Example of Question

Question :

1) Sebuah pengawal pneumatik jenis berkadaran digunakan untuk mengawal suhu dalam proses melebur. Suhu titik set ialah 750 Celsius dan julat ralat suhu ialah 0 - 1000 Celcius. Ruang berkadaran ditentukan pada 15 %. Julat keluaran tekanan dari pengawal ialah 20 - 100 KN/m^2 dan nilai keluaran tekanan meningkat bila suhuh meningkat. Jika nilai keluaran tekanan diset pada 60 KN/m^2 untuk titik set suhu, cari :

a) Nilai suhu untuk keluaran tekanan 20 KN/m^2

b) Nilai suhu untuk keluaran tekanan 100 KN/m^2

c) Nilai tekanan bila suhu 735 Celcius


Answer :

a)              P = 200 KN/m^2    ,    P = 0 %
               
                 P(t) = Kp Ep + P(0)  ,      Kp =  100
                                                                 PB
                 P(t) = 100 Ep + 50                 =  100
                           15                                    15
           
                    0  = 100 Ep + 50
                            15

            100 Ep =  0 - 50
             15

                   Ep =  -50  x 15
                            100
                   
                   Ep = 7.5 %


             E = SP - mv   x 100 %
                      range

         - 7.5 = 750 - mv   x 100 %
                    1000 - 0

           -7.5 ( 1000 )  = 750 - mv
                 100
           
                       -75 = 750 - mv
                     
                        mv = 750 + 75

                             = 825 Celcius


b)          P = 100 KN/m^2    ,    P = 100 %
               
                 P(t) = Kp Ep + P(0)  ,      Kp =  100
                                                                    PB
                 P(t) = 100 Ep + 50                 =  100
                            15                                   15
           
                100  = 100 Ep + 50
                           15

            100 Ep =  100 - 50
             15

                   Ep =  50  x 15
                            100
                   
                   Ep = 7.5 %

                   E = SP - mv  x 100 %
                           range

                7.5  = 750 - mv   x 100 %
                             1000

         7.5 ( 1000 ) = 750 -  mv
               100

                75 = 750 - mv

                mv = 750 - 75

                      = 675 Celcius


c)                  Ep = SP - mv  x 100 %
                               range

                     P(t) = 750 - 735   x 100 %
                                  1000

                     Ep = 1.5 %

                     P(t) = Kp Ep + P (0)
                         
                            = 100  (1.5) + 50
                                15

                             = 60 %

                         P = mv - min  x 100 %
                               max- min
                       
                        60 = mv - 20  x 100 %
                               100 - 20

              60 ( 80 ) = mv - 20
                 100

                      48   = mv - 20

                     mv   = 48 +  20

                     mv = 68

                       

CONTROLLER PRINCIPLE

Block diagram :-

Definition :- Use material handling activities to improve control of production,                                      inventory and other handling

Examples of Block diagram

Formula in controller principle :-

• Controller output in % = current output - minimum output     x 100 %
                                        maximum output - minimum output

• Measured value in % = mv - minimum mv      x 100 %
                                        max mv - min mv 

• Set point % =      SP - min value           x 100 %
                        max value - min value

• Error % =             SP - MV                X 100 %                                    max value - min value

ON-OFF CONTROL

* The controller output swing betwwen 0% and 100% but an additional hysteresis element (neutral zone)

Formula

• Positive error band = max permissible positive error   x 100 %
                                                  temp. range

• Negative error band = max permissible negative error   x 100 %
                                                 temp range

• Proportional Band =                                 100                          
                                                    proportional gain (KP)

• Controller output, P =     Kp Ep + P(0)

• Proportional controller , E  =  SP - MV ,    P(t) = Kp Ep + P(0)

BASIC ELEMENT IN CONTROL SYSTEM

3) BASIC ELEMENT IN CONTROL PROCESS

please click on this link :

http://staff.fit.ac.cy/eng.os/LectureC2_AMEM326.pdf

AUTOMATIC CONTROL SYSTEM

5) AUTOMATIC CONTROL SYSTEM

An  automatic  control  system  is  a  preset  closed-loop  control  system  that  requires  no  operator action.    This  assumes  the  process  remains  in  the  normal range  for  the  control  system. An automatic control system has two process variables associated with it:  a controlled variable and a manipulated variable.

A controlled variable is the process variable that is maintained at a specified value or within a specified range.In the previous example, the storage tank level is the controlled variable.

 A manipulated variable is the process variable that is acted on by the control system to maintain the  controlled  variable  at  the  specified  value  or  within  the  specified  range. In  the  previous example, the flow rate of the water supplied to the tank is the manipulated variable.

Functions of Automatic Control

In any automatic control system, the four basic functions that occur are:

• Measurement

• Comparison

• Computation

• Correction

                               An automatic system


Advantages : 

• Precision
• High in speed
• Recovery time
• High efficiency
• Repeatibility
• Safety

Disadvantages :

• Strong technical knowledge to design well
• More attention to safety 
• High in maintenance

TERM USED IN CONTROL SYSTEM PROCESS

2)TERM OF PROCESS CONTROL :

• Process variable - The actual value in the control loop, temperature, pressure, flow, composition, pH, etc

• Set point - The set point is the desired value of the process variable

• Error - In the control loop the error = set point - process value

• Controller - Output signal from the controller.

• Measurement - Measurement is the same as the process value.

• Alternating Current - Electrical current that reverses its direction of flow at regular intervals

• Calibration - The comparison of a measuring device (an unknown) against an equal or better standard

• Delay - A term commonly used in stead of dead time

• Deviation - Any departure from a desired or expected process value

• Mode - The controller can be set in auto, manual, or remote mode

OPEN LOOP & CLOSE LOOP AND BASICS ELEMENT OF CONTROL SYSTEM

4) OPEN LOOP SYSTEM & SCHEMATIC DIAGRAM


Definition:An open-loop controller, also called a non-feedback controller, is a type of controller that computes its input into a system using only the current state and its model of the system. An open-loop controller is often used in simple processes because of its simplicity and low cost, especially in systems where feedback is not critical. A typical example would be a conventional washing machine, for which the length of machine wash time is entirely dependent on the judgment and estimation of the human operator

An open loop system

CLOSED LOOP SYSTEM & SCHEMATIC DIAGRAM

Definition:

A type of control system that automatically changes the output based on the difference the feedback signal to the input signal. 

A closed loop system

INTRODUCTION TO CONTROL SYSTEM

CONTROL SYSTEM ENGINEERING

INTRODUCTION
Control engineering is based on the foundations of feedback theory and linear system analysis, and it generates the concepts of network theory and communication theory. Accordingly, control engineering is not limited to any engineering discipline but is applicable to  aeronautical, chemical, mechanical, environmental, civil, and electrical engineering. A control system is an interconnection of components forming a system configuration that will provide a desired system response.

A control system is a device, or set of devices, that manages, commands, directs or regulates the behavior of other device(s) or system(s). Industrial control systems are used in industrial production.

There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls. There is also fuzzy logic, which attempts to combine some of the design simplicity of logic with the utility of linear control. Some devices or systems are inherently not controllable.

A control system is a system by virtue of which any quantity or condition (called controlled variable) of interest of a machine, mechanicsm or equipment can be controlled as per desire. Usually, the system has a command signal applied at the input and the controlled variable exhibited at the output. For example, the force applied on to an accelerator pedal causes the speed of the engine vehicle to increase. Here, force is the command signal and the speed of the engine is the controlled variable.

The term "control system" may be applied to the essentially manual controls that allow an operator, for example, to close and open a hydraulic press, perhaps including logic so that it cannot be moved unless safety guards are in place.

CONTENT

• Electrical - Electrical Control Systems specializes in the design and manufacture of high quality industrial control systems and offer innovative and practical solutions to all your automation requirements ranging from simple MCC and dedicated controller applications, to networked PLC and SCADA systems.

• Pneumatics - Pneumatic systems are used extensively in industry, and factories are commonly plumbed with compressed air or compressed inert gases. This is because a centrally located and electrically powered compressor that powers cylinders and other pneumatic devices through solenoid valves can often provide motive power in a cheaper, safer, more flexible, and more reliable way than a large number of electric motors and actuators. Pneumatics also has applications in dentistry, construction, mining, and other areas.

          They have two main advantages and disadvantages of pneumatics :

1. Advantages	Disadvantages
   Reliable and economical actuators	Good maintenance is required.
   Flexible and modular control components	Building monitoring is limited

Pneumatic circuit.

• Hydraulics -  A hydraulic drive system is a drive or transmission system that uses pressurized hydraulic fluid to drive hydraulic machinery. The term hydrostatic refers to the transfer of energy from flow and pressure, not from the kinetic energy of the flow.
  A hydraulic drive system consists of three parts: The generator (e.g. a hydraulic pump), driven by an electric motor, a combustion engine or a windmill; valves, filters, piping etc. (to guide and control the system); the motor (e.g. a hydraulic motor or hydraulic cylinder) to drive the machinery.
  Many types of equipment rely on some form of hydraulic control system, including aircraftand aerospace vessels. Marine vessels and elevators also use these types of controls, as do hydraulic cranes. Cars and trucks typically contain hydraulic brake systems, and a variety of industrial and manufacturing machines also rely on these controls for safe and effective operation. 
  Hydraulic control systems can influence the motion or operation of a machine in several ways. The most basic involves manual control, where a human or robotic users flips a switch, pulls a lever or turns a steering wheel. This motion drives hydraulic fluid throughout the system to accomplish the desired action. Other systems rely on automatic controls rather than manual input. For example, a sensor on a crane may detect heavy loads and automatically send extra fluid towards the crane's lifting system. This fluid in turn creates excess lifting power to safely move the heavy load. Similar systems rely on pressure sensors, electronic eyes, and a variety of additional inputs.
  
  
  They have two main advantages and disadvantages of hydraulics :
  
  

  Advantages	Disadvantages
  It uses 'incompressible' fluid which results in a greater, more efficient & consistent work or power output. This is due to the fact that hydraulic fluid molecules are able to resist compression under heavy load hence minimal energy loss is experienced and work applied is directly transferred to the actuating surfaces.	Hydraulic fluid is highly corrosive to most of the aircraft materials.
  As opposed to pneumatic system which uses air, a leakage in a hydraulic system is easier to spot during ground maintenance operations.	Due to the heavy loads experienced in a typical hydraulic system, structural integrity is a must which also means higher structural weight for the aircraft in addition to the weight of its hydraulic lines, pumps, reservoirs, filters, & etc.
  Hydraulic fluid operates very well in a very hot working environment, it is able to sustain its airworthiness viscosity, density & fluid temperature even if it subjected under extreme heat. This is specially important on aircraft structures that is abundant of hot working conditions during flight operations	Hydraulic system is susceptible to contaminations & foreign object damage (FOD).
  	If disposed improperly, a hydraulic fluid is an environmental risk.

hydraulic system