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How does an Infared Thermometer work?

W

whit3rd

Jan 1, 1970
0
How does an Infared Thermometer work?

There's an optical system that couples a small thermistor to incoming
light. Then, there's a low-noise sense amplifier that amplifies t he
resistance deviation, and an anticipation circuit or algorithm that
compensates for the sluggish response of the thermistor's temperature
to its heat source. And there's a calibration curve.

Basically, it's like warming your hands at the fire. The hotter the
fire, the warmer your hands get. Put a pinhole in front of the
fire to keep the fire's size from affecting the result...
 
G

Grant

Jan 1, 1970
0
There's an optical system that couples a small thermistor to incoming
light. Then, there's a low-noise sense amplifier that amplifies t he
resistance deviation, and an anticipation circuit or algorithm that
compensates for the sluggish response of the thermistor's temperature
to its heat source. And there's a calibration curve.
Bolometer?

Basically, it's like warming your hands at the fire. The hotter the
fire, the warmer your hands get. Put a pinhole in front of the
fire to keep the fire's size from affecting the result...

High temperature pyrometers use a thermocouple stack (well, they did back
in late '70s when I worked with them). A water cooled jacket establishes
the cold end of the thermocouple and cools the lens. Low temperature ones
can work on same principle, but use exotic lens material like arsenic
trisulfide or germanium to pass the longer infrared wavelengths.

Motor driven optical choppers were used back then too, for trans-ambient
measurement.

PIRs work by utilising a segmented lens to create the chopper effect
to contrast the moving body from the background temperature.

Grant.
 
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