130-28176 Parallax Inc, 130-28176 Datasheet - Page 231

• 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

Chapter 7: Closed Loop Process Control · Page 221
Chapter 7: Closed Loop Process Control
An open-loop control system can deliver a desired output if the process is well
understood and all conditions affecting the process are constant. However, Experiment #4
showed us that an open-loop control system couldn’t guarantee the desired output from a
process that was subject to even mild disturbances. There is no mechanism in an open-
loop system to react when disturbances affect the output.
In Chapter 6, the temperature was read by the BASIC Stamp, but only for the purpose of
monitoring it. This could have been done as easily with a simple voltmeter. Although
you were able to find a PWM drive setting that would yield the desired temperature in
Chapter 6, when a long-lasting disturbance changed the system dynamics, the fixed
setting was no longer valid.
Closed-loop control provides automatic adjustment of a process by collecting and
evaluating data and responding to it accordingly.
A typical block diagram of an
automatic control system is depicted in Figure 7-1.
Figure 7-1 Closed Loop Control Block Diagram
In this diagram, an appropriate sensor is measuring the controlled variable. The signal-
conditioning block takes the raw output of the sensor and converts it into data for the
controller block. The setpoint is an input to the controller block that represents the