Great shakes

Transatlantic collaboration results in self-generating wireless sensor system aimed at cutting time-consuming maintenance and saving energy.

A battery-free wireless sensor system that relies on power from a vibration energy-harvesting micro-generator and a supercapacitor is undergoing trials to monitor operations at a Norwegian gas plant.

The micro-generator, a collaboration between the UK’s Perpetuum and CAP-XX in the US, is being used at the Nyhamna gas plant.

The sensors are monitoring the condition of rotating equipment, which is the main culprit in production shutdowns. They are reporting back temperature and overall vibration every five minutes.

Plants and refineries monitor pumps, machines and processes to ensure optimum safety and efficiency. Condition monitoring traditionally involves maintenance engineers collecting data, or using battery-powered wireless sensors.

Yet batteries may survive only up to five years in harsh environments, so in plants with thousands of battery-powered wireless sensor nodes, replacing and disposing of batteries can be expensive.

‘The micro-generator and super- capacitor combination eliminates battery reliability issues and time-consuming maintenance, while enabling significant savings in operational costs and energy use,’ said Stephen Roberts, Perpetuum’s technical manager.

The new system begins to work when Perpetuum’s microgenerator converts unused mechanical vibration into useable electrical energy. After being stored in a supercapacitor, this energy is claimed to be able to power wireless sensor nodes indefinitely.

The supercapacitor stores the energy harvested by the micro-generator and then delivers the peak power needed to transmit sensor condition data over wireless networks such as IEEE 802.15.4 (Zigbee) and 802.11 (WLAN).

John Parker, Perpetuum’s senior engineer, said the micro-generator is needed to transmit these signals.

‘A radio transmitter wants a lot of power in a very short period of time, and our generator only supplies a modest amount of power all the time,’ he said.

It supplies a constant source of power between 0.5 and 50 miliwatts where radio transmission can require hundreds at once.

‘By using the supercapacitor we can save that modest amount of power over an hour,’ said Parker. ‘When the radio wants it, it can take it — it’s like a reservoir.’

He said Perpetuum decided to use CAP-XX’s supercapacitors because its product far surpassed competitors. ‘The company has supercapacitors that work over the full industrial temperature range,’ he said. ‘Many of its competitors only work at between -20 and +60ºC, whereas CAP-XX’s work at between -40 and +80ºC. It is very important for reliability.’

The two companies installed their system at Nyhamna 18 months ago and Parker said so far all was well.

Perpetuum was set up in 2004 as a Southampton University spin-out, where the concept for the technology originated. Parker said it has taken this long to get it used by the oil and gas industry because of the high risks involved.

‘The oil and gas industry is very conservative,’ he said. ‘The safety, environmental and cost implications are very high.’

With positive results coming from the Norwegian plant, Parker said there is a good chance that in the future Perpetuum and CAP-XX will be promoting the technology together to condition monitoring system manufacturers.

Pierre Mars, CAP-XX vice-president of applications engineering, said many will be attracted by the lack of maintenance required by the technology.

‘Wireless system manufacturers can easily design battery-free systems using this fit-and-forget self-generating power source,’ he said.