Medical flow measurement with drop counters. Methods for improving accuracy

Several methods for improving the accuracy of drop counters are presented. A table gives a summary of the characteristics of the sensors described and the results achieved as compared with a reference balance. A disadvantage of all sensors considered is the effect of their inclination, which can cause errors in measurement in clinical applications. Another common disadvantage of all methods is that they are sensitive to mechanical shock and oscillation. Further developments may include utilization of statistical methods and filtering algorithms to improve accuracy. Especially interesting for the measurement of drop volume are sensors that measure travel time using multiple light-barriers or other configurations. Another point of interest may be the measurement of the volume of the growing drop. Optical principles seem to be a very promising means for this type of measurement. For the measurement of drop mass, it is very advantageous to combine gravitational and momentum measuring methods to provide two independent values. A major advantage of this technique is its independence of the liquid type, if used as a balance. The mass flow sensor detects very low flow rates and can be used with different media without recalibration. In future studies, silicone with a stiffness independent of temperature changes will be investigated. Another aim for further development is application to flow rates below 1 mL/h.