Development of a capacitance method measuring wave configuration on liquid film surfaces

Studies on flow characteristics of liquid film falling down along flat surfaces have many fields of engineering application. Exact measurements of wave configurations which are formed on the film surface and those changing process are the most important to understand the nature of the liquid film kinetics. Among the measuring techniques of the wave configuration the capacitance method has some advantages, because the change in capacitance between the film surface and the probe is picked up without contact to the film itself. However, some problems, which should be improved, are still left. They are, for example, the non-linearity of the probe output with film thickness or drifting outputs due to temperature variations of the system. In the present report a development of new system is described. The capacitance is measured by the frequency modulation method. A logarithmic circuit is utilized to improve the non-linear character. The data are processed with A-D converter. As a result of much effort, the surface area of the probe, important to the high resolution of wave shape, can be 1/4 ∼ 1/10 times smaller and the responding speed which is important in observing the changing process, becomes 10 ∼ 100 times larger as compared with older systems. We finally succeed in parallel running of two systems with high sensitivity and wider band. (author)