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Flow Technology Overview

Differential Pressure Flow Measurement

Differential pressure flow measurement technology has been field proven over many decades and is an industrial standard across industries for a variety of applications. The primary benefit of differential pressure measurement is that it is a very rugged technology where the measurement sensors can be calibrated and certified in the field, typically without removal from the process application. In addition, the measurement principles are not sensitive to installation orientation, vibration, and require little maintenance to provide accurate flow measurement over many years. Atmosphere Engineering standardized on differential pressure flow measurement technology in 2002 and has since installed thousands of sensors in the thermal processing industry with great success.

Measurement Theory

It is generally known that as any gas or liquid moves past an object, a pressure loss is created. The higher the flow rate of the gas or liquid, the larger the pressure loss will be for any given object. Therefore, measuring the pressure loss before and after the object will provide a direct correlation to measuring the velocity of the gas or liquid moving past the object. The rigorous examination of the exact relationships regarding these principles as well as many other flow/pressure related problems are studied and examined in the engineering field known as Fluid Dynamics. For the purpose of this document, the following simplified equation to differential pressure flow measurement provides the basic relationships for gas flow measurement.

Simplified Orifice Equation


Q = Cf x A x Cd x (DP / SG)0.50 (1)



Q = Volumetric Flow Rate

Cf = Engineering Unit Conversion Factor

A = Area of Orifice

Cd = Discharge Coefficient of Orifice

DP = Pressure Drop across Orifice

SG = Specific Gravity of Gas

No Flow: P1 = P2

Full Flow: P1 > P2

Technology Features & Benefits

  • No fragile moving parts to wear out
  • No oil or float assemblies to maintain
  • Fast and Accurate response to flow changes
  • Flow measurement accuracy can be certified at anytime
  • Flow Sensor can be calibrated in-situ and without disassembly
  • Not susceptible to soot or particulates in the gas stream provided that particles can fit through orifice