 # Melexis 90615 usage

Hi...

I wanted to validate my understanding of the field of view (FOV) for the Melexis mlx90615 sensor. I'm not sure if I'm reading / interpreting their statement of FOV being 100.

I'm using this formula: objectsize = distance/tan(angle) distance = objectsize * tan(angle)

So, for the Melexis90615_SSGDAA, if FOV is 100 then tan(100) = 5.67.

If I want to focus on the temp of an object that is 1/4 in diameter, I would want to hold it about 1.41 inches above it, right?

distance = .25 (1/4 diameter circle) * 5.67 = 1.41 inches away...

This is what it says on the Melexis datasheet: http://www.melexis.com/Assets/IR-sensor-thermometer-MLX90615-Datasheet-5477.aspx page: 21

Field of view is determined at 50% thermopile signal and with respect to the sensor main axis. Parameter MLX90615SSG-XAA Peak direction ±0° FOV width 100°±5°

Not quite. You have the tangent formula upside down, and the field of view is symmetric about the center line, so

tan(FOV_angle/2) = (object_width/2)/distance

or

distance = (object_width/2)/tan(FOV_angle/2)

For an object 0.25 inches wide and FOV=100 degrees

distance = (0.125 inches)/tan(50 degrees) = 0.1 inches

For that wide angle sensor, the general rule is "a bit closer than half the object size".

Thank you for clarifying this...