A resistance temperature device (RTD) is a thermal sensor that works on the measurement principle that the electrical resistivity of any material varies directly with its degree of sensible heat energy. The relationship between the environmental temperatures and the resistance of these devices is highly predictable. This allows for a consistent and accurate measuring of the amount of sensible heat in the detector. When the devices are supplied with stable source of current and resultant voltage drop across the resistor measured, its force that opposes flow of current can be computed, and its sensible heat also determined.
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.
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.
Platinum detecting wire should be kept free from any contamination so as to ensure it retains its stability. A platinum film or wire should be supported on a former so that it gets minimal strains from its former or minimal differential expansion, even though it is often resistant to vibration. RTD assemblies manufactured using iron or copper are also used in number of applications.
In industries where operations take place beyond 660 degrees Celsius, RTDs are not usually used as they get uncontrollably contaminated. Their resistivity is essentially zero at three Kelvins, therefore rendering them useless. Compared to thermistors, RTDs have slower response time and are less sensitive to small temperature changes. A resistance temperature device is, however, used to make thermometers which have low drift, high accuracy and wide operation range.
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.
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.
Platinum detecting wire should be kept free from any contamination so as to ensure it retains its stability. A platinum film or wire should be supported on a former so that it gets minimal strains from its former or minimal differential expansion, even though it is often resistant to vibration. RTD assemblies manufactured using iron or copper are also used in number of applications.
In industries where operations take place beyond 660 degrees Celsius, RTDs are not usually used as they get uncontrollably contaminated. Their resistivity is essentially zero at three Kelvins, therefore rendering them useless. Compared to thermistors, RTDs have slower response time and are less sensitive to small temperature changes. A resistance temperature device is, however, used to make thermometers which have low drift, high accuracy and wide operation range.
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