[ This morning i first checked the internet speed and just smiled because it was very low yesterday might be due to rain fall happend day before yesterday night. I use my mobile internet via hotspot.]
Building Contact-Less Thermometer
Section One: Sensor Selection and its datasheet Reading.
I found sensor MLX90614 is suitable for our development as this itself is an IR Thermometer in a TO-39 package.
On searching its availability online I found the lowest price from the following vendor.
MLX90614 Datasheet.
Lets get into the details of this sensor.
MLX90614 (An IR Thermometer) 
This sensor is basically the combination of IR Sensitive thermopile detector chip (part number: MLX81101) and signal conditioning ASSP (MLX90302), therefore it reduces all the core complexity for detecting and measuring the temperature and thus allowing us to focus only on reading the measurements form its memory location and putting it on a small display.
-
In fact this IR Thermometer is also Factory Calibrated in wide temperature
range: -40°C…+125˚C for sensor temperature and
-70°C…+380˚C for object temperature. -
Measurement Resolution of 0.02*Celecius (This is the least measurement count).
-
High Accuracy of 0.5*Celcius.
Note: Lets understand working of this sensor more technically as I stated earlier.
IR Thermometer focuses on the light coming from the object in the form of Infrared (IR) rays and channelize this IR radiation to the detector which is known as Thermopile. Inside this Thermopile IR radiation is turned into heat which then turned into electricity.
The electric signal generated by IR Thermopile is passed to signal conditioning unit specially designed to process it. This unit basically amplify the signal, then covnvert it to stream of bits (using 17 bit ADC) and then fed it to DSP (digital signal processor) where signal is treated with FIR and IIR low pass filters for further reduction of the band width of the input signal to achieve the desired noise performance and refresh rate. The output of IIR filter is the measurement results.
Based on this measurement results, the object temperature To and ambient temperature Ta is calculated and get stored in two dedicated location of RAM, which can be read via I2C interface or via the PWM digital output.
The measured value is the average temperature of all objects in the Field Of View (FOV) of the sensor.
Coming to operational Specifications
Operating voltage: 3v - 5v.
Operating current: 2mA.
Interfacing (Connecting) to Microcontroller/Arduino Board: There are two methods for it
- I2C Two-Wire Protocol.
- 10-bit PWM Output.
In this development we will use I2C Two-Wire Protocol.
Some very important point to be consider while development as per datasheet.
“ 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.”
Thus we need to carefully design the placement of electronics inside the encloser.
We can also discuss other datasheet parameters which you think may be essential for our development.