Environmental test chamber for the support of learning and teaching in intelligent control

International Journal of Electrical Engineering Education, Oct 2004 by Taylor, C James

Abstract

The paper describes the utility of a low cost, 1 m^sup 2^ by 2m forced ventilation, micro-climate test chamber, for the support of research and teaching in mechatronics. Initially developed for the evaluation of a new ventilation rate controller, the fully instrumented chamber now provides numerous learning opportunities and individual projects for both undergraduate and postgraduate research students.

Keywords MATLAB/Simulink; micro-climate; multivariable control; ventilation rate

The desire for cost-effective teaching of mechatronics is balanced by the ideal of giving students the opportunity to solve real design problems. Innovations in the use of simulation tools such as MATLAB/Simulink for teaching signal processing, intelligent control and related subjects may provide low cost options, but can lead to a reduction in the 'hands-on' experience for the student.

In this regard, the present paper describes the utility of a low cost, 1 m^sup 2^ by 2m forced ventilation test chamber, for the support of research and teaching in the Engineering Department at Lancaster University. Initially developed for the evaluation of a new ventilation rate controller for agricultural buildings,1 the fully instrumented chamber now provides numerous learning opportunities and individual projects, for both undergraduate and postgraduate research students in the department.

Here, a computer controlled axial fan is positioned at the outlet in order to draw air through the chamber, whilst a ventilation rate sensor measures the associated flow rate. Ventilation rate has been shown to be one of the most significant inputs on the microclimate surrounding plants or animals within the majority of agricultural buildings, including livestock housing, glasshouses and storage warehouses, so good control of this variable is essential.2-4 A 3-dimensional array of 20 thermocouples, together with a computer controlled heating element positioned at the inlet, completes the basic specifications of the chamber.

The chamber provides an ideal opportunity for the practical implementation, comparative evaluation and refinement of new control methodologies, since it requires either single-input, single-output (SISO), or full multivariable control, of both ventilation rate and temperature. These are highly coupled variables, each with rather different nonlinear dynamic characteristics. In particular, whilst small perturbations in ventilation rate are typically characterised by first order dynamics, the temperature response is best represented by a second order differential or difference equation.

Both variables show evidence of pure time delays and both have a nonlinear gain. For example, at high applied voltages, the steady state airflow rate converges asymptotically to a maximum value determined by the characteristics of the fan. In this manner, the steady state power takes the form of the S-shaped curve illustrated in Fig. 1, requiring some form of adaptive, scheduled or nonlinear control for optimal performance. In this regard, the chamber is presently being utilised to support research into the state dependent parameter (SDP) system identification methodology5 and proportional-integral-plus (PIP) control.6-8

In addition to this generic research, it is clear that control of the 3-dimensional environment of air-spaces is of increasing interest, with applications in both agriculture and the human built environment, including the automotive industry. In this regard, the chamber allows for research into shifting air flow patterns and incomplete mixing, with the aim of developing an associated distributed multivariable control system for micro-climate.

However, the focus of the present paper is on the chamber's use as a tool for learning and teaching. With a settling time of -10 s for ventilation rate and -10 min for temperature, open and closed loop experiments are feasible within the timescale of a standard laboratory class. In this regard, the author uses the equipment to support courses in signal processing, intelligent control and MATLAB/Simulink programming. Furthermore, it has already inspired innovative projects for 3rd/4th year undergraduate students, as well as postgraduate MSc and PhD students. In supporting the design philosophy of the Department, it provides a valuable modelling and control systems tool, that supersedes existing simulation-based projects in this area.

The chamber, sensors and associated software interfaces are described in the next two sections of the paper. This is followed by examples of their utility as a research and teaching aid respectively. One particular worked example is then considered, namely PIP control of ventilation rate while, finally, the conclusions are presented.

Environmental chamber

The chamber was designed and constructed by Dr Phil Leigh1 in 2001, for an initial cost of under £5000, including sensors, software and the accompanying PC. The schematic layout of the chamber is illustrated in Fig. 2, where the numbers [1]-[19] are referred to below.