Fluke 561s - Manual (Page 11)

Operating the Thermometer
7
D:S=12:1
38 mm @
300 mm
75 mm @
900 mm
132 mm @
1500 mm
1.5 " @
12 "
3 " @
36 "
5.3 " @
60 "
S
D
efh005f.eps
Figure 5. Distance and Spot Size
Field of View
Make sure that the target is larger than the spot size. The smaller the target, the closer you
should be to it. See Figure 6.
Yes No
efh004f.eps
Figure 6. Field of View
Emissivity
Emissivity describes the energy-emitting characteristics of materials. Most organic materials
and painted or oxidized surfaces have an emissivity of about 0.95.
If possible, to compensate for inaccurate readings that may result from measuring shiny metal
surfaces, cover the surface to be measured with masking tape or flat black paint
(<148
° C/300 ° F) and use the high emissivity setting. Allow time for the tape or paint to reach
the same temperature as the surface beneath it. Measure the temperature of the tape or
painted surface.
If you cannot paint or use tape, then you can improve the accuracy of your measurements with
the emissivity selector. Even with the emissivity selector, it can be difficult to get a completely
accurate infrared measurement of a target with a shiny or metallic surface. Experimentation,
using the probe to determine benchmark temperatures, and experience will help you choose the
best setting for specific measurements.
The Thermometer has three emissivity settings: low (0.3), medium (0.7), and high (0.95). Refer
to Table 2. The reference to emissivity settings in the table are suggestions for typical
situations. Your particular situation may differ.