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Difference Between Thermocouple and Rtd

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Thermocouple and Rtd: Introduction

RTDs and thermocouples are two types of sensors used to measure heat on scales like Kelvin and Fahrenheit. Many times, people are faced with the difficult decision of whether to utilize thermocouple and rtd because such devices are used in a wide variety of settings and applications. Each type of temperature sensor has unique benefits and drawbacks that make it appropriate for particular situations and scenarios. In this article, we will first learn what is thermocouple and rtd.

Last updated date: 26th Sep 2023
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What is Thermocouple?

The junction formed by the joining of two distinct kinds of metals at one end of a thermocouple is called the junction. A voltage is produced that is related to temperature when the junction of the two metals is heated or cooled.

Thermocouple probes, thermocouple probes with connections, thin film thermocouples, transition joint thermocouple probes, infrared thermocouples, bare wire thermocouples, and even just thermocouple wire are just a few of the types in which these sensors are produced.

Due to their large variety of types and technical characteristics, thermocouples are frequently utilized in numerous applications. To better choose the appropriate thermocouple type and material for an application, it is crucial to understand their fundamental structure, functionality, and ranges.

Material Used for Thermocouple:

Regarding thermocouple sensors, various conductive metals will generate varying amounts of very tiny voltage or charge.

The most popular thermocouple kinds are identified by a lettering scheme, including K, J, T, and E. Each letter designates a particular pairing of the two metals that make up the thermocouple.

These metal mixtures are chosen for their particular qualities, such as precision, responsiveness, and temperature range.

For instance, a K-type thermocouple, which is frequently used in high-temperature applications like furnaces and boilers, is built of the metals Chromel and Alumel.

A J-type thermocouple, on the other hand, is utilized in low-temperature applications like refrigeration systems and is built of iron and constant metals.

The proper thermocouple type must be chosen in order to obtain reliable temperature readings because it depends on the particular application.

What is Rtd?

The resistance temperature detector is referred to as RTD. It is a temperature sensor that enables sensing electrical wire resistance to determine temperature. This electrical cable serves as a thermometer. In essence, a metallic wire is present, and when the quantity of heat experienced by the metallic substance increases, there is a change (rise) in resistance because of variation in the wire's degree of heat. But as heat is applied to the wireless, the resistance of the wire reduces.

In this manner, the rise or fall in the wire's resistance indicates a change in temperature, therefore it is possible to forecast temperature variation by resistance variation.

RTDs are often built using metals whose resistance is known, allowing for simple interpretation and recording of the change in value. Copper, nickel, platinum, and other common metals are included in the construction of RTDs.

It should be noted that platinum typically has a wide operating temperature range with consistent resistance properties. but it stops being linear for nickel over 300° C.

Material Used for Rtd:

Nickel is the best material to utilize in tough situations because of its strong corrosion resistance. It is a popular choice because it is also reasonably inexpensive when compared to other materials.

Nickel, on the other hand, has a relatively high-temperature coefficient, which means that the temperature has little effect on how resistant it is.

The high-temperature coefficient of platinum, on the other hand, makes it a highly accurate thermometer. Additionally, it resists corrosion, making it perfect for usage in challenging conditions.

But because it is so much more expensive than nickel, platinum may not be as desirable in other applications.

Copper also has a high electrical conductivity, which makes it perfect for situations where a quick response time is needed. In comparison to platinum, it is also comparatively inexpensive.

However, copper is less appropriate for usage in hostile conditions since it does not have the same level of corrosion resistance as nickel or platinum.

Difference Between Thermocouple and Rtd:

Let us now differentiate between thermocouple and rtd in a tabular form. 




Operating principle 

Temperature varies as generated emf changes. 

Resistance changes cause the temperature to vary.

Response time 

0.1-10 seconds 

1-50 seconds


Non- linear 






Measures temperature of chemical and petroleum plants and detects the temperature of metals and aluminum for industrial purposes.

They are used to measure engine temperature along with the temperature of the amplifier and oil temperature sensor, etc.

Physical Size

Comparatively small 


Self- heating 

Not exist 


Advantages and Disadvantages of Thermocouple and Rtd:

Both RTDs and thermocouples are temperature sensors, and which one to employ should depend on the needs of the application. Depending on the circumstances of the application, every sensor has advantages and disadvantages of its own.

RTDs are often more precise, stable, and linear up to 600 °C (1112 °F) in temperature range. Lower temperature ranges, where more accuracy, stability, and repeatability are needed, are better suited for RTD sensors.

In contrast, thermocouples are less precise, less stable, and more prone to drift over time. However, depending on the type of thermocouple, thermocouples have a quicker temperature response, are more durable, and can resist harsher circumstances like vibration and temperatures up to and over 2000 °C (3632 °F).


This article highlighted the differences between thermocouples and RTDs in terms of their temperature sensing applications. The main takeaways are as follows: RTDs offer higher accuracy with a precision of 0.5°C compared to thermocouples' accuracy of 2°C. Thermocouples have a wider temperature range of -250°C to +1800°C, while RTDs operate between -200°C and +850°C. RTDs have a response time of 1-2 seconds, whereas thermocouples respond faster. Thermocouples are more cost-effective for applications that prioritize affordability over accuracy. On the other hand, RTDs are known for their durability and stability due to high-quality materials. Ultimately, the choice between RTDs and thermocouples depends on the specific requirements of the temperature sensing application at hand.

FAQs on Difference Between Thermocouple and Rtd

1. What is thermocouple?

Thermocouples are temperature sensors that produce a voltage by combining two distinct metals, which can then be read to determine the current temperature. The thermocouples can be constructed using various metal combinations to produce various calibrations with various temperature ranges and sensor properties.

2. What is rtd?

Metals' electrical resistance increases as heat is applied, making them hotter; conversely, it reduces as heat is applied, making them colder. RTDs are temperature sensors that gauge local temperature changes by monitoring changes in the electrical resistance of metals. The electrical resistances of the metals used in RTDs must be known to individuals and recorded for easy reference in order for the results to be interpreted. As a result, RTDs are frequently made of the metals copper, nickel, and platinum.

3. Differentiate between thermocouple and rtd.

The most popular sensor types for measuring temperatures are Thermocouples and Rtd. These are used over the alternatives for measurements because they eliminate the laborious conversion process and provide the measurements quickly. The fundamental difference between thermocouples and Rtd is how they are made and how they operate.

4. Write in brief about thermocouple and rtd.

RTDs and thermocouples, in short, each have advantages and downsides. Additionally, each brand of RTDs and thermocouples has pros and cons of its own. The specific demands and capacities of the organizations making up the buyers' target market should be compared to the specific capabilities of the brands that are on the market. In general, RTDs produce better and more accurate readings while thermocouples are more affordable, durable, and capable of measuring a wider range of temperatures.

5. Mention examples of thermocouple and rtd.

This article's introduction stated that RTD and thermocouples could be used in a variety of industrial applications, including regulating temperature in ovens, heaters, and freezers in the food and beverage sector.

In your car, where sensors for engine temperatures, exhaust gas temperature, and even engine oil temperature are all monitored, you can find them as well.