Resistance temperature device (RTD), are detectors used to record the amount of sensible heat in a substances by correlating the resistivity of the element with its sensible heat energy. Several RTD elements are made of fine wire wound around a glass core or ceramic. The element is normally fragile; therefore, it is placed inside a probe that is sheathed to protect it.
Most commonly used RTD sensing elements constructed of nickel, copper and platinum have a repeatable, and unique and predictable thermal conductivity versus resistance relationship within the thermal operation range. Platinum is the most stable over the largest thermal energy range. Nickel elements have limited range of operation because the amount of change in resistivity per degree of change in internal thermal energy becomes very non-linear above 300 degrees Celsius.
The significant behavior of the metals used in manufacturing resistive elements is the ability to approximate their resistivity versus thermal energy relationship ranging from zero to a hundred degrees Celsius. Industrial standards have also been established so as to ensure the elements meet the required standards and accuracy. Functional characteristics of the sensors can also be found by applying values of nominal resistivity and tolerance.
Apart from the different materials, RTD can be made in two configurations: thin film and wire wound. A wire wound configuration shows an outer wound or an inner coil RTD. Inner coil construction is made up of a resistive coil that runs through an opening in a ceramic, whereas an outer wound consists of winding the resistive material around a glass cylinder or ceramic having a glass dollop.
RTD can also be made inform of thin film or wire wound. Wire wound show an external winding or an internal coil. Inner coil comprises of a resistive coil that passes through a cavity in a ceramic, while an outer wound comprises of windings of the resistive substance element around a ceramic or a glass cylinder. Wire wound elements exhibits excellent accuracy, especially over varying thermal energy in materials.
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.
Most commonly used RTD sensing elements constructed of nickel, copper and platinum have a repeatable, and unique and predictable thermal conductivity versus resistance relationship within the thermal operation range. Platinum is the most stable over the largest thermal energy range. Nickel elements have limited range of operation because the amount of change in resistivity per degree of change in internal thermal energy becomes very non-linear above 300 degrees Celsius.
The significant behavior of the metals used in manufacturing resistive elements is the ability to approximate their resistivity versus thermal energy relationship ranging from zero to a hundred degrees Celsius. Industrial standards have also been established so as to ensure the elements meet the required standards and accuracy. Functional characteristics of the sensors can also be found by applying values of nominal resistivity and tolerance.
Apart from the different materials, RTD can be made in two configurations: thin film and wire wound. A wire wound configuration shows an outer wound or an inner coil RTD. Inner coil construction is made up of a resistive coil that runs through an opening in a ceramic, whereas an outer wound consists of winding the resistive material around a glass cylinder or ceramic having a glass dollop.
RTD can also be made inform of thin film or wire wound. Wire wound show an external winding or an internal coil. Inner coil comprises of a resistive coil that passes through a cavity in a ceramic, while an outer wound comprises of windings of the resistive substance element around a ceramic or a glass cylinder. Wire wound elements exhibits excellent accuracy, especially over varying thermal energy in materials.
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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This article collected, selected and written by: Author Van Hoc
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