Wireless and Battery-less temperature measurements

01 July 2009

Senseor has announced three wireless temperature sensing solutions based on SAW (Surface Acoustic Wave) sensors particularly designed for demanding industrial applications. Senseor’s solutions are totally passive. Sensors are powered by the energy of radio waves emitted by the associated reader unit when remotely interrogating the devices in real-time.

Without batteries or active electronic components sensing solutions are appropriate for use in explosive atmospheres or irradiated environments at temperatures reaching +175°C with almost unlimited autonomy. In addition, by avoiding problematical wires the maintenance-free and light-weight sensors can be mounted onto an extensive range of rotating and moving machinery parts or implemented in inaccessible places.

As a result, two thermowell-packaged wireless temperature probes SED-100 and SED-120 have been launched (sizes available on request). They are designed for wireless temperature measurement inside critical equipment, or at the heart of industrial processes, and are said to comply with well-established standards within the industry.

Furthermore Senseor announced the launch of a system to monitor surface temperature, the SA-D003.

Each measurement solution comprises a reader unit (also referred as interrogator) and the sensor, mounted with its associated antenna. The interrogation distance between the sensor and the reader unit can reach up to several meters in open space. To make it short, the technological advantage behind surface acoustic waves relies on the reverse piezoelectric effect.

On the one hand, the electromagnetic wave sent by the interrogator is received then converted into an acoustic wave, by means of a transducer located at the surface of a piezoelectric crystal (typically quartz).

Temperature variations related to the nearby environment of the SAW sensor trigger a modification of the acoustic wave’s physical properties when propagating along the surface of the device. In return, the modified acoustic wave is then transformed back into an electromagnetic wave to be retrieved by the reader unit.

The integrated building block of those above-presented sensing solutions, SE-AS10 SAW sensor, is also commercially available as sole device, capable to sense temperatures ranging from -20 to +175°C with a measurement precision of ±2°C. This small sensing element (5 x 5 x 1.5 mm³) can be associated with different types of customised antennas, depending on the environment characteristics as well as implementation constraints.

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