class 39 final control elements - actuators

ICE401: PROCESS INSTRUMENTATION

AND CONTROL

Class 39

Final Control Elements - Actuators

Dr. S. Meenatchisundaram

Email: [email protected]

Process Instrumentation and Control (ICE 401)

Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

Actuators:



• Actuators are devices used to produce action or motion.

• Input (mainly electrical signal, air, fluids)

• Electrical signal can be low power or high power.

• Actuators output can be position or rate i. e. linear displacement or

velocity. Actuation can be from few microns to few meters.

Classification of Actuators:



Type of motion

Linear Rotary

Type of medium

Hydraulic pneumaticelectrical

ACTUATORS

Actuators:



• Linear actuator: solenoid, Hydraulic/Pneumatic.

• Rotary actuator: motor, Hydraulic/Pneumatic.

• A solenoid is a coil wound into a tightly packed helix.

• In physics, the term solenoid refers to a long, thin loop of wire, and

wrapped around a metallic core.

• Which produces a magnetic field when an electric current is passed

through it.

Solenoid Controlled Valves:



Hydraulic Actuators:



• Hydraulic Actuators are used in industrial process control, employ

hydraulic pressure to drive an output member.

• Principle: Pascal’s Law

“Pressure exerted anywhere in a confined incompressible fluid is

transmitted equally in all directions throughout the fluid, acts upon

every part of the confining vessel at right angles to its interior

surfaces”.

• F = PxA

Hydraulic Actuators:



Working of Hydraulic Actuators:



• Α directional control valve controls the direction of oil flow in the

system and, therefore, the direction of motion of the cylinder piston.

• The valve has four ports, labelled Ρ, Τ, Α, and Β. Ρ and Τ stand for

pressure and tank (or reservoir), and Α and Β are output ports. The

valve can be operated in three different positions.




• The oil from the pump flows through path Ρ-Α of the valve to the

upper end of the cylinder.

• The oil pushes the piston downward, which lowers the attached load.

At the same time, the oil at the lower end of the cylinder flows back to

the reservoir through path Β-Τ of the directional control valve.




• When the directional control valve lever is released, the valve

automatically returns to the center (neutral) position.

• In this position, all four ports are blocked and oil cannot escape from

either side of the cylinder. This stops the movement of the piston and

causes oil to flow from the pump back to the reservoir through the

pressure relief valve.

Rotary Hydraulic Actuators:



Pneumatic Actuators:



• A pneumatic actuator converts energy (typically in the form

of compressed Air) into motion. The motion can be rotary or linear,

depending on the type of actuator.

• A Pneumatic actuator mainly consists of a piston, a cylinder, and

valves or ports.

• Pneumatic systems are very common, and have much in common with

hydraulic systems with a few key differences.

Working of Pneumatic Actuators:



• Pneumatic actuators are generally relatively simplistic and depend on

their own ability to convert potential energy into kinetic energy.

Constructional Features of Pneumatic

Cylinders:



Hydraulic & pneumatic actuators: Cylinders



Electrical Actuators:



• Electric motors are the most common source of torque for mobility

and/or manipulation in machines.

• The physical principle of all electric motors is that when an electric

current is passed through a conductor (usually a coil of wire) placed

within a magnetic field, a force is exerted on the wire causing it to

move.

Components of An Electric Motor:



• The principle components of an electric motor are:

• North and south magnetic poles to provide a strong magnetic field.

Being made of bulky ferrous material they traditionally form the outer

casing of the motor and collectively form the stator

• An armature, which is a cylindrical ferrous core rotating within the

stator and carries a large number of windings made from one or more

conductors.

• A commutator, which rotates with the armature and consists of copper

contacts attached to the end of the windings

• Brushes in fixed positions and in contact with the rotating commutator

contacts. They carry direct current to the coils, resulting in the required

motion.

class 39 final control elements - actuators

Engineering