Some Info out of my Training Letter B737:
The fuel flow transmitter uses the angular momentum of a rotor to measure the mass flow rate. It is made to minimize the drop in fuel pressure across the transmitter. External power is not necessary. Fuel goes in the transmitter and flows to a swirl generator. The swirl generator causes the fuel to swirl around or turn as the fuel goes through the angled fins. The swirling fuel causes the rotor to turn. The rotor has two magnets attached to its surface. One magnet on the rotor induces a start pulse in a coil each time the magnet passes the coil. Fuel then flows to a spring restrained turbine. The turbine moves radially as the fuel passes through it. The turbine has a signal blade which protrudes back to the rotor. A stop pulse is induced each time the second magnet on the spinning rotor passes the signal blade. The time interval between the start and stop pulses is measured by the fuel flow indicator and converted to a fuel flow rate.
