Difference Between Thermistor and RTD

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

Thermistor vs RTD

The main difference between thermistors and RTD is that in a thermistor, semiconductor materials get utilized. The reaction time for changes is quick. In RTD, refined metals like platinum, nickel have a constructive (positive) temperature coefficient, and the reaction pattern for a temperature change is gentle.

Thermistor vs RTD

The thermistor gets used for measuring temperature for home appliances 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 temperature 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 Between Thermistor and RTD

Parameters of ComparisonThermistorRTD
Material UsedIt is made up of a semi-conductor.It is made up of refined metals such as nickel, copper, and platinum.
AccuracyIt has a high accuracy rate and detects the slightest change.It is not very accurate.
Response timeIt has a fast response time.It has a slow response time.
CostIt is expensive.It is not very expensive.
TemperatureIt 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, which is 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, 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 temperature between -2000 to 6000 C and, 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 of platinum. It is wound in a coil and placed inside a ceramic and glass insulator. This sensor is longer and delicate as compared to 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 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 the 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.

RTD’s are beneficial in automotive, marine, and industrial applications.

Main Differences Between Thermistor and RTD:

  1. The thermistor generally gets utilized in the home appliance for measuring small temperatures. Industries measuring high temperatures use RTD.
  2. The thermistor is sensitive to change to 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.
Difference Between Thermistor and RTD

Conclusion

The thermistor measures the temperature of small devices. The thermistor is best suited when the temperature remains constant.

They are sensitive to temperature change and measures gas, liquids, or solids. The RTD measures high temperatures and is helpful in different industries.

The RTD is accurate, consistent, and suitable for extreme environmental conditions. 

The thermistor and RTD are temperature sensing devices. The thermistor materials are semiconductors, and metals like platinum, nickel are used in RTD.

The thermistor can detect a minute temperature change, and RTD is used to measure sizeable temperature variations.

References

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