Me 224 Experiments
ME224 Lab4
Introduction The purpose of this lab is to build a temperature monitor and controller for a small aluminum block. Techniques involved in this lab include using transistors as switches, calibrating transducers, and writing control programs in LabVIEW. The main piece of equipment used in this lab is an aluminum block apparatus; the block has several holes drilled into it and embedded in them is a resistance heater, a thermistor, and a thermometer. In addition, a simple circuit is attached to the aluminum block with breadboarding for connection to the circuits built in the lab. The embedded resistance heater is used to heat the aluminum block. The heater is essentially a resistor that generates heat by the principle of Joule’s Law in which a current running through a resistor converts electrical energy into heat energy. Joule heating can be expressed by the relationship Q = I2 * R * t where Q is the heat (J) generated by a constant current I (A) flowing through a conductor of resistance R (Ω) for a given time t. [1] Although electric resistance heating converts nearly 100% of the electricity to heat, the overall process is still inefficient since the electricity is usually produced from oil, gas, or coal generators that convert only about 30% of the fuel’s energy into electricity. [2] Due to the energy loss in electricity generation and transmission, electric resistance heating is often more expensive than heat produced using combustion appliances, such as natural gas, propane, and oil furnaces. Thermistors are temperature sensing elements composed of sintered semiconductor materials such as silicon carbide that exhibit large changes in resistance in response to small changes in temperature. [3] Unlike most resistors, thermistors decrease in resistance as temperature increases because of their negative temperature coefficients as derived from their material properties. This relationship between resistance and temperature is better described by the equation
Introduction The purpose of this lab is to build a temperature monitor and controller for a small aluminum block. Techniques involved in this lab include using transistors as switches, calibrating transducers, and writing control programs in LabVIEW. The main piece of equipment used in this lab is an aluminum block apparatus; the block has several holes drilled into it and embedded in them is a resistance heater, a thermistor, and a thermometer. In addition, a simple circuit is attached to the aluminum block with breadboarding for connection to the circuits built in the lab. The embedded resistance heater is used to heat the aluminum block. The heater is essentially a resistor that generates heat by the principle of Joule’s Law in which a current running through a resistor converts electrical energy into heat energy. Joule heating can be expressed by the relationship Q = I2 * R * t where Q is the heat (J) generated by a constant current I (A) flowing through a conductor of resistance R (Ω) for a given time t. [1] Although electric resistance heating converts nearly 100% of the electricity to heat, the overall process is still inefficient since the electricity is usually produced from oil, gas, or coal generators that convert only about 30% of the fuel’s energy into electricity. [2] Due to the energy loss in electricity generation and transmission, electric resistance heating is often more expensive than heat produced using combustion appliances, such as natural gas, propane, and oil furnaces. Thermistors are temperature sensing elements composed of sintered semiconductor materials such as silicon carbide that exhibit large changes in resistance in response to small changes in temperature. [3] Unlike most resistors, thermistors decrease in resistance as temperature increases because of their negative temperature coefficients as derived from their material properties. This relationship between resistance and temperature is better described by the equation
Cited: 1. Donald G. Fink and H. Wayne Beaty, Standard Handbook for Electrical Engineers, Eleventh Edition,McGraw-Hill, New York, 1978, ISBN 0-07-020974-X, pages 21-144 to 21188 2. United States. U.S. Department of Energy. Electric Resistance Heating. Web. . 3. . "Thermistors.". OMEGA Engineering, INC., n.d. Web. 31 May 2012. . 4. Ho, Dean. ME 224 Laboratory 4 Manual. Laboratory Report. Evanston: Northwestern Univeristy, 2011 5. "The Thermistor.". Princeton University, n.d. Web. 31 May 2012. . 6. O 'Hanian, H. C. Physics, Vol. 1. New York: W. W. Norton, pp. 484-487 and 493-496, 1985. 7. Amos S W & James M R (1999). Principles of Transistor Circuits. ButterworthHeinemann. 8. Hewes, John. "Transistors." . The Electronics Club, 2011. Web. 31 May 2012. . 9. S. Gaudin, "The transistor: The most important invention of the 20th century?," Computerworld, 12 December 2007. 10. R. Chohan and M. Hashemian, "Response Time of Platinum Resistance Thermometers in Flowing Gases," Fire and Materials, vol. 14, no. 1, pp. 31-36, 1989.