122-28176 Parallax Inc, 122-28176 Datasheet - Page 297

• 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

proportional drive was inversely proportional to the error and was added to total drive.
The temperature oscillates briefly around the setpoint prior to stabilizing. This response
is known as "Critically Damped" because the value quickly settles into the setpoint with
few oscillations.
Run #2: Kp= 1.0
For a similar disturbance, the temperature rose and overshot by approximately the same
amount as Run #1, but required more oscillations before setting into the setpoint.
Compare the amount of %Dp for the same error as Run #1. With a higher gain, there is
more forceful action. Due to the high number of oscillations, this system is "Under
Damped". With a gain of 1, the system is operating with a 100% proportional band.
That is, full control of the output occurs over full range of the control band. Note that at
about time 11, the signal is at the top of the control band (100% of band). The output is
at the bottom of the drive output (0% due to 50% - 50% proportional). Similarly, when
temperature is at the bottom of the band (about time 10.5), the output is at maximum
(100% due to 50% bias + 50% proportional).
Compare this to the drive in Run #1. The output was 100% when the temperature was at
96 °F, twice the width of the control band. Run #1 has a proportional band of 200%.
Run #3: Kp = 2
With a gain of 2.0, more forceful action is taken based on the same error.
temperature continually oscillates around the setpoint. This system is termed "Unstable".
If gain is increased much more, the system would be operating in an on-off mode cycling
between 0% and 100% as small errors drives the output one way and then the other.
Run #4: Kp=0.1
With a very low gain, the temperature slowly drifts up and settles into the setpoint
because of the very low drive added due to error. This system is "Over Damped".
Challenge 8-3: Proportional Calculations
1. Draw a 200% proportional band curve for a system with a setpoint of 110 °F and
2. Calculate the proportional gain.
3. Based on the graph, what would the output be at 111 °F, 106 °F, and 115 °F?
a band of +/− 2 °F.
The