Below is a complete, representative selection report for a real-world duty: crude oil allocation metering on a North Sea topside platform. The inputs, Reynolds calculation, shortlisted meters, scoring, and discounted technologies all mirror what the live selector produces in under a minute when you enter your own process conditions.
Limited upstream straight run (2 × DN), retrofit on existing skid
Derived parameters
Reynolds number (Re)
≈ 81,000
At 120 m³/h, DN 100, ρ = 802 kg/m³, μ = 4.2 cP. Well above the vortex stability threshold (Re > 20,000) at design flow, but drops to ≈ 27,000 at minimum flow and to ≈ 18,000 at occasional low-end (40 m³/h) — which puts vortex in marginal territory and shows up in the shortlist.
Bulk velocity at design flow
≈ 4.1 m/s
Below the 6 m/s velocity ceiling for crude duty (erosion / dropout). Comfortable.
Turndown across full duty
4.5 : 1
Within Coriolis and ultrasonic ranges (typically 50:1 and 20:1 respectively). At the edge of stable vortex (10–20:1 max for liquids).
Ranked shortlist
Four meters were technically viable after the discount stage (below). The scoring weights accuracy, installed-cost, pressure drop, straight-run compatibility, certification fit, and lead time. Higher is better.
#192/100
Coriolis — Micro Motion Elite CMF300M (DN 80)
Reduced-bore Coriolis sized one nominal pipe diameter down. Direct mass measurement removes the need for separate density correction and survives the limited upstream straight run with no derating.
Accuracy±0.05% of rate, mass
Pressure drop≈ 0.55 bar at 180 m³/h
Why it scored well
Direct mass flow — fits the allocation use case without density tracking error
No upstream straight-run requirement — full accuracy at 0 × DN
SIL 2 single-channel, SIL 3 in redundant pair
Onboard Smart Meter Verification (proof test without removal)
Where it costs points
Highest CAPEX of the shortlist (≈ £14–18k installed depending on transmitter pack)
0.55 bar pressure drop is the most of the shortlist — verify header hydraulics
Engine note: Selector reduced one line size to keep mass-flow accuracy at the top of its operating window across the full 40–180 m³/h band. The reduced-bore variant is the standard custody / allocation choice for crude duty.
#286/100
Coriolis — Endress+Hauser Promass F 300 (DN 100)
Twin-tube Coriolis at line size. Slightly lower scoring than the reduced-bore Elite because at 40 m³/h the meter is operating in the lower third of its certified range — fine for allocation, marginal for tight custody.
Operating below 30% of certified range at low end of duty — accuracy degrades to ±0.1% of rate
Lead time has been longer than Emerson for this configuration in recent quarters
Engine note: Strong alternative if header hydraulics rule out the Elite's 0.55 bar pressure drop. The Promass Q would close the low-end accuracy gap but is overspecified for this duty.
5-path inline ultrasonic. Lower CAPEX and near-zero pressure drop. Slightly higher uncertainty than Coriolis and requires more straight run than is available — selector flagged this as the trade-off.
Accuracy±0.2% of reading after wet calibration
Pressure drop≈ 0 bar (full-bore)
Why it scored well
No pressure drop
Lower CAPEX than either Coriolis option (≈ £9–12k installed)
Naturally redundant — single failure on one path does not stop measurement
Where it costs points
10 × DN upstream straight run recommended — installation is only 2 × DN. Flow conditioner required.
Volume-only measurement — separate density tracking needed for mass / allocation
Accuracy degrades on entrained gas (water cut < 0.5% is fine; if water cut creeps up to > 2% the meter's uncertainty doubles)
Engine note: Selector recommends including a Vortab or Daniel flow conditioner if this option is chosen. Calculated cost saving vs. Elite shrinks to ≈ £2–3k once the conditioner and a density transmitter are included.
#474/100
Vortex — Rosemount 8800D Reduced-Bore (DN 80)
Reduced-bore vortex. Functional for allocation but rated last on the shortlist — the duty Reynolds number swings across the lower edge of stable vortex shedding at minimum flow, and there is no direct mass output.
Accuracy±0.65% of rate (liquid, reduced-bore)
Pressure drop≈ 0.12 bar at 180 m³/h
Why it scored well
Lowest CAPEX of the shortlist (≈ £4–5k installed)
No moving parts, very long service life
Compact installation envelope
Where it costs points
At 40 m³/h the duty Reynolds number drops to ≈ 18,000 — at the lower edge of stable vortex shedding. Accuracy degrades to ±1% of rate or worse at minimum flow.
Volume measurement only — requires separate density input for mass
20 × DN upstream straight run recommended; available run is 2 × DN
Engine note: Selector lists this option but flags the Re-number turndown problem. Acceptable if the 40 m³/h low-end case is rare and brief; not the right meter if production is expected to spend time there.
Technologies discounted at shortlist stage
Every meter technology is considered up front. These five were ruled out before scoring — usually because the duty physically excludes them.
Technology
Why it was discounted
Electromagnetic
Crude oil is non-conductive (< 5 µS/cm). Electromagnetic meters require ≥ 5 µS/cm conductivity. Meter would not function.
Differential pressure (orifice / Annubar)
Achievable uncertainty on crude oil allocation at this turndown (3:1 design, 4.5:1 occasional) is ≈ ±1.5% — exceeds the ±0.25% accuracy target. Discounted at shortlist stage.
Turbine (Cox / Daniel)
Sand or sediment carryover from upstream separator failures would damage rotor bearings. Bearing life concerns on multi-year unattended topside duty discounted this option.
Variable area (rotameter)
Industrial scale: not viable above ~ DN 50 / 1 m³/h on crude.
Thermal mass
Suitable for clean gas only — not for liquid hydrocarbon duty.
Recommendation
The selector recommends the Micro Motion Elite CMF300M (DN 80, reduced-bore Coriolis) as the primary specification. Headline reasons:
Direct mass measurement makes the meter immune to the small density drift that would otherwise show up in allocation accounting on a multi-tenant header.
No upstream straight-run requirement — the 2 × DN available on the retrofit skid is more than sufficient. Every other shortlisted option would need either a longer run or a flow conditioner.
Smart Meter Verification lets the operator run a SIL-traceable in-situ proof test without breaking process containment — material operational cost saving over the meter's service life on a manned topside.
If header hydraulics cannot accept the 0.55 bar pressure drop, the Promass F 300 (DN 100) at 0.18 bar is the drop-in alternative.
For custody-grade duty (rather than allocation) the recommendation would shift to the Elite CMF300A (the OIML R117-approved metrology variant) with a wet-calibration certificate at the chosen reference conditions.
About this example
The numbers above are technically representative but illustrative — the specific 92 / 86 / 81 / 74 scores are written for clarity, not copied from a live engine run. Your own selector run uses the live recommendation engine on your inputs, with current vendor datasheets and current lead-time data.
InstruSelect is an independent selection tool. We do not accept vendor sponsorship for ranking position. Manufacturer names referenced above appear because they are widely-deployed in the duty class — not because of any commercial relationship.
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