ELECTRICAL ACTUATORS &CONTROLLERS3

A potentiometer informally a pot, is a three-
terminal resistor with a sliding contact that forms
an adjustable voltage divider If only two terminals
are used, one end and the wiper, it acts as
a variable resistor or rheostat.

 Audio control
 Television
 Motion Control
 Transducers
 Computation-In analog computers,

 A reference input is sent to the servo amplifier,
which controls the speed of the servomotor.
 Directly mounted to the machine is a feedback
device (either an encoder or resolver).
 This device changes mechanical motion into
electrical signals and is used as a feedback loop.
 This feedback loop is then sent to the error
detector, which compares the actual operation
with that of the reference input.
 If there is an error, that error is fed directly to
the amplifier, which makes the necessary
corrections.

 Servo Motors are DC Motors with a servo
mechanism to provide a precise angular
motion.
 Pulse width modulation (PWM) technique is
used to set the angle of rotation.
 Generally RC servo motors have a rotation
limit of 900to 1800 but servos with high
rotation angles are also available.

 A servo needs three inputs to operate - one
for positive voltage, second for ground and
third one for PWM.
Small R/C servo mechanism
1. electric motor
2. position
feedback potentiometer
3. reduction gear
4. actuator arm

 is basically a two-phase induction motor,
capable of reverse operation.
 To achieve the dynamic requirements of a
servo system, the servomotor must have a
small diameter, low inertia, and high-
resistance rotors.
 The low inertia allows for fast starts, stops,
and reverse of direction.
 The high-resistance rotor provides for almost
linear speed/ torque characteristics and
accurate control.

 are generally small and powerful for their
size, and easy to control. Common types of
DC servomotors include brushless or gear
motors.

 Permanent magnet
 Shunt wound
 Disc armature
 Coreless or slotless

Torque, T
Speed, ω
Load
Operating
Points
DC Servo
AC Servo
Stepper

 Synchro transmitters are as described, but 50 and 60-
Hz synchro receivers require rotary dampers to keep
their shafts from oscillating when not loaded (as with
dials) or lightly loaded in high-accuracy applications.
 A different type of receiver, called a control
transformer (CT), is part of a position servo that
includes a servo amplifier and servo motor. The
motor is geared to the CT rotor, and when the
transmitter's rotor moves, the servo motor turns the
CT's rotor and the mechanical load to match the new
position. CTs have high-impedance stators and draw
much less current than ordinary synchro receivers
when not correctly positioned.
 Synchro transmitters can also feed synchro to digital
converters, which provide a digital representation of
the shaft angle.

 converts the angular position of its rotor (mechanical
input) into an electrical output signal.
 When ac excitation voltage is applied to the rotor of
a synchro transmitter, the resultant current produces
an ac magnetic field around the rotor winding.
 The lines of force cut through the turns of the three
stator windings and, by transformer action, induce
voltage into the stator coils.
 The effective voltage induced in any stator coil
depends upon the angular position of that coil's axis
with respect to the rotor axis.
 When the maximum effective coil voltage is known,
the effective voltage induced into a stator coil at any
angular displacement can be determined

 are electrically identical to torque
transmitters of the same size except for the
addition of some form of damping.
 In some sizes of 400-Hz Synchros, units are
designated as torque receivers but may be
used as either transmitters or receivers.

 is just what its name implies-a control
synchro device accurately governing some
type of power amplifying device used for
moving heavy equipment.

 The command input shaft is mechanically linked to
R1, and the load is mechanically linked to R2.
 A supply voltage is applied across both
potentiometers. The system is designed so that when
the input and output shafts are in the same angular
position, the voltages from the two potentiometers
are equal and no error voltage is felt at the amplifier
input. If the input shaft is rotated, moving the wiper
contact of R1, an error voltage is applied to the servo
amplifier. This error voltage is the difference
between the voltages at the wiper contents of R1 and
R2. The output of the amplifier causes the motor to
rotate the load and the wiper contact of R2. This
continues until both voltages are again equal. When
the voltages are equal, the motor stops. In effect,
the position of the output shaft has been sensed by
the balanced potentiometer.

A stepper motor is an electromechanical
device which converts electrical pulses into
discrete mechanical movements. The shaft
or spindle of a stepper motor rotates in
discrete step increments when electrical
command pulses are applied to it in the
proper sequence.
Assignment-
detailed working &applications-servo ,
synchro, stepper motors(PM, VR,Tacho
generator)

 are those which are attached to circuits that
conduct compressed air rather than a flow of
electrons
 The difference is that in these systems, when
the presence of compressed air is flowing
through one circuit, the force of that energy
opens up a switch and begins to flow into a
second circuit.
 In both of these varieties though there needs to
be a sensor present so that the switching can
occur.

 is a comparative device that receives an
input signal from a measured process
variable, compares this value with that of a
predetermined control point value (set
point), and determines the appropriate
amount of output signal required by the final
control element to provide corrective action
within a control loop

 An electronic sensor (thermocouple, RTD or
transmitter) installed at the measurement
location continuously sends an input signal to
the controller.
 At set intervals the controller compares this
signal to a predefined set point.
 If the input signal deviates from the set
point, the controller sends a corrective
output signal to the control element.

 An electronic controller is best suited for
applications where large load changes are
encountered and/or fast response changes
are required.

 Dicussion-applications,advantages,
diadvantages,comparison

PID combines
 Proportional
 Integral and
 Derivative functions into a single unit.

Proportional control reacts to the size of the
deviation from set point when sending a
corrective signal. The size of the corrective
signal can be adjusted in relation to the size
of the error by changing the width of the
proportional band.
A narrow proportional band will cause a large
corrective action in relation to a given
amount of error, while a wider proportional
band will cause a smaller corrective action in
relation to the same amount of error

 Integral control reacts to the length of time
that the deviation from set point exists when
sending a corrective signal. The longer the
error exists, the greater the corrective
signal.

 Derivative control reacts to the speed in
which the deviation is changing.
 The corrective signal will be proportional to
the rate of change within the process

 The proportional, integral, and derivative
terms are summed to calculate the output of
the PID controller.

 Auto-tuning will automatically select the
optimum values for P, I and D, thus
eliminating the need for the user to
calculate and program these values at system
startup.
 This feature can be overridden when so
desired. On some models, the control
element can be manually operated.

 refers to a control system usually of a
manufacturing system process or any kind
of dynamic system, in which
the controller elements are not central in
location (like the brain) but are distributed
throughout the system with each component
sub-system controlled by one or more
controllers.
 is a computerized control system used to
control the production line in the industry
 The entire system of controllers is connected by
networks for communication and monitoring.
 is a very broad term used in a variety of
industries, to monitor and control distributed
equipment.

DCS is a very broad term used in a variety of industries,
to monitor and control distributed equipment.
 Electrical power grids and electrical generation
plants
 Environmental control systems
 Traffic signals
 Radio signals
 Water management systems
 Oil refining plants
 Metallurgical process plants
 Chemical plants
 Pharmaceutical manufacturing
 Sensor networks
 Dry cargo and bulk oil carrier ships

PROCESS
Final
control
element
Data
acquisition
Main
Computer
Display

 is a type of industrial control system (ICS).
 ICS are computer controlled systems that
monitor and control industrial processes that
exist in the physical world.
 SCADA systems historically distinguish
themselves from other ICS systems by being
large scale processes that can include
multiple sites, and large distances.

 Industrial processes include those of
manufacturing, production, power
generation, fabrication, and refining, and may run in
continuous, batch, repetitive, or discrete modes.
 Infrastructure processes may be public or
private, and include water treatment and
distribution, wastewater collection
and treatment, oil and gas pipelines, electrical power
transmission and distribution, wind farms, civil
defense siren systems, and large communication
systems.
 Facility processes occur both in public facilities
and private ones, including buildings, airports, ships,
and space stations. They monitor and
control heating, ventilation, and air conditioning
systems (HVAC), access, and energy consumption.

 A human–machine interface or HMI is the apparatus or
device which presents process data to a human operator,
and through this, the human operator monitors and
controls the process.
 A supervisory (computer) system, gathering (acquiring)
data on the process and sending commands (control) to the
process.
 Remote terminal units (RTUs) connecting to sensors in the
process, converting sensor signals to digital data and
sending digital data to the supervisory system.
 Programmable logic controller (PLCs) used as field devices
because they are more economical, versatile, flexible, and
configurable than special-purpose RTUs.
 Communication infrastructure connecting the supervisory
system to the remote terminal units.
 Various process and analytical instrumentation

 First generation: "Monolithic"
 Second generation: "Distributed"
 Third generation: "Networked"

ELECTRICAL ACTUATORS &CONTROLLERS3

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