Learn how to select the proper temperature sensor for your low power design by knowing the different types of temperature sensors available in the market and the key features you should take into account for your specific application.

Farsens has recently been selected as a finalist of the RFID Journal LIVE! 2014Best in Show’ award. We have been chosen for one of our latest development: the Pyros tag.

Pyros temperature sensor tags

Pyros UHF RFID thermistor temperature sensor tags with different thermistor probes

It is basically a wireless and battery-free UHF RFD temperature sensor tag. The innovation is that instead of being an ambient temperature sensor tag, it features a thermistor, which is an analog sensor –compared to the ambient temperature sensor, which are generally digital – that can measure surface or contact temperature.

I thought it would be a good idea to take the opportunity of this week’s post to share an overview of the differences between temperature sensors so you can learn how to use them in your low power designs.

There are multiple ways of measuring temperature but these are the most common ones:

Thermocouples

Based on the Seebeck effect, thermocouples rely on the fact that when two dissimilar metals touch, the contact point creates a small voltage difference at both ends of the thermocouple as a function of the temperature.

By measuring this voltage, thermocouples provide very accurate temperature readings while remaining very low cost components. This is the very reason why these are probably the most widely used temperature sensors.

Resistance Temperature Detectors (RTDs)

RTDs are based on metal wires or films that when heated, change their resistance. As the temperature increases, the resistance of the metal wires increases with a relative linearity which makes these devices a good candidate to measure temperature through their resistance value changes.

The most common RTDs are Platinum (PTs). They usually have values of 100Ohm or 1 KOhm – it is very common to hear a PT100 or PT1000 temperature sensor.

Thermistors

Like RTDs, thermistors are based on measuring resistance values that change as a function of temperature. However, the materials used are ceramics or polymers. Thermistor resistance values and sensitivity are higher than those of the RTDs, so they can measure temperature with a higher accuracy over a shorter temperature range (up to 300°C).

Semiconductors

Temperature sensors are based on the principle that the base-emitter voltage of a diode-connected transistor is inversely proportional to its temperature.

These sensors are used in applications where the temperature is within a -55°C to 150°C range. This range compared to the one achieved by RTDs and thermocouples is small but they have the advantage of being small, accurate, inexpensive and easy to interconnect to other ICs. These digital can be connected to microcontrollers through I2C or SPI protocols.

These different operating principles lead to different temperature sensor performances. We will discuss about what key characteristics you should be looking at to select the proper temperature sensor in a coming post. Stay tunned!