FLOW RATE DETECTOR

PURPOSE:To detect the small flow rate of cryogenic vaporizing fluid, etc., precisely by using the value Cv that a valve lift controller which controls a flow rate control valve outputs and the differential pressure in fluid pressure between an upstream and a downstream side close to the flow rate control valve. CONSTITUTION:The fluid flowing in piping 1 is varied by operating the valve lift of the flow rate control valve 6 on the basis of the signal from the valve lift controller 14. The valve lift signal Cv delayed by a specific time through a delay circuit 15 is inputted to a Cv function generator 16, which sends out the value Cv to a multiplier 17 nearly synchonizing with the flow rate control valve 6. On the other hand, fluid pressures PU and PL of the upstream and downstream sides of the flow rate control valve 6 which are transmitted to pressure transducers 9 and 11 are converted into electric signals, which are inputted to a deviation device 12. The square root of the absolute value of the obtained differential pressure PU-PL is extracted by a computing element 13 for extraction of square root and the result is inputted to the multiplier 17, which multiplies the input by the value Cv and a constant to output a flow rate Q.