Hello,
I am using an IR thermometer (MLX90614 from Melexis) to measure the temperature of a surface. This device is in a TO-can, and I am using the standard package version (cf. first page of the datasheet, option code A). I would like to place a lens in front of this IR thermometer so that I can measure the temperature of the surface with a spot size of 3 mm.
How do I select or calculate the required
(a) focal length of the lens; (b) lens diameter; (c) distance of the lens to the detector
I would like the lens to be situated at a distance of 5 cm from the measurement surface. I assume that I would require the lens to have an IR response and appropriate coating, since according to the thermometer datasheet, the spectral response of the IR thermometer is limited from 5.5 um to 15 um by a filter.
Would similar principles also hold for the selection of a lens in front of a photodiode? Can anyone suggest how I might go about selecting the lens? Is a good reference work available?