MLX90621

16x4 IR array

Datasheet

39001090621

Page 41 of 44

Datasheet IR16x4

Rev 3.0

15 September 2016

measurements. Note that the basic FOV specification takes 50% of IR signal as threshold (in order to define the area,

where the measurements are relevant), while the entire FOV at lower level is capable of introducing lateral IR signal

under many conditions.

When a hot (cold) air stream hits my MLX90621 some error adds to the measured temperature I read. What is it?

IR sensors are inherently sensitive to difference in temperatures between the sensitive element and everything

incident to that element. As a matter of fact, this element is not the sensor package, but the sensor die inside.

Therefore, a thermal gradient over the sensor package will inevitably result in additional IR flux between the sensor

package and the sensor die. This is real optical signal that cannot be segregated from the target IR signal and will add

errors to the measured temperature.

Thermal gradients with impact of that kind are likely to appear during transient conditions. The sensor used is

developed with care about sensitivity to this kind of lateral phenomena, but their nature demands some care when

choosing place to use the MLX90621 in order to make them negligible.

I measure human body temperature and I often get measurements that significantly differ from the +37°C I

expect.

IR measurements are true surface temperature measurements. In many applications this means that the actual

temperature measured by an IR thermometer will be temperature of the clothing and not the skin temperature.

Emissivity (explained first in this section) is another issue with clothes that has to be considered.

There is also the simple chance that the measured temperature is adequate – for example, in a cold winter human

hand can appear at temperatures not too close to the well-known +37°C.