Emerson Rosemount 8750 flow sensor

Emerson Rosemount 8750 flow sensor

Overview

The Rosemount Annubar averaging pitot tube flow meter represents Emerson’s proprietary differential pressure (DP) flow measurement technology, designed to measure liquid, gas, and steam flow across a wide range of industrial applications-37. Unlike traditional DP devices such as orifice plates or venturi tubes, the Annubar sensor maintains a minimal profile inside the pipe, significantly reducing permanent pressure loss while delivering reliable measurement accuracy-2.

Note: This document focuses on Rosemount Annubar differential pressure flow measurement technology. For applications requiring conductive liquid measurement, Rosemount offers alternative solutions including the Rosemount 8750W magnetic flow meter series (utility water applications) and the Rosemount 8705 flanged magnetic flow meter series (½–36 inch line sizes)-12-20.

Product Series Overview

Rosemount 485 Annubar Primary Element

The Rosemount 485 Annubar is the industry-standard averaging pitot tube, built with a patented T-shaped sensor design that creates a fixed separation point for DP signal improvement across a wider flow rate-30. Key specifications include:

The sensor incorporates a stagnation zone that reduces noise and measurement inaccuracies while keeping particulates from clogging-30. The T-shape design enables temperature, pressure, and flow measurements through a single pipe penetration, eliminating multiple process penetrations and potential leak points-2.

Rosemount 585 Annubar Primary Element for Severe Service

Engineered for extreme operating conditions, the Rosemount 585 Annubar features solid sensor construction capable of withstanding temperatures up to 1500°F (815°C)-3. This model is particularly suitable for high-temperature steam, superheated gas, and severe service environments where standard sensors would fail.

A key feature of the Rosemount 585 is its symmetrical sensor design, which allows for bi-directional flow measurements without sensor modification or replacement-3. The availability of Alloy 800H material makes this model the recommended choice for applications exceeding 1000°F (538°C)-.

Rosemount 285 Annubar Primary Element

The Rosemount 285 Annubar is designed for low-to-medium pressure and temperature applications, featuring an innovative appearance with a temperature sensing port that achieves optimal accuracy and repeatability-. This model is versatile enough for both circular pipes and square/rectangular ducts, offering direct or remote mounting options-. A key advantage of the 285 series is the Pak-Lok compression fitting design, which simplifies installation and removal without requiring a complete system shutdown.

Integrated Flow Meter Solutions

Rosemount 3051CFA Annubar Flow Meter

The Rosemount 3051CFA combines the industry-proven 3051C pressure transmitter with advanced Annubar primary element technology-58. This integrated solution offers:

The integrated design reduces leak points by up to 70% and simplifies installation-39. Diagnostics include basic diagnostics, process alerts, loop integrity, and plugged impulse line detection-58.

Rosemount 3051SFA Annubar Flow Meter

For applications demanding superior accuracy and fully compensated mass flow measurements, the Rosemount 3051SFA offers a no-equal solution with built-in flow calculations-57:

This model features Callendar-Van Dusen sensor matching for improved temperature accuracy and an Ultra for Flow performance class achieving ±0.04% of reading accuracy-57.

Rosemount 2051CFA Annubar Flow Meter

A cost-effective solution with industry-standard performance:

SIL 2/3 certified to IEC 61508, this model includes a local operator interface (LOI) for field commissioning-39.

Working Principle

The Annubar operates on the averaging pitot tube principle. Multiple upstream pressure ports distributed across the pipe diameter all lead to a single high-pressure tapping point, providing an average upstream pressure measurement-37. The downstream port is connected directly to a low-pressure tapping point. As fluid flows past the sensor, differential pressure (DP) develops between the upstream and downstream sides, which is proportional to the square of the fluid velocity per Bernoulli’s theorem-37.

The patented T-shaped sensor design creates a fixed separation point that improves DP signal quality across a wider flow range compared to traditional pitot tube designs-2. The textured front surface of the Annubar primary element is specifically designed for high Reynolds number applications, typically gas and steam service-.

Key Technical Specifications

Pressure and Temperature Ratings

Flow Performance

Material Options

The Annubar series offers extensive material selection to accommodate diverse process conditions:

316/316L Stainless Steel: Standard material for general-purpose applications

Alloy C-276: Superior corrosion resistance for aggressive chemical environments

Alloy 800H: High-temperature service exceeding 1000°F (538°C)

Additional alloys: Available upon request for specialized applications

Process Connections and Mounting

Flanged connections: ANSI B16.5, Class 150–2500

Pak-Lok assemblies: Compression fitting design for simplified installation and removal

Flo-tap design: Available on 485 and 585 models, enables hot-tap installation without process shutdown-

Duct mount options: Type D1 and D2 configurations for rectangular duct applications-

Installation Guidelines

Orientation Requirements

Proper sensor orientation is critical for accurate measurement:

Liquid applications: Sensor positioned between 15° to 45° from vertical down to ensure electrodes remain covered by process fluid-

Gas applications: Sensor located on upper half of the pipe, at least 45° above horizontal line-

Steam applications: Specific orientation guidelines apply depending on installation configuration-

Straight Run Requirements

To ensure specification accuracy, installation must maintain adequate straight pipe diameters:

Consult manufacturer guidelines for specific application requirements. Flow straighteners can reduce required straight run lengths.

Alignment Tolerances

Maximum misalignment tolerance is ±3° from specified orientation-. The sensor must be mounted with the flow direction arrow (shown on the sensor identification tag) pointing in the direction of flow.

Flo-Tap Hot-Tap Installation

Models 485 and 585 feature Flo-tap design, allowing sensor installation and removal without process shutdown-. This capability is particularly valuable for:

Continuous processes where shutdown is cost-prohibitive

Maintenance and recalibration of sensors in critical service lines

Initial installation in live pipelines

Advantages of Annubar Technology

Low Permanent Pressure Loss

Annubar sensors create less permanent pressure loss than virtually any other DP flow primary element-37. The minimal obstruction design reduces pumping energy requirements, delivering significant operational cost savings over the instrument’s lifecycle.

Suitable for Large Diameter Lines

The forces exerted on primary flow elements can be substantial in large pipelines. Annubar models are available with full-diameter support at both ends, providing robust performance while remaining economical for large line sizes-37.

Multi-Variable Capability

The T-shaped sensor design enables temperature, pressure, and flow measurements through a single pipe penetration-2. This eliminates multiple penetrations, reducing potential leak points and installation costs.

Minimal Maintenance Requirements

With no moving parts, the Annubar requires minimal maintenance. The stagnation zone design captures particulate matter before it reaches measurement ports, reducing clogging and eliminating noise interference-.

Cost-Effective Installation

Annubars do not require special flanges, spool sections, or extensive piping modifications. Standard ANSI/ASME flanges or Pak-Lok assemblies can be used, making the differential pressure transmitter the most expensive component in the installation-37.

Diagnostics and Communication

Modern Annubar flow meter systems incorporate advanced diagnostics:

Basic Diagnostics: Standard health monitoring

Loop Integrity Diagnostics: Detect electrical loop issues before they impact measurement

Plugged Impulse Line Diagnostics: Identify clogged impulse piping to prevent measurement degradation

Process Alerts: Notify operators of abnormal process conditions

Smart Meter Verification: Available on select models for remote performance validation

Communication options include:

WirelessHART® technology delivers >99% data reliability and is supported by the SmartPower™ module, providing up to 10-year maintenance-free operation with field-replaceable power modules-58.

Safety Certifications

Key Annubar models are certified to:

SIL 2/3 to IEC 61508 by independent third parties

NACE® MR-0175 / ISO 15156 for sour service applications

Hazardous location certifications (varies by model and configuration)

Applications

The Rosemount Annubar is suitable for a wide range of industrial flow measurement applications:

Hydrocarbon processing: Crude oil, refined products, natural gas

Chemical processing: Corrosive and aggressive fluids (Alloy C-276 option)

Power generation: Steam flow, boiler feedwater, cooling water

Pulp and paper: Black liquor, white liquor, steam

Water and wastewater: Raw water, treated water, sludge (with appropriate material selection)

HVAC and utilities: Chilled water, hot water, compressed air, steam

Mining and minerals processing: Slurries and abrasive fluids

Ordering Information

Complete Annubar flow meter systems are available as fully assembled, leak-tested, and calibrated units ready for installation. Complete flow assemblies reduce leak points by up to 70% compared to field-assembled components-39. Each flow meter includes:

Annubar primary element (model specific: 285, 485, or 585)

Pressure transmitter (3051SFA, 3051CFA, or 2051CFA)

All required mounting hardware and gaskets

Factory calibration certificate

Comprehensive documentation package

Comparison: Annubar vs. Magnetic Flow Meter Technologies

For users evaluating flow measurement technologies, it is important to understand the distinction:

The Rosemount 8705 flanged magnetic flow meter sensors feature welded, sealed coil housing, 0.25% standard accuracy with 0.15% high accuracy option, and 7–16Ω sensor coil resistance with upper range limit of 39.37 ft/s (12 m/s)-20. The Rosemount 8750W series offers line sizes from 0.5 to 48 inches with PTFE or Neoprene liners, standard 0.5% accuracy (optional 0.25% high accuracy), and advanced diagnostics including empty pipe detection and coated electrode detection-12.