WHAT IS A ?
A is a special instrument used for the measurement of I a . It does not only record the of the but also control the , by governing the amount of fuel fed to the .
The various types of include:
- Thermo-electric known as the “Thermo-couple”: the thermos-couple is an electric that makes use of the principle that when two dissimilar are joined to form a complete circuit and the two junctions maintained at a different , an electric current flows in the circuit. The magnitude of the current depends upon the metals used and the difference of the junctions.
The hot junction which is placed I the is often made up of of platinum ad an alloy of platinum and rhodium welded together. Leads from these are carried to a sensitive galvanometer which constitutes the cold junction and the galvanometer is calibrated, that instead of indicating electric units, it reads in degrees of .
A ballast resistance is incorporated in the galvanometer to ensure that it has a large resistance compared with the circuit so that any changes and thus any changes of resistance of the compensating leads will be too small to affect the accuracy of the system. The range is usually between 00C and 14.500C. it is used to measure up to 1450oC.
2. Radiation : while the thermocouple must be exposed to the hot substance whose is to be measured. It is not suitable for continuous use at temperatures exceeding 15000 However, the heat or light emitted by the hot body may be used to measure its .
The radiation is usually arranged to collect the heat energy passing through the peep-hole of a . In other words, the instrument ‘views’ that part of the inside wall of the which is opposite the peep hole. The diagram above illustrates the principle of the variable-distance instrument. Heat from the hot body AB enters the tube and is focused by a concave mirror, on to a small sensitive . The of the will be much lower than that of the hot body but its will vary in accordance with variations in the hot body . The galvanometer attached to the is calibrated in terms of the of the hot body.
Temperatures up to 20000C may be measured in this way. In this method, a perfect black body is one which radiates the maximum amount of heat energy at a particular .
3. Optical : this measuring instrument compares the intensity of light being emitted from the with that from some standard source. There are two distinct types of optical ; the disappearing filament and the wanner Optical .
In the disappearing filament , the glow of a standard filament lamp is varied until it marches the light from the and disappears when viewed through the telescope.
The current flowing through the lamp is varied by a resistance, and when a color match is obtained i.e. “when the filament has the same brightness as the hot body”, the lamp filament disappears from sight. The lamp current required to cause this will be indicated on an ammeter. It maybe calibrated so that it reads in degrees of , instead of the electric current. The disappearing filament is suitable for temperatures between 8000C and 3000oC. it is used to measure high beyond the range of the or to of a surface upon which it would be inconvenience or impossible to place on instrument of this type i.e. like the .
IMPACT OF TO MODERN MEASUREMENT
The has made it possible to measure and other quantities based on the . Modern speedometers and other importance measuring devices are using the principle of the foran accurate reading. It made the reading of any level of number to be possible. meter helps the engineers to know the data of any object while standing from a far. Such is an idea for those working in the metallurgical .
Originally posted 2018-12-04 13:35:05.
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