An intelligent flow sensor system with zero drift self calibration function

Abstract

A double operation modes intelligent flow sensor system with zero drift self calibration function is reported in this paper. In order to improve the sensitivity and the stability, the sensor chip was fabricated on ceramic substrate, and using lift off process to pattern the heater and sensing detectors. The heating and sensing elements are Ti/Pt resistors and with the temperature coefficient is 3050ppm, Ti layer was introduced to improve the adhesion between Pt layer and the front surface of ceramic substrate. Direct Chip Attach(DCA) packaging was adopted to protect the chip and the circuits below it. The Constant Temperature Difference(CTD) control mode is introduced to detect high velocity flow, while calorimetric operation mode is used for low flow velocity measurement. The sensor is designed to operate in the two modes at the same time, and their outputs are detected by a Micro Controller Unit(MCU). Because the calorimetric control mode presents low zero point drift, it is used to calibrate the zero point of CTD control mode. The intelligent sensor system was tested in flow tunnel, if the calorimetric control mode shows the flow velocity less than 20m/s, the MCU computes the difference of the two modes outputs and gets a calibration voltage to change the zero point of the CTD control mode. When the calorimetric control mode shows the flow velocity higher than 20m/s, the last calibration zero point of the CTD control mode is considered as a accurate value. After calibration, the relative error of flow velocity measurement is less than 5% from 0m/s to 60m/s.