Measure the apparent temperature of the aluminum foil and write it down.
10727003;a2
Figure 18.4 Measuring the apparent temperature of the aluminum foil
5
18.2.1.2
Step 2: Determining the emissivity
Select a place to put the sample.
1
Determine and set reflected apparent temperature according to the previous procedure.
2
Put a piece of electrical tape with known high emissivity on the sample.
3
Heat the sample at least 20 K above room temperature. Heating must be reasonably even.
4
Focus and auto-adjust the camera, and freeze the image.
5
Adjust
Level
and
Span
for best image brightness and contrast.
6
Set emissivity to that of the tape (usually 0.97).
7
Measure the temperature of the tape using one of the following measurement functions:
■
Isotherm
(helps you to determine both the temperature and how evenly you have heated
the sample)
■
Spot
(simpler)
■
Box Avg
(good for surfaces with varying emissivity).
8
Write down the temperature.
9
Move your measurement function to the sample surface.
10
Change the emissivity setting until you read the same temperature as your previous measure-
ment.
11
Write down the emissivity.
12
Note:
62
Publ. No. T559733_en-US Rev. a571 – ENGLISH (EN) – November 4, 2011
18 – Thermographic measurement techniques
