When examining the term “epoxy NTC thermistor”, epoxy refers to the component’s epoxy coating. A Thermistor is a resistor that changes its resistance value with temperature. Technically, all resistors are thermistors, their resistance changes slightly with temperature but the change is usually very small and difficult to measure. Thermistors are made such that their resistance changes drastically with temperature so that it can be 100 ohms or more of change per degree.
For the corresponding resistance value of a specific temperature, the resistance/temperature table as shown in the figure below can be used to understand the change of resistance and temperature.
There are two kinds of thermistors, NTC (negative temperature coefficient) and PTC (positive temperature coefficient). In general, you will see NTC sensors used for temperature measurement. PTC’s are often used as resettable fuses - an increase in temperature increases the resistance which means that as more current passes through them, they heat up and ‘choke back’ the current, quite handy for protecting circuits.
As an example from Adafruit Industries LLC 372, let’s see the product detail.
372 is an epoxy-coated precision 1% 10K thermistor which is an inexpensive way to measure temperature in weather or liquids. The resistance in 25 °C is 10K (+/- 1%). The resistance goes down as it gets warmer and goes up as it gets cooler.
Need to measure something damp?
Epoxy-coated thermistors are often used for air conditioners, water lines, and other places where they can get damp. The PVC coating of the wires is good up to 105 °C so this isn’t good for very hot stuff.
Note that even though the thermistor can go up to 125°C the cable itself maxes out at 105°C so this thermistor is not good for measuring very hot liquids
372 also includes an additional 1% 10K resistor which you can use for calibration or for a resistor divider.
372 Product and Technical Details:
• Resistance at 25 degrees C: 10K +/- 1%
• B25/50: 3950 +/- 1%
• Thermal time constant <= 15 seconds
• Thermistor temperature range: -55 °C to 125 °C
• 28 AWG PVC Wire
Dimensions:
• Diameter: 0.13”/ 3.3mm
• Length: At least 457mm / 18" long