122-28176 Parallax Inc, 122-28176 Datasheet - Page 260

• 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 each element in PID, the control action is based on the error, either current,
accumulated over time, or change with respect to time. Mathematically, integrals and
derivatives are based on an infinite number of points in the time continuum. Consider
Figure 8-2 showing an actual reading oscillating around a setpoint. Data is measured and
action taken at every possible point. The integral evaluation provides the area under the
curve. As an example, if the error resulted in a certain amount of power being expended,
the integral of the error would provide the total power used over time. The mathematical
result would provide a very precise value for the area under the curve. Note that if a
value above the setpoint were considered a positive error, data below the setpoint would
be a negative error. If the areas A and B were equal and these two areas were integrated,
the result would be 0.
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Error (E) is the measurement from the desired setpoint to the actual system
condition, such as a difference between the desired temperature and the actual
temperature.
Proportional Drive continuously evaluates error and adds or subtracts output
drive in an attempt to drive the system back to the setpoint. Too low? More
drive. Too high? Less drive. The gain is used to adjust how much action is
taken based on the error.
Integral Drive measures the duration and magnitude of the error and adds or
subtracts to eliminate the long lasting error. The longer the error and the greater
the amount of error, the greater the integral drive will be. Gain is used to adjust
the amount of action based on the duration and magnitude of error.
Derivative Drive measures how quickly error changes in respect to time. The
faster the error changes, the more action that will be taken to oppose the change
to bring the system back under control. The gain once again is used to adjust the
amount of action based on this calculation.
Figure 8-2
Continuous
Measurement for
PID