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12. Predictive Measurements
12-1 A Description of Predictive Measuring
Infrared moisture content testers can be used to measure the moisture content of a wide range of
different materials, thus making it possible to measure the moisture content of almost anything.
This is the most important feature found in infrared testers not found in other types of testers.
At the same time, however, because an infrared moisture content tester operates by heating
samples to evaporate the moisture content, it takes a fair amount of time to obtain measurements.
In order to make it possible to shorten the amount of time required for taking measurements and
to provide a means of approximating the moisture content measurements which would be ob-
tained using standard methods, predictive measuring mode has been developed.
In predictive measuring mode,
1
An estimate is calculated of the final moisture content while drying is still in progress.
2
It is necessary to specify three settings before measuring: the drying temperature, the pre-
dicted value convergence range, and the bias.
3
This mode is designed for use only with materials which display a drying curve of the type
generally referred to as an ‘S curve’.*
1
*
1
When compared to other curves showing the degree of drying which takes place when the mois-
ture content of a given material changes as drying progresses, an ‘S-curve’ is a curve in which the
degree of change in moisture content (i.e.,
∆
M) in the initial stages of drying is low and then
increases towards the middle of the drying process and then decreases progressively as the
drying process nears completion.
Drying temperature
Since the desired value is that which would be obtained when operating in automatic halting
mode, the drying temperature specified should be the same as that which would be specified in
automatic halting mode.
Predicted value convergence range
When operating in predictive operating mode, predicted values are internally calculated every 30
seconds, and while variation occurs in the calculated values, the degree of variation grows smaller
as more and more time elapses. The FD-720 has been designed to treat the final predicted value
as having been obtained when the range of variation falls within the predicted value convergence
range. The range of allowable variation in predicted final moisture content is referred to as the
predicted value convergence range.
The predicted value convergence range may be specified as a percentage anywhere from 0.1 to
9.9 percent. While specifying a higher value for the predicted value convergence range causes the
final predicted value to be calculated more quickly, the specification of a higher value may also
result in greater degrees of error occurring in predicted values. Conversely, while it is possible to
obtain more stable sets of predicted values when a lower value is specified for the predicted value
convergence range, specifying lower values tends to make it take significantly longer to calculate a
final predicted value. The value specified for the predicted value convergence range should ac-
cordingly be specified according to your objectives. Note that the default setting for the FD-720
is a value of 0.5 percent.
Summary of Contents for FD-720
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