ABSTRACT
Whereas measuring pressure (difference) is easy, measuring flow is difficult. A large variety of methods exists, some of which will be described. Several techniques reduce the difficult problem of measuring flow to the easier problem of measuring a pressure difference, using a fixed or variable resistance R and the relationship ΔP=R F, which of course holds only for laminar flows. In order to obtain reliable and noise-free measurements, it is important to have a high enough pressure differential. But in order not to significantly disturb the flow, a low resistance must be used. Different devices offer different solutions to the required compromise.
