Relationship between differential pressure and flow

When a differential pressure cell is used to transmit a flow measurement the output of the transmitter is not linear. Therefore, in many flow measurement installation a square root extractor is fitted to the output of a differential pressure transmitter.

Relationship between differential pressure and flow


DP flow can be derived from the bernoulli equation


By assuming density is constant, the continuaty equation can be writte A1V1 = A2V2

The equation can be abbreviated as follows:

  1. Cancel the potential energy in bernoulli equation (assume the pipe is level )

  2. Solve V1 and V2 using the continuity equation

  3. Substitude V1 in term of V2


Then the velometric flow equation can be obtained by multiplying by the cross sectional area of the throat,


if the mass flow is required, multiply both sides by flowing density