The ABB device hasn’t missed a single reading in the three months since it was installed, and has not had to resort once to its on-board battery backup, according to Tata Steel.
The trial was initiated to see how the technology would cope in one of the harshest operating environments in industry. The thermocouple is installed on one of the plant’s steam lines, which operates at 120oC. The harvesting technology requires a temperature difference of just 30oC between the process and its surroundings in order to drive the instrument’s electronics and transmit its readings.
This contrasts with the results from a second thermocouple, which was installed nearby to test what happens when an energy harvesting instrument is installed without the necessary temperature difference. This second instrument has had to rely on its battery for the entire duration of the test.
Tata Steel has also been trialling wireless adapters fitted to a pair of pressure transmitters. The adapters enable all the instruments to communicate with one another, and with the plant’s control system via a wireless gateway.
“We’ve installed a mesh of instruments around the blast furnace to test how they cope,” says Mr Kumar. “The mesh has proved to be robust and the results are very promising going forward.”
He says that the instruments are able to talk to the gateway up to 50m away if there is a clear line of sight. In practice there are numerous walls, pipes and other obstructions around the plant, which brings that distance down.
In fact, the energy-harvesting thermocouple has been operating successfully at a distance of around 20 metres from the gateway. “It hasn’t dropped a reading during the entire trial,” says Mr Kumar.
And even though one of the pressure transmitters is situated inside a pump house that makes it unable to “see” the gateway directly, it has been communicating successfully with the thermocouple, which then passes on the data to the gateway. “It’s quite a clever and robust way of communicating,” says Mr Kumar. “With the instruments communicating with their neighbours as well as the gateway, the mesh can continue to function even if one of them is damaged or unavailable.”
With wiring and installation costs typically accounting for almost 50 percent of the total cost of an industrial instrument, it makes both financial and technological sense to use wireless devices wherever possible.
Energy harvesting provides an ideal alternative to wired or battery-powered devices in processes suited to the use of wireless devices. Energy harvesting takes energy from the environment and converts it into usable electrical energy, which is then used to power the wireless device. As well as thermal energy, energy harvesting technology can also be used to derive power from solar radiation, vibration and kinetic energy from flowing media or moving parts.