Flow Meter Calibration/ Process Flow Calibration Capability:

A transit time flow meter uses two ultrasonic transceivers, a fixed distance apart, to inject sound waves into the fluid. Sound waves hitch a ride on the medium they are transmitted in, so the sound travelling in the direction of fluid flow will be faster than the speed of sound in the same fluid with no flow. Similarly, the sound transmitted against the flow will travel at a slower speed compared to its speed in the static fluid.

The master meter measures the time of flight of ultrasonic pulses travelling with the flow and those travelling against it. Simple math shows fluid velocity is proportional to the time taken for the sound to travel between the sensors.

Where: 

V = Fluid velocity
K = Calibration constant
tus = upstream transit time
tds = downstream transit time
L = Time of Flight distance between sensors
θ = Incident angle of ultrasonic waves

Note the calibration constant K takes various linear properties into account, including variation in the pipe’s internal structure, such as roughening or corrosion that can affect turbidity of the fluid. Check out why it’s important to regularly Calibrate your fluid meter and not just run factory set verification routines.