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