There are a lot of different types of temperature sensors for various applications. I am mostly interested in human body temperature measurement. After some reading I'vee been able to distinguish three groups of sensors: analog (like TMP36) digital (like DS18B20:)here is the datesheet of DS18B20:http://www.componentschip.com/details/Maxim-Integrated/DS18B20.html infrared (like MLX90614) While I understand the difference in measurement type/methodology, accuracy and communication I am not sure how they work under the hood. I've been trying to understand schematics in documentations but because I haven't got lot of experience in that matter I failed. What I've found out or what I feel about this sensors is: analog sensors are using some kind of temperature variable transistor/resistor to get readings value. infrared sensors use infrared detection to determine the temperature. This sensor is I guess the easiest to understand because heat emits some kind of infrared and the point here is just to detect how much of this light is emitted. I have no idea how does digital works. Can someone please give me maybe more complex explanation of this sensors, the best would be with some references.
Mozo B. wrote: > I have no idea how does digital works. As temperature is an analog value under the hood every temperatur has an anlog frontend. And after getting an analog temperature value out of this, there may follow an AD converter with an interface to form a digital temperatur sensor. Thats all.
: Edited by Moderator
Mozo B. wrote: > This sensor is I guess the easiest to understand because > heat emits some kind of infrared and the point here is just to detect > how much of this light is emitted. That ist correct, but Sensors which register midrange infrared radiation are often based on thermoelements (Seebeck-effect), whereas contact thermometers are based on the temperature dependency of the threshold voltage of a silicon diode. Thermoelements most often are made from other materials than silicon and therefore are not easily integrated on a silicon die. That makes the infrared sensitive variety more expensive. But there are more differences. IR thermometers measure the radiant power of the emitting surface wheras contact sensors (NTCs, Diodes) measure the true temperature of the object. Therefore IR-thermometers in most cases are faster, but they can produce large errors when measuring a surface with low emissivity e.g. a shiny metal surface.
P.S.: Her ist a microphotograph of the Melexis IR-Sensor: https://www.eevblog.com/forum/projects/unknown-digital-infrared-thermometer-chips/?action=dlattach;attach=143314;image In the middle you can see the thermopile wich consists of a large number of thermoelements. Because the output voltage of a thermoelement is very very small, many of them are electrically connected in series in order to give a greater voltage to the silicon based microchip which is located above the thermopile. That silicon die does all the voltage to digital conversion and also handles the serial protocol with the outside world. What one cannot see: There also is a thermometer based on diode voltage drop integrated in the silicon die. This is necessary because thermoelements produce a voltage proportional to the temperature difference of their "hot" and "cold" junction. Therefore the integrated diode thermometer is necessary to compensate for temperature fluctuations of the whole device.