The pneumotachograph is based on the principle of Poiseuille’s Law, which states that, assuming laminar flow in a narrow tube, flow is proportional to the pressure drop per unit length of a narrow tube. A continuous measurement of this pressure drop (the difference in pressure between two points in the tube), provides a differential relationship between pressure and flow.
In the Fleisch pneumotachograph, laminar flow is achieved by distributing the air flow into a large number of narrow, parallel tubes.
In order to avoid condensation of water vapour in the tubes, the pneumotachograph is equipped with a heating element, and a thermistor to facilitate thermoregulation. The heating element is waterproof, and the whole pneumotachograph may be immersed in liquid for cleaning and disinfecting.
Examples of EMMS Fleisch Pneumotachographs