Note: Descriptions are shown in the official language in which they were submitted.
1 BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to mobile grain
harvesting equipment and, more particularly, to combine
harvesters and the like in which means for improving the
efficiency of the grain separation or harvesting process is
provided.
2. Description of the Prior Art
A~ mobile combines are harvesting in the field, the
grain is threshed and separated from the straw and stored in
a storage bin within the combine for later delivery to ~nother
vehicle for transport from the field. This is the most
economical method for harvesting grain. In general, the
harvesting process of all combines is alike, that is, the
material harvested enters the conbine through a header portion
and is elevated through the ele~ator housing into the threshing
and separating units within the combine. The threshing and
separating units receive the unthreshed crop material and
generally separate the grain from the straw by means of a
rubbing or beating motion. The grain and other unthresed crop
material separated from the straw falls fron the threshing and
separating units onto the grain handling and cleaning means
while the straw is discharged from the rear of the threshing
and separating units onto a beater element which expels the
threshed straw through an opening in the hood of the combine.
~ he grain handling and cleaning means includes means
to separate the light straw material or chaff from the grain
and means to segregate the unthreshed material (known in the
art as tailings) from the grain in order to collect the clean
grain in a grain bin or tank located at the top of the combine.
.
1 The grain handling and cleaning means is generally conventional
and comprises oscillating grain pan and sieves and a fan for
the separation process. The grain pan, disposed beneath the
threshing and separating units, receives the threshed material
therefrom and discharges the threshed material to oscillating
sieves disposed rearwardly and below the grain pan. That is,
the vibration or oscillation of the grain pan causes the grain
and threshed material to move rearwardl~ to be discharged onto
the sieves below and thus subjected to the air flow from the
grain handling and cleaning fan. The fan, moreover, blows a
sufficient volume of air through ~he apertures provided in the
sieves to aerodynamically separate the grain from the chaff.
Accordingly, the chaff and other small trash material are
suspended in the airstream and are discharged through a rear
opening in the combine while the grain drops to the sieves
below. The first sieve or chaffer sieve is provided with
means for adjusting the apertures such that the grain received
thereon may fall therethrough while the larger trash material
is shaken rearwardly for discharge out of the combine. In
addition, the second or clean grain sieve disposed beneath
the first or chaffer si~vo includes adjustable apertures such
that only the grain drops therethrough to a guide where it
may be collected for elevation to the grain bin. Any larger
material (generally known in the art as tailings) discharged
onto the lower second sieve i9 discharged rearwardly and
collected within ~he combine to be elevated and discharged
into the feed section of the threshing and separating units
for reprocessing of the grain attached thereto. Thus, an
excellent separation or cleaning of the grain is obtained
along with a separate and rapid discharge of straw, trash
and chaff material from the combine.
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1 In certain operating conditions, however, perhaps more
often with ~ew high capacity combines wherein a large amount
of short straw is produced b~ the threshing operation and in
muddy conditions whereby the mud and straw combination form a
coagulated mass, the short straw or coagulated straw-mud mass
often overloads the cleaning and handling system. Eurthermore,
if the harvesting operation is being attempted at too great a
load for the cleaning means to handle, the threshed material,
including the chaff and straw, overloads the cleaning and
handling system. When the sieves become overloaded with chaff
and trash straw material or the coagulated straw-mud mas~,
separation of the grain is not performed and a short straw
and chaff material mat forms on the sieves further reducing
the separation process. In addition, as the mat is moved
rearwardly and discharged from the combine, some of the grain
entrained therein is also discharged or lost thereby raducing
the economic efficiency of the machine and from a practical
viewpoint reducing the over-all yi~ld of the harvest.
It has been noted that during the harvesting operation,
a localized straw mat buildup on the sieves effectively causes
a localized blockage of the air flow through the sieves
reducing the aerodynamic separation produced by the fan.
Further, as the flow of air through the sieves is blocked,
additional straw and chaff material collapse from the air-
stream onto the straw mat on the sieve forming a tighter
and larger mat which progressively grows along the sieve
reducing grain separation and increasing grain loss through
the rear of the combine. As the blockage of the sieve
increases, the increasing incoming material causes the
"collapsed area", that is, the area through the sieves in
3 ~
1 which there is no air ~low, to enlarge. In addition, the
tailings returns increase dramatically addiny more material
to the inconing flow. When the straw mat fills the sieve
blocking the front part thereof, pure aerodynamic separation
fails and the overload is complete. In ~his stage, the grain
is captured in the collapsed mat and rid~s over the sieve
and is discharged onto the ground.
Accordingly, there is a need tv provide means for
detecting the overload buildup or a localized blockage o~ the
sieves and to indicate this condition to the operator of the
combine.
5UMMARY OF THE INYENTION
According to the invention, apparatus is provided for
detecting and alerting tne operator of a combine harvester of a
sieve overload condition or formation thereof. Illustra~ively,
the apparatus of this invention comprises sensing means dis-
posed within the ombine to alert the operator of a sieve
blockage or overload condition.
Specifically, the apparatus of this invention comprises
a monitor circuit coupled to a sensor disposed within the
combine. The sensor is responsive to the air flow through the
sieves and provides signals indicative of the flow therethrough
and of blocked flow due to sieve blockage or overload. The
monitor circuit i8 responsive to the blockage signal and
provides a signal for operation of warning devices to alert
the operator.
More specifically, the apparatus of this invention
conprises a monitor circuit including equalizing means to
balance the sensor signal and to compensate the signal for
varying combine internal air temperatures. The monitor circuit
,
~3~
1 further includes a threshold circuit for establishing a
predetermined lower limit which if exceeded will be indicative
of sieve blockage, and a detector circuit for comparing the
wind sensor signals to the lower limit signals for fault or
blockage detection. If the detector circuit discovers a fault,
a signal is produced which activates the warning devices to
alert the operator before full sieve oYerload is e~tablishedO
The various features of novelty which characterize the
invention are pointed out with particularity in the claims
annexed to and forming a part of this specification. For a
better understanding of the invention, its operating advantage~
and specific bbjects attained by its use, reference should be
had to the accompanying drawings and descriptive matter in
which there is illustrated and described a preferred embodiment
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevation of a combine harvester,
partially in section, that embodies principles of the invention.
Figure 2 is a block diagram of the invention.
Figure 3 is a blown up view of a portion of the
internals of the combine of Eigure 1 showing the preferred
location of a portion of this invention.
Figures 4 through 8 are circuit diagrams of portions of
the block diagram of Figure 2.
DESCRIPrION OF THE_PR$FERRED E~BODIMENT
For a more complete appreciation of the invention,
attention is invited to the following description of an
illustrative embodiment of the invention. In the following
description, this invention is described in association with a
self-propelled combine harvester as described hereinabove.
- .
3~
lIt is noted that the direction of travel designated by arrow
A (Fig. 1) iS opposite to the direction of movement of the
crop material through the combine and, as the terms grain and
straw are used principally throughout the specification, it
should be understood that these terms are not intended to be
limiting. The term ~grain~' as used herein refers to all crop
material that may be threshed by the mechanism described
herein. Similarly, the term "straw" refers to all discardable
crop material.
10The com~ine harvester illustrated in Figure l includes
a mobile main frame or housing means 20 supported on front
drive wheels 21 and rear steerable wheels 22, the wheels being
traversely spaced apart on opposite sides of the fr~me.
crop elevator housing 23 and a header 24 are mounted on the
front of the main housing 20 to harvest the grain crop and feed
it to the threshing and separating units 26 mounted in the
main housing 20. The threshing and separating units thresh
and separate the grain from the crop material and discharge
the grainless crop material (straw) onto a rear beater 25 for
discharge from the rear of the combine, generally through a
large bottom opening in the hood 27. Grain cleaning means 28
are provided within the main housing for separating the straw
and chaff from the grain. An encasement 30 extends below the
main frame for housing a fan 32 and the grain and tailings
collecting means 34 and 36 respectively. On the top of the
combine i9 an engine 38 and a grain tank 40 with a hinged
unloadin~ auger, not shown. An operator~s cab 42 is mounted
on the front of the housing 20 a~ove the crop ele~ator housing
23.
30As indicated hereinabove, the threshing and separating
unit~ 26 separate the grain from the straw and discharge the
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1 grain and other crop bearing material onto the cleaning means
28. The cleaning means 28 includes a grain pan 44 and sieves
46 which cooperate with the fan 32 to clean the grain as
indicated previously~ The sieves 46, how~ver, may develop
- a localized blockage thereon of straw material which prevents
the cleaning means from separating the grain from the discardable
material. Furthermore, this localized blocXage or overload may
increase in size as more material collapses thereon effectively
blocking the entire sieve 46.
In accordance with this invention, apparatus 50 (Fig. 2) ~ -
is provided to indicate to the operator of the combine C that
a blockage or sieve overload is developing on the sieves 46
in order that the operator may taXe effective steps to prevent
sieve overload. The apparatus 50 comprises means 52 disposed
in cooperation with the air flow from the fan 32 to sense the
air flow, a monitor 54 coupled to the sensor means 52 and a
warning device 56 coupled and responsive to the monitor to
alert the operator of a localized sieve overload or mat-like
development on the sieves. As indicated in Fig. 2, the monitor
54 comprises an equalizing means 58 coupled to the sensing means
52 for balance and compensation as further explained herein.
The monitor further comprises a threshold means 60 coupled to
e~ualizing means 58 and a detector means 62, the detector means
62 being coupled to both the equalizing means 58 and the
threshold means 60.
In the preferred embodiment of the invention, the sensor
means 52 is disposed in the air flow from the fan 32 and,
more specifically, in the vicinity of the rear portion of the
sieves 46. Attention is invited to Fig. 3 in which is shown an
isometric blow up view of the threshing and separating units 26,
1 cleaning means 28 including fan 32, grain pan 44 and sieves 46.
In this embodiment of the invention, the sieves 46 are separated
into a plurality of longitudinal (with respect to the combine C)
sections, for example, Sl through S6~ and the sieves Sl through
S6 are separated by vertical slats as dividers 47. Within each
section (Sl-S6) a wind sensor 64 (only one being shown~ of
sensing means 52 is disposed in the air flow passing through the
cleaning sieves 46. Furthermore, although other locations for
and combinations of sensors are possible, in the preferred
~mbodiment o this invention, the wind sensors 54 are disposed
longitudinally across the rear portion of the sieves 46 (~ne to
each section sl-S6) as it has been found that the initial
localized blockage of the sieves occurs within this rear portion
thereof. The wind sensors 64 are attached to the underside of
the sieve within the air flow from ~he fan 32 such that it can
sense the air passing through the sieve without being disturbed
by the crop material itself.
In the preferred embodiment of this invention, the wind
sensor 64 comprises a D.C. powered positive temperature
coeficient thermistor 64A which provides a signal indicative
of the wind or air flow from the fan 32 through the sieve
sections (Sl~$6) of each respective thermistor by means of the
heat transfer from the thermistor. A particularly useful
characteristic of a positive temperature coefficient (PTC)
thermistor, as applied to this invention, is that the resistance
of the PTC thermistor increases ~o rapidly at its cnaracteristic
or operating temperature that the PTC thermistor seeks an
e~uilibrium near that characteristic t~perature substantiall~
independent of the heat loss from the surface of the thermistor.
In a "high" wind condition or for this invention a clean s~eve,
-8-
- 1 for example, the PTC thermistor maintains the characteristic
operating temperature by means o~ a lower electrical resistance
which draws more electrical power, balancing the heat loss.
Correspondingly, in a ~low~ wind, sieve blockage conditions, the
PTC thermistor resistance increases and the higher electrical
resistance reduces the electrical power to match the lower heat
loss. Although the PrC thermistor temperature is slightly
higher in the ~low~ wind condition, wind conditions hardly
affect or change the characteristic or operating temperature due
to the rapid change in resistance with temperature of the PTC
device. It is noted, moreover, that the current through the PTC
thermistor varies substantially with the wind conditions a~dat
a constant supply voltage the current is proportional to the
heat loss from the thermistor, as further explained herein.
Thus, it is noted that a positive temperature coefficient
thermistor is a sensor which seeks a certain operating
temperature or maximum temperature which substantially will not
vary at different supply voltage levels or as the heat transfer
therefron increases or decreases. Accordingly, a positive
temperature coefficient thermistor 64A offer~ a safety feature
not found in other types of self-heated heat transfer wind
sensors, such as a hot-wire aneomometer. That is, as the power
supplied to the sensor increases, the temperature thereof remains
substantially constant at its maximum operating temperature,
which may be selected in advance as a temperature su~stantially
below the ignition temperature of the material within the
combine, thereb~ preventing a disaster which could occur if
other typ~ self-heated or heat transfer sensors were used.
In the preferred embodiment shown in Fig. 3, the sensor
means 64 is attached to or mounted on the lower portion of the
1 sieve 46 through insulation means 66, such as a ~r plastic,
B which effectively insulates the thermistor 64A from the sieve
while securely fixing the thermistor within its respective
sieve section (Sl-S6) and within the air flow.
Attention is now invited to Fig. 4 wherein the sensor means
52 is shown including a plurality of wind sensors 64, one each
for each sieve 46 section Sl through S6. Each wind sensor 64
is coupled by leads a through f to the equalizing means 58.
Equalizing means 58 includes respective amplifier means 70a
through 70f, for each wind sensor 64, and a temperature bias
means 72. The ternperature bias means 72 includes a temperature
sensor 74 disposed within the combine C, preferably within the
vicinity of the cleaning means 28. The temperature sensor 74
is preferably an unheated thermistor exposed to the air
ternperature within the c~mbine. The temperature sensor 74 is
coupled in series with a resistor Rl and the cor~bination theEeof
is coupled in parallel with a resistor R2. One terminal of
sensor 74 and resistor R2 is grounded, whereas the other
terminal of resistor R2 is coupled in parallel to a resistor
R3 which is coupled to a D.C. supply not shown. The parallel
combination o resistors Rl,R2,R3 and sensor 74 is coupled to
the non-inverting terminal of an amplifier 76. The inverting
terminal of amplifier 76 is coupled to the output of amplifier
76 in a voltage follower manner. The output of the amplifier 76
is coupled to the inverting terminal of each amplifier means 70a
through 70f through resistor R4 for purposes explained
hereinbelow.
In the preferred embod~ment of the invention, each wind
sensor 64 of the ~ieve sections Sl through S6 are coupled b~ -
leads a through f, respectively, to the non-inver~ing terminal
--10--
~L~3~
1 of its respective amplifier means 70a through 70f. The amplifier
means for each sensor 64 (a through f) each includes the resistor
R4 coupled to its inverting terminal, as explained above, a
resistor R5 coupled in feedback relation from the output terminal
to the inverting terminal and a capacitor Cl also coupled in
feedback relation from the output terminal to the inverting
terminal. In addition, the amplifier means of 70a through 70f
includes a variable resistor R6 series coupled to resistor R5.
Thç respective amplifier means for each sensor 64 (a through f) -
each includes a resistor R2a through R2~, respectively, having one
terminal coupled to the non-inverting terminal of the respective
amplifier means 70a through 70f and the other terminal coupled to
ground. As explained hereinabove, at a constant supply voltage,
the PTC thermistor current is proportional to the heat loss from
the thermistor. Accordingly, the respective thermistor signal
of sensors 64 (a through f) coupled to respective amplifier means
is directly responsive to the th~rmistor current flowing through
respective resistors R2a through R2f. The output lead of each
respective amplifier means is labelled h through m respectively.
The output of the equalizer 58 is coupled to threshold means
60 and more specifically the respective outputs h through m are
coupled to a maximum signal circuit 80 Fig. S. The maximum signal
circuit 80 includes respective amplifier and diode combination 82h
through 82m having the diode output coupled together and the
combination coupled to the inverting terminal of the amplifier
and ground such that the output of the combination represents
the output from a perfect diode. The non-inverting terminal of
the respective amplifiers is coupled to the output of respective
amplifier means and, accordingly, the output signal from each
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1 individual wind sensor 64 of this preferred embodiment of the
invention i5 couplsd through its respective amplifier means 70a
through 70f to a respective amplifier-diode combination 80h
through 80m via its respective lead (h through m), Figures 4
and 5.
The output of the maximum signal circuit 80 is coupled
through a resistor R7 to a circuit 84, which includes a resistor
R8 and an amplifier 86 connected as a voltage follower, hav~g
an output lead n. One terminal of the resistor R8 is coupled
to a terminal of resistor R7 and the non-inverting terminal of
the amplifier 86, the other terminal of resistor R8 is coupled
to ground such that resistors R7 and R8 are coupled in a
common voltage divider manner.
Attention is now invited to Fig. 6 wherein the detector
means 62 is shown having input leads h through m coupled to
corresponding leads (h through ~) of equalizer 58 and an input
lead n coupled to the output of threshold means 60 or more
specifically output lead n of the circuit 84. The detector
means 62 comprises a comparator circuit 88 and, as shown in
this preferred embodiment of the invention, a comparator circuit
88h through 88m for each input lead h through m, i.e., for each
respective wind sensor 64. Each respective comparator circuit
88 comprises an amplifier 90h through m each having its
inverting te~ninal coupled to the respective input l~ad (h
through m) of equalizer 58 and its non-inverting terminal
coupled to the input lead n from the limiter circuit 84 through
a resistor Rg. The output of each respective amplifier is
coupled through a resistor Rlo to the non-inverting terminal.
The respective outputs o through t of amplifiers 90h through
90m of the comparator circuit 88 are coupled to the warning
means 56, as explained hereinbelow.
.
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1 The warning means 56 (Fig. 7) comprises switch means 92
responsive to the output from the detector 62. The switch
means 92 comprises respective transistors 940 through 94t, one
for each wind sensor 64 for each sieve location S1 through S6
having its base electrode coupled through a resistor R11 to the
respective input lead (o through t~ from the comparator circuits
88. The warning means 56 further comprises a signalling device,
such as a plurality of light emitting diodes 960 through 96t
coupled to a direct current power supply D.C. not shown and to
the respective collector terminals of the transis~ors 940
through 94t via a resistor Rl~. The emitter terminal of the
respective transistors is coupled to ground through a switch 98.
In this preferred embodiment of the invention, the warning
means ~6 further comprises a counter 100 which in this
embodiment of the invention is an analog type counter responsive
to the output leads o through t from detector 62 and an alarm
device 101 which may be a light, a bell or horn or both coupled
to a power supply not shown. The alarm device is also coupled to
the counter 100 through a switch 102 and to ground through the
switch 98.
In operation, the apparatus of this invention provides a
warning signal to the operator of the combine of a sieve
blockage or overload development, as described hereinbelow,
although it is apparent that the apparatu8 of this invention
could also provide in the alternative a signal to the fan 32 or ~.:
other means within the combine to remove the blockage. In
operation, the respective wind sensors 64, in particular, the
positive temperature coefficient thermistors 64A are provided
with power which heats the thermistor to a preselected operating
temperature substantially below the flash temperature of.the - -
1 crop and straw material within the combine. The sensors 64
provide a signal, responsive to the heat transfer therefrom, as
explained hereinabove, to the individual respective amplifiers
70a through 70f within the equalizer 58. In addition, the
ambi~nt temperature within the combine is sensed by the unheated
thermistor sensor 74 of the temperature bias means 72, which
provides a temperature bias signal Q to the inverting terminal of
the amplifier 70. This temperature bias signal or offset voltage
provides a ~emperature signal to the respective amplifiers which
compensates ~he heat transfer signal from the respective
thermi8tors for the ambient temperature within the combine and,
, . .. .
therefore, the signal from each wind sensor 64 is independent
of the 1mbient temperature within the combine. Further, this
offset signal Q is such that although the heated wind sensors
will produce a signal even when there is no wind or air flow
in a shutdown condition for example, the output signal from the
respective amplifiers on leads h through m will go to zero.
In this embodiment of the invention, the signal Q has the form:
/ 105 - T \
Q = Q ~ A J
where Q20 is the value of Q at 20C,
TA is the temperature of the air in the combine in
degrees ce~trigrade (C), and
105 and 85 are temperature values in (C), and
which is merely a corrected temperature signal, as a function
of the combine air temperature.
It is noted that the convective heat transfer from or to a
fluid to or from a heat transfer sensor is a function of the
temperature and the fluid flow. As the sensor temperature signal
has been compensated by the temperature bias signal or offset
signal Q, the outp~t from the respective amplifiers is a function
of the fluid flow, and in particular, the square root of the
wind speed.
3~
1 As there are six sieve locations Sl through S6 in this
preferred embodiment each having a respective wind sensor 64
producing an output on leads a through f, respectively, each
amplifier 70a through 70f may produce different initial signals.
Accordingly, balancing means, i.e., the variable resistors R6
previously mentioned in connection with amplifiers 70b through
70f are adjusted to balance ~he output signal from these
respective amplifiers to the output signal of amplifier 70a.
It is app~rent that this operation may be performed by any
standard or general electrical balancing or comparison technique.
Upon completion of the balancing of the respective individual
signals from the plurality of amplifier-sensor c~mbinations to
one particular amplifier-sensor combination, the output from all
of the amplifier sensors will be insensitive to uni~orm
disturbances, such as changes in combine fan, wind speed, as
well as to changes in combine air temperature, as previously
indicated.
The output signals from the respective amplifiers 70a through
70f are coupled via respective leads h through m to the maximum
signal circuit 80, or to the respective amplifier-diode com-
binations 82h through 82m such that the maximum output signal
from leads h through m is coupled to the circuit 84. ~lthough
it is noted that initially the amplifiers 70a through 70f are
balanced to provide uniform signals, in the event that a blockage
occurs locally in the sieves 46, the respective wind sensor 64 -~
associated with that location will detect that blockage and
provide a reduced signal.
The output signal from the maximum signal circuit 80 is
coupled through resistors R7 and R8 in a voltage divider fashion
preselected to produce a preselected output signal magnitude
-- . ., .. . . . - - ..
p~
1 fron amplifier 86 of circuit 84. Thls preselected signal
magnitude represents the lower limit signal, based on the
minimum wind speed, which the apparatus will sense without
setting off the alarm. For example, in t~e preferred embodiment
shown herein, t~e voltage divider resistors R7 and R~ were pre-
selected to produce an outpu~ signal P from amplifier 86 equal
to 0.633 times the maximum signal G of circuit 80. This signal
P - 0.633G, it is noted, is substantially equivalent to a 60%
loss in wind speed as measured by wind sensors 64 as the signal
thereof is a function of the square root of wind speed.
The output signals from respecti~e amplifiers 70a through 70f
and amplifier 86 are coupled to the detector 62, i.e., to
respectivs comparator circuits 88h through m,as previously
explained, wherein the wind sensor signals are each compared to
the lower ~imit signal P (0.633G) by the respective comparator
circuits. The output signal from the respective comparator ~-
circuits are each coupled to the warning m~ans 56 for alerting
the operator if the lo~er limit signal is greater than the wind
sen~or signal.
For example, assume that a localized sieve blockage has
occurred at the sieve location associated with wind sensor 64
coupled to lead f. Accordinqly, as the output of the respective
ampliier 70f associated therewith is a function of the s~uare
root o the wind speed, the output signal thereof will be reduced
from ~he signals associated ~ith the amplifier-sensor combinations
not so blocked. Thus, if the output signal of the blocked
amplifier-sensor of lead f is 0.5 that of the remaining
amplifier-sensor signals G, the following occurs. The maximum
signal circuit 80 and limiter circuit 84 produce a predetermined
signal of 0.633G. The detector circuit 62 compares each
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- ~ ,
, ', ~
1 respective input signal from the respective amplifiers 70a
through 70f with the lower limit signal of lead n to detect a
faul~, i.e., a blockage. As the signals from the wind sensors
64 on leads a tl~ough e are all approximately equal to G,
these signals when compared to the lower limit signal 0.633G
are greater than the lower limit and a ~Ow output or negative
polarit~ output signal is produced by the comparator circuits
88h through 8 ~ and is coupled to leads o through s. The low
or negative polarity output signals reverse biases the respective
transistors 940 through 94s preventing conductio~. As there is
no conduction through the transistors, the respective light
emitting diodes 960 thxough 96s do not illuminate, as there is
no blockage in their respective sieve sections to which the
operator should be alerted. However, as the signal from lead f
of a blocked sieve section is assumed equal to 0.5G (for this
illustration), the comparator circuit 88m associated therewith
through lead m will produce a HIG~ or positive polarity signal
when compared to the lower limit siynal 0.633G. $he HIGH or
positive polarity signal from t~e comparator 88 is coupled via
lead t to the respective traasistor 94t coupled therewith. The
HIGH signal forward biases the transistor allowing it to conduct,
thereby causing the respective lisht emitting diode to illumin~te
and warn the operator of a sieve blockage at that res~ective
sieve location in order that appropriate action may be taken.
Thus, the sensing means is used to detect the airstream gradient
a~ the sieves.
In addition, if one particular sieve location is not
significant enough to alert the operator to pursue appropriate
action, a counter 100 coupled to the comparator circuits via
respective leads o through t may count the number of sieve
_17-
~ .
- - :
1 locations which are blocked as determined by theoutput signals
on leads o through t and a~ap].y an appropriate signal when the
preselected number of blocked sieves is established. The signal
from the counter merely turns ~ON~ the switch 102 allowing
the alarm 101 to respond to aler~ the opera~or. Switch 98,
moreover, prevents the a~rm from working at the low wind speeds
which would occur when the fan is not operating.
Attention is invited to Fig. 8 in which the threshold
means 60 includes an average signal circuit 110 conprising
input loads h through m from the respective output of amplifiers
70a through 70f coupled through respective resistors R13 to the
non-inverting te~minal of an amplifier 112 coupled as a voltage
follower, for providing a signal M based on the average of the
input signals ~rom the respective wind sensors. In this
embodiment, the voltage divider resistors R7 and ~8 and
amplifier 86 of circuit 84 produce a preselected output signal
of .707M. This output signal is equivalent to a 50% reduction .
or loss in wind speed.
In accordance with this invention, apparatus for sensing
` 20 the blockage of the sieves and alerting the opePat~r
is provided.
_1~
