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.
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.
The major categories of RTDs include: strain free elements, thin film elements, coiled elements, wire-wound elements and strain free elements. Wire wound elements have great accuracy, particularly over wide temperature ranges. The diameter of the coil also provides a compromise between mechanical stability and also permitting expansion of the wire to reduce mechanical strain and consequential drift. The detecting wire is wound around an insulating core or mandrel.
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.
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.
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.
The major categories of RTDs include: strain free elements, thin film elements, coiled elements, wire-wound elements and strain free elements. Wire wound elements have great accuracy, particularly over wide temperature ranges. The diameter of the coil also provides a compromise between mechanical stability and also permitting expansion of the wire to reduce mechanical strain and consequential drift. The detecting wire is wound around an insulating core or mandrel.
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.
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.
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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