122-28176 Parallax Inc, 122-28176 Datasheet - Page 226

• 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

Page 216 · Process Control
Figure 6-23 PWM Open-Loop Control
Around a PWM of 28%, the temperature was in the desired band and fairly stable. At
this point, the energy into the system equaled the energy lost for the temperature. What
happened when air was blown across the enclosure? There was greater energy lost, and
the 28% drive was insufficient to maintain temperature in the band. Given a constant
disturbance and time, the incubator would have stabilized at a lower temperature. In this
BASIC Stamp program, the temperature is simply acquired and displayed. It is not used
for control of the system beyond proper spanning of the ADC.
Consider the earlier analogy of controlling the cabin temperature of an automobile. A
typical temperature control is simply a dial or slider that is adjusted to supply air from
cold to hot. After driving for a while, you have 'tweaked' the temperature control to your
comfort on a hot summer day. Suddenly, a bank of clouds rolls in, blocking the sun.
Within a few minutes your cabin temperature is suddenly too chilly. The removal of heat
energy via the air conditioner is in excess of the energy entering the cabin from the sun
and engine. This is an open-loop system in that the car's controller is not regulating the
temperature but simply supplying a set amount of heating or cooling. As losses or gains