Heating element selection method

1. A method for obtaining a heating element for an electronic vapor provision system, the method comprising:

providing a sheet of electrically conductive porous material;

directing light onto at least a portion of the sheet;

detecting an amount of the light transmitted through the at least the portion of the sheet;

comparing the amount of light detected to a range of light transmission values known to correspond to a predetermined range of electrical resistance values required for the portion of the sheet; and

selecting the at least the portion of the sheet for use as a heating element if the amount of detected light lies within the range of light transmission values, and otherwise rejecting the at least the portion of the sheet.

2. The method according to claim 1 , wherein the electrically conductive porous material comprises a mesh of metal fibers.

3. The method according to claim 2 , wherein the mesh of metal fibers comprises a mesh of sintered stainless steel fibers.

4. The method according to claim 1 , wherein the sheet comprises at least a partially formed heating element, and the at least the portion of the sheet comprises substantially the whole sheet.

5. The method according to claim 1 , wherein the at least the portion of the sheet has dimensions corresponding to dimensions of the heating element, the sheet has dimensions larger than the dimensions of the heating element, and selecting the at least the portion of the sheet for use includes separating the at least the portion from the sheet for formation into the heating element.

6. The method according to claim 5 , wherein the separating comprises laser cutting or stamping.

7. The method according to claim 1 , wherein detecting an amount of the light transmitted through the at least the portion of the sheet comprises calculating an average transmitted light intensity for the at least the portion, the range of light transmission values being a range of average light transmission values.

8. The method according to claim 7 , wherein the average transmitted light intensity is an average calculated from light detected from only part of the at least the portion of the sheet.

9. The method according to claim 8 , wherein the part of the at least the portion corresponds to an expected path for current flow through the heating element when in use in an electronic vapor provision system.

10. The method according to claim 1 , further comprising using a light source to direct the light and using a light detector to detect the transmitted light, and wherein the range of light transmission values is known to correspond to a predetermined range of electrical resistance values from a relationship between the light transmission and the electrical resistance derived from measurements made on samples of the electrically conductive porous material using the light source and the light detector, or a different light source and a different light detector configured to operate as the light source and the light detector.

11. The method according to claim 1 , further comprising processing the at least the portion of the sheet in a way that modifies its electrical resistance value.

12. The method according to claim 11 , wherein the predetermined range of electrical resistance values is predetermined having a reference to the modification in electrical resistance value to be effected by the processing.

13. The method according to claim 1 , further comprising using a light source to direct the light and using a light detector to detect the transmitted light, and further comprising, before providing the sheet of electrically conductive porous material:

using the light source and the light detector, or a different light source and a different light detector configured to operate as the light source and the light detector, to detect an amount of light transmitted through each of a plurality of samples of the electrically conductive porous material;

measuring an electrical resistance of each of the plurality of samples;

determining a relationship between the light transmission and the electrical resistance using the detected amount of light and the measured electrical resistance; and

extracting from the relationship the range of light transmission values corresponding to the predetermined range of electrical resistance values.

14. The method according to claim 1 , wherein the light has a wavelength in a range of 620 nm to 720 nm.