To calibrate a thermistor so it can be used as a thermometer
Variables
Independent variable = temperature (oC)
Dependent variable = resistance of thermistor (Ω)
Control variables:
Temperature gradient controlled by stirring
Equipment
Power source
Thermistor
Fixed resistor
Ohm-meter
Bunsen burner, tripod and gauze
Beaker filled with crushed ice
Stirring rod
Liquid in glass or mercury thermometer with range -10 - 100oC
Resolution of measuring equipment:
Thermometer = 1oC
Ohm-meter = 0.01 Ω
Method
Set up the equipment with the thermistor immersed in the ice, the ohm-meter connected to record the resistance of the thermistor by placing it in parallel across it, and the fixed resistor in series with the thermistor
Place the beaker of ice onto the tripod, without lighting the Bunsen burner
Measure and record the temperature and reading on the ohm-meter
Light the Bunsen burner and keep to a gentle flame
Stir the ice / water gently at all times to keep the temperature as even as possible throughout the beaker
At approximately 5oC intervals record the new temperature and resistance reading
Continue until the water is boiling
Analysis
Plot a graph of resistance against temperature
Use the temperature graph to find the resistance at a given temperature
Evaluating the Experiment
Systematic Errors:
Read the thermometer at eye level
Check the zero error on the ohm-meter by connecting the leads across the terminals
Random Errors:
Allow time for the temperature to reach equilibrium
Stir the water before readings
Ensure thermometer bulb is completely submerged in the water and level with the thermistor
Turn off current between readings to avoid heating in the wires
Safety Considerations
Risk of instability, use a stand and clamp to support leads
Hot equipment and boiling water must be handled with care and allowed to cool down where possible
Keep plastic cables / leads away from hot metal
Check the voltage limit of the thermistor and stay within guidelines