TABLE II

Summary of the Advantages and Limitations of All Tested Sensors

Sensor Type	Advantage	Limitation
Airflow	Contact-free measurement Liquid independent Very sensitive to venting airflow	Slow signal generation (indirect measurement) Sensitive to environment Long distance between the reservoir and the dispensing needle
Capacitive Pressure	Contact-free measurement High accuracy and precision Direct measurement of the pressure of the dispensed fluid Troubleshooting analysis possible by specific pattern recognition	Susceptible to electromagnetic fields (shielding necessary) Air bubbles strongly influence the signal Distance between the point of measurement and the dispensing needle
MEMS	Well established technology High accuracy and precision	Sensor in direct contact with the fluid Air bubbles influence the measurement signal Sensor material incompatible with medical standards Distance between the point of measurement and the dispensing needle
Optical	Contact-free measurement High accuracy and precision Fast, analogue signal generation Located at the orifice of the filling needle	Jet velocity information is not measured Color, turbidity directly influence the signal Different stray light conditions Quantification of results rather complex
Capacitive	Contact-free measurement High accuracy and precision Fast, analogue signal generation Located at the orifice of the filling needle Independent of fluid properties like viscosity, color, turbidity	Jet velocity information is not measured Wetting of the sensor electrodes might imply cross-contamination Permittivity of the fluid influences the signal