Thermocouple Sensor: What it is, types, and Buying Guide

A thermocouple is a device known for temperature measurement and consists of various sensor types for consumers to choose from. Ranging from K type thermocouple to J type, to T type and more, understanding its differences and buying one that’s suitable for your next thermocouple Arduino project may not be an easy task to handle!

Fear not though, through this guide, I’ll be helping you out by explaining:

  • What is a thermocouple?
  • How does a thermocouple work?
  • What is the type of thermocouples?
  • How to choose a thermocouple?
  • How to use a thermocouple with Arduino?

What is a thermocouple? Definition

K-Type Thermocouple

A thermocouple is a sensor made of two pieces of metal used to measure temperature. These two pieces of metals are welded together at one end, creating a junction where the temperature is measured.

The above picture is a K type thermocouple available here at Seeed! You can click here to learn more!

How do thermocouples work?

Thermocouples working principle

Thermocouple work on the principle of Seebeck effect (also known as thermoelectric effect), a principle discovered by German physicist Thomas Johann Seebeck back in the 18th century.

The Seebeck effect states that when two different metal is joined together at two junctions, an electromotive force (emf) is generated.

To further understand this working principle, we’ll take a look at a thermocouple circuit!

Thermocouple circuit explanation

The diagram below showcases an electrical circuit that’s commonly seen in thermocouples. Here’s how thermocouples work through this illustration:

  • The two pieces of metal are welded together at one end, creating a junction
  • The hot junction is the heat source that generates a temperature
  • When there’s a change in temperature, a voltage differential is produced across the metals
  • Thermocouple reference tables are then referred to interpret the voltage for the temperature to be calculated

What are thermocouples used for?

Now that we’ve understood how thermocouples work, we’ll now take a look at its applications.

Thermocouples are used in not only industrial applications but in your day to day appliances as well:

  • Industrial applications:
    • Temperature measurement of metals
    • Temperature measurement for kilns, engines, processes
    • Food industry; milk pasteurization and cryogenic
  • Day to day applications:
    • Thermocouple furnace
    • Stoves
    • Toasters

Overall, thermocouples are a widely used type of temperature sensor for measurement and control, although it contains differences when compared to other temperature sensor types such as RTD and thermostat. We’ll talk about the differences later on.

What’s the difference between thermocouple, RTD, thermistor?

A thermocouple can be compared alongside the RTD and thermistors as they are all common types of sensors for temperature measurement.

Note: The following table is for comparative purposes only, where the suitability of each sensor depends on what you’re trying to do with it

RTD Thermisistor Thermocouple
How temperature is measured Uses metal resistors and measure temperature through resistance changes Uses ceramic/polymer resistor and measure temperature through resistance changes Uses two metal wires and measure temeperature through voltage differential in the junctions
Typical temperature range -200 to 650°C -100 to 325°C 200 to 1750°C
Cost Most expensive Low cost to moderate Lowest
Sensing sensitivity Poor sensitivity with general response time being 1 to 50s Decent sensitivity with general response time Good sensitivity with general response time being 0.10 to 10s
Linearity Fairly linear Exponential Non-Linear
Thermal Excitation Required, current source Required, voltage source None required
Long-term stability Stable, 0.05°C Stable, 0.2°C Variable
Best used for More consistent readings with typical accuracy being ±0.1°C Consistent readings with typical accuracy being ±0.1°C Higher temperature range with typical accuracy being ±0.5°C

Apart from the above comparison between thermocouples, rtd, and thermistors, differences between thermocouple and thermopile are commonly talked about as well.

To help you simply understand, there’s only one main difference you’ll have to take note:

  • A thermocouple is a sensor made of two pieces of metal used to measure temperature.
  • A thermopile is a device that converts thermal energy into electrical energy

What are the types of Thermocouples?

Now that you’ve understood what thermocouples are and how it works, we’ll now dive deeper into what are the types of thermocouples?

There is 8 thermocouples type, classified as “base metal and noble metal namely the following:

  • Thermocouple type that’s made from Base Metal:
    • K type
    • J type
    • T type
    • E type
    • N type
  • Thermocouple type that’s made from Noble Metal:
    • R type
    • S type
    • B type

K type Thermocouple (Most popular)

Undoubtedly the most popular thermocouple type is the K type thermocouple. Known for its wide temperature range and durability, it’s one that many consider!

Here is all about the K type thermocouple:

Lead material used:

  • Nickel-Chromium (+), Alumel (-)

Color-Code:

  • ANSI (America): Yellow (+), Red (-)
  • IEC: Green (+), White (-)

Temperature range:

  • -200°C to 1250°C
  • Fahrenheit: –328 to 2,282F

Accuracy

  • Standard: +/- 2.2°C or +/- 0.75%
  • Special limits of error: +/- 1.1°C or +/- 0.4%

J type Thermocouple (less powerful option then the K)

Second, on the base metal list is the J type thermocouple. Despite having a smaller temperature range and less capable of sensing at higher temperatures, it’s still a common option!

Here’s all about the J type Thermocouple:

Lead material used:

  • Iron (+), Constantan (-)

Color-code:

  • ANSI (America): White (+), Red (-)
  • IEC: Black (+), White (-)

Temperature Range:

  • -210 to 760°C
  • Fahrenheit: –346 to 1,400F

Accuracy:

  • Standard: +/- 2.2°C or +/- 0.75%
  • Special limits of Error: +/- 1.1°C or +/- 0.4%

T type Thermocouple (Low-temperature option)

Thirdly, T type thermocouples. Commonly used in food industry applications that require extremely low temperatures such as cryogenics, it’s one that offers lower temperature readings despite a smaller temperature range.

Here’s all about the T type Thermocouple:

Lead material used:

  • Copper (+), Constantan (-)

Color-code:

  • ANSI (America): Blue (+), Red (-)
  • IEC: Brown (+), White (-)

Temperature range:

  • -270 TO 370°C
  • Fahrenheit: –454 to 700F

Accuracy:

  • Standard: +/- 1.0°C or +/- 0.75%
    Special Limits of Error: +/- 0.5°C or 0.4%

E type Thermocouple (Higher accuracy than K&J)

Before you read the title and go is Type E the best thermocouple type because it has higher accuracy than the popular ones, hold on!

E type thermocouple does offer higher accuracy and a stronger signal than type K&J but only at moderate temperature ranges and below!

Here’s all about the E type thermocouple!

Lead material used:

  • Nickel-Chromium (+), Constantan (-)

Color-code:

  • ANSI (America): Purple (+), Red (-)
  • IEC: Purple (+), White (-)

Temperature range:

  • -200 to 900°C
  • Fahrenheit: -328 to 1652F

Accuracy:

  • Standard: +/- 1.7°C or +/- 0.5%
  • Special Limits of Error: +/- 1.0C or 0.4%

N type Thermocouple (Expensive version of Type K)

The N type Thermocouple shares similar features with the popular K type in terms of temperature limit and accuracy and though it is priced more expensive.

Here’s all about the type N thermocouple:

Lead material used:

  • Nicrosil (+), Nisil (-)

Color-code:

  • ANSI (America): Orange (+), Red (-)
  • IEC: Rose (+), White (-)

Temperature Range:

  • -270 to 392°C
  • Fahrenheit: -454 to 2300F

Accuracy:

  • Standard: +/- 2.2°C or +/- 0.75%
  • Special Limits of Error: +/- 1.1°C or 0.4%

S type Thermocouple (Hightemperature thermocouple)

First of the three noble metal type thermocouples is the Type S. Designed with high temperatures sensing capabilities, it’s commonly used in conditions that require that. Such conditions being Pharmaceutical industries, BioTech, etc.

Here’s all about the Type S Thermocouple:

Lead material used:

  • Platinum Rhodium (+), Platinum (-)

Color code:

  • ANSI (America): Black (+), Red (-)
  • IEC: Orange (+), White (-)

Temperature Range:

  • 0 to 1450°C
  • Fahrenheit: 32 to 2642F

Accuracy:

  • Standard: +/- 1.5°C or +/- 0.25%
  • Special Limits of Error: +/- 0.6°C or 0.1%

R Type Thermocouple (Similar but more expensive than type S)

Second the three noble metal type thermocouples are type R. Similarly to the type S, it’s designed with high temperatures sensing capabilities. However, R type is more expensive than S type since it’s composed with a higher percentage of Rhodium.

Here’s all about the Type R Thermocouple:

Lead material used:

  • Platinum Rhodium (+), Platinum (-)

Color-code:

  • ANSI (America): Black (+), Red (-)
  • IEC: Orange (+), White (-)

Temperature Range:

  • 0 to 1450°C
  • Fahrenheit: 32 to 2642F

Accuracy:

  • Standard: +/- 1.5°C or +/- 0.25%
  • Special Limits of Error: +/- 0.6°C or 0.1%

B type Thermocouple (Highest temperature limit)

Lastly on this list is the type B Thermocouple. Thought that the Type R and Type S offer a high-temperature limit? The B type improves on that by having a higher temperature limit among all that are listed!

Not only does it offer the highest temperature limit, but it also maintains accuracy and stability at those high temperatures as well!

Here’s all about the Type B Thermocouple:

Lead material used:

  • Platinum Rhodium (+), Platinum Rhodium (-)

Color Code:

  • ANSI (America): Black (+), Red (-)
  • IEC: Orange (+), White (-)

Temperature Range:

  • 0 to 1700°C
  • Fahrenheit: 32 to 3100F

Accuracy:

  • Standard: +/- 0.5%
  • Special Limits of Error: +/- 0.25%

What are the differences between all Thermocouple Type

Here’s a summarized comparative table between all thermocouple types. You may refer to this in making a decision on how to choose a thermocouple

Lead Material Used Color-Code Temperature Range Accuracy
K type Nickel-Chromium (+)
Alumel (-)
ANSI (America): Yellow (+), Red (-)

IEC: Green (+), White (-)
200°C to 1250°C

Fahrenheit: –328 to 2,282F
Standard: +/- 2.2°C or +/- 0.75%

Special: +/- 1.1°C or +/- 0.4%
J type Iron (+)
Constantan (-)
ANSI (America): White (+), Red (-)

IEC: Black (+), White (-)
-210 to 760°C

Fahrenheit: –346 to 1,400F
Standard: +/- 2.2°C or +/- 0.75%

Special: +/- 1.1°C or +/- 0.4%
T type Copper (+)
Constantan (-)
ANSI (America): Blue (+), Red (-)

IEC: Brown (+), White (-)
-270 TO 370°C

Fahrenheit: –454 to 700F
Standard: +/- 1.0°C or +/- 0.75%

Special: +/- 0.5°C or 0.4%
E type Nickel-Chromium (+)
Constantan (-)
ANSI (America): Purple (+), Red (-)

IEC: Purple (+), White (-)
-200 to 900°C

Fahrenheit: -454 to 1600F
Standard: +/- 1.7°C or +/- 0.5%

Special: +/- 1.0C or 0.4%
N type Nicrosil (+)
Nisil (-)
ANSI (America): Orange (+), Red (-)

IEC: Rose (+), White (-)
270 to 392°C

Fahrenheit: -454 to 2300F
Standard: +/- 2.2°C or +/- 0.75%

Special: +/- 1.1°C or 0.4%
S type Platinum Rhodium (+)
Platinum (-)
ANSI (America): Black (+), Red (-)

IEC: Orange (+), White (-)
0 to 1450°C

Fahrenheit: -32 to 2642F
Standard: +/- 1.5°C or +/- 0.25%

Special: +/- 0.6°C or 0.1%
R type Platinum Rhodium (+)
Platinum (-)

Higher percentage of Rhodium
ANSI (America): Black (+), Red (-)

IEC: Orange (+), White (-)
0 to 1450°C

Fahrenheit: -32 to 2642F
Standard: +/- 1.5°C or +/- 0.25%

Special: +/- 0.6°C or 0.1%
B type Platinum Rhodium (+)

Platinum Rhodium (-)
ANSI (America): Black (+), Red (-)

IEC: Orange (+), White (-)
0 to 1700°C

Fahrenheit: 32 to 3100F
Standard: +/- 0.5%

Special: +/- 0.25%

How to choose a thermocouple sensor?

Selecting a thermocouple ultimately comes down to what you’re planning to use it for. You can firstly refer to the table from the above section for an overall understanding of all the thermocouple types before considering the factors below:

Temperature range:

  • For the widest temperature range: Choose the type k thermocouple
  • For stability in high temperatures: Choose the type N thermocouple
  • For low-temperature usage: Choose the type T thermocouple

The environment you’re using it in:

  • For usage in a safe environment with no chemical or abrasions; choose an ungrounded thermocouple as it offers faster response times
    • Ungrounded thermocouple are thermocouple wires that are exposed, not touching the sheath
  • For usage in an environment prone to chemical or abrasions, grounded thermocouple work best

How to use thermocouple with Arduino?

Be it whether you’ve made up your mind on which type of thermocouple to buy or not, with just a
thermocouple alone, it’s insufficient for usage with an Arduino.

Hence, this section will provide recommendations on products that you can use your thermocouple with your Arduino!

Grove – High Temperature Sensor

The Grove – High Temperature Sensor uses a K type thermocouple Temperature detection, with a Thermistor to detect The ambient Temperature as Temperature compensation. 

Thanks to our Grove system, and a dedicated Grove port on this sensor, you can connect it to your Arduino through plug-and-play, making thermocouple Arduino a simple reality!

Interested to find out more? You can head to our product page here! We provide a thermocouple Arduino guide alongside it as well!

Thermocouple Amplifiers

Another option you can consider pairing your thermocouple with an Arduino is with our selection of thermocouple amplifiers!

Note: Our selection of thermocouple amplifiers all have cold junction compensation, and a thermocouple-to-digital converter inside.

Grove – 1-Wire Thermocouple Amplifier (MAX31850K)

You’ve probably heard about MAX31855 thermocouple amplifiers but this thermocouple amplifier that’s based on MAX31850 offers the same resolution when compared.

Specifically made for the type k thermocouples, it has a 64-bit ROM and 1-wire interface, allowing for multiple thermocouples to be used with only one microcontroller!

Interested to find out more about its features and specifications, and applications? You can head to our product page here! We provide an Arduino guide alongside it as well!

Grove – I2C Thermocouple Amplifier (MCP9600)

The other option would be this thermocouple amplifier that’s based on the MCP9600. When compared to the MAX31855, this option offers a higher resolution despite using the same I2C interface.

Similarly to the previous thermocouple amplifier option, this module is designed to be used in conjunction with a k-type thermocouple as well!

Interested to find out more about its features and specifications, and applications? You can head to our product page here! We provide an Arduino guide alongside it as well!

Summary

That’s all today for today on thermocouples and a guide to selecting one. I hope with this blog, you’ve understood more about thermocouples, the types, and how to select a suitable one for your next thermocouple Arduino project!

For more information on the k type thermocouple we offer, you can check out our product page!

For more information on Thermocouple Amplifies alongside max31855 comparison, you can check out this article!

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