Thermistor vs RTD: Difference and Comparison

Measuring temperature is crucial at home and in an industrial setup. Both thermistors and RTD are measuring devices and play a critical role in our lives.

The thermistor is a sensitive resistor commonly found in most household devices. The RTD stands for Resistance Temperature Detector. With the usage of metals, it is part of industrial use.

Key Takeaways

1. Thermistors show a higher sensitivity to temperature changes, while RTDs provide greater stability and accuracy.
2. RTDs have a linear relationship between resistance and temperature, while thermistors have a non-linear relationship.
3. Thermistors are more cost-effective, whereas RTDs are better suited for high-temperature applications.

Thermistor vs RTD

Thermistors work on the principle of resistance change with temperature and are used in applications where high accuracy is not required. RTDs work on the principle of resistance change with temperature but are made of pure metal wire and used in applications requiring high accuracy.

The thermistor is used for measuring home appliances’ temperature and measures a temperature range of -55* Celsius and +114* Celsius.

It can detect the slightest temperature change, and the cost of the thermistor is high. It is a thermal resistor made of semiconductor materials with both positive and negative temperature coefficients.

The RTD measures temperatures up to 850* Celsius and gets utilized in industries measuring large temperatures. It is less accurate and not quick to respond to change.

The size of RTD is large and comparatively cheaper than the thermistor. The RTD comprises metals, which have a positive coefficient, and the graph of RTD is linear.

Comparison Table

Parameters of Comparison	Thermistor	RTD
Material Used	It is made up of a semi-conductor.	It is made up of refined metals such as nickel, copper, and platinum.
Accuracy	It has a high accuracy rate and detects the slightest change.	It is not very accurate.
Response time	It has a fast response time.	It has a slow response time.
Cost	It is expensive.	It is not very expensive.
Temperature	It is between the temperature of -55 °C and 114 °.	It is up to 850 ° C.

What is a Thermistor?

The term thermistor originates from the thermal and resistor. A thermistor is a resistor whose resistance is inclined to thermal reading.

It is a resistance thermometer made from metallic oxide and engraved into a bead, disk, or cylinder shape, then inserted into glass or epoxy.

Extreme temperatures are not easily measurable. They are precise in measuring temperatures within a defined range of 50 degrees Celsius of the target temperature. 

Thermistors are durable and not expensive devices. Devices resistant to temperature utilize a thermistor. A digital thermometer, ovens, refrigerators, and vehicles to measure coolant and oil.

Applications that require heating and cooling protection circuits have thermistors.

The thermistor is empirical for compound appliances like laser optical blocks, charge-coupled devices, and stabilization detectors.

How does the thermistor work:

Thermistors can get further classified as the Negative Temperature Coefficient(NTC) and Positive Temperature Coefficient(PTC). In NTC, when the resistance lessens, the thermal reading increases. In PTC, the thermal reading increases with resistance. This function helps in a fuse.

The material in the thermistor plays a crucial role in the function of resistance and temperature. The graph displaying the relationship between both is nonlinear. It constantly forms a curve and not a straight line.

The change in resistance gets converted to temperature as this is measurable data.

The various shapes depend on the surface monitored(solid, liquid, gas) and the material utilized. They are enclosed either in glass, resin, baked-on phenolic, or pained based on the application.

There must be maximum surface contact with the device to be monitored. They are suited when a temperature needs monitoring. It is sensitive to the slightest change in temperature.

What is an RTD?

The Resistant Temperature Detector(RTD) is a temperature sensor. It works based on the resistance of the metal to temperature change.

The RTD preference over other applications is accuracy, have ease of use, repeatability, and cost. These sensors get utilized in domestic and industrial applications.

Resistance thermometers measure temperatures between -2000 to 6000 C; some are as high as 1000 C. The most commonly utilized sensors are wire-wound RTD and thin-film RTD elements.

• Wire-wound RTD-It is a small-diameter wire mainly made of platinum. It is wound in a coil and placed inside a ceramic and glass insulator. This sensor is longer and more delicate as compared to a thin film. The accuracy is precise over a broader range of temperatures.
• Thin-film RTD elements-Thin film elements get made by depositing a thin layer of platinum on a ceramic base and further coating it with epoxy or glass to enhance the protection of the thin film. This RTD performs better in vibration application or spot temperature. RTD gets denoted by the element and the resistance value. For example, Pt100 has a platinum element and resistance of 100 Ohms.

The electric resistance measurement is Ohms, and they are then converted into temperature based on the element. The response time is about 0.5 and 5 seconds making it best for an application without a quick response.

RTDs are beneficial in automotive, marine, and industrial applications.

Main Differences Between Thermistor and RTD:

1. The thermistor gets utilized in the home appliance for measuring small temperatures. Industries measuring high temperatures use RTD.
2. The thermistor is sensitive to changes in temperature. The RTD does not immediately respond to a change in temperature.
3. The thermistor measures temperature between the range of -55 degrees Celsius and +114 degrees Celsius. The RTD measures temperature up to 850 degrees Celsius.
4. The graph between resistance and temperature is nonlinear in the thermistor. In RTD, the graph representing the resistance and temperature is linear.
5. The thermistor gets produced using semiconductor materials. The RTD has metals with a positive temperature coefficient.

References

1. https://www.sciencedirect.com/science/article/pii/0019057894901007
2. https://aip.scitation.org/doi/abs/10.1063/1.4750142