•Flow is restricted by a shaped indentation in the side of the pipe or by a metal wedge inserted in the pipe.

•The formation of vortices is related to pressure drop which is directly proportional to square root of flow rate.

• Flow coefficient is about 0.8 and is essentially constant at low flow rates, even at low NRe as low as 500, unlike orifice meters.

•Relatively simple  operating device

•Requires calibration of the meter
 

Advantages:

• Highly accurate, approximately +0.5% of the measured rate.

• Can measure flow rates of hard-to-handle fluids such as liquids containing solid particles or undissolved gases or gases carrying drops of condensate.

•Relatively expensive, but as such accuracy and price go hand in hand,  it is not actually a disadvantage of sorts.