Platinum thermometer

The power compensation DSC instrument was first described by Watson et al.3) and by O Neill4) and it was developed into a commercial instrument by the Perkin-Elmer Corporation. It utilises separate sample and reference holders of low thermal mass, with individual heaters and platinum thermometers, as shown schematically in Fig. 1. In addidion to controlling the average temperature the instrument employs a... 

X-ray diffractometry was performed, by methods described in a companion paper (8), between 80 and 600 K at ambient pressure on thin solid wafers cut from the prepared samples. Mounted with high temperature cement on relatively massive metal backing plates, these wafers could be maintained at temperatures constant to within 3 K, as measured by either a platinum thermometer or a copper-constantan thermocouple. The... 

Very rapid and efficient stirring of the water in the calorimeter was necessary and a correction for the heat produced by this (in some cases 10 per cent of the whole energy supplied) was necessary. Temperatures were read on a mercury thermometer compared with a standard mercury thermometer and a platinum thermometer. Griffiths, who took the e.m.f. of the Clark cell as 1 4342 volt, found, in 15° g.cal. and nitrogen thermometer temperatures, 4=572 60 at 40 15° and 578 70 at 30 00°, and by combining his results with those of Dieterici at 0° and of Regnault between 63° and 100° he concluded that ... 

Figure 3 shows the test section and instrumentation. Ten wall temperatures on the tube external surface were measured with 0.5 mm diameter calibrated type E thermocouples electrically insulated from the aluminium. Fluid inlet and outlet temperatures were measured with 1 mm diameter calibrated type K thermocouples. Cah-bration was carried out with a Rosemount 162-CE platinum thermometer. Due to the high thermal conduchvity of the aluminium and the low thickness of the tube walls the measured temperature is very close to the wall temperature in contact with the fluid (the difference less than 0.01 K). The inlet fluid pressure was measured with a calibrated Rosemount type 11 absolute pressure sensor. Two calibrated differential pressure sensors measured the pressure loss through the test section. A Rosemount Micro-motion coriolis flowmeter was used to... 

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. 

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. 

An amended version of the IPTS-68 was adopted in 1975 (Comptes Rendus, 1975). Any measured temperature, T a, was unchanged by that amended version. It differed from the 1968 version only in that an alternative fixed point was introduced (the argon triple point as an alternative to the oxygen boiling point) (see Table I), the specified natural isotopic composition of neon was changed slightly, the reference function for the standard platinum thermometer was given in an improved form,... 

Prepared from magnesium or magnesium oxide and o-cyanobenzamide (40), magnesium phthalocyanine has been the subject of much study since it is a synthetic analog of chlorophyll. Perhaps understandably, much of this work has been connected with photosynthesis, luminescence, fluorescence, etc. (see Section V,B). The molecular weight of magnesium phthalocyanine has been measured ebullioscopically in naphthalene (228). Because of the very low solubility of the substance, a very accurate platinum thermometer was employed. Nevertheless the successful measurement represents quite an achievement. 

The resistance of the platinum thermometer was measured by means of a Mueller bridge. The electrical input energy was determined from the measurements of the current and potential across a 100 Q Constantan wire heater and the time interval of heating. The heater current and potential were measured by means of a Wenner potentiometer in conjunction with a resistor and a volt box. The time interval of heating was measured by means of a precise interval timer. 

Trapeznikova et al. studied the heat capacity of NiCl2 at temperatures between 13 and 130 K. They used a glass calorimeter and a platinum thermometer heater. The discrepancy between their results and those of Busey and Giauque probably indicates that their glass calorimeter and their thermometer did not attain thermal equilibrium [52BUS/GIA]. 

A resistance thermometer is included in a circuit that measures the electric resistance. Platinum resistance thermometers are widely used because of their stability and high sensitivity (0.0001 K). Thermistors use metal oxides and can be made very small they have greater sensitivity than platinum thermometers hut are not as stable over time. 

In resistance thermometers (or RTDs) one uses the dependency of electrical resistance on the temperature [2). The resistance of metals almost always rises with temperature. In practice one uses platinum thermometers. A light platinum wire on a ceramic support is covered with a protective layer of glass, enamel, or magnesium oxide. This measurement resistance is the end of one someasurement element, which ends in connecting terminals. The whole assembly is in a sleeve, which is solidly connected to the measuring point in the apparatus with flanges or screws (Figure 12.2). 

For estample, platinum has a temperature coeffident of resistance a = 0.00385 ii/ (Q°C) in the range 0 to 100°C. The measuring range of commercial-purity platinum thermometers is situated between about 200 and 850° C and the accuracy of these thermometers is +0.15% of span over the full range [4]. Resistance versus temperature can usually be described by just a quadratic function, which can be linearized in measurement amplifiers. If large temperature ranges are not present, the linearization can often be omitted. The resistance is usually measured in a bridge drcuit [2]. 

Mathematically this situation is expressed by Eqs. (l)-(3). The heat flow into the reference calorimeter, dQj /dt, is equal to the thermal conductivity, K, multiplied by the difference between the measured reference temperature at the platinum thermometer, and the true temperature, Tr. A typical... 

For the international practical temperature scale the platinum thermometers serve as standard (interpolation) instruments with characteristics values such the reduced resistance, the temperature coefficient of the resistance and the platinum temperature. Interpolation polynomials of the third to fifth degrees, using as the principal reference points 0, 100 and 419.58 °C (fusion of Zn) are used most frequently (as a standard accessory of commercial products). Another form of resistance thermometers are films or otherwise deposited layers (0.01 to 0.1 pm thick). They can be suitably covered to protect against corrosive media and platinum deposited on ceramics can withstand temperatures up to 1850 K. Non-metals and semiconductor elements can be found useful at low temperatures. 

As indicated above, silicon sensors have become the standard in diode thermometry and an extensive amount of data exists for them. Typical long-term stability is on the order of 50 mK, while short-term stability can be as low as a few millikelvin. This stability makes the diode competitive with industrial grade platinum thermometers with the added benefit of being usable to as low as 1 K. The upper temperature limit for commercially available diode sensors is around 400 K. This limit is determined by the properties of silicon, the metallurgy of the contact areas, and also by the construction materials and techniques used in device packaging. 

For the differential configuration, the two junctions were separated vertically by a distance of 100 mm, so that temperatures in the region of the surface could be measured relative to that of the bulk liquid. For the absolute configuration, the reference junction was the ice-point while a single calibration point was made against a Platinum thermometer in rapidly boiling LIN. The pool depth was kept between 200 and 250 mm. 

Platinum thermometer. This thermometer is known for its high accuracy, stability, resistance to corrosion, and other characteristics. It has a simple relation between resistivity and temperature, shown in Eq. (M-1). 

Precision platinum thermometer. This thermometer is used to define the International Practical Temperatme Scale fi om —297.3 to 1168.3°F. The purity and physical properties of the platinum of which the thermometer is made are prescribed to meet dose specifications. Different procedures are used for making precision thermometers to cover different temperature ranges. 

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. 

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