Closed-Loop System Flashcards
Change in any variable that may cause the controlled variable of the process to change
Load
Desired value of the controlled variable
Set point
Negative Error, π formula
π = πππ ππππ π£πππ’π β ππππ π’πππ π£πππ’π
If the load value increases, the process and measured values will also increase, making the error even more positive.
Positive feedback
If the load value increases, the process and measured values will also increase, making the error negative.
Negative feedback
Assume no change in the load.
The set point would be changed in accordance with the desired variation.
Servo problem
Assume no change in set point.
There will be an importance in maintaining the controlled variable in spite of changes in load.
Regulator problem
Moves the valve stem as the pressure on a spring-loaded diaphragm changes
Pneumatic device (valve motor)
Positions of a plug in the orifice of the valve body
Stem
As the air pressure increases, the plug moves downward and restricts the flow of fluid through the valve
Air-to-close valve
The valve opens and allows greater flow as the valve-top air pressure increases
Air-to-open valve
Often constructed so that the valve stem position is proportional to the valve-top pressure
Valve motor
Fluid flow is proportional to the valve-top pneumatic pressure at steady-state
Linear valve
Means that stem position does not respond instantaneously to a change in the applied pressure from the controller (pneumatic valve always has dynamic lag)
Dynamic lag
Inserted into the controller so that the error reaches some finite positive value before the controller βturns on.β
Dead band
A phenomenon where the controller will rapidly cycle on and off as the error fluctuates about zero
Phenomenon of chattering
Additional control mode introduced if we cannot tolerate any residual error
Integral mode ultimately drives the error to zero
Integral control
The reciprocal of (tau_integral)
Reset rate
Acts upon the derivative of the error, so it is most active when the error is changing rapidly.
PD control
Other terms used to describe derivative action
- Rate Control
- Anticipatory control
Based on how rapidly the error is changing, not the magnitude of the error or how long the error has persisted.
Derivative action
Cause significant problems for derivative action because of the rapidly changing slope of the error caused by noise.
βNoisyβ error signals
Defined as one for which the output response is bounded for all bounded inputs (BIBO)
Stable system
System exhibiting an unbounded response to a bounded input
Unstable system
Minimum or maximum limit value
Saturation
A linear control system is unstable if any roots of its characteristic equation are on, or to the right of, the imaginary axis. Otherwise, the system is stable.
Stability for linear systems
