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8.1.3 Ending Criteria
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ENDING CRITERIA
The ending criterion is used by the
instrument to automatically end a test.
This feature makes it unnecessary for the
operator to monitor the instrument while it
is performing a test. All ending criteria
are available on the MAX
®
4000XL, but
only PREDICTION and RATE are
available on the MAX
®
4000.
The decision of which ending criterion to use is application dependent. Best results are
typically given with PREDICTION or RATE, rather than TIME. Experiment with your
particular sample to determine which criterion is best for your product.
For PREDICTION, the MAX
®
4000 predicts what the final result should be by
extrapolating the current moisture loss curve. Prediction begins about a minute after
peak rate loss. The test ends when the actual moisture loss is within X% of the predicted
value, where X is typically 90; this is the “reliability” value listed in the Test Results.
Prediction can reduce test times by 1 to 5 minutes. Set X to a higher value if 90 is not
producing good results. If the moisture loss curve shape does not fit the Prediction
model, then it will produce poor results; Prediction does not work on all samples.
For RATE, the MAX
®
4000 ends the test after the sample weight loss rate has fallen
below a preset value. This is the most common ending criteria and works well with
samples that show a consistent moisture rate loss at some point in the process. The
parameter may be set for values from 0.0010% to 9.9999% loss rate on the MAX
®
4000XL. (0.01% to 9.99% on the MAX
®
4000). A good value to use is the (Expected
Moisture Result) / 30, but do not use a value outside the range 0.0050% to 0.5%. For
example, if the Expected Moisture Result is 3.00%, then use a Rate EC of
0.100%/minute. Note: A test with a RATE ending criteria will always last at least one
minute, however, the test will end in 4 minutes if a peak rate of at least 0.0010% is not
detected.
The MAX
®
4000 assumes that the sample contains volatile material that will completely
evaporate after some time. It further assumes that the rate of moisture loss (or weight
change) will increase to a maximum point and then gradually decrease to zero. Selecting
some threshold rate values will cause the test to end before the sample is completely dry.
Rate is useful to profile a sample's weight loss. Some testing applications are faster using
the rate ending criteria, while others are faster using the prediction ending criteria.
