In the clinical temperature range the thermistor undergoes greater resistance change than the platinum resistance thermometer and, as with the latter, it is often used in a Wheatstone bridge circuit. Immersion depth is also an issue. Mostly, platinum is used in resistance thermometer. Platinum is the most reliable metal due to its linear resistance to temperature relationship over a large temperature range. Standard sensors are are available from many manufacturers with various accuracy specifications and numerous packaging options to suit most applications. Be careful in the selection of a PRT to ensure that the type selected is appropriate for use as a calibration reference over the range of interest and with the required accuracy. For the lowest temperatures (below –100°C) use an LN2 comparison device and for the highest temperatures (above 500°C) use a calibration furnace. Standard Platinum Resistance Thermometers (SPRTs) are used to interpolate temperature in the range from -189.3442°C to 660.323°C on the International Temperature Scale of 1990 (ITS-90). A platinum resistance thermometer (PRT) is a thermometer constructed from a high purity platinum element (wire-wound coil or thin film) placed in a tube of metal or glass and sealed with an inert atmosphere and/or mineral insulator. δ = constant δ lies between 1.488 to 1.498. If the readout is not designed for temperature calibration and/or a switching system is not available, then two or more readouts will probably be required. The different resistance values and different sheath materials are intended for different temperature ranges. Over the range of –200 to 660°C, a 25W SPRT will vary in resistance from approximately 4.6W to 84.4W, a 100W PRT from approximately 18W to 338W. 2 Polish National Temperature Standard for Low-Temperature Range ITS-90 in the low-temperature range (where capsule thermometer CSPRT is used) is defined by the resistance platinum thermometers calibrated at the following fixed points: triple point of hydrogen … Platinum resistance thermometers (PRTs) offer excellent accuracy over a wide temperature range (from -200 to +850 °C). That is, there are minimum requirements for the purity of the platinum wire and the type of construction used. Standard platinum resistance thermometers (PRTs) are very high accuracy instruments which are sensitive to electrical noise and their thermal treatment is crucial. RTD - or Resistance Temperature Detectors - is a temperature sensor that contain a resistor that changes resistance value as its temperature changes. They should be reserved for high accuracy applications only. Additionally, some DMMs use unconventional values of source current such as decades of 2 or 3 rather than 1 (2 mA or 3 mA, not 1 mA). This results in less confusion as to the suitability of the instrument for a particular application and almost guaranteed good performance if calibrated and used correctly. Extensive Range of Platinum Resistance Thermometer (RTD's) A platinum RTD (Resistance Temperature Detector) with a resistance of 100 ohms at 0°C which changes with temperature. The thermistor has the added advantage that the metal oxide bead can be made very small and that it can be manufactured more cheaply than the platinum resistance thermometer. The resistance of the metal is directly proportional to the temperature. Even an excellent instrument may not perform adequately in a specific application if it is not matched to that application. The probe must be immersed sufficiently without subjecting the transition junction (where the leads join the probe) to extreme temperatures. ITS-90 is designed to represent the thermodynamic (absolute) temperature scale (referencing absolute zero) as closely as possible throughout its range.Many different thermometer designs are required to cover the entire range. Many modern thermometer readouts are designed to cover this span on a single range. Additionally, if the reference probe is a glass sheath SPRT, then some form of protection should be used at higher temperatures to prevent devitrification of the glass sheath and contamination of the platinum sensor. Therefore, we must understand the requirements to an extent that allows us to adapt our process, if necessary, to accommodate a new or unusual configuration. No single instrument will be suitable for use over the entire range shown above. Platinum is usually used due to its stability with temperature. I. The relative change in resistance (temperature coefficient of resistance) varies only slightly over the useful range of the sensor. The two most important considerations are uniformity and stability. Platinum Resistance Thermometer Thermocouple Thermistor Sensor Platinum-wire wound or flat- film resistor Thermoelement, two dissimilar metals/alloys Ceramic (metal oxides) Accuracy (typical values) 0.1 to 1.0°C 0.5 to 5.0°C 0.1 to 1.5°C Long term Stability Excellent Variable, Prone to ageing Good Temperature range-200 to 650°C -200 to1750°C -100 to 300°C ), then certainly it can be used for both. (b) Calculate the boiling point of brine (t) from the formula from: t/100 = Lt/L100 = Rt/R100. Ensure that the readout has a resistance range appropriate for the reference probe and UUTs for which it is intended. Calibration is performed by measurement of the resistance of the unit under test (UUT) while it is exposed to a temperature. Support requests for items purchased from, or serviced directly by Fluke and general Metrology questions can be submitted via our online Support Request form and a Fluke representative will be in contact with you. In a Pt100 RTD, the ’Pt’ stands for platinum (platinum wire or film) and ’100’ means that the temperature sensor has a resistance of 100 Ohms at 0°C. We must solve these problems satisfactorily to provide a proper calibration. Advantages: Measures high temperatures. The 5626/5628 probes provide a calibrated accuracy of ± 0.006 °C at 0 °C with a range of –200 to 661 °C and include an accredited calibration. It is used both for precision measurements of the highest accuracy and for routine industrial work. (a) Plot a graph of resistance against temperature and thence determine the temperature coefficient of resistance for platinum. 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