Thermometer thermocouple

In addition to the mercuiy-in-glass thermometer, other temperature-sensing elements may be used for psychrometers. These include resistance thermometers, thermocouples, bimetal thermometers, and thermistors. 

Reliable micro-scale measurement and control of the temperature are required in developing thermal micro-devices. Available measurement techniques can be largely classified into contact and non-contact groups. While the resistance thermometer, thermocouples, thermodiodes, and thermotransistors measure temperature at specific points in contact with them, infrared thermography, thermochromic liquid crystals (TLC), and temperature-sensitive fluorescent dyes cover the whole temperature field (Yoo 2006). 

A particularly difficult problem in microwave processing is the correct measurement of the reaction temperature during the irradiation phase. Classical temperature sensors (thermometers, thermocouples) will fail since they will couple with the electromagnetic field. Temperature measurement can be achieved either by means of an immersed temperature probe (fiber-optic or gas-balloon thermometer) or on the outer surface of the reaction vessels by means of a remote IR sensor. Due to the volumetric character of microwave heating, the surface temperature of the reaction vessel will not always reflect the actual temperature inside the vessel [7]. 

Thermal transmission methods are relatively new techniques for adhesive inspection. Heat flow is determined by monitoring the surface temperature of a test piece a short time immediately after external heating or cooling has been applied. Subsurface anomalies alter the heat flow pattern and, thereby, affect the surface temperature. The surface temperature difference can be detected by thermometers, thermocouples, or heat-sensitive coatings. Liquid crystals applied to the joint can make voids visible if the substrate is heated. 

Thermostat bath with a heater, adjustable thermoregulator, and stirrer thermometer with a resolution of at least 0.01 K (a platinum resistance thermometer, thermocouple or quartz thermometer could be used see Chapter XVII) illuminating light and cathetometer for reading the vertical position of the menisci number of sealed capillaries of uniform bore containing varying amounts of carbon dioxide, prepared in advance. 

In this section, the design and operation of familiar liquid thermometers, thermocouples, platinum resistance thermometers, thermistors, and optical pyrometers are discussed in detail. Briefer descriptions are also given of a variety of special thermometric devices such as quartz thermometers, germanium resistance thermometers, and sihcon-diode thermometers. 

Dry-bulb temperature, T—the abscissa of the chart. This is the air temperature as measured by a thermometer, thermocouple, or other conventional temperature-measuring instrument. 

Differential scanning calorimetry (DSC) is a calorimetric method that finds widespread use in many fields, including protein dynamics, polymers, pharmaceuticals, and inorganic materials. DSC measures energy (heat) flow into a sample and a reference substance as a function of controlled increase or decrease of temperature. In a typical power-compensated DSC (Fig. 3.2), the sample and reference are placed on metal pans in identical furnaces each containing a platinum resistance thermometer (thermocouple) and heater. During a thermal transition (e.g., when a physical change in the sample occurs),... 

Because of the ease with which electric signals can be transmitted and manipulated it is not surprising to find that electrical thermometers are the most widely used thermometers in control systems. Both the thermoelectric type thermometer (thermocouple) and the resistance thermometer can be made small, and hence quite high response speeds are realizable. Even sheathed couples can be obtained which have time constants as low as three seconds. In these instruments the hot junction of the couple is welded directly to the sheath. 

Photothermal detection has been accomplished in several ways mechanical or electrical thermometer (thermocouple), molecular thermometer, optical interferometry, photoacoustic (PA), thermal lens (TL), or the transient grating (TG) method. Although PA and TL detections are not included in this chapter, some of the experimental results of these methods are referred to in other sections, mostly for comparison purposes with the TG measurement. Characteristic features of these methods are presented in Section 1I.E. 

In principle, any device that has one or more physical properties uniquely related to temperature in a reproducible way can be used as a thermometer. Such a device is usually classified as either a primary or secondary thermometer. If the relation between the temperature and the measured physical quantity is described by an exact physical law, the thermometer is referred to as a primary thermometer otherwise, it is called a secondary thermometer. Examples of primary thermometers include special low-pressure gas thermometers that behave according to the ideal gas law and some radiation-sensitive thermometers that are based upon the Planck radiation law. Resistance thermometers, thermocouples, and liquid-in-glass thermometers all belong to the category of secondary thermometers. Ideally, a primary thermometer is capable of measuring the thermodynamic temperature directly, whereas a secondary thermometer requires a calibration prior to use. Furthermore, even with an exact calibration at fixed points, temperatures measured by a secondary thermometer still do not quite match the thermodynamic temperature these readings are calculated from interpolation formulae, so there are differences between these readings and the true thermodynamic temperatures. Of course, the better the thermometer and its calibration, the smaller the deviation would be. 

Radiation thermometers can be sensitive to radiation in all wavelengths (total-radiation thermometers) or only to radiation in a band of wavelengths (spectral-radiation thermometers). Thermocouple and thermopile junctions or a calorimeter are the usual detectors in a total-radiation thermometer. For spectral systems, the classification is normally based on the effective wavelength or wavelength band used—as determined, for example, by a filter, which allows only near-monochromatic radiation to reach the detector, or by the use of a detector sensitive only to radiation in a specific wavelength band. Radiation thermometers utilize the visible portion of the radiation spectrum, infrared thermometers or scanners measure infrared radiation, and spectroscopic thermometers operate with radiation that is normally of shorter wavelength than the other two methods. 

In batch distillation the column temperature increases during the course of the operation, frequently by sudden increments the adjustment of the jacket temperatures by hand is consequently a matter of some difficulty. As the result of temperature lag, differences up to 30 deg. C between the jacket and column may occur, but these differences may be reduced considerably by automatic control. For this purpose air thermometers, thermocouples or resistance thermometers can be employed as sensing devices. Thermocouples are placed at the top and bottom of the column these together act on-the coil of a galvanometer, the position of which is sensed at short intervals by an electric switching device. The latter opens or closes the circuit... 

The temperature distribution within the cryostat was measured with six 20-gauge copper-constantan thermocouples located throughout the cryostat, these thermocouples being referenced to the resistance thermometer. Thermocouple emf s were measured with an L N Type K-3 potentiometer in conjunction with a Model 9834 electronic dc null detector. Inasmuch as these differential thermocouples generate small emf s, their accuracy is limited by the potentiometer, this accuracy being 0.02°C in this investigation. During operation the temperature distribution in the bath liquid was within 0.1°C of the resistance thermometer. 

Main experimental apparatus include safety helmet, safety cover, dry bulb thermometer, wet bulb thermometer, thermocouple thermometer, stopwatch, gas chromatograph and so on. 

It is essential that any thermometers, thermocouples, thermistors, etc. used in the thermostat bath and equilibrium cell are accurately calibrated with reference to a standard thermometer. This point cannot be emphasized too strongly. 

Probe Thermometers. Volume expansion thermometers use the expansion of liquids with rising temperature through a narrow tube. The expansion coefficient, defined as the increase in volume per unit volume per unit rise in temperature, is 0.00018 per Kelvin for mercury and 0.00109 per Kelvin for ethyl alcohol colored with dye. Calculating temperature from the actual random thermal motion velocity of every molecule, or the energy contained in a vibrational excitation of every molecule, is impractical. So temperature is measured indirectly in most applications. Different metals expand to different extents when their temperature rises. This difference is used to measure the bending of two strips of metal attached to one another in outdoor thermometers. Thermocouples use the Seebeck or thermoelectric effect discovered by Cerman physicist Thomas Johann Seebeck, in which a voltage difference is produced between two junctions between wires of... 

Devices for measuring temperature include the common mercury in glass thermometer, thermocouples, electrical resistance and optical techniques. 

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. 

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