Note: Descriptions are shown in the official language in which they were submitted.
573~3
The present invention relates to the art of qualita~
tively measuring the properties of wood pulp in a dilute stock
slurry. More specifically, the present invention relates to a
method and apparatus for photometrically identifying the per-
centage of shives in a stock flow stream.
As a broad generalization, the process of pulping wood
for papermaking comprises a series o~ chemical and mechanical
steps to disintegrate the natural state of wood into individual
or small bundles of cellulose fiber. However, since wood is not
a homogenous material, the standardized or uniform process of an
industralized pulp flow stream does not have the same result on
all elements of a tree.
One particular notable natural wood anomaly is the
occurrence of fi~er bundles bound together by transverse ray
cells. A singular, consolidated bundle grouping is known to the
papermaker as a "shive". Such transversely bound bundles are
extremely tenacious in their resistance to defiberizin~ processes.
Although wood pulp is normally screened one or more
times along the process stream, it is impossible to segregate
all shives having 4-8 mm length and 100 to 140 ~um width from
acceptable fiber bundles of less than half the shive size.
Nevextheless, it is important to the papermak~r that the pre-
sence of shives be maintained below a certain percentage quantity
in the stock due to their consequential deleterious effect on a
paper web.
The generally practiced industry technique for moni-
toring the relative presence of shives in a pulp stream is to
periodically count, manually, the individual shi~e incidence
in a standard area, randomly selected, sample of paper ~ade from
the pulp. This practice, of course, is extremely time consuming
109573t3
and occasions a large delay interim between the time that pulp
lands upon the papermachine and knowledgeable recognition of the
relative shive incidence. Consequently, it is not unusual that
machine operators will be plagued with web breaks and unacceptable
paper quality due to excess shives long before the cause of the
trouble is known.
Recently, work has begun on the development of more
timely techniques for shive monitoring. One published report of
such work is found in the October, 1975 journal of the Technical
Association of The Pulp and Paper Industry (TAPPI, ~olume 58, No.
10, page 120). This report describes an optical detector which
passes two perpendicularly disposed light beams in a common plane
transversely through a windowed conduit carrying a pulp sample
stream. Respective photodetector responses to the shading effect
of fibers crossing the beam paths are measured to yIeld a length,
width and thickness determination for each fiber, By means of
internally programmed limits, the event of a passing shive may be
immediately identified and counted. The frequency of such shive
counts is compared to the consistency and flow rate of the sample
which must be carefully controlled.
Although the aforedescribed optical shive counter manu-
factured by Tellusond of Stockholm, Sweden, is extremely accurate,
it is still a laboratory device which requires the isolation of a
pulp sample from the production flow stream for accurate consis-
tency and flow rate control.
Stock consistenciesina production flow stream are main-
tained in the range of 1 to 4~ based on dry ~iber weight.
However, the Tellusond shive counter requires a batch quantity
stock sample accurately measured to 0.01 g/~ and a 10 minute
processing period for each batch. These circumstances dictate
1~95738
an instrument preparation procedure which includes withdxa~al of
an adequate stock quantity of substantially unknown cons'~stency
from the production line, analyzing the sample for total fiber
content and accurately mixing a sufficient stock quantxty to an
accurately known consistency. This procedure may be mechanxzed
for an automatic sampling and measuring cycle but the necessary
support apparatus is elaborate and subject to considerable
maintenance.
United States Patent No~ 3,461J030 to M. A, Keyes
describes a different type of wood pulp slurry measuring device
which relies upon the dielectric quality of celluloæe to impose
a voltage variation between two electrodes ~s fibers suspended
in a known electrolyte are passed therebetween. Sim;~lar to the
Tellusond optical device, the Keyes instrument integrates a
cross-sectional area measurement of an individual fiber with a
transit time measurement to derive a volumetric conclusion. Con-
sistency of the slurry is obtained by combining the fiber volume
conclusion with a simultaneous slurry volume measurement, Although
the Keyes instrument is disclosed in the context of a consistency
measuring instrument, it is conceivable that it may be adapted
to shive measurement simply because it obtains a quantitative
measure of individual fiber or particle volume. Nevertheless,
the inventor did not disclose a recognition of this capacity or
how such an adaptation may be devised.
In light of such afor~described prior art, there here-
tofore remained a need for an instrument that will continuously
measure the relative presence of shives in a mill pr~duction
stock flow stream. The specification of this need by the pulp
and papermaking industry is further complicated by the absence
30 of a satisfactory pulp sampling technique that is simple, con~
10~5~3~3
tinuous and relatively maintenance free.
Cellulose fibers have an unusuall~ high affinity for
adhesion to each other and to foreign surfaces. Any surface
exposed to a pulp stream is ~uickly coated with a layered growth
of fiber. This growth continues un il other forces such as gra-
vity or fluid shear exceed the adhesion strength of the fiber
bond thereby causing a breaking off of an accumulated quantity.
Consequently, maintenance of a continuous flow stream of pulp is
a scalar and velocity design problem. Relatively small pipe-
lines will be quickl~ plugged by fiber accumulation if not self-
cleaned by an appropriately high flow velocity. For these reasons
it is difficult to continuously extract from a large production
line a small but representative sample of pulp for testing pur-
poses. Accordingly, it is also an objective of the present in-
vention to teach a method and apparatus for continuously extract-
ing a low quantity pulp sample that is representative of the
primary flow stream but will not plug.
According to the invention, there is provided a method
of determining the relative quantity of shives in a flowing pri-
mary stream of fibrous particles comprising the steps of extract-
ing a representative sample flow stream of fibrous particles with- -
ing the flow stream, adjusting the consistency of the sample flow
stream to 0.1% or less, conducting the consistency adjusted sam-
ple stream past a photodetector, obtaining a composite d.c. first
signal flow from the photodetector comprising a variable amplitude
pulse continuum wherein each pulse represents the passage of in-
dividual fibrous particles past the photodetector, the magnitude
of such amplitude variations being directly proportional to the
size of the fibrous particles, obtaining a second signal flow of
pulses from the first signal flow wherein each pulse in the se-
C
~S7313
cond signal flow represents a pulse in the first signal flow hav-
ing an amplitude greater than a reference amplitude, setting the
reference amplitude to a value representing the minimum size of
a shive particle, generating first and second time rate analog
signals from each of the first and second signals by counting
the number of pulses respectively therein within a common time
interval, and combining the first and second time rate analog
signals to obtain a ratio therebetween.
According to another aspect of the invention, an
apparatus for dete~mining the relative presence of shives within
a paper slurry of 0.1% consistency or less comprises a conduit
having a transparent photodetector window for carrying a flow
stream of the slurry therethrough, a photodetection cell compris-
ing a light source and light sensor for generating a first elec-
tric signal responsive to the quantity of source light received
by the sensor after passing through the window and a flow stream
of the slurry therein, signal discriminating means for segregat-
ing variable amplitude pulse components of the first signal from
an average d.c. value of the first signal and transmitting the
variable amplitude pulse component as a second signal, the vari-
able amplitude pulses being derived from the presence of parti-
culates in the slurry flowing past the window and blocking the
incidence of light on the sensor, the amplitude of each pulse
being directly proportional to the size of the respective parti-
cle, comparative discriminator means responsive to the second
signal to generate a third signal pulse for each pulse in the
second signal having an amplitude exceeding a predetermined refer-
ence value distinctive to a shive particle~ first pulse counting
means for cyclically determining the number of second signal p~ls-
es received thereby in a fixed time interval and emitting a
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~9573~
fourth signal that is cyclically adjusted and proportional to the
time rate flow of the first signal pulses, second pulse counting
means for cyclically determining the number of third signal pul-
ses received there~y in the same fixed time interval as applied
to the first pulse counting means and emitting a cyclically ad-
justed fifth signal proportional to the time rate flow of the
second signal pulses, and signal ratio ~eans for combining the
fourth and fifth signals to derive a relative proportionality
therebetween and emit a sixth signal proportional to the relative
proportionality.
According to a further aspect of the invention, an
apparatus for determining the relative presence of shives in a
production flow stream of paper pulp slurry comprises sample ex-
traction means for continuously extracting a sample flow of the
paper pulp slurry from within a pressurized conduit carrying the
production flow stream, sample conduit means for delivering the
sam~le flow through a photodetection window, photodetection means
comprising a light source and a light sensor operatively disposed
on opposite sidesof the window for generating a composite first
signal having a variable amplitude pulsing constituent responsive
to the passage of fiber particles through the window, the ampli-
tude of individual pulses being proportional to the size of res-
pective, individual particles, signal discriminating means for
segregating the pulsing constituent of the first signal from an
average d.c. value thereof and transmitting the pulsing consti-
tuent as a second signal, comparative discriminator means res-
ponsive to the second signal to generate a third signal pulse flow
wherein each third signal pulse corresponds to a second signal
pulse having an amplitude corresponding to a shive size particle
in the sample flow, first pulse counting means for cyclically de-
- 4b -
1~5738
termining the number o~ second signal pulses received thereby in
a fixed time interval and emitting a cyclically adjusted first
rate signal proportional to the time flow rate of the second
signal pulses, second pulse counting means for cyclically deter-
mining the number of the third signal pulses received thereby in
the fixed time interval and emitting a cyclically adjusted second
rate signal proportional to the time flow rate of the third sig-
nal pulses, and, signal ratio means for combining tile first and
second rate signals to derive a relatiYe proportionality there-
between.
According to another aspect of the invention, there isprovided an apparatus for determining the relative presence of
shives within a paper pulp slurry of 0.1% consistency or less
comprising, a conduit having a transparent photodetector window
for carrying a flow stream of the slurry therethrough, a photo-
detection cell comprising a light source and light sensor for
generating a first electric signal responsive to the quantity of
source light received by the sensor after passing through the
window and a flow stream of the slurry therein, signal filter
means for segregating variable amplitude pulse components of
the first signal from an average d.c. value of the first signal
: and transmitting the variable am~litude pulse component as a se-
cond signal, the variable amplitude pulses being derived from
the presence of particulates in the slurry flowing past the win-
dow and blocking the incidence of light on the sensor, the ampli-
tude of each pulse being directly proportional to the size of the
respective particle, comparative discriminator means responsive
to the second signal to generate a third signal pulse for each
pulse in the second signal having an amplitude exceeding a pre-
determined reference value distinctive to a shive particle,
- 4c -
1~95738
first pulse counting means for counting a predetermined number of
second signal pulses received thereby and emitting a gate signal
upon arrival at the predetermined number, second pulse counting
means for counting the number of third signal pulses received
thereby in a counting interim, the counted number of third sig-
nal pulses representing a ratio value of the number of shive par-
ticles per predetermined number of slurry particles, the second
pulse counting means including fourth signal means for emitting
a fourth signal proportional to the ratio value, and means res-
ponsive to the gate signal to terminate the counting interim andreset the first and second pulse counting means to a count re-
ference point.
In the preferred apparatus disclosed herein an extrac-
tion device directs a ~iber-free water stream across an open gap
within a large production flow stream of pulp into a sample ex-
traction conduit. Pressure on the fiber-free water stream is
significantly higher than the production line pressure to main-
tain a relatively low energy loss across the open gap. Principles
of fluid flow induction draw pulp fiber from the production stream
in the proximity of the gap to be carried along the extraction
conduit. Although consistency dilution occurs, the sample ex-
traction flow stream is sustained at a substantially constant flow
rate, therefore, the quantity of pulp extracted at any given mo-
ment may be directly related to the momentary production stream
- 4d -
,,
~ ~f3
~5738
consistency.
For purposes of shive density monitoring the sample
extraction flow stream is preferablyadjusted toprovide anapproxi-
mate 0.05%pulp consistency althoughthis valueis notparticularly
critical. A consistency o~ 0.1% or less is suitable.
The dilute sample is then conducted past a photometric
window between a light source and a single photodetector having
an approximate 1/2 inch (1.25 cm) flow channel gap ther~between.
Voltage measuring devices signify both the event of a
passing fiber or shive and the relative size thereof due to the
particle shadow on the detector. The magnitude of voltage res-
ponse to such passing shadows is directly related to the size of
the shadow and hence, the size of the particle. Since shives are
significantly larger than acceptable fiber bundles, the detector
voltage responses may be se~regated accordingly by appropriate
signal discriminating devices.
Simultaneously, signals proportional to the ab olute
or total particle flow rate are ratioed with the total shive
flow rate to yield a signal that is directly proportional to
the shive density in the sample stream.
Accurate knowledge of sample consistency is irrelevant
since the inven~ion relates a first countednumber ofparticles to
a second countednumber ofstives, the first numberbeing inclusive
of the second number. Consequently, the absolute quantity of
these numbers in the sense of consistency or dry pulp quantity
per unit slurry vo]ume is unnecessary to conclude the desired
objective of shive density.
Accordingly, a continuous indication of shive density
may be reported in such form as to automatically actuate
appropriate alarms when the density e~ceeds acceptable limits.
-- 5 --
~!
~9573~3 `
Moreover, the point in the production flow stream at which the
sample is extracted may be selectively chosen sufficiently far
upstream of the papermachine headbox so as to provide adequate
time for evasive or corrective action before a high shive densi-
ty increment of pulp enters the headbox.
Relative to the drawing wherein like reference charac-
ters designate like or similar elements throughout the several
figures:
FIGURE 1 is a piping schematic for the present pulp
sampling system;
FIGURE 2 is a longitudinal section view of the photo-
detecting window section of the continuous flow sample stream;
FIGURE 3 is a cross-sectional view of the sample stream
window taken along cut lines III-III of Figure 2;
FIGURE 4 is a signal flow schematic for the electronic
portion of the meter;
FIGURE 5 schematically illustrates an alternative por-
tion of the basic Figure 4 signal management system.
FIGURE 6 schematically illustrates a digital signal
embodiment of the system; and
FIGURE 7 is a comparative performance graph for the
subject invention.
The mechanical schematic of Figure 1 illustrates the
sample extraction system of the invention which may be inserted
through a single aperture 11 in a production stock line pipe or
vessel wall 10. The wand 13 of the extractor comprises a small
conduit 14 for the delivery of fiber-free water at a relatively
constant flow rate to a discharge nozzle 15 which is axially
aligned with a square cut opening 16 of extraction conduit 17.
A gap 1~ is provided between the tip of nozzle 15 and
113~5738
opening 16. This gap 1~ is positioned centrally within the
stock line 10 to be swept by a representative flow of the stock
therein. Regarding cross-sectional placement of the gap 18
within the production line, the usual instrumentation caveats
apply such as avoidance of flow stagnation regions in pipe bends
and near the side walls.
Grommet 19 provides a fluid pressure seal of the
aperture 18 around the conduits 14 and 17.
There is little criticality in the design parameters
of the sample extraction system except that the clear water
supply pressure in conduit 15 should be substantially greater
than that of the stock line pressure. The system bears resem-
blance to a conventional jet pump or aspirator except for the gap
18. In the case of jet pumps and aspirators, release of the
energy carrying jet stream occurs within the boundary confines
of a larger volume induction chamber to provide a localized low
pressure zone having communication with the induced fluid. None
of the energy carrying induction fluid is lost from the flow
system and no intermingling of the induced and induction fluids
occurs outside of the induction chamber boundary. In the case
of the present invention, intermingling of the induced and
induction fluids occurs in the relatively infinite volume of
the induced fluid vessel. Moreover, induction fluid may be,
and in all probability is, lost from the total flow stream.
Although energy efficiency of the present invention is less than
that of jet pumps and aspirators, this circumstance is, in ab-
solutes, insignificant or irrelevant to the objective of ex-
tracting a low volume sample flow from the 1% to 4~ consistency
main stream 10 free of pipe plugging concerns~
In a representative actual use of the invention, a 1/4
~,
1C~9573~3
inch conduit 15 carrying a 1 gpm flow rate at 50 psi discharged
a jet stream across a 3/4 inch gap 18 through and transversely
of a 4.5% consistency, 0.5 psi pulp flow stream into the bare
open end of a 1/4 inch conduit to lift an approximately .5 to
1.0~ consistency pulp sample through a 10 foot head.
Of course, system designs may be optimized from the
perspective of minimum energy loss across the gap 18 and maxi-
mum total head and velocity within the extraction tube 17.
However, from the specific example described, simple experimen-
tation will usually provide an operative system suitable forthe following objectives.
As a further note to the sample extraction system,
the described circumstance of jet stream discharge nozzle 15
having the same dimensional size as the sample line 17 capture
opening 16 should not be considered as a limiting specification
since relatively larger area capture openings 16 are known to
operate well and in some circumstances, with greater efficiency.
Similarly, divergent capture openings 16 have been success-
fully utilized. Such divergent opening arrangements are phy
sically configured to a converge-divergent venturi with the
throat region removed to accommodate the mixing gap 18.
The extracted sample flow in conduit 17, if within
the broad consistency range of less than 0.1% tolerated by the
shive meter, may be delivered directly through a transparent
window pipe section 30 between a light source 31 and a photo-
detector 32. ShouId consistency of the extracted stock sample
prove greater than the suggested maximum, additional dilution
water may be added at a mixing point 33.
The window section 30 of the sample line 29 shown by
Figures 2 and 3 may be simply devised from a short section of
- 8 -
s738
1/2 inch i.d. thermoplastic tubing having a heat formed section 33
with generally parallel opposite side walls 34. To the outer
surface of these parallel side walls 34 are bonded light source
and detector elements 31 and 32. Prototype instruments used an
Optron Inc., 1201 Tappan Circle, Carrollton, Texas 75006, OP214
LED light emitting diode for the light source 31 and a correspond-
ing Optron Inc. OP603 light responsive diode for the detector 32.
Signal processing circuitry for the invention is schemat-
ically represented by Figure 4 which shows the variable amplitude,
direct current signal output of the sensor 32 first received by
an amplifier Al which increases the signal strength to a suitably
higher value. National Semiconductors Ltd. of 331 Cornelia St.,
Plattsburgh, N. Y. manufactures an amplifier model LM 747 suit-
able for use in the Al application.
The average d.c. value signal output of amplifier Al is
inverted and further amplified by an amplifier A3 such as the
National Semiconductors model LM 751CV to power the light source
31 in such a way that a constant or steady-state average quanti-
ty of light is maintained on the sensor 32 notwithstanding water
color, internal surface slimeing of the sample tube 29 or ageing
of the light source 31.
Capacitance C filters the total signal fram amplifier
Al to pass only pulse constituents due to shadows across the
sensor 32 when particles in the slurry pass between the source
31 and sensor 32.
Amplifier A2 further magnifies the filtered pulse
signal for amplitude discrimination by comparative amplifiers
CPl and CP2. These amplitude comparison devices are of a type
such as the National Semiconductors model LM 319D which compare
each incoming pulse from amplifier A2 with a predetermined re-
,~..i,
~9573~3
ference value rl and r2, respectively, and emit a correspondingpulse only if the incoming pulse equals or exceeds the reference
value. In the present invention, the reference value of rl is
set four to five times greater than the value of r2 so that CPl
will transmit only those high amplitude pulses which signify
the passage of a shive. Simultaneously, the value of r2 is set
so that CP2 will transmit pulses representative of both fiher
and shives.
~espective outputs from the comparative amplifiers
CPl and CP2 are conducted to pulse generators PGl and PG2 such
as the Signetics Corp., Wolf Rd. and Arques Ave., Sunnyva]e,
Calif., 555 timer which emits a constant amplitude, constant
width, square wave pulse in response to each variable width,
pulse received. These square wave pulses are repetitively
averaged over brief intervals, 50 seconds for example, by ampli-
fiers A4 and A5 such as the Analog Devices Inc., Rte. 1,
Industrial Park, P.O. Box 280, Norwood, Mass. 02062, AD 504 J
which provides an analog responsive voltage variation propor-
tional to the instant pulse receipt rate. At this juncture,
the variable voltage signal of amplifiers A4 and A5 may be
assigned a dimensional proportionality such as volts per shive
per second in the case of A4 or volts per particle per second
in the case of A5. These dimensions correspond to the fact that
the momentary flow rate of both shives and total particles is
being determined by an absolute event count over a brief time
interval. The voltage of amplifiers A4 and A5 directly corres-
ponds to the magnitude of the event count.
These voltage signals from the amplifers A4 and A5
may be directly combined in a division function by ratio circuit
R such as an Anaiog Devices Inc., supra, AD530 which delivers a
~- - lG ~
1~57;~
DC voltage signal proportional to the shive flow rate divided by
the particle flow rate, a dimensionless value of the stated
objective.
This dimensionless ratio signal may be further ampli-
fied by A6 to proportionately actuate an appropriately calibrated
meter 40 or chart recorder 41.
Similarly, the ratio signal may be processed by a
voltage comparison circuit CP3 similar to those of CPl and CP2
which actuates an alarm 42 when the ratio signal value rises
above an acceptable reference magnitude r3.
A digital signal management technique suitable for the
present invention is represented by Figure 6. As in the Figure -~
4 analog system, comparative amplifiers C~l and CP2 issue a pulse
for each shive and particle, respectively. Responsive to a
particle pulse tr~in of n fiber pulses received by digital
counter DC 2, a gate pulse g.p. is issued to digital counter
DCl which is simultaneously counting the receipt of shive pulses.
The beginning and end of gate pulse g.p. are used to start and
stop the counting function of DCl.
At the end of each gate interval, the accumulated
shive count in DCl, which represents the number of shives per n
fiber particles, is transferred to a latch and display module
DDl. Receipt of the shive count by DDl initiates transmission
of a reset signal to the counters DCl and DC2 from a reset
generator RG thereby resuming the particle and shive pulse
counting interims.
This Figure 6 digital embodiment of the invention
provides the papermaker with a digital display of the objective
dimensionless shive ratio.
Another signal management technique adaptable to the
:~.
1~S~38
invention relates to a logari~hmic scale of relative shive in-
cidence. A logarithmic standard for acceptable pulp is sub-
jective in that a plurality of pulp grade ranges are established
above a worst-condition reference grade. Such a standard may
begin with a sample of the highest shive incidence pulp a par-
ticular mill is known to produce. A standard handsheet is formed
from this first sample and retained for future reference.
A portiOn of the first sample is diluted with shive-
free pulp at some convenient ratio, 1:1 for example, to obtain
a second sample from which a second, reference handsheet is
formed and retained.
This process is repeated until a handsheet is formed
which represents the lowest shive incidence pulp the mill is
known to produce.
Although any dilution ratio may be used, the 1:1
ratio example represents a logarithmic system to the base 2
wherein each grade above the reference has half the absolute
number of shives as the next grade lower. Distinctive about
the log base 2 scale is that the human eye can consistently
discern and accurately classify a handsheet from an unknown
sample by mere visual comparison with the retained reference
samples. Moreover, the degree of accuracy obtained is suffi-
cient for most papermaking purposes.
Relating the present invention to such a shive in-
cidence standard, simply involves insertion of a log circuit L
of the desired base in the signal flow stream following the
ratio circuit R as represented by the dotted line arrow in
Figure 4. Such circuits are standard modular components of
the type manufactured by Analog Devices Inc., supra, as catalog
number AD755.
- 12 -
,
7;~
By converting the arithmetic ratio of shive incidence
in a stock flow stream to the logarithm of that ratio, the total
response scale of the instrument is greatly reduced and thereby
-more meaningful for production line consideration.
Another obvious variation of this theme, shown by
Figure 5, is to convert the output signal of both A5 and A6 to
proportional log functions by circuit modules Ll and L2 such
as the Analog Devices AD756P similar to L above and merely
subtract, by means of a simple summing circuit ~, one signal
from the other. The resulting difference is the same logarithm
of the arithmetic ratio described above.
The graph of Figure 7 represents typical performance
of the invention as applied to a mill production stock stream.
The graph ordinate scales laboratory determination of shive in-
cidence in a given pulp sample by skilled personnel. The graph
abscissa scales the response of the subject inventlon to the
same pulp sample. Comparison with the ideal correspondence
rate illustrated by the dashed line testifies to the invention
accuracy over a widely varying range of shive incidence.
In summary, therefore, the invention provides a direct,
continuous sampling technique for extracting a representative
fraction of a production flow stream for test purposes.
The shive meter, per se, detects and counts
particlespassing the window zone 33 by virtue of the shadow
cast thereby on the photodetector cell 32. Simultaneously,
shadows due to shives which are at least four times as great
as shadows due to accepta~le fiber bundles are discriminated
exclusively on the basis o~ shadow size in a single light plane
without regard to total volume~
-13-
~6~9573~3
Signal management techniques filter and screen the
composite signal from the photodector to separate base level
d.c. values from the pulse values caused by passing particle
shadows. Whether the particle source of the passing shadow
was a shive or a fiber bundle is determined by the relative
amplitude of the consequent pulse. Total particle pulses are
inventoried along one signal line whereas shive particle caus-
ed pulses, simultaneously included with the total inventory,
are separately inventoried along another, parallel signal line.
The number of pulses in each signal line is counted
over a fixed time interval identical to both lines. Thereby,
corresponding pulse rates are provid~d. Division of one pulse
rate by the other provides a dimensionless ratio between the
two as a quantified indication of the relative shive incidence
in the flow stream.
Note will be taken that this approach to the objec-
tive is independent of stock consistency beyond the point that
two or more particles will cast a single shadow on the detec-
tor. This circumstance occurs with consistencies of greater
than 0.1%. Therefore, so long as the sample consistency is
less than 0.1~, consistency or flow rate variations are
immaterial.
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