Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved OBJECTIVES: By the end of this chapter, you should be able to:- Explain the meaning of open loop control.Explain the meaning of open loop control. Understand the basic concept of open loop control.Understand the basic concept of open loop control. Name the type of open loop control.Name the type of open loop control. Give an example of an open loop control system.Give an example of an open loop control system. Draw a signal flow diagram of the open loop control system.Draw a signal flow diagram of the open loop control system.

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved OVERVIEW

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved DEFINITION O/L PROCESS InputOutput One direction system (SISO) Output variables are influence directly by input variables A signal path without feedback Output remain constant for a constant input Output is directly proportional to input and any change in input will change output accordingly

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved SISO Process Control

Industrial Electronic Department 6 Turntable Speed Control -Open Loop Control The system uses a battery source to provide a voltage that is proportional to the desired speed. This voltage is amplified and applied to the motor.

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved TYPE OF OPEN LOOP CONTROL OPEN LOOP CONTROL SYSTEMS Program Control Holding Element Control Sequence Control Path Pattern Control Time-Schedule Control Command Control Light Dimmer Light Bulb with start and stop button Plate cams rotate at constant speed Cam shaft of a machine tool Filling and capping system

TYPE OF OPEN LOOP CONTROL  Command control There is a direct connection between the command variable and the output variable of the control system, eg: switch on/off the lamp  Holding element control When the command variable is removed or withdrawn, the value of the variable obtained is preserved. Only when the opposing signal of a different kind or when an opposing command variable or a command variable of different kind appear, the output variable brought back to starting value.  Programmed control 1. Time schedule- command variable is supplied by a time controller transmitter eg; timer fan 2. Path pattern- the command variable is supplied by a programmed transmitter. The output variable of which is dependent on the path covered by the moving of the controlled arrangement. Eg CNC machine 3. Sequence control-the program transmitter and progress depending upon the condition reached at that time. The next program is triggered when the preceding one ends. This is effected mostly by sensing device transmitter.eg. conveyor

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved EXAMPLE: O/L CONTROL Automatic lawn sprinkler system Clock timer opens a water valve for several minutes each day. Does not check to see if lawn needed water and would even turn on the sprinklers in the rain. Controller adjusts the final control element without measuring the process.

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved EXAMPLE: O/L CONTROL Cycle timer that operates a drain valve At pre-determined intervals, the timer causes the drain valve to open even if there is nothing to drain. Controller adjusts the final control element without measuring the process.

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved EXAMPLE – OPEN LOOP 1. Manual Washing Machine 2. Light Dimmer 3. Microwave Oven 4. Filling Machine 5. Pick And Place Machine 6. Packaging Machine

Industrial Electronic Department Copyright of German Malaysian Institute. All rights reserved CONCLUSION In practice open loop control will never be perfect because:- 1.There will always be disturbances in system 2.No feedback monitoring Therefore OPEN LOOP systems do not results in accurate control.