Accurate and Reliable Orifice Meters

by | Oct 24, 2019 | Measurement Instrumentation

Jim Cahill

Chief Blogger, Editor

A few weeks ago at the Emerson Exchange conference in Nashville, I wrote a real-time blog post on an experts’ session on flow measurement technologies. Since no one flow measurement technology excels for all applications, this session proved to be a lively & humorous one where each of the Emerson experts extolled the virtues of their flow metering technology and the shortcomings of some of the other technologies.

Representing the oldest and most widely used flow measurement technology, differential pressure measurement, was Emerson’s Steve Ifft. I mention all this because Steve wrote an article for Oil & Gas Engineering magazine, Five reasons orifice meters lead the way.

Oil & Gas Engineering: Five reasons orifice meters lead the waySteve opens the article noting that the most common DP measurement:

…is done with orifice plates that consist of an orifice with a concentric round hole machined to a specific size.

This orifice plate creates a:

…restriction to flow, while pressure taps on the upstream and downstream side of the restriction provide the necessary differential pressure.

These orifice meters are used commonly in natural gas custody transfer and other monitoring and process control applications.

The five reasons Steve gives for using orifice meters include:

  1. Highly accurate measurements
  2. Ease of use & maintenance
  3. All-conditions operation
  4. Compliance standards met
  5. Networking innovations

I’ll share what he writes about the first reason and invite you to read the article for the rest.

First, orifice plate meters provide accurate measurements.

With mass flow rate ─ e.g. million standard cubic feet per day (mmscfd) ─ being the primary output of a flowmeter, flow rate uncertainty is one of the most important performance specifications for DP meters. Here, orifice meters have a mass flow rate uncertainty in the range of ±0.7% of rate as shown in the American Petroleum Institute (API) orifice meter standard (API 14.3 [1]), which compares favorably to heavily calibrated turbine, ultrasonic and vortex meters.

One area not fully understood around orifice meters concerns turndown ratio – the ratio of the maximum to minimum flow rate within a stated flow measurement uncertainty. Some years ago, when a manometer tube indicated the DP and, prior to modern instrumentation, orifice meters had a flow rate turndown limited to 3:1. Today’s advanced digital DP transmitters used with orifice meters make accurate 14:1 flow turndown possible with a single orifice plate and single transmitter.

Visit the Orifice Fittings for Differential Pressure Flow Measurement in the Daniel brand section on Emerson.com for more on this accurate and robust flow measurement technology. You can also connect and interact with other flow measurement experts in the Measurement Instrumentation group in the Emerson Exchange 365 community.

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.