Thermistor Characteristics

Objectives: To study the resistance- temperature characteristics of the thermistor.

Apparatus: Thermistor, mercury thermometer, beaker with water, heater assembly, digital multimeter

Introduction:

Thermistors, like resistance temperature detectors (RTD), are thermally sensitive semiconductors whose resistance varies with temperature. Thermistors are manufactured from metal oxide semiconductor material encapsulated in a glass or epoxy bead. Thermistors have either a negative temperature coefficient (NTC) or a positive temperature coefficient (PTC). The first, more common, has a resistance that decreases with increasing temperature while the latter exhibits increased resistance with increasing temperature. Thermistors typically have a very high sensitivity (~200 Ω/°C), making them extremely responsive to changes in temperature.

Procedure:

• Note down the room temperature from mercury thermometer. Insert it in water and note down the initial temperature of water T₀. (Click on the image to enlarge)

• Attach two terminals of thermistor to appropriate terminals of digital multimeter to measure resistance of the thermistor. Insert it in water and note down the initial reading of resistance R₀. (Click on the image to enlarge)

• Switch on the heater and note down thermistor readings for every 1^oC rise in temperature upto 80^oC. (Click on the image to enlarge)

• Watch the video and generate the data set for “heating”.

• Once the temperature reaches 85^oC, switch off the heater and now take same readings for cooling of water upto initial reading. 
• Watch the video and generate the data set for “cooling”.

• Plot the graph for resistance vs temperature. 
• Plot the graph for ln(R) vs T and find the calibration equation for the thermistor.

Observations:

T₀ = _______________^oC

R₀ =_______________Ω

Plot a graph between T [X-axis] and ln(R) [Y-axis].

The calibration equation for the thermistor is______________________________