Mechanical innovation opens pressure measurement horizons

As digital technologies continue to evolve at a fast and furious pace, it's sometimes easy to forget all the mechanical innovations Emerson has developed throughout the years to deliver pressure measurement solutions that today perform better than ever—yet are simultaneously easier to engineer, install and maintain.

Early success with the Rosemount™ 1151 Pressure Transmitter arose from a dogged focus on building the most accurate, rugged and stable sensor possible. But as sales of the Rosemount 1151 took off in the 1970s, the company’s engineers took aim at a wider range of applications to drive the technology’s broader use.

For example, differential pressure (DP) flow measurement across a traditional orifice plate primary flow element incurs significant pressure losses, which means wasted energy. Such applications also require long runs of straight pipe that complicate installation. And in both DP flow and level measurement applications, a laundry list of fittings, tubing, heat tracing and other components resulted in solutions that were complex to engineer, tricky to assemble in the field and susceptible to process leakage as well.

Pressure drop woes?

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Emerson found a key answer to the pressure drop problem with the Annubar flow solution, an averaging pitot tube primary flow element first introduced in the early 1970s. The original Annubar consisted of a cylindrical probe inserted through the diameter of a pipe with openings along the length of both the upstream and downstream faces of the probe. The differential pressure between the upstream and downstream ports yields an accurate flow rate accounting—without incurring the high permanent energy loss penalty of other flow meter technologies.

Emerson acquired the Annubar primary element’s original creator, Dieterich Standard, and has continued to innovate on the original. Now in its fifth-generation design (pictured), today’s Rosemount Annubar™ primary element includes an innovative upstream slot that provides for comprehensive averaging, while the sensor’s T-shape creates large stagnation zones on the backside to reduce noise. Today’s model also can be specified with an integral thermowell to derive fully compensated, real-time mass, volumetric and energy flow rates from a single pipe penetration. The product even can be hot-tapped for installation without shutting down the line and into lines up to 96 in. (2400 mm) in diameter.

The Annubar primary element incurs one of the lowest permanent pressure losses of any flow device, including venturi, wedge, turbine, v-cone and orifice/nozzle flow meters. Lower pressure loss means reduced pumping/compression costs, increased capacity and lower capital costs commensurate with the purchase of a smaller compressor, pump or boiler. A lower pressure drop can also mean increased flow through existing lines and higher throughput for gravity-fed systems.

No straight pipe? No problem.

Achieving a pressure-stable measurement that is truly representative of the entire flow profile across a pipe has always been a challenge. In order to achieve an accurate measurement the traditional orifice plate DP flow meter, which consists of a sharply cut circular hole in the center of a plate, also requires long lengths of straight pipe run both upstream and downstream in order to derive an accurate flow measurement. Such extra straight-pipe requirements of 40 or more diameters add to the flow meter’s installation expense and space requirements. Flow conditioners are sometimes used to provide a more uniform flow with less straight pipe, but the addition of another component (and potential leak points) adds to expense and installation complexity.

Turning their attention to this longstanding fluid mechanical challenge, Emerson engineers created the Conditioning Orifice—a plate with not one but four holes (pictured) that dramatically reduced the need for straight-pipe run by as much as 90 percent. Introduced in 2003, the Rosemount 1595 Conditioning Orifice Plate also provided a 30 percent improvement in accuracy and marked a key breakthrough in the broader application of DP transmitters for the measurement of flow.

From transmitter to solution

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Another essential way in which Emerson boosted the appeal of its pressure measurement solutions was through a concerted effort to reduce the complexity of their application. Now formalized throughout the company as Human-Centered Design (HCD) principles, the effort starts from a deep understanding of how its customers engineer, purchase, install and maintain solutions in the field—and strives to identify innovative ways to reduce complexity throughout their lifecycle.

In the realm of DP flow and level measurement, the introduction of the Rosemount 3051 Pressure Transmitter with its unique patented Rosemount Coplanar™ connectivity platform allowed a smaller, lighter and easier installation, as well as a 50 percent reduction in potential leak points. It also paved the way for the factory shipment of complete measurement solutions, including the integration of primary elements for DP flow applications, instrument manifolds for pressure applications and diaphragm seal assemblies for DP level applications.

The Rosemount 405 Compact series of DP flow meters, for example, unify and ease the engineering and installation aspects of Annubar, Orifice and Conditioning Orifice primary element technologies.

A single seamless process for specification, ordering and installation reduces risk and delivery time and can cut total acquisition costs by as much 55 percent. Flow meters arrive fully assembled, factory leak-tested and ready to install. The inclusion of an integral thermowell for temperature measurement minimizes pipe penetrations. The elimination of impulse lines reduces potential leak points by 80 percent. And an integral centering mechanism for Compact solutions ensures the mechanism is properly installed in the pipe to within ANSI/API guidelines.

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Similarly, in the realm of DP level measure-ment, Emerson’s Electronic Remote Sensor (ERS)™ System calculates differential pressure electronically using two pressure sensors linked together with an electrical cable, rather than with mechanical components. This results in a system that provides faster response and eliminates the need for impulse and capillary lines, fittings, heat tracing and other external and potentially maintenance-intensive elements. Further, Tuned System™ assemblies eliminate excess capillary and oil volume—improving time response by 80 percent, and reducing temperature drift by 20 percent.

These are just a few highlights of Emerson's first 50 years of mechanical innovation in the realm of industrial pressure measurement. Combine these with continued advances in sensor performance, digital analytics and wireless connectivity, and it’s clear that Emerson’s Rosemount pressure products are positioned to lead the process industry with instrument innovation for another 50 years.