TECHNICAL NOTES FOR USERS - NOTE #033
The Procedure for Calibration For Infrared Moisture Meters
page 2
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either manually (recommended) or programmatically. Levels, like 30, 40, 50, 60, 70, 80 and 85 %RH are
usually quite sufficient. Going higher than that is possible but in many chambers water condensation may occur
on the walls causing uncontrolled wetting of the sample accidentally. In many papers, 85 %RH will generate a
moisture around 16 % or higher. Some chambers may be able to go cleanly over 90 %RH and one might be able
to increase the sample moisture over 40 % with some grades. Special wetting methods are called if really high
moisture levels in the sample are needed. If you lower the %RH you will not return to the same moisture points
as before. That is due to the paper hysteresis phenomenon.
7. Feed the collected data into your spreadsheet program and draw a picture of it thus forming the actual calibration curve.
You should have pairs of numbers (signal --- weight). The signal reading is around 1.0. If it is around 100 you
will need to divide it by 100. At bone dry end it is usually around 0.95 and at 30% it could be around 1.25.
8. Decide whether the results are reasonable by looking at the graph generated from the data. If not, you have to get more
data from step 6. You could run the chamber up and down slowly to get more data. Note that thick papers with
BW higher than 100 g/m2 require longer stabilization times. With very thick papers the settling time may be hours.
9. Having obtained a reliable calibration curve, decide which points on it actually are adequate for representing it with the
accuracy you have specified. You can use only 2 to 10 of them for the calibration table. Straight part of the curve
can be handled with a single line segment. Usually thin papers (BW < 60 g/m2) have a straight line as the curve
and thick papers have some curvature at the dry end and a straight line above 8 %.
10. Take a printout of the numeric calibration point table and graph and identify and mark the selected points with step
numbers.
11. In the meter, select an empty or unused table
12. Go to the MULTI calibration menu
13. Set the step number in "2=#STP".
14. Press "4" and type in the corresponding signal (now scaled down if you earlier scaled it up) as a decimal number. The
value is typically between 0.90 and 1.50. Use always as many decimals as there are available and try to round
them correctly.
15. Press "5" and set the corresponding moisture value.
Do not use the Execution ("3") in this method! Else the signal
value is replaced with the current signal reading. This option depends on the model of the meter used. AK30 has
CALIBR and EDIT separately. Editing is safe to do.
16. Repeat the steps 13., 14. and 15. until all calibration points are fed in. Make sure the number of points used is the
same as in the upper menu is indicated (option "3"). Correct if not.
17. In the upper menu, check the calibration mode to be MULTI.
18. Save the calibration table by pressing the Save key. You can also edit the name of the new table by selecting the option
"3" in the main menu. Save again the table there after editing it. Model D meter will save the new table by itself.
You can press the ESC key a few times and start measuring with the new table.
19. For most accurate work you might want to check the reading and make a fine tuning to have a perfect result. It is advisable
to dry the sample again and determine its dry weight as guided before. Then allow the sample to wet again to some
level around the most useful moisture range where to usually measure it, by using your chamber. Use the new
calibration table to read the moisture of the sample and the weight of it too. The Excel sheet will now reveal the
