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.
Various materials are used in constructing the devices so as to achieve different relationship between resistivity and thermal energy. Thermal sensitive materials used in constructing the devices include nickel, platinum, and copper. Platinum is the most commonly used material. The materials also offer good tolerance classes and nominal resistivity at zero 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.
Thin film elements have a detecting device which is formed by depositing a relatively thin layer of resistive substance, usually platinum, on a ceramic substrate. The main disadvantage of this type is that they are less stable compared to the wire-wound and coiled counterparts. They also have different expansion rates brought about by the substrate deposited that creates a strain gauge effect.
Thin film elements have detecting components that is formed by depositing a relatively thin layer of resistive substance, usually platinum, on a ceramic substance. This layer is always below a hundred angstroms. The thin film deposit is coated with glass or epoxy to protect it from contamination and also to act as strain relief for foreign lead-wires. This type of RTD are however not as stable as the coiled or wire wound types.
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.
Any appliances made from a resistance temperature device are not suitable for industrial applications that operate above six hundred degrees Celsius. This is because the platinum becomes contaminated with impurities produced from the metal sheath of the thermometer. The appliances are however suitable for precision applications and have wide operating range.
Various materials are used in constructing the devices so as to achieve different relationship between resistivity and thermal energy. Thermal sensitive materials used in constructing the devices include nickel, platinum, and copper. Platinum is the most commonly used material. The materials also offer good tolerance classes and nominal resistivity at zero 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.
Thin film elements have a detecting device which is formed by depositing a relatively thin layer of resistive substance, usually platinum, on a ceramic substrate. The main disadvantage of this type is that they are less stable compared to the wire-wound and coiled counterparts. They also have different expansion rates brought about by the substrate deposited that creates a strain gauge effect.
Thin film elements have detecting components that is formed by depositing a relatively thin layer of resistive substance, usually platinum, on a ceramic substance. This layer is always below a hundred angstroms. The thin film deposit is coated with glass or epoxy to protect it from contamination and also to act as strain relief for foreign lead-wires. This type of RTD are however not as stable as the coiled or wire wound types.
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.
Any appliances made from a resistance temperature device are not suitable for industrial applications that operate above six hundred degrees Celsius. This is because the platinum becomes contaminated with impurities produced from the metal sheath of the thermometer. The appliances are however suitable for precision applications and have wide operating range.
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