3. Applied Automation April 2014 • A3
A4 Electric motor power
measurement and analysis
Over the next three issues of AppliedAutomation, we will discuss a
three-step process for making precision electrical and mechanical
power measurements on a variety of motors and variable speed drive
systems. We will also show how these measurements are used to
calculate the energy efficiency for motor and drive systems.
A8 Selecting the right control chart
Knowing right way to look at collected manufacturing or process data turns
numbers into valuable information; here’s how to choose the right control
chart to make real-time control monitoring more valuable.
A12 Linear position sensors gain acceptance
Today’s industrial process control applications increasingly use automated
systems to optimize operations and ensure a safer, more productive process.
Linear position sensors used in these automated systems provide highly
accurate feedback on product parameters, control states, and outputs to
machine controllers.
Contents
A12
COMMENT
S
ystem integrators represent a significant
demographic of the AppliedAutomation
readership. Regardless of whether
automation end users are discrete,
process, batch, or hybrid manufacturers, or
whether they are utilities or municipalities,
chances are your organization has had some
contact with automation system integrators.
Automation system integration is among
the many information channels on the Control
Engineering and Plant Engineering Websites.
Content specific to this topic can be located by
searching the archives maintained by both of
these CFE Media publications.
Several types of media are included in this
content. For example, Control Engineering
magazine publishes the Automation Integrator
Guide annually. Each issue features articles
about automation system integration best
practices, industry outlooks, and an industry
directory with profiles of automation system
integrators. The online version of this directory
is a tool for identifying automation system
integrator talent. This searchable guide provides
information about company size, industries
supported, engineering specialties, product
experience, professional affiliations, and other
important search criteria.
Webcasts and training videos are available
online by accessing the Education & Training
and People and Training tabs on the Control
Engineering and Plant Engineering Websites,
respectively.
Each year, a panel of Control Engineering
editors and industry expert judges select
System Integrator of the Year Award winners
by evaluating business skills, technical
competence, and customer satisfaction.
Winners are then inducted into the Control
Engineering System Integrator Hall of Fame.
Control Engineering also names System
Integrator Giants, the 100 largest automation
system integration firms, according to revenue,
that respond to the magazine’s annual survey.
Finding system integration resources
Jack Smith
Editor
A4
4. A4 • April 2014 Applied Automation
cover story
Electric motor power
measurement and analysis
Understand the basics to drive greater efficiency.
E
nergy is one of the high-
est cost items in a plant
or facility, and motors
often consume the lion’s
share of plant power, so making sure motors
are operating optimally is vital. Accurate power
measurements can help to reduce energy consumption, as
measurement is always the first step toward better perfor-
mance and can also help extend the life of a motor. Small
misalignment or other issues are often invisible to the
naked eye, and the slightest wobble in a shaft can nega-
tively affect productivity and quality, and even shorten the
life of the motor.
Over the next three issues of AppliedAutomation, we
will discuss a three-step process for making precision
electrical and mechanical power measurements on a
variety of motors and variable speed drive (VSD) sys-
tems. We will also show how these measurements are
used to calculate the energy efficiency for motor and
drive systems.
In addition, we will provide an understanding of how to
make precision power measurements on complex distorted
waveforms, as well as what instruments to use for different
applications.
Basic electrical power measurements
Electric motors are electromechanical machines that
convert electric energy into mechanical energy. Despite
differences in size and type, all electric motors work in
much the same way: an electric current flowing through
a wire coil in a magnetic field creates a force that rotates
the coil, thus creating torque.
Understanding power generation, power loss, and the
different types of power measured can be intimidating, so
let’s start with an overview of basic electric and mechani-
cal power measurements.
What is power? In the most basic form, power is work
performed over a specific amount of time. In a motor,
power is delivered to the load by converting electrical
energy per the following laws of science.
In electrical systems, voltage
is the force required to move
electrons. Current is the rate of the
flow of charge per second through
a material to which a specific
voltage is applied. By taking the
voltage and multiplying it by the
associated current, the power can
be determined.
P = V x I where power (P) is in watts, voltage (V) is in
volts, and current (I) is in amperes.
A watt (W) is a unit of power defined as one Joule
per second. For a dc source the calculation is simply
the voltage times the current: W = V x A. However,
determining the power in watts for an ac source must
include the power factor (PF), so W = V x A x PF for ac
systems.
The power factor is a unitless ratio ranging from -1 to
1, and represents the amount of real power performing
work at a load. For power factors less than unity, which is
almost always the case, there will be losses in real power.
This is because the voltage and current of an ac circuit are
sinusoidal in nature, with the amplitude of the current and
voltage of an ac circuit constantly shifting and not typically
in perfect alignment.
Since power is voltage times current (P = V x I), power
is highest when the voltage and current are lined up
together so that the peaks and zero points on the voltage
and current waveforms occur at the same time. This would
be typical of a simple resistive load. In this situation, the
two waveforms are “in phase” with one another and the
power factor would be 1. This is a rare case, as almost all
loads aren’t simply and perfectly resistive.
Two waveforms are said to be “out of phase” or “phase
shifted” when the two signals do not correlate from point to
point. This can be caused by inductive or nonlinear loads.
In this situation, the power factor would be less than 1,
and less real power would be realized.
Due to the possible fluctuations in the current and the
voltage in ac circuits, power is measured is a few differ-
ent ways.
Real or true power is the actual amount of power being
By Bill Gatheridge
Yokogawa
FIRST OF THREE PARTS
APRIl: Electric motor power measure-
ment and analysis
JunE: Selecting the right instruments
AuguST: Electrical power measurements
for a 3-phase ac motor.
5. Applied Automation April 2014 • A5
Figure 1: The slightest wobble in a shaft can negatively affect productivity and quality. All graphics courtesy: Yokogawa
used in a circuit, and it’s measured in watts. Digital power
analyzers use techniques to digitize the incoming voltage
and current waveforms to calculate true power, following
the method in Figure 2:
Figure 2: True power calculation.
In this example the instantaneous voltage is multiplied
by the instantaneous current (I) and then integrated over a
specific time period (t). A true power calculation will work
on any type of waveform regardless of the power factor
(Figure 3).
Figure 3: These equations are used to calculate a true power mea-
surement and true RMS measurements.
Harmonics create an additional complication. Even
though the power grid nominally operates at a frequency
of 60 Hz, there are many other frequencies or harmonics
that potentially exist in a circuit, and there can also be a
dc or dc component. Total power is calculated by consider-
ing and summing all content, including harmonics.
The calculation methods in Figure 3 are used to pro-
vide a true power measurement and true root mean
square (RMS) measurements on any type of waveform,
including all harmonic content, up to the bandwidth of the
instrument.
Power measurement
We’ll next look at how to actually measure watts in a
given circuit. A wattmeter is an instrument that uses volt-
age and current to determine power in watts. The Blondel
Theory states that total power is measured with a mini-
mum of one fewer wattmeter than the number of wires. For
example, a single-phase two-wire circuit will use one watt-
meter with one voltage and one current measurement.
A single-phase three-wire split-phase system is often
found in common housing wiring. These systems require
two wattmeters for power measurement.
Most industrial motors use three-phase three-wire
circuits that are measured using two wattmeters. In the
same fashion, three wattmeters would be necessary for a
three-phase four-wire circuit, with the fourth wire being the
neutral.
Figure 4 shows a three-phase three-wire system with
load attached using the two-wattmeter method for mea-
surement. Two line-to-line voltages and two associated
phase currents are measured (using wattmeters Wa and
6. A6 • April 2014 Applied Automation
Wc). The four measurements (line-to-line and phase current
and voltage) are utilized to achieve the total measurement.
Figure 4: Measuring power in a three-phase three-wire system
with two wattmeters.
Since this method requires monitoring only two current
and two potential transformers instead of three, installation
and wiring configuration are simplified. It can also measure
power accurately on a balanced or an unbalanced system.
Its flexibility and low-cost installation make it a good fit for
production testing in which only the power or a few other
parameters need measurement.
For engineering and research and development work,
the three-phase three-wire with three-wattmeter method is
best as it provides additional information that can be used
to balance loading and determine true power factor. This
method uses all three voltages and all three-currents. All
three voltages are measured (a to b, b to c, c to a), and all
three-currents are monitored.
Figure 5: When designing motors and drives, seeing all three volt-
ages and currents is key, making the three-wattmeter method in
the figure above the best choice.
Power factor measurement
In determining the power factor for sine waves, the
power factor is equal to the cosine of the angle between
the voltage and current (Cos Ø). This is defined as the
“displacement” power factor, and is correct for sine waves
only. For all other waveforms (non-sine waves), the power
factor is defined as real power in watts divided by appar-
ent power in voltage-amperes. This is called the “true”
power factor and can be used for all waveforms, both sinu-
soidal and non-sinusoidal.
Figure 6: Total power factor is determined by summing the total
watts divided by the total VA measurement.
Figure 7: Using the two-wattmeter method, the sum of the total
watts (W1
+ W2
) is divided by the VA measurements.
However, if the load is unbalanced (the phase currents
are different), this could introduce an error in calculat-
ing the power factor because only two VA measurements
are used in the calculation. The two VAs are averaged
because it’s assumed they’re equal; however, if they’re
not, a faulty result is obtained.
Therefore, it’s best to use the three-wattmeter method
for unbalanced loads because it will provide a correct
power factor calculation for either balanced or unbal-
anced loads.
Figure 8: With the three-wattmeter method, all three VA measure-
ments are used in the above power factor calculation.
Power analyzers use the method above, which is
called the 3V-3A (three-voltage three-current) wiring
method. This is the best method for engineering and
design work because it will provide a correct total power
factor and VA measurements for a balanced or unbalanced
three-wire system.
Basic mechanical power measurements
In an electric motor, the mechanical power is defined as
the speed times the torque. Mechanical power is typically
defined as kilowatts or horsepower, with 1 W equaling 1
Joule/sec or 1 Nm/sec.
cover story
7. On a quarterly basis, Plant Engineering
conducts research studies on the
various topics as they pertain to the
manufacturing industries.
Studies include—
•Energy
Management
•Workforce
Development
•Safety
•Maintenance
Download the Plant EngineeringEditorial Research Studies:
www.plantengineering.com/
media-library/research
Applied Automation April 2014 • A7
Figure 9: Mechanical power measurements in watts are defined as
2π times the rotating speed (rpm) divided by 60 times the torque
(Nm).
Horsepower is the work done per unit of time. One
hp equals 33,000 lb-ft/min. Converting hp to watts is
achieved using this relationship: 1 hp = 745.69987 W.
However, the conversion is often simplified by using 746
W/hp (Figure 10).
Figure 10: Mechanical power measurement equations for horse-
power often use a rounded figure of 1 hp = 746 W.
For ac induction motors, the actual or rotor speed is
the speed at which the shaft (rotor) rotates, typically
measured using a tachometer. The synchronous speed is
the speed of the stator’s magnetic field rotation, calculat-
ed as 120 times the line frequency divided by the number
of poles in the motor. Synchronous speed is the motor’s
theoretical maximum speed, but the rotor will always turn
at a slightly slower rate than the synchronous speed due
to losses, and this speed difference is defined as slip.
Slip is the difference in the speed of the rotor and the
synchronous speed. To determine the percentage of
slip, a simple percentage calculation of the synchronous
speed minus the rotor speed divided by the synchronous
speed is used.
Efficiency can be expressed in simplest form as the
ratio of the output power to the total input power or
efficiency = output power/input power. For an electri-
cally driven motor, the output power is mechanical while
the input power is electrical, so the efficiency equation
becomes efficiency = mechanical power/electrical input
power.
Bill Gatheridge is a product manager at Yokogawa. He is
a member and vice chairman of the ASME PTC19.6 com-
mittee on electrical power measurements for utility power
plant performance testing.
8. A8 • April 2014 Applied Automation
DATA CAPTURE
Selecting the right control chart
For real-time monitoring, a control chart is a statistical tool to analyze the past and
predict the future. Choosing the wrong one from among hundreds increases the risk
of errors. Advice follows on how to choose the right control chart.
K
nowing right way to look at collected manu-
facturing or process data turns numbers into
valuable information; here’s how to choose
the right control chart to make real-time con-
trol monitoring more valuable.
Would a manufacturer knowingly embark
on a fixed-cost job without first understanding the risks
of losing money, shipping defective product, missing
the delivery schedule, running on incapable equipment,
or using unqualified employees? While all these risks
are understood because the price quoted for the job
includes an allowance for their associated costs, many
of these risk items are actually either unknown or not
fully defined. Thus, decisions to pursue a job are usually
based on history, opinion, and faith alone.
Luckily, the chance of a catastrophic financial hit
due to these unknowns is relatively small as long as
the profit margins remain high enough after negotia-
tions. However, as margins are squeezed and demands
increase, manufacturers must understand these uncer-
tainties better to ensure they avoid the financial break-
ing point. The good news is that understanding risk and
making better business decisions is as simple as apply-
ing statistical monitoring and analytics.
Real-time monitoring,
control charts
Statistics is the science of pre-
dicting the future. Industrial statis-
tical methods are the application
of statistical methods where the
population of “things to measure”
is produced in real time. For real-
time monitoring, the prescribed
statistical tool is a control chart.
Academic training introduces stu-
dents to three types of variables
charts (Xbar-R, Xbar-s, and IX-MR)
and four types of attribute charts
(p, np, u, and c). There are hun-
dreds of control charts from which
to choose. Regardless of statistical
background, not having the right
control chart increases the risk of
encountering Type I (false positive)
and Type II (false negative) errors.
The purpose of a control chart is
to describe a process’s personality
in terms of normal versus abnor-
mal levels of variation. When using
control charts for real-time deci-
sion making, corrective actions are
recommended only when variation
levels or patterns exceed the statis-
1) What is the sample size? 2) Will multiple parts be combined on the same chart?
3) Will test characteristics with different target values be combined on the same chart? For
example, if the sample size is 1, multiple parts will be combined, but all the targets are the
same, so the perfect control chart to use is the Group IX-MR. Alternately, if the sample size
is 5 with multiple parts and different targets, the chart to use is the Group Target Xbar-R.
Courtesy: InfinityQS International
Variable control chart decision tree
Steve Wyse
Infinity QS International
10. A10 • April 2014 Applied Automation
DATA CAPTURE
tically defined levels of what’s nor-
mal. When inferior sampling strate-
gies are implemented or the wrong
control chart is deployed, the risk of
making unwise adjustments (Type I
error) or missing a signal that war-
rants attention (Type II error) is
elevated.
Why invest time and effort in col-
lecting and analyzing data just to
make wrong decisions? Taking the extra step to learn
how to pick the right chart could mean the difference
between failure and success.
Ask these questions to choose a control chart
Fortunately, selecting just the right control chart
requires answering only a handful of questions that
will pinpoint the perfect chart to use from a pool of 12
potential, standard variables charts.
Basic questions for variables data are:
1. What is the sample size?
2. Will multiple parts be combined on the same
chart?
3. Will test characteristics with different target values
be combined on the same chart?
To answer these questions
properly and ultimately select the
correct control chart, a thoughtful
sampling strategy is key. In some
cases, simple strategies will suffice
where a machine is set up to run
the same part for weeks or months,
and only one or two characteristics
are measured to monitor the health
of that process. For example, a
machine that makes 0.07 mm pencil
lead will be busy as long as 0.07
mm mechanical pencils are being used and this par-
ticular product is being sold. Of course, there are many
contributing factors that will cause a lead machine to
misbehave, but as far as a statistical sampling strat-
egy, diameter and length may be all that’s monitored.
Depending on the historical adjustment frequencies,
five leads may need to be collected only once an hour.
Though this may be a common case for textbooks, it
reflects the real world for only a few industries.
For most manufacturers, machines are used to run
many different shapes, sizes, weights, materials, col-
ors, and features. To accomplish this, one machine is
designed to accept different programs, tooling, fixtures,
speeds, feeds, pressures, temperatures, flow rates,
and others. The uncertainties and combinations of
things that could go wrong multiply with every added
level of machine flexibility. In these
cases, one must create customized
sampling strategies and pick the
best statistical monitoring tool(s)
unique to each machine’s input and
product output complexities.
Items to consider in a sampling
strategy include sampling fre-
quency, sample size, test charac-
teristics, measurement devices, and
methodologies. These decisions help define the best
way to illustrate and update the visual output as new
data is captured. Essentially, the data describes the
process’s personality so it is easier to understand what
normal variation one can expect and what constitutes a
significant deviation from the norm.
Variation, different units
With a strategic sampling strategy in place, it is
much easier to answer the questions necessary to use
the variable control chart decision tree (see graphic).
In addition to a sampling strategy, more complicated
scenarios require only two more questions:
1. Will within-piece and piece-to-piece variation be
monitored?
2. Will different types of tests with different units of
measure be combined on the same
chart?
Adding these two questions
expands the list of potential control
charts to 48. With each of those 48
charts, one could apply even more
refinements, taking the potential
number of charts into the hundreds.
Above all, remember that a
control chart is the vehicle that
will help those involved to remain
engaged with the data collected. By engaging with the
right data and using the right control chart, no fortune-
teller is needed to predict risks and make better busi-
ness decisions.
Steve Wise is vice president of statistical methods,
InfinityQS International Inc.
Go online
www.controleng.com/archives
March, with this article, link to process details in
an InfinityQS International whitepaper, “A Practical
Guide to Selecting the Right Control Chart.”
www.infinityqs.com
Taking the extra step to
learn how to pick the
right chart could mean
the difference between
failure and success.
Pick the best statistical
monitoring tool(s) unique
to each machine’s input
and product output
complexities.
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& Manufacturing
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September 10, 2014
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will present the 2014 Global Automation &
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12. T
oday’s industrial process control applications
increasingly use automated systems to optimize
operations and ensure a safer, more productive
process. Linear position sensors used in these
automated systems provide highly accurate
feedback on product parameters, control states,
and outputs to machine controllers.
Whether implemented as a stand-alone component or
as part of a control or safety system, the linear variable dif-
ferential transformer (LVDT) is capable of providing linear
displacement measurements from micro inches to several
feet, under various operating and environmental conditions
with high accuracy and reliability. Essentially, the LVDT
plays an important role in machine control by providing
feedback about product location. To some extent, it is the
LVDT that ensures proper machine operation.
Mechanics of a LVDT
In basic terms, a LVDT
is an electromechanical
device that converts linear
position or motion to a
proportional electrical out-
put (see Figure 1). More
specifically, the LVDT pro-
duces an electrical output
signal directly proportional
to the displacement of a
separate movable core.
Typically, the ferrous
core within the LVDT is
attached to the moving
element on the piece of
equipment requiring posi-
tion feedback.
The basic LVDT design
consists of three elements:
1. One primary winding
2. Two identical second-
ary windings
3. A movable magnetic armature or “core.”
The primary winding is excited with an ac supply
generating a magnetic field which, when the core is
placed in the central or “null” position, includes equal
voltages in both of the secondaries. The secondaries
are wired series opposed so that their combined output
represents the difference in voltage indicated in them,
which in this case is zero. As the core is moved left or
right, the difference in inducted voltages produces an
output that is linearly proportional in magnitude to the
displacement of the core. Its phase changes 180-deg
from one side of the null position to the other.
In the oil and gas industry, compact LVDTs are used
in the position feedback control of down-hole drilling
equipment such as bore scopes that measure the ID
of the drilled hole. The sensor coil assembly and sepa-
rable core inherent to the technology can withstand
extremely high pressures of the environment as the
mechanical configuration of the coil assembly is vented
(pressure balanced)
to the pressure of the
nonconductive medi-
ums. As the sensor coil
assembly can withstand
a combination of high
pressure, elevated tem-
peratures, shock, and
vibration, the LVDT is
able to make measure-
ments in down-hole
drilling equipment pos-
sible where space is
at a premium and the
environment is hostile.
In operation, the
LVDT’s primary winding
is energized by alter-
nating current of appro-
priate amplitude and
frequency, known as
the primary excitation.
The LVDTs’ electrical
output signal is the dif-
A12 • April 2014 Applied Automation
SENSORS
Linear position sensors
gain acceptance
Linear variable differential transformers can deliver better machine operation.
Figure 1: The basic LVDT design. All images courtesy: Macro Sensors
By Eileen Otto
Macro Sensors
13. ferential ac voltage between two secondary windings,
which varies with the axial position of the core within
the LVDT coil. Usually this ac output voltage is con-
verted by suitable electronic circuitry to high-level dc
voltage or current for convenient use by a computer or
other digital output device.
Because there is normally no contact between
the LVDT’s core and coil structure, no parts can rub
together or wear out. This means that a LVDT features
unlimited mechanical life. This factor is highly desirable
in many industrial process control and factory automa-
tion systems.
Enhanced use in process control
Recent innovations in construction materials, manu-
facturing techniques, and low-cost microelectronics have
revolutionized the LVDTs into a more reliable and cost-
effective technology for process control applications. In
the past, electronics necessary to operate LVDTs prop-
erly were complicated and expensive, prohibiting their
wide use in process control applications for displacement
measurement.
Modern ASIC and microprocessors give LVDT tech-
nology more complex processing functions and enable
signal conditioning within the sensor housing so LVDTs
generate digital outputs directly compatible with comput-
er-based systems and standardized digital buses. As a
result, today’s linear position sensors can provide more
accurate and precise measurement of dimensions in a
wider variety of quality control, inspection equipment, and
industrial metrology applications including online parts
inspection, servo-loop positioning systems, and manufac-
turing process control.
For applications where sensors must operate in
extreme environments, the sensing element can be seg-
regated from the electronic circuitry, unlike capacitive,
magnetostrictive, and other high-frequency technologies.
Connected by long cables up to 31 m (100 ft), ac-oper-
ated LVDTs can work with remotely located electronics
that power the sensors, and amplify and demodulate their
output. Output is, then, displayed on a suitable readout
and/or inputted into a computer-based data acquisition
system for statistical process control. This ability to trans-
mit data to a remote computer has made linear position
sensors popular in quality assurance schemes.
Smaller diameters, new materials
While linear position sensors were once considered
too long for applications with limited space, new wind-
ing techniques and computer-based winding machines
allow the linear position sensor body to be reduced
while maintaining or increasing stroke length. With the
improved stroke-to-length ratio (now up to 80%), the
LVDT becomes a viable position measurement device for
machine tool positioning, hydraulic cylinder positioning,
and valve position sensing.
Smaller, contactless linear position sensors also fea-
ture a lightweight low mass core that is ideal (see Figure
2) for process control applications having high-dynamic
response requirements, such as plastic injection molding
machines, automatic inspection equipment, and different
robotic applications requiring displacement feedback to
ensure proper machinery operation.
LVDTs are also configurable in a variety of mechani-
cal and electrical designs to meet the measurement and
environmental requirements of various process control
applications. New corrosion-resistant/high-temperature
materials such as Monel or Inconel enable the LVDT to
operate in more hostile environments, including those
with high and low temperature extremes, radiation expo-
sure, or vacuum pressure conditions. For applications
where sensors must withstand exposure to flammable
or corrosive vapors and liquids, or operate in pressur-
ized fluid, its case and coil assembly can be hermetically
sealed using a variety of welding processes.
For example, in power generation applications (see
Figure 3), linear position sensors designed for high
temperature and mild radiation resistance can perform
in power plants to provide feedback on the position
of nuclear steam and gas turbine control valves for
increased plant efficiency and reduced operating costs.
In a typical power plant, steam turbines contain a
number of control valves—a reheat stop value, an inter-
ceptor valve, a governor valve, and a throttle valve.
Typically, plants have very precise control schemes for
valve position to increase operating efficiency and save
fuel. Operating within the harsh environment of a power
or steam plant, linear position sensors can determine if
valves are fully opened or closed to within a thousandth
of an inch, providing output to remote electronics that can
Applied Automation April 2014 • A13
Figure 2: In the oil and gas industry, compact LVDTs are used in the
position feedback control of down-hole drilling equipment such as
bore scopes that measure the ID of the drilled hole.
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be monitored by operators
if something is not working
properly. The combination of
LVDTs with modern comput-
erized turbine control systems
saves power companies mil-
lions of dollars per year.
Sensors also play an
important role in the predic-
tive maintenance of gas tur-
bines as part of process con-
trol systems used to monitor
shell expansion and bearing
vibration. When installed on
turbine shells, hermetically
sealed LVDTs measure shell expansion, providing linear
output that operators can utilize to determine proper ther-
mal growth of a turbine shell during start-up, operation,
and shutdown.
LVDTs designed to withstand shocks and heavy
pounding are used in the press and dye industry for the
mechanical control of machine operations as improper
operation can lead to broken dyes that result in downed
machines, while the ambiguous force of presses can
lead to misshapen and out-of-spec parts. Spring-loaded
LVDTs are installed on
presses so that the plunger
of the sensor is compressed
as the punch press comes in
contact with the metal being
shaped. The output of the
LVDT is fed back into the
machine’s control system,
providing feedback on how
far a press has moved and
when to stop.
For more than six
decades, LVDTs have served
as part of measurement and
control systems, providing
essential information without which many process con-
trol systems couldn’t function. From its limited use as a
laboratory tool more than three decades ago, the LVDT
has evolved into a highly reliable and cost-effective linear
feedback device, making it the preferred technology for
critical and reliable linear displacement measurements in
an array of industrial process control applications.
Eileen Otto is the sales and marketing manager at
Macro Sensors.
SENSORS
Figure 3: Hermetically sealed linear position sensors offer a
highly accurate and long life solution for the position mea-
surement of steam control valves in power generation plants.
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