Doser system for regulating pressure in a control chamber of a test stand

Claim 1

In a test stand having a normally sealed control chamber having a fluid pressure (Pc) therein for simulating an operational parameter for a device, a doser system for establishing a desired pressure (Px) within said control chamber, said doser system comprising: a first housing having a first inlet port connected to a source of high pressure fluid (Ps) and a first outlet port connected to said control chamber, said first housing having a first surrounding said first outlet port; a second housing having a second inlet port connected to said control chamber and a second outlet port connected to the surrounding environment having a third pressure (P r ), said second housing having a second seat surrounding said second inlet port; a first solenoid valve located in said first housing and having a first plunger with a first face urged toward said first seat; a second solenoid valve located in said second housing and having a second plunger with a second face urged toward said second seat; a pressure transducer connected to said control chamber for developing a feedback signal indicative of the fluid pressure (Pc); and control means connected to receive an input signal from an operator corresponding to said desired pressure (Px) and connected to said pressure transducer to receiver said feedback signal, said control means responding to said input signal by supplying one of said first and second solenoid valves with an error signal derived from the difference between (Px) and (Pc), said error signal moving either said first face away from said first seat to allow high pressure fluid (Ps) to be communicated to said control chamber or said second face away from said second seat to allow fluid to flow from said control chamber through said outlet port to establish a current fluid pressure (Pc') in said control chamber, said control means continuing to supply an error signal to one of said first and second solenoid valves until (Pc') is equal to (Px), said error signal being a series of fixed frequency pulses which logarithmically vary in duration as (Pc') approaches (Px), each pulse in said series of pulses being incrementally less in duration than the preceding pulse, said pulse supplied to said first or second solenoid valves being of such duration that the effect of each valve movement is reflected in a difference between (Px) and (Pc) before the next pulse is computed to thereby assure continuous brief movement of the selected first or second valves until the error signal is reduced to a desired level and Px is equal to Pc.