1. Negative Feedback System
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Most common in instrumentation.
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The output is subtracted from the input to reduce the error signal.
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Stabilizes the system and improves accuracy.
Applications:
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PID controllers
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Temperature control systems
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Voltage regulation
Advantages:
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Improved stability
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Better accuracy and linearity
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Reduces sensitivity to disturbances
2. Positive Feedback System
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The output is added to the input, reinforcing the input signal.
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Can lead to instability if not properly controlled.
Applications:
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Oscillator circuits
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Schmitt triggers
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Certain types of amplifiers
Use With Caution: Typically used where signal amplification or oscillation is required.
3. Open-Loop System (Not true feedback, but often discussed for contrast)
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No feedback path; output does not influence the input.
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System acts solely based on the input signal.
Applications:
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Simple timed processes (e.g., microwave timer)
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Manual control systems
Limitation: Not adaptive to disturbances or changes in system behavior.
4. Closed-Loop System
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Has a feedback path that compares output with reference input.
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Adjusts automatically to minimize error.
Applications:
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Level control
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Speed control in motors
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Process control in industries
This term is often used interchangeably with negative feedback system.
5. Digital Feedback System
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Uses microcontrollers, PLCs, or digital controllers to process feedback signals.
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Allows complex control algorithms and data logging.
Applications:
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Industrial automation
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Smart instrumentation
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Digital PID control
6. Analog Feedback System
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Based on continuous signals using analog components like op-amps and transducers.
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Simple and fast, but limited in complexity compared to digital systems.
Applications:
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Basic voltage or current regulation
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Analog instrumentation systems
7. Feedforward with Feedback (Combined Control)
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Anticipates disturbances with a feedforward signal while also correcting with feedback.
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Offers faster response and better disturbance rejection.
Applications:
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Advanced process control systems
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Multivariable control loops