Development of Scalable Torque Sensor for Radial Fans

To evaluate fan performance, key parameters such as airflow rate, pressure, and temperature at both the inlet and outlet, along with motor speed and power, are typically measured while the fan is operated at specific speeds by an electric motor. In theory, the shaft torque of the motor can be calculated from the measured values. However, in practice, the shaft torque of the motor varies depending on motor efficiency and fan efficiency. The complex relationship between motor efficiency and fan efficiency necessitates the mechanical measurement of braking torque in a motor driven fan system. This article proposes a scalable measurement unit that can be used for mechanical torque measurement in radial fans. In this context, the proposed fan torque measurement unit is built as a prototype by performing kinematic and dynamic analysis. For the testing of the unit, forward curved blade radial fans preferred in braking applications were used. The electrical voltage and current of the dc motor were measured and the power consumption values were calculated accordingly. Furthermore, a vane-like air intake mechanism is implemented to adjust the air flow. This allowed the demonstration that varying speed-torque characteristics can be achieved using the same fan-motor configuration. Overall, the results show that torque estimation based solely on electrical power measurement is unreliable, underscoring the importance of direct mechanical torque measurement. The study offers important contributions to the braking torque measurement of the fans and to the efficiency analysis of fan-motor systems.