Difference Between RTD and Thermocouple

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RTD and Thermocouple

RTD, which stands for Resistance Temperature Detectors, is the common type of sensor used for temperature measurements. Similar to RTD, Thermocouple is also widely used for measuring temperature range. These two sensor types are chosen over other methods for measurements due to their ease of use. Additionally, these avoid the tiresome conversion process while processing temperature measurements. However, there are some points of difference between RTD and Thermocouple, which are important to understand. This article highlights the important distinctions between RTD and a thermocouple. 


What is Resistance Temperature Detector (RTD)?

Resistance Temperature Detectors refers to sensor types. Its resistance changes with the change of temperature. Talking about RTD vs. Thermocouple, RTD’s resistance increases with the increase in temperature, whereas there is a decrease in thermocouple’s resistance. These sensors are passive devices, which means that RTDs do not generate output on their own. The element present in Resistance Temperature Detectors consists of a film prepared of a pure metal or a wire coil. These are comparatively immune to electrical noise and hence, are well-suited for measuring temperatures in industrial applications. 


What is the Use of Thermocouples?

A thermocouple is a sensor device that comprises two non-similar conductors. The conductors used to produce a voltage that is proportional to a difference in temperature between the conductor's ends. In comparison to other temperature measurements, thermocouples need no external form of excitation as these are self-powered. Thermocouples measure the unfamiliar temperature of the body with reference to the other body’s known temperature. RTD and Thermocouple are user-friendly and help in getting the results rapidly. 

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The diagram shows that two material wires are used in thermocouples that form a junction. It allows thermocouples to measure the high-temperature range.


Benefits of Using Resistance Temperature Detectors?

  • RTDs offer accurate measurements and thus proven to be the most precise temperature sensors.

  • It has tremendous sensitivity over the narrow spans.

  • It has low susceptibility to RFI and EMI.

  • RTDs offer stable output that lasts for longer periods.

  • These offer immunization against the electrical noise. 

  • The lifespan of RTDs is for many years.


Applications of Resistance Temperature Detectors

Resistance Temperature Detectors can be used in:

  • Refrigeration servicing

  • Micro Electronics

  • Plastics processing

  • Air Conditioning servicing

  • Temperature measurement of air, gas, and liquid

  • Petrochemical processing

  • Textile production

  • Stoves and grills

  • Micro Electronics

  • Measurement of exhaust gas temperature 


Benefits of Using Thermocouple

Due to their small size and quick response, Thermocouples are widely used in industrial applications.

  • It resists vibrations and shocks.

  • It is useful for a broad range of temperatures.

  • Thermocouples are the most durable sensors for temperature measurements.

  • It is user-friendly and retrieves the results promptly.


Applications of Thermocouples

  • Thermocouples are widely used in:

  • Diagnostics testing for diesel engines 

  • Various gas appliances like boilers, water heaters, and ovens

  • Hospital thermometers 

  • Temperature sensors in thermostats 

  • Gas turbine exhausts, kilns, and other industrial applications 


Different Situations Where You Prefer RTD Over Thermocouple

  • Combined with Transmitters: It’s easy to combine RTD with transmitters that enable the temperature data to be directed to a remote control location. It also allows the users to view the local display of the temperature. 

  • Laboratories and Industrial Purposes: In terms of accuracy when we set up RTD vs. thermocouple, RTD is much more accurate as compared to the thermocouple and hence more preferable for laboratories and industrial purposes.

  • Automotive Industries: When the temperature process has a range in-between -200 to 500-degree Celsius, then industrial RTD is much superior over thermocouple. 

  • Medical Electronics: When it comes to a low amount of shifts for RTD vs. thermocouple, RTD shows a very virtuous good stability and linear display as well. However, thermocouples are poor in terms of stability and hence less preferable for industrial applications.


The picture shows that thermocouples are useful to measure a high range of temperatures. However, RTD is useful for low-temperature measurements.

To sum up, the critical differences between RTDs and Thermocouples include:

What are the Differences Between RTD and Thermocouple?

Point of Difference

Thermocouple

RTD

Self-heating 

None

Crucial to taken into consideration

Poorest for

Long-term stability concerns

Surface readings

Worth for

High-temperature analyses

Consistent readings

Hysteresis

Excellent

Average

Extension cable

Yes, must-watch Th/c

No

Issues related to noise

Some noise problems

No

Cost

Not much expensive 

More expensive than thermocouple 

Excitation

No

Yes

Signal Strength

Low as it is susceptible to EMI

Higher-strength as it is more resistant to EMI

Interchangeability

Good interchangeability 

Excellent interchangeability

Tip Sensitivity

Good

Low

Maximum measurement Range

From -180-degree Celsius to +2320-degree Celsius

From -200-degree Celsius to +500-degree Celsius

Long-term stability

Good only when the right type is chosen according to the temperature

Good

Repeatability

Low

Good

Resistance to vibration

Yes

None

Accuracy 

Poor

Good

FAQ (Frequently Asked Questions)

1. How Does an RTD Operate?

There are some basic principles on which an RTD operates. With the increase in temperature, current flow resistance also increases. The electric current will pass from the sensor, and the resistance will be measured by using a resistance element. Thus, due to this interaction, the current and resistance calculation in the metal is detected.

2. What is the Basic Principle of Thermocouples?

Thermocouple operates with a Peltier effect. When you apply a voltage between the electrodes that are connected to the semiconductor material, it creates a Peltier effect. In this, two metals will join that form two junctions in the temperature. Peltier emf is introduced between the junction of the circuits. The junction in the circuit produces some difference in the temperatures, which leads to the working of thermocouples.