Training Module
D
Describe
Coriolis
Mass Flowmeters
Human Development
Consultants Ltd.
Describe Coriolis
Mass Flowmeters
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ISBN 1-55338-012-6
Canadian Cataloguing in Publication Data
1. Flow meters. I. HDC Human Development Consultants.
TC177.D48 2001 681’.28 C2001-900252-1
This training kit consists of the following parts:
♦ Training Module and Self-Check
♦ Blank Answer Sheet
♦ Knowledge Check and Answer Key
♦ Job Aid
Published by HDC Human Development Consultants Ltd.
Published in Canada
HDC Human Development Consultants Ltd.
Website:
E-mail:
Phone:
www.hdc.ca
[email protected]
(780) 463-3909
February, 2001
Human Development
Consultants Ltd.
Describe Coriolis
Mass Flowmeters
Contents
Training Objectives
1
1
Introduction
1
2
Principle of Operation
5
3
Components
13
3.1
3.2
3.3
3.4
13
15
16
16
4
Strengths and Limitations
17
4.1 Strengths of Coriolis Mass Flowmeters
4.2 Limitations of Coriolis Mass Flowmeters
17
18
5
Accuracy and Versatility
19
6
Installation
20
6.1 Multiple Flowmeters
6.2 Orientation of Flow Tubes
6.3 Anchoring for Stability and Minimizing External
Vibrations
6.4 Installation Guidelines
21
22
February, 2001
2.1
2.2
2.3
2.4
The Coriolis Effect
Coriolis Effect Applied
Dual-Tube Coriolis Flowmeter
Measuring Density
Sensor
Transmitter
Interface
Auxiliaries
5
6
10
11
22
23
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Describe Coriolis
Mass Flowmeters
Human Development
Consultants Ltd.
Contents
(continued)
7
Operations Responsibilities
24
7.1 Operator Responsibilities
7.2 Maintenance Responsibilities
24
25
8
Zeroing and Proving
25
8.1 Zeroing Coriolis Mass Flowmeters
8.2 Proving Coriolis Mass Flowmeters
25
27
9
Troubleshooting
28
10
Self-Check
29
11
Self-Check Answers
36
12
Glossary
36
February, 2001
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Human Development
Consultants Ltd.
Training
Objectives
NOTE
Describe Coriolis
Mass Flowmeters
Upon completion of this training kit, you will be able to:
Describe the purpose and importance of mass flowmeters
Describe Coriolis mass flowmeter operation
Describe common Coriolis mass flowmeter components
Describe Coriolis mass flowmeter installation requirements
Describe operations and maintenance responsibilities for
Coriolis mass flowmeters
Describe Coriolis mass flowmeter proving activities
Describe fundamental Coriolis mass flowmeter
troubleshooting techniques
Refer to the glossary, located at the end of this module, for an
explanation of terms.
1 Introduction
Flowmeters are devices used to measure the rate of flow of
fluids. Accurate flow rate measurements are critically important
in industries dealing with flowing fluids (gases, liquids, and
slurries), including:
food and beverage
automotive
water and waste water treatment
oil and gas
pipelines
chemical
hydroelectric power generation
pharmaceutical
cosmetics
A company’s profit or loss can depend on measurement
accuracy. Over the years, many different types of flowmeters
have been developed to measure flow rates of different fluids.
The goal has been to increase flow measurement accuracy and
reliability in a wide range of flow rates and a wide variety of
fluids. Each flow rate and each fluid offers special
measurement problems.
February, 2001
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Human Development
Consultants Ltd.
Describe Coriolis
Mass Flowmeters
The most common types of flowmeters determine flow rate by
measuring one of the following:
differential pressure: orifice plates, venturi tubes, pitot
tubes (often called head meters)
fixed volume: piston, gear (often referred to as positive
displacement (PD) meters)
velocity: turbine, vortex shedding, electromagnetic,
ultrasonic
mass: Coriolis, thermal
The first three categories of flowmeters (differential pressure,
fixed volume, and velocity) measure the volume flow of fluids.
Volume flow is expressed as units of volume over time (e.g.,
m3/s (ft3/min)). Mass flow must be calculated from the
measured volume flow and density.
Figure 1—Relationship Between Volume and Mass
Volume is the measure of the size of a body or substance in space, i.e., the amount of space
a body or substance occupies.
Mass is the measure of a body’s or
substance’s resistance to being accelerated,
i.e., resistance to changes in its linear motion.
Unlike volume, mass is unaffected by
changes in pressure and temperature.
Density is the mass of a substance per unit
volume.
Volume =
Mass
Density
Note that the terms mass and weight are often (incorrectly) used interchangeably:
the kilogram, a metric unit of measurement, is a measure of mass
the pound, an imperial unit of measurement is a measure of weight
Note:
Mass is not dependant on gravity. (For example, the mass of an object is the same on the
moon as on earth. However, an object weighs less on the moon than on earth.)
Figure 1 illustrates the relationship between volume and mass relative to temperature: as
temperature increases, volume increases, but mass remains constant.
In gases, as pressure increases, volume decreases, but mass remains constant.
February, 2001
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Human Development
Consultants Ltd.
Describe Coriolis
Mass Flowmeters
Mass flowmeters measure the rate of mass flow directly. Mass
flow is expressed as units of mass over time (for example,
kilograms per hour). Because additional measurements and
calculations are not needed, mass flowmeters can provide
more accurate flow measurement than volume flowmeters.
Mass Flowmeters
Mass flowmeters are capable of handling not only gas and
liquid flows but also almost all flowing media such as
sludges
suspensions
corrosive fluids
highly viscous fluids
In addition to directly measuring mass, mass flowmeters can be
used to directly measure density of the fluid.
Mass flowmeters have a wide range of applications, including:
process control applications where accurate mass flow rate/
density measurement is important
product loading/transfer applications
mixing applications where blending ratio/mixture
concentration is critical
Mass flowmeters are accurate enough to be used to measure
fluids for the purposes of transfer of ownership of a product
(custody transfer) and material balance determinations (i.e.,
ensuring the material mass feeding a process is accounted for
in the products leaving the process).
There are two principal types of industrial mass flowmeters:
Coriolis mass flowmeters
thermal mass flowmeters which introduce heat into the fluid
and then measure the temperature change. The
temperature change is directly proportional to the mass flow
rate.
February, 2001
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Describe Coriolis
Mass Flowmeters
Human Development
Consultants Ltd.
Figure 2—Typical Uses of Coriolis Mass Flowmeters
Custody Transfer
accurately metering a product being sold
Product Transfer from Tank Farm
transferring an accurate quantity of
material from a storage tank
seller
tank
storage tank
buyer
tank
Continuous Product Mixing
producing a specific mixture strength by blending
accurately-metered amounts of 2 products
product A
product B
tank
Mixing Batches to Fill Containers
producing a batch repeatedly to fill
containers on a conveyor belt
each batch must have the same specific
mixture strength, produced by blending
accurately-metered amounts of 2
products
product A
product B
mixing tank
Measuring Oil Well Flows and Liquid Composition
determining water content of oil well flows and total
volumes of oil and water produced by the well
water content is calculated from the liquid mixture
density
Density Measurement
measuring the density of a product by
drawing a slipstream sample through the
Coriolis meter
concentration can be calculated from the
density measurement
gas
oil well fluid
separator
(gas/oil/
water)
oil/
water
oil/water
February, 2001
flow line
to
downstream
processing
product
flow
slipstream
sampling
flow line
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Human Development
Consultants Ltd.
Describe Coriolis
Mass Flowmeters
Coriolis Mass Flowmeters
This training kit describes the Coriolis mass flowmeter. The kit
describes the operating principle, generic components,
installation, calibration, maintenance, and proving requirements
of Coriolis mass flowmeters. The kit targets process operators
and maintenance personnel responsible for the safe and
effective operation of Coriolis mass flowmeters.
Troubleshooting techniques are also presented for generic
Coriolis mass flowmeter applications.
2 Principle of Operation
The underlying principle of the Coriolis mass flowmeter is a
phenomenon of physics called the Coriolis effect.
2.1 The Coriolis Effect
The Coriolis effect is the tendency for any moving body on or
above the earth’s surface (e.g., a wind or an ocean current) to
drift sideways because of the earth’s eastward rotation. The
Coriolis effect causes moving fluids to curve to the right of the
direction of main flow in the Northern Hemisphere and to the
left in the Southern Hemisphere.
The effect of the Coriolis force is present in any rotating
system. As illustrated in Figure 3, the Coriolis effect depends
on three parameters: a mass, a rotating body, and a motion of
the mass relative to the rotating body.
Newton's first law of motion states that a body in motion will
maintain its speed and direction of motion unless acted on by
an outside force. The Coriolis force is an outside force that
causes a body in motion on a rotating body to follow a curved
path instead of a straight path.
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Human Development
Consultants Ltd.
Describe Coriolis
Mass Flowmeters
Figure 3—Coriolis Force
Coriolis force
trajectory of mass under the
influence of the Coriolis force
mass
radial velocity
(motion of mass
relative to
rotating body)
angular velocity
of rotating body
and the mass
Coriolis forces are at work when 3 parameters are present:
- a mass
- a rotating body
- a motion of the mass relative to the rotating body
2.2 Coriolis Effect Applied
The simplest Coriolis-type meters consist of a single straight
tube through which the fluid medium flows. An electromagnet is
used to vibrate the tube (i.e., create a rotating body), usually at
the tube’s resonant frequency. Depending on the metal the
tube is made of, the tube vibrates at about 80 Hz (Hertz, cycles
per second); depending on the size of the tube, the tube moves
hundredths of a mm (in.) or less per cycle. When the fluid in the
tube is not flowing, the Coriolis force does not influence the
fluid. When the fluid is flowing, however, the Coriolis force
February, 2001
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Describe Coriolis
Mass Flowmeters
Human Development
Consultants Ltd.
causes the fluid to oppose the induced vibration. This
opposition causes the tube to twist in the form of a sine wave.
Figure 4A illustrates a vibrating fluid-filled tube (whose
vibrations are greatly exaggerated to illustrate the principle);
Figure 4B illustrates the same vibrating tube in which the fluid is
now flowing. Figures 5A and 5B represent the end view of a
U-shaped tube, one with no flow, the other with flow.
Figure 4—Single, Straight Coriolis Tubes, one with No Flow, the other With Flow
A. No Flow
mass
angular velocity
Liquid-filled tube with no flow
A vibration is magnetically induced in the tube.
B. With Flow
Coriolis force
radial velocity
Liquid-filled tube with flow
As the liquid flows through the tube, the liquid opposes the vibrating motion and
causes the tube to twist. The amount of twist is proportional to the fluid mass flow rate.
February, 2001
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Human Development
Consultants Ltd.
Figure 5—
Single,
U-Shaped
Coriolis Tubes,
one with No
Flow, the other
With Flow
Describe Coriolis
Mass Flowmeters
A. No Flow
Liquid-filled U-shaped tube (seen from the end)
A vibration is magnetically induced in the tube; an
electromagnet is used to make the tube vibrate.
B. With Flow
Liquid-filled U-shaped tube (seen from the end)
As the liquid flows through the tube, the tube twists. When
the vibration reverses direction, the tube twists in the
opposite direction.
The changes in the motion of the flow tube are minute and
must be detected electronically. A magnetic detector, consisting
of a magnet and coil, is installed at both the inlet and outlet
ends of the tube. Either the magnet or the coil is attached to the
sensor tube so that as the tube vibrates, either the magnet or
the coil moves relative to the other. The movement of the
magnet against the coil produces an alternating electrical
current in the form of a sine wave. The output signal is a
measure of the relative velocity or displacement of the tube.
February, 2001
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Describe Coriolis
Mass Flowmeters
Human Development
Consultants Ltd.
Figure 6—
Sine Waves
Generated at
the Inlet and
Outlet Ends of
the Sensor
Tube
A. No Flow
outlet
inlet
time
B. With Flow
x
outlet
time
lag
x
x
time
lag
x
inlet
time
Figure 6 illustrates the sine wave pattern produced at both the
inlet detector and the outlet detector; Figure 6A illustrates the
two waves created in the vibrating tube when the fluid in the
tube is not flowing. The two waves are synchronized: both ends
of the tube move up at the same time and down at the same
time. Figure 6B illustrates the two waves when the fluid in the
tube is flowing. The relative velocity or displacement at the
outlet detector lags the relative velocity or displacement at the
inlet detector, indicating the twisting motion due to the Coriolis
effect. The time lag is proportional to the mass flow rate. As the
mass flow increases, the twisting motion increases and the time
lag increases.
February, 2001
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Human Development
Consultants Ltd.
Describe Coriolis
Mass Flowmeters
A transmitter uses the time lag to calculate the mass flow rate.
An interface translates the transmitter data into a readable form
for the operator.
2.3 Dual-Tube Coriolis Flowmeter
Many different tube designs are available: straight, U-shaped,
delta, omega in either single- or dual-tube configurations (see
Figure 7). Each design has specific applications to which it is
best suited.
Figure 7—
Coriolis
Flowmeter Tube
Designs
Single Tube Straight
Single Tube
Double Tube U-Shaped
Single Tube U-Shaped
Omega Shaped
Delta Shaped
The dual-tube loop design is a widely used type of Coriolis
flowmeter. In the dual-tube flowmeter, manifolds (i.e., flow
splitters) divide the flow into two equal streams at the inlets of
the two tubes and recombine the flow at the outlets. The fluid to
be measured flows equally through the two tubes. An electromagnetic drive coil causes both loops to oscillate rapidly, 180
degrees out of phase: as one loop moves upward, the other
moves downward. Each loop is anchored at two points and
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Describe Coriolis
Mass Flowmeters
vibrated between these two anchors. As the fluid flows through
the oscillating flow tubes, the Coriolis effect causes the flow
tubes to twist.
Detectors are attached at both the inlet and the outlet ends of
the tubes to measure the amount of tube twisting. Because the
vibrations of each tube are 180 degrees out of phase, the
meter’s sensitivity is doubled. Additionally, one tube serves as
the other tube’s reference point thereby canceling the effects of
external noise such as vibration.
2.4 Measuring Density
The Coriolis mass flow meter applies two physical principles to
measure density:
End of Sample
A full licensed copy of this kit includes:
• Training Module and Self-Check
• Knowledge Check and Answer Key
• Blank Answer Sheet
• Job Aid
February, 2001
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