Home » Orifice Flowmeter Rangeability
Flow Measurement

Orifice Flowmeter Rangeability

Orifice, combined with differential pressure transmitter, is the mostly used flow measurement device in oil & gas plant because of low cost and its ease of installation and maintenance.

Flowmeter Rangeability

However, orifice only allows 3:1 rangeability to maintain accuracy. This means, if one wants to measure maximum flow of 10 MMscfd, then the minimum flow measurement that could be measured is only 3.3 MMscfd.

According to Bernoulli principle, the relationship between flow and pressure drop of fluid passing through an orifice is given by the following formulae:

Orifice Formulae

Q = Volumetric flowrate
dP = Measured pressure drop ρ = Density
Ao = Cross-sectional orifice area
Cf = Constant

Hence, flow value could be obtained by measuring pressure drop and the relationship between them is square root.

Let’s say the orifice is intended for flow measurement of 0-10 MMscfd which is represented by 0-100 inH2O pressure drop (as show on below curve)

Differential Pressure versus Flow Rate

At maximum flow of 10 MMscfd, a change of 1% of full flow (0.1 MMscfd) to 9.9 MMscfd will be represented by a change of 2% of dP (from 100 inH2O to 98.01 in H2O).

The following table summarized the value of flow, its corresponding pressure drop, and its dP change in percentage of full scale for 1% change of full flow at the specified flow.

The less flow to be measured, the more sensitivity suffers.

Orifice Flow Table

Read Next:

Source: instrument-control blog

Share With Your Friends

Related Articles

Importance of Flow Meter Turndown Ratio

S Bharadwaj Reddy

Optical flow meter Principle

S Bharadwaj Reddy

Flow Switch : What is it ?

S Bharadwaj Reddy

Different Flow Measurement Technologies

S Bharadwaj Reddy

Flow Meter Characteristics

S Bharadwaj Reddy

Flow Instruments – Selection, Principle & Application

S Bharadwaj Reddy

Leave a Comment

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More

Orifice Flowmeter Rangeability

WordPress Image Lightbox
Send this to a friend