Each of the meters above function well with many common flow sensor types used in the field:
Paddlewheel Flow Sensors - Flowing liquid turns a paddlewheel, which sends out a pulse proportionate to flow rate. It can be used with pipe sizes as small as 1" with flow rates of 2 to 1,850 GPM.
Mag Meters - The Electromagnetic Flow Meter measures flow by passing the liquid through a magnetic field and measuring the voltage produced. Since the induced voltage is proportional to the average flow velocity and the inside diameter of the pipe is known, the volumetric flow rate can be calculated. It can be used with any pipe size.
Ultrasonic Flow Meters - This sensor is attached to the outside of the pipe. It operates by transmitting a high frequency signal off of solids entrained in the liquid and reading the return signal. The detected frequency shift is proportional to the liquid velocity (Doppler Effect). It can be used with any pipe size.