows the absolute resistance of the same type of heater to vary due to manufacturing tolerances without triggering adverse conditions. It also allows for detection of incompatible heaters.

The use of the initial resistance measurement and subsequent resistance change also allows for a more accurate threshold to be set for determining a particular adverse condition. The ratio of the resistance change to the initial resistance is not dependent on variations in the size or shape of the heater due to manufacturing tolerances and on variations in the parasitic contact resistance within the system, but only on the material properties of the heater and the aerosol-forming substrate.

The circuit may not actually calculate a ratio or change in resistance and compare the ratio to a threshold, but may make an equivalent comparison of the resistance measurement to a threshold derived from one or more resistance storage values and one or more resistance measurements. For example, the circuit may compare a heater element resistance measurement at a time after initial delivery of power from the power source to the electric heater to a value calculated from the initial resistance and a threshold value stored in memory.

The circuit may be configured to measure an initial resistance of the heater element and a resistance of the heater element at a time after initial delivery of power from the power source to the electric heater. If the time between resistance measurements is known or determined, then the rate of change of resistance can be calculated, which corresponds to the rate of temperature change for a given heater element resistivity. The system may be configured to always supply the same power to the heater, or the one or more thresholds may depend on the power supplied to the heater.

The initial resistance may be measured before the heater is first used. If the initial resistance is measured before the heater is first used, then it can be assumed that the heater element is at about room temperature. Since the expected change in resistance over time may depend on the initial temperature of the heater element, measuring the initial resistance at or near room temperature allows a narrower expected band of behavior to be set.

The initial resistance may be calculated as the initial resistance measurement minus an assumed parasitic resistance created by other electrical components and electrical contacts within the system.

The system may include a device and a cartridge removably coupled to the device, wherein the power source and circuitry are in the device and the electric heater and aerosol-forming substrate are in the removable cartridge. As used herein, a cartridge being "removably coupled" to a device means that the cartridge and device can be coupled or uncoupled from each other without significant damage to the device or the cartridge.

The circuit may be configured to detect insertion and removal of the cartridge into and from the device. The circuit may be configured to measure the initial resistance of the heater when the cartridge is first inserted into the device but before any significant heating has occurred. The circuit may compare the initial resistance measurement to an acceptable resistance range stored in memory. If the initial resistance is outside the acceptable resistance range, it can be considered counterfeit, incompatible, or damaged. In that case, the circuitry may be configured to prevent the supply of power until the cartridge has been removed and replaced by a different cartridge.

Cartridges having different characteristics may be used with the device. For example, two different cartridges with differently sized heaters may be used with the device. Larger heaters may be used to deliver more aerosol to users having personal preferences for aerosol.

The cartridge may be refillable, or may be configured to be disposed of when fully depleted of aerosol-forming substrate.

An aerosol-forming substrate is a substrate capable of releasing volatile compounds that can form an aerosol. The volatile compounds may be released by heating the aerosol-forming substrate.

The aerosol-forming substrate may comprise a plant-based material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco containing material. The aerosol-forming substrate may comprise a homogeneous plant-based material. The aerosol-forming substrate may comprise homogenised tobacco material. The aerosol-forming substrate may comprise at least one aerosol-former. The aerosol former is any suitable known compound or mixture of compounds that facilitates the formation of a thick and stable aerosol when used and that is substantially resistant to thermal degradation at the operating temperatures at which the system operates. Suitable aerosol-forming agents are well known in the art and include (but are not limited to): polyhydric alcohols such as triethylene glycol, 1, 3-butanediol, and glycerin; esters of polyhydric alcohols, such as glycerol mono-, di-or triacetate; and aliphatic esters of mono-, di-or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyols or mixtures thereof, such as triethylene glycol, 1, 3-butanediol, and most preferably glycerol. The aerosol-forming substrate may comprise other additives and ingredients, such as flavourants.

The cartridge may contain a liquid aerosol-forming substrate. For liquid aerosol-forming substrates, certain physical properties of the substrate, such as vapour pressure or viscosity, are selected in a manner suitable for use in an aerosol-generating system. The liquid preferably comprises a tobacco-containing material comprising volatile tobacco flavour compounds that are released from the liquid upon heating. Alternatively or additionally, the liquid may comprise a non-tobacco material. The liquid may include water, ethanol or other solvents, plant extracts, nicotine solutions, and natural or artificial flavors. Preferably, the liquid further comprises an aerosol former. Examples of suitable aerosol formers are glycerol and propylene glycol.

The advantage of providing a liquid storage portion is that the liquid in the liquid storage portion is protected from ambient air. In some embodiments, ambient light also cannot enter the liquid storage portion, so that the risk of light-induced liquid degradation is avoided. In addition, a higher level of hygiene can be maintained.

Preferably, the liquid storage portion is arranged to contain liquid for a predetermined number of puffs. If the liquid storage portion is not refillable and the liquid in the liquid storage portion has been used up, the liquid storage portion must be replaced by a user. During such replacement, contamination of the user with liquid must be prevented. Alternatively, the liquid storage portion may be refillable. In such cases, the aerosol-generating system may be replaced after a certain number of refills of the liquid storage portion.

Alternatively, the aerosol-forming substrate may be a solid substrate. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds which are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former. Examples of suitable aerosol formers are glycerol and propylene glycol.

If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosol-forming substrate may comprise, for example, one or more of: a powder, granules, pellets, chips, strands, strips or sheets, the material comprising one or more of herbaceous plant leaf, tobacco rib material, reconstituted tobacco, extruded tobacco, cast tobacco and expanded tobacco. The solid aerosol-forming substrate may be in bulk form or may be provided in a suitable container or cartridge. Optionally, the solid aerosol-forming substrate may contain additional tobacco or non-tobacco volatile flavour compounds which are released upon heating of the substrate. The solid aerosol-forming substrate may also contain capsules, for example comprising additional tobacco or non-tobacco volatile flavour compounds, and such capsules may be melted during heating of the solid aerosol-forming substrate.

As used herein, homogenized tobacco refers to a material formed by agglomerating particulate tobacco. The homogenized tobacco may be in the form of a sheet. The homogenised tobacco material may have an aerosol former content of greater than 5% by dry weight. Alternatively, the homogenised tobacco material may have an aerosol former content of between 5 wt% and 30 wt% on a dry weight basis. Sheets of homogenised tobacco material may be formed by agglomerating particulate tobacco obtained by grinding or otherwise comminuting one or both of a tobacco lamina and a tobacco stem. Alternatively or additionally, the sheet of homogenised tobacco material may comprise one or more of tobacco dust, shredded tobacco and other particulate tobacco by-products formed during, for example, processing, handling and transport of tobacco. The sheet of homogenised tobacco material may comprise one or more intrinsic binders that are endogenous binders of the tobacco themselves, one or more exogenous binders that are exogenous binders of the tobacco themselves, or a combination thereof, to assist in coalescing the particulate tobacco; alternatively or additionally, the sheet of homogenised tobacco material may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol-formers, humectants, plasticisers, flavourants, fillers, aqueous and non-aqueous solvents and combinations thereof.

Optionally, the solid aerosol-forming substrate may be provided on or embedded in a thermally stable carrier. The carrier may take the form of a powder, granules, pellets, chips, noodles or flakes. Alternatively, the support may be a tubular support having a thin layer of solid matrix deposited on its inner surface, or its outer surface, or both its inner and outer surfaces. Such tubular supports may be formed, for example, from paper, or paper-like materials, non-woven carbon fibre mats, low mass open mesh metal screens, or perforated metal foils or any other thermally stable polymer matrix.

The solid aerosol-forming substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gum or slurry. The solid aerosol-forming substrate may be deposited over the entire surface of the carrier or, alternatively, may be deposited in a pattern so as to provide uneven flavour delivery during use.

The solid aerosol-forming substrate may be provided in the form of a smoking article (such as a cigarette) to be used with a device comprising a heater, a power supply and an electrical circuit.

The circuit may be configured to detect insertion and removal of the aerosol-forming substrate into and from the device. The circuit may be configured to measure the initial resistance of the heater when the aerosol-forming substrate is first inserted into the device but before any significant heating has occurred. The circuit may compare the initial resistance measurement to an acceptable resistance range stored in memory. If the initial resistance is outside the acceptable resistance range, the aerosol-forming substrate may be considered counterfeit, incompatible or damaged. In that case, the electrical circuit may be configured to prevent the supply of electrical power until the aerosol-forming substrate has been removed and replaced.

The electric heater may comprise a single heating element. Alternatively, the electric heater may comprise more than one heating element, for example two, or three, or four, or five, or six or more heating elements. The one or more heating elements may be suitably arranged so as to most efficiently heat the liquid aerosol-forming substrate.

The at least one electrical heating element preferably comprises an electrically resistive material. Suitable resistive materials include (but are not limited to): semiconductors such as doped ceramics, electrically "conducting" ceramics (e.g., molybdenum disilicide), carbon, graphite, metals, metal alloys, and composites made of ceramic and metallic materials. Such composite materials may comprise doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals. Examples of suitable metal alloys include stainless steel, constantan, nickel-containing alloys, cobalt-containing alloys, chromium-containing alloys, aluminum-containing alloys, titanium-containing alloys, zirconium-containing alloys, hafnium-containing alloys, niobium-containing alloys, molybdenum-containing alloys, tantalum-containing alloys, tungsten-containing alloys, tin-containing alloys, gallium-containing alloys, manganese-containing alloys, and iron-containing alloys, and superalloys based on nickel, iron, cobaltGold, stainless steel,Alloys based on ferro-aluminium and alloys based on ferro-manganese-aluminium.Is a registered trademark of Titanium Metals Corporation. In a composite, the resistive material may optionally be embedded in, encapsulated by or coated by an insulating material or vice versa, depending on the kinetics of the energy transfer and the desired external physico-chemical properties. The heating element may comprise a metal etched foil insulated between two layers of inert material. In that case, the inert material may compriseFull polyimide or mica foil.Is a registered trademark of e.i.du Pont de Nemours and Company.

The at least one electrical heating element may take any suitable form. For example, the at least one electrical heating element may take the form of a heating blade. Alternatively, the at least one electrical heating element may take the form of a sleeve or matrix or a resistive metal tube having different electrically conductive portions. The liquid storage portion may incorporate a disposable heating element. Alternatively, one or more heating pins or rods travelling through the centre of the liquid aerosol-forming substrate may also be suitable. Alternatively, the at least one electrical heating element may comprise a sheet of flexible material. Other alternatives include heating wires or filaments, such as Ni-Cr (nickel-chromium), platinum, tungsten or alloy wires, or heating plates. Optionally, the heating element may be disposed in or on a rigid carrier material.

In one embodiment, the heating element comprises a grid, array or fabric of conductive filaments. The conductive filaments may define gaps between the filaments, and the width of the gaps may be between 10 μm and 100 μm.

The conductive filaments may form a grid having a size between 160 and 600 U.S. Mesh (Mesh US) (+/-10%) (i.e., between 160 and 600 filaments per inch (+/-10%)). The width of the gap is preferably between 75 μm and 25 μm. The percentage of the open area of the mesh as a ratio of the gap area to the total area of the mesh is preferably between 25% and 56%. The mesh may be formed using different types of weaves or lattice structures. Alternatively, the conductive filaments consist of an array of filaments arranged parallel to each other.

The diameter of the conductive filaments may be between 10 μm and 100 μm, preferably between 8 μm and 50 μm and more preferably between 8 μm and 39 μm. The filaments may have a circular cross-section or may have a flattened cross-section.

The area of the grid, array or weave of conductive filaments may be small, preferably less than or equal to 25mm²Allowing it to be incorporated into handheld systems. The grid, array or weave of conductive filaments may, for example, be rectangular and have dimensions of 5mm by 2 mm. Preferably, the grid or array of conductive filaments covers between 10% and 50% of the area of the heater assembly. More preferably, the grid or array of conductive filaments covers between 15% and 25% of the area of the heater assembly.

The filaments may be formed by etching a sheet of material such as foil. This may be particularly advantageous when the heater assembly comprises an array of parallel filaments. If the heating element comprises a mesh or fabric of filaments, the filaments may be formed separately and knitted together.

Preferred materials for the conductive filaments are 304, 316, 304L, 316L stainless steel.

The at least one heating element may heat the liquid aerosol-forming substrate by means of conduction. The heating element may at least partially contact the substrate. Alternatively, heat from the heating element may be conducted to the substrate by means of a heat conducting element.

Preferably, in use, the aerosol-forming substrate is in contact with the heating element.

Preferably, the electrically operated aerosol-generating system further comprises a capillary material for transporting the liquid aerosol-forming substrate from the liquid storage portion into the electric heater element.

Preferably, the capillary material is arranged to be in contact with the liquid in the liquid storage portion. Preferably, the capillary wick extends into the liquid storage portion. In that case, in use, liquid is transferred from the liquid storage portion to the electric heater by capillary action in the capillary wick. In one embodiment, the capillary wick has a first end and a second end, the first end extending into the liquid storage portion for contact with liquid therein and the electric heater is arranged to heat liquid in the second end. When the heater is activated, the liquid at the second end of the capillary wick is vaporized by at least one heating element of the heater to form a supersaturated vapour. The supersaturated vapour is mixed with and carried in an air stream. During flow, the vapor condenses to form an aerosol, and the aerosol is carried toward the mouth of the user. The liquid aerosol-forming substrate has physical properties including viscosity and surface tension which allow liquid to be transported through the capillary wick by capillary action.

The capillary wick may have a fibrous or sponge-like structure. The capillary wick preferably comprises a bundle of capillaries. For example, the capillary wick may comprise a plurality of fibers or filaments, or other fine bore tubes. The fibres or filaments may be substantially aligned in the longitudinal direction of the aerosol-generating system. Alternatively, the capillary wick may comprise a sponge or foam-like material formed into a rod shape. The rod shape may extend along the longitudinal direction of the aerosol-generating system. The structure of the wick forms a plurality of small pores or tubes through which the liquid can be transported by capillary action. The capillary wick may comprise any suitable material or combination of materials. Examples of suitable materials are capillary materials, such as sponges or foams, ceramic or graphite-like materials in the form of fibers or sintered powders, foamed metal or plastic materials, for example fibrous materials made from spun or extruded fibers, such as cellulose acetate, polyester or bonded polyolefin, polyethylene, polyester or polypropylene fibers, nylon fibers or ceramics. The capillary wick may have any suitable capillarity and porosity for use with different liquid physical properties. Liquids have physical properties including, but not limited to, viscosity, surface tension, density, thermal conductivity, boiling point, and vapor pressure that allow the liquid to be transported through a capillary device by capillary action.

The heating element may be in the form of a heating wire or filament surrounding and optionally supporting the capillary wick. The capillary properties of the wick are combined with the liquid properties to ensure that the wick is consistently wet in the heated region during normal use when a large amount of aerosol-forming substrate is present.

Alternatively, as described, the heater element may comprise a mesh formed from a plurality of conductive filaments. The capillary material may extend into the gaps between the filaments. The heater assembly may draw the liquid aerosol-forming substrate into the gap by capillary action.

The housing may contain two or more different capillary materials, wherein a first capillary material in contact with the heater element has a higher thermal decomposition temperature and a second capillary material in contact with the first capillary material but not in contact with the heater element has a lower thermal decomposition temperature. The first capillary material effectively acts as a spacer separating the heater element from the second capillary material so that the second capillary material is not exposed to temperatures above its thermal decomposition temperature. As used herein, "thermal decomposition temperature" means the temperature at which the material begins to decompose and lose mass by generating gaseous byproducts. Advantageously, the second capillary material may occupy a larger volume than the first capillary material and may hold more aerosol-forming substrate than the first capillary material. The second capillary material may have superior wicking properties to the first capillary material. The second capillary material may be less expensive or have a higher filling capacity than the first capillary material. The second capillary material may be polypropylene.

The power supply may be any suitable power supply, such as a DC voltage source. In one embodiment, the power source is a lithium ion battery. Alternatively, the power source may be a nickel metal hydride battery, a nickel cadmium battery, or a lithium based battery, such as a lithium cobalt, lithium iron phosphate, lithium titanate, or lithium polymer battery. Alternatively, the power supply may be another form of charge storage device, such as a capacitor. The power source may need to be recharged and may have a capacity that allows sufficient energy to be stored for one or more smoking experiences; for example, the power source may have sufficient capacity to allow continuous aerosol generation for a period of about six minutes, corresponding to the typical time taken to draw a conventional cigarette, or for a period of multiple six minutes. In another example, the power source may have sufficient capacity to allow a predetermined number of puffs or discrete activations of the heater.

Preferably, the aerosol-generating system comprises a housing. Preferably, the housing is elongate. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composites containing one or more of those materials, or thermoplastics suitable for food or pharmaceutical applications, such as polypropylene, Polyetheretherketone (PEEK) and polyethylene. Preferably, the material is lightweight and non-breakable.

Preferably, the aerosol-generating system is portable. The aerosol-generating system may be an electrically heated smoking system and may have a size comparable to a conventional cigar or cigarette. The aerosol-generating system may be a smoking system. The smoking system may have a total length of between about 30mm and about 150 mm. The smoking system may have an outer diameter of between about 5mm and about 30 mm.

The circuit preferably comprises a microprocessor, and more preferably a programmable microprocessor. The system may contain a data input port or wireless receiver that allows software to be uploaded to the microprocessor. The circuit may contain additional electrical components. The system may include a temperature sensor.

If an adverse condition is detected, what the system does may not provide an indication to the user that an adverse condition has been detected. This may be done by visual, audible or tactile warning. Alternatively or additionally, the circuit may automatically limit or otherwise control the power supplied to the heater when an adverse condition is detected.

There are many possible ways in which the circuitry may be configured to control the power supplied to the electric heater in the event that an adverse condition is detected. It may be desirable to reduce or stop the supply of power to the heater if insufficient aerosol-forming substrate is delivered to the heating element or the solid aerosol-forming substrate dries. This may be used to ensure that a consistent and pleasant experience is provided to the user, and to reduce the risk of overheating and reduce the generation of undesirable compounds in the aerosol. The supply of power to the heater may be stopped or limited for a short time or until the heater or aerosol-forming substrate is replaced.

The system may comprise a puff detector for detecting when a user puffs on the system, wherein the puff detector is connected to the circuit and wherein the circuit is configured to supply power from the power source to the heater element when the puff detector detects a puff, and wherein the circuit is configured to determine whether an adverse condition exists during each puff.

The puff detector may be a dedicated puff detector that directly measures the air flow through the device, such as a microphone-based puff detector, or may indirectly detect the puff, such as based on a temperature change within the device or a resistance change of the heater element.

The circuit may be configured to supply a predetermined power to the heater element for a time period t after initial detection of a puff or initial power supply to the heater₁And the circuit may be configured to determine the heater element resistance at time t based on the heater element resistance during each puff₁To determine the change in resistance of the heater element. The time period t can be set₁Selected shortly after the initial detection of puff or shortly after the first application of power to the heater. This is particularly advantageous during first use after replacement of the consumable if the circuit detects an incompatible or counterfeit heater or aerosol-forming substrate. For example, the duration of a typical puff may be 3s, and the response time of the puff detector may be about 100 ms. Then t may be₁Is selected to be between 100ms and 500msI.e. during the pumping period before the heater temperature stabilizes. Alternatively, the time period t may be set₁The time is selected to anticipate that the heating element temperature has stabilized.

The circuit may be configured to prevent the supply of power from the power source to the heater element in the event that there is an adverse condition for a predetermined number of consecutive user puffs.

The circuitry may be configured to continuously determine whether an adverse condition exists and prevent or reduce the supply of power to the heater when an adverse condition exists and continue to prevent or reduce the supply of power to the heater element until the adverse condition no longer exists.

In liquid and wick based systems, excessive pumping may cause the wick to dry out, since the liquid cannot be replaced quickly enough near the heater. In these environments, it is desirable to limit the supply of power to the heater so that the heater does not become too hot and produce undesirable aerosol components. Once an adverse condition is detected, power to the heater may be stopped until a subsequent user puff.

Similarly, excessive pumping may not allow the heater to cool as expected between pumps, resulting in a gradual undesirable rise in heater temperature as pumping progresses. This is true for systems based on liquid or solid aerosol-forming substrates. To monitor cooling between puffs, the circuit may be configured to track the ratio over time, and if the difference between the ratio maximum and the subsequent ratio minimum does not exceed a difference threshold stored in memory, power supplied to the heater may be limited or an indication provided.

The circuit may be configured to prevent the supply of power to the heater element for a predetermined stop period when an adverse condition exists.

The electrical circuit may be configured to prevent the supply of electrical power to the heater until the heater or a consumable portion containing the aerosol-forming substrate is replaced.

Alternatively or additionally, the circuitry may be configured to continuously calculate whether the ratio has reached a threshold and compare the time taken for the ratio to reach the threshold with a stored time value, and in the event that the time taken to reach the threshold is less than the stored time value or the ratio does not reach the threshold for an expected period of time, determine that an adverse condition exists and prevent or reduce the supply of power to the heater. If the threshold is reached faster than expected, it may indicate a dry heater element or dry substrate, or may indicate an incompatible, counterfeit or damaged heater. Similarly, if the threshold is not reached within the expected period of time, it may indicate a counterfeit or damaged heater or substrate. This may allow for a quick determination of counterfeit, damaged or incompatible heaters or substrates.

As described and indicating a dry condition at the heater element, it was found that adverse conditions may indicate a heater with electrical characteristics outside of the expected characteristic range. This may be due to heater failure, because material accumulates on the heater over its lifetime, or because it is an unauthorized or counterfeit heater. For example, if a manufacturer uses stainless steel heater elements, the initial resistance of those heater elements at room temperature may be expected to be within a particular resistance range. Further, it is contemplated that the ratio between the initial resistance of the heater and the change in resistance relative to the initial resistance has a particular value due to its dependence on the heater element material. If, for example, a heater element formed of Ni-Cr is used, the ratio will be lower than expected since Ni-Cr has a much lower temperature coefficient of resistance than stainless steel. Accordingly, the circuit may be configured to determine an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is less than a minimum threshold, and limit the supply of power to the heater based on the result. This will prevent the use of some unauthorized heaters. If the ratio is below a minimum threshold, the circuitry may prevent power supply to the heater.

A plurality of different thresholds may be used to generate different control strategies for different conditions. For example, a highest threshold and a lowest threshold may be used to set the limit at which replacement of the substrate heater is required before further power is supplied. The circuit may be configured to prevent the supply of power to the heater until the heater or aerosol-forming substrate is replaced if the ratio exceeds a highest threshold or is less than a lowest threshold. One or more intermediate thresholds may be used to detect excessive pumping activity at the heater that results in dry conditions. The circuitry may be configured to prevent the supply of power to the heater for a certain period of time or until a subsequent user puff if the intermediate threshold is exceeded but the highest threshold is not exceeded. The one or more intermediate thresholds may also be used to trigger an indication to the user that the aerosol-forming substrate is nearly exhausted and will soon need to be replaced. The circuit may be configured to provide an indication, which may be visual, audible or tactile, if the intermediate threshold is exceeded but the highest threshold is not exceeded.

One method for detecting a counterfeit, damaged or incompatible heater is to check the resistance of the heater or the rate of change of resistance of the heater when the heater is first used or inserted into a device or system. The circuit may be configured to measure the initial resistance of the heater element within a predetermined period of time after the supply of power to the heater. The predetermined time period may be a short time period and may be between 50ms and 200 ms. For heaters containing a grid heating element, the predetermined period of time may be about 100 ms. Preferably, the predetermined period of time is between 50ms and 150 ms. The circuit may be configured to determine an initial rate of change of resistance during a predetermined period of time. This may be done by taking a plurality of resistance measurements at different times during a predetermined time period and calculating a rate of change of resistance based on the plurality of resistance measurements. The circuit may be configured to measure the initial resistance of the heater or the rate of change of resistance of the heater in the form of a separate routine that uses much lower power to supply power to the heater to heat the aerosol-forming substrate, or may measure the initial resistance of the heater before significant heating has occurred during the period between the initial period in which the heater is activated. The circuit may be configured to compare the initial resistance of the heater or the initial rate of change of resistance of the heater to a range of acceptable values and if the initial resistance or initial rate of change of resistance is outside the range of acceptable values, the supply of power to the electric heater may be prevented or an indication provided until the heater or aerosol-forming substrate is replaced.

If the initial resistance or the initial rate of change of resistance is within the range of acceptable values, the circuit may be configured to determine that an acceptable heater is present when the ratio between the initial resistance of the heater and the change in resistance relative to the initial resistance is less than a maximum threshold or greater than a minimum threshold stored in the memory, and control the power supplied to the electric heater based on whether an acceptable heater is present, or provide an indication if an acceptable heater is not present.

The circuitry may be configured to determine that an acceptable heater is present within the first second of supplying power to the heater.

In a second aspect, there is provided a heater assembly comprising:

an electric heater comprising at least one heating element; and

a circuit connected to the electric heater and including a memory, the circuit configured to determine that an adverse condition exists when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold or less than a minimum threshold stored in the memory or when the ratio reaches a threshold stored in the memory outside of an expected period of time, and to control power supplied to the electric heater based on whether an adverse condition exists or to provide an indication based on whether an adverse condition exists.

The heater assembly may be configured for use in an aerosol-generating system and may be configured to heat the aerosol-forming substrate in use.

In a third aspect, there is provided an electrically operated aerosol-generating system comprising:

a power source; and

a circuit connected to the power source and including a memory, the circuit configured to be connected to an electric heater in use and to determine an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold or less than a minimum threshold stored in the memory or when the ratio reaches a threshold stored in the memory outside of an expected period of time, and to control power supplied to the electric heater based on whether an adverse condition exists or to provide an indication based on whether an adverse condition exists.

In a fourth aspect of the invention, there is provided an electrical circuit for use in an electrically operated aerosol-generating device, the electrical circuit being connected, in use, to an electrical heater and to a power source, the electrical circuit comprising a memory and being configured to determine an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold or less than a minimum threshold stored in the memory or when the ratio reaches a threshold stored in the memory outside an expected period of time, and to control the power supplied to the electrical heater based on whether an adverse condition is present or to provide an indication based on whether an adverse condition is present.

In a fifth aspect of the invention there is provided an electrical circuit for use in an electrically operated aerosol-generating device, the electrical circuit being connected, in use, to an electrical heater for heating an aerosol-forming substrate and to a power supply, the electrical circuit comprising a memory and being configured to measure an initial resistance of the heater or an initial rate of change of resistance of the heater over a predetermined period of time after power is supplied to the heater, to compare the initial resistance of the heater or the initial rate of change of resistance of the heater with a range of acceptable values, and to prevent the supply of power to the electrical heater or provide an indication until the heater or the aerosol-forming substrate is replaced if the initial resistance or the initial rate of change of resistance is outside the range of acceptable values.

The predetermined time period may be a short time period and may be between 50ms and 200 ms. For heaters containing a grid heating element, the predetermined period of time may be about 100 ms. Preferably, the predetermined period of time is between 50ms and 150 ms. The circuit may be configured to determine an initial rate of change of resistance during a predetermined period of time. This may be done by taking a plurality of resistance measurements at different times during a predetermined time period and calculating a rate of change of resistance based on the plurality of resistance measurements.

If the initial resistance is within the range of acceptable resistance values, the circuit may be configured to determine a ratio between the initial resistance of the heater and the change in resistance from the initial resistance, and compare the ratio to a maximum or minimum threshold value stored in memory, and if the ratio is less than the maximum threshold value or greater than the minimum threshold value stored in the memory, determine that an acceptable heater is present, and control the power supplied to the electric heater based on whether an acceptable heater is present, or provide an indication based on whether an acceptable heater is present.

In a sixth aspect, there is provided a method of controlling the supply of power to a heater in an electrically operated aerosol-generating system, the system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the method comprising:

determining an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold or less than a minimum threshold stored in a memory or when the ratio reaches a threshold stored in the memory outside of an expected period of time, and controlling the power supplied to the electric heater or providing an indication to a user depending on whether an adverse condition exists.

The method may include measuring an initial resistance of the heater element and measuring a resistance of the heater element at a time after initial delivery of power from the power source to the electric heater.

The method may include supplying constant power to the heater while supplying power. Alternatively, variable power may be supplied depending on other operating parameters. In such a case, the threshold may depend on the power supplied to the heater.

The method may comprise determining the initial resistance before first use of the heater. If the initial resistance is measured before the heater is first used, then it can be assumed that the heater element is at about room temperature. Since the expected change in resistance over time may depend on the initial temperature of the heater element, measuring the initial resistance at or near room temperature allows a narrower expected band of behavior to be set.

The method may include calculating the initial resistance as the initial resistance measurement minus an assumed parasitic resistance caused by other electrical components and electrical contacts within the system.

The electrically operated aerosol-generating system may comprise a puff detector for detecting when a user puffs on the system, and the method may comprise supplying power from the power supply to the heater element when the puff detector detects a puff, determining whether an adverse condition exists during each puff, and preventing the supply of power from the power supply to the heater element in the event that an adverse condition exists for a predetermined number of consecutive user puffs.

The method may comprise preventing the supply of power from the power supply to the heater element in the presence of an adverse condition.

The method may include continuously determining whether an adverse condition exists and preventing the supply of power to the heater when an adverse condition exists and continuously preventing the supply of power to the heater element until the adverse condition no longer exists.

The method may include preventing the supply of power to the heater element for a predetermined stop period when an adverse condition exists.

Alternatively or additionally, the method may comprise continuously calculating whether the ratio has exceeded a threshold and comparing the time taken to reach the threshold with a stored time value, and in the event that the time taken to reach the threshold is less than the stored time value, determining an adverse condition and controlling the supply of power to the heater.

In a seventh aspect, there is provided a method of detecting an incompatible or damaged heater in an electrically operated aerosol-generating system, the system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the method comprising:

an incompatible or defective heater is determined when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold value or less than a minimum threshold value stored in a memory or when the ratio reaches a threshold value stored in the memory outside of an expected period of time.

The method may comprise preventing the supply of power to the electric heater or providing an indication until the heater or aerosol-forming substrate is replaced, in the event that it is determined that an incompatible heater is present.

The method may further comprise measuring the initial resistance of the heater or the initial rate of change of resistance of the heater over a predetermined period of time after power is supplied to the heater, comparing the initial resistance of the heater or the initial rate of change of resistance of the heater to a range of acceptable values, and if the initial resistance or initial rate of change of resistance is outside the range of acceptable values, preventing power supply or providing an indication to the electric heater until the heater or aerosol-forming substrate is replaced.

The predetermined time period may be a short time period and may be between 50ms and 200 ms. For heaters containing a grid heating element, the predetermined period of time may be about 100 ms. Preferably, the predetermined period of time is between 50ms and 150 ms.

Determining an initial rate of change of resistance during the predetermined time period may be accomplished by taking a plurality of resistance measurements at different times during the predetermined time period and calculating a rate of change of resistance based on the plurality of resistance measurements.

The method may further comprise detecting when a heater or aerosol-forming substrate is inserted into the system. The method may be performed immediately after detecting that a heater or aerosol-forming substrate has been inserted into the system.

In an eighth aspect of the invention there is provided a method of detecting an incompatible or damaged heater in an electrically operated aerosol-generating system, the system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the method comprising:

measuring an initial resistance of the heater or an initial rate of change of resistance of the heater for a predetermined period of time after power is supplied to the heater, comparing the initial resistance of the heater or the initial rate of change of resistance of the heater with a range of acceptable values, and if the initial resistance or initial rate of change of resistance is outside the range of acceptable values, preventing power supply or providing an indication to the electric heater until the heater or the aerosol-forming substrate is replaced.

The predetermined time period may be a short time period and may be between 50ms and 200 ms. For heaters containing a grid heating element, the predetermined period of time may be about 100 ms. Preferably, the predetermined period of time is between 50ms and 150 ms.

Determining an initial rate of change of resistance during the predetermined time period may be accomplished by taking a plurality of resistance measurements at different times during the predetermined time period and calculating a rate of change of resistance based on the plurality of resistance measurements.

The method may further comprise detecting when a heater or aerosol-forming substrate is inserted into the system. The method may be performed immediately after detecting that a heater or aerosol-forming substrate has been inserted into the system.

In a ninth aspect, there is provided a computer program product directly loadable into the internal memory of a microprocessor, comprising software code portions for performing the steps of the sixth, seventh or eighth aspects when the product is run on a microprocessor in an electrically operated aerosol-generating system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the microprocessor being connected to the electric heater and to the power supply.

The computer program product may be provided as a piece of downloadable software or on a computer-readable storage medium.

According to a tenth aspect, there is provided a computer readable storage medium having stored thereon a computer program according to the ninth aspect.

Features described in relation to one aspect of the invention may be applied to other aspects of the invention. In particular, features described in relation to the first aspect may be applicable to the second, third, fourth and fifth aspects of the invention. The features described in relation to the first, second, third, fourth and fifth aspects of the invention may also be applicable to the sixth, seventh and eighth aspects of the invention.

The invention is defined in the claims. However, a non-exhaustive list of non-limiting examples is provided below.

Example 1: an electrically operated aerosol-generating system comprising:

an electric heater comprising at least one heating element for heating the aerosol-forming substrate;

a power source; and

a circuit connected to the electric heater and to the power source and including a memory, the circuit configured to determine an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold value stored in the memory or less than a minimum threshold value stored in the memory or when the ratio reaches a threshold value stored in the memory outside of an expected period of time, and to limit power supplied to the electric heater or provide an indication if an adverse condition exists.

Example 2. an electrically operated aerosol-generating system according to example 1, wherein the system comprises a device and a removable cartridge, wherein the power source and the electrical circuit are in the device and the electric heater is in the removable cartridge, and wherein the cartridge comprises a liquid aerosol-forming substrate.

Example 3. an electrically operated aerosol-generating system according to example 1 or 2, wherein in use the aerosol-forming substrate is in contact with the heating element.

Example 4. the electrically operated aerosol-generating system of any of examples 1 to 3, comprising a puff detector for detecting when a user puffs on the system, wherein the puff detector is connected to the electrical circuit and wherein the electrical circuit is configured to supply power from the power supply to the heating element when the puff detector detects a puff, and wherein the electrical circuit is configured to determine whether an adverse condition exists during each puff.

Example 5. an electrically operated aerosol-generating system according to any of examples 1 to 4, wherein the system is an electrically heated smoking system.

Example 6. a heater assembly, comprising:

an electric heater comprising at least one heating element; and

a circuit connected to the electric heater and including a memory, the circuit configured to determine that an adverse condition exists when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold stored in the memory or less than a minimum threshold stored in the memory or when the ratio reaches a threshold stored in the memory outside of an expected period of time, and to control power supplied to the electric heater based on whether an adverse condition exists or to provide an indication if an adverse condition exists.

An example 7. an electrically operated aerosol-generating device, comprising:

a power source; and

a circuit connected to the power supply and including a memory, the circuit configured to be connected to an electric heater in use and to determine an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold stored in the memory or less than a minimum threshold stored in the memory or when the ratio reaches a threshold stored in the memory outside of an expected period of time, and to control power supplied to the electric heater based on whether or not an adverse condition exists or to provide an indication if an adverse condition exists.

Example 8 a circuit for use in an electrically operated aerosol-generating device, the circuit being connected, in use, to an electric heater and to a power supply, the circuit comprising a memory and being configured to determine an adverse condition when a ratio between an initial resistance of the heater and a change in resistance from the initial resistance is greater than a maximum threshold stored in the memory or less than a minimum threshold stored in the memory or when the ratio reaches a threshold stored in the memory outside an expected period of time, and to control the power supplied to the electric heater based on whether or not an adverse condition is present, or to provide an indication if an adverse condition is present.

Example 9 a circuit for use in an electrically operated aerosol-generating device, the circuit being connected, in use, to an electric heater for heating an aerosol-forming substrate and to a power supply, the circuit comprising a memory and being configured to measure an initial resistance or rate of initial change of resistance of the heater within a predetermined period of time after power is supplied to the heater, to compare the initial resistance or rate of initial change of resistance of the heater with a range of acceptable values, and if the initial resistance or rate of initial change of resistance is outside the range of acceptable values, to prevent power from being supplied to the electric heater or to provide an indication until the heater or aerosol-forming substrate is replaced.

An example 10. a method of controlling the supply of power to a heater in an electrically operated aerosol-generating system, the system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the method comprising:

determining an adverse condition when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold value stored in memory or less than a minimum threshold value stored in memory or when the ratio reaches a threshold value stored in the memory outside of an expected period of time, and limiting power supplied to the electric heater or providing an indication to a user depending on detecting an adverse condition.

Example 11 the method of example 10, further comprising measuring an initial resistance or rate of initial change of resistance of the heater over a predetermined period of time after supplying power to the heater, comparing the initial resistance or rate of initial change of resistance of the heater to a range of acceptable values, and if the initial resistance or rate of initial change of resistance is outside the range of acceptable values, preventing power from being supplied to the electric heater or providing an indication until the heater or the aerosol-forming substrate is replaced.

Example 12. the method of example 10 or 11, further comprising detecting when a heater or aerosol-forming substrate is inserted into the system.

An example 13 a method of detecting an incompatible or damaged heater in an electrically operated aerosol-generating system, the system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the method comprising:

an incompatible or defective heater is determined when a ratio between an initial resistance of the heater and a change in resistance relative to the initial resistance is greater than a maximum threshold value stored in memory or less than a minimum threshold value stored in memory or when the ratio reaches a threshold value stored in memory outside of an expected period of time.

An example 14. a method of detecting an incompatible or damaged heater in an electrically operated aerosol-generating system, the system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying electrical power to the electric heater, the method comprising:

measuring an initial resistance or rate of initial change of resistance of the heater within a predetermined period of time after power is supplied to the heater, comparing the initial resistance or rate of initial change of resistance of the heater with a range of acceptable values, and if the initial resistance or rate of initial change of resistance is outside the range of acceptable values, preventing power from being supplied to the electric heater or providing an indication until the heater or aerosol-forming substrate is replaced.

Example 15 a computer program product directly loadable into the internal memory of a microprocessor, comprising software code portions for performing the steps of any of examples 10 to 14 when said product is run on a microprocessor in an electrically operated aerosol-generating system comprising an electric heater comprising at least one heating element for heating an aerosol-forming substrate and a power supply for supplying power to the electric heater, the microprocessor being connected to the electric heater and to the power supply.

Drawings

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

FIGS. 1a to 1d are schematic diagrams of a system according to an embodiment of the invention;

FIG. 2 is an exploded view of a cartridge for use in the system as shown in FIGS. 1 a-1 d;

figure 3 is a detailed view of the filaments of the heater showing a meniscus of liquid aerosol-forming substrate between the filaments;

FIG. 4 is a schematic illustration of the change in resistance of the heater during a user puff;

FIG. 5 is a circuit diagram showing how the resistance of a heating element can be measured;

FIGS. 6 (a), (b) and (c) illustrate the control method after an adverse condition is detected;

figure 7 is a schematic diagram of a first alternative aerosol-generating system;

figure 8 is a schematic diagram of a second alternative aerosol-generating system; and is

FIG. 9 is a flow chart illustrating a method for detecting an unauthorized, damaged, or incompatible heater.

Detailed Description

Fig. 1a to 1d are schematic views of an aerosol-generating system comprising a cartridge according to an embodiment of the invention. Fig. 1a is a schematic view of an aerosol-generating device 10 and a separate cartridge 20, which together form an aerosol-generating system. In this example, the aerosol-generating system is an electrically operated smoking system.

The cartridge 20 contains an aerosol-forming substrate and is configured to be received in the cavity 18 within the device. The cartridge 20 should be replaceable by a user when the aerosol-forming substrate provided therein is exhausted. Fig. 1a shows the cartridge 20 just before insertion into the device, wherein the arrow 1 in fig. 1a indicates the direction of insertion of the cartridge.

The aerosol-generating device 10 is portable and has a size comparable to a conventional cigar or cigarette. The device 10 comprises a body 11 and a mouthpiece portion 12. The body 11 contains a battery 14 (e.g., a lithium iron phosphate battery), circuitry 16, and a cavity 18. The circuit 16 comprises a programmable microprocessor. The mouthpiece portion 12 is connected to the body 11 by a hinged connection 21 and is movable between an open position as illustrated in figure 1 and a closed position as illustrated in figure 1 d. The mouthpiece portion 12 is placed in an open position to allow insertion and removal of the cartridge 20, and in a closed position when the system is to be used to generate an aerosol. The mouthpiece portion comprises a plurality of air inlets 13 and outlets 15. In use, the user sucks or sucks on the outlet to draw air from the inlet 13 through the mouthpiece portion to the outlet 15 and then into the mouth or lungs of the user. An internal baffle 17 is provided to force air flowing through the mouthpiece portion 12 through the cartridge.

The cavity 18 has a circular cross-section and is sized to receive the housing 24 of the cartridge 20. Electrical connections 19 are provided at the sides of the cavity 18 to provide electrical connections between the control electronics 16 and the battery 14 and corresponding electrical contacts on the cartridge 20.

Fig. 1b shows the system of fig. 1a with the cartridge inserted into the cavity 18 and the cover plate 26 being removed. In this position, the electrical connector abuts an electrical contact on the cartridge.

Figure 1c shows the system of figure 1b with the cover 26 completely removed and the mouthpiece portion 12 being moved to the closed position.

Figure 1d shows the system of figure 1c with the mouthpiece portion 12 in the closed position. The mouthpiece portion 12 is held in the closed position by a clip-on mechanism. The mouthpiece portion 12 in the closed position holds the cartridge in electrical contact with the electrical connector 19 so that a good electrical connection is maintained in use regardless of the orientation of the system.

Fig. 2 is an exploded view of the cartridge 20. The cartridge 20 includes a generally cylindrical housing 24 having a size and shape selected to be received in the cavity 18. The housing contains capillary material 27, 28 soaked in a liquid aerosol-forming substrate. In this example, the aerosol-forming substrate comprises 39 wt% glycerin, 39 wt% propylene glycol, 20 wt% water and a flavour, and 2 wt% nicotine. The capillary material is a material that actively transports liquid from one end to the other and may be made of any suitable material. In this example, the capillary material is formed from polyester.

The housing has an open end to which the heater assembly 30 is secured. The heater assembly 30 includes a substrate 34 having an opening 35 formed therein; a pair of electrical contact portions 32 fixed to the substrate and separated from each other by a space 33; and a plurality of electrically conductive heater filaments 36 spanning the openings and secured to the electrical contact portions on a side opposite the openings 35.

The heater assembly 30 is covered by a removable cover plate 26. The cover plate comprises a liquid impermeable plastic sheet that is glued to the heater assembly but can be easily peeled off. Bosses are provided on the sides of the cover plate to allow the user to grasp the cover plate when peeling it off. It will now be apparent to those of ordinary skill in the art that although gluing is described as the method of securing the impermeable plastic sheet to the heater assembly, other methods familiar to those of skill in the art, including heat sealing or ultrasonic welding, may also be used, so long as the cover sheet can be easily removed by the consumer.

In the cartridge of fig. 2 there are two separate capillary materials 27, 28. A disc of first capillary material 27 is provided to contact the heater elements 36, 32 in use. A larger body of second capillary material 28 is provided on the first capillary material 27 on the side opposite the heater assembly. Both the first and second capillary materials retain the liquid aerosol-forming substrate. The first capillary material 27 contacting the heater element has a higher thermal decomposition temperature (at least 160 ℃ or higher, e.g., about 250 ℃) than the second capillary material 28. The first capillary material 27 effectively acts as a spacer separating the heater elements 36, 32 from the second capillary material 28 so that the second capillary material is not exposed to temperatures above its thermal decomposition temperature. The thermal gradient across the first capillary material exposes the second capillary material to a temperature below its thermal decomposition temperature. The second capillary material 28 may be selected to have superior wicking properties to the first capillary material 27, may hold more liquid per unit volume than the first capillary material and may be less expensive than the first capillary material. In this example, the first capillary material is a heat resistant material, such as a fiberglass or fiberglass-containing material, and the second capillary material is a polymer, such as a suitable capillary material. Exemplary suitable capillary materials include those discussed herein, and in alternative embodiments may include High Density Polyethylene (HDPE) or polyethylene terephthalate (PET).

The capillary materials 27, 28 are advantageously oriented in the housing 24 to deliver liquid to the heater assembly 30. When the cartridge is assembled, the heater filaments 36, 37, 38 may be in contact with the capillary material 27 and may therefore deliver the aerosol-forming substrate directly to the mesh heater. Fig. 3 is a detailed view of the filaments 36 of the heater assembly showing a meniscus 40 of liquid aerosol-forming substrate between the heater filaments 36. It can be seen that the aerosol-forming substrate contacts a majority of the surface of each filament, so that a majority of the heat generated by the heater assembly passes directly into the aerosol-forming substrate.

Thus, in normal operation, the liquid aerosol-forming substrate contacts a substantial portion of the surface of the heater filament 36. However, when the majority of the liquid substrate in the cartridge has been used, less liquid aerosol-forming substrate will be delivered to the heater filament. In the case of less volatile liquid, less energy is absorbed by the vaporization enthalpy and more energy supplied to the heating wire is directed to raise the temperature of the heating wire. Thus as the heater element dries, the rate at which the temperature of the heater element increases will increase for a given applied power. The heater element may dry out because the aerosol-forming substrate in the cartridge is almost spent or because the user draws very long or very frequently and the liquid is not delivered to the heater filament as quickly as it vaporises.

In use, the heater assembly operates by resistive heating. Current is passed through the filament 36 under the control of the control electronics 16 to heat the filament to within a desired temperature range. The grid or array of filaments has a significantly higher electrical resistance than the electrical contacts 32 and the electrical connectors 19, so that higher temperatures are localized to the filaments. In this example, the system is configured to generate heat by providing an electrical current to the heater assembly in response to a user puff. In another embodiment, the system may be configured to generate heat continuously while the device is in an "on" state. Different materials for the filaments may be suitable for different systems. For example, in a continuous heating system, graphite wires are suitable because they have a relatively low specific heat capacity and are compatible with low current heating. In a suction drive system that generates heat in a short time using high current pulses, stainless steel wires with a high specific heat capacity may be more suitable.

The system includes a puff sensor configured to detect when a user is drawing air through the mouthpiece portion. A puff sensor (not illustrated) is connected to the control electronics 16, and the control electronics 16 is configured to supply current to the heater assembly 30 only when it is determined that a user is puffing the device. Any suitable airflow sensor may be used as the suction sensor, such as a microphone or a pressure sensor.

To detect this increase in the rate of change of temperature, the circuit 16 is configured to measure the resistance of the heater wire. The heater wire in this example is formed of stainless steel and therefore has a positive temperature coefficient of resistance. This means that as the temperature of the heater filament increases, its resistance also increases.

Fig. 4 is a schematic of the change in resistance of the heater during a puff taken by the user. The x-axis is the time after the initial detection of user suction and hence the supply of power to the heater. The y-axis is the resistance of the heater assembly. It can be seen that the heater assembly has an initial resistance R1 before any heating has occurred. R1 is composed of parasitic resistance RP due to the electrical contact portion 32 and the electrical connection piece 19 and the contact portion therebetween and resistance R0 of the heater wire. As power is applied to the heater during user suction, the temperature of the heater wire, and thus the resistance of the heater wire, increases. As illustrated, at time t₁Here, the resistance of the heater assembly is R2. From initial resistance to time t₁The change in heater assembly resistance at resistance is thus Δ R — R2-R1.

In this example, it is assumed that the parasitic resistance RP does not change as the heater wire heats up. This is because RP can be attributed to non-heated components such as the electrical contact portions 32 and the electrical connection members 19. The RP value is assumed to be the same for all cartridges and the value is stored in the memory of the circuit.

The correlation between the resistance of the heater filament and its temperature is given by the following equation:

R2＝R0×(1+α×ΔT)+RP (1)

where α is the temperature coefficient of the heater filament resistance and Δ T is the initial temperature and time T before applying power to the heater₁Temperature change between temperatures.

A threshold K is stored in the circuit, where K is equal to α Δ Tmax. If at time t₁The temperature rises above Δ Tmax, then an adverse condition is considered to exist, such as a dry condition at the heater.

From equation 1:

K＝α×ΔTmax＝ΔR/R0 (2)

thus, to detect a rapid increase in temperature indicative of a dry condition at the heater filament, the value of the ratio Δ R/R0 may be compared to the value of the stored value of K. If Δ R/R0> K, then a dry condition exists at the heater.

This comparison may be performed by circuitry, but the inequalities may be rearranged to meet the requirements of the electronic processing operation, particularly avoiding the need to perform any segmentation. In this example, software running on a microprocessor in the circuit makes the following comparison derived from equation 1:

if R2> (R1 × (K +1) -K × RP), then drying conditions are present at the heater

(3)

R2 and R1 are both measured values, and K and RP are stored in memory. It is desirable to measure the value of R1 before any heating is performed, in other words before the heater is first activated, and that this measurement is used for all subsequent puffs. This avoids any error due to residual heat from previous pumping. R1 may be measured only once for each cartridge and the detection system for determining when a new cartridge is inserted, or R1 may be measured each time the system is switched on.

Other adverse conditions besides dry heater conditions can be detected in this way. If a cartridge having a heater formed of materials with different temperature coefficients of resistance is used in the system, the circuitry may detect it and may be configured not to supply power to it. In this example, the heater wire is formed of stainless steel. A cartridge with a heater formed of Ni-Cr will have a lower temperature coefficient of resistance, meaning that its resistance rises more slowly with increasing temperature. Thus if the value K2 (which corresponds to the expected value for the stainless steel heater element at time t) would be equal to α Δ Tmin₁Lowest temperature rise) is stored in memory, if R2 is present<(R1 × (K2+1) -K × RP), then the loop determination corresponds to an adverse condition of an unauthorized cartridge being present in the system. FIG. 9 illustrates a process for detecting incompatible heaters.

The system may therefore be configured to compare R2 or Δ R/R0 or even Δ R/R1 to the high and low storage thresholds in order to determine adverse conditions. R1 may also be compared to one or more thresholds that check that it is within an expected range. It may even be that one high storage threshold is exceeded and different actions are taken depending on which high threshold is exceeded. For example, if the highest threshold is exceeded, the circuit may prevent further power supply until the heater and/or substrate is replaced. This may indicate a completely depleted substrate or a damaged or incompatible heater. A lower threshold may be used to determine when the substrate is near depletion. If this lower threshold is exceeded, but the higher threshold is not exceeded, the circuit may simply provide an indication, such as an illuminated LED, that the display substrate will soon require replacement.

The ratio of ar/R0 may be continuously monitored to determine if the heater is sufficiently cool between puffs. If the ratio does not reach below the cool threshold between puffs because the user puffs very frequently, the circuitry may prevent or limit the supply of power to the heater until the ratio falls below the cool threshold. Alternatively, a comparison may be made between the maximum value of the ratio during pumping and the minimum value of the ratio after pumping to determine whether sufficient cooling has occurred.

Additionally, the ratio Δ R/R0 may be continuously monitored and, surprisingly, the time it reaches a threshold compared to a time threshold. If Δ R/R0 reaches the threshold much faster or slower than expected, it may indicate an adverse condition, such as an incompatible heater. The rate of change of Δ R may also be determined and compared to a threshold value. If Δ R rises very quickly or very slowly, it may indicate an adverse condition. These techniques may allow for extremely fast detection of incompatible heaters.

Fig. 5 is a schematic circuit diagram showing how the resistance of the heating element can be measured. In fig. 5, a heater 501 is connected to a battery 503 that supplies a voltage V2. The heater resistance to be measured at a particular time is R_{Heating device}. An additional resistor 505 of known resistance r is inserted in series with the heater 501 and connected to a voltage V1, the voltage V1 being intermediate between ground and the voltage V2. In order for the microprocessor 507 to measure the resistance R of the heater 501_{Heating device}The current through heater 501 and the voltage across heater 501 can be measured. Then, canThe resistance is determined using the following well-known formula:

V＝IR (4)

in FIG. 5, the voltage across the heater is V2-V1, and the current through the heater is I. Thus:

an additional resistor 505, whose resistance r is known, is used to determine the current I, again using equation (1) above. The current flowing through resistor 505 is I and the voltage across resistor 505 is V1. Thus:

thus, combinations (5) and (6) give:

thus, when using an aerosol-generating system, microprocessor 507 can measure V2 and V1, and knowing the value of R, the heater resistance R at different times can be determined_{Heating of}A device.

The circuitry may control the supply of power to the heater in a number of different ways upon detection of an adverse condition. Alternatively or additionally, the circuit may simply provide an indication to the user that an adverse condition has been detected. The system may include an LED or display, or may contain a microphone, and these components may be used to alert the user of an adverse condition.

Fig. 6 (a) illustrates a first control process for the suction driving system. In the flow illustrated in fig. 6 (a), where Δ R/R0 exceeds the high threshold of a single puff, the circuit continues to supply power to the heater. Fig. 6 (a) shows three consecutive puffs during which the high threshold is exceeded. Power to the heater is stopped only if ar/R0 exceeds the high threshold for a particular number of consecutive puffs (such as 3, 4, or 5 puffs). A single threshold-exceeding situation may be the result of a very long user aspiration, but several consecutive aspirations during which the high threshold is exceeded are more likely the result of the cartridge becoming empty. At that point in time, the cartridge may be deactivated, for example by blowing a fuse within the cartridge, or the circuit may block the supply of further power until the cartridge is replaced or refilled.

Fig. 6 (b) discloses another control process that may be used as an alternative to or in addition to the process described with reference to fig. 6 (b). In the control process of fig. 6 (b), once it is determined that the high threshold has been exceeded, the circuit stops the supply of power to the heater until the end of the user's puff. When a new user puff is detected, power is supplied to the heater again. This may be useful to prevent the heater from becoming too hot even when the user is sucking excessively. As with stopping power, an indication that a threshold has been reached may be provided.

Fig. 6 (c) illustrates an alternative control process in which the circuit stops the supply of power to the heater once it is determined that the high threshold has been exceeded. The power supply is also blocked for subsequent user puffs. In order to supply power to the heater again, the user may have to replace the cartridge or perform a reset operation. This control process may be used in conjunction with the processes described with reference to fig. 6 (a) and 6 (b), but based on higher thresholds than those used in the processes described with reference to fig. 6 (a) and 6 (b). A higher threshold may be indicative of a completely depleted aerosol-forming substrate or of a defective or incompatible heater.

Although the invention has been described with reference to a cartridge-based system with a mesh heater, the same adverse condition detection method may be used in other aerosol-generating systems.

Fig. 7 illustrates an alternative system according to the present invention that also uses a liquid matrix and capillary material. In fig. 7, the system is a smoking system. The smoking system 100 of figure 7 comprises a housing 101 having a mouth end 103 and a body end 105. In the body end, a power supply and circuitry 109 in the form of a battery 107 is provided. A puff detection system 111 is also provided in cooperation with the circuitry 109. In the mouthpiece end, a liquid storage portion in the form of a cartridge 113 containing a liquid 115, a capillary wick 117 and a heater 119 are provided. Note that the heater is only schematically shown in fig. 7. One end of the capillary wick 117 extends into the cartridge 113, and the other end of the capillary wick 117 is surrounded by a heater 119. The heater is connected to the circuit via a connection 121, which may pass along the outside of the cartridge 113 (not shown in fig. 7). The housing 101 further comprises an air inlet 123, an air outlet 125 at the mouthpiece end, and an aerosol-forming chamber 127.

In use, the operation is as follows. Liquid 115 is transported by capillary action from the end of the cartridge 113 that extends from the wick 117 into the cartridge to the other end of the wick that is surrounded by the heater 119. When a user draws on the aerosol-generating system at the air outlet 125, ambient air is drawn through the air inlet 123. In the arrangement illustrated in fig. 7, the puff detection system 111 senses the puff and activates the heater 119. The battery 107 supplies electrical power to the heater 119 to heat the end of the wick 117 surrounded by the heater. The liquid in the end of wick 117 is vaporized by heater 119 to produce a supersaturated vapour. At the same time, the vaporized liquid is replaced with another liquid that moves along the wick 117 by capillary action. The resulting supersaturated vapour mixes with the air stream and is carried in the air stream from the air inlet 123. In the aerosol-forming chamber 127, the vapour condenses to form an inhalable aerosol, which is carried towards the outlet 125 and into the mouth of the user.

In the embodiment shown in fig. 7, as in the embodiment of fig. 1a to 1d, the circuitry 109 and puff detection system 111 are programmable.

The capillary wick may be made of a variety of porous or capillary materials and preferably has a known predetermined capillarity. Examples include ceramic-based or graphite-based materials in the form of fibers or sintered powders. Cores with different porosities may be used to accommodate different liquid physical properties, such as density, viscosity, surface tension, and vapor pressure. The wick must be adapted so that when the liquid storage portion has sufficient liquid, the desired amount of liquid can be delivered to the heater.

The heater may comprise at least one heating wire or filament extending around the capillary wick.

As in the systems described with reference to figures 1 to 3, if the liquid in the cartridge is used up or if the user performs an extremely long deep draw, the capillary material forming the wick may dry out near the heater wire. In the same manner as described with reference to the systems of fig. 1-3, the change in resistance of the heater wire during the first portion of each draw can be used to determine if an adverse condition, such as a dry wick, is present.

Systems of the type illustrated in fig. 7 may have appreciable variation in heater resistance, even between cartridges of the same type, due to the variation in length of the heater wire wrapped around the wick. The invention is particularly advantageous due to the following circumstances: it does not require circuitry to store the maximum heater resistance value as a threshold; but instead uses the resistance increase relative to the initial resistance measurement value.

Figure 8 illustrates yet another aerosol-generating system in which the invention may be implemented. The embodiment of figure 8 is an electrically heated tobacco device in which the tobacco-based solid substrate is heated but not combusted to produce an aerosol for inhalation. In fig. 8, the components of the aerosol-generating device 700 are shown in a simplified manner and are not drawn to scale. Elements not relevant for understanding this embodiment have been omitted to simplify fig. 8.

The electrically heated aerosol-generating device 200 comprises a housing 203 and an aerosol-forming substrate 210 (e.g. a cigarette). The aerosol-forming substrate 210 is pushed inside the cavity 205 formed by the housing 203 into thermal proximity with the heater 201. The aerosol-forming substrate 210 releases various volatile compounds at different temperatures. By controlling the operating temperature of the electrically heated aerosol-generating device 200 below the release temperature of some volatile compounds, the release or formation of these aerosol components can be avoided.

Within the housing 203 is a power source 207, such as a rechargeable lithium ion battery. The circuit 209 is connected to the heater 201 and the power supply 207. The circuit 209 controls the power supplied to the heater 201 so as to adjust the temperature thereof. The aerosol-forming substrate detector 213 may detect the presence and characteristics of the aerosol-forming substrate 210 in thermal proximity to the heater 201 and signal the presence of the aerosol-forming substrate 210 to the circuitry 209. The provision of a matrix detector is optional. An air flow sensor 211 is provided within the housing and is connected to the circuitry 209 to detect the flow rate of air through the device.

In the depicted embodiment, the heater 201 is one or more resistive tracks deposited on a ceramic substrate. The ceramic substrate is in the form of a sheet and is inserted into the aerosol-forming substrate 210 in use. The heater forms part of the apparatus and can be used to heat many different substrates. However, the heater may be a replaceable component, and the replacement heater may have a different resistance.

A system of the type described in fig. 8 may be a continuous heating system in which the temperature of the heater is maintained at a target temperature while the system is on, or it may be a suction driving system in which the temperature of the heater is increased by supplying more power during a period when suction is detected.

In the case of the suction drive system, the operation is similar to the poles described with reference to the previous embodiments. If the substrate dries near the heater, the resistance of the heater will rise more quickly for a given applied power than if the substrate still contains aerosol former (which can vaporise at a relatively low temperature).

In the case of a continuous heating system, there will initially be a drop in heater temperature as a result of the cooling effect of the air flow through the heater as the user draws on the system. In a similar manner as described, when puff is first detected, the heater resistance may be measured and recorded as R1, and as the system returns the heater to the target temperature, may be at time t after puff detection₁A subsequent resistance R2 is measured. As previously described for determining whether the substrate is drying near the heater, Δ R and R0 may then be calculated as previously described, and the ratio of Δ R/R0 may then be compared to a stored thresholdAnd (4) the ratio. The substrate may dry out either because it has been exhausted through use, or because it is old or has been improperly stored, or because it is counterfeit and has a different moisture content than the authentic aerosol-forming substrate.

The system of fig. 8 includes a warning LED 215 in circuit 209 that illuminates when an adverse condition is detected.

FIG. 9 is a flow chart illustrating a method for detecting an unauthorized, damaged, or incompatible heater. In a first step 300, insertion of a cartridge (including a heater) into the device is detected. The heater resistance R is then measured in step 300₁. This occurs at a predetermined time period, such as 100ms, after power is supplied to the heater. In step 320, the resistance measurement R is measured₁Compared to an expected or acceptable resistance range. The acceptable resistance range takes into account manufacturing tolerances and variations between the real heater and the substrate. If R is₁Outside the expected range, then the process proceeds to step 330 where an indication (e.g., an audible alarm) is provided and the supply of power to the heater is prevented, as it is deemed incompatible with the device. The process then returns to step 300 to await detection of insertion of a new cartridge.

As a measure of the initial resistance R in step 300₁Alternatively or in addition to the measurement, the initial rate of change of resistance may be measured for a predetermined period of time (such as 100ms) after the supply of power to the heater. This may be done by taking a plurality of resistance measurements at different times during a predetermined period of time and then calculating an initial rate of change of resistance from the plurality of resistance measurements and the time at which those measurements were taken. In the same manner that a particular heater design can be expected to have an initial resistance within an acceptable range of values, the particular heater design can be expected to have an initial rate of change of resistance within a range of acceptable rates of change of resistance value for a given applied power. The initial rate of change calculated value of resistance may be compared to an acceptable range of rates of change of resistance values and if the calculated value of rate of change of resistance is outside the acceptable range, the process proceeds to step 330.

If R is determined in step 320₁At a desired resistanceWithin range, then the process proceeds to step 340. In step 340, power is applied to the heater for a time period t₁Thereafter, the ratio Δ R/R0 is calculated. Advantageously, let t₁Selected to be a short period of time before significant aerosol generation occurs. In step 350, the value of the ratio Δ R/R0 is compared to an expected or acceptable range of values. The range of expected values again takes into account variations in manufacturing the heater and substrate assembly. If the value of Δ R/R0 is outside the expected range, then the heater is deemed incompatible and the process passes to step 330 and then back to step 300 as previously described. If the value of Δ R/R0 is within the expected range, then the process proceeds to step 360, where power is supplied to the heater to allow aerosol generation on demand by the user.

Although the invention has been described with reference to three different types of electrical smoking systems, it will be clear that it is applicable to other aerosol generating systems.

It should also be clear that the invention can be implemented in the form of a computer program product for execution on a programmable controller within an existing aerosol-generating system. The computer program product may be provided as a piece of downloadable software or on a computer-readable medium, such as a compact disc.

The exemplary embodiments described above are illustrative and not restrictive. In view of the exemplary embodiments discussed above, other embodiments consistent with the above exemplary embodiments will now be apparent to those of ordinary skill in the art.