17
16
5.7 Measurement considerations
Holding the meter by its handle, point the IR Sensor toward the object whose
temperature is to be measured. The meter automatically compensates for temperature
deviations from ambient temperature. Keep in mind that it will take up to 30 minutes
to adjust to wide ambient temperatures are to be measured followed by high
temperature measurements, some time (several minutes) is required after the low
(and before the high) temperature measurements are made.
This is a result of the cooling process, which must take place for the IR sensor.
5.8 How it Works
Infrared thermometers measure the surface temperature of an object. The unit’s
optics sense emitted, reflected, and transmitted energy, which is collected and
focused onto a detector. The unit’s electronics translate the information into a
temperature reading, which is display on the unit. In units with a laser, the laser is
used for aiming purposes only.
5.8.1 Field of View
Make sure that the target is larger than the unit’s spot size. The smaller the target,
the closer you should be to it. When accuracy is critical, make sure the target is at
least twice as large as the spot size.
5.8.2 Distance & Spot Size
As the distance (D) from the object increases, the spot size (S) of the area measured
by the unit becomes larger. See: Fig: 1.
5.8.3 Locating a hot Spot
To find a hot spot aim the thermometer outside the area of interest, then scan across
with an up and down motion until you locate hot spot.
5.8.4 Reminders
1. Not recommended for use in measuring shiny or polished metal surfaces
(stainless steel, aluminum, etc.).See Emissivity
2. The unit cannot measure through transparent surfaces such as glass. It will
measure the surface temperature of the glass instead.
3. Steam, dust, smoke, etc., Can prevent accurate measurement by obstructing the
unit’s optics.
5.9 Emissivity
Emissivity is a term used to describe the energy-emitting characteristics of
materials. Most (90% of typical applications) organic materials and painted or
oxidized surfaces have an emissivity of 0.95 (pre-set in the unit). Inaccurate
readings will result from measuring shiny or polished metal surfaces. To compensate,
cove the surface to be measured with masking tape or flat black paint. Allow time for
the tape to reach the same temperature as the material underneath it. Measure the
temperature of the tape or painted surface.
Emissivity Values
Substance
Thermal
emissivity
Substance
Thermal emissivity
Asphalt
0.90 .. 0.98
Cloth (black)
0.98
Concrete
0.94
Human skin
0.98
Cement
0.96
Lather
0.75 to 0.80
Sand
0.90
Charcoal (powder) 0.96
Earth
0.92 .. 0.96
Lacquer
0.80 .. 0.95
Water
0.92 .. 0.96
Lacquer (matt)
0.97
Ice
0.96 .. 0.98
Rubber (black)
0.94
Snow
0.83
Plastic
0.85 .. 0.95
Glass
0.90 .. 0.95
Timber
0.90
Ceramic
0.90 .. 0.94
Paper
0.70 .. 0.94
Marble
0.94
Chromium oxides
0.81
Plaster
0.80 .. 0.90
Copper oxides
0.78
Mortar
0.89 .. 0.91
Iron oxides
0.78 .. 0.82
Brick
0.93 .. 0.96
Textiles
0.90
