Abstract
The accuracy of the switching pressure of fluidic comparators is investigated by considering the statistical properties of the switching process. The switching process of wall-attachment amplifiers is classified into an initial switching process and a random switching process. The accuracy of the fluidic comparators is mainly concerned with the random switching process, where the main jet is switched by the random fluctuation superposed on the jet deflection after the full development of the attachment bubble.
First, the probability distribution function of the switching delay for the random switching process is studied for step inputs. The assumption of the exponential distribution function for the switching delay was verified by experiments, and the statistical parameters in the mathematical model were determined.
Next the accuracy of the switching pressure is discussed for rectangular pulse inputs and ramp inputs by referring to practical applications of the fluidic comparators. A typical application is seen in on-line measuring and sorting systems of mechanical parts, where the inputs to the comparators are approximated by rectangular pulses with short durations. In this case, it is desirable that the input pressure range of the uncertain switching be as narrow as possible. The uncertain switching pressure range decreases by increasing the input pulse duration. The switching probability for various input pressures and pulse durations was calculated by the mathematical model and verified by experiments.
Another typical application of the fluidiccomparators is seen in process control systems such as pressure control or liquid level control, where the input pressure changes slowly. The swithcing of the comparator is desired to take place at a sepcified pressure level. As the estimation of the accuracy of the comparators, the average value and the variance of the switching pressure for ramp input were calculated by the mathematical model and were verified by experiments.
