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CHE00033 - DESIGN OF DC DIMMER FOR TEMPERATURE CONTROL STUDY


ABSTRACT

For many students, understanding concepts taught in the classroom improves significantly when they have the opportunity to gain hands-on experience in a laboratory. Students know analysis and not synthesis and do not have a full appreciation for the importance of dynamics in real process. This work presents low cost experimental kits for use in undergraduate process control education. The prototype for a temperature control experiment using a standard household light bulb is detailed. A step input was employed such that the light bulb is initially off and is turned on once. The Arduino Analog Read block, Digital Write block, IO Setup block, and Real-Time Pacer block are all part of the Arduino package. The remaining blocks are part of standard Simulink libraries, specifically, they can be found under the Math, Sinks, and Sources libraries.

In this experiment, Simulink was employed to command the relay, to read the data from the temperature sensor, and to plot the data in real time. Embedded control logic on-board, the Arduino board was demonstrated. This model reads the temperature data via an Analog Read on channel A0. This data is then converted from counts to degrees Celsius. The raw temperature data is expressed in numbers of bits. The model then displays the stored data on a scope and is written to the MATLAB workspace for further analysis.

This model commands the fan to be open (1) or closed (0) (corresponding to the fan on and off, respectively) via a Digital Write on LCD screen. The intensity of the light bulb is regulated by altering the dimmer level.

CHAPTER ONE

1.0       Introduction

Process Control has often stood out in the chemical engineering curriculum as a necessary topic that is oddly disconnected from the rest of the curriculum. While control modeling still relies on conservation laws and other fundamentals of chemical engineering, its mathematical focus on process descriptions in the Laplace domain has made it appear t-o students as a course distinct from “regular” chemical engineering.

In reality, process control is the key to industrial practice and will draw upon an engineer’s theoretical knowledge and practical experience to be effective. A series of inexpensive experimental kits have been designed for use in undergraduate process control education. Each simple system involves a number of analog and/or digital process inputs and outputs that are both observable and tangible thus lending to their pedagogical value. (Hossein Toghiani, 2012)

The kits utilize a USB interface data acquisition board to connect with software package such as MATLAB/Simulink. This allows the students to propose and carry out number of open- and closed-loop activities. One such system involves the use of a DC controlled dimmer to manipulate the   intensity of a standard light bulb, which in turn affects an adjacent temperature measurement taken using a thermocouple. (Christopher E. Long, 2006)

1.1       Problem Statement

Engineering is a practical discipline. It is a hands-on profession where doing is the “key”. Engineering Education is not achieving the demands required by industries or students. The Engineering Education must be more designed oriented and more exciting to students. The first course in control is poorly understood and lacks motivation to students.

1.2 Aim and Objectives

1.2.1    Aim

The aim of this activity with the light bulb is to demonstrate how to control switched systems.

1.2.2    Objectives

Laboratory Exercises reinforce theoretical concepts taught in classroom. Typical students remember 5% of what they hear, 10% of what they read, 75% of what they do. The objectives of the project are;

(i) to allow students model the relationship between the intensity of the light-bulb and the surrounding temperature from open loop data.

(ii) to allow students maintain the desired temperature at various set-points in the presence of process disturbances such as cooling caused by the introduction of fan (i.e. implementation of closed-loop control schemes).

(iii) to allow the existence of a “test bed” for a number of studies in a variety of contexts throughout the semester of an undergraduate control course. 

1.3       Justification

Hands-on experimentation typically supports the theoretical coursework covered in the traditional lecture periods. Students are able to spend some allotted time in a laboratory environment carrying out experiments. However, quite often the allotted time is not sufficiently long enough to allow each individual student to get an appreciable amount of time working alone on an experiment.

Instead, time constraints typically force them into working in groups. Similarly, students having difficulty mastering certain material do not necessarily get an abundance of time. Students enrolled in “distance learning” programs are not always able to travel to participate in laboratory exercises.

1.4       Scope/Limitation of Work

As mentioned before, the low cost nature and portability of the experimental kits allows for their use for class work and homework alike. Effectively, the experimental kit is not a single assignment, but rather an experimental system that can act as a test bed for any number of studies in a variety of contexts throughout the semester of an undergraduate controls course.

Initially, students can study the relationship between the process input and output. Specifically, the gain of the system can be determined across the complete range of operation. The nonlinearity of this particular system can then be seen by the generation of the steady-state locus. Similarly, students can perform open-loop step test on the system and derive appropriate system models.

Fig. 1.1 Photograph of the Low-cost Temperature Control Light-bulb Experiment     (top view)

Students are able to develop and test control methodologies in MATLAB/Simulink such as Proportional-Integral-Derivative (PID) control and model-based control strategies such as Internal Model Control (IMC).

1.5       Organization of the Project

This work is organized as follows:

  • A summary of the ideal experimental characteristics motivating this work is provided.
  • The prototype of the low cost temperature control experiment is detailed.
  • The uses of such an experimental kit are demonstrated.
  • Finally, technologies for remote experimentation are discussed.