A differential pressure liquid flow sensor for flow regulation and dosing systems

Abstract

A liquid flow sensor based on the measurement of the pressure difference across a flow restriction integrated between two silicon pressure sensors is presented. Depending on the channel size, the FS flow measurement ranges from 50 pl/hr up to 20 ml/hr, with a non-linearity better than 1 %FS. This device is used in a system consisting of a silicon micro-pump and an electronic controller to achieve a high precision flow rate. The fast response of the sensor, < 2 ms, allows for minute dosing with a resolution of 0.1 pl. Introduction Silicon fluid handling systems have been built in the past years for use in chemical analysis and medical applications. These systems generally lack a consistent liquid delivery over an extcnded period of time, typically tens of hours. Thus, they require frequent rccalibration to ensure the accuracy needed. However, their capability of delivering minute quantity of liquid makes them very attractive for such applications. The addition of a sensor that measure the actual flow in such systems allows for improved consistency and accuracy. This paper presents the design, fabrication and the characterization of such a sensor. Sensor description The sensors have been fabricated starting from piezoresistive low pressure sensor wafers devcloped at ASCOM. The addition of a restriction channel between two adjacent pressure sensor die forms the flow sensor device, as depicted in figure 1. The risk of unstability and degradation of the sensor is rcduced because only the backside of the sensors is exposed to the liquid. ~104 in Flow out Figure 1. Device cross section (principle) 0-7803-2503-6