122-28176 Parallax Inc, 122-28176 Datasheet - Page 306

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Note the response of %Dd:
Derivative control drives to oppose the rising or falling temperature. When K
changed to 10, a small change in error produces very large changes in drive. The
response of the system is such that there were almost no oscillations. With Proportional-
Derivative control, a high proportional gain will assist control of the system by having a
fast response, and results in very little proportional error. With derivative control, the
heavy oscillations associated with a high proportional gain can be damped, resulting in a
very fast, stable response. But too much derivative gain can lead to very unstable control
of the system. Around time 24, the gain was increased to 50. With just a little
disturbance, the erratic behavior of the system can be seen. As proportional drive tried to
raise the temperature to the setpoint, derivate control fought any upwards motion. The
total drive cycled continually between 0% and 100% as the error went one way and then
the other. If this were an oil-flow system, consider what the pump must sound like
during this control!
Derivative can be very good for limiting the effect of an error. Imagine operating at the
setpoint, and quick, short disturbance causes the temperature to drop suddenly.
Derivative drive will rapidly increase the output to limit the amount of the temperature
drop. We were not able to show this response well with our slow-responding system.
Can you?
Challenge 8-6: Derivative Control Testing
Can a system be controlled on derivative drive alone?
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Temperature increasing → %Dd is negative.
Temperature decreasing → %Dd is positive.
Temperature constant → %Dd is 0.
After establishing operation near the setpoint, set Kp, Ki to 0 and %Bias to 0.
Set Kd to a value of your choosing.
Provide a cooling disturbance and test control of the system.
Allow operation for several minutes.
Discuss the results of your testing.
P
is