INTRODUCTION TO CONTROL SYSTEM

What is that control system?

Control system is tool or a sets of instruments which manage, order or control arrange behaviour of certain implements others. There is two type control system, namely logic gate and feedback control or linear.

Control system types.

There is THREE type control system that based on supply source.Systems are as follows: 

i. Control system is pneumatic.
ii. Control system is hydraulic.
iii. Control system electric.

i. 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. These systems may be represented by diagram basic block in figure 1.5a and figure 1.5b.

ii. 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. These systems may be represented by diagram basic block in Rajah 1.6a and figure 1.6b.

iii. Electric control system Electric control system is a control system which uses electric current whether direct current (AT) or current shuttle as supply source.Generally  Electric Control System requires:

• Electricity supply (AT) or (DC)
• Element entry (switch, sensor, valve,electronic component)
• Element product (Motor, light and so on)
• Connector cable

Electric Control System can be handled human and automatic. These systems may be represented by diagram basic block in figure 1.7a and figure 1.7b.

Term used in process control

In this section we will give focus on terms that commonly used inprocess 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 is a 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 element

proses level control

1. A level transmitter (LT), a level controller (LC), and a control valve (LV) are used to control the liquid level in a process tank.
2. 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.
3. 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.
4. The level controller evaluates the measurement, compares it wiyh a desired set point (SP), and produces a series of corrective action that are sent to the control valve.
5. The valve controls the flow of fluid in the outlet pipe to maintain a level in the tank.

process temperature control

Measurement

1. To control a dynamic variable in a process, must have information about the entiry or variable itself.This information is obtained by measuring the variable.
2. Measurement refers to the conversion of the process variable into an analog or gigital signal that can be used by the control system.
3. The device that performs the initial measurement is called a sensor or instrument.
4. Typically measurements are pressure, level, temperature, flow , position and speed.
5. 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

1. In the evaluation step of the process control sequences, the measurement value is examined, comparedwith the desired value  or set point, and the amount of corrective action needed to maintain proper control is determined.
2. A device called a controlle can be pneumatic, electronic or mechanical device mounted in a control panel or on the process equipment.
3. It can also be part of a computer control.
4. System, in which case the control function is performed by software.

Control element

1. The control element in a control loop is the device that exerts a direct influence on the process or manufacuring sequence.
2. This final control element accepts an input from the controller and transforms it into some proportional operation that is performed on the process.
3. in most cases, this final control element will be a control valve that adjusts the flow of fluid in a process.
4. Devices such as electrical motors, pumps, and dampers also used as control elements.

Two types of control systems

1. open loop

• no feedback
• difficult to control output with accuracy
• a common example of an open- loop control system is an electric toaster in he kitchen.

2. close loop

• must have feedback
• must have sensor on output
• almost always negative feedback

http://www.youtube.com/watch?v=YlmRa-9zDF8