A computer-interfaced falling ball viscometer.

We have developed a system that greatly facilitates viscosity measurement under low-shear conditions, based upon a falling ball viscometer interfaced to a personal computer. Three optical sensors indicate the rate of passage of a steel ball falling through a micro-capillary tube, and a potentiometer detects the angle of the tube. The resulting data are passed from a custom program with a graphical user interface to a spreadsheet. The spreadsheet then calculates and stores a value for the viscosity of the sample, using the data passed to it from the viscometer, and a look-up table of stored slope and intercept values calculated from precision viscosity standards. We used the viscometer to determine the kinetics of actin polymerization, and to measure the viscosity of F-actin-aldolase gels. This system provides significantly greater reproducibility and speed in data acquisition than does the traditional 'eyeball and stopwatch' method, and data reduction is virtually instantaneous.