OPEN AND CLOSE LOOP

Open-Loop Control Systems.
Those systems in which the output has noeffect on the control action are called open-loop control systems

Closed-Loop Control Systems.

Feedback control systems are often referred to as closed-loop control systems.In a closed-loop control system the actuating error signal, which is the difference between the input signal and the feedback signal(which may be the output signal itself or a function of the output signal and its derivatives and/or integrals), is fed to the controller so as to reduce the error and bring the output of the system to a desired value.

CLOSED-LOOP CONTROL SYSTEM

Advantages of Open Loop

Simple construction and ease of maintenance.

• Less expensive than a corresponding closed-loop system.
• There is no stability problem.
• Convenient when output is hard to measure or measuring the output precisely is economically not feasible.

Disadvantages of Open Loop

• Disturbances and changes in calibration cause errors,and the output may be different from what is desired.
• To maintain the required quality in the output,recalibration is necessary from time to time.
• They are less accurate.
• If external disturbances are present, output differs significantly from the desired value.

TERMS USED IN CONTROL PROCESS

• Variable Process - proses pembolehubah
• Servo Controlled -pengawal serbo
• Feedback             -suap balik
• Process                -proses
• Set Point              -titik mula
• Error                    -ralat
• Controller            -pengawal
• Measurement      -pengukuran