122-28176 Parallax Inc, 122-28176 Datasheet - Page 261

• 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

The derivative evaluation provides a measurement of the change in value with respect to
time (the faster the error changes, or the slope at that instant, the higher the magnitude of
the error.) At point 1 of Figure 8-2, the value is changing very rapidly with a positive
slope (rising).
(decreasing).
Analog circuits using op-amps can provide true proportional, integral and derivative drive
where the waveform is processed on a continuous basis. At any given instant, the error is
measured and processing of that error is made.
measurement is not possible. Samples are taken at intervals, and approximations are
made to provide PID control. Before we test the microcontroller performing PID control,
let's first look at a system controlled with analog PID.
Electronic Systems Technologies students, at Southern Illinois University Carbondale,
regularly construct and test the floating-ball project as shown in Figure 8-3. An infrared
beam is used to detect the position of the magnetic ball. Drive to the electromagnet is
used to control the position of the ball. The setpoint is the desired voltage representing
the light falling on the detector based on the ball partially in the beam. The actual ball
position is detected based on the amount of light striking the phototransistor and
producing an output at the collector. The error is the difference between the actual and
desired voltages. As the ball begins to drop (light level increases), drive to the magnet
must increase, and as the ball gets pulled up (light level decreases), the drive to the
magnet must be decreased. When properly adjusted, or tuned, the ball will maintain a
relatively stable position, "floating" in the beam.
At point 2, the value is changing slowly with a negative slope
In microcontrollers, instantaneous
Figure 8-3
Floating Ball
Project