Digital Regulation of Gas Flow Rates and Composition of Gas Mixtures

A digital principle is described which permits a linear regulation of gas flow rate. The regulator unit consists of a set of on-off valves connected to parallel flow resistors. The conductivities of the resistors are 1, 2, 4, 8,...,n and combinations of the resisters give the flow rates 1, 2, 3, 4,..., 2
n
-1. thus a stepwise regulation with a unit step of less then 1 percent of the maximal flow rate can be obtained by a step of 7 values and resisters. By using two ways valus and complementing with a second gas, binary mixtures of controlled composition (molor fraction) are produced. An apparatus is described which utilizes the above principle for mixing oxygen and nitrogen. The flow resisters are made of plastic tubing, and magentic values are used to permit electric control. The limitations of the applicability of tubler resistors due to nonlinear phenomena are discussed.