WHAT IS THE HISTORY OF INFRARED TEMPERATURE MEASUREMENT?
The Royal Astronomer Sir William Herschel discovered "Dark Heat" radiation in 1800. In 1880 the term "infrared" was coined. Samuel Langley invented the bolometer that measures variations of resistance when heated.
In 1901 a bolometer could detect a cow at 400 meters. After World War II, many countries invested huge amounts of money in IR for military applications. Low-cost non contact infrared thermometers are achieved by using a proprietary ASIC or a System on Chip (SoC) technology incorporating MEMS-based advanced thermal sensors. This advanced low-power design also results in the longest battery life of a non contact infrared IR thermometer.
WHAT IS INFRARED?
Infrared just like any light ray, is an Electromagnetic Radiation, with lower frequency (or longer wavelength)
Anything material above absolute zero (-273.15 degrees Celsius or 0 Kelvin), radiates in the infrared. Even ice emits infrared radiation.
WHY CAN'T I SEE INFRARED?
Human eyes are design for visible light, but two species are known to detect infrared: some rattle snakes and beetles. Even though infrared is not visible to the human eye, your skin can sense infrared. When beside a campfire, you can feel the warmth of heat radiated from the fire.
WHAT KIND OF THEORY & TECHNOLOGY IS INVOLVED IN A Non contact Infrared THERMOMETER?
Quantum physics is the key theory: the total radiation energy is proportional to the fourth power of the absolute temperature (Stefan-Boltzmann Law). Wien Displacement Law: the product of the peak wavelength and the temperature is found to be a constant. Wien was awarded the Nobel Prize for Physics for the year 1911.
non contact INFRARED thermometers - HOW they WORK
The sensor in a non contact infrared thermometer (IRT) collects a small amount of energy (usually 0.0001 watt) radiated from the target, generates an electrical signal that is amplified by a precision amplifier and converted into voltage output. A processor digitizes the signal by a 16bit Analog-to-Digital Converter, an Arithmetic Unit solves a temperature equation based on Planck’s Radiation Law, compensates for the ambient temperature and emissivity resulting in a temperature reading within a fraction of a second after you push the “trigger” on the non infrared thermometer.
CAN a non infrared THERMOMETER MEASURE AIR TEMPERATURE?
Yes, and no. No, because air (i.e., Oxygen and Nitrogen molecules) do not absorb or emit infrared radiation. However, you can aim an infrared thermometer at anything having the SAME temperature as the air such as a leaf or grass (under sunshade) or indoors such as your desk, a piece of paper having the same temperature as the air. The key to measuring "air temperature" is to measure "anything that should have the same temperature as the air".
CAN I MEASURE THE BODY TEMPERATURE OF AN ANT with a non contact INFRARED thermometer?
You can aim the non contact infrared thermometer at a small object such as an ant, but what you measure is an average temperature of the ant & the adjacent surface because the Field-Of-View of the non contact infrared thermometer is much larger than the ant. But, if a large collection of ants occupies the whole FOV of the infrared thermometer, then one can measure their average body temperature. This FOV is the main consideration to obtaining the correct temperature reading from an infrared thermometer.
HOW FAR AWAY CAN I MEASURE with a non contact infrared thermometer?
Can one measure the temperature of a wall from a 5-meter distance or the temperature of a mountain from 1km? Yes, as long as the FOV is filled by the target. Also, many IRTs measure in the 8um to 15um wavelength band where the atmosphere is almost totally transparent.
Can the infrared thermometer operate in complete darkness? Yes, that's why DOD & military are interested in IR. In fact, early IR technology was developed for military applications.
CAN a non contact infrared thermometer PENETRATE A BUILDING, MEASURE WHAT'S INSIDE?
No, because an infrared thermometer only measures surface temperature.
BUT I REMEMBER IR CAN PENETRATE SOMETHING?
In the 8um to 15um wavelength band IR can penetrate PE film (for example: a plastic trash bag). You can hide something warm behind a PE film (such as your hand) and the non-contact infrared thermometer can detect the presence of the object.
CAN I MEASURE THE BODY TEMPERATURE OF A FISH IN MY AQUARIUM?
No, water & glass are transparent for visible light, but for IR, it's almost completely "opaque". One can only measure the temperature of the glass. How about my pet's temperature? by pointing a non contact infrared thermometer at your dog, you measure the surface temperature of the fur. What you see is what you get.