Aerosol-generating systems with liquid level determination and methods of determining liquid level in aerosol-generating systems

1. An electrically operated aerosol-generating system comprising:

a liquid storage portion configured to store a liquid from which aerosol may be generated;

an electric heater, the electric heater associated with a temperature coefficient of resistance;

a capillary wick extending between the liquid storage portion and the electric heater, the capillary wick configured to convey liquid from the liquid storage portion to the electric heater;

an electric power supply; and

electric circuitry connected to the electric heater, the electric circuitry including a resistor electrically connected in series with the electric heater, a processor, a memory, and a detection device, the detection device configured to sense a draw of air through the electrically operated aerosol-generating system, the processor configured to control a supply of electric power from the electric power supply to the electric heater to controllably activate the electric heater, the resistor having a known electrical resistance, the memory configured to store the temperature coefficient of resistance of the electric heater, the known electrical resistance of the resistor, and an empirically-determined relationship between temperature differences of the electric heater and amounts of liquid in the liquid storage portion,

wherein the processor is configured to

activate the electric heater for a first heating time period, in response to air being drawn through the electrically operated aerosol-generating system, such that

liquid in the capillary wick is vaporized during the first heating time period, and

the electric heater is deactivated at an ending of the first heating time period based on an end of the drawing of air through the electrically operated aerosol-generating system,

activate the electric heater for a second heating time period to supply a predetermined amount of power to the electric heater in response to an elapse of a first cooling time period after the ending of the first heating time period, the second heating time period beginning at a first time and ending at a second time such that the electric heater is deactivated at the second time, wherein the second heating time period is shorter than the first heating time period and is sufficiently short such that a temperature of the electric heater remains below a vaporization temperature of the liquid and the liquid in the capillary wick is not vaporized during the activation of the electric heater for the second heating time period,

record a first temperature measurement of the electric heater at the second time at the ending of the second heating time period, such that the first temperature measurement is recorded while the temperature of the electric heater remains below the vaporization temperature of the liquid and the liquid is still wicking on to the capillary wick,

activate the electric heater for a third heating time period to supply the predetermined amount of power to the electric heater in response to an elapse of a second cooling time period after the ending of the second heating time period, the third heating time period beginning at a third time and ending at a fourth time such that the electric heater is deactivated at the fourth time, wherein the third heating time period is shorter than the first heating time period and is sufficiently short such that the temperature of the electric heater remains below the vaporization temperature of the liquid during the activation of the electric heater for the third heating time period,

record a second temperature measurement of the electric heater at the fourth time at the ending of the third heating time period, such that the second temperature measurement is recorded while the temperature of the electric heater remains below the vaporization temperature of the liquid and the liquid is still wicking on to the capillary wick,

determine a temperature difference of the electric heater between the first temperature measurement of the electric heater and the second temperature measurement of the electric heater, and

determine an amount of liquid in the liquid storage portion based an applying the temperature difference of the electric heater to the empirically-determined relationship between temperature differences of the electric heater and amounts of liquid in the liquid storage portion,

wherein the first and second temperature measurements of the electric heater are recorded, at the second and fourth times, respectively, based on

the processor measuring a voltage across the electric heater,

the processor measuring a voltage across the resistor that is electrically connected in series with the electric heater,

the processor determining an electrical current through the electric heater based on the known electrical resistance of the resistor and the voltage across the resistor and further based on the resistor being electrically connected in series with the electric heater,

the processor determining an electrical resistance of the electric heater based on the voltage across the electric heater and the electrical current through the electric heater, and

the processor determining a temperature of the electric heater based on the electrical resistance of the electric heater and the temperature coefficient of resistance of the electric heater.

2. The electrically operated aerosol-generating system according to claim 1 , wherein the capillary wick has a fibrous or spongy structure.

3. The electrically operated aerosol-generating system according to claim 1 , wherein the liquid storage portion is configured to retain the liquid in a liquid carrier material.

4. The electrically operated aerosol-generating system according to claim 1 wherein the second heating time period is between 0.05 and 0.5 seconds.

5. The electrically operated aerosol-generating system according to claim 1 , wherein the elapse of the first cooling time period is between 0.2 and 2 seconds after the ending of the first heating time period.

6. The electrically operated aerosol-generating system according to claim 1 , wherein the electric circuitry is configured to determine whether to subsequently activate the electric heater for the second heating time period upon the elapse of the first cooling time period after the first heating time period based on a previously determined amount of liquid or based on stored heater activation data.

7. The electrically operated aerosol-generating system according to claim 1 wherein the electrically operated aerosol-generating system is an electrically operated vaping system.

8. A method for determining an amount of liquid in an electrically operated aerosol-generating system, the electrically operated aerosol-generating system including a liquid storage portion configured to store a liquid from which aerosol may be generated, an electric heater, a capillary wick between the liquid in the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater, and electric circuitry connected to the electric heater, the electric circuitry configured to control activation of the electric heater, the method comprising:

activating the electric heater for a first heating time period in response to air being drawn through the electrically operated aerosol-generating system, such that

liquid in the capillary wick is vaporized during the first heating time period, and

the electric heater is deactivated at an ending of the first heating time period based on an end of the drawing of air through the electrically operated aerosol-generating system,

activating the electric heater for a second heating time period in response to an elapse of a first cooling time period after the ending of the first heating time period, the second heating time period beginning at a first time and ending at a second time such that the electric heater is deactivated at the second time, wherein the second heating time period is shorter than the first heating time period such that a temperature of the electric heater remains below a vaporization temperature of the liquid and the liquid in the capillary wick is not vaporized during the activation of the electric heater for the second heating time period,

recording a first temperature measurement of the electric heater at the second time at the ending of the second heating time period, such that the first temperature measurement is recorded while the temperature of the electric heater remains below the vaporization temperature of the liquid and the liquid is still wicking on to the capillary wick;

activating the electric heater for a third heating time period in response to an elapse of a second cooling time period after the ending of the second heating time period, the third heating time period beginning at a third time and ending at a fourth time such that the electric heater is deactivated at the fourth time, wherein the third heating time period is shorter than the first heating time period such that the temperature of the electric heater remains below the vaporization temperature of the liquid during the activation of the electric heater for the third heating time period,

recording a second temperature measurement of the electric heater at the fourth time at the ending of the third heating time period, such that the second temperature measurement is recorded while the temperature of the electric heater remains below the vaporization temperature of the liquid and the liquid is still wicking on to the capillary wick,

determining a temperature difference between the first temperature measurement and the second temperature measurement, and

determining an amount of liquid in the liquid storage portion based on applying the temperature difference to an empirically-determined relationship, stored in a memory of the electric circuitry, between temperature differences and amounts of liquid in the liquid storage portion.

9. The method according to claim 8 , wherein the second heating time period is between 0.05 and 0.5 seconds.

10. The method according to claim 8 , wherein the elapse of the first cooling time period is between 0.2 and 2 seconds after the ending of the first heating time period.

11. The method according to claim 8 , further comprising:

determining whether to subsequently activate the electric heater for the second heating time period upon the elapse of the first cooling time period after the first heating time period based on a previously determined amount of liquid or based on stored heater activation data.