An automatic control system is a preset closed-loop control system that requires no operator action. This assumes the process remains in the normal range for the control system. An automatic control system has two process variables associated with it: a controlled variable and a manipulated variable.
A controlled variable is the process variable that is maintained at a specified value or within a specified range.In the previous example, the storage tank level is the controlled variable.
A manipulated variable is the process variable that is acted on by the control system to maintain the controlled variable at the specified value or within the specified range. In the previous example, the flow rate of the water supplied to the tank is the manipulated variable.
Functions of Automatic Control
In any automatic control system, the four basic functions that occur are:
- Measurement
- Comparison
- Computation
- Correction
Advantages :
- Precision
- High in speed
- Recovery time
- High efficiency
- Repeatibility
- Safety
Disadvantages :
- Strong technical knowledge to design well
- More attention to safety
- High in maintenance
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