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September 2007 Sensors & Transducers

Frost & Sullivan Technical Insights

Wireless sensor networks not only create savings in capital expenditure but also increase safety due to the elimination of wiring in an industrial environment. Wireless sensing systems have an edge over wired solutions especially when it comes to in situ monitoring of parameters.

This capability increases the reliability of machines being monitored leading to a drastic decrease in downtime. The possibility of achieving nil-downtime of machines is greater with wireless technology. However, wireless sensors also suffer from certain inherent drawbacks.

Wireless sensors require power from a battery for operation. Batteries have a fixed lifetime and have to be replaced at periodic intervals. Battery disposal issues also act as a deterrent to the long-term usage of battery powered wireless sensors. Moreover, the cost of replacing batteries and the downtime associated with this periodic maintenance procedure could be high in harsh industrial environments. This drawback has led to the merging of energy harvesting devices with wireless sensor nodes.

Wireless condition monitoring of rotating machines with vibration energy harvesting devices has been successfully implemented by Prueftechnik Condition Monitoring, Ismaning, Germany, along with its partners Perpetuum Southampton, UK, and Nanotron Technologies, Berlin, Germany. The product named VIBNODE RFA is a compact wireless vibration monitoring solution for fixed-speed rotating machines with an energy harvesting device to power the wireless module. The vibration monitoring instrument manufactured by Prueftechnik has been coupled with the wireless component from Nanotron and vibration energy harnessing device from Perpetuum.

Wireless battery-free sensors are a reality with the energy harvesting microgenerators manufactured by Perpetuum. The microgenerator harvests the 'twice-line-frequency' commonly found in machines driven by AC motors. The microgenerators have the capability to generate power between the ranges of 0,5 mW to 40 mW proportional to the extent of vibration available.

The wireless component of the VIBNODE RFA condition monitoring system is built on technology developed by Nanotron technologies. The technology called Chirp Spread Spectrum (CSS) is highly suitable for applications which require high-transmission reliability as well as low-power consumption. CSS technology functions based on chirp pulses similar to those used by bats and dolphins in nature.

CSS technology for commercial data transmission applications has been patented by Nanotron Technologies. CSS technology operates in the 2,45 GHz ISM band and achieves a maximum data rate of 2 Mbps. The condition monitoring solution creates cost savings of 50%, that would otherwise be incurred by cabling costs and power supply issues.

For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, patrick.cairns@frost.com, www.frost.com

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