PASCO TD-8579A COMPUTER-BASED THERMAL EXPANSION APPARATUS - Manual (Page 4)

012-07599C Computer-based Thermal Expansion Apparatus
1
®
Introduction
Introduction
The PASCO Model TD-8579A Computer-based Thermal Expansion Apparatus provides easy and accurate
measurements for the coefficient of linear expansion for brass, copper, and aluminum. The PASCO
Model TD-8579A differs from the previous model TD-8578 in that it uses a Rotary Motion Sensor instead
of a dial gage for measuring length changes in the rod, a Thermistor Sensor instead of an ohmmeter, and
is compatible with a ScienceWorkshop® interface for recording sensor measurements in a computer.
The new PASCO CI-6527A Thermistor Sensor can be connected to the apparatus and a ScienceWorkshop
interface for viewing temperature readings inside DataStudio. With the new thermal expansion model,
students no longer have to convert resistance readings to temperature values using a conversion table.
DataStudio® provides immediate temperature feedback in either absolute temperature (degrees Kelvin),
degrees Celsius (C) or Fahrenheit (F). A setup diskette comes with the apparatus, which includes the pre-
defined variables and equations for measuring temperature in degrees Celsius.
For the length measurement, the brass, copper, or aluminum tube is placed on the expansion base. The
length of the tube is measured at room temperature, then steam is passed through it. The expansion of the
length of the metal rod is measured with 0.006 mm resolution using the Rotary Motion Sensor. Tempera-
tures are measured to within +0.2 °C using a thermistor attached to the center of the tube. To investigate
the expansion of the metals at additional temperatures, hot or cold water can be passed through the metal
tubes.
Complete step-by-step instructions and a data sheet for results are provided in this manual.
Temperature Measurement with the Thermistor and Thermistor Sensor
A thermistor's resistance varies reliably with temperature. Typically, as the temperature of a metal rod
increases, the resistance decreases proportionally until the temperature equilibrates. Although the relation-
ship between temperature and resistance is not linear, a linear approximation can be accurately used to
interpolate between table data points with an accuracy of approximately +0.2
0 C.
The 10 k
Ω
thermistor used to measure the rod's temperature is embedded in the thermistor lug. Once
thermal equilibrium has been reached, the heat is highly uniform along the length of the rod. The foam
insulator is used to inhibit heat loss through the thermistor lug so the lug temperature closely follows the
rod's temperature. The insulator does not have any appreciable effect on the local temperature of the rod
itself.
Using the PASCO Thermistor Sensor with a ScienceWorkshop interface, the resistance is measured and
directly converted to a temperature measurement, which displays in DataStudio.