122-28176 Parallax Inc, 122-28176 Datasheet - Page 293

• 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

With a gain of 3, and an error of 30%:
Note that the greater the error, the greater the drive due to proportional control. Consider
what this means to our incubator. Let's assume a bias of 50% only got the temperature to
99.7F. This would produce an error of +30% for a total drive of 80% (with a K
With a PWM duty cycle of 80%, what will the temperature in the incubator do? Increase.
As the actual temperature approaches the setpoint, what happens to the proportional
drive? It becomes less and less, backing off on total drive. Consider when temperature is
at 99.9 °F. The error is +10%. What does this do for total drive?
Notice that as the temperature approaches the setpoint, the drive is less. This may result
in the temperature stabilizing below the setpoint, which is called steady-state error.
Proportional Band
Let's consider one more term: Proportional Band. Actually, we've already discussed all
there is to know. It's simply another way of looking at the gain. Proportional band
defines the percentage of the control band over which the system will take proportional
control action.
%Drive
%Drive
%Drive
%Drive
PROP
PROP
TOTAL
TOTAL
= K
= K
= %Drive
= %Drive
P
P
%E = 1 x 30% = 30%
%E = 3 x 30% = 90%
BIAS
BIAS
+% Drive
+% Drive
PROP
PROP
= 50% + 30% = 80%
= 50% + 10% = 60%.
P
of 1).