General
Engineering and Design Data Menu
Industrial
Electric Motor Application, Design and Installation Menu
Industrial
Electric Motor Supply
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- Angular accuracy
- The measure of shaft positioning accuracy on a
servo or stepping motor.
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- Back EMF
- The voltage generated when a permanent magnet
motor is rotated. This voltage is proportional to
motor speed and is present regardless of whether the
motor winding(s) are energized or de-energized.
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- Bipolar chopper driver
- A class of step motor driver which uses a switch
mode (chopper) technique to control motor current
and polarity. Bipolar indicates the capability of
providing motor phase current of either polarity (+
or -).
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- Breakaway torque
- The torque required to start a machine in motion.
Almost always greater than the running torque.
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- Brushless motor
- Class of motors that operate using electronic
commutation of phase currents, rather than
electromechanical (brush-type) commutation.
Brushless motors typically have a permanent magnet
rotor and a wound stator.
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- C-face mounting
- A standard NEMA mounting design, where the
mounting holes in the face are threaded to receive
the mating mount.
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- Class B insulation
- A NEMA insulation specification. Class B
insulation is rated to an operating (internal)
temperature of 130°C.
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- Class F insulation
- A NEMA insulation specification. Class F
insulation is rated to an operating (internal)
temperature of 155°C
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- Class H insulation
- A NEMA insulation specification. Class H
insulation is rated to an operating (internal)
temperature of 180°C.
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- Closed loop
- A broadly applied term, relating to any system in
which the output is measured and compared to the
input. The output is then adjusted to reach the
desired condition. In motion control, the term
typically describes a system utilizing a velocity
and/or position transducer to generate correction
signals in relation to desired parameters.
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- Cogging (Cogging torque)
- A term used to describe non-uniform angular
velocity. Cogging appears as a jerkiness, especially
at low speeds.
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- Commutation
- 1. A term which refers to the action of steering
currents or voltages to the proper motor phases so
as to produce optimum motor torque. In brush type
motors, commutation is done electromechanically via
the brushes and commutator. In brushless motors,
commutation is done by the switching electronics
using rotor position information obtained by Hall
sensors, a Tachsyn, or a resolver.
- 2. Commutation of step motors is normally done
open loop. Feedback from the motor is not required
to hold rotor position precisely.
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- Continuous rated current
(ICR) (Amperes)
- The maximum allowable continuous current a motor
can handle without exceeding the motor temperature
limits
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- Continuous rated torque (TCR)
(lb-in.)
- The maximum allowable continuous torque a motor
can handle without exceeding the motor temperature
limits
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- Continuous stall current
(ICS) (Amperes)
- Amount of current applied to a motor (at locked
rotor conditions), which results in rated
temperature rise. Refer also to definition of
"Continuous stall torque"
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- Continuous stall torque (TCS)
(lb-in.)
- The amount of torque at zero speed, which a motor
can continuously deliver without exceeding its
thermal rating. Determined by applying DC current
through two windings with rotor locked, while
monitoring temperature. Specified with motor
windings at maximum rated temperature, with motor in
25 degrees C ambient, mounted to a heat sink. Refer
to individual specs for heat sink size.
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- Current at peak torque (IPK)
(Amperes)
- The amount of input current required to develop
"peak torque". This is often outside the
linear torque/current relationship.
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- Current, Rated
- The maximum allowable continuous current a motor
can handle without exceeding motor temperature
limits.
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- D-flange mounting
- This type of mount has clearance holes on the
flange, and the mounting bolts stick out through the
flange from the motor side. This mount is common in
cases where the motor is integral to the machine.
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- Demag current
- The current level at which the motor magnets will
start to be demagnetized. This is an irreversible
effect, which will alter the motor characteristics
and degrade performance. Also known as peak current.
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- Detent torque
- The maximum torque that can be applied to an
unenergized step motor without causing continuous
rotating motion.
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- DPBV - Dripproof Blower
Ventilated
- Type of motor cooled by blowing air through the
inside of the motor using an attached blower.
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- Drive
- An electronic device that controls torque, speed
and/or position of an AC or brushless motor.
Typically a feedback device is mounted on the motor
for closed-loop control of current, velocity and
position.
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- Driver
- Electronics which convert step and direction
inputs to high power currents and voltages to drive
a step motor. The step motor driver is analogous to
the servomotor amplifier's logic.
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- Duty cycle
- For a repetitive cycle, the ratio of on time to
total cycle time.
- Duty cycle (%) = [On time / (On time + Off time)]
x 100%
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- Dynamic braking
- A passive technique for stopping a permanent
magnet brush or brushless motor. The motor windings
are shorted together through a resistor which
results in motor braking with an exponential
decrease in speed.
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- Efficiency
- The ratio of power output to power input.
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- Electrical time constant
(te) (Seconds)
- The time required for current to reach 63.2% of
its final value for a fixed voltage level. Can be
calculated from the relationship te=L/R where L is
inductance (henries) and R is resistance (ohms).
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- Encoder
- A feedback device which converts mechanical motion
into electronic signals. The most commonly used,
rotary encoders, output digital pulses corresponding
to incremental angular motion. For example, a
1000-line encoder produces 1000 pulses every
mechanical revolution. The encoder consists of a
glass or metal wheel with alternating transparent
and opaque stripes, detected by optical sensors to
produce the digital outputs.
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- Feedback
- A signal which is transferred from the output back
to the input for use in a closed loop system.
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- Ferrite
- A type of permanent magnet consisting of ceramic
compounds made up of oxides of iron, barium and
strontium.
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- Form factor
- The ratio of RMS current to average current. This
number is a measure of the current ripple in a SCR
or other switch-mode type of drive. Since motor
heating is a function of RMS current while motor
torque is a function of average current, a form
factor greater than 1.00 means some fraction of
motor current is producing heat but not torque.
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- Four quadrant
- Refers to a motion system which can operate in all
four quadrants; i.e., velocity in either direction
and torque in either direction. This means that the
motor can accelerate, run, and decelerate in either
direction.
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- Friction
- A resistance to motion caused by contact with a
surface. Friction can be constant with varying speed
(Coulomb friction) or proportional to speed (viscous
friction).
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- Hall sensor
- A feedback device which is used in a brushless
servo system to provide information for the
amplifier to electronically commutate the motor. The
device uses a magnetized wheel and hall effect
sensors to generate the commutation signals.
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- Holding torque
- Sometimes called static torque, holding torque
specifies the maximum external torque that can be
applied to a stopped, energized motor without
causing the rotor to rotate. Generally used as a
figure of merit when comparing motors.
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- Horsepower
- An index of the amount of work a machine or motor
can perform. One horsepower is equal to 746 watts.
Since power is equal to torque multiplied by speed,
horsepower is a measure of a motor's torque and
speed capability; e.g., a 1 HP motor will produce 36
lb-in. at 1,750 rpm.
- Formula:
- HP = Torque (lb-in.) x Speed (RPM)/63,025
- or
- HP = Torque (lb-ft.) x Speed (RPM)/5,252
- or
- HP = Volts x Amps x Efficiency/746
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- Hybrid step motor
- A motor designed to move in discrete increments of
steps. The motor has a permanent magnet rotor and a
wound stator. Such motors are brushless. Phase
currents are commutated as a function of time to
produce motion.
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- Idle current reduction
- A step motor driver feature that reduce the phase
current to the motor when no motor motion is
commanded (idle condition) for a specified period of
time. Idle current reduction reduces motor heating
and allows high machine throughputs from a given
motor.
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- Indexer
- Electronics which convert high level motion
commands from a host computer, PLC or operator panel
into step and direction pulse streams for use by the
step motor driver. Indexers can be broadly divided
into two classes. A preset indexer typically accepts
distance, velocity and ramp time inputs only. The
more sophisticated programmable indexer is capable
of complex motion control and includes program
memory.
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- Inductance (L) (mH -
millihenries line-to-line)
- The electrical equivalent to mechanical inertia;
that is, the property of a circuit, which has a
tendency to resist current flow when no current is
flowing, and when current is flowing has a tendency
to maintain that current flow. Pacific Scientific
measures inductance (line-to-line) with a bridge at
1000 Hz and with the rotor positioned so the back-EMF
waveform is at the peak of the sinusoid.
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- Inductance (mutual)
- Mutual inductance is the property that exists
between two current carrying conductors or coils
when magnetic lines of force from one link with
those of the other.
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- Inertial match
- For most efficient operation, the system coupling
ratio should be selected so that the reflected
inertia of the load is equal to the rotor inertia of
the motor.
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- Insulation Class
- The rating assigned to the maximum temperature
capability of the insulating components in a motor
or other piece of equipment.
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- Mechanical time constant
(tm) (Seconds)
- In a simple first order system, the time required
for the motor's speed to attain 63.2% of its final
value for a fixed voltage level. Can be calculated
from:
- where:
- J is inertia in lb-in./s2
- R is resistance in ohms
- KT is torque constant in lb-in./amp.
- 8.87 is a conversion factor
- tM is calculated in seconds
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- Microstepping
- An electronic technique for increasing a step
motor's position resolution and velocity smoothness
by appropriately scaling the phase currents.
Microstepping is also a technique used to reduce or
eliminate the effects of system resonance at low
speeds.
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- Mid-range instability
- A phenomenon in which a step motor can fall out of
synchronism due to a loss of torque at mid-range
speeds. The torque loss is due to the interaction of
the motor's electrical characteristics and the
driver's electronics. Some drivers have circuitry to
eliminate or reduce the effects of mid-range
instability.
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- NEMA - National
Electrical Manufacturer's Association
- Acronym for an organization which sets standards
for motors and other industrial electrical
equipment.
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- NTC - Negative
Temperature Coefficient
- A negative temperature coefficient thermistor is
used to detect and protect a motor winding from
exceeding its maximum temperature rating. Resistance
of the device decreases with an increase in
temperature.
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- Open-loop
- A system in which there is no feedback. Motor
motion is expected to faithfully follow the input
command. Stepping motor systems are an example of
open-loop control.
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- Overload capacity
- The ability of a drive to withstand currents above
its continuous rating. It is defined by NEMA as 150%
of the rated full-load current for "standard
industrial DC motors" for one minute.
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- Peak torque (Tpk)
(lb-in.)
- The maximum torque a brushless motor can deliver
for short periods of time. Operating PacTorq motors
above the maximum torque value can cause
demagnetization of the rare-earth magnets. This is
an irreversible effect that will alter the motor
characteristics and degrade performance. This is
also known as peak current.
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- Not to be confused with system peak torque, which
is often determined by amplifier peak current
limitations, where peak current is typically two
times continuous current.
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- Poles
- Refers to the number of magnetic poles arranged on
the rotor of the brushless motor. Unlike an AC
motor, the number of poles has no direct
relationship to the base speed of the motor.
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- Power factor
- Ratio of true power (kW) to apparent power (kVA).
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- PTC - Positive
Temperature Coefficient
- A positive temperature coefficient thermistor is
used to detect and protect a motor winding from
exceeding its maximum temperature rating. Resistance
of the device increases with an increase in
temperature.
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- Pull-out torque
- The maximum friction load, at a particular
inertial load, that can be applied to the shaft of a
synchronous motor (running at constant speed) and
not cause it to lose synchronism.
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- Pulse rate
- The frequency of the step pulses applied to a step
motor driver. The pulse rate, multiplied by the
resolution of the motor/driver combination (in steps
per revolution), yields the rotational speed in
revolutions per second.
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- Pulse Width Modulation (PWM)
- 1. A PWM controller (amplifier) switches DC supply
voltage on and off at fixed frequencies. The length
of the on/off interval or voltage waveform is
variable.
- 2. Pulse width modulation (PWM), describes a
switch-mode (as opposed to linear) control technique
used in amplifiers and drivers to control motor
voltage and current. PWM offers greatly improved
efficiency compared to linear techniques.
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- Regeneration
- The action during motor braking, in which the
motor acts as a generator and takes kinetic energy
from the load, converts it to electrical energy, and
returns it to the amplifier.
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- Repeatability
- The degree to which a parameter such as position
or velocity can be duplicated.
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- Resistance, Hot (RH)(Ohms
line-to-line)
- The motor's terminal resistance value specified at
the hot winding temperature, which is at the motor's
maximum rated temperature.
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- Resolution
- The smallest increment into which a parameter can
be broken down. For example, a 1000 line encoder has
a resolution of 1/1000 of a revolution.
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- Resolver
- An electromagnetic feedback device which converts
angular shaft position into analog signals. These
signals can be processed in various ways, such as
with an RDC (resolver-to-digital converter) to
produce digital position information. There are two
basic types of resolvers; transmitter and receiver.
A transmitter-type is designed for rotor primary
excitation and stator secondary outputs. Position is
determined by the ratio of the sine output amplitude
to cosine output amplitude. A receiver-type is
designed for stator primary excitations and rotor
secondary output. Position is determined by the
phase shift between the rotor output signal and one
of the primary excitation signals.
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- Resonance
- Oscillatory behavior caused by mechanical
limitations.
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- Restart torque
- The maximum friction load, at a particular
inertial load, that can be applied to the shaft of a
synchronous motor without causing it to lose
synchronism when accelerating to a constant speed
from standstill.
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- Ringing
- Oscillation of a system following a sudden change
in state.
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- RMS Current - Root Mean
Square Current
- In an intermittent duty cycle application, the RMS
current is equal to the value of steady state
current which would produce the equivalent motor
heating over a period of time.
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- RMS Torque - Root Mean
Square Torque.
- In an intermittent duty cycle application, the RMS
torque is equal to the value of steady state torque
which would produce the equivalent motor heating
over a period of time.
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- Rotor
- The moving part of the motor, consisting of the
shaft and magnets. These magnets are analogous to
the field winding of a brush-type DC motor.
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- Settling time
- The time required for a parameter to stop
oscillating or ringing and reach its final value.
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- Shock loading
- A load that produces extremely high peak torques
for very short durations. This type of load is
associated with conveyorized grinding, crushing and
separation processes.
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- Stall Torque
- The amount of torque developed with voltage
applied and shaft locked, or not rotating. Also
known as locked-rotor torque.
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- Stator
- The non-moving part of the motor. Specifically, it
is the iron core with the wire winding in it that is
pressed into the frame shell. The winding pattern
determines the voltage constant of the motor.
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- Step angle
- The angular distance the shaft rotates upon
receipt of a single step command.
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- Stiffness
- The ability to resist movement induced by an
applied torque. Stiffness is often specified as a
torque displacement curve, indicating the amount a
motor shaft will rotate upon application of a known
external force when stopped.
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- Synchronism
- A motor rotating at a speed corresponding
correctly to the applied step pulse frequency is
said to be in synchronism. Load torques in excess of
the motor's capacity (rated torque) will cause a
loss of synchronism. This condition is not damaging
to a step motor.
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- TENV - Totally Enclosed
Non-Ventilated
- Acronym describing a type of motor enclosure,
which has no outside air going into it. It is cooled
only by convection to the frame, which is usually
finned.
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- Thermal protection
- A thermal sensing device mounted to the motor to
protect it from overheating. This is accomplished by
disconnecting the motor phases from the drive in an
over temperature condition.
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- Thermal resistance (Rth)
(°C/watt)
- An indication of how effectively a unit rids
itself of heat; a measure of temperature rise per
watts lost. In Pacific Scientific literature, it is
the specified value from the motor windings to the
ambient, under locked rotor conditions.
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- Thermal time constant (tth)
(minutes)
- The time required for a motor to attain 63.2% of
its final temperature for a fixed power input.
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- Torque Constant (KT =
lb-ft./A)
- An expression of the relationship between input
current and output torque. For each ampere of
current, a fixed amount of torque is produced.
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- Torque-to-inertia ratio
- Defined as the motor's holding torque divided by
the inertia of its rotor. The higher the ratio, the
higher a motor's maximum acceleration capability
will be.
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- Unipolar driver
- A step motor driver configuration that uses a
unipolar power supply and is capable of driving
phase current in only one direction. The motor phase
winding must be center tapped (6 or 8 lead) to
operate with a unipolar driver. The center tap is
used instead of providing the current reversal of a
bipolar driver.
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- Viscous Damping (KDV)
(lb-in./kRPM)
- Inherent losses are present in all motors which
result in lower torque delivered at the output shaft
than developed at the rotor. Losses which are
proportional to speed (i.e. speed dependent terms
such as windage, friction, eddy current) are related
through the motor's "viscous damping"
constant, measured as the slope of the damping
curve.
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- Voltage constant (KE) (V/kRPM
peak, line-to-line)
- May also be termed back-EMF constant. When a motor
is operated, it generates a voltage proportional to
speed, but opposing the applied voltage. The shape
of the voltage waveform depends upon the specific
motor design. For example, in a brushless motor, the
waveshape may be trapezoidal or sinusoidal in
nature. All Pacific Scientific brushless motor
designs have a sinusoidal voltage constant. For a
sine waveform, the voltage constant can be measured
from line-to-neutral or line-to-line and expressed
as a peak value or "RMS" value.
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