Emerson Rosemount 486 Annubar Primary Element

Emerson Rosemount 486 Annubar Primary Element

Introduction

In industrial flow measurement applications where large pipe diameters, high temperatures, and diverse fluid types intersect, traditional flow metering technologies often impose significant costs and operational constraints. Orifice plates create permanent pressure loss that reduces system efficiency. Coriolis meters become prohibitively expensive at larger line sizes. Turbine meters introduce moving parts that require ongoing maintenance and replacement.

The Emerson Rosemount 486 Annubar Primary Element addresses these challenges through averaging pitot tube technology—a proven differential pressure (DP) flow measurement solution that delivers reliable accuracy with minimal pressure loss and no moving parts.

The 486 Annubar is an insertion-type averaging pitot tube designed for volumetric flow measurement of gases, steam, and liquids across a broad spectrum of industrial applications. Operating on the fundamental principles of fluid dynamics—specifically the relationship between flow velocity and differential pressure as described by Bernoulli’s equation—the 486 sensor generates a DP signal proportional to the square of the flow rate. This signal is transmitted to a compatible Rosemount pressure transmitter, such as the 3051S, 2051, or 3051CFA series, which converts the raw DP into a standardized 4-20 mA output, pulse/frequency signal, or digital communication protocol.

This technical datasheet provides comprehensive specifications, performance data, and application guidance for engineering professionals seeking a cost-effective, low-maintenance solution for flow measurement in pipelines from 2 to 96 inches in diameter.

What Is the Rosemount 486 Annubar Primary Element?

The Rosemount 486 Annubar is a member of the Rosemount Annubar family of averaging pitot tubes, which includes the Rosemount 485 Annubar Primary Element, the Rosemount 486, and the Rosemount 585 Severe Service Annubar Primary Element. The Annubar technology utilizes a patented T-shaped sensor design inserted into the flow stream through a single pipe penetration.

Unlike a single-point pitot tube that measures velocity at only one location, the averaging pitot tube incorporates multiple pressure sensing ports distributed across the pipe diameter. The Rosemount 486 sensor averages these individual velocity measurements to produce a differential pressure signal that accurately represents the average flow velocity across the entire pipe cross-section. This averaging approach significantly improves measurement accuracy compared to single-point devices, particularly in applications where the flow profile may be distorted by upstream piping configurations.

The 486 complete flowmeter system consists of the Annubar primary element integrated with a Rosemount pressure transmitter, such as the 3051SFA Annubar Flowmeter or 3051CFA Annubar Flowmeter configuration. This fully integrated solution eliminates the need for separate instrument tubing, valves, fittings, valve manifolds, and mounting brackets, substantially reducing welding and installation time.

Key Technical Specifications

Performance Specifications

Accuracy Performance

Note: As the meter Reynolds Number decreases below the stated limit to 10,000, the accuracy error band increases linearly to ±3.0%. For Reynolds Numbers down to 5,000, the error band increases linearly from ±3.0% to ±10.0%.

Process Conditions

For superheated steam applications above 1000°F (538°C), the Rosemount 585 Annubar Primary Element with Alloy 800H sensor material is recommended.

Wetted Materials

The 486 Annubar Primary Element is available in multiple material options:

316/316L Stainless Steel — Standard option for general industrial applications

Alloy C-276 (Hastelloy) — For highly corrosive chemical environments

Sensor Surface Finish

The front surface of the Annubar primary element is textured for high Reynolds number applications, typically encountered in gas and steam service. This surface texture creates a more turbulent boundary layer on the front of the sensor, producing a more predictable and repeatable flow separation point at the sensor’s edges. The appropriate surface finish for each application is determined by Emerson’s Instrument Toolkit sizing software.

Fluid Compatibility

The Emerson Rosemount 486 Annubar Primary Element is suitable for measurement of:

Important Note: The minimum fluid conductivity limitation that applies to magnetic flow meters (such as the Rosemount 8711 and 8721 series) does not apply to the 486 Annubar. The 486 can measure any fluid—conductive or non-conductive—as long as it is clean enough to prevent clogging of the sensing ports.

Key Features and Design Advantages

Patented T-Shaped Sensor Geometry

The Annubar primary element features a proprietary T-shaped cross-section that creates a fixed flow separation point across a wide range of flow velocities. This design produces a stronger, more stable differential pressure signal while reducing signal noise compared to other averaging pitot tube shapes. The T-shape also positions a stagnation zone that minimizes measurement inaccuracies and prevents particle accumulation that could lead to clogging.

Minimal Permanent Pressure Loss

Because the 486 Annubar sensor maintains a small profile within the pipeline, it generates significantly lower permanent pressure loss compared to orifice plates, venturis, or other constriction-based flow meters. This low pressure drop translates directly into energy savings—whether through reduced compressor work for gases, lower pumping power for liquids, or decreased fuel consumption for steam generation.

No Moving Parts

The 486 Annubar primary element contains no moving components, eliminating wear-related failure modes and reducing maintenance requirements. Calibration intervals can extend up to 10 years under normal operating conditions with clean fluids, delivering significant maintenance cost savings.

Flo-Tap Mounting for Hot-Tap Installation

The 485 and 585 models within the Annubar family feature Flo-Tap design, enabling installation without process shutdown. The Flo-Tap assembly can be hot-tapped without interrupting process flow, allowing you to add and install flow measurement points without process and system shutdowns. Installation can be completed in less than three hours with the line under pressure.

Lightweight Design for Large Line Sizes

At larger pipe diameters, the Annubar sensor’s insertion design offers substantial weight and cost advantages over full-bore flow meters. A 96-inch Annubar primary element weighs a fraction of an equivalent spool-piece flow meter, reducing shipping costs, installation labor, and structural support requirements.

Wide Range of Mounting Options

The Rosemount 486 supports multiple mounting configurations:

Direct mount — Transmitter mounts directly to the Annubar primary element

Remote mount — Transmitter mounted separately with impulse piping

Flanged mounting — For larger line sizes and higher pressure ratings

Packing gland fittings — For insertion and retraction under pressure

Installation Guidelines

Upstream and Downstream Straight Pipe Requirements

Proper installation is critical to achieving specified accuracy. The following minimum straight pipe lengths are recommended:

If proper lengths of straight run are not available, position the mounting such that 80% of the run is upstream and 20% is downstream. The Annubar probe senses a total pressure (impact and static pressure) through the upstream slots and a low pressure through the downstream ports.

Sensor Positioning

The 486 Annubar sensor must be installed with the sensing ports properly oriented relative to the flow direction. The sensor’s identification tag indicates the correct flow direction, and the T-shaped profile must be positioned with the high-pressure ports facing upstream. For horizontal pipelines when measuring gases, the sensor should be installed with a minimum 5-degree upward angle to allow condensate drainage.

Transmitter Integration

The 486 primary element can be integrated with several Rosemount transmitter platforms:

Rosemount 3051SFA — Compact Annubar Flowmeter with integral transmitter

Rosemount 3051CFA — Annubar Flowmeter with coplanar transmitter mounting

Rosemount 2051CFA — Cost-effective Annubar Flowmeter solution

Each transmitter option supports HART, Foundation Fieldbus, Modbus, or WirelessHART communication protocols, enabling seamless integration into existing control system architectures.

Available Model Configurations

The Rosemount 486 Annubar Primary Element is available in a range of configurations based on line size, process conditions, and mounting requirements. Each complete order requires submission of a Configuration Data Sheet for application verification and sensor sizing.

Key ordering parameters include:

Line size (nominal pipe diameter)

Process fluid (liquid, gas, or steam with properties)

Operating pressure and temperature (minimum, normal, maximum)

Flow rate range (minimum, normal, maximum)

Pipe schedule/wall thickness

Mounting type (direct mount, remote mount, packing gland)

Process connection (flanged, threaded, weld-in)

Wetted material (316/316L SS, Alloy C-276, etc.)

Transmitter integration (3051S, 3051C, 2051, or customer-supplied)

Comparison: Rosemount 485 vs. 486 vs. 585

Within the Rosemount Annubar product family, three primary models serve distinct application needs:

When to choose the 485: Applications requiring real-time mass and energy flow measurements with integral temperature compensation. When to choose the 486: General industrial flow measurement where DP-only volumetric flow is sufficient and hot-tap capability is not required. When to choose the 585: Severe service, high-temperature (up to 1500°F), or bidirectional flow applications.

Comparison: Rosemount 486 vs. Other Flow Meter Technologies

Industry Applications

The Emerson Rosemount 486 Annubar Primary Element is suitable for flow measurement across a wide range of industries:

Frequently Asked Questions

Q: What is the minimum Reynolds Number for the Rosemount 486?

A: The minimum rod Reynolds Number varies by sensor size: 6,500 for Sensor Size 1, 12,500 for Sensor Size 2, and 25,000 for Sensor Size 3. Below these values, accuracy degrades as described in the accuracy specifications section.

Q: Can the Rosemount 486 be used for bidirectional flow measurement?

A: Standard 486 sensors are not bidirectional. For applications requiring reverse flow measurement, the Rosemount 585 with symmetrical sensor design is recommended.

Q: Is the Rosemount 486 compatible with WirelessHART transmitters?

A: Yes. When paired with a Rosemount 3051S wireless transmitter, the 486 primary element can be integrated into a WirelessHART network for remote monitoring applications.

Q: What is the recommended calibration interval?

A: Under normal operating conditions with clean fluids, calibration intervals of up to 10 years are achievable. For dirty or erosive applications, more frequent verification may be required.

Q: How does the Rosemount 486 differ from the 485 model?

A: The primary difference is that the 485 includes integral temperature measurement capability for multivariable mass flow calculations, while the 486 is typically configured for DP-only flow measurement. Both offer similar accuracy and pressure ratings. Additionally, the 485 features Flo-Tap hot-tap mounting capability.

Q: What transmitters are compatible with the 486 primary element?

A: Compatible transmitters include the Rosemount 3051S, 3051C, 2051, and 3095 platforms. For factory-assembled flowmeter systems, the 3051SFA and 2051CFA are standard configurations.

Q: Can the Rosemount 486 be installed under pressure (hot tap)?

A: The standard 486 model does not feature Flo-Tap design. For hot-tap installation without process shutdown, refer to the Rosemount 485 or 585 models.

Q: What is the maximum line size supported?

A: The Rosemount 486 can be sized for pipelines up to 96 inches (2,400 mm) in diameter.

Q: Does the Rosemount 486 require conductive fluids?

A: No. Unlike magnetic flow meters such as the Rosemount 8711 and 8721 series, the 486 Annubar can measure any fluid—conductive or non-conductive—including gases, steam, hydrocarbons, and non-conductive liquids.