I'm doing a project that will scan body temperature, I'm using MLX90614 as my sensor. My problem is that it always scans low temperatures like 33 degrees to 34 degrees Celcius only. Can someone guide me on this one?
The problem is , that may well be the surface temperature of the skin you are pointing it at ..
Really to check you are getting the correct results trying pointing at a Matt black surface of a container of water with a known good thermometer in it . Say with hot and then iced water.
The sensor has a 90 degree field of view and will be sensitive to the emissivity of the surface - dark objects radiate IR better than light ones , and will give different results - d from the data sheets it is calibrated for emissivity of 1 - black body radiation - ( ideal Matt black surface)
If you are holding the sensor you will make a temperature gradient across it , affecting your result.
Also posting your sketch would help and also your wiring diagram - note that 3v and 5v versions of the sensor are available .
From data sheet “It is very important for the application designer to understand that these accuracies are only guaranteed and achievable when the sensor is in thermal equilibrium and under isothermal conditions (there are no temperature differences across the sensor package). The accuracy of the thermometer can be influenced by temperature differences in the package induced by causes like (among others): Hot electronics behind the sensor, heaters/coolers behind or beside the sensor or by a hot/cold object very close to the sensor that not only heats the sensing element in the thermometer but also the thermometer package.
This effect is especially relevant for thermometers with a small FOV like the xxC and xxF as the energy received by the sensor from the object is reduced. Therefore, Melexis has introduced the xCx version of the MLX90614. In these MLX90614xCx, the thermal gradients are measured internally and the measured temperature is compensated for them. In this way, the xCx version of the MLX90614 is much less sensitive to thermal gradients, but the effect is not totally eliminated. It is therefore important to avoid the causes of thermal gradients as much as possible or to shield the sensor from them.
As a standard, the MLX90614 is calibrated for an object emissivity of 1. It can be easily customized by the customer for any other emissivity in the range 0.1...1.0 without the need of recalibration with a black body.
The 10-bit PWM is as a standard configured to transmit continuously the measured object temperature for an object temperature range of -20...120 ̊C with an output resolution of 0.14 ̊C. The PWM can be easily customized for virtually any range desired by the customer by changing the content of 2 EEPROM cells. This has no effect on the factory calibration of the device.”
Human skin has an emissivity of around 0.8 , you can compensate for that in your sketch . Bear in mind any surface wind across the skin will lower its temperature - feel around your body ( in private) , some bits are hot , some cold
How can I integrate the emissivity on my sketch? I have been setting the range of temperature on my code but the result is always at 33 to 34 degrees C.
You need to:
Post your sketch and do some of the tests I suggest to check basic accuracy . Are you saying it reads 33-34 degrees what ever you point it at ?? If so you have a wiring/sensor :sketch issue , none of which we know about …..so post data sheet for your actual device and a wiring diagram , plus picture of your setup, the sketch and anything g else of importance after reading “ how to get the best from the forum”
How about measuring the actual temperature of the object you see sensing with a thermometer and comparing
Melexis has an application note on the emissivity settings. You can set it in the sensor, or apply the correct in your code.
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