Electrical control system
In generally electrical control system is a control system which uses electric current whether direct current (DC) or alternating current as supply source. In other words it can be describe as Kirchoff's Circuit Law. Kirchoff's Circuit Law can be divided into two that is:
Kirchoffs First Law – The Current Law, (KCL)
-It states that the “total current or charge entering a junction or node is exactly equal to the charge leaving the node as it has no other place to go except to leave, as no charge is lost within the node“.
-In other words , I(entering) + I(entering) = 0. It also know as Conservation of Charge.
Kirchoffs Second Law – The Voltage Law, (KVL)
-It states that “in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop” which is also equal to zero.
-In other words the algebraic sum of all voltages within the loop must be equal to zero. It also know as Conservation of Energy.
Pneumatic control system
Pneumatic control system is a system which uses air that in compress to generate force / energy
to carry out work. Pneumatic system many in find out in system industrial like food industry, petrochemical and industry which uses robotics.Generally pneumatic system need:
-Air supply is compressed
-Control valve
-Tube link
-Transducer induce
The pneumatic control system can be handled human and automatic.
Advantages of pneumatic systems
Pneumatic control system is a system which uses air that in compress to generate force / energy
to carry out work. Pneumatic system many in find out in system industrial like food industry, petrochemical and industry which uses robotics.Generally pneumatic system need:
-Air supply is compressed
-Control valve
-Tube link
-Transducer induce
The pneumatic control system can be handled human and automatic.
Advantages of pneumatic systems
-Infinite availability of the source
air is available in the world around us in unlimited quantities at all times and places.
-Easy channeled
easily passed or move from one place to another through a pipe.
-Temperature is flexible
even in quite extreme conditions, the air was still able to work.
-Safe
air can be loaded more safely than it is not flammable and does not short circuit occurs or explode.
-Clean
air around us are tend to clean without chemicals that are harmful, and also, it can be minimized or cleaned with some processes.
-Can be stored
air can be stored through the seat tube fed excess air pressure.
Disadvantages of pneumatic systems
-Requires installation of air-producing equipment
air should be well prepared to meet the requirements such as dry, clean, and contain the necessary lubricant for pneumatic equipment. Therefore require installation of pneumatic systems are relatively expensive equipment, such as compressors, air filter, lube tube, dryer, regulators.
-Easy to leak
pressurized air is like to always occupy the empty space and the air pressure is high.Therefore we need a seal so that air does not leak. Seal leakage can cause energy loss.
pressurized air is like to always occupy the empty space and the air pressure is high.Therefore we need a seal so that air does not leak. Seal leakage can cause energy loss.
-Potential noise
pneumatic using open system, meaning that the air that has been used will be thrown out of the system, the air comes out pretty loud and noisy so will cause noise
pneumatic using open system, meaning that the air that has been used will be thrown out of the system, the air comes out pretty loud and noisy so will cause noise
-Easy condenses
pressurized air is easily condensed, so before entering the system must be processed first in order to meet certain requirements, such as dry, have enough pressure, and contains a small amount of lubricant to reduce friction in the valves and actuators.
pressurized air is easily condensed, so before entering the system must be processed first in order to meet certain requirements, such as dry, have enough pressure, and contains a small amount of lubricant to reduce friction in the valves and actuators.
Hydraulic control system
Hydraulic control system is a system which uses fluid to generate force / energy to carry out work
Hydraulic system many in use in automobile industry like power system, system brake, crane,
jack car,satellite and so on. Fluid that commonly used is oil.Generally hydraulic system need :
-Supply fluid is Hydraulic
-Control valve
-Cylinder
The hydraulic control system can be handled human and automatic.
Car hydraulic jack
Backholes
Advantages of hydraulic systems
-Large load capacity with almost high accuracy and precision.
-Smooth movement.
-Automatic lubricating provision to reduce to wear.
-Division and distribution of hydraulic force are easily performed.
-Limiting and balancing of hydraulic forces are easily performed.
Disadvantages of hydraulic systems
-A hydraulic element needs to be machined to a high degree of precision.
-Leakage of hydraulic oil poses a problem to hydraulic operators.
-Special treatment is needed to protect them from rust, corrosion, dirt etc.,
-Hydraulic oil may pose problems if it disintegrates due to aging and chemical deterioration.
-Hydraulic oils are messy and almost highly flammable.
General Term used in Process Control
In this section we will give focus on terms that commonly used process control.
-System : An interconnection of elements and devices for a desired purpose.
-Process : The device, plant, or system under control.
-Feedback control system: Feedback control system where product always compared with entry set point and difference between value made foundation for control.
-Servo control : Servo control is a feedback control system where the product is position,
velocity or acceleration.
-Dynamic variable : Dynamic variable is physical any parameter that variable the value
spontaneously or through external influences.
-Error signal : Difference between entry signal and feedback signal/product.
-Process compound variable :Process compound variable is process which contains
more than one variable.
-Controller : Device which control process certain system and acts against error
signal to reduce error to product like is wanted.
Basic Process of Control System
Level control of Tank
-A level transmitter (LT), a level controller (LC), and a control valve (LV) are used to control the liquid level in a process tank.
-The purpose is to maintain the liquid level at some prescribed height (H) above the bottom of the tank.It is assumed that the rate of flow into the tank is random.
-The level transmitter is a device that measures the fluid level in the tank and converts it into a useful measurement signal, which is sent to a level controller.
-The level controller evaluates the measurement, compares it with a desired set point (SP), and produces a series of corrective action that are sent to the control valve.
-The valve controls the flow of fluid in the outlet pipe to maintain a level in the tank.
Process Temperature Control
-To control a dynamic variable in a process, must have information about the entry or variable itself.This information is obtained by measuring the variable.
-Measurement refers to the conversion of the process variable into an analog or digital signal that
can be used by the control system.
-The device that performs the initial measurement is called a sensor or instrument.
-Typically measurements are pressure, level, temperature, flow , position and speed.
-The result of any measurement is the conversion of a dynamic variable into some proportional
information that is required by the other elements in the process control loop or sequences.
Evaluation
- In the evaluation step of the process control sequences, the measurement value is examined,
compared with the desired value or set point, and the amount of corrective action needed to maintain
proper control is determined.
-A device called a controller can be pneumatic, electronic or mechanical device mounted in a
control panel or on the process equipment.
-It can also be part of a computer control.
-System, in which case the control function is performed by software.
Control element
-The control element in a control loop is the device that exerts a direct influence on the process or manufacturing sequence.
-This final control element accepts an input from the controller and transforms it into some proportional operation that is performed on the process.
-In most cases, this final control element will be a control valve that adjusts the flow of fluid in a process.
-Devices such as electrical motors, pumps, and dampers also used as control elements.
Type of Control Systems
There are various types of control system but all of them are created to control outputs. The system used for controlling the position, velocity, acceleration, temperature, pressure, voltage and current etc.
A control system in which the control action is totally independent of output of the system then it is called open loop control system. Manual control system is also an open loop control system. Fig - 1 shows the block diagram of open loop control system in which process output is totally independent of controller action.
Practical Examples of Open Loop Control System
-Electric Hand Drier
Hot air (output) comes out as long as you keep your hand under the machine, irrespective of how much your hand is dried.
-Automatic Washing Machine
This machine runs according to the pre-set time irrespective of washing is completed or not.
-Bread Toaster
This machine runs as per adjusted time irrespective of toasting is completed or not.
-Automatic Tea/Coffee Maker
These machines also function for pre adjusted time only.
-Timer Based Clothes Drier
This machine dries wet clothes for pre – adjusted time, it does not matter how much the clothes are dried.
-Light Switch
Lamps glow whenever light switch is on irrespective of light is required or not.
-Volume on Stereo System
Volume is adjusted manually irrespective of output volume level.
Advantages of Open Loop Control System
-Simple in construction and design.
-Economical.
-Easy to maintain.
-Generally stable.
-Convenient to use as output is difficult to measure.
Disadvantages of Open Loop Control System
-They are inaccurate.
-They are unreliable.
-Any change in output cannot be corrected automatically.
Closed Loop Control System
Control system in which the output has an effect on the input quantity in such a manner that the input quantity will adjust itself based on the output generated is called closed loop control system. Open loop control system can be converted in to closed loop control system by providing a feedback. This feedback automatically makes the suitable changes in the output due to external disturbance. In this way closed loop control system is called automatic control system. Figure below shows the block diagram of closed loop control system in which feedback is taken from output and fed in to input.
Practical Examples of Closed Loop Control System
-Automatic Electric Iron
Heating elements are controlled by output temperature of the iron.
-Servo Voltage Stabilizer
Voltage controller operates depending upon output voltage of the system.
-Water Level Controller
Input water is controlled by water level of the reservoir.
-Missile Launched & Auto Tracked by Radar
The direction of missile is controlled by comparing the target and position of the missile.
-An Air Conditioner
An air conditioner functions depending upon the temperature of the room.
-Cooling System in Car
It operates depending upon the temperature which it controls.
Advantages of Closed Loop Control System
-Closed loop control systems are more accurate even in the presence of non-linearity.
-Highly accurate as any error arising is corrected due to presence of feedback signal.
-Bandwidth range is large.
-Facilitates automation.
-The sensitivity of system may be made small to make system more stable.
-This system is less affected by noise.
Disadvantages of Closed Loop Control System
-They are costlier.
-They are complicated to design.
-Required more maintenance.
-Feedback leads to oscillatory response.
-Overall gain is reduced due to presence of feedback.
-Stability is the major problem and more care is needed to design a stable closed loop system.
