Paper Technology International 2020 - Journal - Page 70

PAPERTECHNOLOGYINTERNATIONAL
values with extreme accuracy. The unit will provide /- 1 gsm
resolution, so that even lightweight sheet consistencies can be
measured accurately.
In the past, only heavy weight sheets could be measured
in open draws because the sensor head had to be in contact with
the sheet, and only special cases could tolerate this without the
risk of sheet breaks. Our “new generation” technology now allows
the sheet to be as far as 10 millimeters away from the sensor head
and still provide /- 1 gsm resolution, so that even lightweight sheet
consistencies can be measured accurately.
In the past, only heavy weight sheets could be
measured in open draws because the sensor
head had to be in contact with the sheet,
and only special cases could tolerate
this without the risk of sheet breaks.
Our “new generation” technology now
allows the sheet to be as far as several
millimeters away from the sensor head,
and still obtain a high accuracy and
precision ( /- 1gsm water content).
This unit is being evaluated for
the “holy grail” of tissue manufacture,
ie, measuring Post Pressure Roll Consistency
(PPRC) on the Yankee dryer itself. As work progresses, additional
papers will be made public
Figure 3: A new generation sensor that can measure
sheet consistency contactless in open draws with high
accuracy
CASE STUDY ONE
For The last 15 years, the greatest expansion in the
paper industry has been the TAD segment. The complexity of
these machines frequently present challenges to the installation of
instrumentation, but recent work with paper companies has shown
that microwave moisture measurement is possible and provides
accurate sheet moisture levels without the need for grab samples.
Obtaining grab samples can be a safety risk, and the lab-measured
consistency is often called into question.
(Figure 4) is a simplified drawing of where the instrument was
located vs. where the grab samples were obtained. The vacuum box
shown on the drawing was not in use for the purpose of these trials.
Figure 4: shows location of the instrument, and the
location of where lab samples were obtained.
In our first round of trials data was gathered that compared the
microwave instrument readings to grab sample lab readings while
various process variables were changed, designed in improve and/
or reduce water removal performance. These results are shown in
Figure 5.
The R squared value indicates how well the data conforms
to a linear regression. The 0.93 level shows that the data has a
good correlation to a straight line, but as obvious on the graph, the
absolute values don’t agree.
The microwave transducer produces a field that is several
cm wide and several cm high. The exact location of wherein the
field that the fabric and sheet matrix pass through the field, needed
to be corrected. When this adjustment was made, subsequent
measurements across numerous grade changes showed excellent
correlation comparing sheet water content to total water content in
the sheet and fabric (Figure 5). It is a straightforward conversion
from water content in the sheet to consistency by removing the
water content of the fabric.
Figure 5: shows a good level of R-squared (coefficient of determination).
68

Paperturn flipbook