Differential pressure flow meter
Differential pressure flow meters are differential pressure drop devices in which the flow is calculated by measuring the pressure drop over an obstruction inserted in the flow. Installing one in fully flowed straight piping produces a difference in the static pressures between the positive pressure tap in the inlet and the negative pressure tap at the narrowest cross-section. See Fig. 1: Differential pressure flow meter
The flow rate can be determined by this differential pressure from the material characteristics of the fluid from the geometric data (under operating conditions) and the applicable factor (to be found in standards).
Examples of differential pressure flow meters include orifices (standard orifice in accordance with DIN EN ISO 5167-2), nozzles (standard and Venturi nozzles in accordance with DIN EN ISO 5167-3) and Venturi tubes (DIN EN ISO 5167-4).
Fig. 1 Differential pressure flow meter shows the approximate flow and pressure profiles in a measuring section (using an orifice as an example).
The mass rate of flow with respect to the measured differential pressure is determined by the following equation:
Correspondingly, the volume flow rate (qv) is calculated using the following equation respective of the density (ρ) of the fluids in relation to the temperature and pressure of the relevant volume:
If greater accuracy is required when measuring the flow rate with a differential pressure flow meter, the inlet flow to the differential pressure flow meter must exhibit a high level of uniformity. This is achieved using long, straight inlet sections or various components in the supply section (e.g. flow straighteners or flow converters in accordance with DIN EN ISO 5167-1). See Fig. 1: Differential pressure flow meter
