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Ultrasonic Flow Metering

An Ultrasonic Flowmeter is a device which measures volumetric flow and is non intrusive. It measures the average velocity along the path of an emitted beam of ultrasound. This it does  by averaging the difference in measured transit time between pulses of ultrasound into and against the direction of the flow. There are two physical designs one which is based on a spool installed between flanges in a process line, the second is "clamp on ultrasonic meters" where the ultrasonic transmitter and sensors are installed on the exterior of the pipe. Both Ultrasonic Flow Meters designs are relatively maintenance free, however the clamp on technology has advantages in that they can be retrofitted to existing lines without costly piping modifications.

The following papers are compliments of  Zedflo Australia

It should be noted that  Siemens Acquired Controlotron in 2006

Ultrasonic Flow Meters

Controlotron’s WideBeam™, Cavity-Free™ Ultrasonic Flowmeters Achieve Process and Natural Gas Custody Transfer Accuracy and Performance - Controlotron’s WideBeam™, Cavity-Free™ ultrasonic flowmeters have been proven to meet the recently released API standards for liquid custody transfer. This same Cavity- Free technology is now available for gas applications and will meet AGA-9 standards for custody transfer. The two major types of ultrasonic flowmeters available for gas custody transfer measurement are conventional ‘insert’ type meters and Controlotron’s unique WideBeam™, ‘Cavity-Free’ design.
Lightning Protection of Ultrasonic Flow Meters - This document outlines important recommendations for all installations requiring protection from lightning damage-Eli Spalten Senior Applications Engineer, Controlotron
3.12 How Can the Guesswork be Taken Out of Flow Measurement? - Clamp-on Ultrasonic Flow Technology offers several advantages over other flow measurement methods, number one being the utilization of external sensors. They are quickly and easily mounted on the outside of the pipe, making them the perfect choice for retrofit applications and applications where corrosive, toxic or high pressure liquids and gases rule out the option of cutting the pipe. With the use of the WideBeam technology, clamp-on flowmeters  have proven their superiority in both the field and the lab. They offer several benefits:
(a) Measurement of practically any liquid and gas
(b) Performance unaffected by viscosity, flow rate, pipe size, solids and aeration content
(c) High accuracy and repeatability through automatic temperature compensation and zero drift correction
(d)  Installation flexibility on pipe sizes up to DN 9140 (360”)
Controlotron Non-Intrusive Ultrasonic Flowmeters - Controlotron products share many common technological advances. They use Controlotron’s exclusive WideBeam® Transducers, which……
- Ensure accurate flow measurement regardless of the liquid type or temperature.
- Enable operation with up to 50% aeration, and indicate its presence.Are resistant to Aberrated Flow Profile and Crossflow errors.
- Provide continuous Automatic Zero Adjustment to prevent Zero Drift.
- Are fully maintainable without need to open pipeline or stop flow.
- Provide sonic identification of product type and quality.
- Provide all conventional digital and analog data outputs.
Reflexor™  Doppler Technology - The Technology - from Controlotron - Doppler flowmeters inject sound into the liquid by a transmit transducer at a known angle and reflects off a moving particle or bubble. The frequency is shifted proportional to velocity of the particle or bubble. The reflected signal is captured by the receive transducer and demodulated by the electronics.
Flowmeters For Water & Wastewater Applications - Unfortunately, there are many preconceptions and misconceptions about the use of ultrasonic flowmeters within a wastewater treatment plant. This Industry Note will provide a clear insight into the proper selection and use of the two types of ultrasonic flowmeters; transit-time and Doppler - From  Controlotron
The Effect of Temperature Gradients on Ultrasonic Flow Measurement - Claus Nygaard Rasmussen - It has been established that ultrasonic flow meters are influenced by thermal conditions, this technical paper addresses this - from Siemens Flow Instruments.
The Case for Widebeam Ultrasonic Flow Measurement - Matt Bird - The most commonly used method of flow measurement is Transit Time Ultrasonic Flow measurement. Two types available, externally mounted Diametral and insertion type Chordal, have different advantages and disadvantages. This article examines the pros and cons of the Diametral and Chordal Measurement systems, and offers a third solution - from Siemens Flow Instruments.
WideBeam™  Transit-Time Technology - An excellent overview of the Technology - Thanks to DanCo Systems

Clamp On Ultrasonic Flow Meters

Cost-EfficientOn-Site Check Metering Made Easy - Brian Roughan - When a flowmeter in operation has to be verified, it usually must be uninstalled and transported to a facility for the necessary verification or check-metering. With an on-site verification device, though, this task is made much faster, easier and at a fraction of the cost. When using the right meter, the result can even be as accurate as any off-site verification.
Comparative Advantages of Clamp-on Transit-time Ultrasonic Flowmeters over Conventional Intrusive Flowmeters- Recent developments have enabled today’s clamp-on transit-time ultrasonic flowmeter technology to reach a level of applicability, functionality, economy and performance which establishes this instrument as the prime candidate to replace most, if not all, the conventional intrusive flowmeters in most of their niche applications. This paper describes the advances that have taken place and how users of conventional intrusive flowmeters may evaluate for themselves the advantages available to them by use of the clamp-on transit-time ultrasonic flowmeter in place of any of their prior intrusive flowmeter types - Joseph Baumoel, President, Controlotron
The Ultimate Flowmeter, High Precision - Low Cost -Joe Baumoel, President,Controlotron Corporation -  High precision and low cost are usually incompatible concepts. Providing precision is usually the thing that leads to high cost in a flowmeter. However, start with a high cost-high precision clamp-on ultrasonic flowmeter and take out the costly functions and features that are not needed for most applications and you have a non-intrusive high precision-low cost flow meter!
Clamp on Ultrasonic Flowmeters - Your Questions Answered - Thanks to our Sponsor Zedflo Australia
Suggested Permanent Multifunction Clamp-On Dual Channel/PathTransit-Time Ultrasonic Flowmeter Specification - A useful typical specification from Controlotron
Clamp-On Ultrasonic Meter Applications - William E. Frasier - I have applied the Siemens clamp-on meter in many configurations in the field and will describe purposes and findings on the way to precise meter certainty. The clamp-on system provides an effective new tool for insight into the flowing regime within a pipe - from the American School of Gas Measurement Technology.

Other Useful Clamp on Ultrasonic Flow Meter Links

Fundamental Principles of Clamp-on Ultrasonic Flow Meters - Overview of selection, Installation, Operation and maintenance of clamp-on meters - William E. Frasier Jr -  This paper is aimed at ultrasonic natural gas meters that use transit time across the gas pipe as the measurement variable. Custody transfer meters using sensors wetted with gas are the more familiar meter format. Clamp-on meters are quite similar - from the American School of Gas Measurement Technology.
Clamp-on Ultrasonic Flowmeter Improvements - Ultrasonic flow measurement technology offers a low-cost method to measure flow. The advantage of clamp-on ultrasonic flow sensors is installation without stopping a process to put a hole in a pipe to insert a conventional sensor. From InTech and the ISA. 
A Clamp-On Ultrasonic Flowmeter for Gases - Michael J. Scelzo - Despite the industrial success of clamp-on ultrasonic flowmeters for liquid measurement, it has long been accepted as if it were a fundamental limit imposed by nature, that this technology could not be used to measure the flow of gases in metal pipes. The incorrect conclusion, that clamp-on gas flow metering is impossible, developed because the acoustic impedance of gases, even at pressure, is much less than the acoustic impedance of metals - from GE Measurement & Control Systems.
Full Steam Ahead - Clamp-on Flow Measurement no Longer just for Liquids - Daryl Belock - When plant engineers look for a non-intrusive flow measurement solution, clamp-on ultrasonic flowmeters are typically the first technology considered. Users traditionally have considered clamp-on technology only for liquid applications. For years flowmeter manufacturers have been asked,“Do you have a clamp-on solution for steam?” Until recently the answer has been no, but new technology now makes clamp-on steam flow measurement a reality for many common types of steam flows - from GE Measurement & Control Systems.
Water System Standardises on Clamp-On Ultrasonic Flowmeters - Daryl Belock & Phil McDonald - from GE Measurement & Control Systems.
3.12 Strength in Numbers - Matching Lamb Wave Sensors to the Resonant Frequency of a Pipe Wall - James Doorhy - Clamp-on ultrasonic flowmeter technology offers several major advantages over other methods of flow measurement when it comes to accounting for what, and how much, is flowing through a pipe. These benefits are derived primarily from one very important feature of clamp-on ultrasonic meters — i.e., their external sensors. Unlike traditional insert sensors, external sensors do not require pipes to be cut or operations to be halted in order to complete the installation process. Instead, the sensors are mounted on the exterior of the pipe and measure flow by transmitting acoustic signals into the pipe wall before entering the fluid - from Flow Control.

Ultrasonic Flowmeters for Custody Transfer

The following papers are from the American School of Gas Measurement Technology
Fundamentals of Multipath Ultrasonic Flow Meters for Gas Measurement -  Eric Thompson - This paper outlines the operating principles and application of ultrasonic gas flow metering for custody transfer. Basic principles and underlying equations are discussed, as are considerations for applying ultrasonic flow meter technology to station design, installation, and operation - from the American School of Gas Measurement Technology.
Ultrasonic Meter Flow Calibrations - Considerations and Benefits - Joel Clancy - The primary method for custody transfer measurement has traditionally been orifice metering. While this method has been a good form of measurement, technology has driven the demand for a new, more effective form of fiscal measurement. Ultrasonic flowmeters have gained popularity in recent years and have become the standard for large volume custody transfer applications for a variety of reasons - - from the American School of Gas Measurement Technology.
Ultrasonic Gas Flow Meters For Custody Transfer Measurement - Jim Micklos - This paper outlines the operating principals and application of ultrasonic gas flow metering for custody transfer. Basic principles and underlying equations are discussed, as are considerations for applying ultrasonic flow meter technology to station design, installation, and operation.
Ultrasonic Flow Meter Calibration Considerations And Benefits - Wayne Haner - The increased use of natural gas as the primary source of energy internationally, combined with the increased market price is driving the expansion and modernization of gas transportation infrastructure and is encouraging more accurate measurements of gas flows. To ensure the fair transaction at custody transfer locations, gas pipeline companies are demanding credibility and excellence of meter calibration as a main parameter in ensuring accountability for the gas invoiced.

Ultrasonic Flowmeter Diagnostics

12.11 Guidance Note - Application of Ultrasonic Flow Meter Diagnostics - Improvements in digital signal processing techniques have enabled large amounts of data to be processed and stored in real time. Manufacturers of modern flow meter devices such as ultrasonic meters (USMs) have taken advantage of these improvements and are now using diagnostic parameters to perform a ‘health-check’ of the meter when in operation. This can help the diagnosis of potential problems with the measured fluid or the measurement system - from NEL.

Leak Detection and Prevention

3.12 Clamp-on Leak Detection Solution for Enhanced Pipeline Management - When a pipeline leak occurs, it causes a sudden decrease in pressure at the leak origin. This pressure transient radiates both upstream and downstream from the line breach and decreases the density of the liquid, which results in a sudden drop in the liquid‘s sonic propagation velocity (Vs). The change in Vs is detected at each site station and time stamped with the arrival of the pressure wave‘s leading edge. As a result, the highly accurate FUS-LDS can locate a leak event within ±150 meters - from Siemens.
Leak Detection & Pipeline Management Solutions - SCADA based leak detection systems depend on data from existing Turbine or PD Flowmeters, and pressure and temperature instruments originally installed by others. These instruments were not originally specified to provide the extraordinarily high accuracy and calibration stability needed for leak detection. Therefore, system performance cannot be assured by the SCADA system supplier. No single party can be held responsible for SCADA based leak detection system performance. All elements of the LD system are provided by Controlotron to assure the specified leak detection accuracy. Controlotron takes responsibility for system installation, start-up, optimization and maintenance. In addition, the LD system’s compensated volume balance principle provides continuous leak detection, not the “one shot” leak detection provided by pressure based SCADA systems.
Leak Detection and Prevention - Joseph Baumoel, Controlotron, USA, Provides an overview of the ongoing problem of pipeline spills and evaluates the technologies available for the identification and control of pipeline leaks.
3.12Technical Review of Leak Detection Technologies - Volume I - Crude Oil Transmission Pipelines - Analysis of recent data from the U.S. Department of Transportation Office of Pipeline Safety (DOT-OPS) indicates that, despite stricter regulations and enforcement, the rate at which pipeline accidents occurs has not significantly changed over the last two decades (Hovey and Farmer, 1999). The statistics suggest that short pipelines will have at least one reportable accident during a 20-year lifetime and longer pipelines (800 or more miles of line pipe) can expect a reportable incident every year. Research indicates that the best opportunities to mitigate pipeline accidents and subsequent leaks are through prevention measures such as aggressive controller training and strict enforcement of safety and maintenance programs (Hovey and Farmer, 1999; Borener and Patterson, 1995). The next most productive enhancement comes from implementing better pipeline monitoring and leak detection equipment and practices. Early detection of a leak and, if possible, identification of the location using the best available technology allows time for safe shutdown and rapid dispatch of assessment and cleanup crews. An effective and appropriately implemented leak detection program can easily pay for itself through reduced spill volume and an increase in public confidence - from Alaska Department of Environmental Conservation.

Ultrasonic Flare Flow Meters

How much Do You Flare? - How to Measure Flare Flow Rates Reliably and Accurately - Ultrasonic Flowmeters help compliance with Environmental Emission Requirements, reduce Leaks and Understand their Process Losses -  from GE Measurement & Control Systems.

Other Ultrasonic Flowmeter Links

The following Technical Papers are from ICEweb Sponsor Emerson Process Management
Operation of Ultrasonic Flow Meters at Conditions Different Than Their Calibration-  Mr William Freund, Daniel Measurement and Control/ Mr Klaus Zanker, Daniel Measurement and Control/ Mr Dale Goodson, Daniel Measurement and Control /Dr James E. Hall, Letton-Hall Group/ Mr Andrew W. Jamieson, 4C Measurement.  Currently, calibration of an ultrasonic flow meter for natural gas measurement is conducted under the conditions available at the flow calibration facility. Since almost all of these facilities utilize natural gas flowing in a pipeline, it is usually not possible to vary parameters such astemperature, pressure and gas composition, each of which affect the speed of sound. When the ultrasonic meters are then used in applications where these parameters are different from their calibration values, does the calibration still apply? Thanks to our valued sponsor Emerson Process Management and the The Letton-Hall Group.
Energy Measurement using Ultrasonic Flow Measurement and Chromatography - The Technician’s Perspective-Charles W. Derr and Charles F. Cook, Daniel Measurement and Control.
A Powerful New Diagnostic Tool for Transit Time Ultrasonic Meters - Mr. W. R. Freund, Jr &  Mr. K. J. Zanker -  Ultrasonic flow meters produce a wealth of information that can be used to evaluate meter performance. Users can monitor this information to determine if any maintenance is required thus eliminating the need for routine maintenance and recalibration. Unfortunately this usually means rather heavy user involvement to track and analyze the information produced by the ultrasonic meter. This paper presents a new diagnostic indicator which, together with a few other indicators, confirm correct meter operation. Most of the diagnostics are null indicators or can be configured as null indicators, i.e. the indicated values are near zero when the meter is operating normally. These indicators are focused on the time measurement and therefore do not necessarily give information on bad flow conditions such as a half open valve immediately upstream of the meter.
An Overview and Update of AGA Report No.9 - This paper reviews some of history behind the development of AGA Report No. 9 (often referred to as AGA 9), key contents and includes information on meter performance requirements, design features, testing procedures, and installation criteria.
Gas Ultrasonic Flow Meter Station Design - This paper highlights some of the considerations that differentiate USM stations from conventional meter station practices. It is the subtle details that yield the big rewards. Consideration checklists are detailed and the prime importance items discussed. There is more design detail than many people realise and all items are important to a successful station. 
Ultrasonic Meter Station Design Considerations Technical White Paper - This paper addresses several issues that an engineer should consider when designing ultrasonic meter installations
Diagnostic Ability of the Four Path Ultrasonic Flow Meter - Klaus J. Zanker - The primary function of the ultrasonic meter is to measure the actual volume flow rate. The process involves measuring four velocities on chords located in four different radial positions and in two different vertical planes. The eight transducers are fired about 50 times per second and the transit times to traverse each chord in both directions are measured. This vast array of data can be processed to yield useful diagnostic information, which forms the subject of this paper and shows that the four-path ultrasonic meter does much more than just measure the flow rate. It has sufficient diagnostic ability to confirm the authenticity of the measurement, and develop the source for conditional based maintenance and re-calibration.
How Today's Ultrasonic Meter Diagnostics Solve Metering Problems - This paper discusses both basic and advanced diagnostic features of gas ultrasonic meters (USM), and how capabilities built into today’s electronics can identify problems that often may not have been identified in the past. It primarily discusses fiscal-quality, multi-path USMs and does not cover issues that may be different with non-fiscal meters. Although USMs basically work the same, the diagnostics for each manufacturer does vary. All brands provide basic features as discussed in AGA 9. However, some provide advanced features that can be used to help identify issues such as blocked flow conditioners and gas compositional errors.

Other useful technical information

Ultrasonic Flowmeters -By David W. Spitzer -  Parts 1 to 4  - The flowmeters to be discussed use ultrasonic energy or correlation as their primary flow measurement technique. Therefore, a common class of "ultrasonic flowmeters" comprised of an open channel flowmeter (such as a flume or weir) that incorporates an ultrasonic level measurement is specifically excluded from this discussion. Ultrasonic flowmeters use sensors to generate ultrasonic waves and direct them into the flowing stream. Information from the remnants of these sound waves is used to determine the flow of fluid passing through the flowmeter. Ultrasonic flowmeters have no moving parts.
Ultrasonic Flowmeters Move Into the Mainstream - Walt Boyes, Editor in Chief -Thanks to ControlGlobal.com 
Ultrasonic Flow Measurement - Technology -From www.sensorland.com
Are Ultrasonic Flowmeters Right for You?- From Automation World
Ultrasonic Doppler Flowmeters- Flow reference from Omega
Effluent Flow with Suspended Solids -Facing Rising Treatment Costs, Paper Mill Reconsiders Flowmeter Installation - This article describes some solutions to this issue - David W. Spitzer, P.E.- Thanks to flowcontrolnetwork,com
University Chilled Water Plant Plays it Cool with Ultrasonic Flowmeters - An application article - From InTech and the ISA

 The following excellent Ultrasonic Flowmeter Papers are from Cameron-Caldon
General Principles of LEFM Time-of-Flight Ultrasonic Flow Measurements - Herb Estrada - A time-of-flight ultrasonic flow measurement system projects acoustic energy along one or more diagonal paths through the pipe in which flow is to be measured, this paper explains these principles.
Identifying and Bounding the Uncertainties in LEFM Flow Measurements- Herb Estrada - It is appropriate to ask how the errors of individual elements, biases and time varying random errors, should be combined. In the treatment of uncertainties in LEFM flow measurements, it has been Caldon’s practice to follow the guidance of ASMEstandard for heat balance testing, with respect to estimating and combining potential errors from various sources in the measurement system.
Theory of Ultrasonic Flow Measurement, Gases & Liquids- Herb Estrada - Ultrasonic flow measurement systems (UFMs) are being applied with increasing frequency to hydrocarbon flow measurements. Most of these UFM s are transit time (also called time-of-flight) systems—they measure the transit time of ultrasonic energy pulses traveling with and against the direction of flow. This paper will outline the principles of three kinds of transit time UFMs.
Installation Effects and Diagnostics Interpretation using Caldon Ultrasonic Flow Meter -H. Estrada/ T. Cousins/D. Augenstein - This is a comprehensive review of Installation and diagnostics.
Proving Liquid Ultrasonic Flow Meters - Don Augenstein - This paper’s objective is to provide UFM users with relevant information necessary to understand how UFMs operate particularly with respect to measurement variability and its effect upon proving along with investigating potential factors that influence UFM statistics and repeatability.
Proving of Multi-Path Liquid Ultrasonic Flowmeters - T. Cousins, D. Augenstein - This paper identifies the factors affecting the provability of multi-path chordal ultrasonic meters. It also presents proving data for such meters, for a range of meter sizes, at several independent certified hydraulic laboratories around the world, as well as data from meters at various field installations. These data show that repeatability is predictable and generally is controlled by hydraulic/turbulence statistics. The statistics are zero biased and subject to the flow conditions at the site. The understanding of the proving characteristics gained by this analysis leads to proving procedures whereby a specified calibration accuracy, such as the ±0.027% of the API Standards, can be achieved. The paper describes this process and demonstrates its application using field data.

The following papers are from the American School of Gas Measurement Technology

3.12Fundamental Principles of Clamp-on Ultrasonic Flow Meters - Overview of Selection, Installation, Operation and Maintenance of Clamp-on Meters - William E. Frasier Jr -This paper is aimed at ultrasonic natural gas meters that use transit time across the gas pipe as the measurement variable. Custody transfer meters using sensors wetted with gas are the more familiar meter format. Clamp-on meters are quite similar.
Principles Of Operation For Ultrasonic Gas Flow Meters - John Lansing - This paper discusses fundamental issues relative to ultrasonic gas flow meters used for measurement of natural gas. A basic review of an ultrasonic meter’s operation is presented to understand the typical operation of today’s Ultrasonic Gas Flow Meter (USM). The USM’s diagnostic data, in conjunction with gas composition, pressure and temperature, will be reviewed to show how this technology provides diagnostic benefits beyond that of other primary measurement devices. The basic requirements for obtaining good meter performance, when installed in the field, will be discussed with test results. Finally, recommendations for installation will be provided, including an example of a good piping design.
Ultrasonic Meters for Residential and Commercial Applications - Paul Honchar - An ultrasonic meter falls into the classification of inferential meters. Unlike positive displacement meters that capture volume to totalize volume, inferential meters measure flowing gas velocity to totalize volume. Orifice meters use pressure drop to measure velocity to infer volume and turbine meters use the speed of the rotor to measure velocity to infer volume, while ultrasonic meters use sound waves to measure flowing gas velocity to infer volume. Ultrasonic meters have been around for many years in primarily liquid measurement. However, their application in the measurement of natural gas is relatively new, and has become more commercialized over the last decade - from the American School of Gas Measurement Technology.
Continuous Monitoring of Ultrasonic Meters - Randy Miller - Utilizing electronic flow computers and SCADA systems to collect and analyze ultrasonic meter data can provide many benefits for a Natural Gas Pipeline Company. The Natural Gas Pipeline industry has seen tremendous changes in the past 20 years including a smaller multi skilled workforce. In fact, a Measurement Technician on a facility may be responsible for a wide range of tasks and skills necessary for operating and maintaining a pipeline. Much of their measurement work is performed with less frequency, and on more complex equipment than ever before. Gaining the proficiency needed to recognise and troubleshoot ultrasonic meter problems, let alone subtle changes that can provide an eye into potential measurement inaccuracies, requires time and experience to learn. By bringing the meters diagnostic data in via SCADA, we can provide alarms and trending capabilities that are not dependent on the frequency at which a Technician can visit a measurement facility. It is also not dependent on whether a Technician has necessary expertise to recognise potential meter problems - from the American School of Gas Measurement Technology.