Difference Between Thermistor And RTD

Knowledgebase

Thermistors and RTDs (Resistance Temperature Detectors) are two of the most common temperature-sensing devices used in a wide range of commercial, industrial, and residential applications. Both thermistors and RTDs have their own advantages and disadvantages, so it is important to know the differences between them when selecting a temperature sensor for a given application.

Thermistor VS RTD

What Is A Thermistor?

Thermistors are temperature sensors made from semiconductor materials. They have a negative temperature coefficient, meaning that as the temperature increases, their resistance decreases. Thermistors offer fast response time and high accuracy at lower temperatures but can be unstable or inaccurate when used at higher temperatures.

What Is An RTD?

RTDs are electro-mechanical temperature sensors made with a resistance element and typically constructed from copper, nickel, or platinum. They have a positive temperature coefficient, meaning that as the temperature increases their resistance also increases. RTDs offer high accuracy and stability over a wide temperature range but tend to be more costly than thermistors.

What Is Its Ideal Accuracy?

  • Thermistor: Thermistors are accurate to within +/- 1 to 5 degrees Celsius depending on the type and brand of a thermistor.
  • RTD: RTDs can typically be accurate within +/- 0.05 degrees Celsius or better.

Which One Is Better For Which Situation?

  • Thermistor: Thermistors are best suited for applications that require fast response and accuracy at lower temperatures, such as in the automotive industry.
  • RTD: RTDs are better for applications that require accurate readings over a wide temperature range, including industrial and chemical processes and food production. They are also more durable than thermistors and can withstand extreme temperatures or hazardous environments.

How Does A Thermistor Work?

  1. Thermistors work by using the principle of electrical resistance to measure temperature changes.
  2. A thermistor is a semiconductor device that contains two terminals and is sensitive to heat.
  3. When current passes through the thermistor, its resistance will change depending on the temperature.
  4. By measuring this change in resistance, the temperature can be determined.

How Does An Rtd Work?

  1. An RTD consists of a metal element such as copper, nickel, or platinum that is wound into a coil and placed inside a tube.
  2. As the temperature increases, the resistance of the metal element changes proportionally.
  3. This change in resistance is measured using a Wheatstone bridge circuit, which then produces an output voltage that can be used to read the temperature.
See Also:  Difference Between PEX And PB Piping

Types Of Thermistors: Ptc & Ntc

  1. NTC Thermistors: NTC thermistors are the most common type of thermistor and have a negative temperature coefficient, meaning their resistance decreases as the temperature increases.
  2. PTC Thermistors: PTC thermistors, or “Positive Temperature Coefficient” thermistors, have a positive temperature coefficient, meaning that their resistance increases as the temperature increases.

Types Of RTD Elements

  1. Platinum RTDs: Platinum RTDs are the most commonly used type of RTD and offer high accuracy, stability, and durability over a wide temperature range.
  2. Nickel RTDs: Nickel RTDs are less expensive than platinum but tend to be less accurate and more prone to drift over time.
  3. Copper RTDs: Copper RTDs are the least expensive and least accurate of the three types but offer fast response times.

Application:

Thermistor:

  1. Home appliances.
  2. Automotive electronics.
  3. Industrial automation systems.

RTD:

  1. Heating and cooling systems.
  2. Thermal process control equipment.
  3. Medical monitoring devices.

Are There Other Application Limits For Rtds And Thermistors?

RTDs:

  1. RTDs are limited by the composition of their resistance elements, so they do not work well at extremely high temperatures.
  2. They also have a higher power consumption and require an external source to operate because of their low resistance values.

Thermistors:

  1. Thermistors generally have a lower temperature range than RTDs, usually not exceeding 150°C.
  2. As thermistors depend on a semiconductor material to function, they are highly susceptible to breakage or damage when exposed to extreme temperatures or hazardous environments.
  3. Their small size can also make them difficult to connect or handle in certain applications. thermistors are sensitive to circuit noise and require smoothing capacitors for accurate readings. They may also require additional components such as resistors to adjust their resistance values when used with different instrumentation.​

Comparison Chart

PROPERTY Thermistor: RTD:
Definition: A temperature sensor made from semiconductor materials. An electro-mechanical temperature sensor made with a resistance element.
Best Suited For: Fast response time and high accuracy at lower temperatures.  Accurate readings over a wide temperature range.
Ideal Accuracy: +/- 1 to 5 degrees Celsius depending on the type and brand of a thermistor.  +/- 0.05 degrees Celsius or better.
Types: NTC and PTC Platinum, Nickel, and Copper.
Symbol: Triangle with curved sides. Square with rounded corners.
Material: Semiconductor material. Metal elements such as copper, nickel, or platinum.
Cost: Low cost. More expensive than thermistors.
Response Time: Fast response time. Slower response time than thermistors.
Temperature Range: Lower temperature range. Wide temperature range.
Characteristic: Resistance changes with temperature. Resistance proportionally changes with temperature.
Durability: Vulnerable to extreme temperatures or hazardous environments. More durable than thermistors and can withstand extreme temperatures or hazardous environments.
Sensitivity: Highly sensitive to temperature. Moderately sensitive to temperature.
Size & Weight: Smaller and lighter. Larger and heavier.
Resistivity: Low resistivity. High resistivity.
Hysteresis Effect: Low hysteresis effect. High hysteresis effect.
Drift Rate: Low drift rate over time. Higher drift rate over time.
Temperature range: -55 to 150°C -200 to 850°C.
Repeatability and stability: Good repeatability and stability over time. Better repeatability and stability than thermistors.
Linearity: Non-linear.  Linear.
Standardization: Not standardized. Standardized according to ASTM and IEC standards.
Wire Length: Longer wire lengths can affect accuracy. Shorter wire lengths do not impact accuracy.
See Also:  Difference Between NiMH And mAh Batteries

So Which Sensor Is Better, An Rtd Or A Thermistor?

RTDs offer better accuracy and repeatability over wide temperature ranges, while thermistors provide a lower-cost solution with faster response times in shorter temperature ranges. Both sensors have their advantages and disadvantages so it is important to consider your needs carefully before deciding which one to use.

FAQs

Where Are RTD And Thermistors Used?

RTDs are used in applications such as heating and cooling systems, thermal process control equipment, and medical monitoring devices. Thermistors are used in home appliances, automotive electronics, and industrial automation systems.

What Is The Maximum Temperature Range For RTD And Thermistor?

RTDs have a temperature range of -200 to 850 °C, while thermistors usually have a range of -55 to 150°C.

Why Pt100 Is Used In RTD?

The PT100 is a type of RTD sensor with a resistance that changes proportionally to temperature. It is commonly used because it has high accuracy and stability over wide temperature ranges.

Why Is RTD Called Pt100?

PT100 stands for Platinum Resistance Temperature Detector. This indicates that the RTD is made from platinum, and has a resistance of 100 ohms at 0°C.

What Is Hysteresis Effect?

The hysteresis effect is when the output of a system or device does not return to its original state after an input signal is removed. Thermistors have a lower hysteresis effect than RTDs, while RTDs are more accurate over long periods of time due to their higher hysteresis effect.

Is A Pt100 A Thermistor?

No, a PT100 is not a thermistor. It is a type of RTD (Resistance Temperature Detector) that uses platinum for its resistance element, and has a resistance of 100 ohms at 0°C. Thermistors are made from semiconducting materials and respond to changes in temperature more quickly than RTDs.

Is RTD Digital Or Analog?

RTDs are analog sensors, which means they measure temperature continuously.

Is The Thermistor Active Or Passive?

Thermistors are passive sensors, which means they do not require an external power source. They rely on the energy from the environment to provide a change in resistance when exposed to changes in temperature.

Are Thermistors Accurate?

Thermistors generally have higher accuracy than RTDs over shorter temperature ranges, but their accuracy decreases with longer temperature ranges. When used correctly, thermistors can be reasonably accurate in most applications.

What Is The Principle Of RTD?

The principle of RTD is based on the resistance-temperature relationship. As temperature increases, the resistance of an RTD changes in a predictable and linear fashion. This allows for accurate measurements to be taken when used with instrumentation.

What Is The Principle Of Thermistor?

The principle of thermistor is based on the temperature-dependent resistance of semiconducting materials. As the temperature increases, the resistance decreases in a predictable and non-linear fashion. This allows for fast measurement readings to be taken when used with instrumentation.

Conclusion

RTDs and thermistors both have their advantages and disadvantages, so it is important to consider your needs before deciding which one to use. RTDs offer better accuracy and repeatability over wide temperature ranges while thermistors provide a lower cost solution with faster response times in shorter temperature ranges. Both sensors can be used with instrumentation to take accurate measurements in many environments.

Leave a Comment

MdmTool

A website that provides helpful guides and solutions for tools. We aim to provide the most comprehensive and up-to-date information, so that you can make the best decisions for your selecting the right tools for your business.
https://mdmtool.com/

Tool Categories

Cutters

Measuring Tools

Drills

Our Moto

At MdmTool.com, we believe that everyone should have access to the best tools available. Whether you're a professional tradesman or a DIY enthusiast, we want to help you find the right tools for the job.

More questions? Get in touch