130-28176 Parallax Inc, 130-28176 Datasheet - Page 285

• Manufacturer Part Number: 130-28176
• Description: KIT PARTS PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 130-28176

• Accessory Type: Education Kit
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Board of Education Full Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

%Drive Bias, %Drive Proportional and so on.
operation becomes:
As discussed, a system in equilibrium is where the energy gains in that system equals the
energy losses. When a system is designed, the engineers will have anticipated typical
losses on the system. The bias drive is the drive used to compensate for normal losses. In
terms of control, you've already performed this in earlier chapters. The amount of PWM
drive was adjusted until the incubator was at or near the setpoint of 101.5 °F. This would
be the bias drive for the incubator.
Bias drive provides a best-case starting point for control of a system. When a system,
such as an incubator, is engineered, it is possible to design it so that a 50% drive to the
heating element will control it very near the setpoint under normal conditions. This
design provides for up-to 50% of the drive to be removed or up-to an additional 50% to
be added for control of the system. Consider an outdoor incubator. If 50% drive on the
heaters is good for a nice spring day, an additional 50% drive can help warm it on very
cold winter days, or cutting back the drive by 50% on very hot summer days will help
keep it at the setpoint.
For the eggs in our incubator to hatch healthy chicks, 50% drive on our heater would
provide sufficient energy to maintain temperature in the incubator near 101.5 °F under
our average laboratory conditions. Unfortunately, our system is not well engineered.
Being a non-insulated polystyrene test tube with a small resistor for a heater, chances are
that exactly 50% drive will not provide the exact amount of energy needed to meet our
desired setpoint.
Note that this bias temperature may fluctuate due to room conditions, and that depending
on conditions, your results may vary and 50% may be well above 101.5 °F.
Parts required:
Same as Activity #1
√
%DRIVE
Co
%Drive
Enter, save and run IncubatorPID-SP.bs2.
PID
= B
TOTAL
TOTAL
= %Drive
= %DRIVE
BIAS
BIAS
+ %DRIVE
PROP
The new equation for the systems
+ %DRIVE
INT
+ %DRIVE
DERIV