General Thermography Frequently Asked Questions page 2

page 1 | page 2 | page 3 | FAQs Index

What is a Qualitative Infrared Camera?
What is a Quantitative Camera?
What is Temperature?
What is Absolute Zero?
What is Heat?
What are the Laws of Thermodynamics?
What is Conduction?
What is Convection?
What is Emissivity?
What are Palettes?

What is a Qualitative Infrared Camera?

• Qualitative cameras do not measure temperature. They simply display temperature differences in a few different palettes including black and white. These infrared cameras or thermal imagers are generally used by law enforcement, home inspectors, or coast guard for a number of purposes.
• The police use infrared cameras to identify criminal activity at night just like we’ve seen on COPS.
  Home and building inspectors use these systems to look for moisture intrusion or energy loss in building envelopes.
• And the coast guard or any other water bound vessel may use infrared for search and rescue or to see through certain weather conditions such as fog or rain.
• Firefighters also use qualitative cameras to see through smoke and locate survivors in burning buildings.
  

What is a Quantitative Camera?

• Quantitative cameras can measure temperature. These cameras are technically known as imaging radiometers.
• Their purpose is to measure the radiant energy coming from a target to identify problem areas in electrical equipment, machinery, rotating equipment, kilns, boilers, and just about any kind of process that you can think of.
• We also use quantitative cameras to monitor different types of processes or process equipment, and even the human body.

What is Temperature?

• Temperature is a measurement of the average kinetic energy of the vibrating molecules that the temperature measurement device is relating to.
• Temperature specifies the state of a body with respect to its ability to impart energy to other bodies.
  

What is Absolute Zero?

Theoretical temperature when molecules lose all vibrational kinetic energy. All objects above absolute zero ( -273° C or - 459° F) emit infrared energy.

What is Heat?

Heat is energy in transit from areas of higher molecular motion (higher temperature) to areas of lower molecular motion (lower temperature) independent of direction. When all of the molecules have the same kinetic energy we have a state called thermal equilibrium. There is no heat transfer in this state.

What are the Laws of Thermodynamics?

• 1st Law
– Energy must be conserved or exactly accounted for (it can be changed from one form to another form)
– Heat that flows to an object must go somewhere, it cannot be created or destroyed
– Energyin = Energyout + Energystored
• 2nd Law
– Heat always flows from a point of higher temperature to a point at lower temperature

What is Conduction?

Conduction is a point-by-point process of heat transfer. If one part of a body is heated by direct contact with a source of heat, the neighboring parts become heated successively. Thus if a metal rod is placed in a burner, heat travels along the rod by conduction. This may be explained by the kinetic theory of matter. The molecules of the rod increase their energy of motion. This violent motion is passed along the rod from molecule to molecule. In considering the flow of heat by conduction, it is sometimes helpful to compare the flow of heat to the flow of electricity. The temperature difference can be thought of as the pressure, or voltage, in an electrical circuit. The ability of a substance to transfer heat (its thermal conductivity) can be compared to electrical conductivity. When the temperature difference (or voltage) between two points is great, the driving force to move heat (or current) is high. The quantity of heat (or current) transferred will depend upon the temperature difference (or voltage difference) and the resistance to the flow of heat (or current) offered by the conductor.

What is Convection?

The method of heat transfer called convection depends upon the movement of the material which is heated. It applies to free-moving substances; that is, liquids and gases. The motion is a result of changes of density that accompany the heating process. Water in a tea kettle is heated by convection. A stove heats the air in a room by convection. When a liquid or gas is heated, its density (mass per unit volume) decreases; that is, it becomes lighter in weight. A warmer volume of gas will rise while a colder, and thus heavier, volume of gas will descend. This process is described as natural convection. A familiar example of natural convection is the circulation of air from a hot-air furnace. When a liquid or gas is moved from one place to another by some mechanical force, the process is known as forced convection. The circulation of air by an electric fan is an example of forced convection.

What is Emissivity?

The rate at which infrared energy is emitted by an object compared to that of a Blackbody at the same temperature and in the same wavelength.

What are Palettes?

Color palettes are convenient ways for you to see a thermal image. For instance, you may chose to have cold be the color blue, medium yellow and red hot. Or you might want everything black and white with everything over 80°F red. Or you might want cold to be purple and hot to be yellow.