Importance

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Abstract

A gas blending system includes a proportional mixing valve having a valve element movable between first and second limits of travel corresponding to a minimum and maximum percentage, respectively, of one of the gases in the blended mixture. The position of the valve element is detected by a detection mechanism, producing a position signal inputted to a microcomputer. The microcomputer also receives a control signal representing a desired percentage of one of the gases to be blended. The microcomputer calculates a desired valving element position as a function of the value of the control signal, and generates a drive signal as a function of a comparison made by the microcomputer between the detected valve element position and the desired position. A motor drives the valve element to the desired position in response to the drive signal. The system also includes an accumulator for accumulating a selected volume of gas mixture flowing from the outlet of the valve prior to delivery of the mixture to a downstream demand. The accumulator increases the effective peak flow rate capacity of the system, while 'smoothing out' instantaneous changes in downstream flow rate demand before the effects of such changes are experienced at the valve.

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