MLX90615SSG-DAA Melexis Inc, MLX90615SSG-DAA Datasheet - Page 26

• Manufacturer Part Number: MLX90615SSG-DAA
• Description: THERMOMETER IR DUAL 3V MED TO-46
• Manufacturer: Melexis Inc

Specifications of MLX90615SSG-DAA

• Featured Product: MLX90615 Series Infrared Thermometers
• Sensing Temperature: -40°C ~ 115°C
• Output Type: PWM, SMBus™
• Voltage - Supply: 2.6 V ~ 3.6 V
• Accuracy: ±0.5°C
• Package / Case: TO-46-4 Metal Can
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

MLX90615
Infra Red Thermometer
environmental and object temperature is at given reflectivity ( with an opaque for IR material reflectivity equals
1.00 minus emissivity ) the bigger errors it produces.
After I put the MLX90615 in the dashboard I start getting errors larger than specified in spite that the
module was working properly before that. Why?
Any object present in the FOV of the module provides IR signal. It is actually possible to introduce error in the
measurements if the module is attached to the dashboard with an opening that enters the FOV. In that case
portion of the dashboard opening will introduce IR signal in conjunction with constraining the effective FOV
and thus compromising specified accuracy. Relevant opening that takes in account the FOV is a must for
accurate 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 MLX90615 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 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 MLX90615 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 MLX90615 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
MLX90615. 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.
3901090615
Page 26 of 28
Data Sheet
Rev 002
12 Oct 2010