Industrial platinum resistance thermometer

Industrial platinum resistance thermometer sensors Effects of unbalanced voltages on the performance of 30 cage induction motors BS EN 60751/1996... 

H. Breunig, F. Lieneweg. Handbucb der technischen Temperaturmessung. Vieweg, 1976. lEC 60751 (1983-01). Industrial Platinum Resistance Thermometer Sensors. International Electrotechnical Commission, 1983. 

ASTM El 137-97. Standard Specification for Industrial Platinum Resistance Thermometers. American Society for Testing and Materials, 1997. 

Industrial platinum resistance thermometers (IPRTs), 24 447 cahbration of, 24 448—449 resistance-temperature characteristics of, 24 448... 

Thick-film techniques, industrial platinum resistance thermometer manufacture using, 24 447 Thick-film technology... 

Whereas it is no longer an interpolation standard of the scale, the thermoelectric principle is one of the most common ways to transduce temperature, although it is challenged in some disciplines by small industrial platinum resistance thermometers (PRTs) and thermistors. Thermocouple junctions can be made very small and in almost infinite variety, and for base metal thermocouples the component materials are very cheap. Properties of various types of working thermocouple are shown in Table 3 additional properties are given in Reference 5. 

BS 1904 1984. British Standard 1904 (British Standards Institution, London). Industrial platinum resistance thermometers sensors. 

Table 1 Temperature accuracy of industrial platinum resistance thermometers (IPRTs) according to the most common standard, which is known variously as EC, DIN, ASTM, 0.00385-type, and/or the European curve. Note that t is the temperature in degrees Celsius...

Resistance Temperature Detectors, Rgure 1 (a) The normaiized resistance of an industrial platinum resistance thermometer 0PRT or RTD) as... 

For the vast majority of applications, the extreme accuracy of SPRTs cannot justify their high cost, large size, and fragile construction. Instead, manufacturers offer a wide selection of industrial platinum resistance thermometers (IPRTs), which are smaller, far more robust, and only slightly less aceurate than SPRTs. They can be either wire-wound or made of thin films evaporated on a substrate, and are most commonly provided with 100 resistance at... 

Industrial platinum resistance thermometer. The requirements for reproducibility and limit of error for thermometers of this type are lower than those for standard thermometers so are the manufacturing precautions lowered for these thermometers. 

Accessories. Some forms of Wheatstone-bridge circuits are used for the measurement of temperature with base-metal or industrial platinum resistance thermometers, while the Mueller bridge is used with precision platinum resistance thermometers. 

An instrument for measuring temperatures, in the rubber industry the term is usually applied to an instrument for determining the surface temperature of mill and calender rolls, moulds, etc. The instrument is usually based on thermocouples or, where higher accuracy is required, platinum resistance thermometers. Infrared (IR) techniques are now used which have the advantage of non contact but require careful calibration for the emissivity of the surface. 

High purity platinum wire is used in resistance thermometers because the temperature coefficient of resistance of pure platinum is linear over a wide temperature range. The platinum resistance thermometer is the recognized instrument for the interpolation of the international practical temperature scale from—259.35 to 630.74°C. Whereas such precision measurements require very high purity platinum, for most routine industrial measurements lower purity metal can be tolerated. Conventional wire-wound devices are quite fragile and this disadvantage has led to the introduction of printed resistance thermometers, which are cheap to produce and much more durable. They can be used as an inexpensive replacement for thermocouple applications in intermediate temperature applications. 

For industrial purposes, resistance thermometers are made usually either of platinum or of nickel, the latter material being fairly satisfactory for temperatures below 300 C. In the form of platinum thermometer made by Leeds Northrup Co. about 40 cm. of fine wire is wound upon a mica frame into a spiral coil about 4 cm. in length and 0.7 cm. in diameter. The length of the wire is so adjusted that the resistance of the coil is about 8.3 ohms at 0°C. The frame is made of crossed strips of thin mica notched at the edges to hold the wire in place. From the ends of this coil lead wires of platinum or gold are carried to the terminal head of the thermometer. The lead wires are insulated and held apart by mica discs through which the wires are threaded. 

While most measurements of tempemture in industrial processing simply involve the use of thermocouples or platinum resistance thermometers, there are some applications involving microwave fields or chemical environments for which this might not be possible. In that case a fibre-optic sensor is the instrument of choice. These sensors are often also sensitive to stmin, so they may be used to obtain a measure of pressure and local deformation. The operating principle is discussed in the following section. 

OTHER COMMENTS Platinum metal is used in the manufacture of apparatus used in laboratories and industries, including thermocouples, acid-proof containers, chemical reaction vessels, platinum resistance thermometers, electrodes, etc. has found applications in dentistry, electroplating industry, and in the jewelry industry soluble platinum salts have been used as catalysts in the production of high octane gasoline, vinylesters, petrochemicals, and pharmaceuticals platinum metals, as well as soluble platinum salts, have been employed as oxidation catalysts in the manufacture of sulfuric acid, nitric acid from ammonia, and acetic acid soluble platinum salts have been used and reused in the reclamation of platinum ore. 

For temperatures above about 20 K, the metallic resistance thermometers are more sensitive than the nonmetallic resistance thermometers. Temperatures above 20 K can be measured routinely with an industrial-type platinum resistance thermometer with an accuracy of better than 100 mK with time responses somewhat better than 1 s. Accuracy at the millidegree level requires a precision capsule type platinum resistance thermometer and careful calibration. 

Nickel resistance thermometer. This thermometer has been adapted satisfactorily in industrial applications for a temperature range from -100 to 300°F. The nickel resistance thermometer is less stable than platinum thermometers, but its low cost favors its usage. 

Bead thermistors are formed by placing two wires, commonly of platinum, in dose proximity and paralld to each other and bridging them with a drop of slurry, which is then sintered into a hard bead and encapsulated in protective glass. Such thermistors are quite stable, approaching, over narrow temperature limits, the stability of industrial metallic thermometers. However, the resistance tolerance may vary from unit to unit by as much as 20%, and matching or interchangeability is usually achieved by selection. Beads can be made quite small, which may allow application in, eg, temperature probes mounted in intravenous needles. 

The thermometer is protected by a porcelain tube glazed on the outside, or by a quartz tube which fits into the terminal head. Por industrial use the refractory tube is itself protected by an outer metal tube. The metal tube is usually fitted to an extra terminal head through which the lead wires to the line are carried. On account of the deterioration of the platinum, thermometers constructed of fine wire are not very satisfactory for industrial use above 900°C. Heavy platinum wire, 0.6 mm. in diameter, may be employed up to 1,100°C. but the resistance of the thermometer is so low that it is necessary to use methods of measurement which do not depend upon constancy in the resistance of the lead wires, e.g. Thomson bridge or potentiometer. 

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