GB1404498A - Digital metering system - Google Patents

Abstract

1404498 Automatic process control AVON PRODUCTS Inc 18 Oct 1972 [22 Oct 1971] 47980/72 Heading G3N In controlling the addition of a material to a fluid stream, the quantity of fluid entering the stream is cumulatively measured and a pre-set discrete quantity of the material is added each time a predetermined increment of the fluid has entered the stream. In Fig. 1, the amount of liquid entering stream 18 from a tank 11 is cumulatively measured by weighing the tank with load cells 17 and converting their output into binary coded decimal form in an A/D converter 77. A counter 79 is initially set to the initial output of 77. A comparator 81 triggers a logic circuit 83 whenever the weight signal drops below the value in counter 79 to cause a pump 43 to add a predetermined amount of perfume from tank 31 to the stream 18 and to cause a burst generator to decrement counter 79 by a predetermined amount, adjustable beween 1 and 100. The pump 43 is a piston pump, the piston being driven by a screw (45), Fig. 2 (not shown) turned by a stepping motor 41, the direction of which is automatically reversed, together with valves 35, 37, 51, 59 when an encoder 87 senses the piston has reached the end of its stroke. An alarm is provided in the event that the pump continues operating for longer than a pre-set time. Circuits are described for ensuring the correct order of operation of the values during start up and to delay opening valve 53 until the flow front has reached 29.