RMG ERZ2000-NG, Operating Manual

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6 Flow meters
Manual ERZ 2000-NG · EN07 · 2019, May 13th
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6.5 Orifice plate diameter
Flow rate measurement with a reduced flow cross-section is a prevalent method used
for fluids, vapors and gases. In generally, it is a very durable method with which very
high accuracy can be achieved with the requisite effort. The method is used in official
custody transfer applications and is often used as a reference for other methods. Af-
ter initial measuring ranges of 1:2 to 1:3, a larger pressure range of measuring rang-
es from 1:30 to 1:50 is possible with more precise pressure probes (usually only 1:3
to 1:10 in official custody transfer applications). Details are defined in the standard
ISO 5167-1 / 2:2003 (previously DIN 1952), as well as in DVI 2041 for special appli-
cations.
As a flow measuring device, the narrowing as an orifice plate is usually implemented
as a component of an orifice plate measuring segment. The flow rate detection takes
place with the differential pressure built up via the orifice plate. For correct flow rate
calculation, knowledge of the viscosity, density and isentropic exponent is necessary.
Figure 182: Orifice plate flow rate meter measuring principle
clarifies the measuring
principle.
Figure 182: Orifice plate flow rate meter measuring principle
With greater speed fluctuations in gases, the density and temperature change asso-
ciated with the pressure change are considered. The following applies for an ideal
gas: