# How many tubes for a Coriolis flowmeter?

## One is good, two is better, but why four?

05/12/2011

Dear Control Engineering: The recent story on large Coriolis flowmeters says the design uses four tubes. I’ve seen two-tube flowmeters, so is using more better? Will six or eight be next? It sounds like those fancy razor blades.

Understanding how Coriolis flowmeter technology works will help explain the concept, but it may not help with your shaving.

Recall if you will that Coriolis technology depends on sending your fluid through a vibrating tube. (Here’s a short tutorial as a refresher.) The mass of the flowing fluid changes the nature of the vibrations which provides data for the flow calculation. Single-tube Coriolis flowmeters have the problem that they are affected by ambient vibrations. The sensor has a hard time telling if it is seeing changes induced by the flow or it’s reading vibrations coming through the floor from that compressor down the aisle.

Adding a second tube helped designers reduce that effect by measuring the difference between the two tubes. This allows the device effectively to cancel ambient vibrations.

The move to four tubes is more complicated, so I put the question to Michael Nuber, who is E+H’s product manager for Coriolis flowmeters in Switzerland. He explains, “There are several advantages of the four tube design over conventional designs. First, it allows for better immunity towards external effects. The two-tube design is already a marked improvement, as one tube always moves in the opposite direction of the other, thus intrinsically stabilizing the measurement system. Each of the tubes is always impacted in the opposite way by external effects like pipeline vibrations.

“Having four tubes adds another dimension. Think of it this way: imagine the two tubes vibrating in one plane, for example along the x-axis. By adding two tubes for a total of four, and using what I call the ‘intelligent mechanical design,’ you also add another plane, the y-axis. That means that the whole measurement system is not only immune to external effects in one plane, but also in another plane that is angled at 90°. The x-y plane then allows for compensating virtually in any direction the external effect might come from.

“Second, having four tubes allows us better use of the circular area. In the same way that a high-performance car engine may have four valves instead of two for each cylinder, it allows us to use smaller measuring tubes. Those allow for reduced wall thicknesses, granting better density accuracy. In addition, the bending stiffness of the smaller tube is lower, either allowing for a higher sensitivity at the same overall length, or the same sensitivity while reducing the length of the sensor.”

Peter Welander, pwelander@cfemedia.com

The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers.
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide explains how the operation of hydraulic systems for subsea applications requires the user to consider additional aspects because of the unique conditions that apply to the setting
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
Optimize controls via cloud software, ladder logic simulation, industrial wireless best practices
Augmented reality and virtual reality education, autotuning PID control, cybersecurity advice, educating engineers
Ladder logic best practices and object-oriented programming, safety instrumented systems, enclosure design issues and challenges, process control advice
This article collection contains several articles on how today's technologies heap benefits onto an edge-computing architecture such as faster computing, better networking, more memory, smarter analytics, cloud-based intelligence, and lower costs.
Data centers, data closets, edge and cloud computing, co-location facilities, and similar topics are among the fastest-changing in the industry.
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. Featured articles in this digital report compare PLCs and programmable automation controllers (PACs), industrial PCs, and robotic controllers.
SCADA standardization, capital expenditures, data-driven drilling and execution
Machine learning, produced water benefits, progressive cavity pumps
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers.
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide explains how the operation of hydraulic systems for subsea applications requires the user to consider additional aspects because of the unique conditions that apply to the setting
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
Optimize controls via cloud software, ladder logic simulation, industrial wireless best practices
Augmented reality and virtual reality education, autotuning PID control, cybersecurity advice, educating engineers
Ladder logic best practices and object-oriented programming, safety instrumented systems, enclosure design issues and challenges, process control advice
This article collection contains several articles on how today's technologies heap benefits onto an edge-computing architecture such as faster computing, better networking, more memory, smarter analytics, cloud-based intelligence, and lower costs.
Data centers, data closets, edge and cloud computing, co-location facilities, and similar topics are among the fastest-changing in the industry.
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. Featured articles in this digital report compare PLCs and programmable automation controllers (PACs), industrial PCs, and robotic controllers.
SCADA standardization, capital expenditures, data-driven drilling and execution
Machine learning, produced water benefits, progressive cavity pumps
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers.
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide explains how the operation of hydraulic systems for subsea applications requires the user to consider additional aspects because of the unique conditions that apply to the setting
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
Optimize controls via cloud software, ladder logic simulation, industrial wireless best practices
Augmented reality and virtual reality education, autotuning PID control, cybersecurity advice, educating engineers
Ladder logic best practices and object-oriented programming, safety instrumented systems, enclosure design issues and challenges, process control advice
This article collection contains several articles on how today's technologies heap benefits onto an edge-computing architecture such as faster computing, better networking, more memory, smarter analytics, cloud-based intelligence, and lower costs.
Data centers, data closets, edge and cloud computing, co-location facilities, and similar topics are among the fastest-changing in the industry.
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. Featured articles in this digital report compare PLCs and programmable automation controllers (PACs), industrial PCs, and robotic controllers.
SCADA standardization, capital expenditures, data-driven drilling and execution
Machine learning, produced water benefits, progressive cavity pumps
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.