Thermometers transfer standard

The defining standard thermometers are thermometers specified for ITS-90. They should be calibrated by NIST at regular time intervals, and are then used to calibrate transfer or working standard thermometers. Transfer standard thermometers serve as intermediate standards to reduce the use and drift of the defining standard thermometers. 

Transfer standard thermometer Working standard thermometer... 

A standard used in calibration that is the same type of thermometer as the thermometers to be calibrated. Calibration against a defining standard thermometer or a transfer standard thermometer is required at periodic intervals to ensure accuracy. 

Transfer or working-standard thermocouples (including connecting wires—see Fig. 16.17) are individually calibrated by comparison calibration against a defining standard thermometer (such as an SPRT) or another transfer standard thermometer (usually a thermocouple). 

The type-S thermocouple, though no longer used as a defining standard for ITS-90, is still a reasonably accurate transfer standard thermometer. The precision of a type-S thermocouple at temperatures between 600 to 1000°C is about 0.02°C, and its accuracy is about 0.2 to 0.3°C. At lower temperatures (between about 0 and 200°C), a base-metal-type thermocouple (e.g., type T) is capable of a precision of about 0.01°C and an accuracy of 0.1°C. 

Nuclear quadrupole resonance thermometers [83] can be used between 20 and 400 K. In the ultralow temperature range below 1 K, a direct measurement of temperature is feasible by using the spectrometer to measure the intensity ratio of magnetic resonance lines [84]. A precision and accuracy of 1 mK can be achieved. However, these thermometers are quite expensive and are therefore used most often as transfer standards... 

Solidification Point — shall not be less than 73.0° when deed in the same type of apparatus as shown in this Vol under Diphenylphthalate. Melt a 50g sample in a covered 250ml beaker by immersing its lower half in a water bath at 90 to 95° for 15 mins, and transfer the liquid to the tube C (See Fig on p D1473) filling it to within ca 1.5 inches of the top. Close the tube with stopper (a), provided with standard thermometer T, correction thermometer Tj and stirring rod R. Immerse the stoppered rube in a water bath at 85—90° for 5 mins, wipe it off and place inside tube B, which is, in turn, placed inside 1 liter jar A. Proceed now exactly as descrihed under Diphenylphthalate... 

The International Practical Temperature Scale of 1968 (IPTS-68) is currently the internationally accepted method of measuring temperature reproducibly. A standard platinum resistance thermometer is the transfer medium that is used over most of the range of practical thermometry. 

Although, as shown in this monograph, mechanical agitation is provided in a number of different ways, the most common method is by a stirrer in a standard vessel. In many mechanically agitated reactors, the vessel contains internals such as baffles (particularly for low-viscosity fluids), feed and drain pipes, heat transfer coils, and probes (e.g., thermometers or thermocouples, pressure transducers, level indicators). The degree of mixing and power requirement depend on the nature of the internals present in the vessel. 

A) Preparation of Naphthol Yellow S. Place 20 ml of concentrated sulfuric acid in an eight-inch test tube and heat to 100° in a water bath. Place a thermometer in the tube, and add 5 g of finely powdered commercial a-naphthol in about 1-2 minutes. Prepare a standard temperature bath for heating at about 120°, and transfer the tube into this bath. Heat for 3 hours. Remove the tube and allow to cool to room temperature, then pour with vigorous stirring into 30 ml of water. Place in a 250-ml beaker 5 ml of concentrated nitric acid and 1.5 ml of water. Cool in an ice bath, and add slowly the solution of the naphthol trisulfonic acid prepared above, keeping the temperature at 30-35°. After two minutes add slowly 4 ml of concentrated nitric acid, and stir. After five minutes remove the beaker from the ice bath, allow to stand for 15 minutes at room temperature, then warm to 50° for 10 minutes. Cool, and add 30 ml of saturated salt solution. Filter the nitro compound, and wash three times with saturated salt solution. Remove the cake to a 250-ml beaker and add 30 ml of water. Heat to 80°, and add solid sodium carbonate until the solution is neutral. Add 4 g of solid potassium chloride, and cool. Filter the precipitated dye, and dry on a filter disc or a porous plate. 

Preparation. A solut ion of hydrazoic acid in benzene or chloroform is prepared in a three-necked flask fitted with an efficient stirrer, a dropping funnel, a thermometer, and a gas-exit tube. A paste is prepared from 65 g. (1 mole) of sodium azide and 65 ml. of warm water, 400 ml. of benzene or chloroform is added, the mixture is cooled to 0°, and 0.5 mole of coned, sulfuric acid is added dropwise with control of the temperature to 0-5°. The organic layer Is separated and dried over sodium sulfate. The concentration of the solution of hydrazoic acid is determined by transferring a sample with pipette and pipetter (Fig. H-2) to a glass-stoppered bottle, shaking it with distilled water, and titrating with standard alkali. 

Well-designed low-pressure gas thermometers can be used to determine (really approximate) the thermodynamic temperature. However, from a practical standpoint, where precision and simplicity in the implementation and transfer are the major considerations, secondary thermometers were chosen as the defining standard thermometers for a practical temperature scale. This scale was defined by the use of fixed reference points whose thermodynamic temperatures were determined from gas thermometer measurements. The International Committee of Weights and Measures (Comite International des Poids et Mesures, CIPM) is responsible for developing and maintaining the scale. 

National standard laboratories, such as the National Institute of Standards and Technology (NIST) in the United States, implement and maintain the practical temperature scale for their respective countries. They also help in the transfer of the scale by calibrating the defining standard thermometers These defining standard thermometers are costly to maintain and are primarily used in temperature calibration laboratories in industry or universities They are directly or indirectly used for calibration of thermometers used in actual applications. 

FIGURE 16.8 PRT design typical used as transfer or working standard thermometer. (Courtesy ofRosemount, Inc)... 

Figure 5.6 Thermal conductivity apparatus and coaxial-cylinder cell, developed by Yata et al (1979a). (a) 1 high pressure vessel 2 fluid separator 3 heater 4 heat insulator 5 support table for bath 6 heat transfer fluid (water or glycerin) 7 screw propeller 8 standard resistance thermometer 9 thermocouples and heaters, (b) 1 inner cylinder 2 outer cylinder 3 upper guard cylinder 4 lower guard cylinder 5 inner heater 6 thermocouples 7 upper alumina insulator 8 lower alumina insulator 9 mica spacer 10 alumina piece 11 brass screw 12 alumina pin 13 brass screw 14 compensative heater 15 top closure of high pressure vessel.

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