A describing function for the multiple nonlinearities present in 2-stage electrohydraulic control valves

AN EARLIER PAPER1 introduced a method for handling multiple nonlinearities through describing functions, and developed such describing functions for single-stage electrohydraulic control valves. This work is extended in this paper to 2-stage valves of the type shown in Fig. 1. Most of the essential nonlinearities are included in the describing function which is brought to a form similar to that for the single-stage valve.1 Precalculated charts are utilized which help to make reasonable the amount of labor of computing the describing function for a specific valve. An example in the paper illustrates the use of the describing function, and very good agreement with analog computer studies is demonstrated.