5.1.1 Autonome drahtlose Sensorik für die Prozessindustrie
- 16. GMA/ITG-Fachtagung Sensoren und Messsysteme 2012
2012-05-22 - 2012-05-23
- 5.1 Autonome Sensoren
- M. Ulrich, K. König, H. Kaul, P. Nenninger - ABB AG, Ilmenau
- 499 - 507
Wireless devices have received increasing attention in the process industry over the last years. After wireless technology has dramatically changed the way we live our lives and do business, the next logical step is to introduce this technology into production processes, as well.
As the primary means of collecting information about the process, field instruments are vital to the operation of plants in the process industry. Generally, communication and power supply of such sensors are done by hard wiring, which can be very complex and laborious. In particular, sensors in remote locations, on rotating parts, and sensors added to an already-operating plant instead of during commissioning could benefit the most from a wireless solution. Since a plant can only be operational if all necessary assets are functioning correctly, demands on reliability in the process industry are far more stringent than for consumer devices.
Although specialized wireless solutions exist in the process industry since the 1960s, until now, they have been successful only in specialized markets or products. From the experience with fieldbus technology, it is clear that any wireless protocol that aims at achieving critical mass requires an industry standard with many device manufacturers adapting it. Such a standard is now established as wirelessHART, which combines state-of-the-art wireless technology with the ease of use of the HART protocol. Plants in process automation usually have a projected lifetime of about twenty years and longer. In order to maximize the return on investment, plant utilization should be as high as possible over the lifetime of the plant, thus unscheduled downtimes must be minimized. Asset monitoring is a new trend targeting to detect possible defects in equipment before they cause breakdown and to allow the root cause to be eliminated in a scheduled manner. In order to do so, additional sensor information is required, which further increases the number of sensors installed. For any sensor, total cost should be as low as possible in order to maximize the benefit. Since wiring and installation can amount to almost 90 % of the total cost for the device, wireless is a logical option in this scenario.
Wireless devices and sensors offer more installation flexibility and reduced installation costs due to the absence of wiring effort. Although primary cells (batteries) offer an autonomous energy supply in principle, this solution suffers from strongly limited lifetime, and hence potentially high maintenance
cost through battery exchange and increased risk of failure. Therefore, additional energy sources are necessary for a more efficient way of operating wireless devices.
Energy harvesting (EH) offers to improve the maintenance-free lifetime of wireless devices into the lifetime range of process plants by using autonomios power supplies which are based on the convertion of ambient energy or energy coming from the process itself into usable electrical energy. In principle, this kind of energy exists in abundance in many processes, in forms such as thermal gradients, vibrations, flow or light (see Figure 1). Using suitable generators, this energy can be used to power wireless devices, allowing for truly autonomous field devices [Nen11-1].