Thermocouple Types, Sensor Ranges & Materials Used

There are many different types of thermocouples. Each of the thermocouple types are given a coding letter to denote each of the alloy combinations. The most common code letters are K, J, T and N. Other types include R, S, E, B, C, G and W.

Each type of thermocouple has its own alloy pair which is carefully selected and calibrated to meet the international standards with which we must comply. The standard that governs thermocouples in the UK and Europe is BS EN 60584 and ASTM Standard E230, which provides specifications for the common industrial grades, including the letter designations used for each type of thermocouple. These standards ensure accuracy and consistency in temperature measurement.

A thermocouple consists of a welded ‘hot’ junction between two dissimilar metals. These are usually wires with a reference junction at the opposite end.

The thermocouple type is suited to different applications and temperature ranges. See the table below for appropriate operating ranges.

Type J

Thermocouple

Thermocouple Types Chart and Ranges

What temperature range are thermocouples suitable for?

This is very much dependent on type but the overall range for all thermocouple types is -200°C to +1800°C. There are many factors to consider when selecting a thermocouple type for an application, including conductor size and temperature range. We would be happy to offer assistance in choosing between the different thermocouple types. The life of a thermocouple is also something to consider, particularly at extreme temperatures and it may be worth considering Infrared Pyrometers instead which can measure temperature from outside the process.

Below is a list of the thermocouple types available and the temperature ranges they work within.

Types of Thermocouple and Ranges

Process Parameters offer an extensive range of thermocouple sensor types for a broad spectrum of applications ranging from automotive sensors through to flare stack thermocouples. Below is a range of thermocouple probe types manufactured in-house by us.

We manufacture sensors to suit your drawing or specification so if you do not see your design below then please contact us for further information.

Plain Stem c/w Pot seal and cable

Mineral Insulated c/w either pot seal / cable, connector or head

Plastics Thermocouples

Surface Thermocouples

Fixed Process Thread Thermocouples

Ceramic Thermocouples with Support Tube & Head

HVAC & Air Temperature Sensors

Immersion Thermocouple

CHECK OUR THERMOCOUPLE SENSOR RANGE

to get an idea of the typical design available

check the range

Thermocouple Junction Types

What is meant by thermocouple junction types Exposed, Ground and Insulated Hot Junction?

Exposed Hot Junction

An exposed junction is where the two wires that make the junction are left without an external protection sheath. In the simplest form, this could mean just a bare wire design or the junction can be constructed so that it extends out the end of a protection sheath. Exposed junctions give the fastest response time of any thermocouple construction but are only suitable for unpressurised, dry and non-corrosive applications. However, the voltage is generated not at the junction itself, but in the thermal gradient along the wire, making exposed junctions ideal for measuring small changes in temperature.

Grounded Hot Junction

A grounded thermocouple has the thermocouple electrically connected, or grounded, to the protection sheath, normally by welding or silver soldering so that it becomes an integral part of the sensor tip. This type of construction can also give fast response times but with the added advantage of being suitable for pressurised applications. This junction type is popular in the Plastics Industry.

Insulated Hot Junction

As the name suggests the thermocouple junction in this design is electrically insulated from the protection sheath. Response times are slower with this construction but this is now the most common type due to its ability to avoid interference from earth loops in machinery.

Thermocouple Connector Types

Two-pin thermocouple connectors

with polarised pins

Thermocouple connectors are perfect for connecting thermocouple probes to extension or compensating cables. Each connector has polarised pins to ensure correct connection. Process Parameters offer an extensive range of thermocouple connector types for use with both Thermocouples and Platinum Resistance Thermometers. The range consists of Miniature and Standard sizes in two pin or three pin available to suit temperature ranges of 200 deg C, 350 deg C, 650 deg C, and other temperature measurements. Process Parameters can support your connector requirements whatever the design.

Thermocouple sensor Material types

Below is a table of the materials used for each the thermocouple types.

Type K = Nickel / Chromium(+), Nickel / Aluminium (-)
Type T = Copper (+), Copper / Nickel (-) Also known as Constantan
Type J = Iron (+), Copper / Nickel (-) Also known as Constantan
Type E = Nickel / Chromium(+), Copper / Nickel (-) Also known as Constantan
Type N = Nickel / Chromium / Silicon (+), Nickel / Silicon / Magnesium (-)
Type R = Platinum / 13% Rhodium (+), Platinum (-)
Typs S = Platinum / 10% Rhodium (+), Platinum (-)