Paper Technology International 2020 - Journal - Page 69

PAPERTECHNOLOGYINTERNATIONAL
Reduce costs and process variation with microwave instrumentation
Frank Cunnane, Product Specialist, Cristini NA
INTRODUCTION:
Since the introduction of planar microwave technology, new applications continue to be found for this investigative tool. Starting
first in the forming section, it replaced older gamma gauge tools which require federal licensing, extensive record keeping, and the need for
a Radiation Officer on site. This technology went forward into the press section, initially to measure felt moisture, then later to measure felt
and sheet moisture, and now to measurement of the sheet consistency itself in open draw configurations.
In the past year these tools have been expanded to help control sheet properties as well as a new application for the TAD segment of the
tissue industry, the fastest growing segment in the paper industry. Data is shown that allows predictable sheet consistency in the heart of
the process. Work is ongoing to predict sheet consistency in Unorun sections. The results from that application will be published soon.
A. Principles of Operation
Older technology relied upon nuclear radiation from socalled “back-scatter” gauges. There were numerous issues with
nuclear technology, not the least of which were inherent radiation
risk, governmental regulation, having a separate radiation officer,
and disposal of the radioactive source material after its useful life.
A new generation of instruments has been developed using
microwave technology. These units use less radiation than a cell
phone and is safe to the touch.
(Figure 1 opposite) demonstrates that a fabric or a fabric/
sheet passing over the head will cause a change in the flux of the
microwave field set up between the incoming source (antenna) and
the receiver. The fact that microwaves cause resonance in water
molecules above the sensor, means that all the sensor perceives
is the water itself, not the fiber, the fabric, or the surrounding
machinery.
B.The Instruments Themselves
In the forming section the FiberScanOnLine can be mounted
anywhere that the roughly 10 X 12 cm head can fit. Since the
instrument does not see the machine framing in its measurements,
tight fitting spaces can be accommodated between table elements.
Forming Section Microwave Moisture-measuring
In tissue manufacturing, most forming sections allow little
or no access for measurement of water content, so we will focus on
applications in the press section and in TAD manufacturing.
Press Section Moisture Measurement
In the press section, there are two instruments that can
be used. The first, the PresScan (Figure 2 opposite), is used to
measure felt moisture, and felt/sheet moisture combined. Standard
applications involve determining the efficiency of uhle boxes and
doing water balances to determine the relative contribution of each
dewatering element. The most common application is in reducing
vacuum consumption for uhle boxes and suction rolls.
These instruments are also available with traversing
scanning capability. These units measure felt moisture, permeability
and temperature. These EasyScan units are equipped with
sophisticated 3D felt mapping capability and can be interfaced
with the machine’s DCS. A portable version of this felt scanning
unit called the PermFlow DUO is used for manual felt traversing.
Figure 1: New planar sensor operates without a resonance
chamber
Real-time permeability profiles present opportunities for cost savings
and process control heretofore not possible.
The Fixed Head for Measuring Felt and Felt/Sheet Moisture
Figure 2: The microwave field generated by this sensor
measures a high range of moisture-containing media.
Sheet Consistency Measuring Sensor
For applications that need to measure sheet consistency
with high accuracy in open draws or on fabrics such as TAD or
Transfer fabrics, there is a third instrument, the SmartScan. This
instrument, shown in (Figure 3 overleaf) measures lower moisture
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