Note: Descriptions are shown in the official language in which they were submitted.
CA 02557951 1997-12-12
Electromagnetic Field Perturbation Sensor and Methods for Measuring
Water Content in Sheetmaking Systems
Related Applications
This is a divisional of Canadian Patent Application No. 2,277,837.
Background of the Invention
1. Field of the Invention
The present invention generally relates to systems for controlling continuous
sheetmaking systems and, more specifically, to sensors and methods for
measuring the
fiber weight of wetstock in a paper making machine.
2. State of the Art
In the art of modern high-speed papermaking, it is well known to continuously
measure
certain properties of the paper material in order to monitor the quality of
the finished
product. These on-line measurements often include basis weight, moisture
content, and
sheet caliper (i.e., thickness). The measurements can be used for controlling
process
variables with the goal of maintaining output quality and minimizing the
quantity of
product that must be rejected due to upsets in the manufacturing process.
The on-line sheet property measurements are often accomplished by scanning
sensors
that periodically traverse the sheet material from edge to edge. For example,
a high-
speed scanning sensor may complete a scan in a period as short as twenty
seconds,
with measurements being read from the sensor at about 50 milliseconds
intervals. It is
also know that a series of stationary sensors can be used to make similar on-
line
measurements.
In the manufacture of paper on continuous papermaking machines, a web of paper
is
formed from an aqueous suspension of fibers (stock) on a traveling mesh
papermaking
CA 02557951 1997-12-12
fabric and water drains by gravity and suction through the fabric. The web is
then
transferred to the pressing section where more water is removed by pressure
and
vacuum. The web next enters the dryer section where steam heated dryers and
hot air
completes the drying process. The paper machine is, in essence, a water
removal,
system. A typical forming section of a papermaking machine includes an endless
traveling papermaking fabric or wire which travels over a series of water
removal
elements such as table rolls, foils, vacuum foils, and suction boxes. The
stock is carried
on the top surface of the papermaking fabric and is de-watered as the stock
travels over
the successive de-watering elements to form a sheet of paper. Finally, the wet
sheet is
transferred to the press section of the papermaking machine where enough water
is
removed to form a sheet of paper.
Papermaking devices well known in the art are described for example in U.S.
Pat. No.
5,400,258. Many factors influence the rate at which water is removed which
ultimately
affects the quality of the paper produced. As is apparent, it would be
advantageous to
monitor the dynamic process so as to, among other things, predict and control
the dry
stock weight of the paper that is produced.
It is conventional to measure the moisture content of sheet material upon its
leaving the
main dryer section or at the take up reel employing scanning sensors. Such
measurement may be used to adjust the machine operation toward achieving
desired
parameters. One technique for measuring moisture content is to utilize the
absorption
spectrum of water in the infra-red. Monitoring or gauge apparatus for this
purpose is
commonly in use. Such apparatus conventionally uses either a fixed gauge or a
gauge
mounted on a scanning head which is repetitively scanned transversely across
the web
at the exit from the dryer section and/or upon entry to the take up reel, as
required by
the individual machines. The gauges typically use a broad-band infra-red
source and
one or more detectors with the wavelength of interest being selected by a
narrow-band
filter, for example, an interference type filter. The gauges used fall into
two main types:
the transmissive type in which the source and detector are on opposite sides
of the web
and, in a scanning gauge, are scanned in synchronism across it, and the
scatter type
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CA 02557951 1997-12-12
(sometimes called "reflective" type) in which the source and detector are in a
single
head on one side of the web, the detector responding to the amount of source
radiation
scattered from the web.
Summary of the Invention
The present invention is a sensor which is sensitive to three properties of
materials: the
conductivity or resistance, the dielectric constant, and the proximity of the
material to
the sensor. Depending on the material, one or more of these properties will
dominate.
The basic embodiment of the sensor of the present invention includes a fixed
impedance element coupled in series with a variable impedance block between an
input
signal and ground. The fixed impedance element and the variable impedance
block
form a voltage divider network such that changes in impedance of the impedance
block
results in changes in voltage on the output of the sensor. The impedance block
represents the impedance of the physical configuration of at least two
electrodes within
the sensor of the present invention and the material residing between and in
close
proximity to the electrodes. The impedance relates to the property of the
material being
measured.
The configuration of the electrodes and the material form an equivalent
circuit which can
be represented by a capacitor and resistor in parallel. The material
capacitance
depends on the geometry of the electrodes, the dielectric constant of the
material, and
its proximity to the sensor. For a pure dielectric material, the resistance of
the material is
infinite between the electrodes and the sensor measures the dielectric
constant of the
material. Alternatively, for a highly conductive material, the resistance of
the material is
much less than the capacitive impedance, and the sensor measures the
conductivity of
the material.
In one embodiment, the sensor is used to measure the conductivity of an
aqueous
mixture (referred to as wetstock) in a papermaking system. In this case, the
conductivity
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CA 02557951 1997-12-12
of the wetstock is high and dominates the measurement of the sensor. The
proximity is
held constant by contacting the support web in the papermaking system under
the wet
stock. The conductivity of the wetstock is directly proportional to the total
water weight
within the wetstock, consequently providing information which can be used to
monitor
and control the quality of the paper sheet produced by the papermaking system.
In
order to use the present invention to determine the weight of fiber in a
wetstock mixture
by measuring its conductivity, the wetstock must be in a state such that all
or most of
the water is held by the fiber. In this state, the water weight of the
wetstock relates
directly to the fiber weight and the conductivity of the water weight can be
measured
and used to determine the weight of the fiber in the wetstock.
In another embodiment, the sensor is used to measure the weight of plastic. In
this
application the conductivity is negligible and the capacitive impedance is
inversely
proportional to the dielectric constant and the amount of plastic between the
electrodes
of the sensor.
In still another embodiment, the fixed impedance element is embodied as an
inductor
and the input signal is an analog signal. In this embodiment, the impedance of
the
inductor can be selected to be a particular magnitude by setting the frequency
of the
input signal. The advantage of this embodiment is that for optimum sensor
sensitivity
the impedance of the fixed impedance element can be set to the same range as
the
impedance of the sensor. Hence, in the case in which the impedance of the
sensor
varies due to fluctuations in operating conditions of the system or the
material being
sensed, the impedance of the inductor can be customized to match the sensor
impedance without any hardware changes.
The sensor apparatus of the present invention includes a sensor having a cell
array
including two elongated grounded side electrodes and a center elongated
electrode
spaced-apart and centered between the side electrodes. The center electrode is
made-
up of a string of sub-electrodes. A cell within the array is defined as
including one of the
sub-electrodes and the portions of the side electrodes situated adjacent to
the center
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CA 02557951 1997-12-12
sub-electrode. The sub-electrode of each cell is independently coupled to an
input
signal provided by a signal generator through an impedance element. In one
embodiment, resistive elements are used for each impedance element. Each cell
forms
a voltage divider network made-up of the resistive element coupled between the
signal
generator and the center sub-electrode of a given cell and of a resistance
resulting from
the effective water resistance between the center electrode and each of the
portions of
the side electrodes adjacent to the center electrode for the given cell. The
output of
each cell is taken from the center electrode, i.e. the point between the
resistive element
and the cell. As the conductance of the aqueous mixture changes so does the
output
voltage of the cell. The output voltage of each cell is coupled to a detector
which, in one
embodiment, includes circuitry for enhancing the signal such as an amplifier
for
amplifying the output signal from each cell and a rectifier. In one embodiment
of the
present invention the detector includes circuitry for converting the output
voltages from
each cell into data relating to the weight of the aqueous mixture or to other
aqueous
mixture characteristics.
The apparatus of the present invention may optionally include a feedback
circuit which
is used to adjust the input signal provided from the signal generator to
compensate for
changes in properties of the aqueous mixture that is not being sensed, but
that also
may affect the output voltages of the cells. The feedback circuit includes a
reference cell
having three electrodes in a similar configuration as a single cell within the
cell array.
The reference cell also has a center electrode coupled to the signal generator
through a
resistive element and is placed in recycled aqueous mixture from the cell
array and
consequently the reference cell is immersed in an aqueous mixture having
essentially
the same chemical and temperature properties as the aqueous mixture that the
cell
array is in. Furthermore, the characteristic that is being measured (e.g.
weight changes)
is held constant on the reference cell while all other characteristics which
may affect the
output voltage from the reference cell are allowed to fluctuate. As a result,
all voltage
changes from the reference cell are due to property changes of the aqueous
mixture
(e.g. temperature, chemical composition) other than the characteristic that is
being
measured (e.g. weight changes). The voltage from the reference cell is then
converted
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CA 02557951 1997-12-12
into a feedback signal and then used to adjust the signal from the generator
to
compensate for changes in aqueous mixture conductivity other than changes in
weight.
In another embodiment, the array is configured so as to have two elongated
electrodes;
a first grounded electrode and a second partitioned electrode made-up of sub-
electrodes. A single cell includes one of the sub-electrodes and the portion
of the
grounded electrode adjacent to the sub-electrode. As with the previous
embodiment,
each sub-electrode is independently coupled to the signal generator through
one of a
plurality of impedance elements and the voltage changes are detected on the
sub-
electrode.
A third embodiment of the cell array is for detecting changes in dielectric of
the material
between the electrode. This cell array includes first and second partitioned
elongate d
electrodes each made up of a set of first and second sub-electrodes,
respectively. A
single cell includes adjacent spaced-apart pairs of first and second sub-
electrodes. The
first sub-electrode in a given cell is independently coupled to the signal
generator
through an impedance element and the voltage changes are detected on the
second
sub-electrode in the given cell are due to changes in the dielectric constant
of the
material are directly proportional to the weight of the material between the
first and
second sub-electrodes.
In one embodiment of the present invention, the apparatus is used in a
sheetmaking
system which includes a web. The sensor is positioned under the web such that
it is
either parallel to the cross-direction or machine direction of the sheetmaking
system and
is in contact with the wetstock.
Brief Description of the Drawings
FIG. 1A shows a basic block diagram of the apparatus of the present invention
and 1 B
shows that equivalent circuit of the sensor block.
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FIG. 2 shows a prior art sheetmaking system including the sensor of the
present
invention in accordance with one implementation of the sensor of the present
invention.
FIG. 3 shows a block diagram of the sensor of the present invention including
the basic
elements of the sensor.
FIG. 4A shows an electrical representation of an embodiment of the sensor of
the
present invention.
FIG. 4B shows a cross-sectional view of a cell used within the sensor of the
present
invention and its general physical position within a sheeting system in
accordance with
one implementation of the sensor of the present invention.
FIG. 5A shows a second embodiment of the cell array used in the sensor of the
present
invention.
FIG. 5B shows the configuration of a single cell in the second embodiment of
the cell
array shown in FIG. 5A.
FIG. 6A shows a third embodiment of the cell array used in the sensor of the
present
invention.
FIG. 6B shows the configuration of a single cell in the third embodiment of
the cell array
shown in FIG. 6A.
FIG. 7 shows a basic block diagram of another embodiment of the present
invention.
Description of the Preferred Embodiments
The present invention relates to a sensor apparatus for detecting properties
of material
and, in one embodiment, for determining the weight of fiber in wetstock in a
sheet
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CA 02557951 1997-12-12
making system. In its broadest sense, the sensor can be represented as a block
diagram as shown in FIG. 1A, which includes a fixed impedance element (Zfixed)
coupled in series with a variable impedance block (Zsensor) between an input
signal
(Vin) and ground. The fixed impedance element may be embodied as a resistor,
an
inductor, a capacitor, or a combination of these elements. The fixed impedance
element
and the impedance of Zsensor form a voltage divider network such that changes
in
impedance of Zsensor results in changes in voltage on Vout. The impedance
block
Zsensor shown in FIG. 1A is representative of two electrodes and the material
residing
between the electrodes. The impedance block, Zsensor, can also be represented
by the
equivalent circuit shown in FIG. 1 B, where Rm is the resistance of the
material between
the electrodes and Cm is the capacitance of the material between the
electrodes.
The above-described sensor is sensitive to three physical properties of the
material
being detected: the conductivity or resistance, the dielectric constant, and
the proximity
of the material to the sensor. Depending on the material, one or more of these
properties will dominate. The material capacitance depends on the geometry of
the
electrodes, the dielectric constant of the material, and its proximity to the
sensor. For a
pure dielectric material, the resistance of the material is infinite (i.e.
Rm=~) between the
electrodes and the sensor measures the dielectric constant of the material.
Alternatively, for a highly conductive material, the resistance of the
material is much less
than the capacitive impedance (i.e. Rm«Zcm), and the sensor measures the
conductivity of the material.
To implement the above-described sensor, a signal Vin is coupled to the
voltage divider
network shown in FIG. 1A and changes in the variable impedance block (Zsensor)
is
measured on Vout. In this configuration the sensor impedance, Zsensor, is:
Eq. 1 Zsensor = Zfixed*Vout/(Vin+Vout).
The changes in impedance of Zsensor relates physical characteristics of the
material
such as material weight, temperature, and chemical composition. It should be
noted that
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CA 02557951 1997-12-12
optimal sensor sensitivity is obtained when Zsensor is approximately the same
as or in
the range of Zfixed.
In a physical implementation of the sensor shown in FIG. 1A for performing
individual
measurements of more than one area of a material, one electrode of the sensor
is
grounded and the other electrode is segmented so as to form an array of
electrodes
(described in detail below). In this implementation, a distinct impedance
element is
coupled between Vin and each of the electrode segments. In an implementation
for
performing individual measurements of more than one area of a material of the
sensor,
the positions of the fixed impedance element and Zsensor are reversed from
that shown
in FIG. 1A. In this implementation, one electrode is coupled to Vin and the
other
electrode is segmented and coupled to a set of distinct fixed impedances
which, in turn,
are each coupled to ground. Hence, neither of the electrodes are grounded in
this
implementation of the sensor.
In one particular embodiment, the above-described sensor is used for measuring
physical characteristics of an aqueous mixture (referred to as wetstock) in a
sheetmaking system by detecting conductivity changes of the wetstock.
FIG. 2 shows a typical sheetmaking system for producing a continuous sheet of
paper
material 18 including a headbox 10, a steambox 20, a calendaring stack 21, a
take-up
reel 22 and sensor array 23. In the headbox 10, actuators are arranged to
control
discharge of wetstock onto supporting web 13. The sheet 18 is trained to
travel between
rollers 14 and 15, and to pass through a calendaring stack 21. The calendaring
stack 21
includes actuators 24 that control the compressive pressure applied across the
paper
web. The finished sheet product is collected on a reel 22. In practice, the
portion of the
paper making process near a headbox is referred to as the "wet end", while the
portion
of the process near a takeup reel is referred to as the "dry end".
In one implementation, the sensor is mounted beneath supporting web 13 for
sensing
certain properties of the wetstock on the web. FIG. 3 illustrates a block
diagram of one
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CA 02557951 1997-12-12
implementation of the sensor apparatus including cell array 24, signal
generator 25,
detector 26, and optional feedback circuit 27. Cell array 24 is made-up of two
elongated
grounded electrodes 24A and 24B and center electrode 24C spaced apart and
centered
between electrodes 24A and 24B and made-up of sub-electrodes 24D(1 )-24D(n). A
cell
within array 24 is defined as including one of sub-electrodes 24D situated
between a
portion of each of the grounded electrodes 24A and 24B. For example, cell 2
includes
sub-electrode 24D(2) and grounded electrode portions 24A(2) and 24B(2). For
use in
the system as shown in FIG. 2, cell array 24 resides beneath and in contact
with
supporting web 13 and can be positioned either parallel to the machine
direction (MD)
or to the cross-direction (CD) depending on the type of information that is
desired. In
order to use the sensor apparatus to determine the weight of fiber in a
wetstock mixture
by measuring its conductivity, the wetstock must be in a state such that all
or most of
the water is held by the fiber. In this state, the water weight of the
wetstock relates
directly to the fiber weight and the conductivity of the water weight can be
measured
and used to determine the weight of the fiber in the wetstock.
Each cell is independently coupled to an input voltage (Vin) from signal
generator 25
through an impedance element Zfixed and each provides an output voltage to
voltage
detector 26 on bus Vout. Signal generator 25 provides Vin. In one embodiment
Vin is an
analog waveform signal, however other signal types may be used such as a DC
signal.
In the embodiment in which signal generator 25 provides a waveform signal it
may be
implemented in a variety of ways and typically includes a crystal oscillator
for generating
a sine wave signal and a phase lock loop for signal stability. One advantage
to using an
AC signal as opposed to a DC signal is that it may be AC coupled to eliminate
DC off-
set.
Detector 26 includes circuitry for detecting variations in voltage from each
of the sub-
electrodes 24D and any conversion circuitry for converting the voltage
variations into
useful information relating to the physical characteristics of the aqueous
mixture.
Optional feedback circuit 27 includes a reference cell also having three
electrodes
similarly configured as a single cell within the sensor array. The reference
cell functions
CA 02557951 1997-12-12
to respond to unwanted physical characteristic changes in the aqueous mixture
other
than the physical characteristic of the aqueous mixture that is desired to be
measured
by the array. For instance, if the sensor is detecting voltage changes due to
changes in
weight, the reference cell is configured so that the weight remains constant.
Consequently, any voltage/conductivity changes exhibited by the reference cell
are due
to aqueous mixture physical characteristics other than weight changes (such as
temperature and chemical composition). The feedback circuit uses the voltage
changes
generated by the reference cell to generate a feedback signal (Vfeedback) to
compensate and adjust Vin for these unwanted aqueous mixture property changes
(to
be described in further detail below). The non-weight related aqueous mixture
conductivity information provided by the reference cell may also provide
useful data in
the sheetmaking process.
FIG. 4A shows an electrical representation of cell array 24 (including cells 1-
n) and the
manner in which it functions to sense changes in conductivity of the aqueous
mixture.
As shown, each cell is coupled to Vin from signal generator 25 through an
impedance
element which, in this embodiment, is resistive element Ro. Referring to cell
n, resistor
Ro is coupled to the center sub-electrode 24D(n). The outside electrode
portions 24A(n)
and 24B(n) are both coupled to ground. Also shown in FIG. 4A are resistors Rs1
and
Rs2 which represent the conductance of the aqueous mixture between each of the
outside electrodes and the center electrode. The outside electrodes are
designed to be
essentially equidistant from the center electrode and consequently the
conductance
between each and the center electrode is essentially equal (Rs1=Rs2=Rs). As a
result,
Rs1 and Rs2 form a parallel resistive branch having an effective conductance
of half of
Rs (i.e. Rs/2). It can also be seen that resistors Ro, Rs1, and Rs2 form a
voltage divider
network between Vin and ground. FIG. 4B also shows the cross-section of one
implementation of a cell electrode configuration with respect to a sheetmaking
system in
which electrodes 24A(n), 24B(n), and 24D(n) reside directly under the web 13
immersed
within the aqueous mixture.
The above-described sensor apparatus is based on the concept that the
conductivity Rs
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CA 02557951 1997-12-12
of the aqueous mixture and the weight/amount of an aqueous mixture are
inversely
proportional. Consequently, as the weight increases/decreases, Rs
decreases/increases. Changes in Rs cause corresponding fluctuations in the
voltage
Vout as dictated by the voltage divider network including Ro, Rs1, and Rs2.
The voltage Vout from each cell is coupled to detector 26. Hence, variations
in voltage
directly proportional to variations in conductivity of the aqueous mixture are
detected by
detector 26 thereby providing information relating to the weight and amount of
aqueous
mixture in the general proximity above each cell. Detector 26 may include
means for
amplifying the output signals from each cell and in the case of an analog
signal will
include a means for rectifying the signal to convert the analog signal into a
DC signal. In
one implementation well adapted for electrically noisy environments, the
rectifier is a
switched rectifier including a phase lock-loop controlled by Vin. As a result,
the rectifier
rejects any signal components other than those having the same frequency as
the input
signal and thus provides an extremely well filtered DC signal. Detector 26
also typically
includes other circuitry for converting the output signals from the cell into
information
representing particular characteristics of the aqueous mixture.
FIG. 4A also shows feedback circuit 27 including reference cell 28 and
feedback signal
generator 29. The concept of the feedback circuit 27 is to isolate a reference
cell such
that it is affected by aqueous mixture physical characteristic changes other
than the
physical characteristic that is desired to be sensed by the system. For
instance, if
weight is desired to be sensed then the weight is kept constant so that any
voltage
changes generated by the reference cell are due to physical characteristics
other than
weight changes. In one embodiment, reference cell 28 is immersed in an aqueous
mixture of recycled water which has the same chemical and temperature
characteristics
of the water in which cell array 24 is immersed in. Hence, any chemical or
temperature
changes affecting conductivity experienced by array 24 is also sensed by
reference cell
28. Furthermore, reference cell 28 is configured such that the weight of the
water is held
constant. As a result voltage changes Vout(ref. cell) generated by the
reference cell 28
are due to changes in the conductivity of the aqueous mixture, not the weight.
Feedback
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signal generator 29 converts the undesirable voltage changes produced from the
reference cell into a feedback signal that either increases or decreases Vin
and thereby
cancels out the affect of erroneous voltage changes on the sensing system. For
instance, if the conductivity of the aqueous mixture in the array increases
due to a
temperature increase, then Vout(ref. cell) will decrease causing a
corresponding
increase in the feedback signal. Increasing Vfeedback increases Vin which, in
turn,
compensates for the initial increase in conductivity of the aqueous mixture
due to the
temperature change. As a result, Vout from the cells only change when the
weight of
the aqueous mixture changes.
One reason that the cell array is configured as shown in FIG. 3, with the
center
electrode placed between two grounded electrodes, is to electrically isolate
the center
electrode and to prevent any outside interaction between the center electrode
and other
elements within the system. However, it should also be understood that the
cell array
can be configured with only two electrodes. FIG. 5A shows a second embodiment
of the
cell array for use in the sensor. In this embodiment, the sensor includes a
first grounded
elongated electrode 30 and a second partitioned electrode 31 including sub-
electrodes
32. A single cell is defined as including one of the sub-electrodes 32 and the
portion of
the grounded electrode 30 which is adjacent to the corresponding sub-
electrode. FIG.
5A shows cells 1-n each including a sub-electrode 32 and an adjacent portion
of
electrode 30. FIG. 5B shows a single cell n, wherein the sub-electrode 32 is
coupled to
Vin from the signal generator 25 through a fixed impedance element Zfixed and
an
output signal Vout is detected from the sub-electrode 32. It should be obvious
to one
skilled in the field of circuit design that the voltage detected from each
cell is now
dependent on the voltage divider network, the variable impedance provided from
each
cell and the fixed impedance element coupled to each sub-electrode 32. Hence,
changes in conductance of each cell is now dependent on changes in conductance
of
Rs1. It should also be understood that the remainder of the sensor functions
in the
same manner as with the embodiment shown in FIG. 4A. Specifically, the signal
generator provides a signal to each cell and feedback circuit 27 compensates
Vin for
variations in conductance that are not due to the characteristic being
measured.
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It should be understood that the cells shown in FIGS. 5A and 5B may
alternatively be
coupled such that Vin is coupled to electrode 30 and each of sub-electrodes 32
are
coupled to fixed impedance elements which, in turn, are coupled to ground.
In still another embodiment of the cell array shown in FIGS. 6A and 6B, the
cell array
includes first and second elongated spaced apart partitioned electrodes 33 and
34,
each including first and second sets of sub-electrodes 36 and 35,
(respectively). A
single cell (FIG. 6B) includes pairs of adjacent sub-electrodes 35 and 36,
wherein sub-
electrode 35 in a given cell is independently coupled to the signal generator
and sub-
electrode 36 in the given cell provides Vout to a high impedance detector
amplifier
which provides Zfixed. This embodiment is useful when the material residing
between
the electrodes functions as a dielectric making the sensor impedance high.
Changes in
voltage Vout is then dependent on the dielectric constant of the material.
This
embodiment is conducive to being implemented at the dry end (FIG. 2) of a
sheetmaking system (and particularly beneath and in contact with continuous
sheet 18)
since dry paper has high resistance and its dielectric properties are easier
to measure.
In still another embodiment, the fixed impedance element is embodied as an
inductor or
capacitor and the input signal is an oscillating waveform as shown in FIG. 7.
The
advantage of this embodiment is that the fixed impedance of the inductor or
capacitor
can be set by adjusting the frequency of the input signal (Z~nductor =
L*2~Fv~n or Zap
=1/(2~Fvin *C)). Furthermore, for the case of measuring conductivity, changing
the
frequency of the input signal does not change the impedance of the cell. By
customizing
the impedance of the inductor or capacitor to be close to or approximately
equal to the
impedance of the sensor, optimal sensitivity is obtained. In addition, this
optimization
can be obtained without any hardware changes.
The foregoing has described the principles, preferred embodiments and modes of
operation of the present invention. However, the invention should not be
construed as
limited to the particular embodiments discussed. Instead, the above-described
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embodiments should be regarded as illustrative rather than restrictive, and it
should be
appreciated that variations may be made in those embodiments by workers
skilled in
the art without departing from the scope of present invention as defined by
the following
claims.
15
