Calibrating a thermistor

[richMMIV]

For the "build your own sensor" part of my AS work I am using a thermistor in a potential divider in order to measure the melting point of a chemical.
My teacher has OKed this but says that i need to calibrate the sensor in, for example, melting ice. I am not sure exactly what this involves, other than changing the value of the other resistor in the potential divider. Am I just trying to get a sensible value for the voltage output? What value should i be trying to acheive?
Is the curve produced by a thermistor not non-linear? In this case how do I, after calibration; and after i have a voltage output value for when my chemical has melted/solidified; find the temperature value from the output, without using the data sheet for the thermistor?
Any help you could offer would be appreciated.

 

[Aaron Barnard]

Calibrating your thermistor will involve measuring the voltage output at different temperatures. You will need to measure the voltage at a known temperature and adjust the resistor values in the potential divider to get the desired voltage output. For example, if you want to measure the melting point of ice, you might calibrate the thermistor by measuring the voltage output when the temperature is 0°C.

The curve of a thermistor is non-linear, so after calibration you won't be able to use a simple equation to convert your voltage output into temperature. Instead, you will need to use interpolation to estimate the temperature from the measured voltage output. You can use the data sheet for the thermistor to look up the corresponding temperature for each voltage measurement; then use linear interpolation between these points to estimate the temperature for any voltage between the known points.