Watch a video of a wireless, battery-free RFID thermistor monitoring temperature of a metal plate surface.

Temperature sensors are amongst the most widely used sensors for environment monitoring. Be it in applications such as food processing, HVAC environmental control, medical devices, chemical handling or automotive under the hood monitoring (e.g., coolant, air intake, cylinder head temperatures, etc.), temperature is a variable need to be controlled.

As discussed in this previous post, there are different temperature sensor types. Some of them are only suitable for ambient temperature monitoring but others can also be used for contact temperature monitoring.

RFID thermistor with Peltier metal plate

RFID thermistor vs. commercial temperature sensor with Peltier metal plate

Coupling RFID with thermistors

Even if temperature sensors are used in lots of applications, there are many more solutions in which temperature monitoring would be desired. The typical limitations for their implementation are the need of wiring and power.

Full passive RFID temperature sensors can be a good solution for this. The video below shows a Pyros battery-free RFID thermistor tag monitoring the temperature of a metal plate – not the temperature around it but the temperature of the material.

The tags harvest the energy from the RF field that a UHF RFID reader creates. Then uses that power to drive the sensor and send the data back to the reader. All is done wirelessly and without batteries on the sensor tag.

This allows RFID sensors to be placed in locations where access is limited or undesired. The thermistor will always be ready to make a measurement without ever requiring a battery change – no machine stop, no maintenance cost.

Using RFID thermistor tags

Using thermistor sensors along with passive UHF RFID tags can be a very good idea. We already talked about monitoring surface temperature of rotary parts with RFID thermistor tags. There are other interesting applications such as:

  • Temperature monitoring of braking systems. Materials in wheels are subject to aggressive temperature changes when vehicles brake.
  • Temperature monitoring in switchgear. Temperature surpassing certain levels in critical switchgear components are an indication that significant degradation of metal contacts and insulation may have taken place, thus increasing the probability of internal short-circuits.

RFID thermistor tags are ideal for applications where periodic control of assets is important. It can either be made when assets are static such as the case of monitoring switchgear or when on duty, such as the case of monitoring wheel temperature of a moving tram with a fixed reader – you would place the reader in a position right after you expect the tram to brake heavily.

More than thinking about getting rid of wires or batteries, sometimes is more about being able to monitor temperature in places you never were able to because there was no way of using wires nor batteries.

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