Understanding Infrared Thermography Reading 3

Pyrometer
A pyrometer is a device that is used for the temperature measurement of an object.
The device actually tracks and measures the amount of heat that is radiated from an
object. The thermal heat radiates from the object to the optical system present inside
the pyrometer. The optical system makes the thermal radiation into a better focus and
passes it to the detector. The output of the detector will be related to the input thermal
radiation. The biggest advantage of this device is that, unlike a Resistance
Temperature Detector (RTD) and Thermocouple, there is no direct contact between
the pyrometer and the object whose temperature is to be found out.
Optical (brightness) Pyrometer
In an optical pyrometer, a brightness comparison is made to measure the temperature.
As a measure of the reference temperature, a color change with the growth in
temperature is taken. The device compares the brightness produced by the radiation
of the object whose temperature is to be measured, with that of a reference
temperature. The reference temperature is produced by a lamp whose brightness can
be adjusted till its intensity becomes equal to the brightness of the source object. For
an object, its light intensity always depends on the temperature of the object, whatever
may be its wavelength. After adjusting the temperature, the current passing through it
is measured using a multimeter, as its value will be proportional to the temperature of
the source when calibrated. The working of an optical pyrometer is shown in the figure
below.
Charlie Chong/ Fion Zhang
http://www.instrumentationtoday.com/optical-pyrometer/2011/08/