3
Accurate Sensors Technologies
2.2.1 Measurement of temperature is not affected by low or changing emissivity values
If the value of emissivity in both colours (wavelengths) are same as like for the black body (where emissivity =1.0)
or for grey body where emissivity is less than 1.0 but a constant number and the emissivity of the target would not
get influenced. But actually grey body does not exist in nature. The emissivity of all real objects changes with
temperature and wavelength at variable degrees, depending on the material. 2 colour pyrometer is more accurate
than single colour pyrometer when emissivity is uncertain or changing but emissivity should change by same factor
in both wavelength bands. Accuracy of result measurement is dependent on the type of material being measured
and the application for which it is used.
2.2.2 The measuring object is smaller than spot size
If the target object is moving or it is smaller than the spot size, the amount of radiated energy is also reduced. But
the ratio of energies is unaffected and hence the measured temperature remains accurate.
2.2.3 The spot is partially blocked or obscured
The energy emitted from a target is usually reduced when target object is being blocked or some portion of the
optical head is blocked. But the ratio of the energies is not affected and hence the measured temperature remains
extremely accurate.
2 colour pyrometer is better than 1 or single colour in the following conditions:-
lWhen path of sight is partially blocked.
lWhen any of the sensors is subjected to dirt and/ or moisture, smoke accumulating on the lens surface.
lWhen dirt, smoke & moisture is present in the atmosphere between the sensor and target.
The pyrometer temperature measurement method utilizes the fact that objects emit thermal radiation in an
amount that directly corresponds to their own temperature and surface emissivity. Two color pyrometer involves
measuring thermal radiance at two different wavelengths and inferring the temperature from the ratio of these
spectral radiances. Radiance ratio thermometers can be significantly more accurate than single band
thermometers in many applications and hence known to be work in smart mode.
The pyrometer sensor detects the amount of infrared radiation emitted by the measured object (target). The
infrared signal is analyzed and the temperature it represents is analyzed by built-in microprocessor.
üPreheating üMelting
üAnnealing üSintering
üTempering üSoldering
üWelding üRolling
üForging üBrazing
üHardening üNormalizing
üAST pyrometer üManual
üConnection cable 12-core (length - 5 m) üCertificate of calibration
üAST software CD üUSB Grabber Card
Standard Item supplied with AST A250+/A450+ FO PL
The applications in which AST pyrometers can be used are
