| A |
|
| Acceleration |
The action of
changing speed from any speed to a higher speed, irrespective
of direction. Depending on drive design, the control of acceleration
time may be known as "Up time", "Up rate" or similar variant.
It is important to remember that some drive designs apply a
single rate control to positive going speed demand changes irrespective
of polarity. For example, consider a drive running backwards
at half speed being asked to run forwards at half speed. The
speed demand can be considered to be positive going, but the
period between the drive running at half speed backwards and
zero speed is termed deceleration and the period between zero
speed and running at half speed forwards is termed acceleration.
See also Angular acceleration, Linear acceleration. |
| Adaptive control |
A general term
for changing one parameter against another. For example an adaptive
current loop may apply differing gain characteristics depending
on whether the armature current is discontinuous or continuous. |
| Angular acceleration |
A positive rate
of change of position about a fixed point or axis. Measured
in radians/second/second. |
| Angular deceleration |
A negative rate
of change of position about a fixed point or axis. Measured
in radians/second/second. |
| Angular velocity |
A rate of rotation
about a fixed point or axis. Measured in radians/second. |
| Anti-parallel |
A term describing
the bridge configuration of a regenerative drive. Essentially
means "back to back" with the positive end of one bridge connected
to the negative end of the other and vice versa allowing four
quadrant operation. Also known as Inverse parallel. |
| Armature |
The rotating
part of a motor, constructed of a series of current carrying
coils . |
| Armature choke |
Sometimes (unconventionally)
called a reactor, this device is connected in series with the
motor armature and adds inductance to the overall armature circuit
in order to increase the armature time constant and improve
form factor. Typical values tens of milli Henries. |
| Armature time constant. |
Expressed in
seconds and calculated from L (inductance in Henries) / R (resistance
in Ohms). Minimum value recommended for a single phase drive
is 10mS, 3.3mS for a three phase drive assuming the drives are
used on a 50Hz supply although 20mS and 6.6mS would be preferable. |
| Armature voltage feedback |
A method for
approximately measuring motor speed in constant field motors.
See also Back E.M.F. |
| Autotune |
A term used
to describe any process whereby the drive optimise itself to
the motor. The most common application of autotune is the drive
current loop, where the drive automatically disables field current
then perturbates current demand at increasing frequency in order
to establish the point of current discontinuity and set appropriate
proportional gain and integral time constant. |
| Auxilliary |
Any secondary
function for example an additional speed demand input. Also
used to differentiate between various power supplies required
by a drive, for example where the drive requires separate supplies
for the thyristor bridge, coding, field etc. |
|
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| B |
|
| Back E.M.F. |
The rotation
producing voltage in a motor, which is the armature voltage
applied to terminals of the motor less (or plus, if regenerating)
the armature resistance voltage drop. See also I.R. drop. |
| Bridge |
A term used
to describe the power circuit of the drive, consisting of thyristors
only in a fully controlled bridge and a combination of thyristors
and diodes in a half controlled bridge. |
| Brushgear |
The term used
to describe that part of a motor which is responsible for transferring
electrical power to the commutator. Encompasses brushes, brush
holders , springs etc. |
| Base speed |
The motor speed
produced when full rated armature voltage is presented to the
armature terminals, given that the correct field is present.
See also Field weakening. |
|
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| C |
|
| Choke |
See Armature
choke. |
| Closed loop |
A generic term
used to describe any process where the action of a loop is monitored
and the feedback thus derived is used to modify its action.
For example, monitoring material tension by use of a load cell
roller, comparing that with desired tension and using that information
via a P.I.D. loop to modify the speed of a driven nip responsible
for producing the material tension. Can be considered to be
analytical rather than predictive. See also Open loop. |
| Coding |
A term applied
to the method of ensuring the drive thyristors fire at the correct
point in time against the main supply, essentially by detecting
zero crossover points. |
| Common |
A term used
to indicate the return path for a signal, or a fixed point against
which measurements are taken. It is important to realize that
the use of this term does not necessarily indicate that it is
itself at a low potential. For example, the common on an un-isolated
drive will be at mains potential and must not be grounded. |
| Compound wound |
A term used
to describe a motor field configuration, meaning that the motor
in question has both series and shunt wound flux producing fields.
See also Shunt wound, Series wound. |
| Constant power |
This term is
applied to field weakening motors and describes the region above
base speed where armature voltage is kept approximately constant
regardless of speed. If the armature current is allowed to be
limited at the same level throughout the field weakening range,
armature voltage X armature current is constant hence constant
power. This term is not automatically applied to field weakening
motors, as certain of these require armature current profiling
in the field weakening region to aid commutation. |
| Constant torque |
This term is
applied to both field weakening and constant field motors. As
torque is proportional to flux and armature current, maximum
torque is always available regardless of speed whenever the
field is at full strength. The term therefore applies to constant
field shunt wound motors all the time, and to field weakening
motors below base speed. |
| Contactor |
The device used
to switch main power to a drive. In the case of a three phase
drive it is usually important that the drive controls the contactor
- i.e. that emergency stop sequencing cannot interrupt the contactor
coil supply. |
| Continuous current |
A term used
to indicate the level of armature current at which the current
waveform lifts off zero and becomes continuous. Adaptive current
loops use knowledge of this point to determine where the current
loop gain break point is to be set. |
| Current control |
Otherwise known
as torque control, a method whereby the drive speed loop is
bypassed or saturated and the drive current loop is either directly
addressed or limited externally. |
| Current limit |
The method by
which the maximum excursion of integrated speed error is limited.
Usually involves a form of automatic profiling so that more
than 100% current is available for acceleration or deceleration,
for example. |
| Current loop |
A generic term
used to describe that part of the drive circuitry which integrates
the error between current demand and feedback and eventually
produces firing phase angle demand. The "innermost" loop in
a simple drive system. |
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| D |
|
| D.C.V.T. |
An abbreviation
for direct current voltage transformer, this device usually
consists of a V.C.O. (voltage controlled oscillator) followed
by a transformer followed by a rectifier. The device isolates
and scales high level d.c. voltages and is used in older drive
systems as a method for providing armature voltage feedback.
|
| Deceleration |
The action
of changing speed from any speed to a lower speed, irrespective
of direction. Depending on drive design, the control of deceleration
time may be known as "Down time", "Down rate" or similar variant.
It is important to remember that some drive designs apply a
single rate control to negative going speed demand changes irrespective
of polarity. For example, consider a drive running forwards
at half speed being asked to run backwards at half speed. The
speed demand can be considered to be negative going, but the
period between the drive running at half speed forwards and
zero speed is termed deceleration and the period between zero
speed and running at half speed backwards is termed acceleration.
See also Angular deceleration, Linear deceleration. |
| Demand |
A generic term
used to describe any request for action, such as current demand,
speed demand. |
| Discontinuous current |
See Continuous
current. |
| Dynamic response |
A wide ranging
term used to describe how the drive or motor reacts to any change
in demand. Encompasses all loop time constants and gain components,
for example speed loop dynamic response depends on speed loop
error, integral time constant, feedforward, together with the
dynamic response of the following current loop. |
| Dynamometer |
A common application
for DC drives, this is a system for testing other devices such
as automotive engines by applying controlled loading. Incorporates
additional control loops around force measurement devices. |
| Derivative |
Sometimes known
as feedforward, this is the "D" in the commonly used abbreviation
P.I.D. A method for applying an extra gain component to the
edge of a change in demand. Similar in action to the output
of a capacitor when its input is subjected to a change in DC
level. |
| Duty cycle |
A means of describing
the cyclical work demand on a system. For example, a drive that
is required to run for 10 seconds then stop for 10 seconds could
be described as having a 50% duty cycle, one required to run
for 5 seconds and stop for 15 seconds could be described as
having a 25% duty cycle. (% term is probably the most precise
way of describing duty cycle, although they are sometimes expressed
in other ways such as 1/1. Using % term is less open to misinterpretation.)
|
| Dynamic braking |
A means of braking
a motor that does not rely on the drive having regenerative
capability, also occasionally employed on drives that do have
regenerative capacity for safety reasons. Essentially the method
involves using a contactor to connect a low ohm value resistor
directly across the motor armature whilst at the same time quenching
the drive. In order for the system to work it is essential that
the motor field is maintained during braking, otherwise it will
not work as a generator. |
| Dynamic losses |
Mechanical or
electrical losses in a system that are as a result of dynamic
changes such as acceleration. They are not necessarily subtractive
- for example, dynamic losses in a rewind mean that not all
the torque produced by the drive/motor system is translated
into material tension, whereas an unwind system having dynamic
losses will produce more material tension then would be produced
by drive/motor torque. See also Static losses. |
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| E |
|
| Efficiency |
The method of
describing how much of the power delivered to a system is available
for use by the controlled device. For example, a motor/gearbox
having a full working rating of 100A but requiring 10A to turn
the gearbox would be said to be 90% efficient. |
| Error |
In a P.I.D system,
error is the difference between demand and feedback having been
multiplied by the Proportional term. |
| E.M.C. |
The abbreviation
for Electro Magnetic Compatibility, a vast set of regulations
pertaining to installations within the European Union. When
pertaining to drives, the phrase is usually taken to imply electrical
noise suppression and immunity requirements and it is the responsibility
of the drive manufacturer to provide guidelines regarding installation,
and the resulting E.M.C. behaviour is the responsibility of
the system manufacturer. |
| Enable |
See Quench. |
| Encoder |
A digital device
used to measure shaft speed, having an output in so many pulses
per revolution and usually a marker pulse once per revolution.
1000 pulses/rev would be typical, with two sets of pulses 90
degrees apart together with their inverse. |
| Excitation |
A term commonly
used to mean field on a motor. |
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| F |
|
| Field |
The wound or
permanently magnetised part of a motor that is responsible for
producing magnetic flux in which the armature turns. See Compound
wound, Series wound, Shunt wound. |
| Field time constant |
Expressed in
seconds and calculated from L (inductance in Henries) / R (resistance
in Ohms). Typically around 1 - 2 seconds, it is important to
allow sufficient time for the field to decay after removing
power before open circuiting the field, when employing field
reversal techniques for example. |
| Field weakening |
The technique
of extending a motor speed range by reducing field flux at speeds
above base speed, thus maintaining a relatively constant armature
voltage. See also Constant power. |
| Filter |
The name for
any device that imposes a time constant on or removes harmonics
or disturbances from a signal. Current common usage is for a
device that is installed on the a.c. supply to a drive for the
purposes of E.M.C. noise immunity and suppression. |
| F.L.C. |
Abbreviation
for Full Load Current, being the maximum rated armature current
expressed in Amperes. |
| Flux |
The magnetic
field produced by either permanent magnet or electromagnetic
wound fields in motors. |
| Force venting |
Otherwise known
as force cooled, and as opposed to natural venting or natural
cooling this term represents the use of a fan or blower to increase
air flow through a motor for cooling purposes. |
| Form factor |
The ratio of
the R.M.S. to the mean value of armature current - usually assumed
to be around 1.5 for a single phase drive and 1.05 for a three
phase drive. This needs to be taken into account when sizing
fusing, contactors, wiring etc. in the a.c. supply to drives. |
| Four quadrant |
The ability
of a drive to control torque and speed in all directions. In
other words, ability to motor and brake in both forward and
reverse directions of rotation. So called because of the common
diagrammatic method of representing the effects. |
| Fully controlled |
When applied
to a thyristor bridge, this term means that all the devices
within the bridge are thyristors as opposed to a mix of thyristors
and diodes. See also Half controlled. |
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| G |
|
| Gain |
Strictly speaking,
another way of describing Proportional terms. Also occasionally
used in the same way as Stability to describe the overall P.I.D.
performance of a drive speed and current loops. See also P.I.D.
|
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| H |
|
| Half controlled |
When applied
to a thyristor bridge, this term means that half of the devices
within the bridge are thyristors and half are diodes. See also
Fully controlled. |
| Healthy |
An output from
the drive indicating it is not in a fault condition. In the
case of three phase drives having external contactors it is
usually assumed that the drive cannot be other than healthy
when the contactor is de-energised and power is not applied
to the bridge. See also Ready. |
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| I |
|
| Inverse parallel |
See Anti-parallel. |
| Integral |
Usually expressed
as a time constant, this is the "I" in the commonly used abbreviation
P.I.D. A method for applying a linearly increasing or decreasing
output change in response to error between demand and feedback.
Essentially, an Integrated output will move in one direction
or the other whenever its input is not zero. |
| Inertia |
The tendency
of a mass at rest to resist motion, or the tendency to resist
change of motion. |
| I.R. drop |
A motor armature
has resistance across which volts are dropped according to current
flow. This means that not all the terminal voltage is translated
into speed producing back E.M.F. and leads to a speed difference
between full load and no load. This can be compensated for by
the introduction of I.R. compensation, which takes a proportion
of current feedback and introduces it as an additional speed
demand. |
| I²T |
A measure of
energy let through expressed in Amps²Seconds used by fuse
manufacturers of semiconductor protective fuses. |
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| J |
|
| Jog |
The term used
to describe a short duration of rotation, usually implying that
the drive is not latched into a running condition permanently.
|
| Jumper |
A device, either
hardware or software, that connects one point of a drive circuit
to another in order to provide a specific function. |
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| L |
|
| Line reactor |
Sometimes (unconventionally)
called a choke, this is inductance added to the main bridge
a.c. supply to the drive. Typical values tens of micro Henries.
Reduces disturbance to the supply caused by commutation notches
and also helps to protect the drive from supply disturbances. |
| Linear acceleration |
A positive rate
of change of position. Measured in metres/second/second. |
| Linear deceleration |
A negative rate
of change of position. Measured in metres/second/second. |
| Linear velocity |
A rate of displacement.
Measured in metres/second. |
| Load |
A general term
used to describe the opposing force causing the drive to produce
torque. |
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| M |
|
| Misfire |
A term used
to describe a fault phenomena whereby one or more of the drive
bridge thyristors does not fire, causing distortion of the armature
current waveform. Can lead to heating of the motor armature.
Usually protected against by more sophisticated drives. |
| M.M.I. |
Abbreviation
for Man Machine Interface, a term that has become adopted by
drives manufacturers meaning the device by which drives can
be interrogated, programmed etc. For example, the keyboard and
display on a digital drive. |
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| N |
|
| Naturally cooled |
A term applied
to those motors not fitted with force venting fans or blowers,
these motors rely on the use of an internal fan which turns
as the motor turns - these motors therefore rely on rotation
for cooling and it is not good practice to use this type of
motor in applications requiring high torque at low speed. |
| Noise immunity |
See E.M.C. |
| Non Isolated |
Non isolated
drives are lower cost, but are only suitable for simple systems
as they have their control electronics floating at a high potential.
They cannot be connected to other equipment such as other drives,
control systems etc. |
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| O |
|
| Open loop |
A term used
to describe a control system that does not employ a feedback
device and thus can be considered to be predictive rather than
analytical. A good example would be a winder system that computes
diameter, and sets torque accordingly in an attempt to control
material tension. See also Closed loop. |
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| P |
|
| Permanent magnet field |
The type of
motor in which the field is not an electromagnetic wound coil
but a fixed magnet. |
| P.I.D. |
The commonly
used abbreviation for Proportional, Integral and Derivative
- the three terms in a typical control loop. |
| Proportional |
Sometimes known
as gain, this is the "P" in the commonly used abbreviation P.I.D.
A method for multiplying error between demand and feedback by
a set amount. |
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| Q |
|
| Quench |
Also described
as Enable, a term used to describe the action of preventing
a drive from producing armature current. Usually implies that
the control loops are in a reset state. This is a more precise
term than Stop, as that term does not necessarily mean the drive
is unable to produce current, merely that it is at rest. |
| Quiescent |
Another way
of describing Steady state, whereby the drive is not necessarily
at rest but is in a condition where it is not subject to any
change in demand. |
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| R |
|
| Ramp |
A term used
to describe the application of a controllable rate of change
to a signal, such as an acceleration time. |
| Ready |
As distinct
from Healthy, this output from the drive is usually taken to
mean that the drive - particularly three phase drives with external
contactor control - have power applied and are not in an alarm
state. |
| Reference |
A term commonly
used by drive manufacturers to mean either a signal used as
a demand (such as a speed reference) or the point against which
such a signal can be compared. |
| Regenerative |
Often shortened
to regen, the ability of a drive to return current to the mains
supply for example when braking a motor. |
|
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| S |
|
| Setpoint |
An alternative
term for Reference, but more specific - this term can only be
applied to a demand not the point to which it can be compared. |
| Semiconductor fusing |
The only method
by which a thyristor bridge can be reliably protected in the
event of an external fault such as an armature short circuit.
See also I²T. |
| Series wound |
A term used
to describe the type of motor field that is arranged in series
with the armature windings. Not ideal for use with d.c. drives
as they have low torque capability at low speeds, torque being
dependant on flux which is produced by the current flowing through
the armature and field. |
| Shunt wound |
A term used
to describe the type of motor field that is arranged separately
from the armature windings and which therefore can be supplied
with a fixed voltage. The ideal motor type for use with d.c.
drives. |
| Single ended |
A term often
used instead of single quadrant, meaning a drive that is capable
of a only one direction of rotation and motoring current only. |
| Single quadrant |
See Single ended.
See also Four quadrant. |
| Snubbers |
A term commonly
used to describe suppression devices used on thyristor bridges.
|
| Speed loop |
A generic term
used to describe that part of the drive circuitry which integrates
the error between speed demand and feedback and eventually produces
current demand. The "outermost" loop in a simple drive system. |
| Speed holding |
The ability
of a drive to maintain a desired speed, assuming that load is
constant. |
| Stability |
The ability
of a system to reach a desired state without continual overshoot
and undershoot, and its ability to retain that state following
an external disturbance. Also used to describe an adjustable
control in simpler drives not having access to all speed and
current loop P.I.D. settings. |
| Static losses |
Mechanical or
electrical losses in a system that are as a result of friction,
or any other opposition to a move away from rest. They are not
necessarily subtractive - for example, static losses in a rewind
mean that additional torque is required from the drive/motor
system when moving away from rest if constant material tension
is to be maintained, whereas an unwind system having static
losses will produce more material tension when moving away from
rest than is produced by drive/motor torque. See also Dynamic
losses. |
| Steady state |
See Quiescent. |
|
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| T |
|
| Tachogenerator |
Sometimes shortened
to tacho or even tach, this is an analogue device - in effect
a small d.c. generator - used to measure shaft speed as a feedback
device. Typical output 60V/1000 r.p.m. There are also a.c. versions
which require rectification before they can be used with d.c.
drives, but these types are best avoided as they will not differentiate
between forward and reverse rotation. They will also not perform
well at low speeds because of the volt drops associated with
rectification. |
| Three quadrant |
A term sometimes
used to describe a drive normally used for motoring in either
direction and having regenerative braking (but not continuous
controlled regenerative) capability. See also Four quadrant. |
| Thyristor |
Otherwise known
as an S.C.R. (silicon controlled rectifier) used as the power
switching device in most d.c drive bridges. |
| Torque control |
See Current
control. |
| Two quadrant |
The term used
to describe a drive that is capable of operation either in both
directions but a single direction of current only, or in a single
direction with motoring and braking capability. See also Four
quadrant. |
|
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| U |
|
| Universal (AC/DC) motors |
A phrase applied
to series field wound motors. These are known as universal because
they may be driven by either an AC or DC supply. (AC supply
is possible because the field flux reverses at the same time
as the armature current as the two circuits are in series. Rotation
direction is therefore maintained.) See also Series Wound. |
|
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| V |
|
| V.S.D. |
An abbreviation
for variable speed drives, this term is occasionally used to
refer to d.c. drives, but is not limited to them as the family
would also include inverters, vector drives, servos etc. |
| V.D.R. |
An abbreviation
for Voltage Dependant Resistor, a device that is designed to
be installed on the a.c supply to a drive. Normally having a
high impedance, it rapidly drops its impedance value to absorb
any spikes that may be present on the supply. |
|
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| W |
|
| Windage losses |
One component
of Dynamic losses, caused by air resistance. |
|
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| Z |
|
| Zero interlocking |
This term describes
two commonly used techniques, preventing the start up of a drive
without a zero speed reference and the automatic quenching of
a regenerative drive below a small speed demand to prevent creep. |
