Basic (uncorrected), ETC (temperature compensated), PTZL (Pressure, Temperature, and Z
compensated) or Mini Max (integral
Mercury Mini Max corrector)
Orifice Metering Systems
metering is approved for billing purposes, provided that the requirements
listed below are met and the utility submits an acceptable In-Service
Performance Plan to the Commissions Engineering Division.
üAmerican Gas Association Report No. 3: Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids,
Part 1: General Equations and Uncertainty
üAmerican Gas Association Report No. 3, Part 2: Specification and Installation Requirements
üAmerican Gas Association Report No. 3, Part 3: Natural Gas Application
Orifice meters shall be permissible in applications
where the uncertainty of the orifice meter is less than 1.0% for all historical
and/or expected sustained demand levels of gas flow. The uncertainty of the
orifice meter shall be calculated as specified by the American Gas Association
Report Number 3 (AGA 3), Part 1.The utility
must demonstrate the uncertainty calculation result is less than 1.0% for all
expected sustained demand levels of flow. To ensure the uncertainty
requirements are met across the expected flow range, a stacked differential
pressure transducer arrangement may be used.
Each orifice meter installation shall meet the
geometrical, dimensional, and installation requirements as specified by the AGA
3, Part 2 standard in effect at the time of construction. Note that earlier editions
of AGA 3 may have requirements that affect the uncertainty of the orifice meter
adversely, resulting in greater uncertainty. Therefore, the AGA 3, Part 2
edition number must be greater than or equal to the AGA 3, Part 1 edition
number used to calculate uncertainty.
Calculation of flow through the orifice meter shall be
performed as specified by AGA 3 using real-timedata for differential
pressure, static pressure, and flowing temperature. Specific gravity shall be
measured and representative of the gas flowing through the orifice meter.
Orifice bore diameter and meter tube diameter shall be used in calculating flow
as specified by AGA 3.