Open loop and closed loop
- 4. A closed loop system is also referred as a feedback control system. These systems record the output instead of input and modify it according to the need. It generates preferred condition of the output as compared to the original one. It doesn’t encounter any external or internal disturbances.
- 6. Practical Examples of Open Loop Control System Electric Hand Drier – Hot air (output) comes out as long as you keep your hand under the machine, irrespective of how much your hand is dried. Automatic Washing Machine – This machine runs according to the pre- set time irrespective of washing is completed or not. Bread Toaster - This machine runs as per adjusted time irrespective of toasting is completed or not. Automatic Tea/Coffee Maker – These machines also function for pre adjusted time only. Timer Based Clothes Drier – This machine dries wet clothes for pre – adjusted time, it does not matter how much the clothes are dried. Light Switch – lamps glow whenever light switch is on irrespective of light is required or not. Volume on Stereo System – Volume is adjusted manually irrespective of output volume level.
- 7. Practical Examples of Closed Loop Control System Automatic Electric Iron – Heating elements are controlled by output temperature of the iron. Servo Voltage Stabilizer – Voltage controller operates depending upon output voltage of the system. Water Level Controller– Input water is controlled by water level of the reservoir. Missile Launched & Auto Tracked by Radar – The direction of missile is controlled by comparing the target and position of the missile. An Air Conditioner – An air conditioner functions depending upon the temperature of the room. Cooling System in Car – It operates depending upon the temperature which it controls.
- 8. Sr. No. Open loop control system Closed loop control system 1 The feedback element is absent. The feedback element is always present. 2 An error detector is not present. An error detector is always present. 3 It is stable one. It may become unstable. 4 Easy to construct. Complicated construction. 5 It is an economical. It is costly. 6 Having small bandwidth. Having large bandwidth. 7 It is inaccurate. It is accurate. 8 Less maintenance. More maintenance. 9 It is unreliable. It is reliable. 10 Examples: Hand drier, tea maker Examples: Servo voltage stabilizer, perspiration
- 9. Advantages of Open Loop Control System Simple in construction and design. Economical. Easy to maintain. Generally stable. Convenient to use as output is difficult to measure. Disadvantages of Open Loop Control System They are inaccurate. They are unreliable. Any change in output cannot be corrected automatically.
- 10. Advantages of Closed Loop Control System Closed loop control systems are more accurate even in the presence of non-linearity. Highly accurate as any error arising is corrected due to presence of feedback signal. Bandwidth range is large. Facilitates automation. The sensitivity of system may be made small to make system more stable. This system is less affected by noise. Disadvantages of Closed Loop Control System They are costlier. They are complicated to design. Required more maintenance. Feedback leads to oscillatory response. Overall gain is reduced due to presence of feedback. Stability is the major problem and more care is needed to design a stable closed loop system.