Resistance temperature device (RTD) applies the concept that electrical resistivity of any element has a direct variation with its thermal energy. The relationship between sensible heat in the environment and resistivity of the elements can be easily predicted. RTD devices are permanently replacing the use of thermocouple thermometers in several industrial applications that operate below 600 degrees Celsius. This is due to their repeatability and higher accuracy.
RTD is usually manufactured using a pure material, mainly platinum, copper or nickel. The material used always has a predictable variation of resistivity as its internal energy changes. It is this predictable change that is applied to determine its thermal energy changes. Platinum is a noble metal having the most stable conductivity versus resistivity relationship within a range of different thermal conductivity range. Platinum is also the best material for RTDs since it follows a linear relationship in a highly repeatable manner.
Even though any value is achievable for nominal resistivity, the most common is platinum 100 ohm. Tolerance class also determines the accuracy of the sensor. Different industry standards have also been put in place to ensure accuracy is achieved. In addition, using values of tolerance and nominal resistivity, the functional features of their sensor can be defined.
Calibration may be performed beyond a hundred degrees Celsius or below zero degrees Celsius. In this case, the comparison method or the fixed point method may be used. Fixed point calibration uses the best accuracy calibration by using freezing point, triple point or melting point of pure substances such as zinc, argon and tin to generate a known repeatable fixed point temperature.
Thin film RTD consists of a thin layer of resistive substance deposited on a ceramic by a process called deposition. A resistant meander is then etched onto the detector, and lesser trimming then applied in achieving the required nominal value of its sensor. The resistive substance is then guarded with a thin layer of glass. Lead wires are also welded to form pads with the detector and then covered using a glass dollop.
Thermometers made using RTDs have improved accuracy, repeatability and stability in most cases unlike the thermocouple types. To measure their opposition to flow of current, a small current has to be passed through the device being tested. This results in resistive heating, resulting in significant loss of accuracy if the design of does not adequately consider the heat path, or the limits set by the manufacturer are not adhered to. For most precise applications, four wire connections are often used.
To ensure the stability of platinum wires is retained, they should be kept free from any contamination. When measuring their resistivity, a small current should be passed through the device being tested. Mechanical strain on the thermometers can also lead to inaccuracy. To avoid this, four-wire connections are used for most precise applications.
At very low internal thermal energy of the elements, because there are very few phonons, resistivity of an RTD depends only on boundary scattering and impurities. However, any appliance that use resistance temperature device has excellent accuracy, wide operation range, low drift and is also suitable for precision applications. These outstanding characteristics qualify them to be best in any industrial applications that require high efficiency.
RTD is usually manufactured using a pure material, mainly platinum, copper or nickel. The material used always has a predictable variation of resistivity as its internal energy changes. It is this predictable change that is applied to determine its thermal energy changes. Platinum is a noble metal having the most stable conductivity versus resistivity relationship within a range of different thermal conductivity range. Platinum is also the best material for RTDs since it follows a linear relationship in a highly repeatable manner.
Even though any value is achievable for nominal resistivity, the most common is platinum 100 ohm. Tolerance class also determines the accuracy of the sensor. Different industry standards have also been put in place to ensure accuracy is achieved. In addition, using values of tolerance and nominal resistivity, the functional features of their sensor can be defined.
Calibration may be performed beyond a hundred degrees Celsius or below zero degrees Celsius. In this case, the comparison method or the fixed point method may be used. Fixed point calibration uses the best accuracy calibration by using freezing point, triple point or melting point of pure substances such as zinc, argon and tin to generate a known repeatable fixed point temperature.
Thin film RTD consists of a thin layer of resistive substance deposited on a ceramic by a process called deposition. A resistant meander is then etched onto the detector, and lesser trimming then applied in achieving the required nominal value of its sensor. The resistive substance is then guarded with a thin layer of glass. Lead wires are also welded to form pads with the detector and then covered using a glass dollop.
Thermometers made using RTDs have improved accuracy, repeatability and stability in most cases unlike the thermocouple types. To measure their opposition to flow of current, a small current has to be passed through the device being tested. This results in resistive heating, resulting in significant loss of accuracy if the design of does not adequately consider the heat path, or the limits set by the manufacturer are not adhered to. For most precise applications, four wire connections are often used.
To ensure the stability of platinum wires is retained, they should be kept free from any contamination. When measuring their resistivity, a small current should be passed through the device being tested. Mechanical strain on the thermometers can also lead to inaccuracy. To avoid this, four-wire connections are used for most precise applications.
At very low internal thermal energy of the elements, because there are very few phonons, resistivity of an RTD depends only on boundary scattering and impurities. However, any appliance that use resistance temperature device has excellent accuracy, wide operation range, low drift and is also suitable for precision applications. These outstanding characteristics qualify them to be best in any industrial applications that require high efficiency.
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