Emerson Rosemount 405A Annubar Flow Meter

Emerson Rosemount 405A Annubar Flow Meter

Introduction

In the world of industrial differential pressure flow measurement, traditional orifice plates and venturi tubes have long dominated the landscape. But they come with significant drawbacks: permanent pressure loss that drives up energy costs, impulse piping that invites leak points, and labor-intensive installation procedures. The Emerson Rosemount 405A Compact Annubar Primary Element was engineered to eliminate these inefficiencies.

The 405A Compact Annubar is an averaging pitot tube that installs directly between raised-face flanges, entirely eliminating the need for impulse piping and additional pipe penetrations. This design substantially reduces installation time, lowers material costs, and minimizes permanent pressure loss, translating directly into energy savings over the life of the instrument.

This technical datasheet provides comprehensive specifications, performance data, and application guidance for engineering professionals seeking a cost-effective, low-maintenance flow measurement solution for gases, steam, and clean liquids in pipelines from 2 to 8 inches in diameter.

What Is the Rosemount 405A Compact Annubar Primary Element?

The Rosemount 405A Compact Annubar is a member of the Rosemount Annubar family of averaging pitot tubes, alongside models such as the Rosemount 485 Annubar Primary Element (full-featured insertion type with integral temperature measurement), the Rosemount 486 Annubar Primary Element (general industrial averaging pitot tube), the Rosemount 585 Annubar Primary Element (severe service, high temperature, bidirectional), and the Rosemount 405A.

What distinguishes the 405A Compact Annubar is its compact, flange-mounted design. Unlike traditional averaging pitot tubes that require insertion through a pipe wall penetration, the 405A sensor is engineered to mount directly between existing raised-face flanges using an integral centering ring. This approach eliminates the need for impulse piping, additional process penetrations, and complex mounting hardware, reducing installation time from hours to minutes and minimizing potential leak points.

The Rosemount 405A achieves flow measurement through the same fundamental principle as all Annubar sensors: averaging pitot tube technology. Multiple pressure sensing ports distributed across the pipe diameter collect flow velocity samples. The sensor averages these individual measurements to produce a differential pressure signal that accurately represents the average flow velocity across the entire pipe cross-section. This signal is transmitted to a compatible Rosemount transmitter, which converts the raw DP into a standardized 4-20 mA output or digital communication protocol.

The 405A primary element is available as a standalone component for field integration with existing transmitters, or as a complete factory-assembled flowmeter system integrated with the Rosemount 3051S, 3051C, or 2051 pressure transmitter platforms.

Key Technical Specifications

General Specifications

Pressure and Temperature Limits

Maximum Allowable Differential Pressure by Line Size

The 405A Compact Annubar generates differential pressure signals that vary by line size and operating temperature. The following table lists the maximum allowable DP for each 405A sensor configuration:

These DP values define the operating envelope for each 405A Compact Annubar Primary Element configuration. For applications requiring line sizes beyond 8 inches, consult an Emerson Process Management sales representative for special order availability on 10-inch (250 mm) and 12-inch (300 mm) configurations, designated with special order codes (EXXXX).

Transmitter Assembly Limitations

When the 405A primary element is factory-assembled to a Rosemount pressure transmitter, the complete transmitter assembly must meet specific physical limits to ensure reliable operation. The total weight of the transmitter assembly must not exceed 9.8 pounds (4.45 kilograms), and the total length must not exceed 8.60 inches (218.44 millimeters). Additionally, the stainless steel temperature housing is not recommended for use with primary element technology A in applications with mechanical vibration.

Qualified Vibration Performance

The Rosemount 405A is qualified per IEC61298-3 (1998) for field installations with low vibration levels or pipelines with low vibration levels. The qualification covers vibration parameters of 10-60 Hz at 0.15 mm displacement peak amplitude, and 60-2000 Hz at 2g acceleration.

Key Features and Design Advantages

Compact Flange-Mount Design Eliminates Impulse Piping

The defining characteristic of the 405A Compact Annubar is its ability to install directly between raised-face flanges. This design completely eliminates the need for impulse piping, isolation valves, fittings, and the associated installation labor. A 405A sensor can typically be installed in a fraction of the time required for a conventional orifice plate DP flowmeter, reducing both material costs and labor hours.

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. The flat upstream surface of the 405A sensor provides a fixed separation point that increases the DP signal and improves performance over a wider flow range. The stagnation zone positioned on the back side of the sensor reduces signal noise, minimizes measurement inaccuracies, and prevents particulate accumulation that could lead to sensor clogging.

Integral Centering Ring for Proper Alignment

Each Rosemount 405A is shipped with an integral centering ring that ensures proper sensor alignment within the pipeline. This feature eliminates the need for field measurements or alignment tools, simplifying installation and guaranteeing that the sensing ports are correctly positioned relative to the flow profile.

Integral Thermowell for Temperature Measurement

The 405A Compact Annubar can be specified with an integral thermowell, adding process temperature measurement capability without requiring additional pipe penetrations. When combined with a Rosemount MultiVariable transmitter, the 405A Annubar system provides differential pressure, static pressure, and temperature measurement through a single process connection, enabling fully compensated mass flow measurement.

Minimal Permanent Pressure Loss

Because the 405A sensor maintains a small profile within the pipeline, it generates significantly lower permanent pressure loss compared to orifice plates or other constriction-based DP flow meters. This low pressure drop translates directly into energy savings—reduced compressor work for gases, lower pumping power for liquids, and decreased fuel consumption for steam generation.

No Moving Parts

The Rosemount 405A Compact Annubar 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.

Wide Fluid Compatibility

The 405A Annubar is suitable for measurement of gases, steam, and clean liquids. Unlike magnetic flow meters, which require conductive fluids, the 405A sensor can measure any fluid as long as the fluid is clean enough to prevent clogging of the sensing ports.

Transmitter Integration Options

The 405A Compact Annubar Primary Element can be factory-assembled with several Rosemount transmitter platforms:

When the 405A primary element and transmitter are not factory assembled, they may be shipped separately. For a consolidated shipment, inform the Emerson Process Management representative when placing the order.

Each transmitter supports HART, Foundation Fieldbus, Modbus, or WirelessHART communication protocols, enabling seamless integration into existing DCS, PLC, and SCADA architectures.

Installation Guidelines

Mounting Between Flanges

The Rosemount 405A is engineered to install between raised-face flanges using standard studs and nuts. The integral centering ring automatically positions the sensor correctly within the pipe. For steam applications, the transmitter should be located below the instrument connections of the 405A Compact Annubar primary element to ensure proper condensate drainage.

Steam Application Mounting Recommendations

For the Rosemount 405A model in steam applications, with DP readings as low as 0.75 inches of water column in low-flow conditions, consider installing the primary element in the top mounting for steam configuration. The recommended mounting zone is within 60 degrees of the top of the pipe. For wet steam applications, do not mount the flowmeter at the direct vertical position; mounting at an angle avoids measurement inaccuracy due to condensate accumulation.

Remote Mount Connections

The Rosemount 405A is only available with 1/2-inch – 14 NPT connections for remote mount transmitter configurations. For direct mount configurations, the transmitter mounts directly to the 405A sensor using the factory assembly option codes.

Straight Pipe Requirements

To achieve specified accuracy, the 405A Annubar requires adequate upstream and downstream straight-run lengths. For a single 90-degree elbow upstream, a minimum of 8 pipe diameters upstream and 4 diameters downstream is recommended. For more complex upstream disturbances, consult the Emerson Configuration Data Sheet requirements.

Fluid Compatibility and Limitations

The Emerson Rosemount 405A Compact Annubar is suitable for:

Gases — Natural gas, air, nitrogen, process gases, compressed air

Steam — Saturated steam, low-quality steam applications

Liquids — Clean water, chemicals, hydrocarbons

Important Note: The 405A sensor does not require conductive fluids, unlike magnetic flow meters such as the Rosemount 8711 and 8721 series. The 405A Annubar can measure any fluid as long as the fluid is clean enough to prevent clogging of the sensing ports.

Limitation: Annubar averaging pitot tubes are unsuitable for dirty or sticky fluids, as particulate accumulation can block the pressure sensing ports over time.

Comparison: Rosemount 405A vs. Other Annubar Models

Within the Rosemount Annubar product family, the 405A Compact Annubar serves a distinct application niche:

The 405A Compact Annubar is the ideal choice when installation cost and simplicity are the primary drivers. The 485 Annubar is preferred when integral temperature measurement or hot-tap installation is required. The 585 Annubar is necessary for high-temperature or bidirectional applications.

Comparison: Rosemount 405A vs. Other Flow Meter Technologies

Industry Applications

The Emerson Rosemount 405A Compact Annubar is suitable for flow measurement across a wide range of general industrial applications:

Frequently Asked Questions

Q: What line sizes are available for the Rosemount 405A Compact Annubar?

A: The Rosemount 405A is available in standard line sizes of 2, 3, 4, 6, and 8 inches (50, 80, 100, 150, and 200 mm). These correspond to model designations 405A02 (2 inch), 405A03 (3 inch), 405A04 (4 inch), 405A06 (6 inch), and 405A08 (8 inch). Special orders for 10-inch (250 mm) and 12-inch (300 mm) configurations are available with special order codes EXXXX.

Q: Does the Rosemount 405A require impulse piping?

A: No. The 405A Compact Annubar installs directly between raised-face flanges, eliminating the need for impulse piping entirely.

Q: What is the maximum temperature for the 405A sensor?

A: The Rosemount 405A is rated for process temperatures up to 850°F (454°C) with remote mount transmitter configuration, and up to 450°F (232°C) with direct mount transmitter configuration.

Q: Can the Rosemount 405A be used with dirty or sticky fluids?

A: No. Annubar averaging pitot tubes are unsuitable for dirty or sticky fluids, as particulate accumulation can block the pressure sensing ports over time.

Q: What transmitters are compatible with the 405A primary element?

A: Compatible transmitters include the Rosemount 3051S (option code C11 for factory assembly), Rosemount 3051C (option code S3), and Rosemount 2051C series.

Q: Does the Rosemount 405A require conductive fluids?

A: No. Unlike magnetic flow meters such as the Rosemount 8711 and 8721 series, the 405A Annubar can measure any fluid—conductive or non-conductive—including gases, steam, and non-conductive liquids.

Q: What is the recommended calibration interval?

A: Under normal operating conditions with clean fluids, calibration intervals of up to 10 years are achievable.

Q: Is the Rosemount 405A available with integral temperature measurement?

A: Yes. The 405A Compact Annubar can be specified with an integral thermowell for process temperature measurement without additional pipe penetrations.

Q: What is the maximum allowable DP for the 405A02 (2-inch) configuration?

A: The 405A02 (2-inch) sensor has a maximum allowable differential pressure of 1500 inH₂O (3.73 bar) at temperatures below 450°F. The same maximum DP applies at temperatures from 450°F to 850°F.

Ordering Information

The Rosemount 405A Compact Annubar Primary Element is configured based on line size, process conditions, and transmitter integration requirements. A Configuration Data Sheet must be completed prior to order for application verification and sensor sizing.

Key ordering parameters include:

Line size — 2, 3, 4, 6, or 8 inches (50 to 200 mm)

Process fluid — Gas, steam, or liquid with properties

Operating pressure and temperature — Minimum, normal, maximum

Flow rate range — Minimum, normal, maximum flow rates

Mounting type — Direct mount or remote mount

Transmitter integration — 3051S (C11 option), 3051C (S3 option), 2051C, or customer-supplied

Integral thermowell — Optional for temperature measurement

NACE compliance — NACE MR-0175 / ISO 15156 available