Like I said already a few times is that we use ultrasound for our thesis, I also mentioned that the speed of sound is reliable of temperature and humidity.

So let’s have a closer look at how we measure temperature with sensors, I found this interesting comparison between temperature sensors so I’ll summarize it for you guys.

There are two types of sensors to measure temperature, the contact and the noncontact ones.



Here are the most common contact temperature sensor types:

A thermocouple uses two metals to create a voltage that is dependent of the temperature difference between the ambient and junction temperature. This is already a big advantage because it doesn’t need extra power and it’s also very cheap. They are robust but decay over time and can measure a big range going up to 3,000°C and as low as –250°C. Thermocouples are often used in ground vibration tests.

Thermistors (NTC and PTC) work somewhat like an LDR (light dependent resistor), so it’s a resistor which his resistance value is dependent of its temperature. These are often used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements. So like you see they are mostly used for simple temperature measurements.

Resistance temperature detectors (RTD) are also resistors (thin-film or wire-wound) with a resistance value which is dependent of its temperature. They are very accurate, robust and stable because it’s made of platinum, which is not affected by corrosion or oxidation. Thin-film RTD elements have a thin layer of platinum for its resistor and are used for Health & Usage Monitoring Systems.



The noncontact types are represented by the infrared temperature probes.

So every object that has a temperature above absolute zero emits Infrared radiation which is linked to its surface temperature. So by using an infrared sensor you can measure it, but you still need some electronics afterwards to process the data into something which is readable for the user.ScreenHunter_4

A problem with the use of infrared probes is that the object you want to measure needs to be bigger than the measurement spot like you see here:

measurement spot

One of the big advantages is that they can be used from a big distance and they can measure high temperatures because they don’t contact. Also measuring moving objects is an option.




So hope you now know a bit how they measure temperature in the world of electronics. What would you use to measure the temperature at home?