visilab AK30, AK40, AK50 Technical Notes

TECHNICAL NOTES FOR USERS - NOTE #033

The Procedure for Calibration For Infrared Moisture Meters

page 1

Visilab Signal Technologies Oy

Sepäntie 4 Tel. [phone]
FI-07230 Monninkylä [e-mail] Y0631208-0 ALV Rek.
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Accurate Calibration With AK30/AK40/AK50 Moisture Meters Using a Climate Cham-Accurate Calibration With AK30/AK40/AK50 Moisture Meters Using a Climate Cham-

Accurate Calibration With AK30/AK40/AK50 Moisture Meters Using a Climate Cham-Accurate Calibration With AK30/AK40/AK50 Moisture Meters Using a Climate Cham-

Accurate Calibration With AK30/AK40/AK50 Moisture Meters Using a Climate Cham­berber

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Performing Multipoint Calibration when Working with a Climatic Chamber and a Balance

In this more accurate way the calibration is done as follows. Follow this procedure step by step and you will get the most accurate
calibration to your meter. For best results, extra care is required.

0. By using some general-purpose calibration table of similar basis weight, study the sample on each side with the moisture
meter to observe any differences. Coated side vs. uncoated side may give different readings. You should decide
which is the important one.

1. Cut the sample paper/board to a size suitable for the chamber and the balance's sample holder. Make sure there is no
contact to nearby walls while measuring the weight. Punch a few holes to the sample if your chamber has hooks
for holding the samples. Note that this must be done at an early stage, you cannot do it later when you have started
measurements. Use some reasonable code marking in each sample for easy recognition.

2. Prepare an Excel sheet for collecting data and for automatically calculating moisture readings from the weights when the
dry weight is known. Prepare some graphics too to show the resulting curve after getting in some data. Then you
can copy this sheet as a model for all later calibrations. Visilab can also send you a sample sheet.

3. Place the sample into an oven for two hours at about +102 C

4. While drying, place the balance and the moisture meter into the climatic chamber. If your balance can not withstand
the humid conditions, do the weighing outside the chamber with for example a plastic bag. Start the chamber control
system and adjust the relative humidity to the lowest possible value. Arrange the moisture meter, if possible, so
that you can simultaneously read both the balance and the meter. Using your PC for reading the meter is the best
way to do it. The sample should be later placed so that the surrounding air can circulate around it and the wetting
will be even at every point on the sample. The moisture meter

should be in SCALE calibration mode.

You can use
the table #68 SCALE for this purpose. Then you will use scaling up of the raw moisture signal with a factor of 100
to make its reading easier and more accurate since you have more significant numbers at disposal. The meter should
now be acquiring data to your PC. Tare the balance to zero with the sample holders in place.

5. Quickly move the sample from the oven to your balance for weighing, preferably using an aluminum or plastic bag. If
the balance is in the chamber, place the bag unopened there and weigh it and open it only after closing the door
by using gloves in the walls. If the balance is on top of the chamber with a suitable measuring cabinet, you might
do the weighing there and after that move the sample to the chamber and open the bag. Weighing the sample in
free lab air will destroy the accuracy in one second. Note that plastic bags may cause static electricity which may
distort weighing results at the dry end. The result will be the dry weight of the sample plus the bag. Tare the bag
away from the weight. Try to read also the moisture meter signal by placing quickly the sample under the meter.
That is usually a difficult task as both the weight and the signal increase so rapidly within the first 0..2 % range.
The dry weight is used later in calculating the actual moisture percentages. Note that this step usually causes the
greatest errors to the final absolute calibration accuracy. Errors of the order of +/-0.5 % are common if
exceptionally careful precautions are not taken. Static can be eliminated by an ion gun. The meter's readings at
the very dry end are usually very useful for depicting how the curve will go.

6. Continue reading the moisture signal-weight pairs as the moisture level slowly increases. Make notes of these readings.
At first, you can take readings every minute but as the wetting of the sample will become slower it may be enough
to take samples at longer intervals (5 min, 20 min, 1 hour). If long intervals are used, it is advisable to place the
meter into low power mode and to tare the balance occasionally. Try to keep the chamber at very low humidities
in the beginning (10 %RH) to slow down the wettening. Thereafter, you can increase the %RH to higher levels

2016-04

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TECHNICAL NOTES FOR USERS - NOTE #033

The Procedure for Calibration For Infrared Moisture Meters

page 2

Visilab Signal Technologies Oy

Sepäntie 4 Tel. [phone]
FI-07230 Monninkylä [e-mail] Y0631208-0 ALV Rek.
FINLAND www.visilab.fi VAT FI06312080 Mäntsälä Reg. 365.258

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