Abstract
This paper presents the evaluation of a miniature liquid microflow sensor, directly integrated on a PCB. The sensor operation is based on the convective heat transfer principle. The heating and sensing elements are thin Pt resistors which are in direct electrical contact with the external copper tracks of the printed circuit board. Due to the low thermal conductivity of the substrate material, a high degree of thermal isolation is obtained which improves the operating characteristics of the device. The sensor is able to operate under both the hot-wire and the calorimetric principle. In order to fully exploit the temperature distribution in the flowing liquid, multiple sensing elements are positioned in various distances from the heater. A special housing was developed which allowed implementation of the sensor into tubes of various cross sectional areas. The sensor sensitivity and measurement range as a function of the sensing element distance were quantified. A minimum resolution of 3 μL/min and a measurement flow range up to 500 μL/min were achieved.
Highlights
Several Si-based thermal flow sensors are currently available for measuring gas and liquid flow rates [1,2,3,4,5,6,7,8,9]
Multiple advantages arise from the combination of printed circuit board (PCB) and MEMS techniques, such as the elimination of the need for wire bonding, the low production cost, the reduced amount of time required for the fabrication of the final device, as well as the relatively planar surface of the sensor which allows for minimally invasive flow measurements
The device is based on a technology that allows the development of thermal sensors on printed circuit boards, whereby direct device communication to the outside world is maintained without the use of wire bonding
Summary
The in-depth characterization of the sensor operation which is performed is a rather demanding task, mainly due to the complexity arising from the multiple signals acquired from the resistor array. In a quantitative approach the sensor operation under the hot-wire principle is compared to operation under the calorimetric principle. An elaboration on the multiple resistor array is performed. The simultaneous monitoring of numerous resistors produces data of relatively large size. The recording and manipulation of the acquired data requires thorough processing in order to define the significant parameters and extract the optimum sensor performance. The most important characteristics associated to the sensor operation are the exhibited measurement range, sensitivity and resolution. The effect of the distance of the upstream and the downstream sensing elements on these parameters will be analyzed. The test liquids used in the experiments were water and engine oils of varying viscosity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
