A Thermocouple is a temperature sensor that is mounted on the so-called Seebeck effect It consists of two different metals or metal alloys that are joined together at a measuring point. If a temperature difference arises between the measuring point and the reference point, an electrical voltage is generated that is proportional to the temperature difference.
Due to their robustness, wide measurement range, and fast response times, thermocouples are among the most commonly used temperature sensors in industry, research, testing, and process automation.
How does a thermocouple work?
A thermocouple generates a very small thermoelectric voltage in the millivolt (mV) range as soon as there is a temperature difference between the two junctions of the different metals.
The underlying physical effect is known as Seebeck effect . The voltage generated is measured and converted into a temperature value using standardized calibration curves.
Since thermocouples always measure a temperature difference, a so-called Comparison or reference measurement point required. Modern measurement systems have an integrated Cold Spot Compensation, which automatically takes the reference temperature into account.
Advantages of Thermocouples
Thermocouples offer numerous advantages:
- Wide temperature measurement range
- Fast response times
- Sturdy construction
- High vibration resistance
- Suitable for extreme environmental conditions
- Compact design
- Cost-Effective Temperature Measurement
- Can be used at very high temperatures
This makes them particularly well-suited for industrial processes, testing systems, furnaces, motors, power engineering, and laboratory applications.
Thermocouples in Delphin Measurement Systems
The measurement data acquisition systems from Delphin Technology support the direct measurement of a wide variety of thermocouple types via the integrated analog inputs. In many applications, additional transducers are not required for this purpose. The necessary reference point or cold-junction compensation is already integrated into the device, enabling precise temperature measurement. In addition, temperature data can be recorded, visualized, and analyzed directly.
Thanks to universal measurement data acquisition, thermocouples can be combined with other measured variables—such as pressure, current, voltage, vibration, or flow—and evaluated together.
Thermocouple types
Depending on the temperature range, accuracy requirements, and operating conditions, different types of thermocouples are used. The various types differ in terms of the metals or metal alloys used, as well as their respective characteristic curves.
Type J (Fe-CuNi)
Material: Iron – Konstantan (CuNi)
Features:
- High sensitivity
- Suitable for standard industrial applications
- Good measurement accuracy in the mid-temperature range
- Not ideal for oxidative environments at high temperatures
Typical applications:
- Mechanical engineering
- Heating Technology
- Laboratory Applications
Type N (NiCrSi-NiSi)
Material: Nicrosil – Nisil
Features:
- High long-term stability
- Good resistance to oxidation
- Minimal signs of aging
- An alternative to Type K for demanding applications
Typical applications:
- Power Plant Technology
- Process Industry
- High-Temperature Processes
Type E (NiCr-CuNi)
Material: Nickel-Chromium – Konstantan
Features:
- Very high thermoelectric voltage
- High sensitivity
- Good accuracy even at lower temperatures
Typical applications:
- Laboratory and Testing Technology
- Precision Measurements
Type T (Cu-CuNi)
Material: Copper – Konstantan
Features:
- Very good accuracy at low temperatures
- High stability
- Particularly suitable for low-temperature measurements
Typical applications:
- Refrigeration Technology
- Environmental measurement technology
- Food Industry
Type R (Pt13Rh-Pt)
Material: Platinum-Rhodium (13 %) – Platinum
Features:
- Very high accuracy
- High long-term stability
- Suitable for very high temperatures
Typical applications:
- Calibration Laboratories
- Glass Industry
- High-Temperature Furnaces
Type S (Pt10Rh-Pt)
Material: Platinum-Rhodium (10 %) – Platinum
Features:
- Excellent measurement accuracy
- Very stable performance curve
- Reference Sensor for Calibration Applications
Typical applications:
- Research
- Calibration Technology
- High-precision temperature measurements
Type B (Pt30Rh-Pt6Rh)
Material: Platinum-Rhodium (30 %) / Platinum-Rhodium (6 %)
Features:
- Suitable for extremely high temperatures
- Excellent stability
- Long service life
Typical applications:
- Metallurgy
- High-Temperature Furnaces
- Heat Treatment Facilities
Selecting the Right Thermocouple
The selection of the appropriate thermocouple depends on various factors:
- Temperature range
- Measurement accuracy
- Environmental Conditions
- Chemical Exposure
- Reaction rate
- Long-term stability
- Cost-Effectiveness
For standard applications, types J, N, E, or T are frequently used, while the precious-metal thermocouples R, S, and B are primarily used in high-precision and very high-temperature processes.
Advantages of Temperature Measurement Using Thermocouples
- Measurement of temperatures well above 1,000 °C
- High durability
- Fast response times
- Wide selection of sensor types
- Easy integration into measurement systems
- Proven Technology for Industry and Research