For process gases and vapours that are not natural gas. Density = P·M / (Z·R·T); standard volume assumes ideal gas at base conditions.
Density, isentropic exponent and viscosity are calculated from pressure and temperature with the IAPWS-IF97 steam equations and the IAPWS 2008 viscosity equation (checked against the IAPWS test values). Enter the flowing temperature; if it is at or below saturation, dry saturated steam is assumed. Wet steam is outside the scope of orifice standards.
Enter densities from your lab report or density meter. Liquids do not expand through the orifice, so Y = 1.
Single-hole, thin square-edged plate. Unchoked: the bore is chosen so the permanent pressure loss equals P1 − P2 (ISO / AGA orifice equations). Choked gas or steam: sonic flow through the bore. An engineering estimate, typically within about ±5 %; confirm critical services with the plate maker.
Bore needed to pass the maximum flow at each common ΔP span. ★ = recommended (β near the middle of the device's preferred range, minimum flow above 10 % of span, within limits). Tap a row to use it.
Plate thickness and structural ΔP limits: AGA 3 Part 2 (2000) Table 2-3, stainless steel plates up to 150 °F; bore thickness, bevel and bore tolerance: §2.4.3–2.4.6. Check the plate and fitting maker's data for your service.
Approximate, from the gas composition: ideal heats of combustion at 25 °C from public-domain NIST data, real-gas volume from AGA 8 at the base conditions above, dry gas. Typically within about 0.1–0.2 % of AGA 5 / GPA 2145 / ISO 6976 values. Not for invoicing.
ΔP is proportional to flow². Linear transmitter output; the square root is taken in the flow computer or DCS. The highlighted row is the current reading.
Method of AGA 3 Part 1 §1.12 (meter built to AGA 3 Part 2, no in-situ calibration). Enter your instrument accuracies.
Solid: Z factor. Dashed: density. The dot is your operating point. Z falls below 1 as pressure rises (molecules attract), then climbs again at very high pressure.
AGA 8 DETAIL: JavaScript port of the public-domain NIST reference code (usnistgov/AGA8), checked against NIST's test values. AGA 3 Cd: checked against the Cd tables of AGA 3 Part 1 (maximum difference 0.000005, the table rounding). Thermal expansion coefficients: AGA 3 Part 1 Table 1-1. Uncertainty: AGA 3 Part 1 §1.12 (the Reynolds-number factor is read from its Figure 1-5, approximate). For study and cross-checking only. Custody-transfer flow must come from an approved, verified flow computer.