In-Depth: How Thermal Imaging Works

Courtesy How Stuff Works



how thermal imaging works:

1. A special lens focuses the infrared light emitted by all of the objects in view.

2. The focused light is scanned by a phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermogram. It only takes about one-thirtieth of a second for the detector array to obtain the temperature information to make the thermogram. This information is obtained from several thousand points in the field of view of the detector array.

3. The thermogram created by the detector elements is translated into electric impulses.

4. The impulses are sent to a signal-processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display.

5. The signal-processing unit sends the information to the display, where it appears as various colors depending on the intensity of the infrared emission. The combination of all the impulses from all of the elements creates the image.

Types of Thermal Imaging Devices
Most thermal-imaging devices scan at a rate of 30 times per second. They can sense temperatures ranging from -4 degrees Fahrenheit (-20 degrees Celsius) to 3,600 F (2,000 C), and can normally detect changes in temperature of about 0.4 F (0.2 C).

There are two common types of thermal-imaging devices:

• Un-cooled - This is the most common type of thermal-imaging device. The infrared-detector elements are contained in a unit that operates at room temperature. This type of system is completely quiet, activates immediately and has the battery built right in.

• Cryogenically cooled - More expensive and more susceptible to damage from rugged use, these systems have the elements sealed inside a container that cools them to below 32 F (zero C). The advantage of such a system is the incredible resolution and sensitivity that result from cooling the elements. Cryogenically-cooled systems can "see" a difference as small as 0.2 F (0.1 C) from more than 1,000 ft (300 m) away, which is enough to tell if a person is holding a gun at that distance!

While thermal imaging is great for detecting people or working in near-absolute darkness, most night-vision equipment uses image-enhancement technology.

In-Depth: The EMF Meter

An EMF meter is a scientific instrument for measuring electromagnetic radiation.

There are many different types of EMF meter, but the two largest categories are single axis and tri-axis. Single axis meters are cheaper than a tri-axis meters, but take longer to complete a survey because the meter only measures one dimension of the field. Single axis instruments have to be tilted and turned on all three axes to obtain a full measurement. A tri-axis meter measures all three axes simultaneously, but these models tend to be more expensive.

Most meters measure the electromagnetic radiation flux density, which is the amplitude of any emitted radiation. Other meters measure the change in an electromagnetic field over time.

Electromagnetic fields can be either AC (Alternating Current) or DC (Direct Current). An EMF meter can measure AC electromagnetic fields, which are usually emitted from man-made sources such as electrical wiring, while Gauss meters or magnetometers measure DC fields, which occur naturally in the earth’s geomagnetic field and are emitted from other sources where direct current is present.

EMF meters usually measure radiation in milligaus In absence of a moving magnetic field, an ideal meter will read 0 milligauss. Industrial EMF meters will often read 2-3 milligauss when placed in an open field devoid of emitters such as power lines (either overhead or buried).

The majority of EMF meters available are calibrated to measure electromagnetic radiation, which is alternating at 50/60 Hertz. This is because in recent years people have become concerned about the long-term health effects of exposure to high levels of radiation emitted from some electrical appliances.

There are other meters which can measure field alternating at as little as 20 Hz However these tend to be much more expensive and are only used to specific research.