Precision pneumatic pressure supply system

Abstract

A dual closed loop, precision pneumatic pressure selection, control and display system for use in testing pneumatic apparatus provides precision digital high response analog control of a precision pneumatic valve for establishing, maintaining, and displaying selected reference pressures and rates of change thereof as a ratio between a regulated pressure and a vacuum, the resultant pressure being sensed by a precision pressure sensor of the vibrating diaphragm type. The first closed loop is a digital loop, the desired reference pressure or pressure rate being commanded in any desired pneumatic unit of measure as a binary coded decimal signal and converted to a common unit of measure. The output of the pressure sensor responsive to valve operation is converted to a binary coded decimal signal in said common units, these two signals being digitally compared and the difference between them being converted to an analog signal for adjusting the valve, thereby maintaining the selected pressure. The second loop is a high response, high resolution analog control loop system wherein the analog error signal of the first loop controls valve position, a further output of the pressure sensor being converted to an analog signal and compared with the analog error signal to adjust the valve so as to zero the analog error signal. Thus, the system employs duel control loops combining the high precision of a digital process closed loop. The system uses similar and separately selectable P.sub.S and P.sub.T outputs in terms of inches of mercury, millibars, feet, knots, feet per minute, knots per minute, etc., with channels which may be cross-coupled one to the other to yield Q.sub.C control without requiring a separate sensor.