The most common selection criteria are temperature range, chemical resistance, abrasion and vibration resistance, and installation requirements. Installation requirements will also determine your choice of a thermocouple probe.
There are differenttypes of thermocouplesand their applications may vary. An exposed thermocouple works best whenlong reaction times are required, but an ungrounded thermocouple is better in corrosive environments. To help you determine the best thermocouple for your purposes, here are five considerations:
- Determine the application in which you will use the thermocouple sensor
Thermocouples can be used in many industries and applications, so choosing the right thermocouple for your needs starts with knowing exactly how and where you want to use it. - Determine the temperature ranges the probe will be exposed to
Once you know the thermocouple temperature range you need, you can use our thermocouple range chart to determine which thermocouple is best for the temperature ranges you need.A type K thermocouple offers a wide temperature rangeand is one of the most widely used thermocouples. However, if yourThermocouple probe exposed to extreme temperatures, an N-type thermocouple is more stable at high temperatures and a T-type thermocouple is better at extremely low temperatures
- Determine the importance of fast response time
There are three types of thermocouple connections: floating, grounded, or ungrounded. An exposed endpoint offers the fastest response times. However, if the probe is exposed to corrosive gases or high pressure, an exposed gasket should not be used. An ungrounded thermocouple offers the slowest response time, but may still be the best option if you also want the thermocouple to be electronically isolated and shielded from the shroud. - Consider any chemical, abrasion or vibration resistance.
An exposed thermocouple is limited to non-corrosive applications. A grounded and ungrounded thermocouple can be used in high pressure or corrosive environments, but an ungrounded probe is better when the thermocouple must be electronically isolated and protected by the sheath. When faster response times in a corrosive environment are a priority, a grounded thermocouple is best. - Consider all installation requirements
The thermocouple may need to be compatible with existing equipment. For example, existing holes can determine the diameter of the probe
How to choose a type of thermocouple
Because a thermocouple measures over a wide temperature range and can be relatively robust, thermocouples are widely used in industry. The following points must be answered before selecting a thermocouple:- Determine the application in which the thermocouple will be used
- temperature range
- Chemical resistance of thermocouple or sheath material
- abrasion andvibration resistance
- Installation requirements (may need to be compatible with existing equipment; existing holes may determine probe diameter)
How do you know what type of tour to choose?
Jacketed thermocouple probes are available with one of three connection types: grounded, ungrounded, or exposed. Also watch our video on thermocouple connections:Ground Junction Thermocouples
In a grounded probe tip, the thermocouple leads are physically connected to the inside of the probe wall. This results in good heat transfer from the outside through the probe wall to the thermocouple junction.This means that grounded thermocouples have faster response times than ungrounded thermocouples.
The grounded junction is recommended for measuring static or flow temperatures of corrosive gases and liquids and for high pressure applications. The junction of a grounded thermocouple is soldered to the sheath, allowing faster response than the ungrounded junction type.
However, grounded thermocouples are very susceptible to noise caused by ground loops, resulting in less accurate readings.
Cruce Ungeerdete-Thermoelement
An ungrounded probe has the thermocouple connection disconnected from the probe wall. Response time is slower than the grounded style.On the other hand, the splice is electrically isolated from the casing, preventing electrical noise from interfering with the signal. This results in much higher temperature measurement accuracy, especially on very low level signals.
An ungrounded connection is recommended for measurements in corrosive environments where it is desirable that the thermocouple be electronically isolated and protected by the sheath. The welding wire thermocouple is physically insulated from the thermocouple sheath with MgO (soft) powder.
exposed thermocouples
The exposed junction style thermocouple protrudes from the tip of the sheath and is exposed to the environment. This type offers the best response time but is limited to non-corrosive and non-pressurized applications.An exposed junction is recommended for measuring static or flowing non-corrosive gas temperatures where a fast response time is required. The connection point extends beyond the protective metal casing to allow a precise and fast response. The jacket insulation is sealed where the joint extends to prevent the ingress of moisture or gas that could cause failure.
See the images to the right for a full discussion of connection types.
See this PDF for moreThermocouple Insulation Information.
What thermocouple do I need?
Different temperature ranges for different temperature measurements
A wire thermocouple is the simplest form of thermocouple. It consists of two lengths of thermocouple wire joined by a solder bead. Because the thermocouple wire is exposed, there are several application limitations. The bead wire thermocouple should not be used with liquids that may corrode or oxidize the thermocouple alloy. Metal surfaces can also be problematic. Metal surfaces, especially pipes, are often used to ground electrical systems. Indirect connection to an electrical system may affect thermocouple measurement. In general, wire thermocouples are a good choice for measuring gas temperature. Since they can be made very small, they also offer a very fast response time.
thermocouples donde
A thermocouple probe consists of a thermocouple wire housed in a metal tube. The tube wall is called the probe sheath. Common lining materials are stainless steel and Inconel®. Inconel resists higher temperature ranges than stainless steel; however, stainless steel is often preferred due to its broad chemical compatibility. Other exotic lining materials for very high temperatures are also available. Check out our line of exotic high temperature thermocouple probes.
The thermocouple probe tip is available in three different styles. Grounded, Ungrounded and Exposed. When the tip is grounded, the thermocouple is in contact with the casing wall. A ground connection provides a fast response time, but is the most vulnerable to electrical ground loops. In the case of ungrounded connections, the thermocouple is separated from the enclosure wall by an insulating layer. The tip of the thermocouple protrudes from the cabinet wall with an exposed junction. Exposed thermocouples are best for air measurements.
surface probe
Measuring the temperature of a solid surface is difficult for most types of temperature sensors. To ensure accurate measurement, the entire measurement area of the sensor must be in contact with the surface. This is difficult when working with a hard surface sensor. Because thermocouples are made of flexible metals, the gasket can be flat and thin for maximum contact with a solid, rigid surface. These thermocouples are an excellent option for measuring surfaces. The thermocouple can even be incorporated into a rotating mechanism, making it useful for measuring the temperature of a moving surface. The type K thermocouple is ChrOMEGA™/AlOMEGA™.
wireless thermocouples
These wireless transmitters measure a variety of sensor inputs including, but not limited to, pH, RTD, and relative humidity. Data is transmitted wirelessly to a computer or a network.
The basics
- What is a thermocouple?
- How do thermocouples work?
- types of thermocouples
- choose a thermocouple
- Color codes for thermocouples
- Temperature limits for thermocouples
- Thermocouple response times
- thermocouple wire
- Thermocouple FAQ
Use of thermocouples
- Junction compensation for thermocouples
- Principles of infrared thermocouples
- Using Thermocouples in Electromagnetic Environments
- Use of thermocouples in low noise systems
- Prevention of Vibration Damage to Thermocouples
similar products Learn more about TJ36-ICIN Thermocouple probes with PFA-insulated connection cableorder now
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FAQs
Should I choose a Type K or Type N thermocouple? ›
The type N has better repeatability between 572F to 932F (300C to 500C) compared to the type K. Type N Temperature Range: Maximum continuous operating temperature: up to 2,300F (1,260C)
How to tell the difference between Type J and K thermocouples? ›A type K thermocouple has one red wire and one yellow wire. Type K thermocouples have a useful temperature range of negative 200 to 1,250 degrees Celsius. A type J thermocouple has one red wire and one white wire. Type J thermocouples have a useful temperature range of 0 to 750 degrees Celsius.
What is the difference between thermocouple type T and K? ›Type T thermocouples may be preferable to Type K despite Type K's wide temperature measurement range. Type T can withstand most chemical atmospheres, but can also measure extremely low temperatures with greater accuracy.
What is the most commonly used thermocouple? ›Type K (chromel–alumel) is the most common general-purpose thermocouple with a sensitivity of approximately 41 µV/°C. It is inexpensive, and a wide variety of probes are available in its −200 °C to +1350 °C (−330 °F to +2460 °F) range.
What are Type N thermocouples used for? ›Thermocouple Type N Technical Details
Thermocouple type N is a relativity new type that was made to be an alternative to Type K. It has high stability over time but is more costly than type K at similar temperature ranges. Its sensitivity is about 39 µV/°C, slightly lower compared to type K.
Commercial thermocouples are interchangeable, economical, and supplied with standard connectors. Unlike most other temperature measurement devices, external form of excitation is not required for thermocouples because they are self-powered.
Which classes of thermocouples are the most popular? ›Type K Thermocouple (Nickel-Chromium / Nickel-Alumel): The type K is the most common type of thermocouple. It's inexpensive, accurate, reliable, and has a wide temperature range.
Does thermocouple length matter? ›The length of a thermocouple has no effect on its measurement accuracy or its ability to transfer the signal to the instrument. In other words, thermocouples do not experience “voltage drops” or power loss along its length as a high current power line might possess.
Which thermocouple is best? ›Type T is the most accurate thermocouple and has excellent corrosion resistance. Its temperature range is limited to 370°C and is good with wet gasses and moisture. It is also used for cryogenic applications.
What is the most accurate thermocouple type? ›Accuracy: Type T thermocouples have the tightest accuracy of all the base metal thermocouples at ±1C or ±0.75% whichever is greater. This is followed by Type E (±1.7C or 0.5%) and Types J, K and N (±2.2C or 0.75%) for standard limits of error (per ANSI/ASTM E230).
What is the difference between Type R and Type S thermocouple? ›
Thermocouple Type R is similar to the Type S combination, this thermocouple has the advantage of slightly higher output and improved stability. In general Type R thermocouples are preferred over Type S, and applications covered are broadly identical.
Are all K type thermocouples the same? ›All Thermocouple types work on the same basis, they consist of two wire legs made from dissimilar metals (Nickel-Chromium / Nickel-Alumel in type K) which are fixed together at one end, creating a junction (Fig 1.).
What is the most stable thermocouple? ›Platinum-based thermocouples tend to be the most stable, but they're also the most expensive. They have a useful temperature range from ambient to around 2,000°C, and short term, much greater (-270°C to 3,000°C).
Why is K type thermocouple popular? ›Type K is popular because of its wide temperature range. Of the four major thermocouple types, type K covers the widest range from−200°C to 1,260°C (approximately minus 328°F to 2,300° F).
What are the 4 types of thermocouple probes? ›The most common types are J, K, T and E. Types R, S, C and GB are designed for high temperature applications.
What is the temperature range for J type thermocouple? ›Due to the Curie Point of the iron at 770 °C Type J has a limited temperature range of -40°C to 750°C.It should not be used at high temperatures in an oxidizing atmosphere as iron undergoes a molecular change and permanently loses its standard voltage output versus temperature.
What happens if you use the wrong thermocouple? ›If you accidentally reverse the polarity of the thermocouple lead wires, the measured temperature will be incorrect by the difference in temperature of the two ends of the leads.
Can I replace my own thermocouple? ›Replacing a thermocouple is a relatively easy fix that can take less than two hours. This guide reviews how to replace a thermocouple to ensure gas appliances stay in good working order, as well as how to relight a pilot light.
Is there a universal thermocouple? ›Universal Gas Thermocouple includes universal adapter fittings and is compatible with screw-in, push-in or clamp-type pilot burners. It is designed for gas furnaces and 30 mV systems. The element is built for reliability and long life.
What is the problem with K type thermocouple? ›With repeated exposure to high temperatures, a type K thermocouple becomes less accurate. Aging is a phenomenon that results in higher-than-accurate temperature readings, while drift results in lower-than-accurate readings.
What are the limitations of Type K thermocouples? ›
Type K thermocouples have a general temperature range of -200 to 1260°C (-326 to 2300°F), however there are some caveats to this: If used for temperatures below 0°C special material is needed in order to meet the specified accuracies. Also, Special Limits of Error are not specified for temperatures below 0°C.
What is the fastest thermocouple? ›The fastest-possible temperature sensor is an exposed tip thermocouple.
Does type of thermocouple matter? ›The maximum temperature varies with the diameter of the wire used in the thermocouple. Although the type of thermocouple dictates the temperature range, the maximum range is also limited by the diameter of the thermocouple wire. That is, a very thin thermocouple may not reach the full temperature range.
What are the differences in thermocouples? ›What differentiates one thermocouple from another is the metals in its two wires: the positive leg and the negative leg. Because each thermocouple type has a different pairing, they differ in temperature limits, process conditions (inert, oxidizing, reducing atmospheres, heavy vibration), and so on.
How do I know what size thermocouple to buy? ›- Determine the application where you will use the thermocouple sensor. ...
- Determine the temperature ranges the probe will be exposed to. ...
- Determine how important a fast response time is. ...
- Consider any chemical, abrasion or vibration resistance. ...
- Consider any installation requirements.
Because different thermocouple wires are made of different materials, the resistance will vary based on the type as well as the wire diameter and length.
Should the flame be touching the thermocouple? ›The pilot flame should touch the thermocouple at a specific level. If the flame is blue and weak, and barely reaches the thermocouple, it needs to be stronger. If it extends well above the thermocouple, it's too strong.
What is the life expectancy of a thermocouple? ›Thermocouple life expectancy varies greatly from just a few hours to many years. Many factors in- cluding calibration type, environ- ment, temperature, sensor design, and thermal cycling will determine life expectancy.
Do K type thermocouples need calibration? ›Regardless how it is used, thermocouple wires should be calibrated and checked for physical damage or any deteriorations, because these can cause errors and out of tolerance measurement results.
What does Type R stand for? ›Type-R stands for 'racing'. Honda's engineers set out to develop a racing car for the road, one that would give drivers raw thrills and an immersive experience. They succeeded. The first Type-R impressed even one of the world's greatest racing drivers - Ayrton Senna.
Which is better Type R or Type S? ›
The fundamental difference between the Type S vs. Type R is that the Type S replaced the Type R, and Type S models provide more contemporary features. From 1997-2001, Acura utilized the Type R marque for its performance vehicles, like the Acura Integra Type R.
How do you find the K type of a thermocouple? ›Calculate the average sensitivity (μV/°C) of a type K thermocouple in the temperature range 0 °C to 100 °C. Answer : From Above Table : the change in emf developed by a type K thermocouple from 0 °C to 100 °C, is 4096 μV. The average sensitivity is therefore 4096/100 = 40.96 μV/°C.
Which type of thermocouple is best? ›The Type E thermocouple is suitable for use at temperatures up to 900°C (1650°F) in a vacuum, inert, mildly oxidizing or reducing atmosphere. At cryogenic temperatures, the thermocouple is not subject to corrosion. This thermocouple has the highest EMF output per degree of all the commonly used thermocouples.
What type of thermocouple is most accurate? ›Accuracy: Type T thermocouples have the tightest accuracy of all the base metal thermocouples at ±1C or ±0.75% whichever is greater. This is followed by Type E (±1.7C or 0.5%) and Types J, K and N (±2.2C or 0.75%) for standard limits of error (per ANSI/ASTM E230).
Does the length of a thermocouple make a difference? ›Because different thermocouple wires are made of different materials, the resistance will vary based on the type as well as the wire diameter and length.
Does thermocouple wire size matter? ›The length of a thermocouple has no effect on its measurement accuracy or its ability to transfer the signal to the instrument. In other words, thermocouples do not experience “voltage drops” or power loss along its length as a high current power line might possess.
What is the difference between Type S and Type R thermocouple? ›Thermocouple Type R is similar to the Type S combination, this thermocouple has the advantage of slightly higher output and improved stability. In general Type R thermocouples are preferred over Type S, and applications covered are broadly identical.
Are gas thermocouples universal? ›Universal Gas Thermocouple includes universal adapter fittings and is compatible with screw-in, push-in or clamp-type pilot burners. It is designed for gas furnaces and 30 mV systems. The element is built for reliability and long life.
Do thermocouples need to be welded? ›Welding is the best way to form a reliable thermocouple. A resistance welding machine (spot welder) can be used (with practice), and TIG welding works nicely too. Alternatively, for many applications you can twist the bare ends of the thermocouple wire once or many times.