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Resistance thermometer
Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors that use the electrical resistance of a substance (such as platinum) to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a heat-resistant ceramic or glass core but other constructions are also used. The RTD wire is typically platinum (Pt), nickel (Ni), or copper (Cu). The material has an accurate temperature–resistance relationship which is used to provide an indication of temperature. As RTD elements are fragile, they are often housed in protective probes called thermowells. RTDs have higher accuracy and repeatability than thermocouples, which is why they are slowly replacing them in industrial applications below 600 °C.
Common RTD sensing elements for biomedical application constructed of platinum (Pt), nickel (Ni), or copper (Cu) have a repeatable resistance versus temperature relationship (R vs T) and operating temperature range. The R vs T relationship is defined as the amount of resistance change of the sensor per degree of temperature change. The relative change in resistance (temperature coefficient of resistance) varies only slightly over the useful range of the sensor.[citation needed]
Platinum was proposed by Sir William Siemens as an element for a resistance temperature detector at the Bakerian lecture in 1871: it is a noble metal and has the most stable resistance–temperature relationship over the largest temperature range.
Nickel elements have a limited temperature range because the temperature coefficient of resistance changes at temperatures over 300 °C (572 °F).
Copper has a very linear resistance–temperature relationship; however, copper oxidizes at moderate temperatures and cannot be used over 150 °C (302 °F).[citation needed]
The significant characteristic of metals used as resistive elements is the linear approximation of the resistance versus temperature relationship between 0 and 100 °C. This temperature coefficient of resistance is denoted by α and is usually given in units of Ω/(Ω·°C):[citation needed]
where
Pure platinum has α = 0.003925 Ω/(Ω·°C) in the 0 to 100 °C range and is used in the construction of laboratory-grade RTDs. [citation needed] Conversely, two widely recognized standards for industrial RTDs IEC 60751 and ASTM E-1137 specify α = 0.00385 Ω/(Ω·°C). Before these standards were widely adopted, several different α values were used. It is still possible to find older probes that are made with platinum that have α = 0.003916 Ω/(Ω·°C) and 0.003902 Ω/(Ω·°C).[citation needed]
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Resistance thermometer AI simulator
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Resistance thermometer
Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors that use the electrical resistance of a substance (such as platinum) to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a heat-resistant ceramic or glass core but other constructions are also used. The RTD wire is typically platinum (Pt), nickel (Ni), or copper (Cu). The material has an accurate temperature–resistance relationship which is used to provide an indication of temperature. As RTD elements are fragile, they are often housed in protective probes called thermowells. RTDs have higher accuracy and repeatability than thermocouples, which is why they are slowly replacing them in industrial applications below 600 °C.
Common RTD sensing elements for biomedical application constructed of platinum (Pt), nickel (Ni), or copper (Cu) have a repeatable resistance versus temperature relationship (R vs T) and operating temperature range. The R vs T relationship is defined as the amount of resistance change of the sensor per degree of temperature change. The relative change in resistance (temperature coefficient of resistance) varies only slightly over the useful range of the sensor.[citation needed]
Platinum was proposed by Sir William Siemens as an element for a resistance temperature detector at the Bakerian lecture in 1871: it is a noble metal and has the most stable resistance–temperature relationship over the largest temperature range.
Nickel elements have a limited temperature range because the temperature coefficient of resistance changes at temperatures over 300 °C (572 °F).
Copper has a very linear resistance–temperature relationship; however, copper oxidizes at moderate temperatures and cannot be used over 150 °C (302 °F).[citation needed]
The significant characteristic of metals used as resistive elements is the linear approximation of the resistance versus temperature relationship between 0 and 100 °C. This temperature coefficient of resistance is denoted by α and is usually given in units of Ω/(Ω·°C):[citation needed]
where
Pure platinum has α = 0.003925 Ω/(Ω·°C) in the 0 to 100 °C range and is used in the construction of laboratory-grade RTDs. [citation needed] Conversely, two widely recognized standards for industrial RTDs IEC 60751 and ASTM E-1137 specify α = 0.00385 Ω/(Ω·°C). Before these standards were widely adopted, several different α values were used. It is still possible to find older probes that are made with platinum that have α = 0.003916 Ω/(Ω·°C) and 0.003902 Ω/(Ω·°C).[citation needed]