Underwire water weight turbulence sensor

A system and method of providing on-line turbulence measurements in a sheetmaking machine and using these measurements to perform on-line adjustments to turbulence-inducing and adjusting elements in the sheetmaking machine to optimize final sheet product quality. Turbulence measurements are obtained using water weight sensors in the wet-end of the sheetmaking machine and specifically under wire water weight measurements. Water weight readings are correlated to turbulence intensity levels by correlating ranges of water weights to intensity level intervals. A turbulence processing sensor sorts accumulated water weight measurement readings into intensity level intervals to obtain turbulence measurements or a turbulence profile. The turbulence measurements or profile is provided to a machine element controller which uses the measured turbulence information and target turbulence information to generate control signals. The water weight sensors can obtain independent machine direction (MD) and cross direction (CD) water weight measurements and consequently independent turbulence measurements can be determined so that turbulence can be controlled in both directions. Machine elements are controlled so that turbulence remains uniform across the CD and so that the MD turbulence profile is optimized to resemble a target profile.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to monitoring turbulence in a continuous 
sheetmaking machine process, and more particularly, to a sensor for 
monitoring turbulence on the wire of a sheetmaking machine using wet end 
measurements. 
2. State of the Art 
In the manufacture of paper using a continuous sheetmaking machine, a web 
of paper is formed from an aqueous suspension of fibers (stock). Stock is 
dispersed from a dispensing unit referred to as a headbox onto a traveling 
mesh wire or fabric and water drains by gravity and vacuum suction through 
the fabric. The web is then transferred to the pressing section where more 
water is removed by dry felt and pressure. The web next enters the dry 
section where steam heated dryers complete the drying process. The 
sheetmaking machine is essentially a de-watering, i.e., water removal 
system. In the sheetmaking art, the term machine direction (MD) refers to 
the direction that the sheet material travels during the manufacturing 
process, while the term cross direction (CD) refers to the direction 
across the width of the sheet which is perpendicular to the machine 
direction. Furthermore, in general, the elements of the system including 
the headbox, the web, and those sections just before the dryer are 
referred to as the "wet end". The "dry end" generally includes the 
sections downstream from the press. Papermaking elements and machines are 
well known in the art and are described, for example, in "Handbook for 
Pulp & Paper Technologists" 2nd ed., G. A. Smook, 1992, Angus Wilde 
Publications, Inc., and "Pulp and Paper Manufacture" Vol III (Papermaking 
and Paperboard Making), R. MacDonald, ed. 1970, McGraw Hill. Sheetmaking 
machines are further described, for example, in U.S. Pat. Nos. 5,539,634, 
5,022,966 4,982,334, 4,786,817, and 4,767,935. 
Sheet formation (i.e., small-scale basis weight variation) is a basic sheet 
property that has a significant effect on optical and strength properties 
of the final sheet product. Sheet formation improves when average floc 
(i.e., grouped masses of particles) size or density decreases. Although, 
the stock approach system (i.e., elements prior to the headbox which 
provide the stock) and the headbox are key elements in delivering uniform 
and maximum dispersed stock, this is usually not adequate to produce a 
well-formed sheet. In particular what is further needed is defloccuation 
wherein clumping of the stock particles in a non-uniform manner is 
minimized. Defloccuation or dispersion can be generated in a number of 
ways such as by turbulence-inducing elements below the forming wire, by 
shear inducing elements above the fabric (e.g., dandy roll or top former), 
or by shaking the wire. Moreover, turbulence-induced in a sheetmaking 
machine affects particle orientation which also determines sheet strength. 
In the art of making paper, sheet properties (such as sheet strength, 
thickness, and weight) are continually monitored and the sheetmaking 
machine controlled and adjusted to assure sheet quality and to minimize 
the amount of finished product that is rejected. This control is performed 
by measuring sheet properties at various stages in the manufacturing 
process which most often include basis weight, moisture content, and 
caliper (i.e., thickness) of the sheet, and using this information to 
adjust various elements within the sheetmaking machine to compensate for 
variations in the sheetmaking process. 
Typically, a scanning sensor is used to perform basis weight measurements 
of the finished sheet at the dry end of the sheetmaking machine. Scanning 
sensors are known in the art and are described, for example, in U.S. Pat. 
Nos. 5,094,535, 4,879,471, 5,315,124, and 5,432,353. The basis weight 
measurements obtained from the scanner are used to control elements in the 
sheetmaking machine to adjust basis weight, and hence, paper quality. 
To date, one property that has not been used to monitor on-line paper 
quality is wire turbulence. Instead, turbulence has been evaluated in an 
experimental environment to determine its effect on defloccuation and to 
determine optimum turbulence profiles. In particular, in the article 
"Turbulence Approach to Optimizing Fourdrinier Performance," by B. A. 
Thorp and R. A. Reese (Tappi Journal, March 1985, pp:70-73) turbulence is 
qualified by scale which is based on the number of peaks per unit area and 
by intensity which is based on the height of the peaks. Since these 
properties (i.e., scale and intensity) are based entirely on visual 
attributes, measurement of these properties are performed using equipment 
that will "stop" stock action to permit observation. Hence in this case, 
turbulence is evaluated using high intensity strobes and instant cameras 
with strobe flash units. Once photos are taken, they must be evaluated by 
a trained individual to count peaks per unit area and evaluate peak 
height. As can be imagined, turbulence measurements using this method are 
not immediately available and hence would not be suitable on-line 
information usable in a production environment. What would be desirable is 
to obtain on-line turbulence measurements so as to optimize papermaking 
system parameters in a production environment. 
SUMMARY OF THE INVENTION 
The present invention is a system and method for measuring water flow 
turbulence variations at the wet end of a sheetmaking machine and 
providing on-line control to elements in the system to establish an 
optimum turbulence profile so as to improve formation and strength of the 
finished sheet product. The sheetmaking machine is designed with 
non-scanning sensors which provide simultaneous multiple point wet end, 
water weight measurements across either/or both of the machine direction 
(MD) and cross direction (CD) of the sheetmaking machine. These water 
weight measurements are converted into turbulence measurements or a 
turbulence profile. The turbulence measurements or profile are used to 
adjust turbulence adjusting elements in the sheetmaking machine to improve 
sheet quality. The non-scanning sensors obtain independent MD and CD water 
weight measurements and hence can independently monitor and adjust 
turbulence in each of the cross and machine directions. 
The turbulence measurements are determined by relating water weight 
measurements to turbulence intensity. Accumulated water weight measurement 
readings from each sensor are sorted into predefined intervals of 
intensity in which each interval corresponds to a range of water weight. 
Intensity intervals range from low to high intensity where lower range 
intensity intervals correlate to lower water weight measurements while 
higher range intensity intervals correlate to higher water weight 
measurements. A count of the number of readings per interval is evaluated 
to obtain the turbulence measurement. In one embodiment, a predetermined 
number of water weight measurements taken by each sensor are divided into 
ten intervals of intensity, each interval correlating to a particular 
range of measured water weight. In still another embodiment, a single 
turbulence value is obtained by weighting intervals and adding all 
intervals to obtain a single value. 
In one embodiment, the turbulence measurements provided from more than one 
sensor are processed to obtain an on-line turbulence profile. In 
particular, the turbulence measurement from sensors in the CD, MD, or in 
an array configuration are used to generate a CD, MD, or three-dimensional 
profile of turbulence. A previously determined optimized target turbulence 
profile is compared to the measured on-line profile to obtain an error 
signal which is used as a feed back signal to control system operating 
variables. 
In a particular embodiment, a row of sensors is placed down each side of 
the wire and down the middle to obtain water weight measurements so as to 
generate turbulence measurements. In one embodiment, the wet end sensors 
are under wire water weight (UW.sup.3) sensors which are responsive to 
changes in conductivity of the aqueous stock material at the wet end of 
the system. 
In a measurement system embodiment, water weight measurements are provided 
to a turbulence sensor processor for generating turbulence measurements. 
The turbulence measurements are provided to at least one controller which, 
in response, provides on-line control signals for adjusting operating 
variables of the turbulence adjusting sheetmaking machine elements. In one 
embodiment, operating variables that can be adjusted by the on-line 
control signals include headbox pressure, headbox flow, headbox dilution, 
headbox airpad, and jet-to-wire ratio, slice geometry, slice lip 
"stickdown" position, machine speed, forming board position, amount of 
wire shake, and vacuum effect and position of drainage vacuum elements 
such as foils or vacuum boxes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is a system and method of obtaining on-line 
turbulence measurements and providing on-line control of turbulence 
adjusting elements in a sheetmaking machine to maintain good sheet 
formation. 
FIG. 1 shows a sheetmaking machine for producing a continuous sheet of 
material that comprises processing stages including wetstock source 
elements 10, headbox 11, web or wire 12, forming board 13, calendering 
stack 14, dryer 15, and reel 16. Actuators (not shown) in headbox 11 
discharge wetstock (e.g., pulp slurry) through a plurality of orifices 
referred to as slices onto supporting wire 12 which rotates between 
rollers 17 and 18. The speed at which the stock is discharged from the 
slice is called the slice jet velocity. The slice is completely adjustable 
to give the desired rate of stock flow. The slice geometry and opening 
determine the thickness of the slice jet, while the headbox pressure 
determines the velocity. Foil 19 and vacuum box 20 remove water, commonly 
known as "white water", from the wetstock on the wire into a wire pit (not 
shown) for recycle. Dry end BW measurements can be performed using 
scanning sensor 21 or using a UW.sup.3 sensor (as described herein). A 
scanning sensor 21 continuously traverses the finished sheet (e.g., paper) 
and measures properties to monitor the quality of the finished sheet. 
Multiple stationary sensors can also be used. Scanning sensors are known 
in the art and arc described, for example, in U.S. Pat. Nos. 5,094,535, 
4,879,471, 5,315,124, and 5,432,353, which are incorporated herein. The 
finished sheet is collected on reel 16. 
A plurality of sensors 23 provide multiple point simultaneous wet end water 
weight measurements independently in either/or both the machine direction 
(MD) and the cross direction (CD) in the wet end of a sheetmaking machine. 
The plurality of sensors detect changes in physical properties of the 
wetstock suspension traveling on a wire in the machine direction of the 
sheetmaking machine. The changes in detected physical properties are 
converted to water weight measurements 24 by sensors 23 which, in turn, 
are correlated to intervals of turbulence intensity level by water weight 
turbulence sensor processor 25. The turbulence measurement signal 25A is 
then provided to machine element controller 26. Controller 26 generates 
control signals (e.g., CD26C, MD26C, MD26D, MD26E, MD26A, CD26A, and 
MD26B) to control operating variables of machine elements affecting 
turbulence in the sheetmaking machine depending on predetermined target 
turbulence information 27. 
It should be noted that the position of the sensors shown in FIG. 1 
relative to the wire 12 between rolls 17 and 18 is not indicative of a 
specific placement. Instead, the sensors can be placed anywhere along the 
wire in which the wetstock is in a state such that all or most of the 
water is held by the fiber in the wetstock. Sensors can be arranged into 
an array of sensor cells or individually in either of the cross or machine 
directions. For instance, sensor cells can be configured in a CD array, 
further described herein. In this case, each sensor cell in an array is 
positioned below a portion of the wire in the cross direction which 
supports the wetstock. In one embodiment, a row of individual machine 
direction (MD) sensors are placed along each side of the array and down 
the middle of the array. A profile made up of a multiplicity of water 
weight measurements at different locations can be developed and used to 
determine a turbulence profile. 
It should be noted that the term "water weight" refers to the mass or 
weight of water per unit area of the wet paper stock which is on the wire. 
Typically, the sensors when positioned under the wire are calibrated to 
provide engineering units of grams per square meter (gsm). As an 
approximation, a reading of 10,000 gsm corresponds to paper stock having a 
thickness of 1 cm on the fabric. 
In one embodiment of the present invention turbulence sensor processor 25 
correlates water weight measurements into turbulence measurements by 
accumulating water weight measurement readings from each sensor during a 
given measurement time period. For instance, in the case in which three 
sensors reside along the side of the wire in the machine direction, each 
are providing many water weight readings to turbulence sensor processor 
25. In one embodiment in which under wire water weight (UW.sup.3) sensors 
(as described herein) are used, 1000 measurement readings per second, 
however it should be understood that the number of readings can be more or 
less than 1000 readings per second in other embodiments. Turbulence ranges 
(or intervals) of intensity are defined in terms of ranges of water 
weight. For instance, 10 intervals of turbulence intensity are defined 
such that each range corresponds to a range of water weight. The intensity 
intervals range from the highest intensity interval which corresponds to 
the heaviest water weight range to the lowest intensity interval which 
corresponds to the lightest range of water weight. A predetermined number 
of water weight measurement readings (in this example 1000) are sorted 
into each of the intensity readings. For instance, if the predetermined 
number of readings is 1000, then each of the 1000 measurements are sorted 
into an intensity level interval according to their weight. Table 1 
illustrates water weight measurement readings that are sorted according 
turbulence intensity interval/weight range. 
TABLE 1 
______________________________________ 
##STR1## 
______________________________________ 
I1 = water wt. 0 - water wt. 1 
I2 = water wt. 1 - water wt. 2 
I3 = water wt. 2 - water wt. 3 
. 
. 
. 
I10 = water wt. 9 - water wt. 10 
where water wt. (n) &gt; water wt. (n + 1) 
As can be seen in Table 1 each interval has a corresponding number of 
measurement readings (also referred to as a count or scale). For instance 
interval 1 (the lowest intensity level) has a count of 50 measurement 
readings. Interval 1 corresponds to weights that fall in the range of 
Wt.sub.0 through Wt.sub.1. The turbulence curve shown in Table 1 
represents the turbulence profile at the location of the sensor during the 
measurement time period in which the 1000 measurement readings were taken. 
It should be noted that in one embodiment the total range of weight of all 
of the intervals is based on the normalized average of the total number of 
measurement readings taken (e.g. 1000 readings), a maximum weight 
measurement reading, a minimum weight measurement reading, and the amount 
of turbulence seen by a given sensor. As a result, the range can be 
different for each sensor. For instance, the amount of turbulence (and 
hence water weight) measured closer to the headbox, and in particular the 
forming board, is typically greater than the turbulence seen at the end of 
the wire. Hence, a sensor positioned close to the headbox measures 
significantly greater weights than a sensor farther down the wire towards 
the dry end. Consequently, in one embodiment each sensor's weight range is 
set according to its position along the wire and average weight measured 
during a given measurement time period. 
One manner in which to determine the total weight range for a given sensor 
is to first determine an average weight measured by a given sensor. For 
instance, a given sensor may take 1000 readings having a given average 
weight during a measurement time period. After determining the average 
weight, a maximum weight (e.g. 10.sup.th interval weight, Table 1) and a 
minimum weight (e.g. 1.sup.st interval weight, Table 1) is selected. In 
one embodiment the selected minimum weight of the total weight range is 
open-ended, while the selected maximum weight of the total weight range 
corresponds to the measured maximum weight. The middle interval weight 
(e.g. 5.sup.th interval weight, Table 1) corresponds to the determined 
average weight of the total readings (e.g. 1000 readings). The total range 
can be constantly adjusted for each measurement time period, however, in 
general, a given sensor will typically maintain a given range due to its 
location if no other parameters in the sheetmaking system are adjusted. 
In one embodiment of a sheetmaking machine using the turbulence control 
system shown in FIG. 1, wire 12 is traveling at a speed of 2000 ft/min 
(approximately 33 ft/sec) and 1000 measurement readings are taken per 
second. For each 1000 measurement readings taken, 0.4 inch of the sheet 
passes over the sensor and consequently, for each measurement reading 
taken which occurs in 10 microseconds, 0.004 inch of the sheet passes over 
the sensor. The portion of the sheet being measured during the 10 
microseconds corresponds to the geometry of the sensor taking the readings 
which resides below the wire. 
Once sorted, the count of readings per intensity level interval is 
evaluated by turbulence sensor processor 25 so as to generate a turbulence 
measurement signal 25A. It should be understood that Table 1 illustrates 
the manner in which data is sorted, however, it should be further 
understood that this table need not be generated in order to correlate the 
water weight measurements into turbulence measurement readings. 
The turbulence measurement signal 25A represents many forms of turbulence 
information which depend on the manner in which the correlated turbulence 
intensity level readings are evaluated and processed by turbulence sensor 
processor 25. For instance, in one embodiment, signal 25A provides the 
turbulence curve (see Table 1) from each sensor for the measurement time 
period. This information is then processed by controller 26 to generate 
control CD and MD control signals. 
In another embodiment, turbulence measurement readings are obtained by a 
row of MD sensors during a measurement time period in which each sensor 
simultaneously obtains a set of turbulence measurement readings such as 
shown in Table 1. The measurement readings taken from each sensor during 
the measurement time period is processed so as to generate a single 
turbulence intensity value representing an intensity level of turbulence 
at that sensor in that time period. The collection of single turbulence 
intensity values from each MD sensor is then used to generate an MD 
turbulence profile for that time period. One manner in which to process 
the turbulence measurement readings from a single sensor collected during 
the measurement time period to obtain a single turbulence intensity value 
is to weight the contribution of certain of the intensity intervals shown 
in Table 1, and then add all of the intensity counts to obtain a single 
value as shown in the equation below: 
EQU I=W.sub.1 (I.sub.1 count)+W.sub.2 (I.sub.2 count)+W.sub.3 (I.sub.3 count) . 
. . +W.sub.10 (I.sub.10 count) 
where I.sub.1 count . . . I.sub.10 count are the number of readings falling 
into each of the intensity intervals and W.sub.1. . . W.sub.10 are each 
intensity interval's weighting factor. For intervals in which the most 
common turbulence occurs, the weighting factor is high. Whereas, extremely 
high or low turbulence intensity interval readings which are of no 
interest and rarely occur will have a low weighting factor. The single 
value obtained from each sensor for that measurement period is then used 
to generate a profile in the MD direction. 
An alternative manner in which to determine a single turbulence value is to 
determine the root mean square (RMS) of the water weight measurements 
obtained from each sensor within the measurement time period to obtain an 
average water weight value and then correlate that value to an intensity 
range depending on its weight. 
In one embodiment which includes three rows of sensors in the MD direction, 
one on each side of the wire and one down the middle of the wire, a three 
dimensional turbulence profile can be obtained. Finally a row of sensors 
can be placed across the wire in the CD direction to obtain a CD 
turbulence profile. 
In another embodiment, the sensors are embodied as small arrays of sensor 
cells at each sensor location (e.g., sensor locations 23, FIG. 1). For 
instance, sensor 23 in FIG. 1 in accordance with this embodiment would 
comprise a small array of sensor cells. 
The advantage of obtaining various profiles (e.g., MD, CD) is that each 
have different turbulence requirements. For instance, in general, an 
optimum MD turbulence profile has a higher turbulence initially at the 
beginning of the wire which peaks and then decays as it approaches the end 
of the wire. FIG. 2 shows various optimum MD turbulence profile examples 
which where developed by B. A. Thorp and R. A. Reese in "Turbulence 
Approach to Optimizing Fourdrinier Performance" (Tappi Journal, March 
1985, pp.70-73). The optimum CD turbulence profile, in contrast is uniform 
across the sheet. 
FIG. 1 shows control signals CD26A, MD26A, MD26B, CD26C, MD26C, MD26D, 
MD26E generated by machine element controller 26 in response to the 
measured turbulence signal 25A and target turbulence information 27. FIG. 
2 shows examples of optimized profiles that can be used for target 
turbulence information 27. As shown, turbulence profiles are optimized for 
different system types, sheet weights, operating conditions etc. It should 
be noted that other turbulence profiles may be developed other than those 
shown in FIG. 2. It should also be understood that target information 27 
may be embodied as a single turbulence measurement value instead of a 
profile. Using a target turbulence profile or measurement value (i.e., 
target turbulence information 27) and an actual measured turbulence 
profile or measurement value (i.e., turbulence signal 25A) an error signal 
is determined by controller 26 which in turn is converted into control 
signals MD26A-E and CD26A and C. It should be understood that the MD and 
CD control signals shown in FIG. 1 are representative of, in some cases, 
more than one control signal provided by controller 26. For instance, 
control signal CD26A represents all cross directional control signals for 
controlling the headbox. Consequently, although it is shown in FIG. 1 as a 
single signal, CD26A actually represents all control signals to the 
headbox for controlling turbulence in the cross direction. 
Some sheetmaking machine elements that can be controlled by controller 26 
to adjust turbulence include the headbox, the forming board, the wire, and 
the drainage vacuum elements. Each of these elements have operating 
variables that can be adjusted so as to adjust the turbulence created in 
the sheetmaking machine. 
Headbox operating variables that can be controlled to adjust turbulence 
include headbox dilution, headbox pressure, headbox flow, headbox air 
pads, and jet-to-wire ratio. 
Headbox stock dilution is varied by raising and lowering the slice opening 
of the headbox. Since the wetstock material addition rate is typically 
controlled only by the basis weight valve (not shown) which feeds the 
headbox, a change in slice opening mainly affects the amount of white 
water circulated from the wire pit. The addition of more white water can 
increase turbulence. Hence, adjusting slice opening is one manner in which 
to adjust turbulence. The CD headbox turbulence control signal CD26A is 
provided to headbox slices to affect cross-direction (CD) turbulence. In 
this case, the control signal represents a plurality of control signals 
for independently adjusting each of the plurality of slices to control CD 
turbulence. In one embodiment, the plurality of headbox slices each have 
associated actuators which are controlled by each of the control signals 
which adjust the slice opening size thereby independently adjusting the 
dilution of the wetstock in the CD direction for each slice segment and 
hence CD turbulence. The CD turbulence is adjusted to be constant across 
the CD of the machine. 
In a similar manner, the MD turbulence control signal MD26A controls a 
gross slice opening adjustment to adjust turbulence. In other words, the 
MD control signal is coupled to all of the slice opening actuators so as 
to open or close all slices by the same amount to adjust MD turbulence. 
The headbox slice geometry can also affect the turbulence. In particular, 
every slice has a top lip and an apron (bottom lip). FIGS. 8A-8C shows 
various slice designs. The top lip is adjustable up or down which 
determines the b geometry (i.e. the slice opening between the vertical lip 
and end of apron) and the apron is adjustable in the horizontal direction 
which determines the geometry L (i.e. the projection of the apron beyond 
the inner surface). The L/b ratio of the slice (also referred to as the 
slice geometry) affects the impingement angle of the stock on the wire and 
hence affects turbulence. Consequently, turbulence can be adjusted by 
adjusting individual or all slice geometries using control signals CD26A. 
Another manner in which to affect turbulence is to adjust the "stickdown" 
of the upper slice lip. Referring to FIG. 9, "stickdown" corresponds to 
how far the edge of the upper lip protrudes beyond the wall of the 
headbox. The "stickdown" has the effect of causing a backwash eddy which 
provides shear force turbulence. Hence, adjusting the upper lip of 
individual or all slices up or down with control signals CD26A can be used 
to adjust turbulence. 
In another embodiment, the MD control signal is used to control headbox 
total dilution flow by diluting the wetstock with recycled water that has 
drained from the wire during the formation process thereby affecting 
turbulence. In this case, the MD control signal MD26A controls a white 
water intake valve which determines the amount of white water routed from 
the wire pit under the wire which is used to dilute the wetstock in the 
headbox. 
The jet-to-wire ratio also impacts turbulence since the jet-to-wire ratio 
determines the force at which the jet impinges the wire. The jet-to-wire 
ratio can be changed by adjusting the wire speed or the jet speed. 
The wire speed is typically adjusted by changing the speed of the large 
rolls (17 and 18) at the beginning and end of the wire which it travels 
on. Often times the couch roll, (i.e., the end roll) controls the speed of 
the wire. Hence, in another embodiment of the control system shown in FIG. 
1, the MD control signal MD26B is coupled to and provides control to the 
electromechanical control system for driving rolls 17 and/or 18 so as to 
adjust the driver speed thereby adjusting the jet-to-wire ratio. 
The jet speed is not actually measured, but is inferred from the headbox 
pressure. Consequently, the jet speed is adjusted by fluctuating the 
headbox pressure. Headbox pressure and consequently jet speed is adjusted 
depending on headbox type. Specifically, open headboxes (i.e., non 
pressurized) rely on the height of the stock in the box to determine the 
pressure and hence the jet speed. Hence, in the case of open headboxes 
(i.e., non pressurized) control signal MD26A adjusts the level of wetstock 
in the headbox by controlling the wetstock intake valve. 
Pressurized headboxes are adjusted differently than open boxes. There are 
at least two types of pressurized-type headboxes including hydraulic and 
air cushioned. The pressure in the hydraulic pressurized headbox is 
directly dependent on the feeding pump pressure and hence headbox pressure 
(and turbulence) are adjusted by changing the pump pressure. Hence, to 
adjust the pressure in the hydraulic pressurized headbox, the MD control 
signal MD26A adjusts pump speed which in turn changes pump pressure of the 
feeding pump. 
Alternatively, in an air cushioned pressurized headbox, the pressure is 
dependent on the feeding pump pressure as well as the air in the space 
above the stock (referred to as the "air pad ") in the closed headbox. The 
"air pad " is adjusted by opening a regulator value to allow more air to 
enter or by increasing the level of the stock. Consequently, turbulence 
can be adjusted in an air cushioned pressurized headbox by applying 
control signal MD26A to the regulator valve to adjust the air pad, by 
adjusting the level of stock via controlling the basis weight valve with 
control signal MD26A, or by adjusting pump speed with control signal 
MD26A. 
The forming board in a sheetmaking system functions to sustain the initial 
impact of the jet impinging on the wire. The forming board also determines 
the amount of initial drainage that occurs, depending on its angle with 
respect to the wire. In general, less drainage means more dilution (i.e., 
more liquid) in the wetstock. More liquid allows for more turbulence. 
Alternatively, more drainage means less liquid and less turbulence. Hence, 
in one embodiment of the control system of the present invention, 
turbulence control signals MD26C and CD26C are used to adjust the angle of 
the forming board to control drainage and hence turbulence. In a 
particular embodiment of the present invention, hydraulic lifters 
mechanically attached to the forming board are controlled by control 
signal MD26C and CD26C to adjust the forming board angle. The angle can be 
adjusted in the MD so as to adjust the overall angle of the forming board 
to the wire with the MD26C control signal. The angle in the CD can also be 
adjusted with the CD26C control signal. For instance, one side of the 
forming board may be raised higher than the other side of the forming 
board. 
Vacuum boxes residing under the wire can be adjusted to remove more or less 
liquid to adjust turbulence by increasing and decreasing vacuum power. 
Hence, in another embodiment of the control system shown in FIG. 1, 
control signal MD26D controls the vacuum power of the vacuum boxes to 
adjust turbulence. 
Foils can also be adjusted to affect turbulence. Specifically, the angle of 
the foil with respect to the wire can be adjusted to create more or less 
turbulence. In addition, foils also function to create a vacuum beneath 
the wire. As a result, foil angles can be adjusted to create more or less 
vacuum causing more or less liquid drainage so as to decrease or increase 
turbulence. Hence, in another embodiment of the control system shown in 
FIG. 1 control signal MD26E controls the angle of the foils to adjust 
turbulence. 
Increasing and decreasing the speed of the sheetmaking machine also affects 
turbulence. The machine speed can be adjusted by adjusting the speed of 
both the jet and the wire such that the jet-to-wire ratio is preserved but 
the overall speed of the machine is increased or decreased. In this case, 
control signals MD26B (for adjusting wire speed) and MD26A (for adjusting 
jet speed) are used to adjust turbulence. As described above, the jet 
speed is indirectly adjusted by adjusting the headbox pressure and the 
wire speed is adjusted by the electro-mechanical control system for 
driving rolls 17 and/or 18. 
Turbulence can also be created by shaking the wire of the sheetmaking 
machine. Hence, in another embodiment of the present invention, control 
signal MD26B is used to control how much the wire is shaken to obtain a 
desired amount of turbulence. 
Under Wire Water Weight (UW.sup.3) Sensor 
In its broadest sense, the sensor can be represented as a block diagram as 
shown in FIG. 3A, 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, Zsensor, form a 
voltage divider network such that changes in impedance, Zsensor, results 
in changes in voltage on Vout. The impedance block, Zsensor, shown in FIG. 
3A 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. 3B, where Rm is the resistance of the 
material between the electrodes and Cm is the capacitance of the material 
between the electrodes. The sensor is further described in U.S. patent 
application Ser. No. 08/766,864 filed on Dec. 13, 1996, which is 
incorporated herein. 
As described above, wet end BW measurements can be obtained with one or 
more UW.sup.3 sensors. Moreover, when more than one is employed, 
preferably the sensors are configured in an array of sensor cells. 
However, in some cases when an array does not physically fit in a location 
in the sheetmaking machine, a single sensor cell may be employed. 
The 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=4) between the 
electrodes and the sensor measures the dielectric constant of the 
material. In the case of highly conductive material, the resistance of the 
material is much less than the capacitive impedance (i.e. Rm*Z.sub.cm), 
and the sensor measures the conductivity of the material. 
To implement the sensor, a signal Vin is coupled to the voltage divider 
network shown in FIG. 3A and changes in the variable impedance block 
(Zsensor) is measured on Vout. In this configuration the sensor impedance, 
Zsensor, is: Zsensor=Zfixed*Vout/(Vin-Vout) (Eq. 1). 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 optimal sensor sensitivity is obtained when Zsensor is 
approximately the same as or in the range of Zfixed. 
Cell Array 
FIG. 4 illustrates a block diagram of one implementation of the sensor 
apparatus including cell array 24, signal generator 25, detector 26, and 
optional feedback circuit 27. Cell array 24 includes 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 FIGS. 1 and 2, cell array 24 resides beneath and in contact 
with supporting web 12 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 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 water weight, the 
reference cell is configured so that it measures a constant water weight. 
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. 
Individual cells within sensor 24 can be readily employed in the system of 
FIGS. 1 and 2 so that each of the individual cells (1 to n) corresponds to 
each of the individual UW.sup.3 sensors in the machine or cross direction. 
The length of each sub-electrode (24D (n)) determines the resolution of 
each cell. Typically, its length ranges from 1 in. to 6 in. 
The sensor cells are positioned underneath the web, preferably upstream of 
the wet line, which on a fourdrinier, typically is a visible line of 
demarcation corresponding to the point where a glossy layer of water is no 
longer present on the top of the stock. 
A method of constructing the array is to use a hydrofoil or foil from a 
hydrofoil assembly as a support for the components of the array. In a 
preferred embodiment, the grounded electrodes and center electrodes each 
has a surface that is flushed with the surface of the foil. 
FIG. 5A shows an electrical representation of sensor cell array 24 
(including cells 1-n) and the manner in which it functions to sense 
changes in conductivity of an aqueous mixture (i.e., wetstock). 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. 5A 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. 5B also shows the cross-section of one 
implementation of a cell electrode configuration with respect to a 
sheetmaking machine in which electrodes 24A(n), 24B(n), and 24D(n) reside 
directly under the web 12 immersed within the aqueous mixture. 
The sensor apparatus is based on the concept that the resistance Rs 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 resistivity 
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 such as weight. 
FIG. 5A 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 water weight 
is desired to be sensed then the water weight is kept constant so that any 
voltage changes generated by the reference cell are due to physical 
characteristics other than water 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 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 for configuring the cell array as shown in FIG. 5A, 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. 6A 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. 6A 
shows cells 1-n each including a sub-electrode 32 and an adjacent portion 
of electrode 30. FIG. 6B 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 apparent 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. The remainder of the 
sensor functions in the same manner as with the embodiment shown in FIG. 
6A. 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. 
In still another embodiment of the cell array shown in FIGS. 7A and 7B, 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. 7B) 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 of a sheetmaking machine 
(and particularly beneath and in contact with the dry sheet since dry 
paper has high resistance and its dielectric properties are easier to 
measure. 
Hence, a system and method for measuring turbulence using water weight 
measurements and controlling turbulence is described. 
It should be understood that although the invention will be described as 
part of a fourdrinier sheetmaking machine, the invention is applicable to 
other sheetmaking machines including, for example, twin wire and multiple 
headbox machines and to paper board formers such as cylinder machines or 
Kobayshi Formers. Some conventional elements of a sheetmaking machine are 
omitted in the following disclosure in order not to obscure the 
description of the elements of the present invention. 
The foregoing has described the principles, preferred embodiments and modes 
of operation of the present invention. However, the invention should not 
be construed as being limited to the particular embodiments discussed. 
Thus, the above-described 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 the present invention as defined by the 
following claims.