42511 V4.2 2/08

9

IR Measurement Notes

1. The object under test should be larger than the spot (target) size calculated by the field

of view diagram (printed on the side of the meter and in this guide).

2. Before measuring, be sure to clean surfaces that are covered with frost, oil, grime, etc.

3. If an object's surface is highly reflective, apply masking tape or flat black paint to the

surface before measuring. Allow time for the paint or tape to adjust to the temperature

of the surface it is covering.

4. Measurements through transparent surfaces such as glass may not be accurate.

5. Steam, dust, smoke, etc. can obscure measurements.

6. The meter automatically compensates for deviations in ambient temperature. However,

it can take up to 30 minutes for the meter to adjust to extremely wide changes.

7. To find a hot spot, aim the meter outside the area of interest then scan across (in an up

and down or side to side motion) until the hot spot is located.

Emissivity and IR Measurement Theory

IR Thermometers measure the surface temperature of an object. The thermometer’s optics

sense emitted, reflected, and transmitted energy. The thermometer’s electronics translate

the information into a temperature reading which is then displayed on the LCD.

The amount of IR energy emitted by an object is proportional to an object's temperature

and its ability to emit energy. This ability is known as emissivity and is based upon the

material of the object and its surface finish. Emissivity values range from 0.1 for a very

reflective object to 1.00 for a flat black finish. For the Model 42511, the emissivity is

adjustable from 0.1 to 1.00. Most organic materials and painted or oxidized surfaces have

an emissivity factor of 0.95. When in doubt, set the emissivity to 0.95.

Emissivity Factors for Common Materials

Material under test

Emissivity

Material under test

Emissivity

Asphalt

0.90 to 0.98

Cloth (black)

0.98

Concrete

0.94

Skin (human)

0.98

Cement

0.96

Leather

0.75 to 0.80

Sand

0.90

Charcoal (powder)

0.96

Soil

0.92 to 0.96

Lacquer

0.80 to 0.95

Water

0.92 to 0.96

Lacquer (matt)

0.97

Ice

0.96 to 0.98

Rubber (black)

0.94

Snow

0.83

Plastic

0.85 to 0.95

Glass

0.90 to 0.95

Timber

0.90

Ceramic

0.90 to 0.94

Paper

0.70 to 0.94

Marble

0.94

Chromium Oxides

0.81

Plaster

0.80 to 0.90

Copper Oxides

0.78

Mortar

0.89 to 0.91

Iron Oxides

0.78 to 0.82

Brick

0.93 to 0.96

Textiles

0.90