Thermometers different types

Multi-necked flasks. Various types of multi necked flasks are illustrated in Figs. II, 56, 13-15. The centre socket is usually the largest ( 24 or 34) and the side sockets are generally smaller. The side tube in Fig. II, 56,15, a may be employed for a capillary tube in vacuum distillation b, c and d are different types of thermometer wells . 

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. 

It is believed that Galileo invented the liquid-in-glass thermometer around 1592. Thomas Seebeck discovered the principle behind the TC—the existence of the thermoelectric current—in 1821. The same year Sir Humphry Davy noted the temperature dependence of metals, but C. H. Meyers did not build the RTD until 1932. Today, some 20 different types of temperature sensors are available, and Table 3.160 lists the temperature ranges and accuracies of a number of them. 

Because the temperature ranges and conditions of a system can vary, a variety of materials have been incorporated into different types of thermometers. The following is a list of common thermometer types and the property measured in each to obtain a heat measurement. 

It is possible to compensate on the calibration lines for these limitations to a certain degree. To make this compensation, three different types of liquid-in-glass thermometers have been designed with three different immersion requirements. They are ... 

There are many different types of thermometers available for use in the biomedical temperature range and they provide a wide choice of stability, sensitivity, and ease of use. 

Since temperature measurements are required over such a wide range and diversity of situations, a large number of different types of thermometers with varying levels of accuracy and convenience have been developed over the years. Those most frequently used are based on the expansion of a gas, liquid or solid on changes in electrical resistance on the thermoelectric effect on changes in the thermal radiation of a system on changes in the thermal (Johnson) noise of electrical resistors on changes... 

Beckmann thermometer A type of mercury thermometer designed to measure small differences in temperature rather than scale degrees. Beckmann thermometers have a larger bulb than common thermometers and a stem with a small internal diameter, so that a range of 5°C covers about 30 centimeters in the stem. The mercury bulb is connected to the stem in such a way that the bulk of the mercury can be separated from the stem once a particular 5° range has been attained. The thermometer can thus be set for any particular range. It is named for the German chemist Ernst Beckmann (1853-1923). 

Workplace conditions that influence cold stress are the severity of cold stress, which depends on the air temperature, wind speed, and intensity of physical activity. Air temperature is measured by an ordinary thermometer in degrees Fahrenheit or Celsius. Different types of commercially available anemometers are used to measure wind speed or air movement. These are calibrated in miles per hour (mph). The following is a suggested guide for estimating wind speed, if accurate information is not available ... 

Infrared radiation was first observed by William Herschel in 1800. Using a glass prism and thermometers, he found that there were two maxima, one occurring in the yellow-green portion of the sun s spectrum and the other beyond the red end of the visible spectrum. He mistakenly believed that these maxima were due to two different types of radiation. Between 1835 and 1845, it was postulated and generally accepted that these maxima were actually similar phenomena, differing only in the amount of refraction by the prism. 

The test apparatus consists of volumetric flasks, transfer pipers, a constant-temperature bath, a timer, a viscometer, and a thermometer. The constant-volume device is recommended for use in which the solution, reduced, or inherent viscosity are to be measured at a single concentration. The second device is called a dilution viscometer and it does not require constant liquid volume for operation. This type is basically used for measuring intrinsic viscosity. Different types of commercially available viscometers are shown in Figure 7-8. 

Thermometers. A high quality thermometer is only about 8. It is best to purchase two — one for high temps and the other for low temps. Make certain it is for measuring degrees in centigrade as this is what all formulas require, unless specified differently. Candy, meat and other types of thermometers will not fit your apparatus, are not accurate enough for most reactions and are unacceptable. 

Baths. Baths can dry many solid substances that do not decompose under heat. Some substances can take more heat than others so a thermometer must be used dong with the knowledge of how much heat can he safely used without destroying the product, or changing it into a different substance. The types of baths are many water, air, toluene, sand, oil, and graphite, but they all have the same general rules. Hot plates and heating mantles must follow these rules also. 

Different empirical temperature scales will naturally differ from each other except at the respective fixed thermometnc points, Even different scales of the same type (say different Centigrade scales) will differ at all temperatures, except the steam point and ice point, depending on the fortuitous properties of the system chosen as a thermometer. It is, therefore, necessary to remove these differences and to obtain a more universal scale. This has been achieved in two ways. The practical way of achieving uniformity is to lay down detailed rules concerning the thermometer (actually different thermometers depending on the range of temperatures to be measured). Such rules have been agreed on internationally and... 

Since the mercury in the thread, as well as that in the bulb, is susceptible to thermal expansion, it is important in precise work to take account of the temperature of the thermometer stem. Most thermometer calibrations, especially those for enclosed-stem types, are for total immersion—it is assumed that the thread is at the same temperature as the bulb. Other thermometers are meant to be used with partial inunersion, often to a ring engraved on the stem, and the remainder of the stem is assumed to be at room temperature (say, 25°C). For precise work, stem corrections should be made if the stem temperatures differ significantly from those assumed in the calibration. The correction that should be added to the thermometer reading is given by the equation... 

A differential manometer of the Rayleigh type ( 14.VII A) was used in accurate measurements of the vapour pressure of water, and a simple apparatus for measuring the difference in vapour pressures of two liquids was described by Lord Kelvin. Stock s vapour pressure thermometer ( 19.V1 Q can be used to measure the vapour pressures of liquids, including those at low temperatures. Special techniques are necessary for very small vapour pressures,... 

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... 

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