Patent GB-1281068-A (GB)
Title: Improvements in flow meters
IPC: G01F1/80
Filed: 1969-11-27
Abstract: 1281068 Measuring fluid flow electrically GENERAL ELECTRIC CO 27 Nov 1969 [5 Dec 1968] 58029/69 Heading G1N [Also in Divisions F1 and G4] In a mass flowmeter system of the angular momentum type including a swirl generator 19, speed turbine 22, reaction turbine 29 and torque motor 70 control means responsive to a signal representative of speed from the speed turbine 22 and a signal represetative of the position of the reaction turbine are provided for controlling the output torque of the torque motor in accordance with the product of the speed and position signals so that the reaction turbine 29 is maintained in a balanced position which varies with the mass flow rate of the fluid. The signal representative of speed S1 is obtained from a differential transformer pick-up 35 Fig. 2 (not shown) compressing an E-shaped magnetic core surrounding the casing 12, the shroud 23 of the turbine 22 carrying four equally spaced magnetic cores which as the turbine rotates cause the output of the pick-up 35 to be amplified modulated at a frequency proportional to the speed of the turbine. The reaction turbine 32 Fig. 4 (not shown) of similar construction to the speed turbine is also provided with an E-shaped core differential transformer pick-up 55 but only carries two circumferentially extending magnets 66 and produces a signal 5 2  the amplitude of which is proportional to its deflection caused by the flow of fluid and which is restrained by a torque motor Fig. 6 (not shown). The latter comprises an annular magnetic core mounted around the outside of casing 12 and a ring shaped magnet provided on the shroud 30. In operation the signal S 2  from the reaction turbine pick-up operates servomotor 86 via null balance amplifier 89 to position the shaft 88 and hence potentiometer sliders 84, 83 in accordance with the magnitude of signal 5 2 , potentiometer 79 being supplied with a D. C. voltage representative of the turbine speed signal S 1 <SP>1</SP>. This output voltage S<SP>1</SP> 3  across resistor 91 thus varies as the product of the input signals S 2 <SP>1</SP> and S 1 <SP>1</SP> and the resulting current I<SP>1</SP> m from differential amplifier 81 is applied to two series opposition windings on the torque motor annular magnetic core to adjust the torque output to balance the torque produced by the fluid flow. Increase or decrease in swirl velocity will result in an increase or decrease in the signal S 1 <SP>1</SP> so that the torque motor current Im<SP>1</SP> is increased or decreased to maintain the reaction turbine in its balanced position. If the mass flow rate changes the reaction turbine is rotated to a new position representative of mass flow rate and indicated at 93, the resulting increase in signal S 2 <SP>1</SP> also causing the torque motor control current to be changed to maintain balance at the new  position. The control and indicating network 11 may utilize a digital system Figs. 9-11 (not shown) see Division G4, the torque motor being energized by a pulse, train of which the width of the pulses is proportional to signal S 2 <SP>1</SP> and the repetition frequency is proportional to the speed signal S 1 <SP>1</SP>.