Model 42525A Version 4.0 5/05
6
Emissivity Considerations and Adjustment
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. Emissivity is determined
by the material of the object and the object’s surface finish. Emissivity values range from
0.1 for a very reflective object to 1.00 for a flat black finish. The Model 42525A uses a
factory default emissivity setting of 0.95 (this setting covers most applications).
The closer the meter's emissivity setting is to the actual emissivity of the object under test,
the more accurate the temperature measurements will be. To calculate the emissivity of an
object: Measure an object's temperature using a Type K Thermocouple (use of a surface-
mount thermocouple works best for this purpose) and note the reading. Measure the object
again using the IR sensor. Now, set the emissivity so that the IR measurement matches
the thermocouple reading. To set the emissivity:
1. Press and hold the Emissivity button until the emissivity display starts to flash.
2. Use the UP/DOWN arrow buttons to select the desired emissivity
3. Press and hold the Emissivity button until the display stops flashing to exit
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
Lather
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
Data Hold
Press the HOLD button to freeze the displayed measurement. The “HOLD” icon will appear
on the LCD to indicate that the Data Hold mode is activated. Press the HOLD button again
to exit the Data Hold mode and return to normal operation.
Relative Measurements
While measuring, press the REL button to activate the Relative Mode (REL will appear on
the LCD in the upper right-hand corner). The measurement on the LCD at the time of the
button press will be displayed as 0.0
o
. Subsequent readings will be displayed as a
difference between the stored reading and the actual reading. Relative does not function
when either Data Hold or Data Record is enabled.
