Differential ultrasonic calorimeter for accurate measurement of thermal losses in machinery

Ultrasonic sensors can rapidly respond to changes in the average temperature across a complete ultrasonic pathway. However, these response rates are difficult to achieve using conventional temperature-sensing technologies. This research investigates ultrasound calorimetry and its advantages over the calorimetry implemented using conventional temperature sensors in order to estimate heat losses accurately in electrical motors. The ultrasonic calorimeter is based upon ultrasonic oscillating temperature sensors, which have previously been demonstrated in temperatures that change only in a single direction. A hysteresis effect was observed in the results of the analysis of the temperature-frequency relationship recorded for temperature changes that occurred in both directions. Data sensor fusion was applied to reduce the hysteresis effect and to achieve faster estimates of the temperature inflection point with a standard uncertainty of around 1.34 mK and a measurement resolution of 0.1 mK, comparing to 62.5 mK for inexpensive conventional temperature sensors. The outcomes of the data sensor fusion were tested to evaluate the heat loss in a water-cooled electric motor. The developed instrument costs less than £15 and is capable of evaluating losses up to 7 kW. The major electronic development part of this project is the design of a low-cost electronic modular driver that supports the reliable operation of oscillating ultrasonic sensors. Automatic gain control (AGC) was investigated with the view to prevent the output of the amplifier being driven to saturation. This development resulted in a reduction of 26% in the frequency scatter of the ultrasonic output. An evaluation of different arrangements of ultrasonic oscillating sensors was conducted to study the optimal arrangements of both the transducers and the electronic specifications. Several hundred hours of overnight measurements were completed to establish the best arrangements and operational parameters in order to ensure the repeatability and reproducibility of the system