Temperature Sensors - Thermistor - RTDs Probes & Assemblies

What are Temperature Sensors?

A Temperature Sensor is a device that detects and measures the average heat or thermal energy in a medium and converts it into an electrical signal. A wide variety of temperature sensing devices are available today. Littelfuse offers a broad range of Thermistors, Resistance Temperature Detectors (RTDs), Digital Temperature Indicators, and probes and assemblies for temperature sensing applications worldwide.

How do Temperature Sensors Work?

Each temperature sensor style has its own set of operating principles, features, benefits, considerations, and limitations for optimal use.


      Thermistors (NTCs and PTCs):

  • Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable, and precise change in electrical resistance when subjected to a corresponding change in body temperature.
  • Negative Temperature Coefficient (NTC) thermistors exhibit a decrease in electrical resistance when subjected to an increase in body temperature.
  • Positive Temperature Coefficient (PTC) thermistors exhibit an increase in electrical resistance when subjected to an increase in body temperature.
  • Based on the predictable characteristics and their excellent long-term stability, cost-effective thermistors are generally accepted to be the most advantageous sensor for many applications, including temperature measurement and control.


  • Platinum Resistance Temperature Detectors (RTDs) are temperature sensors that have a positive, predictable, and nearly linear change in resistance when subjected to a corresponding change in their body temperature. 
  • The nearly linear output needed to precisely measure temperature over a very wide range makes RTDs ideal for more-specialized applications requiring very high accuracy (ex. 0.06%/0.15°C) or for applications requiring a lot of precision.

      Digital Temperature Indicators:

  • Digital Temperature Indicators have a positive relationship between resistance and temperature. The response is very much like a digital signal; below the trip temperature, resistance will be low, above the trip temperature, resistance will be very high. 
  • This digital response is ideal for applications where knowing the temperature has increased beyond a specific value is required. With the digital response, no analog to digital conversion is necessary, allowing designers to save time and space.

Can I Customize Temperature Sensors?

Modifications are available to existing standard product packages, such as adding connectors or changing wire size or length, as well as offering special resistance-temperature (R-T) curves, R-T curve matching, and custom lead forming and bending to discrete thermistors. In addition, the following options and services are available.

  • Complete custom sensor packages, including moisture resistant designs
  • Custom resistance-temperature (R-T) characteristics
  • Specialized resistance tolerance or temperature accuracy within specified temperature ranges
  • Sensing element design for best long-term stability
  • Rapid prototyping and quick-turn concept parts including 3D printed parts
  • Prototype units using prototype tooling
  • Reliability/validation testing options
  • Fully designed, production-capable sensor and tooling

Typical Applications for Temperature Sensors

Temperature sensors are used in diverse markets, including:



  • Residential & Commercial A/C
  • Chilled Water Systems
  • Outdoor Temperature Sensors
  • Instant Water Heaters
  • Condenser, Evaporator & Duct Sensors

Renewable Energy

  • Hydrogen Fuel Cell Sensors
  • Battery Fuel Gauges
  • Solar Panel
  • Geothermal
  • Battery Energy Storage Systems
  • Solar Inverters


  • Oven Temperature Control
  • Washing Machines
  • Clothes Dryers
  • Water Heaters
  • Consumer Refrigerators/Freezers

Food Service

  • Commercial Coffee Makers
  • Hot/Cold Beverage Dispensers
  • Food Thermometers
  • Walk-in & Reach-in Refrigerators/Freezers
  • Temperature Controlled Display Cases


  • Blood Analysis Equipment
  • Infant Incubators
  • Skin Temperature Monitors
  • Blood Dialysis Equipment
  • Patient Warming