Melexis 90615 usage

Other Hardware Sensors
1

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°

2

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".

3

Thank you for clarifying this...

4

An additional thought...

Since the distance is so small, what is the effect of putting it directly on the object e.g., even one's skin.

Would placing the sensor directly on the object be much different than lifting the sensor a hair's width over the object?

5

Try it and see.