A Zero Offset Reduction Method for RTD-based Thermal Flow Sensors

Zero offset, which is caused by unavoidable asymmetrical structures of thermal flow sensors, commonly reduces the practical performance of thermal flow sensors. In this work, a zero offset reduction method for thermal flow sensors based on resistive temperature detectors (RTD) is proposed. A micro-machined thermal flow sensor consists of four thick-film resistors is adopted in this work. Among these four resistors, two of them are acted as heaters placed between the other pair of RTDs. An unbalanced heater driving strategy is adopted to cancel the zero offset and a new measurement model is proposed for mass flow rate measurement. Experimental results show that the zero offset has been significantly reduced and the mass flow rate measurement error is less than ±1% F.S. (Full Scale) within the range of 0 mg/s to 0.1 mg/s.