Velleman DVM8855 Notice D'emploi page 10

8. Useful information
Working principle
The Infra Red sensor of the unit detects energy that is emitted, reflected and transmitted by a
surface. This energy is focussed onto a detector that converts this information into a temperature
reading. The laser beam is only used for aiming purposes.
Ambient temperature
The thermometer automatically compensates ambient temperature conditions. Allow the
thermometer to stabilise to ambient temperature for at least 30 minutes for accurate
measurements.
Surface temperature
When going from low temperature to high temperature measurements or vice versa, the IR sensor
of the thermometer needs a few minutes to adjust.
Distance and spot size
Refer to the drawing on page 2 of this manual.
As the distance (D) from the object increases, the spot size (S) of the area measured by the unit
becomes larger. The focal point for this unit is 914mm (36"). Note that the laser beam points 16mm
above the measurement centre point.
Field of view
The target must be larger than the spot size to ensure correct measurement. This means that for
smaller targets, the thermometer must be held closer to the target. For best accuracy, make sure
the target is at least twice as large as the spot size.
Emissivity
Emissivity describes the energy-emitting characteristics of materials. Most organic or oxidized
surfaces have an emissivity of ±0.95 (default setting). Measuring shiny or polished surfaces will be
inaccurate. Use some masking tape or paint to compensate, allow sufficient time for the tape or
paint to reach the surface temperature.
Substance
Asphalt
Concrete
Cement
Sand
Earth
Water
Ice
Snow
Glass
Ceramic
Marble
Plaster
Mortar
Brick
02/03/2009
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DVM8855
Emissivity Substance
0.90 to 0.98 Cloth (black)
0.94 Human skin
0.96 Leather
0.90 Charcoal (powder)
0.92 to 0.96 Lacquer
0.92 to 0.96 Lacquer (matt)
0.96 to 0.98 Rubber (black)
0.83 Plastic
0.90 to 0.95 Timber
0.90 to 0.94 Paper
0.94 Chromium oxides
0.80 to 0.90 Copper oxides
0.89 to 0.91 Iron oxides
0.93 to 0.96 Textiles
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Emissivity
0.98
0.98
0.95 to 1.00
0.96
0.80 to 0.95
0.97
0.94
0.85 to 0.95
0.90
0.70 to 0.94
0.81
0.78
0.78 to 0.82
0.90
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