Introduction of Control System
Example of the OPEN LOOP CONTROL SYSTEM
The control system is define as that it is the control the system but first of all we have discussed about the control system.we know that control system is very important for all engineers. Do you know the first significant control device was JAMES WATT FLYBALL GOVERNER. This was invented in 1767 to keep the speed of the engine constant by regulating the supply of the steam to the engine. The behavior of the system in the control system is described by the differential equation. Do You know that the Minorsky, in the 1922 showed that how to determine the stability from the differential equations describing the system. The differential equation may be ordinary differential equation or the difference equation. in the engineering the control system is describe in two types or control system can be classified into two types . first is open loop control system and another is closed loop control system. see below we have describe in detail what is open loop control system and what is closed loop control system
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Two type of control system.
1:- Open Loop Control System
2:- Close Loop Control System.
1. OPEN LOOP CONTROL SYSTEM
The open loop control system is define as that the open loop control system is also known as control system without feedback or not feedback or no any feedback control system. In the open loop control system the open loop systems the control action is independent of the desired output. In the system the output is not compared with the reference input. The component of the open loop control system are controller and controlled process. But what is controller? so in the definition form, the controller is define as that it may be amplifier, filter etc. depends upon the system. An input is applied to the controller and the controlled process find we get the output.
1:- Immersion rod is the example of the open loop control system. Immersion rod is used at home for convert the cold water into hot water in other word this is used for increase the water temperature. The rod heats the water but how much heating is required is not sense by road because of no feedback to the rod.
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2:- Automatic washing machine is the second example of the open loop control system. we know that washing machine is the use for washing the cloth and it has mostly used in the home. In the machine the operating time is set manually. After the completion of set time the machine will stop, with the result . we may or may not get the desired output or amount of cleanest of washed cloth because in the machine no any feedback is provide too the machine for the desired output.
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3:- The another example of the open loop control system is a field control D.C. motor. We know that motor is the most important for the daily life. and most important electrical equipment.
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4:- For automatic control of traffic the lamps of three different colour , red, yelllow and green are used. The time for each lamp is fixed, the operation of each lamp does not depend upon the density of the traffic but depend upon the fixed time. finally we can say that the control system which operates on the time basis is open loop system.
ADVANTAGE OF THE OPEN LOOP CONTROL SYSTEM
- In the open loop control system the open loop control system are the very simple
- In the open loop control system the less maintenance is required and it has easy that mean not difficult.
- In the open loop control the proper calibration is not a problem.
- In the open loop control system the open loop control system are economical.
DISADVANTAGE OF THE OPEN LOOP CONTROL SYSTEM
- In the control system it is slow.
- In this open loop control system the optimization is not possible.
- These are not reliable that mean open loop control system are not reliable.
- Open loop control system are inaccurate.
2. CLOSE LOOP CONTROL SYSTEM
The control system is define as that the closed loop control are also known as feedback control system .In the closed loop control system the the control action is totally depend on the output. If any control system having one or more feedback paths forming a closed loop control system. In the control system or in the close loop control system the output is compared with the reference input and error signal is produced . The error signal is fed to the controller to reduce the error and desired output is obtain.
The close loop control system are reliable. but it has difficult to build. they are accurate because of feedback. these are less stable .and closed loop control system are optimization is possible.
EXAMPLE OF OPEN LOOP AND FEED CONTROL SYSTEM
In the open loop system, there is no measurement of the output that mean the controlled variable and its comparison with the desired input while in a closed loop system, the actual value of the variable being controlled is measure and compared with the desired value, and action is taken to eliminate the error. The measure and compared are also known as feedback system. the functional element of such system may be represented by block diagram as shown in figure. another example of the open loop control system see below.
In the input variable is voltage v applied to a D.C, motor. A change in the value of "v" can change the value of speed "n", similarly a change in the valve position "x" would be change the flow of rate of the fluid, thereby changing the output variable viz speed "n" the open loop control system of a machine tool table using a stepping motor. In all the above cases, there is no measurement of the output controlled variable and its compression with the desired value . further a change in the load variable on the system may change the output variable and there is no such feedback and control action in the system.
onward show some example of the closed loop system. a system for speed control of a turbo-generator system, with a centrifugal governor, sensing any speed change which may occur say due to load changes. The governor operates a hydraulic amplifier which supplies energy to operate a control valve, which regulates the steam flow from the boiler to the turbine, thereby changing the speed n to the desired valve n, The system may be represented y a block diagram, with various elements as show.
A simple level control system , with the controlled variable being level "h" in the tank. This seemed by a float , which through a level arrangement controls the valve position regulating fluid in flow to the tank. The Change in the level in the tank may be as desired according to the setting of output level, or may accouter duo to any change on the output side. A block diagram of the system is also shown.
A closed loop control system as used for robot control, using a digital computer. A typical robot show below. each rotation is controlled by a separate closed loop system for which block diagram is also see in diagram.
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