Industrial furnaces: such as heat treatment furnaces, ceramic kilns, glass melting furnaces, etc., for monitoring the temperature inside the furnaces. Chemical production: temperature measurement of media in reaction kettles and pipelines to ensure stable reaction conditions. Power industry: temperature monitoring of equipment such as generators, steam turbines, and boilers to prevent overheating failures. Automobile manufacturing: temperature detection of engine exhaust systems and painting drying lines. Food and pharmaceutical industry: temperature control of sterilization equipment and baking ovens to ensure product quality and safety.
How it works
I. Core Composition
A Type K thermocouple consists of two conductors (thermoelectrodes) with different compositions:
Positive electrode (KP): Nickel-chromium alloy (containing 80% nickel and 20% chromium), which has good oxidation resistance and electrical conductivity.
Negative electrode (KN): Nickel-silicon alloy (containing 95% nickel and 5% silicon, and actually a small amount of manganese, cobalt, etc.), which plays a role in compensating and stabilizing thermoelectric properties.
II. Working Principle
It is based on the Seebeck effect (thermoelectric effect): When there is a temperature difference between the hot junction and the cold junction, the difference in free electron density between the two metal conductors causes directional movement of electrons, generating a thermoelectric potential (millivolt-level voltage) in the circuit.
The magnitude of the thermoelectric potential has a certain functional relationship with the temperature difference between the two ends (non-linear, but can be linearized by instruments within the industrial measurement range).
During measurement, the thermoelectric potential is detected by the instrument, and combined with cold junction temperature compensation (usually automatically completed by the instrument), the actual temperature of the hot junction can be calculated.
Advantages
Wide measurement range: The conventional operating temperature is -200ºC~1200ºC, and it can withstand high temperatures of 1300ºC for a short time, covering most industrial temperature measurement needs.
Good stability: When used for a long time in oxidizing atmospheres (such as air, oxygen), the thermoelectric properties are stable with small drift.
High sensitivity: The thermoelectric potential changes by about 41μV per 1ºC temperature change (at 25ºC), which is convenient for accurate measurement by instruments.
Low cost: Using nickel-based alloys, the raw material price is much lower than that of precious metal thermocouples (such as Type S, Type B), with high cost performance.
Good linearity: In the commonly used temperature range (0~1000ºC), the non-linear error between thermoelectric potential and temperature is small, simplifying the design of measurement circuits.
Technical features
Disadvantages
Poor resistance to reducing atmospheres: In reducing atmospheres (such as hydrogen, carbon monoxide), sulfur-containing atmospheres, or vacuum environments, the electrodes are prone to corrosion or embrittlement, and must be used with protective sleeves (such as corundum or metal sleeves).
High-temperature limitation: When used for a long time at temperatures exceeding 1200ºC, the nickel-chromium alloy will experience grain coarsening, leading to increased thermoelectric potential drift and reduced accuracy.
IV. Key Technical Parameters
Accuracy class:
Class 1: Within the range of -40ºC~1000ºC, the allowable error is ±1.5ºC or ±0.4% t (where t is the measured temperature, whichever has the larger absolute value);
Class 2: Within the range of -40ºC~1200ºC, the allowable error is ±2.5ºC or ±0.75% t.
Insulation resistance: At an ambient temperature of 15~35ºC and relative humidity ≤80%, the insulation resistance is ≥5MΩ (test voltage: 100V DC).
Response time: Depends on the material and structure of the protective sleeve. For an exposed measuring tip, it is approximately 0.1~1 second; with a metal sleeve, about 1~5 seconds; and with a ceramic sleeve, around 5~30 seconds.
Nominal pressure: The static external pressure that the protective sleeve can withstand (related to material and temperature). Metal sleeves typically range from 1~30MPa, while ceramic sleeves have a lower range (approximately 0.1~1MPa).
V. Usage Precautions
Environmental adaptation: Avoid direct use in reducing or sulfur-containing atmospheres; select corrosion-resistant protective sleeves (such as 316 stainless steel or corundum).
Cold junction compensation: Since changes in cold junction temperature can affect measurement accuracy, use the instrument's built-in cold junction compensation circuit (e.g., Pt100 thermistor compensation) to eliminate errors.
Insertion depth: The depth at which the measuring end is inserted into the measured medium should be at least 8-10 times the outer diameter of the protective sleeve to ensure sufficient contact with the measured object.
Wiring specifications: The positive and negative electrodes must be connected correctly (usually the positive electrode is marked red, and the negative electrode is marked green or black) to avoid short circuits or poor contact.
Company Profile
Address: Huji Industrial Park, Deshang Expressway, Mudan District, Heze City, Shandong Province, China
Business type: Manufacturer/factory, trading company
Business scope: manufacturing and processing machinery
Management system certification: ISO9001:2015 ISO45001:2018 ISO14001:2015
Main products: Ground flare, Biogas flares, flare stack,
Thermal Oxidation Furnace, Flue gas purification equipment
Heze Zexuan Equipment Manufacturing Co., Ltd. is an enterprise engaged in the manufacture of special equipment for environmental protection; sales of special equipment for environmental protection; application of industrial automation technology; sales of power electronic components; research and development of mechanical equipment; sales of intelligent instruments and meters; manufacturing of intelligent instruments and meters; research and development and promotion of comprehensive utilization of waste gas and VOCs treatment technology.
The company's main products and service directions: manufacturing of ground torches, elevated torches, waste gas venting torches, biogas torches, three waste incinerators, and wastewater treatment equipment, industrial automation and DCS system applications, wastewater treatment projects, VOCs treatment equipment and engineering construction, petrochemical accessories and instrument sales, petrochemical equipment installation, maintenance and repair, etc.; support product customization services and OEM services in the same industry, from design to manufacturing, installation, commissioning, and after-sales one-stop service.
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