Control System consists of various devices which controls the other devices to get desired results. Simply, It’s a system who controls other system. It works like a mathematical function, y = f(x) i.e y acts as output, x acts as input and f acts as control function. There should be a mathematical relation between input and output.
Good Control System have:
• Accuracy ↑
• Sensitivity ↑ (only to input)
• Noise ↓
• Stability ↑
• Bandwidth ↑
• Speed ↑
• Oscillation ↓
Note: ↑ denotes high, ↓ denotes low
1. Manual control system and Automatic control system
2. Open loop control system and Closed loop control system – mostly used
Open Loop Control System :
• Output and Input are independent i.e. Input is not affected by output.
• Manual systems is generally open loop system.
• Examples are : Light switch, Tea/Coffee maker, Bread toaster etc.
• It is of Simple design & construction
• It’s Economical
• It’s easy in maintenance
• It’s stable
• It is less accurate
• It is unreliable
• Change in output is corrected only manually
Closed Loop Control System :
• Output and Input are connected through a feedback system. Output affects input to adjust the desired output.
• It is generally automatic control system.
• Examples are: Electric Iron, AC, Water level controller etc.
Note-Open loop control system can be changed into Closed loop control system, by introducing feedback.
• It is more accurate
• It provides automation
• It is less affected by noise
• Its Bandwidth is large
• It is costly
• Its construction is complicated
• It needs more maintenance
• It has oscillatory response due to feedback
• It is less stable.
Open Loop Control System
Feedback – absent
Maintenance – less
More affected by Noise
Closed Loop Control System
Feedback – present
Maintenance – more
Less affected by Noise