Tuesday, 16 December 2014

Introduction to Control System

What is that control system?

Control system is tool or a sets of instruments which manageorder or control arrange behaviour of certain implements othersThere 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 workPneumatic 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
ii. Hydraulic Application

Constant pressure pumping system
  • to guarantee a regular flow from source to destiny, tyring to hold always a constant preasure
Hydro pneumatic system
  • in this system water pump from the supply system into a preasure tankfor storage. 
  • air in the tank compress by the water entering the tank.
  • as the pressure in the tank increase, preasure in the water distribution system also increase. 

Use of Hydraulic System...
i)  Power steering and braking systems on vehicles 
ii) The mechanism driving driving the big ships
iii) Machine Control System 


a) Hydraulic fluid acts as a lubricant, in addition to the thermal carrier
b) Small hydraulic actuator but can build a large force or torque
c) Hydraulic mover with speed higher response to start, stop and reverse speed fast
d) Hydraulic actuators can be operated in continuous, intermittent and flip
e) Speed drops when the load is small given the low leakage in the actuator


a) Hydraulic power is not easily available compared to the electric power
b) The cost of the hydraulic system is higher than the electrival system to             function similar
c) Fire and explosion hazard unless the use of fluid fuels used
d) Contaminated oil can cause the hydraulic system can't function properly
e) The system is easy to be stringy because of the difficulty in maintaning the hydraulic system free of leaks
Prosess Control
Three main factors or term:
  • Manipulated variables
  • Disturbances
  • Control Variables
i. Controlled Variables
  • Quantify the performance or quality to the final product, which are also called output variables.
 ii. Manipulated Variables
  • adjusted dynamically to keep the controlled variables at their set-points. 
Servo Control
  • change and the manipulated variables is adjusted appropriately to achieve the new operating conditions.
Regulatory Control
  • fix at a constant value. 
  • when any disturbance enters the system the manipulated variables adjust to drive the controlled variable back to its fixed set-point.
  • consist of an assembly of equipment and material that is related to some manufacturing operation or sequence.
  • conversation of the prosess variable into an analog or digital signal that can be use 
  • device (sensor/instrument)

    Basic Process Control System


    •  Illustrates the essential elements of a process.
    • A levell 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 tank. Assume that the rate of flow into the tank is random.
    • The level transmitter is a devices that measures the fluid level in the tank and convert it into a useful measurement signal, sent to a level controller.
    • Level controller evaluates the measurement compares it with a desired set point (SP) and produces a series of corrective actions 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

    Control Element
    • To control a dynamic variable in a process, must have information about the entity 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.
    • Typical 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 sequence.

    • Step of the process control sequence, 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.    
    • controller, the device performs this evaluation. The controller can be a pneumatic, electronic, or mechanical device mounted in a control panel or on the process equipment.
    • it can be also part of a computer control.
    • system, in which case the control function is performed by software.
    •  device that exerts a direct influence on the process of 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.
    • This final control element will be a control valve that adjust the flow of fluid I a process.
    •  devices such as electrical motors, pumps and dampers are also used as control elements.

    The Purpose and use of Open Loop
    • Controlled directly, and only by an input signal.
    • the basic unit of this type consist only of an amplifier and a motor.
    • the amplifier receives a low-level input signal and amlifies it enough to drive the motor to perform the desired job.
    • the output of the amplifier is proportional to the amplitude of the input signal.
    • the phase ( ac system) and polarity (dc system) of the input signal determines te direction that the motor shaft will turn.
    • after amplification, the input signal is fed to the motor, which moves the output shaft (load) in the direction that corresponds with the input signal.
    • the motor will not stop driving the output shaft until the input signal is reduced to zero or removed.
    The Purpose and use of Closed Loop
    • to compare the actual output with the desired output response.
    • a feedback control system is a control system that tends to maintain a prescribed relationship of on system variable to another.
    • a feedback control system uses a function of a prescribed relationship between the output and reference input to control the process.
    • difference between the of the process under control and the reference input is amplified and used to control the process that the difference is continually reduced.
    • the feedback concept has been the foundation for control system analysis and design.
    Open Loop System characteristic

    The accuracy of the open loop system depends upon the calibration of the gains and prior knowledge of the distribance.