Thermometers platinum resistance

The international temperature scale is based upon the assignment of temperatures to a relatively small number of fixed points , conditions where three phases, or two phases at a specified pressure, are in equilibrium, and thus are required by the Gibbs phase rule to be at constant temperature. Different types of thermometers (for example, He vapor pressure thermometers, platinum resistance thermometers, platinum/rhodium thermocouples, blackbody radiators) and interpolation equations have been developed to reproduce temperatures between the fixed points and to generate temperature scales that are continuous through the intersections at the fixed points. 

The calorimetric thermometer measures temperature changes within the calorimeter bucket. It must be able to provide excellent resolution and repeatability. High single-point accuracy is not required since it is the change in temperature that is important in fuel calorimetry. Mercurial thermometers, platinum resistance thermometers, quartz oscillators, and thermistor systems have all been successfully used as calorimelric thermometers. 

Platinum Resistance Thermometer. Platinum resistance thermometers are based on the electrical resistance of Pt. This resistance for Pt wires wound on a mica support and enclosed in a glass or silica vessel can be manufactured to be either 25.5 Q at 0°C or 2.5 Q at 0°C. The electrical resistance, typically measured in a Wheatstone or Mueller bridge, increases by about 0.1 Q or 0.01 Q, respectively, per degree centigrade (0.4%/°C). Empirical equations convert Pt resistance and its small nonlinearities to temperature ... 

The temperature sensors depend upon range and sensitivity requirements. They could include gas-liquid thermometers, platinum resistance thermometers, thermocouples or thermistors. It is advised to have more than one device in the sample and on the copper adiabatic shield. Very good computer adiabatic controllers are easy to construct. One must take into account in programming, the power required for various temperatures to match the heat capacity of the shield, that is, one needs to adjust the power and damping that the power supply puts out according to calorimeter and sample. This may take some preliminary runs to adjust it correctly. 

The fixed points in the lTS-90 are given in Tabie 11.39. Platinum resistance thermometers are recommended for use between 14 K and 1235 K (the freezing point of silver), calibrated against the fixed points. Below 14 K either the vapor pressure of helium or a constant-volume gas thermometer is to be used. Above 1235 K radiometry is to be used in conjunction with the Planck radiation law,... 

The ITS-90 has its lowest point at 0.65 K and extends upward without specified limit. A number of values assigned to fixed points differ from those of the immediately previous scale, IPTS-68. In addition, the standard platinum resistance thermometer (SPRC) is specified as the interpolation standard from 13.8033 K to 961.78°C, and the interpolation standard above 961.78°C is a radiation thermometer based on Planck s radiation law. Between 0.65 and 13.8033 K interpolation of the scale rehes upon vapor pressure and constant-volume gas thermometry. The standard thermocouple, which in previous scales had a range between the upper end of the SPRT range and the lower end of the radiation thermometer range, has been deleted. 

Whereas it is no longer an iaterpolation standard of the scale, the thermoelectric principle is one of the most common ways to transduce temperature, although it is challenged ia some disciplines by small iadustrial platinum resistance thermometers (PRTs) and thermistors. Thermocouple junctions can be made very small and ia 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. 

Temperature The level of the temperature measurement (4 K, 20 K, 77 K, or higher) is the first issue to be considered. The second issue is the range needed (e.g., a few degrees around 90 K or 1 to 400 K). If the temperature level is that of air separation or liquefact-ing of natural gas (LNG), then the favorite choice is the platinum resistance thermometer (PRT). Platinum, as with all pure metals, has an electrical resistance that goes to zero as the absolute temperature decreases to zero. Accordingly, the lower useful limit of platinum is about 20 K, or liquid hydrogen temperatures. Below 20 K, semiconductor thermometers (germanium-, carbon-, or silicon-based) are preferred. Semiconductors have just the opposite resistance-temperature dependence of metals—their resistance increases as the temperature is lowered, as fewer valence electrons can be promoted into the conduction band at lower temperatures. Thus, semiconductors are usually chosen for temperatures from about 1 to 20 K. 

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

Fig. 21. Determination of the Mettler softening point. 1, heating element 2, platinum resistance thermometer 3, sample 4, light source 5, furnace 6, sample cup 7, photo cell 8, collector sleeve (see p. 48 in [25]).

Between the fixed points, temperatures on the ITS-90 are obtained by interpolation using standard instruments and assigned formulae. These standard instruments are the helium gas thermometer (3 K to 24.5 K), the platinum resistance thermometer (13.8 K to 1235 K), and the optical thermometer (above 1235 K). 

The so-called standard instrument is used for interpolation between the fixed points and for the calibration of other thermometers lower in the metrological hierarchy. The standard instrument in the moderate temperature range is a special platinum resistance probe, as it has to fulfill set requirements. It is important in all calibration that traceability to a primary normal, here the fixed-point ITS-90 scale, exists. 

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. 

Electrical resistance thermometers, the most widely used of which is Callendar s platinum resistance thermometer. This is probably the most convenient and accurate apparatus for measuring temperatures between the boiling-point of liquid air (—190° C.) and the melting-point of platinum (1,500° C.). Lead has recently been applied at very low temperatures. 

With the same apparatus as in example (1), the absolute temperature of the gas in its initial state was Ti. The tap was then opened so that the gas rapidly expanded to atmospheric pressure, and the temperature, determined immediately after expansion by a platinum resistance thermometer, or a thermo-element, in the centre of the vessel, was T2. Show that ... 

These fixed points are used to calibrate a different kind of thermometer that is easier to use than a gas thermometer. Over the temperature range from 13.8033 to 1234.93 °A (or K), which is the temperature interval most commonly encountered, the thermometer used for ITS-90 is a platinum resistance thermometer. In this thermometer, the resistance of a specially wound coil of platinum wire is measured and related to temperature. More specifically, temperatures are expressed in terms of W(T9o), the ratio of the resistance R(Ttriple point of water R (273.16 K), as given in equation (1.11)... 

The deviation function AW Too) is obtained as a function of r90 for various temperature intervals by calibration of the platinum resistance thermometer, using specified fixed points from Table A2.1. The form of the AW(Too) function is dependent on the temperature range in which the thermometer is being calibrated. For example, in the temperature subrange from 234.3156 to 302.9146 K, the form of the deviation function is... 

In summary, to obtain 7% from a platinum resistance thermometer, one selects the range of interest, calibrates the thermometer at the fixed points specified for those ranges, and uses the appropriate function to calculate AW(Tw) to be used in equation (A2.5). Companies are available that perform these calibrations and provide tables of W T<)0) versus 790 that can be interpolated to give 7% for a measured W T90). 

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. 

During the reaction of the hot catalyst surface with a flammable gas the temperature of the device increases. The Platinum coil itself serves at the same time as a resistance thermometer. The resistance increase of the coil then is a direct measure for the amount of combusted gas. Usually the amount of heat that develops during combustion is small and amounts to 800 kj/mol for methane, for example [8], Therefore the sensor is connected in a bridge circuit to a second resistor which shows the same setup as the pellistor but is catalytically inactive. The bridge voltage is then controlled by the temperature difference of the two sensors (see Fig. 5.34). 

Between the triple point of equilibrium hydrogen (13.8033 K) and the freezing point of silver (1234.93 K), Tgo is defined by means of platinum resistance thermometers calibrated at specific sets of defining fixed points. The temperatures are given in terms of the ratio of the resistance of the thermometer at temperature Tgo to the resistance at the triple point of water ... 

A second, popular, standard is the platinum-resistance thermometer. Here, the electrical resistance R of a long wire of platinum increases with increased temperature, again with an essentially linear relationship. 

SAQ 1.1 A temperature is measured with the same platinum-resistance thermometer used in Worked Example 1.1, and a resistance R = 11.4 x 10 4 2 determined. What is the temperature ... 

Caprylic/capric triglyceride, cosmetically useful lipid, 7 833t Capsanthin, 24 560 Capsicum group, 23 164-165 Capsorubin, 24 560 Capsular polysaccharides, 20 455 Capsules. See also Microencapsulation extruding, 16 446 pharmaceutical, 18 708 produced by spray drying, 16 447-448 Capsule standard platinum resistance thermometers, 24 445 Captafol, 23 629, 647 Captan, 23 628 Captiva camera, 19 307 Captive hydrogen, 13 841 Captopril, 5 148... 

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

---