Electrical & Instrumentation Toolkit
ORIFICE METERING
ISO-5167 & AGA-3 differential pressure flow measurement.
- ISO 5167-2:2003
- AGA Report No. 3
- Reader-Harris/Gallagher (1998) discharge-coefficient correlation
Orifice Metering is a complete design solution for orifice plate flow measurement to ISO 5167-2 and AGA Report No. 3. From the process composition, operating conditions and any two of orifice bore, differential pressure and flow rate, it solves for the third.
Capabilities
- Plate sizing — orifice bore from pipe size and target flow.
- Transmitter ranging — differential pressure from plate geometry and target flow.
- Meter verification — flow rate from installed geometry and measured differential pressure.
- Flange, corner and D–D/2 tappings, on an ISO 5167 or AGA-3 basis.
- Full measurement record: discharge coefficient, expansion factor, Reynolds number, beta ratio, fluid velocity and permanent pressure loss.
- Propagated uncertainty on the discharge coefficient, the expansion factor and the combined flow figure.
- Exportable PDF audit report.
Why the results hold up
Discharge coefficient and expansion factor follow the Reader-Harris/Gallagher (1998) equation as published in ISO 5167-2:2003 and AGA Report No. 3, with discharge coefficient and Reynolds number iterated together to convergence. Density and isentropic exponent are taken from the Peng-Robinson equation of state for the actual composition, and viscosity from the Pedersen & Fredenslund corresponding-states model — fluid properties are calculated at operating conditions, not entered. Uncertainty is combined by root-sum-square in the form both standards specify, using the uncertainty bands of whichever standard is selected. Applicability limits are checked on every solve.
Verification
ALKANE’s V&V Diagnostics includes an orifice metering suite, which checks the engine against published reference data, including AGA Report No. 3’s Table 7 worked example. Details are on Validation & Verification.
Scope
Concentric, square-edged orifice plates within the correlation’s published bounds — beta ratio 0.10 to 0.75, pipe diameter 50 to 1000 mm, Reynolds number above 5000. Upstream and downstream straight-length compliance is assessed separately against the standard’s own tables.