EVB90620 Datasheet, PDF (37/39 Pages) Melexis Microelectronic Systems – High precision non-contact temperature measurements

MLX90620
16x4 IR array
between the sensor package and the sensor die. This is real optical signal that can not 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 MLX90620 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.
I consider using MLX90620AAA to measure temperature within car compartment, but I am
embarrassed about the Sun light that may hit the module. Is it a significant issue?
Special care is taken to cut off the visible light spectra as well as the NIR (near IR) before it reaches
the sensitive sensor die. Even more, the glass (in most cases) is not transparent to the IR radiation used by
the MLX90620. Glass has temperature and really high emissivity in most cases – it is “black” for IR of
interest. Overall, Sun behind a window is most likely to introduce relatively small errors. Why it is not
completely eliminated after all? Even visible light partially absorbed in the filter of the sensor has some
heating potential and there is no way that the sensor die will be “blind” for that heating right in front of it.
3001090620
Rev 4.0
Page 37 of 40
Datasheet IR16x4
19 September 2012