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Thermocouples & RTD’s


Thermal has been designing and manufacturing thermocouples, temperature probes and sensors capable of measuring temperatures of up to 1800°F for over thirty years. Each probe is manufactured to exacting tolerances and to your specifications whenever needed. Type J & K thermocouples are always available for quick manufacture and shipment. We also keep a large supply of adjustable thermocouples in stock for same day shipment. To request a quote email or simply give us call at 1.800.633.2962 and speak to one of our sales representatives.

Thermocouples are the most widely used temperature sensor for several reasons. They are rugged, low-cost, dependable, and fairly accurate over a useful temperature range of cryogenic to 5,000°F. Since the temperature-sensing hot junction is very small, the measurement is a point measurement with fairly quick response to temperature change.

A full line of resistance temperature detector (RTD) probes or sensors, thermocouple extensions, adapters and accessories are available from Thermal Corporation.

Please see our adjustable thermocouple page for great prices and same day shipment on the most versatile thermocouples out there for the plastics industry.

Common Thermocouple Wire Types
TypeTemperature RangeMaterial
E-300 to 1,600°Chromel/Constantan
J0 to 1,400°Iron/Constantan
K0 to 2,300°Chromel/Alumel
R0 to 2,700°Platinum/Platinum 13% Rhodium
S0 to 2,700°Platinum/Platinum 10% Rhodium
T-300 to 500°Copper/Constantin
Positive Terminal is in boldface

Custom thermocouple probes can always be quickly manufactured in types J or K. RTD probes in 100 ohms with .00385 ohm/ohm/ °C calibration in either two or three wire configurations are also always available for quick delivery. Unless specified otherwise, the probe body and hose are stainless steel. The lead wire is always a stranded wire in either 20 or 24 gauge depending on the probe configuration.

Each thermocouple or RTD probe tip is welded, not brazed, then machined to fit the bottom of a drilled hole unless specified otherwise.

Voltage-Temperature Relationship

The relationship between the temperature difference and the output voltage of a thermocouple is nonlinear and is given by a polynomial interpolation.


The thermocouples values are given to n between 5 and 9.

To achieve accurate measurements the equation is usually implemented in a digital controller or stored in a lookup table. Some older devices use analog filters.


(Excerpted from Wikipedia)

A Brief History of Thermocouples

These wonderful little gadgets have been around for a long time. The first person to discover the effect of electricity being generated by the junctions of two dissimilar metals at differing temperatures was Thomas Johann Seebeck when in 1821 he found that the circuit could move a compass needle. His first thoughts were of magnetism but he soon realized that it was an electrical current that was induced. This is now referred to as The Seebeck Effect.

Seebeck’s work set the platform for Leopoldo Nobili, who, after a stint as one of Napoleon’s artillerymen, developed together with Italian physicist Macedonio Melloni, a thermoelectrical battery in 1826. Three years later Nobili clip_image004wrote “Description d’un thermo-multiplicateur” a description of his work using thermopiles and a galvanometer which was published in the journal Bibliotheque Universelle des Sciences, Belles-Lettres et Arts, 1830, 44, 225-234 Because of this work, Nobili may now be considered as the inventor of the thermocouple.

Where do these discoveries take us? Nearly two hundred years later, the principals and mechanics these men realized are being used in long range space exploration missions reaching distances from the sun where the light is too weak to power a spacecraft with solar panels. Apollo, Pioneer, Viking, Voyager, Galileo and Cassini all used thermoelectric generators. Thanks to Seebeck and Nobili, the electrical power is provided by these thermoelectric generators converting the heat from a plutonium heat source into electricity using thermocouples.