Abstract
With the combination of micropumps and flow sensors, highly accurate and secure closed-loop controlled micro dosing systems for liquids are possible. Implementing a single stroke based control mode with piezoelectrically driven micro diaphragm pumps can provide a solution for dosing of volumes down to nanoliters or variable average flow rates in the range of nL/min to μL/min. However, sensor technologies feature a yet undetermined accuracy for measuring highly pulsatile micropump flow. Two miniaturizable in-line sensor types providing electrical readout—differential pressure based flow sensors and thermal calorimetric flow sensors—are evaluated for their suitability of combining them with mircopumps. Single stroke based calibration of the sensors was carried out with a new method, comparing displacement volumes and sensor flow volumes. Limitations of accuracy and performance for single stroke based flow control are described. Results showed that besides particle robustness of sensors, controlling resistive and capacitive damping are key aspects for setting up reproducible and reliable liquid dosing systems. Depending on the required average flow or defined volume, dosing systems with an accuracy of better than 5% for the differential pressure based sensor and better than 6.5% for the thermal calorimeter were achieved.
Highlights
The field of micropump research is about 30 years old and started with Smits’ patent on a silicon micropump 1984 [1] and the publications of van Lintel in 1987 [2] and Smits in 1989 [3].Since many review papers described different actuation and valve technologies, pump concepts and potential applications mainly in medical devices and in analysis systems, biological research and other areas [4,5,6,7,8,9,10,11].compared to the potential, not many applications have yet been realized
Reservoirs, the can consist of a degasser, filter, pump with driving unit, pressure smoothing element (PSE) and aa can consist of a degasser, filter, pump with driving unit, PSEs and flow sensor
Micro dosing systems based on micropumps are able to accurately deliver defined volumes of liquid down to nanoliters or average flow rates in the range of nL/min to μL/min
Summary
The field of micropump research is about 30 years old and started with Smits’ patent on a silicon micropump 1984 [1] and the publications of van Lintel in 1987 [2] and Smits in 1989 [3].Since many review papers described different actuation and valve technologies, pump concepts and potential applications mainly in medical devices and in analysis systems, biological research and other areas [4,5,6,7,8,9,10,11].compared to the potential, not many applications have yet been realized. Summarizing the applications’ main requirements of performance and reliability, the challenge lies in creating a stable flow or dose a precise amount of volume with micropumps. Many influences such as gas capacitances [12,13,14], particles [12,14,15,16], pressure [17,18], temperature [19], piezo actuator fatigue [20], etc. Have to be controlled in order to achieve high dosing accuracy These obstacles were already evident in an early phase of micropump research, Sensors 2017, 17, 755; doi:10.3390/s17040755 www.mdpi.com/journal/sensors
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