Mass fuel flow measurement system

Claim 1

A fluid flow measurement system comprising the combination of rotatable means mounted in the fluid flow to rotate at a rate dependent on the volume flow rate thereof, wall means defining a passage through which the fluid flows, and a bladed impeller rotatably mounted in the passage so as to be rotated by the flow of fluid therepast, transducer means responsive to rotation of the rotatable means to produce a first electrical signal proportional to the rate of rotation thereof, coil means fixedly mounted on the wall means adjacent the impeller, and means energizing the coil means with a high-frequency electrical signal, the bladed impeller incorporating magnetic material which varies the impedance of the coil means as the impeller rotates so as to modulate the high-frequency carrier, capacitor means responsive to the density of the fluid to produce a second electrical signal dependent on the density of the fluid said capacitor including a pair of capacitor plates defining a passage through which the fluid flows so as to vary the dielectric between the capacitor plates, and an electrical source energizing the capacitor plates and operative to produce an electrical voltage signal dependent on the capacitance between the plates, fixed capacitor means arranged to be energized by the energizing source and having a capacitance such as to produce an electrical voltage signal representing a predetermined minimum fluid density, subtracting means connected to receive the two said electrical Voltage signals and to subtract one from the other so as to produce an intermediate signal representing the amount by which the fluid density exceeds the predetermined minimum density, adding means connected to add the intermediate signal to a reference signal representing the predetermined minimum fluid density whereby to produce the said second electrical signal, a triggerable monostable circuit producing a constant-width output pulse when triggered, triggering means responsive to the first electric signal and operative to repeatedly trigger the monostable circuit in synchronism therewith, amplitude control means responsive to the second electrical signal and operative to control the amplitude of the output pulses of the monostable circuit in dependence on the amplitude of the second control signal, and means responsive to the monostable circuit and operative to produce, as the said output signal, a signal representing the average area under the output pulses of the monostable circuit.