To obtain the lowest overall metering uncertainty, Custody Transfer flow metering stations are often supplied with prover installations or master meter (transfer proving) solutions. The major advantage of a properly designed proving system is that the flow meter can be proved at any time whilst in service, without interfering with its normal operation. ODS Metering Systems design and manufacture our own bi-directional sphere provers and can offer integrated solutions with compact piston provers and master meter (transfer proving) installations.
Use of a prover permits the in-situ calibration of the primary flow element and as such represents the optimal solution from the point of view of minimizing measurement uncertainty. A sphere prover is custom designed and its size is based on type and size of the flow meter, in accordance with API chapter 4. The provers are designed and tested for a volume repeatability (over 3 calibration runs) of better than ±0.01% of mean volume (0.02% peak to peak). Pipe provers can be integrated on the metering skid or delivered as loose skids.
Small Volume Piston (SVP) Provers
A compact ‘small volume piston’ prover can be an alternative to pipe provers because of its portability and space- and weight-saving advantages. The small volume prover (SVP) meets the same stringent uncertainty requirements for meter proving according API. For bigger flow rates the SVP shall use multiple passes per prover run to achieve the required repeatability. Our metering engineers can help you to select and size your prover.
Master Meter Provers
The primary flow element can be calibrated using a ‘master’ meter, which may or may not be of the same type. Master meter proving is used when proving by the direct method can not be accomplished because of meter characteristics, logistics, time, space, safety, and cost considerations. Direct master meter proving is the method in which the proving of a line meter is performed indirectly by means of a prover in series with the master meter and the line meter. In indirect master meter proving scenarios, the ‘master’ meter is periodically removed and calibrated at a traceable facility on a different flow stream and/or conditions and returned to service. In principle proving duty meters with a master meter has greater uncertainty than direct proving with a prover.