Thermocouple Sensors - Thermocouples to your Specifications
What is a thermocouple and how does it work?
A thermocouple is a relatively simple device used to measure temperature. Thermocouple temperature sensors are made from two wires of different metals joined (welded) together to form a measuring junction (also known as a hot junction). This junction and the wires are usually enclosed in a metal sheath which is inserted into the medium where the temperature is to be measured. The opposite end of the two wires are also joined at a point known as the cold junction.
As the temperature at the hot junction changes, it creates a thermal gradient between the hot and cold junctions which generates an electron flow and a resultant electromotive force (EMF), measured in Millivolts. The voltage measured at the ends of the conductors is a function of the temperature difference along the conductor length. This thermoelectric principle was discovered in the early 19th century and is known as The Seebeck Effect.
When used with an appropriate thermocouple display unit, the cold junction is electronically referenced to 0ºC and a formula is applied to the millivolt signal, which can then be converted to °C or °F, using instrumentation. For a more detailed explanation, please see: How a Thermocouple Works.
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Choose the right thermocouple for your appplication
We are the largest manufacturer of thermocouple probes in Europe. We have an enormous range of components in stock, which means we can make virtually any sensor you specify.
We can ship custom built thermocouples typically within five days or sooner.
Mineral Insulated Thermocouples
Rugged sensors, ideal for most applications. Vast choice of terminations e.g. pot seals, cables, connectors, heads etc.Swaged TipThermocouples
Fast response thermocouples ideal for industrial and other applications.
Miniature
Thermocouples
Ideal for precision temperature measurements where minimal displacement and a fast response is required.
Heavy Duty
Thermocouples
For industrial applications such as furnaces, kilns, ovens, boliers, flues etc. Many types of sheath material available.
High Temperature Thermocouples
Various thermocouples specifically for high temperature applications. Wide choice of sheath materials and terminations.
General Purpose
Thermocouples
A wide range of thermocouples to suit many applications. Hand held, surface, bayonet, bolt, patch styles etc.
Hand HeldThermocouple Probes
A range of hand held thermocouple probes to suit a variety of applications from general purpose to surface and air temperature measurements.
Thermocouples for
Surface Measurements
A range of thermocouples to suit various surface temperature measurement applications.
AMS2750 Approved
Thermocouples
Calibrated thermocouples designed to meet the high quality and accuracies demanded for heat treatment and vacuum furnace applications
Industrial Vacuum
Thermocouples
Ceramic sheathed calibrated thermocouples designed specifically in vacuum furnace applications with very low leak rates
ATEX / IECEx Approved
Thermocouples
A large range of thermocouples with a variety of terminations such as pot seal, terminal heads etc with 4 to 20mA current transmiiers also available.
Common Thermocouple Types to IEC 60584-1
Type K - Nickel-Chromium vs Nickel-Aluminium
K type thermocouples, also referred to as Chromel-Alumel, is the most common thermocouple in use in industry today mainly because it is reliable, inexpensive, has a wide temperature range and is reasonably accurate. Type K thermocouples are designed primarily for general temperature measurements in normal atmospheres. Maximum continuous temperature is about 1,100°C, although above 800°C oxidation increasingly causes drift and decalibration. For short term exposure, however, there is a small extension to 1,200°C. For more information, please see our dedicated Type K thermocouple page.
Type J - Iron vs Copper-Nickel
Thermocouple Type J, commonly referred to as Iron/Constantan, this is one of the few thermocouples that can be used safely in reducing atmospheres. However, in oxidising atmospheres above 550°C, degradation is rapid. Maximum continuous operating temperature is around 800°C, although for short term use, temperatures up to 1,000°C can be handled. Minimum temperature is -210°C, but beware of condensation at temperatures below ambient - rusting of the iron arm can result, as well as low temperature embrittlement. For more information, please see our dedicated Type J thermocouple page.
Type T - Copper vs Copper-Nickel
Thermocouple Type T, whose original name was Copper-Constantan, has found quite a niche for itself in laboratory temperature measurement over the range -250°C to 400°C - although above this the copper arm rapidly oxidises. Repeatability is excellent in the range -200°C to 200°C (±0.1°C). Points to watch out for include the high thermal conductivity of the copper arm, and the fact that the copper/nickel alloy used in the negative arm is not the same as that in Type J - so they’re not interchangeable. For more information, please see our dedicated Type T thermocouple page.
Type N - Nickel-Chromium-Silicon vs Nickel-Silicon
Thermocouple Type N, was billed as the revolutionary replacement for the Type K thermocouple (the most common in industrial use), but without its drawbacks - Type N (Nicrosil-Nisil) exhibits a much greater resistance to oxidation-related drift at high temperatures than its rival, and to the other common instabilities of Type K in particular, but also the other base metal thermocouples to a degree. It can thus handle higher temperatures than Type K (1,280°C, and higher for short periods). For more information, please see our dedicated Type N thermocouple page.
Type R - Platinum-13% Rhodium vs Platinum
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. For more information, please see our dedicated Type R thermocouple page.
The above list shows the more popular types of thermocouple used in the UK, other thermocouple types that you might come across are Type S and Type E thermocouples. For very specific, usually high temperature, applications Type B and Type C are sometimes found.
What is the most accurate type of thermocouple?
Type T thermocouples have the tightest tolerance of all the base metal thermocouple types with class 1 material tolerance of 0.5ºC as stated in IEC60584-1.
The above is over a limited working temperature range. Full thermocouple accuracies for all types can be viewed on our thermocouple tolerances page.
Do I need a thermocouple or an RTD?
Choosing a thermocouple over an RT Pt100 will depend on your application and the accuracy requirements as well as the physical demands on the sensor.
Typically, a thermocouple will have a wide temperature range, will exhibit a fast response to changes in termperature, can be manufactured down to a very small size and will be relatively low cost. The downside compared to an RTD sensor is that a thermocouple will be less accurate, less stable and can be prone to long term drift. Thermocouples will require themocouple cable and thermocouple connectors to make circuit connections from the process back to instrumentation such as data loggers, indicators and other devices.
By contrast, an RTD sensor will have a high accuracy with high stability and have a high level of repeatbility whilst being less durable than a thermocouple, with low vibration resistance and a slower response to temperature changes.
Video of How a Thermocouple Works
What are the different types of thermocouple junction?
Insulated Thermocouple Junction Diagram
Hot junction insulated from sheath. Gives floating output with typical insulation resistance for mineral insulated thermocouples in excess of 100 megohms.
Grounded Thermocouple Junction Diagram
The thermocouple junction is welded to the sheath tip giving earthed output and faster response to temperature changes.
Exposed Thermocouple Junction Diagram
Hot junction exposed giving the fastest response, mainly for the measurement of air temperature in ducts. Mineral insulated thermocouples with an exposed junction are restricted to a maximum operating temperature of 600°C.
All of the above are generally known as the 'hot junction' and should not be confused with the 'cold junction' which refers to the junction against which hot junctions are referenced (usually incorporated within instrumentation).
