122-28176 Parallax Inc, 122-28176 Datasheet - Page 280

• 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

In an actual system, just as with the automobile example, the derivative output changes in
a direction and magnitude to counter the error. Acting on the window blinds, as the
sensor suddenly lightened, the output would quickly move the motor with a motion
relative to the change.
Just as with proportional and integral, we can adjust the amount of force applied by
derivative by setting the gain (K
though.
In the examples up until now, the output swung both positive and negative for control of
the system. In most cases, the output will only be in one direction. Consider the car
example. On a level highway, the pedal will be in a position to supply sufficient energy
to keep the car at the setpoint speed. The pedal is adjusted up or down from this center
position to control the speed. In the floating ball example, the electro-magnet will have a
set amount of drive (preferable 50%) when the ball is correctly in the beam. As it rises,
drive will cut back; as it falls, drive will increase.
Bias is used to provide a midpoint drive that, with good engineering, should maintain a
stable system at the setpoint under normal conditions. We will test adding bias to our
calculations and controlling the system with that as the midpoint.
Adding Bias
√
√
√
CalcDeriv:
RETURN
Modify the program to multiply
1.0 second.
Try to hold your hand so that the output does not exceed a value of +/− 400 for
20 seconds.
Even leaving the sensor totally uncovered, the measurement fluctuates due to
noise. Note the amount of output change simply based on the noise.
DEBUG "!O txtLE=", SDEC LastError,CR
ErrorChange= Error - LastError
SignBit = ErrorChange.BIT15
Deriv = ABS(ErrorChange)/Samples * 4
IF SignBit = 1 THEN Deriv = Deriv * -1 ' Re-apply sign
LastError = Error
D
). Too much gain can cause erratic control of a system,
Deriv
by a gain of 10, and set a sample time of
' Calculate derivative output
' Update SP with last error
' Calculate dE
' Save sign, 1 = negative
' Divide by dt
' Save Lat error for this eval