Remote Hot Box Experiment

This experiment is on the time-dependent temperature change inside a heated box with air flow. The apparatus can be used in the 'uncontrolled' or 'controlled' mode. In the former case it enables the temperature to be measured as a function of time as a heat source or cooling fan is put on or off, and in the latter it explores the ability of the heat source or fan to control the temperature using several different types of control algorithms. The apparatus consists of a square box made from plexiglass, a halogen light bulb as a heat source and a thermistor used to measure the internal temperature of the chamber. A variable speed fan is mounted opposite a face plate with several holes to facilitate varying cooling rates.

Uncontrolled Operation

The halogen light bulb as well as the fan can be put on or off manually. The screen plots the temperature (in degrees F) with respect to time. The data file has two columns, the first being time and the second temperature.

Operation with Control

Binary Control (On - Off) The simplest type of control, On - Off, are most commonly found on modern domestic thermostats. When the chamber is cooler than the set-point temperature the heat source is turned on to maximum power. When the internal temperature of the chamber is hotter than the set-point temperature the heat source is turned to off. The control voltage that the heat source is controlled by resembles that of a square wave, where maximum turn-on is = 10 volts and turn-off is = 0 volts. The response of the system depends cooling rate of the chamber which is a factor of the variable speed fan.

Specifications:

Box Size; Heigth 5", Length 5", Depth 5"

Halogen Bulb; 60 watts

Thermistor 10KΩ

Fan Orifice 1.5 "