Problem: Need for Non-contact Method of Measuring Temperature on Rotating Equipment

The primary challenge with tracking temperature on rotating equipment is the need to maintain contact between the sensor (e.g. thermocouple) and the measuring instrument. One option is to use a slipring, which is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. As shown in the figure below, sliprings are mounted onto the rotating structure; carbon bushings are spring loaded to maintain contact with the sliprings as they rotate. The cost and complexity of using sliprings can be significant and in many instances, impractical.

Figure: Sample Slip Ring Construction

Infrared thermometers provide an alternative to complex mechanical solutions like sliprings. Due to their optical nature, infrared thermometers can be focused onto the rotating structure (with the use of a laser guiding device) and be appropriately setup to measure temperature. However, one significant disadvantage of this approach is the inability to obtain temperature measurements at specific target locations on the rotating structure. In some instances it is more important to measure, say the temperature of a specific machine component than it is to measure the rotating rim on which the component is mounted. Also, the infrared thermometer can, at best, indicate the presence of a temperature differential on the rotating component. It cannot specifically isolate the exact location of the temperature differential on the longitudinal axis. Lastly, specific adjustments need to be made to the infrared thermometer to compensate for reflected and refracted radiation from the rotating structure. Although not insurmountable these add to the overall burden of setting up and maintaining an infrared thermometric solution.

Solution: SAW Based Temperature Sensing for Rotating Equipment

SenGenuity has developed a wireless temperature measurement solution that makes use of passive SAW temperature sensors to obtain temperature measurements at specific points on rotating equipment. The sensors are interrogated by a wireless SAW interrogation device via a capacitive plate as shown in the figure below. The measurement of the sensor is synchronized with the speed of the rotating component thereby ensuring accurate temperature measurements. The temperature as well as the identity of the sensor is tracked by the wireless sensing system. Temperature data is obtained either via a PC based application or via the CAN communication protocol.

Figure: Typical Installation on Rotating Machine Component

Wireless temperature sensors address the disadvantages associated with sliprings and infrared thermometers:

• Reduced Complexity: Wireless temperature sensors do away with the complex electromechanical coupling mechanism of the slipring. Instead, an electromagnetic link between the sensor mounted on the rotating structure and the measuring system is used to provide a temperature sensing solution at greatly reduced costs.
• Localized Temperature Measurement: Wireless temperature sensors offer the advantage of being able to be mounted at specific locations on the rotating structure thereby providing localized temperature measurement capabilities.
• Low Maintenance Burden: The overall effort required to maintain a wireless temperature system is nominal. Once installed, SAW based wireless temperature sensors require very little maintenance.

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Applications of Wireless Temperature Measurement Using SAW Resonators

Contact us at sensors@sengenuity.com for more information.