Non-invasive, energy-autonomous and wireless temperature sensor for the process industy
Temperature sensors for application in the process industry are typically mounted in a thermowell. These tubular fittings penetrate the surface of e.g. a pipe and allow to insert a temperature sensing element into the process medium. Although this invasive sensing is state-of-the-art, thermowells suffer from significant drawbacks: Any pipe penetration is a potential cause for leakage and the thermowell itself is prone to corrosion, abrasion and bending stress. Avoiding the thermowell by measuring temperature on the surface of the process container was so far not considered a widespread alternative to invasive sensing. The temperature of the surface is generally not considered representative for the temperature of the process medium. A surface sensor is strongly exposed to the ambient condition and, furthermore, the calibration of such a surface sensor is challenging. In this paper we demonstrate how to overcome these limitations by an optimized thermo-mechanical design and enhanced model-based sensing. In combination with energy autonomous operation and wireless communication our novel non-invasive sensor offers a remarkable flexibility enabling scenarios discussed within the context of internet of things (IoT).
Autonomous wireless sensors for process instrumentation - Autonome drahtlose Sensorik für die Prozessindustrie
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
Thermoelectric thin film power generators: self-sustaining power supply for smart systems
Micropelt develops and markets the world's smallest thermoelectric power generation devices. Due to the silicon-wafer based MEMS-like production process elements with a total thickness of 1 mm and a footprint from less than 1 mm² to 25 mm2 can be realized. The fabrication process is based on standard semiconductor equipment and processes. Therefore ramp-up schemes and economies-of-scale close to those of common chip devices apply to Micropelt products. Micropelt thermogenerators produce much higher output voltages than conventional bulk devices which is due to the fact that their micro-structuring technology produces near 8000 p-n thermo-couples per square centimeter, while conventional thermogenerators typically have less than 10 such thermo-couples on the same area. Consequently Micropelt generators are well suited as the core of an integrated power supply for energy-autonomous miniaturized smart systems with average power consumptions of a few Milliwatts. Micropelt Engineering has proven readiness of their devices for use in a multitude of wireless sensor and micro systems, including smart actuators In this paper we will first introduce the Micropelt technology and further discuss energy harvesting opportunities for novel low power devices and wireless applications based on given waste heat reservoirs.