Here is everything you want to know about a thermocouple on the internet.
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A thermocouple is an essential type of transducer that transforms thermal energy into electrical energy. It is constructed by connecting wires made of different metals to create a junction. When the temperature at this junction changes, a voltage is produced, which can be measured to determine the temperature accurately.
This device operates on the principle of the Seebeck Effect, which indicates that when different metals form a junction, they produce a small, detectable voltage in response to temperature changes at that junction. The voltage generated is influenced by the degree of temperature change and the characteristics of the metals involved.
Comprising two insulated wires of distinct metals connected to a measuring device, a thermocouple serves as both a safety and monitoring instrument for a wide array of processes and machinery, ensuring reliable temperature readings to maintain proper functioning.
Below is an illustration depicting how a thermocouple works. As the temperature rises at the junction of the wires on the left, the associated change in temperature is shown on the gauge on the right.
Thermocouple assemblies are specifically designed for application in tough, extreme, and challenging environments. Selecting the right thermocouple involves considering factors such as temperature range, environmental conditions, and the type of material being measured. Moreover, the thermocouple's dimensions and form are customized to suit particular applications, ensuring optimal accuracy and responsiveness.
A thermocouple is a widely used temperature sensor in industrial and scientific applications, known for its durability, versatility, and ability to measure an extensive range of temperatures. It operates by joining two dissimilar metal wires at a measuring point, known as the hot or sensing junction, while the other ends are connected to a reference, or cold junction. The essential working principle relies on generating a voltage—called a thermoelectric EMF—based on the temperature differences between these junctions. By comparing the small voltage produced at the hot junction to the known temperature at the cold junction, the thermocouple accurately determines and monitors temperature variations in a process or environment.
The science behind thermocouples is rooted in three fundamental thermoelectric phenomena: the Seebeck effect, the Peltier effect, and the Thomson effect. Understanding these effects is critical in optimizing thermocouple temperature measurement, sensor selection, and process control in industries such as manufacturing, chemical processing, and HVAC systems.
The Seebeck effect forms the backbone of thermocouple operation. When two different metals—commonly types such as Type K (Nickel-Chromium/Nickel-Alumel), Type J (Iron/Constantan), or Type T (Copper/Constantan)—are connected at two junctions exposed to different temperatures, a voltage or electromotive force (emf) is generated. The magnitude and polarity of this emf depend not only on the temperature difference, but also on the specific conductivity and thermoelectric properties of the metals used. This unique voltage enables the direct and rapid measurement of temperature changes, making thermocouples an ideal choice for industrial temperature probes, furnace monitoring, and laboratory thermal measurement.
The Peltier effect describes the heating or cooling at the junction of two dissimilar metals when electrical current flows through them. In the context of a thermocouple, a temperature gradient across the two junctions causes a voltage to appear, which is then measured and interpreted as a temperature reading. This effect is harnessed in several types of thermoelectric devices and temperature controllers, highlighting the versatility of thermocouple technology in process automation and instrumentation.
The Thomson effect complements the above principles by explaining the thermal energy absorption or release in a conductor carrying electric current with a temperature gradient along its length. This effect contributes to the thermoelectric emf measured in a thermocouple circuit and must be considered for highly accurate temperature measurements, especially in environments with extended thermal gradients. Understanding the Thomson effect helps select the optimal thermocouple wire material and calibration method to ensure measurement accuracy in industrial sensing applications.
The basic thermocouple circuit, shown in the image below, consists of two wires—labeled A and B—composed of different metals joined together at one end. These create the hot (measuring) junction and the cold (reference) junction, which are maintained at different temperatures for precise temperature measurement. As a result, a Peltier emf is generated across the circuit, directly reflecting the temperature difference between junctions. Accurate temperature monitoring with a thermocouple depends on the type of wire alloys selected and the environmental conditions in which the sensor is installed.
Electrons—a key component in both heat and electricity transfer—move from the hot to the cold end within the metal conductors when exposed to a temperature gradient. This movement effectively converts thermal energy into an electrical signal that can be measured with precision. The foundation of this process, first explored by scientists like Volta and Seebeck, supports the widespread use of thermocouples for reliable temperature measurement across many industries, including food processing, power generation, plastics manufacturing, and metalworking.
The millivolt signal produced by a thermocouple is unique to the combination of conductor materials chosen, which are standardized under IEC 60584 and ANSI/ASTM E230 specifications. Standardization ensures precision and interchangeability across global suppliers and manufacturers, facilitating integration into automation systems and electronic temperature controllers.
Accurate thermocouple readings rely on cold junction compensation—often achieved by maintaining the reference junction at 0°C using an ice bath or an advanced compensation chip. This process corrects for ambient temperature changes, producing reliable readings for process control, industrial automation, and research-grade temperature logging. Using thicker thermocouple wires enables higher temperature measurement, but may lead to a slower response time, which should be considered during sensor selection for high-speed applications such as kilns, extruders, or engine testing.
When both junctions in a thermocouple stabilize at the same temperature, their electrical potential cancels out, resulting in zero current flow. Once a temperature disparity arises, the electro-motive force is generated and measured, with its intensity depending on the metals’ thermoelectric coefficients and the junction temperature difference. Advanced measurement systems interpret this small signal via high-impedance voltmeters, precise potentiometers, or sophisticated data acquisition modules, converting it into real-time temperature data critical for automation, quality control, and regulatory compliance.
Due to the minute voltages generated—often measured in millivolts—thermocouples necessitate accurate measurement devices. Industrial applications commonly rely on high-sensitivity galvanometers, digital data loggers, and voltage-balancing potentiometers, chosen for their ability to amplify and precisely interpret the thermocouple signal. Modern analog-to-digital converters and microcontrollers further enhance temperature sensor integration within complex monitoring and control systems, increasing reliability for process optimization.
A potentiometer, or "pot," is often used to calibrate thermocouple systems by comparing the unknown thermoelectric voltage to a reference source. Its high precision ensures consistent, reproducible temperature measurement—important for pressure vessels, heat exchangers, and laboratory apparatus. The three-terminal variable resistor can also function as a voltage divider in electronic circuits for signal conditioning or calibration.
A galvanometer is designed to measure very small electrical currents and is integral in the detection of null deflection or zero current—functions that are critical in precision thermocouple calibration and sensor diagnostics. This enables engineers to fine-tune temperature sensors and control loops, ensuring high accuracy across industrial, laboratory, and field environments.
For absolute temperature measurement, the cold or reference junction must be maintained at a known temperature—often at the freezing point—to ensure accurate sensor output and process reliability. Many thermocouple assemblies feature an integrated cold junction compensation chip placed near the reference junction, offering compensation for ambient temperature variations and improving accuracy for critical applications, such as pharmaceutical manufacturing, environmental monitoring, and process engineering. Immersing the cold junction in a controlled water or ice bath can further stabilize readings, essential in high-precision and research applications.
Ambient air temperature, humidity, and other environmental factors can impact the reference temperature of a thermocouple. To counteract these influences, automated systems employ reference junction compensation devices or software algorithms. These enhancements help maintain strict measurement tolerances, making thermocouples ideal for safety systems, environmental sensors, and closed-loop feedback in industrial automation.
Additional Considerations: Thermocouples come in various types and calibrations (such as Type K, J, T, N, E, S, R, and B), each suited for specific temperature ranges and chemical environments. Factors to consider when selecting a thermocouple include accuracy, response time, chemical resistance, mechanical durability, and compatibility with your measurement instrumentation. Using specialized thermocouple connectors and extension wires can further prevent signal loss and ensure consistent readings throughout your process line. For hazardous or high-pressure environments, protective sheaths and advanced insulation materials may be required.
A thermowell is an essential accessory designed to shield a thermocouple from potentially damaging process fluids, corrosive chemicals, and high-pressure or high-velocity flow environments. Thermowells encase the sensing element in a closed-end tube or solid bar-stock and are widely implemented in applications such as refineries, power plants, petrochemical processing, and food/beverage manufacturing. By acting as a barrier, thermowells extend the operational lifespan of thermocouple sensors, reduce downtime, and enable safe, efficient sensor replacement or calibration without interrupting ongoing processes.
Thermowells are also classified based on how they connect to a thermocouple or thermistor sensor. Common connection types include:
When selecting a thermowell for your thermocouple or RTD (Resistance Temperature Detector), consider key factors such as process temperature, pressure rating, chemical compatibility, and fluid velocity. Material choices—like stainless steel, Inconel, or Hastelloy—impact durability and resistance to corrosion, while proper sizing and insertion length ensure fast and accurate sensor response. Consulting with a trusted thermowell manufacturer or supplier can help optimize system performance and safeguard your investment in high-quality temperature measurement solutions.
The differences between thermocouples are determined by the types of alloys used to produce their wires. The choice of metal wire depends on factors such as the temperature range to be measured, the environmental conditions, required chemical resistance, and mechanical durability. These crucial factors ensure the selection of the most suitable temperature sensor for a given application—whether for industrial automation, laboratory research, or process control. Thermocouples can be connected in three different ways: exposed, ungrounded or insulated, and grounded.
A thermocouple can be enclosed in a sheath to protect it from atmosphere, chemicals, and minimize the risk of corrosion or oxidation, especially in harsh industrial settings. Common sheath materials include stainless steel, which offers good chemical resistance and durability, Inconel, and Incoloy. Inconel and Incoloy are registered trademarks of Special Metals Corporation and are types of nickel alloys known for their resistance to oxidation and high temperatures. Choosing the right sheath material is essential for achieving optimal sensor life and measurement accuracy in harsh process environments. The temperature ranges for the various types of sheaths are detailed in the chart below.
Vinyl insulation is low-cost, offers good flexibility, and provides adequate electrical performance, making it suitable as a general-purpose material for thermocouple wire insulation in low- to moderate-temperature environments. Vinyl is used in situations where affordability and ease of installation are key factors.
Teflon (PTFE) insulation is more expensive due to its high temperature rating and outstanding chemical resistance, granting robust protection in aggressive chemical and high-humidity environments. It possesses excellent electrical properties but has poor cut-through resistance, requiring additional protection in abrasive conditions. Its high dielectric strength and non-stick properties make Teflon ideal for laboratory, food processing, and pharmaceutical thermocouple applications.
Kapton insulation boasts exceptional physical, electrical, and mechanical properties over a wide temperature range, making it suitable for applications involving extreme heat and vibration, such as aerospace, automotive, and semiconductor manufacturing. Its ability to maintain mechanical strength, even under harsh and dynamic conditions, ensures reliable signal integrity in challenging environments.
Polyethylene insulation is low-cost and offers excellent electrical properties, but it exhibits high flammability and is stiffer than vinyl. It is best used in low-temperature, dry, and static applications where flexibility is less of a concern.
Fiberglass insulation is excellent for high-temperature applications and provides reliable performance in environments prone to hot spots or thermal cycling, such as furnace operations, kilns, foundries, and thermal processing. Its braided construction improves heat resistance and allows use in rugged locations where ordinary insulation would fail.
Ceramic insulation is selected for extreme environments, such as commercial ovens and furnaces. It can monitor ambient temperatures in fireboxes, kilns, or grills and withstands a wide temperature span from -58°F to 2200°F (-50°C to 1204°C). Its thermal shock resistance and chemical stability make it an ideal insulator for high-temperature industrial thermocouple probes.
A conductor jacket can be applied over the primary insulation layer when additional mechanical protection is needed, such as in environments with risk of abrasion or cable movement. For vinyl insulation, the jacket is typically made of nylon; for vinyl or nylon insulation, a polyethylene jacket is used. This external jacket acts as a robust mechanical barrier, reduces the likelihood of electrical short circuits, and enhances the overall durability and lifespan of the thermocouple assembly, especially in industrial automation or manufacturing settings.
The extension wires connect the thermocouple sensor wire to the measuring instrument or data acquisition system. These wires are made from alloys with similar thermal electromotive force (EMF) properties as the thermocouple itself, ensuring accurate signal transmission over distance. While extension wires often use less expensive copper alloys, they must maintain a closely matched thermal coefficient to the thermocouple to avoid measurement inaccuracies. Selecting the right thermocouple extension wire is essential for precision temperature measurement systems in process control, HVAC, and testing laboratories.
The four most common types of thermocouple circuitry are standard single, average, thermopile, and delta. Understanding these configurations is key to optimizing thermal sensor performance, maximizing response time, and ensuring accurate data collection in industrial process monitoring and temperature control systems.
A standard single thermocouple consists of two dissimilar metal wires joined together at a measuring junction. The EMF produced is directly proportional to the temperature difference, making this a fundamental method for temperature monitoring in HVAC, scientific, and process industries.
An average thermocouple configuration involves two or more thermocouples connected in parallel to a common cold junction. If the resistances of the thermocouples are equal, the resulting EMF represents the average temperature of each measuring point. This setup is valuable where batch temperature averaging improves process precision—such as in chemical reactors, environmental chambers, or thermal mapping.
A thermopile consists of multiple thermocouples connected in series, increasing the output voltage and sensitivity of the temperature measurement. The total EMF generated by the thermopile is the sum of the EMFs from all junctions, making this configuration ideal for applications requiring higher signal strength and thermal imaging—such as gas analyzers, infrared thermometers, and non-contact temperature sensors.
A delta thermocouple, also known as a differential thermocouple, is built from two similar wires joined to a dissimilar wire, with separate junctions at different process points. The EMF output measures the differential temperature between two measured locations, offering a direct way to monitor thermal gradients or detect heat loss in industrial processes. In this arrangement, one thermocouple junction must be ungrounded, and specialized differential temperature instruments are required for accurate comparison of heat transfer efficiency or system performance.
Thermocouples are available in various types, each designed for specific temperature ranges, process conditions, and industry requirements. Each type is identified by a letter designation—such as Types K, J, T, E, N, S, R, B, and C—and exhibits distinct characteristics including accuracy, temperature range, signal stability, oxidation resistance, and durability. Understanding the benefits and limitations of each thermocouple type ensures the best choice for your temperature sensing needs, whether for furnace control, food safety, cryogenics, or scientific instrumentation.
The most commonly used thermocouple type is the grounded construction, valued for its rapid response—approximately 50% faster than ungrounded types. In this design, the two sensor wires are welded to the metal probe sheath, ensuring efficient heat transfer and reliable measurements in dynamic or fluid applications.
The ungrounded thermocouple is typically the second choice, where junctions are isolated from the sheath material using a ceramic or oxide insulator. This isolation delivers longer sensor life, higher immunity to electrical interference, and better compatibility with modern instrumentation—making them preferred for lab analysis, electronics, and measuring temperature in hazardous or electrically noisy environments.
The least commonly used thermocouple is the exposed type, where the sensing element protrudes from the metal sheath and is directly exposed to ambient conditions. While this offers the fastest possible response time and excellent surface temperature measurement, its susceptibility to damage limits application to controlled settings—such as R&D labs or clean process gases, where robust probe protection is not required.
Base metal thermocouples are the workhorses of temperature sensing in industrial, commercial, and laboratory applications. Common types include Types C, B, E, J, N, K, R, T, and S, using a variety of metals such as iron, copper, nickel, platinum, rhodium, and chromel. Each thermocouple consists of two different metallic conductors joined to form a measurement junction, with output voltage determined by the Seebeck effect at differing temperatures.
Type C thermocouples, constructed from tungsten and rhenium, are engineered for use in extremely high temperature environments—up to 4200°F (2315°C)—such as aerospace, metallurgical processes, and advanced ceramics manufacturing. Designed for stability in hydrogen, inert, or vacuum atmospheres, they require robust protective sheaths made of molybdenum, tantalum, or Inconel, with insulators like alumina, hafnia, and magnesium oxide to maintain optimum measurement integrity and prevent sensor failure under oxidation risk.
Type E thermocouples feature chromel (a nickel-chromium alloy) as the positive leg and constantan (a copper-nickel alloy) as the negative leg. With a temperature range of -330°F to 1600°F (-200°C to 870°C) and strong EMF versus temperature characteristics, Type E is a top choice for sub-zero and cryogenic temperature readings, as well as mid-range industrial heating. Their robust EMF output enhances resolution in low-temperature laboratory and environmental monitoring. Protection is recommended in sulfur-rich atmospheres to avoid sensor degradation.
Type J thermocouples combine iron (positive leg) and constantan (negative leg), making them suitable for a variety of atmospheres—oxidizing, vacuum, inert, and reducing. Their temperature span (32°F to 1000°F / 0°C to 760°C) and affordability position them as a popular option in plastics processes—including injection molding—process heating, and temperature control systems. Continuous exposure to high humidity or oxidizing conditions may shorten their operational life due to rusting of the iron conductor, so protective measures and ongoing monitoring are critical for longevity.
Type K thermocouples use chromel for the positive leg and alumel (nickel, with aluminum, silicon, and manganese) for the negative leg. Their temperature range spans -300°F to 2300°F (-200°C to 1260°C), and they are renowned for their reliability in general purpose and industrial temperature measurement. Widely used due to cost-effectiveness, corrosion resistance in oxidizing atmospheres, and good signal stability, Type K is often the first choice for furnaces, automotive exhaust, gas turbines, and process engineering. Performance varies at low temperatures or in certain inert gas environments, so proper calibration is essential to achieve best accuracy.
Type N thermocouples feature nicrosil (nickel-chromium-silicon) and nisil (nickel-silicon-magnesium) alloy conductors, offering stability and longevity throughout their wide operating temperature range of 32°F to 2300°F (0°C to 1260°C). Their exceptional resistance to oxidation, green rot, and hysteresis make them highly valued in chemical processing, refining, and the petrochemical industry, especially where constant thermal cycling and high process reliability are demanded.
Type T thermocouples pair copper (positive leg) with constantan (negative leg) and excel in low-temperature, cryogenic, and food processing applications. Their range (-330°F to 700°F / -200°C to 370°C) allows precise control in refrigeration, biomedical, and chemical storage environments, while the anti-decomposition robustness ensures extended service life where accuracy is critical for safety and compliance.
Noble metal thermocouples, also known as platinum thermocouples, include Types B, R, S, and P. These high-precision sensors use precious metal elements—chiefly platinum and rhodium—and are renowned for their accuracy, stability, and longevity at extremely elevated temperatures. They are integral to industries requiring consistent and reliable temperature measurement, such as glass manufacturing, semiconductor fabrication, steel mills, and advanced laboratory research.
The Type B thermocouple is engineered for the most demanding high-temperature applications, offering the highest temperature tolerance among all thermocouple types. Composed of Platinum (6% Rhodium) and Platinum (30% Rhodium), it is stable and accurate up to 3100°F (1700°C), making it ideal for glass and metals processing, high-temperature furnaces, and precision heat treatment.
Type R thermocouples are made from platinum and platinum (13% rhodium), combining resilience with a temperature capability of -58°F to 2700°F (-50°C to 1450°C). With exceptional accuracy and higher rhodium content (than Type S), these are favored for harsh process environments, such as sulfur recovery, glass manufacturing, or pharmaceutical sterilization. They offer similar temperature response and stability to Type S, with expanded durability for both high and low-temperature use.
Type S thermocouples, constructed from platinum and platinum (10% rhodium), are employed in high-temperature environments within the BioTech, medical device sterilization, and pharmaceutical industries, as well as in precision laboratory research. With a maximum temperature of 2700°F (1450°C) and extraordinary measurement stability over time, Type S is an industry standard for reference and calibration applications, as well as for heat treatment process control where reliability and reproducibility are paramount.
Type P thermocouples display a temperature response curve similar to that of Type K at high temperatures, but are constructed from precious metals for superior stability and oxidation resistance. They can operate in oxidizing atmospheres up to 2300°F (1260°C). When integrating a Type P thermocouple into a monitoring system, a Type K extension wire is typically used for signal continuity, maintaining measurement accuracy even in demanding industrial temperature sensing environments.
Thermocouples are popular temperature sensors due to their broad temperature range, durability, and affordability. They are utilized in a variety of applications, including home appliances, industrial processes, electric power generation, furnace monitoring and control, food and beverage processing, automotive sensors, aircraft engines, rockets, and spacecraft.
Their compact size, rapid response time, and ability to withstand shocks and vibrations make thermocouples ideal for precise temperature control and measurement.
Below is a description of some of the various applications for thermocouples:
Thermocouples are ideal for the food industry due to their ability to provide accurate temperature readings quickly. They can be used at various stages of production to ensure proper cooking or storage conditions. Food production thermocouples typically consist of a two-piece unit: a handheld readout and a detachable probe. The probe contains two wires connected at the tip. Flat-headed probes are used to measure surface temperatures, while needle probes are used for internal measurements and to monitor air temperatures in ovens.
Extruders, which operate under high temperature and pressure conditions, require precise temperature measurement. The thermocouple's sensor tip must be placed in the molten plastic, where it can accurately measure the temperature directly within the process. These thermocouples offer high accuracy and rapid response times and often utilize a Type K thermocouple probe to meet the demands of such challenging environments.
A pilot light ignites the furnace burner, and the thermocouple plays a crucial safety role by monitoring the flame. If the thermocouple does not detect a flame, it shuts off the gas supply, preventing gas from accumulating in the furnace and enhancing overall safety. This mechanism ensures that the furnace only receives gas when the pilot light is properly lit, reducing the risk of hazardous gas buildup.
A molten metal thermocouple is designed for use in non-ferrous metal environments and can measure temperatures up to 1250°C. These thermocouples are essential for monitoring and controlling the temperature of liquid metals throughout various stages, including melt preparation, holding, degassing, and casting operations. Their high-temperature capabilities and durability make them crucial for ensuring precision and quality in metal processing.
A thermocouple on a gas appliance plays a critical safety role by signaling the gas valve to remain open when the pilot light is lit. Positioned within the pilot flame, the thermocouple detects the heat and generates a voltage that keeps the gas flowing to the burner. If the pilot flame extinguishes, the voltage produced by the thermocouple drops, causing the gas valve to close and prevent the release of gas, thereby enhancing safety and preventing potential hazards.
Finding suitable instrumentation for high-pressure applications can be challenging due to the extreme temperatures and heavy vibrations involved. In these demanding environments, resistance thermometers (RTDs) and thermocouples are commonly used temperature sensors. However, thermocouples are often the preferred choice due to their robustness, wide temperature range, and ability to withstand high pressures and vibrations effectively.
There are two configurations of thermocouples for high pressure applications, which are pictured below:
Though thermocouples are very reliable and durable, they can fail over time and need to be regularly checked. Regardless of the wide variety of thermocouples available, they all operate on the same basic principle: two connected wires, where one wire serves as the reference junction and the other as the hot or measuring junction.
The testing of the efficiency of a thermocouple involves using a multimeter. Below is a description of a multimeter and instructions on how to test a thermocouple using it.
Multimeters come in various forms and styles. Despite these variations, they all display some basic symbols that indicate their different functions.
There are also prefixes that may be displayed as well.
Multimeters have settings for measuring AC and DC currents.
Some multimeters feature a continuity beeper that sounds when the meter detects a closed circuit. A continuity check is used to verify the presence of a complete path for current flow. The image below shows a multimeter equipped with a continuity beeper.
The multimeter should be able to read ohms, which measure the resistance to current flow in an electrical circuit. Conductors, such as silver, copper, gold, and aluminum, offer little resistance, while insulators have high resistance. These metals are commonly found in thermocouple wires. Since thermocouples generate millivolt signals, the multimeter used for testing must be highly sensitive.
For the resistance test, first remove the thermocouple from the application. Set the multimeter to the ohms option. Place one lead on the side of the thermocouple and the other lead at the end that was inserted into the application. If the thermocouple has proper continuity, the multimeter should display a small resistance reading.
For the open circuit test, first remove the thermocouple from the application. Set the multimeter to measure millivolts. Connect one lead to the side of the thermocouple and the other lead to the opposite end. Heat the end that was previously inserted into the application. The millivolt reading should fall within the acceptable range for the thermocouple type being tested.
The closed circuit test requires a thermocouple adapter. Insert the adapter into the application, then screw the thermocouple into the adapter. Connect one lead of the multimeter to the screw of the adapter and the other lead to the exposed end of the thermocouple. Activate the application to get a reading from the multimeter, which will be displayed in millivolts. If the thermocouple fails this test, it should be replaced.
Thermocouples are a cost-effective method for measuring a wide range of temperatures with accuracy. They are commonly used in boilers, water heaters, ovens, and airplane engines.
When preparing to read a thermocouple, it is necessary to understand a thermocouple reference table. Each type of thermocouple has its own reference table. Below is a portion of the reference table for a Type K thermocouple.
| Type K Thermocouple Reference Table | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| °C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Thermoelectric Voltage in mV | |||||||||||
| -270 | -6.458 | ||||||||||
| -260 | -6.411 | -6.444 | -6.446 | -6.448 | -6.450 | -6.452 | -6.453 | -6.455 | -6.456 | -6.457 | -6.458 |
| -250 | -6.404 | -6.408 | -6.413 | -6.417 | -6.421 | -6.425 | -6.429 | -6.432 | -6.435 | -6.438 | -6.441 |
| -240 | -6.344 | -6.351 | -6.358 | -6.364 | -6.370 | -6.377 | -6.382 | -6.388 | -6.393 | -6.399 | -6.404 |
| -230 | -6.262 | -6.271 | -6.280 | -6.289 | -6.297 | -6.306 | -6.314 | -6.322 | -6.329 | -6.337 | -6.344 |
| -220 | -6.158 | -6.170 | -6.181 | -6.192 | -6.202 | -6.213 | -6.223 | -6.233 | -6.243 | -6.252 | -6.262 |
| -210 | -6.035 | -6.048 | -6.061 | -6.074 | -6.087 | -6.099 | -6.111 | -6.123 | -6.135 | -6.147 | -6.158 |
| -200 | -5.891 | -5.907 | -5.922 | -5.936 | -5.951 | -5.965 | -5.980 | -5.994 | -6.007 | -6.021 | -6.035 |
| -190 | -5.730 | -5.747 | -5.763 | -5.780 | -5.797 | -5.813 | -5.829 | -5.845 | -5.861 | -5.876 | -5.891 |
| -180 | -5.550 | -5.569 | -5.588 | -5.606 | -5.624 | -5.642 | -5.660 | -5.678 | -5.695 | -5.713 | -5.730 |
| -170 | -5.354 | -5.374 | -5.395 | -5.415 | -5.435 | -5.454 | -5.474 | -5.493 | -5.512 | -5.531 | -5.550 |
| -160 | -5.141 | -5.163 | -5.185 | -5.207 | -5.228 | -5.250 | -5.271 | -5.292 | -5.313 | -5.333 | -5.354 |
| -150 | -4.913 | -4.936 | -4.960 | -4.983 | -5.006 | -5.029 | -5.052 | -5.074 | -5.097 | -5.119 | -5.141 |
| -140 | -4.669 | -4.694 | -4.719 | -4.744 | -4.768 | -4.793 | -4.817 | -4.841 | -4.865 | -4.889 | -4.913 |
| -130 | -4.411 | -4.437 | -4.463 | -4.490 | -4.516 | -4.542 | -4.567 | -4.593 | -4.618 | -4.644 | -4.669 |
| -120 | -4.138 | -4.166 | -4.194 | -4.221 | -4.249 | -4.276 | -4.303 | -4.330 | -4.357 | -4.384 | -4.411 |
| -110 | -3.852 | -3.882 | -3.911 | -3.939 | -3.968 | -3.997 | -4.025 | -4.054 | -4.082 | -4.110 | -4.138 |
| -100 | -3.554 | -3.584 | -3.614 | -3.645 | -3.675 | -3.705 | -3.734 | -3.764 | -3.794 | -3.823 | -3.852 |
| -90 | -3.243 | -3.274 | -3.306 | -3.337 | -3.368 | -3.400 | -3.431 | -3.462 | -3.492 | -3.523 | -3.554 |
| -80 | -2.920 | -2.953 | -2.986 | -3.018 | -3.050 | -3.083 | -3.115 | -3.147 | -3.179 | -3.211 | -3.243 |
| -70 | -2.587 | -2.620 | -2.654 | -2.688 | -2.721 | -2.755 | -2.788 | -2.821 | -2.854 | -2.887 | -2.920 |
| -60 | -2.243 | -2.278 | -2.312 | -2.347 | -2.382 | -2.416 | -2.450 | -2.485 | -2.519 | -2.553 | -2.587 |
| -50 | -1.889 | -1.925 | -1.961 | -1.996 | -2.032 | -2.067 | -2.103 | -2.138 | -2.173 | -2.208 | -2.243 |
| -40 | -1.527 | -1.564 | -1.600 | -1.637 | -1.673 | -1.709 | -1.745 | -1.782 | -1.818 | -1.854 | -1.889 |
| -30 | -1.156 | -1.194 | -1.231 | -1.268 | -1.305 | -1.343 | -1.380 | -1.417 | -1.453 | -1.490 | -1.527 |
| -20 | -0.778 | -0.816 | -0.854 | -0.892 | -0.930 | -0.968 | -1.006 | -1.043 | -1.081 | -1.119 | -1.156 |
| -10 | -0.392 | -0.431 | -0.470 | -0.508 | -0.547 | -0.586 | -0.624 | -0.663 | -0.701 | -0.739 | -0.778 |
| 0 | 0.000 | -0.039 | -0.079 | -0.118 | -0.157 | -0.197 | -0.236 | -0.275 | -0.314 | -0.353 | -0.392 |
The first column on the left of the table lists temperatures in increments of ten. The portion of the table to the right shows intermediate distances in increments of one, between the temperature ranges. For example, in the table above, -280°F is the third entry from the top. If the temperature reading on the thermocouple is -284°F, you would locate -280°F in the table and then move to the right to find the number under the column labeled 4. The numbers in this section of the table represent the millivolt readings corresponding to the temperature.
Reference junctions on a thermocouple may experience temperature fluctuations, which can lead to inaccurate readings. To ensure accurate measurements, the reference temperature can be stabilized by immersing the reference junction in water or by using a reference junction compensator. This compensator adjusts for any ambient temperature changes. The image below provides a simplified representation of a compensation calculator.
A homogeneous wire is physically and chemically uniform throughout its length. In a thermocouple circuit made from such a wire, no electromotive force (emf) will be generated, even with changes in temperature or thickness. For a thermocouple to function correctly and produce voltage, it must consist of two different metals joined together, as this is essential for generating an emf based on temperature differences.
The sum of the electromotive forces (emfs) in a thermocouple circuit will be zero if all junctions in the circuit are at the same temperature. Adding different metals to the circuit does not affect the voltage generated, as long as all junctions are at the same temperature. For instance, using copper leads to connect a thermocouple to measurement equipment or employing solder to join metals does not change the measured voltage. This is because the added junctions must be at the same temperature as the original junctions in the circuit, ensuring accurate temperature readings when using thermocouples with digital multimeters or other electrical components.
A thermocouple generates an electromotive force (emf) when two different metals are subjected to different temperatures. When calibrated with a reference temperature, a thermocouple can be connected to additional wires with the same thermoelectric characteristics without affecting the emf measurement. This means that extra wires, which maintain the same thermoelectric properties, can be added to the circuit without altering the emf produced by the thermocouple, as long as the temperature differences between the junctions remain constant.
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