18
SERVICE
5. Adjust the calibration.
a. Scroll to the proper screen for calibration adjustment.
b. Press the I button to adjust the correct value.
Each time the I button is pressed, the value in the corner changes by an increment
of 0.01.
6. Store the new calibration value.
a. Scroll to the proper screen for calibration adjustment.
b. Press the II button to scroll until Sto appears in the lower right corner.
c. Press the I button to store the new calibration value.
d. Return to the main screen and begin a new measurement.
NOTE: If Sto is not pressed, no change is made to the PAWKIT calibration.
7. Verify with a second standard, either the 0.25 or the 0.92 standard.
Choose the standard that is closest to the water activity range of the sample material
being tested. In other words, if it is normally higher than 0.76 a
w
, use the 0.92 standard.
If it is normally lower than 0.76 a
w
, use the 0.25 standard. If the PAWKIT measures the
second standard correctly (±0.02), begin testing the product. If it does not measure
correctly, repeat step3 through step7 for the second standard.
8. If the calibration routine is inadvertently entered, keep pressing the II button until the
main screen appears.
NOTE: The 0.76 standard adjustment adjusts the calibration intercept, while the 0.25 and 0.92 adjusts the slope.
Changes in the intercept are more likely to occur than changes in the slope, so the 0.76 verification check is the
most important and should be done more frequently.
Review the graphical representation of the calibration routine in Figure14.
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