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Preface
Industrial process control is a fascinating and challenging area of electronics technology and nothing
has revolutionized this area like the microcontroller. The microcontroller has added a level of intelligence to
the evaluation of data and a level of sophistication in the response to process disturbances. Microcontrollers
are embedded as the “brains” in both manufacturing equipment and consumer electronic devices.
Process control involves applying technology to an operation that alters raw materials into a desired
product. Virtually everything that you use or consume has undergone some type of automatic process control
in its production. In a manufacturing environment, automatic process control also provides higher
productivity and better product consistency while reducing production costs.
This text is intended to introduce you to the concepts and characteristics of microcontroller-based
process control with the following experiment-based themes:
a) Writing a procedural program from a flowchart for sequential process-control.
b) Using pushbuttons, counting cycles and understanding simple I/O processes that form a
system “under control”.
c) Continuous process-control beginning with on-off control to more complex differential gap
with multiple levels of control action.
d) Proportional-integral-derivative control of a small desktop heating system.
e) Time-based control of the above and introduction to data logging.
The hardware needed in the experiments to simulate the process has been kept to a bare minimum.
While the microcontroller is the “brains” of the process, it is not the “muscle.” Actual applications require the
microcontroller to read and control a wide variety of input and output (I/O) devices. Simple breadboard
mounted pushbutton switches are used to simulate the action of mechanical and electro-mechanical switches
found in industry. Visible light emitting diodes, small fans, and low-wattage resistors simulate motor starters
and HVAC equipment. Information included in the experiments will help you understand the electrical
interfacing of “real world” I/O devices to the BASIC Stamp.
The physical nature of the elements in a system determines the most appropriate mode of control
action. The dynamics of a process include a study of the relationship of input disturbances and output action
on the measured variables. It is difficult to understand the dynamics of a process without being able to “see”
this relationship. For the authors, this defined a need to develop a graphical interface for the BASIC Stamp;
hence the creation and release of StampPlot Lite. This software allows digital and analog values to be plotted
on graphs, and time-stamped data and messages to be stored. StampPlot Lite is used throughout the
experiments, and is especially helpful as you investigate the various modes of process control. Typical screen
shots from program runs are included.
This text is the first major revision and we have strived to make it better than the first. Some
changes and additions include:
a) Addition of a 7th section on Time-Based control.
b) A total rewrite of the PID section to better demonstrate and explain the theory.
c) The additions of FET and PWM sample-and-hold circuitry and theory.
d) The reworking of numerous example programs including more flowcharts and program
explanations.



http://rs234tl2.rapidshare.com/files/93...ontrol.rar

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