Air Piston Calibrator for Microflow Delivery and Measurement Systems

In view of the increasing need of microflow measurement and calibration, this paper presents a liquid flow measurement device to verify the performance of microflow sensors and pumps. The measurement principle of the air piston calibrator was based on the volumetric, time-of-flight approach. The device consisted of a micro-fabricated flow channel mounted on a base chip deployed with electrodes. A gas-liquid interface was introduced in the microchannel and moved along with the liquid flow. Upon passing by the electrodes, the interface brought about resistance variations due to the different permittivity of the gas and liquid. The time period between a pair of signal detected by the electrodes and the corresponding channel volume were then used to determine the flow rate. By the combination of different sized microchannels, a capability of measuring flow rates from 10 nL/min to 1 mL/min was demonstrated. The detection electrodes were optimized prior to their fabrication by numerical simulation. To provide a desired traceability, the volume in the channel between electrode nodes was corrected by the standard flow rate delivered by the calibrated syringe pump. Results showed that, for flow rates from 0.1 μ L/min to 1 mL/min, the mean absolute relative error and standard deviation of relative error of the measurements were lower than 1.1% and 4%, respectively.Copyright © 2007 by ASME