Ultrasonic Flowmeters
A transit time ultrasonic flowmeter is an instrument designed for measuring the
volume flow rate in clean liquids or gases.
From: Measurement and Instrumentation, 2012
Related terms:
Fluid Flow, Electromagnetic Flowmeters, Turbines, Ultrasonics, Transducers, Flowmeter, Open Channel
View all Topics
Ultrasonic Flowmeter
James E. Gallagher, in Natural Gas Measurement Handbook, 2006
6.7 Risk Management
With respect to fiscal measurement, risk management is relatively simple and
supported by senior management. For high fiscal exposure facilities (commodity
value times throughput), higher capital and operating resources are allocated to
manage the risk to an acceptable level. The frequency of inspection, testing, and
verification would be at least every month or by total quantity. The facility is designed
and maintained beyond the minimum industry standards to manage the financial
risks (mismeasurement, litigation, and arbitration). For low fiscal exposure facilities,
lower capital and operating resources are allocated to manage the risk to within an
acceptable level. The facility is designed and maintained to minimum industry standards to manage the financial risks (mismeasurement, litigation, and arbitration).
Calibration of the Primary Device
Ultrasonic flowmeter assemblies are calibrated using the central facility or in situ
method. The ultrasonic flowmeter(s) should be calibrated in three steps:
1.
A dimensional conformance test to determine the flowmeter body mechanical
configuration (path angle, internal diameter, roughness, circularity).
2.
3.
A static (or zero flow) calibration using dry, pure nitrogen gas (99.999%) as the
test medium at the manufacturer's facility.
A dynamic calibration using natural gas as the test medium at an approved
flow laboratory.
The documentation and results of these tests are part of the audit trail for the
ultrasonic flowmeter (calibration documentation) and should be retained for the life
of the facility.
The specifics of the tests should conform to user's specifications and are beyond
the scope of this book. However, the following subsections cover these tests from a
generalized viewpoint.
Static Calibration
To verify the transit-time measurement system of each ultrasonic flowmeter, the
manufacturer performs a static (or zero flow) verification test. A static calibration is
required to ensure that all calibration parameters are entered properly and meter
components are functioning properly.
Under static or nonflowing conditions, the pressure is varied at a constant temperature to monitor the performance of the combined electromechanical device
(the MUSM). The static calibration is performed with pure nitrogen gas as the test
medium. Sonic-Ware®, or a mutually acceptable predictive software program, is used
to predict the acoustic property or SOS of pure nitrogen.
The individual chordal paths are monitored for performance rating (the ratio of accepted pulses to the total pulses transmitted), raw velocity under zero flow conditions
(Vi), and the speed of sound (SOSi).
The overall MUSM performance is monitored for the weighted corrected velocity
(Vavg) and the weighted corrected speed of sound (SOSavg).
Static calibration ensures control of the following variables:
•
Gross clock stability.
•
Proper programming associated with the calibration parameters.
•
Proper electronic board performance.
•
Proper cable lengths or impedance matching.
•
Proper acoustic probes.
•
Proper acoustic path lengths.
The static calibration does not ensure the following variables are in control:
•
Precise clock stability.
•
Range between parallel raw chordal velocities under flowing conditions.
•
Mechanical angle for chordal paths.
•
Delta time delays for each acoustic probe.
•
Digital signal processing or signature recognition software.
•
Integration accuracy.
These variables can be validated only in a dynamic calibration of the ultrasonic
flowmeter.
Dynamic Calibration
To verify the transit-time measurement system of each ultrasonic flowmeter, the
manufacturer performs a dynamic calibration to ensure proper performance under
steady-state, mass flow conditions. The dynamic calibration is performed with natural gas as the test medium at an approved flow laboratory.
Under dynamic conditions, the average pipe velocity is varied at a constant temperature and user specified pressure to monitor the performance of the combined
electromechanical device (the MUSM). To repeat, the dynamic calibration is performed with the actual flowmeter assembly (artifact) including the isolating flow
conditioner and acoustic filter (if required in the design).
A dynamic calibration is required to ensure
•
Configuration parameters are entered properly.
•
The electronic meter components are functioning properly.
•
•
The meter factor, or meter error, offset from unity, over the user-designated
flowmeter range, is within acceptable limits at the user-specified operating
pressure.
The meter factor linearity, or peak-to-peak meter error, over the user-designated flowmeter range, is within acceptable limits at the user-specified operating
pressure.
The flowmeter complies with fiscal repeatability specifications.
•
The flowmeter complies with fiscal reproducibility specifications.
•
Dynamic calibration ensures control of the following variables:
•
Proper programming associated with the configuration parameters.
•
Gross clock stability.
•
Precise clock stability.
•
Proper acoustic probes (matched pairs and so forth).
•
Proper mechanical angle for each transducer probe ( ).
•
Delta time delays for each acoustic probe.
•
Proper acoustic path lengths (APL) for each chord.
•
Proper electronic board performance.
•
Proper cable lengths or impedance matching.
•
Digital signal processing and signature recognition software.
•
Integration accuracy (proprietary or nonproprietary integration).
If the design of the ultrasonic flowmeter requires bidirectional flow, then the
flowmeter assembly (ultrasonic flowmeter, upstream piping section, isolating flow
conditioners, and downstream piping section) are considered two separate flowmeters and designated accordingly. In this light, the artifact flowmeter assembly is
calibrated in both directions and the results archived to allow separate meter factors
for each flow direction. The flow computer is programmed to adopt the proper meter
factors, or meter errors (flow-weighted mean error [FWME], polynomial curve fits,
or algorithms), in accordance with API MPMS Chapter 21, Section 1, “Electronic Gas
Measurement.”
Testing, Verification, Calibration, and Maintenance Intervals
To minimize the financial risks, the frequency of testing, verification, calibration,
certification, and maintenance of the primary device, secondary devices, and tertiary
device are governed by the operator of the facility. Compliance with the API MPMS
Chapter 21, Section 1, “Electronic Gas Measurement,” is required for all installations.
Visual Inspection of Flowmeter Assembly
To ensure compliance with the law of similarity (geometric and dynamic) visual
inspection of the flowmeter assembly internals should be performed at predetermined intervals. The inspection should evaluate the presence of pipeline rouge,
liquids, grease, and particulates. The assembly should be evaluated for blockage of
the HPFC, transducer face and pocket (if applicable), gasket protrusions, internal
flange alignment, and so forth. An ultrasonic flowmeter has a high sensitivity to
internal film buildup (or degradation) of any material on the inside of the flowmeter
body.
Other Primary Tests
To ensure compliance with the central calibration technique, field inspection, and
verification of the flowmeter internal diameter, transducer leakage, software, and
electronic performance should be performed at predetermined intervals. In addition,
assurance is needed of a steady-state mass flow that, for all practical purposes, is
considered clean, single phase, homogeneous, and Newtonian under the operating
conditions of the facility. The ultrasonic flowmeters should be recalibrated dynamically every 5 years after the initial installation at an approved flow laboratory. The
recalibration should be conducted as close as practical to the normal operating
pressure of the facility.
Secondary Devices
The frequency of testing, verification, calibration, certification, and maintenance of
the secondary devices should be performed at intervals that satisfy the requirements
of API MPMS Chapter 21, Section 1, criteria, as a minimum. For higher financial risk
facilities, the intervals usually are more frequent than the API criteria to manage the
financial risks to an acceptable level of the business.
Tertiary Devices
The frequency of testing, verification, calibration, certification, and maintenance of
the tertiary devices should be performed at intervals that satisfy the requirements of
API MPMS Chapter 21, Section 1, criteria, as a minimum. Again, for higher financial
risk facilities, the intervals usually are more frequent than the API criteria to manage
the financial risks to an acceptable level of the business. The documentation and
results of these tests are part of the audit trail for the ultrasonic flowmeter (calibration
documentation) and should be retained for the life of the facility.
> Read full chapter
Real Time Measurement Techniques of
Biofluids
Ali Ostadfar PhD, in Biofluid Mechanics, 2016
8.3.2 Ultrasonic Flowmeter
An ultrasonic flowmeter can measure instantaneous blood flow. An ultrasonic probe
can create sound waves through the living tissues to analyze tissue biocharacters,
such as blood flow rate. Advanced models of ultrasonic flowmeters can even measure
and analyze the blood profile. Transducers have the key role of converting electrical
signals to acoustic waves in ultrasonic devices. Since the transducers have a fixed
diameter, they can produce diffraction shapes which are similar to a hole in optics.
The differences in diameters and shapes help to provide near and far detection fields
[1].
Fig. 8.7 shows the beam shapes for two transducer diameters, D and D/2, at the same
level and frequency on a blood vessel. The figure represents different penetration
fields (near and far field) in respect to the diameter of the transducers which have
positive roles in the range of penetration field. Technically, the best results occur in
range of the near field or the initial distances. Eq. (8.13) explains this aspect of the
ultrasonic principle for the near field and Eq. (8.14) represents the angle of beam
divergence, , for the far field [1];
Figure 8.7. Schematic of two ultrasonic transducers with two different diameters and
same operational frequency which cause different penetration fields.
(8.13)
(8.14)
where is distance of near field, is transducer diameter and is wavelength. These
characters and geometries are shown in Fig. 8.7.
Transit-time flowmeters and continuous-wave Doppler flowmeters are other types
of sonic instrumentation for measuring blood flow rate. There are two arrangements
for transit-time flowmeter technology: (1) two transducers are located diagonally on
two sides of tube (blood vessel) or (2) two transducers are located on one side of a
vessel and a reflector is located on the other side in the middle of them and role of
the reflector is to reflect the waves between the transducers.
The transit-time flowmeter develops a precise measure of the transit time for a
sonic wave to travel from one transducer to another one. The difference between
the integrated transit times of upstream and downstream derives a measurement
for the blood flow rate and the velocity inside the blood vessels. Fig. 8.8 shows the
schematic of the transit-time flowmeter for both systems (Fig. 8.8A and B).
Figure 8.8. Arrangement schematic of transit-time flowmeters for blood flow detection. (A) One side transduces, the other side is the reflector. (B) Diagonal transducers.
The continuous-wave Doppler flowmeter transmits an ultrasonic signal from within
the flow stream. The signal is reflected off blood particles such as blood cells and
returns to the receiver. There is a difference between the sending and receiving
frequency due to the effect of the Doppler frequency shift. The instrument and
analysis system measure and calculate the average velocity of flow. Furthermore,
the flow area can be measured by liquid depth to determine the flow area. Flow
rate can be calculated by multiplying the flow area by the average velocity of the
blood. The following equation shows the relation between frequency and velocity in
a continuous-wave Doppler instrument [1]:
(8.15)
where and are Doppler frequency shift and source frequency respectively, is target
velocity and is velocity of sound.
Fig. 8.9 shows the simplest instrumentation of a continuous-wave Doppler flowmeter that consists of a transmitter and receiver to measure the blood velocity and the
blood flow rate.
Figure 8.9. Schematic of continuous-wave Doppler flowmeter. The sound wave is
beamed through the blood vessel wall, reflected by the red blood cell and received
by a receiver. The output signal transfers to a microprocessor to calculate the blood
velocity and the blood flow rate.
> Read full chapter
Physical Properties and Process Conditions
James E. Gallagher, in Natural Gas Measurement Handbook, 2006
Ultrasonic Noise Generation
If the facility employs ultrasonic flowmeters, the designer should consider sources
of ultrasonic noise. Field experience has shown that “quiet” control valves confuse
ultrasonic flowmeters and cause them to malfunction or turn off completely, because
these control valves are designed to minimize audible noise frequencies by moving
the noise to the ultrasonic frequencies. These designs were motivated by the desire
to comply with OSHA regulations for operating personnel exposure to audible
noise (hearing loss) and environmental considerations for neighboring facilities
(residential and commercial areas). The design of the ultrasonic flowmeter facility
should consider other potential sources of ultrasonic noise.
> Read full chapter
Sampling, Control, and Mass Balancing
Barry A. Wills, James A. Finch FRSC, FCIM, P.Eng., in Wills' Mineral Processing
Technology (Eighth Edition), 2016
Ultrasonic Flowmeters
Two types of ultrasonic flowmeters are in common use. The first relies on reflection
of an ultrasonic signal by discontinuities (particles or bubbles) into a transmitter/receiver ultrasonic transducer. The reflected signal exhibits a change in frequency due
to the Doppler Effect that is proportional to the flow velocity; these instruments are
commonly called “Doppler flow meters”. As the transducer can be attached to the
outside of a suitable pipe section, these meters can be portable.
The second type of meter uses timed pulses across a diagonal path. These meters
depend only on geometry and timing accuracy. Hence they can offer high precision
with minimal calibration.
> Read full chapter
Flow measurement
Alan S. Morris, Reza Langari, in Measurement and Instrumentation (Third Edition),
2021
Transit-time ultrasonic flowmeter
The transit-time ultrasonic flowmeter is an instrument that is designed for measuring the volume flow rate in clean liquids or gases. It consists of a pair of
ultrasonic transducers mounted along an axis aligned at an angle with respect to
the fluid-flow axis, as shown in Fig. 16.14.
Figure 16.14. Transit-time ultrasonic flowmeter.
Each transducer consists of a transmitter–receiver pair, with the transmitter emitting
ultrasonic energy that travels across to the receiver on the opposite side of the pipe.
These ultrasonic elements are normally piezoelectric oscillators of the same type as
used in Doppler-shift flowmeters. Fluid flowing in the pipe causes a time difference
between the transit times of the beams traveling upstream and downstream, and
measurement of this difference allows the flow velocity to be calculated. The typical
magnitude of this time difference is 100 ns in a total transit time of 100 μs, and
high-precision electronics are therefore needed to measure the difference. There
are three distinct ways of measuring the time shift. These are direct measurement,
conversion to a phase change, and conversion to a frequency change. The third
of these options is particularly attractive, as it obviates the need to measure the
speed of sound in the measured fluid as required by the first two methods. A
scheme applying this third option is shown in Fig. 16.15. This also multiplexes the
transmitting and receiving functions, so that only one ultrasonic element is needed
in each transducer. The forward and backward transit times across the pipe, Tf and
Tb, are given by:
Figure 16.15. Transit-time measurement system.
where c is the velocity of sound in the fluid, v is the flow velocity, L is the distance
between the ultrasonic transmitter and receiver, and is the angle of the ultrasonic
beam with respect to the fluid flow axis.
The time difference T is given by:
This requires knowledge of c before it can be solved. However, a solution can be
found much more simply if the receipt of a pulse is used to trigger the transmission
of the next ultrasonic energy pulse. Then, the frequencies of the forward and
backward pulse trains are given by:
If the two frequency signals are now multiplied together, the resulting beat frequency is given by:
c has now been eliminated and v can be calculated from a measurement of F as:
This is often known as the sing-around flowmeter.
Transit-time flowmeters are of more general use than Doppler-shift flowmeters,
particularly where the pipe diameter involved is large and hence the transit time is
consequently sufficiently large to be measured with reasonable accuracy. It is possible then to reduce the inaccuracy value down to ±0.5%. However, the instrument
costs more than a Doppler-shift flowmeter because of the greater complexity of the
electronics needed to make accurate transit-time measurements.
> Read full chapter
Ultrasonic Flowmeter Design
James E. Gallagher, in Natural Gas Measurement Handbook, 2006
15.3 Acoustic Filter
To ensure that control valves do not confuse the ultrasonic flowmeters through
the generation of ultrasonic noise, an acoustic filter is installed in each flowmeter
assembly such that proper maintenance can be accomplished without a station
shutdown. An acoustic filter element also should be installed in each flowmeter
assembly, between the control valve and the ultrasonic flowmeter, consisting of
parallel tubes and a flow-through design to minimize the ultrasonic noise effect
on the MUSM technology. If necessary, multiple tees or elbows may be required
between the control valves and the flowmeter assembly to eliminate the “line of
sight” issue with the noise source.
> Read full chapter
Analysis of energy flows in engine
coolant, structure and lubricant during
warm-up
R.D. Burke, ... I. Pegg, in Vehicle Thermal Management Systems Conference and
Exhibition (VTMS10), 2011
3.3 Theory
The majority of energy analysis was estimated using standard energy balance (see
equation 1). This is readily applied to the coolant circuit where ultrasonic flowmeters
provided non intrusive measures of coolant flow ( ), temperature differences (ΔT)
were easily measured and heat capacity (cp) well documented. The air path was
analysed in the same way, with cylinder air flow estimated including EGR rates. Care
must also be taken when fitting thermocouples to measure gas stream temperatures.
(1)
For the instrumented engine only one build condition has been tested in which no
coolant throttles were installed. However, the results from this test point represent
the average of 9 different repeat tests to ensure good confidence in the results.
Heat fluxes from the combustion chamber were estimated using 1D heat transfer as
described by Lewis et al. [10]. Heat energy from the combustion chamber was then
obtained by integrating heat flux down the cylinder bore. Bearing heat transfer was
estimated in a similar manor but based on two single point temperature readings,
sufficiently distant to increase confidence in their respective readings.
> Read full chapter
Instrumentation
Seán Moran, in Process Plant Layout (Second Edition), 2017
36.5.1 Sensors
In-line flowmeters in liquid service can generally only operate properly when completely flooded, free from flashing and gas entrainment (the exception to this rule
are Doppler ultrasonic flowmeters, which work well with a certain amount of gas
entrainment, though “time of flight” ultrasonic flowmeters do not).
The flooded condition normally prevails in pumped lines, so flowmeters can still
work effectively in vertical, horizontal, or slanted piping as long as pockets have been
avoided in layout. For vertical pipes, the flow direction must be upward to ensure
flooding.
Flowmeters are sometimes installed at a low point in piping to ensure the flooded
condition in gravity-flow lines. To provide the required static head in front of the
meter, it must be positioned in a horizontal section of the pipe (unless feeding to
a seal pot such as a barometric leg), and a slight upward slope should be provided
after the meter to ensure the pipe is fully flooded.
Unless it is desired to measure the static head of liquid (in which case they are
mounted in connection with the liquid at the bottom of vessels), pressure sensors
are mounted in the headspace of vessels. Pressure sensor connections for vapors
and gases in horizontal lines should be on the top half of the lines, while those for
liquids in horizontal lines should be located in the lower half of the lines to encourage
adequate venting of entrained vapors. On no account should connections be made
from the bottom dead center of a line, to avoid the collection of sediment in the
connections.
Temperature instruments in vessels and piping are normally required to measure the
average temperature of the fluid contents. They are therefore usually placed in the
liquid space in vessels, close to outlet nozzles, or at the bottom of the downcomer
in a distillation column.
When required, temperature connections are positioned close to inlet and outlet
at pumps, exchangers, and control valves. These temperature instrument locations
are usually downstream of pressure connections, and upstream of places where
temperature may be heterogeneous such as additive-injection points.
> Read full chapter
Calculations
James E. Gallagher, in Natural Gas Measurement Handbook, 2006
9.7 Mass Flow Rate for Ultrasonic Flowmeter
For single-path or multipath ultrasonic flowmeters, the mass flowrate (qm) is obtained from the following equations:
Combining and rearranging,
where
qm = mass flow rate.
MF = meter factor for the ultrasonic flowmeter.
qav = volumetric flow rate at actual conditions.
tp = fluid density at the flowing conditions.
Am = cross-sectional area of flowmeter.
i = chordal path.
n = number of chordal paths.
Wi = weighting factor for individual chordal path.
Vi= mean velocity measured by the chordal path.
π = international numerical constant, 3.141593.
The internal diameter of the flowmeter body (Dr) is compensated for flowing pressure
(Pf) and temperature (Tf) for accuracy.
In addition,
where Am is the cross-sectional area of the flowmeter body and D is the internal
diameter of flowmeter body at Pf and Tf.
where
D = internal diameter of flowmeter body at Pf and Tf.
Dr = internal diameter of flowmeter body at Tr and Patm.
CTS = correction for temperature on flowmeter body.
CPS = correction for pressure on flowmeter body.
where
Tf = flowing temperature.
Tr = reference temperature.
pipe = linear coefficient of thermal expansion for pipe.
where
Pf = flowing pressure.
Patm = atmospheric pressure.
Dr = internal diameter of flowmeter body at Tr.
Epipe = modulus of elasticity of flowmeter body.
wt = wall thickness of flowmeter body.
Combining and rearranging,
The average indicated flowmeter velocity is
where
Vavg = mean pipe velocity measured by the flowmeter.
i = chordal path.
n = number of chordal paths.
Wi = weighting factor for individual chordal path.
Vi = mean velocity measured by the chordal path.
Assuming a constant SOS of the fluid along each chordal path (a homogeneous fluid
or constant fluid density),
Now for ultrasonic flowmeters, the path length (Li),
Li = f (D, , and transducer pocket depth, if applicable)
So, the path length(s) are calculated using the internal diameter of flowmeter body
at Pf and Tf. Here,
i = chordal path.
Vi = mean velocity measured by the chordal path.
tu = upstream transmit time.
td = downstream transit time.
LI = chordal length.
SOSi = speed of sound of the fluid along the chordal path.
= angle of the transducer.
Average Pipe Velocity
An ultrasonic flowmeter uses the average pipe velocity (Vavg) as the correlating
parameter to linearize the meter factor (MF). The average pipe velocity (Vavg) may
be calculated using the following equation:
where
i = chordal path.
n = number of chordal paths.
Wi= weighting factor for individual chordal path.
Vi = mean velocity measured by the chordal path.
Example of Ultrasonic Calculation
Figure 9-8 shows a sample calculation using the GOM composition at the outlet of
a gas plant.
Figure 9-8a. Ultrasonic calculations for GOM outlet from a gas plant.(Courtesy of
Savant Measurement, © 2000.)Copyright © 2000
Figure 9-8b. Ultrasonic calculations for GOM outlet from a gas plant.(Courtesy of
Savant Measurement, © 2000.)Copyright © 2000
> Read full chapter
Measurement System Design
James E. Gallagher, in Natural Gas Measurement Handbook, 2006
13.20 Tertiary Device (Flow Computer)
The tertiary device is an electronic flow computing device or flow computer. It
receives information from the primary and secondary devices and, using preprogrammed instructions, calculates the custody quantity of the gas flowing through
the primary device. The operator or connecting party should install one flow computer per flowmeter for natural gas measurement facilities. The flow computers shall
comply with API MPMS Chapter 21, Section 1, “Electronic Gas Measurement.” The
flow computer shall be equipped with necessary software password protection to
ensure a proper audit trail and security.
The natural gas quantities should be calculated using the methods prescribed by
•
API MPMS Chapter 14 Part 3 (A.G.A. Report No. 3) for orifice flowmeters.
•
A.G.A. Report No. 9 for multipath ultrasonic flowmeters.
•
API MPMS Chapter 14 Part 2 (A.G.A. Report No. 8) to determine the fluid's
flowing density.
The flow computers
•
Be identical devices.
•
Be installed in the measurement control panel.
•
Be capable of receiving the results of the chromatographic analysis in mol %.
•
Receive a smart dP transmitter input from each orifice flowmeter.
•
Receive a smart static pressure transmitter input from each orifice, ultrasonic,
turbine, or rotary displacment flowmeter.
Receive a smart static temperature transmitter input from each orifice, ultrasonic, turbine, or rotary displacment flowmeter.
Perform gross flow totalization for each orifice, ultrasonic, turbine, or rotary
displacement flowmeter.
Utilize a method for the gas volume correction due to entrained water greater
than 7 ppm per MSCF in compliance with API MPMS Chapter 14 Section 5 (if
applicable).
•
•
•
> Read full chapter
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