GB1097089A - Improvements in or relating to apparatus for controlling the rate of flow of fluid in a number of streams - Google Patents

Abstract

1,097,089. Controlling fluid-flow electrically. FOXBORO-YOXALL Ltd. Dec. 9, 1966 [Dec. 31, 1965], No.55453/65. Addition to 1, 045, 824. Heading G1N. In apparatus for controlling the rate of flow of each of a number of secondary fluids to be blended with a primary fluid in predetermined ratios, the flow rate of the primary fluid is controlled by a master pulse generator 3 (Fig. 1) the flow rate of each secondary fluid is measured by a meter producing a proportional secondary pulse train, and the ratio of the two frequencies is determined at 2 to control a valve in the flow line of the secondary fluid via a controller 4 whereby the flow ratios are maintained at the predetermined values. The frequency of the master pulse generator 3 is determined partly by a voltage device 5 and partly by a proportional-integral controller 6, fed through a reversing switch 7 with a bias signal from unit 8. Thus, when the system is switched on, controller 6 enables the frequency of oscillator 3 to be increased at a steady rate until it reaches maximum value, determined by the saturation output level of controller 6. Similarly, when switch 7 is reversed, the system is switched off at a steady rate. When the flow of a secondary fluid is too small, due to e.g. a blockage, the output signal from the appropriate ratio comparator 2 causes a transistor switching unit 9 to reverse switch 7 so that the frequency of master generator 3 is reduced until the output from the ratio comparator is again within limits. Switch 7 is then again reversed and the system limits about this condition.