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Thermocouples

Thermocouples Alumel, Chromel, Kopel, Constantan, Tungsten-rheniumThermocouple - device for measuring temperature, which consists of two dissimilar metals, joined together at the end of sensing. Various thermocouple (Alumel, Chromel, Kopel, Constantan, Tungsten-rhenium) use different metal alloys.

Thermocouples are widely used to measure the temperature of anything. Due to the robust sensor design for operation in a wide temperature range, temperature measurement using thermocouples widespread.

The widespread use thermocouples is primarily due to its simplicity. The maximum temperature that can measure the wire depends on the thickness of the thermocouple wire.

Another advantage of thermocouples - fast response, the ability to measure small differences in temperature. Thermocouples are necessary for measuring high temperatures in aggressive environments. Thermocouples can provide accurate temperature measurement ± 0,01 ° C.

Advantages

  • Wide operating temperature range;
  • Ease of production and operation, reliability of the material.

Disadvantages

  • Necessary to monitor the reference junction temperature;
  • Thermocouple wire noninert. If the thermocouple wire leaking may fail due to an aggressive environment;
  • Extending the wire may cause negative effects of "antenna";
  • The high cost of the material due to high content of rare metals.

Tips for working with thermocouples

You can increase the accuracy of thermocouples data, if you observe the following rules:

  • Use a large diameter wire, it should not change the temperature of the measurement object;
  • When using a short, thin wire, you should use it close to the object;
  • Thermocouple wire should be protected from mechanical stress and vibration;
  • Use thermocouple wire only operating temperature range;
  • Use thermocouple wire right material when working in harsh conditions;
  • Keep an electronic record of all events and keep the electrical resistance.

Types of thermocouple wire

Thermocouple made of precious metals such as Platinum provides the most accurate data.

The main advantage - a small thermionic heterogeneity, compared with thermocouples of other metals, high resistance to oxidation, much stability. The main disadvantage- the high cost of the material.

Also developed a thermocouple with other precious metals: gold-platinum and platinum-rhodium thermocouple. Research indicates it more stable and accurate operation.

Thermocouples made of non-ferrous metals are used in many industries. The cost is low and resistant to corrosion and vibration. Especially widely used thermocouples in the insulation, which allows measurements in a variety of designs. Advantage - high sensitivity. Disadvantage - the thermoelectric heterogeneity.

Tungsten-rhenium thermocouples used to measure the temperature up to 2500 °C, used in the nuclear energy. It is important to eliminate the effects of an oxidizing atmosphere, which destroys the wire. For tungsten-rhenium thermocouples use a special cover of tantalum and molybdenum.

Non-precious metals thermocouple

Iron-constantan thermocouple

  • Can not be used at temperatures below 0 °C, as the condensation on the iron in wire can cause corrosion;
  • The best option - rarefied atmosphere;
  • Maximum operating temperature of - 500 ° C, the rise of temperature leads to oxidation of contacts. Also oxidized to sulfuric environment;
  • Advantage - low cost.

Chromel-constantan thermocouple

  • Advantage - high sensitivity of the device;
  • Much thermoelectric homogeneity of the electrode materials;
  • Can be used at low temperatures.

Copper-constantan thermocouple

  • Can be used at temperatures below 0 °C;
  • Can be used in excess or lack of oxygen;
  • Can not be used at temperatures above 400 ° C;
  • Sensitive to moisture.

Chromel-alumel thermocouple

  • Widely used in all areas of - 95 ° C to +1150 ° C (depending on the diameter);
  • It is used in an atmosphere with an excess of oxygen;
  • Can not be used in the rarefied atmosphere as chromium can leave Nichrome wire, which changes the indicator measurement;
  • Oxidized to sulfuric environment.

Precious metals thermocouple

Platinum thermocouple

  • Operating temperature up to 1350 °C;
  • Shorttime use at 1590 °C;
  • At temperatures above 900 °C, thermocouple polluting hydrogen, carbon, alloys of copper and iron. Thermocouples can not be strengthened steel pipe;
  • Can be used in acidic atmosphere;
  • At temperatures above 1000 °C, thermocouple contaminate silicon;
  • Avoid using at temperatures below 400 °C.

LLC Renal-d supplies thermocouple wire from Ukraine:

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