ELECTRICAL ACTUATORS

&CONTROLLERSVijayan.K.K

POTENTIOMETERS

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.

APPLICATIONS

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

AS ERROR DETECTOR

SERVO SYSTEM.

SERVO SYSTEM.

SERVO SYSTEM-WORKING 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.

STEPPER MOTOR AND SERVOMOTOR

SERVO MOTOR

SERVOMOTOR

SERVO MOTORS 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 mechanism1. electric motor2. position feedback potentiometer3. reduction gear4. actuator arm

AC SERVOMOTORS  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.

DC SERVOMOTORS are generally small and powerful for

their size, and easy to control. Common types of DC servomotors include brushless or gear motors.

TYPES OF DC SERVOMOTORS

Permanent magnet Shunt wound Disc armature Coreless or slotless

TORQUE-SPEED CURVE OF A DC SERVOMOTOR AND LOAD TORQUE PLOT

Torque, T

Speed, ω

Load

OperatingPoints

DC ServoAC ServoStepper

SYNCHROS- SYMBOLS

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.

SYNCHRO TRANSMITTER 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

SYNCHRO RECEIVER

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.

CONTROL TRANSFORMERS is just what its name implies-a control

synchro device accurately governing some type of power amplifying device used for moving heavy equipment.

SYNCHROS –AS ERROR DETECTOR

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.

STEPPER MOTOR

A stepper motor is an electromechanicaldevice which converts electrical pulses intodiscrete mechanical movements. The shaftor spindle of a stepper motor rotates indiscrete step increments when electricalcommand pulses are applied to it in theproper sequence. Assignment-detailed working &applications-servo , synchro, stepper motors(PM, VR,Tacho generator)

CONTROL VALVES

COMPONENTS – CONTROL VALVES

FILTERS &SEALS

PNEUMATIC INSTRUMENTATION

PNEUMATIC RELAYS

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.

Pneumatic Relays

ACTUATING VALVES

CYLINDERS

CONTROLLERS

A CONTROLLER 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

PRINCIPLES OF OPERATION 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.

COMPARISON BETWEEN MICROPROCESSOR AND MICROCONTROLLER

Dicussion-applications,advantages, diadvantages,comparison

PID CONTROL(PROPORTIONAL–INTEGRAL–

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

PROPORTIONAL (P) 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 (I) 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 (D) 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

PID CONTROLLER The proportional, integral, and

derivative terms are summed to calculate the output of the PID controller.

FINAL FORM OF THE PID ALGORITHM IS

(MV)=manipulated variable

HYDRAULIC PID CONTROLLER

ELECTRONIC PID CONTROLLER

AUTO-TUNING 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.

DISTRIBUTED CONTROL SYSTEM(DCS)

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

DISTRIBUTED CONTROL SYSTEM(DCS)

PROCESSFinalcontrolelement

Dataacquisition

MainComputer

Display

SCADA

SCADA –MIMIC DIAGRAM

SCADA (SUPERVISORY CONTROL AND DATA ACQUISITION)   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. 

APPLICATIONS 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.

SUBSYSTEMS: 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

SCADA ARCHITECTURES

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