Section 1 Feedback Control Loop Problems Flashcards
The major advantage of adaptive gain control is that it lets the user to ___________ the plant across all operating regions.
Linearize
What is another name for adaptive gain control?
Gain scheduling
Describe transfer function behavior in a non-linear plant.
Will be slightly different in different operation regions
What are the 3 ways to deal with non-linearity?
1) Component matching
2) Adaptive gain control/gain scheduling
3) Detuning/acceptance
What is the challenge of using adaptive gain control?
Coming up with the correct approximation for the different regions as it is prone to human error
What solution to non-linearity does not linearize the plant in all operating regions?
Detuning
Flow characteristics of a valve define the flow behavior as the _________________.
valve moves through it’s stroke
What are some sources of non-linearity in a control loop?
1) Primary element eg. flow measurement through an orifice plate
2) Process Variable being measured eg. temperature
What are some linearization methods that can be applied to a control loop?
1) Use a square root extractor
2) Use LN or LOG
What is the difference between installed and inherent valve characteristics?
Inherent:
Based on constant pressure change across the valve and are considered “perfect world” lab environment
Installed:
Based on variation in pressure across the valve as stroke changes and a more real world application
What happens to valve characteristics when the value of r gets lower?
A linear valve starts behaving as a quick opening valve.
An equal percentage valve turns more linear.
What is distortion coefficient?
r, defined as minimum pressure drop divided by total pressure eg. if r=10% that means 10% of the pressure drop across the valve in the system
What is Rangeability?
R, and is defined as maximum controllable flow divided by minimum controllable flow
What are the 3 ways to deal with excessive deadtime in the process?
1) Move instrumentation to minimize deadtime
2) Install a low gain P-only controller (slow response and offset will be present)
3) Smith Predictor Application
How can an operator validate if the system has excessive deadtime?
Calculate the uncontrollability parameter. If UP is:
Between 0.1 - 0.5, deadtime is not an issue and PID tuning can be applied
Between 0.5 - 1, standard PID might work
More than 1, deadtime is an issue and a smith predictor needs to be used
