Design and Comparative Analysis of High-Speed Industrial Fan RPM Measurement Using Noncontact UWB, FMCW, and CW Radars

Industrial air-handling units (AHUs) are an integral part of smart buildings that ensure proper heating, air-conditioning, and air ventilation. Measuring the speed of an industrial fan in terms of revolutions per minute (RPM) plays an important role in determining the optimum airflow in a building, improving energy efficiency, and extending the life span of the rotary parts. This study, the first of its kind, provides a comprehensive framework for remotely measuring the RPM of the electric (room) fans and industrial AHU fans using impulse-radio ultrawideband (IR-UWB), continuous-wave (CW), and frequency-modulated CW (FMCW) radars. A detailed performance comparison of all the radars for RPM measurement is also performed. Data acquisition was conducted under various environmental and operational conditions, by employing three radar systems and a ground-truth reference sensor. Because the UWB and FMCW radars can measure the distance of the target (fan), the proposed strategy works by finding the fan location followed by extracting the RPM by observing phase variations. Through experimental verification, it was found that the maximum peak (MP) near the radar may not be the optimum location for extracting the RPM. Instead, the first peak among the cluster of peaks near the fan, termed the onset peak (OP), showed a lower error rate. The OP approach provides significantly higher accuracy than the MP method by accurately finding the rotations corresponding to the rotary part of the fan, rather than the secondary fan structures. Specifically, the OP spectrum clearly isolates the fan rotational frequency peak, effectively reducing the error. Consequently, an algorithm to find the OP is also included. In contrast, the CW radar directly utilizes Doppler information for RPM measurement. Furthermore, a comparative analysis suggests that the FMCW and UWB radars outperformed the CW radar at close distances, whereas at the farthest distance, the CW radar performed better.