Thermal-wave balancing flow sensor with low-drift power feedback

• Published in: Journal of micromechanics and microengineering 2014-05, Vol.24 (5), p.55016-7
• Main Authors: Dijkstra, M, Lammerink, T S J, Pjetri, O, de Boer, M J, Berenschot, J W, Wiegerink, R J, Elwenspoek, M C
• Format: Article
• Language: English
• Subjects: Amplifiers; Balancing; Chips; Control systems; Drift; Exact sciences and technology; flow sensor; General equipment and techniques; Heaters; Heating equipment; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; power feedback; Resistors; Sensors; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; thermal waves
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/24/5/055016

A control system using a low-drift power-feedback signal was implemented applying thermal waves, giving a sensor output independent of resistance drift and thermo-electric offset voltages on interface wires. Kelvin-contact sensing and power control is used on heater resistors, thereby inhibiting the influence of heater resistance drift. The thermal waves are detected with a sensing resistor using a lock-in amplifier and are mutually cancel­led by a thermal-wave balancing controller. Offset due to thermal gradient across the chip and resistor drift are eliminated by the lock-in amplifier and power controller, and therefore do not influence the sensor output signal. A microchannel thermal-wave balancing flow sensor with integrated Al resistors has successfully been fabricated. The thermal flow sensor is capable of measuring water flow rates with nl ⋅ min−1 precision, up to about 500 nl ⋅ min−1 full scale. Measurement results are in good agreement with a dynamic model of the flow sensor. Drift measurements show the sensor output signal to be compensated for resistance drift and thermal gradient across the chip.