122-28176 Parallax Inc, 122-28176 Datasheet - Page 221

• 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

ACTIVITY #4: OPEN LOOP PWM CONTROL
The simplest form of process control is open loop. The block diagram in Figure 6-21
represents a basic open-loop system.
actuator. The calibrated setting on the actuator determines how much energy is applied.
The process uses this energy to change its output. Changing the actuator’s setting changes
the energy level in the process and the resulting output. If all of the variables that may
affect the outcome of the process are steady, the output of the process will be stable.
The fundamental concept of open-loop control is that the actuator’s setting is based on an
understanding of the process. This understanding includes knowing the relationship of the
effects of the energy on the process and an initial evaluation of any variables disturbing
the process. Based on this understanding, the output “should” be correct. In contrast,
closed-loop control incorporates an on-going evaluation (measurement) of the output, and
actuator settings are based on this feedback information.
Consider the temperature control process shown in Figure 6-22. The fluid being drawn
from the tank must be kept at constant temperature. Obviously, this will require adding a
certain amount of heat to the fluid. (The drive on the transistor determines the power
delivered to the heating element.) The question becomes “How much heat is necessary?”
Energy is applied to the process through an
Figure 6-21
Open-Loop Block
Diagram