Inclusion of normalized mechanical elements that generate a difference of pressure proportional to the speed of the circulating flow.
The mechanical elements installed may affect the overall section of the duct or be introduced as a flow element.
These systems allow us to work in pressurized ducts and large sections being an accurate and reasonably priced method long as working conditions (previously known to perform calculations) do not fluctuate much. Sensotec Instruments offer a complete solution for this measurement system by differential pressure; this is the calculation of the element, the construction and its accessories, and the differential pressure transmitter with methods of computing square roots of the pressure to provide a direct, linear measure.
Amongst the most common ones:
Placas de orificio.
A perforated plate inserted in a pipe causing a flow disturbance due to the bad circulating inside it.
The hole is normalized and the flow is measured from the difference of pressure between both sites of the plate.
The plate hole is normally concentric but may be also eccentric or segmented.
Venturi Tube.
This is a narrowing of the pipe according to a standard profile in the form of two opposed cones. The differential pressure measurement is performed between the input cone (or throat) and the center of the area where the smaller diameter is.
The system needs a previous the system requires a straight and free of obstacles prior section as happens in all flow measurement systems.
Pitot tube
This is one of the oldest system of flow measurement. It is a double tube inserted in a the pipe to measure (each tube correspond to each output measurement of differential pressure). One of them has the input oriented in the same direction of the flow and the other is in the opposite direction. The input speed in direction of the flow is 0 due to stagnation and converts its kinetic energy into an increase in pressure compared to the actual flow pressure.