| |
Proportional Control
5.1
A change or 20% in the process temperature causes a 100% change in the
valve position.
| a. What
is the Gain of the controller? |
| b. What
is the Proportional Band? |
| 5.2 |
In the Balance Beam example, Exercise 3.1,
moving the fulcrum all the way to the right would result in a controller
with characteristics similar to a:
|
| a. rheostat |
| b. thermostat |
| c. deadband
controller |
| d. none
of the above |
| 5.3 |
In the Loop Gains example, Exercise 3.4,
if the differential pressure transmitter is recalibrated from 0-150 gpm to
0-200 gpm: |
| a. Do
the FIC scales need to be changed?
How much? |
| b. How
much must the controller gain be increased to maintain the same loop
response? |
5.4
If the valve is replaced with a larger one:
| a. What
will be the effect on rangeability? |
| b. How
much must the controller gain be changed to maintain the same loop
response? |
5.5
Level Loop Gains
For the above loop:
| 1. |
If a second processing unit was installed identical to
this one except for a larger-diameter tank, what would you do to provide
the same loop response? |
| 2. |
What effect will a sudden increase in inflow would have on
the level if a larger-diameter vessel was used? |
| 3. |
Draw a graph showing process gain and controller gain with
respect to level. |
| 4. |
How must the controller vary the output to recover
consistently from the same disturbance at midrange and at the top or
bottom. |
| 5. |
Where is the process gain the greatest? |
| 6. |
If the loop with the spherical tank was tuned for tight
control at midrange, what would you say about its stability for set
points near the top or bottom. |
5.6
Proportional Response
Fred is losing sales because of his product quality.
In an attempt to improve quality, he installs a proportional-only
controller on the Continuous process with results as shown below.
| 1. |
Assuming that on the above recordings at 145oF is
30% of the process scale and 1550F is 70% of the process scale,
what is the controller gain? |
| 2. |
What would you do to further reduce the cycling amplitude? |
| 3. |
Is this controller direct or reverse acting? |
|
|
