Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 91/06372 2 0 7 2 1 2 9 Pcr/US90/03748
, _A
MULTIPLE R~PPER CONTROL FOR ELECTROSTATIC PRECIPITATOR
F~ack5~ronn(1 ~n(l Sllmm~y of the Invention
This invention relates generally to electrostatic pre~ ilators for air pollution5 control and, more specifically, concerns the control of the rapping process used to
clean the internal collection plates and discharge electrodes of electrostatic
preci~ilatol~.
Continllous emphasis on environmental quality has resulted in increasingly
strenuous regulatory controls on industrial emissions. One technique which has
0 proven highly effective in controlling air pollution has been the removal of nn(lesirable
particulate matter from a gas stream by ele~ oslalic precipitation. An electrostatic
precipitator is an air pollution control device designed to electrically charge and
collect particulates generated from industrial processes such as those occurring in
cement plants, pulp and paper mills and utilities. Particulate laden gas flows through
the precipitator where the particulate is negatively charged. These negatively charged
particles are attracted to, and collected by, positively charged metal plates. The
cleaned process gas may then be further processed or safely discharged to the atmos-
phere.
During co~llinuous operation of an eleclroslalic precipitator, the collector
20 plates, electrodes and other precil~ilator internal components must be periodically
cleaned to remove the dust build-up which ~qccnmlllates on these surfaces. The
cleaning mech~ni~m typically co"sisls of a mechanical rapper. An electronic rapper
controller determines the sequence, intensity, and duration of rapping. Once theparticulate is dislodged from the plates, it falls into collection hoppers at the bottom
25 of the precipitator.
Rappers are electromerll~nical devices that are used to mechanically dislodge
collected particulate/materials within an electrostatic precipitator, electronic filter or
dust collector (hereafter referred to as ESP) by applying direct current (DC) ener-
gization to the rapper. In general, a rapper Collsis~s of a hammer that mechanically
30 strikes an anvil. The anvil is mechanically connected to the internal components of
the ESP, such as the discharge electrodes, collecting plates, gas distribution devices
or any other component cleaned by the rapper. Striking the rapper shaft or anvil with
the hammer llan~ll,ils mechanical forces to these components to dislodge collected
materials. Several rapper variations exist which may be employed in the cleaning35 process.
One rapper variation consists of a cylindrical hammer or plunger and solenoid
coil. The hammer rests on the rapper shaft or anvil. When the solenoid coil is
O 91/06372 PCr/US90/03748
Z072~ 29
energized with a DC voltage the resulting electromagnetic force ~vercollles the force
of gravity and lifts the h~mmer vertically to a height that is determined by theamplitude and length of time of the energization. When said energization is ter-min~terl, the electromagnetic field is removed and the h~mmer drops due to gravita-
s tional forces and strikes the anvil. The hammer then rests on the anvil until the next
energization.
Another rapper variation places a spring behind the cylindrical h~mmer. Whenthe solenoid coil is energized with a DC voltage the reslllting electromagnetic force
will overco",e the force of gravity and lift the h~mmer vertically co",~ressing the
10 spring against the rapper assembly. The height and spring co",~ression are deter-
mined by the amplitude and length of time of the energization. When the energization
is te"";"~led the h~mmer strikes the anvil with a force that is comprised of gravita-
tional force plus the spring expansion.
Another rapper variation places a spring behind the cylindrical h~mmer. This
5 spring is connected to the hammer and holds it above the anvil. When the solenoid
coil is energized with a DC voltage the resulting electromagnetic force will overcome
the force of the spring and accelerate the h~mmer dowl,w~rd to strike the anvil. When
the energization is te, ,..i ,l~te~l, the h~mmer is returned to position by the spring.
The energi~ation of the rapper solenoid coil inllllce~ a flow of electromagnetic20 flux around this coil and which also flows through the cylindrical h~mmer and other
rapper components. In addition, there are stray undesirable flows of electromagnetic
flux some of which pass through the anvil assembly. The amount of lmdesirable
electromagnetic interaction with the anvil and other components is dependent upon
the type and construction of the rapper.
2s Since the energization is DC, and therefore unipolar (i.e., one direction), the
components are exposed to repeated electromagnetic energization with the same
orientation of North and South poles. To illustrate, the electromagnetic flux flow
radiates from the coil in the same direction every time it is energized. The flow
direction moves oulw~rd from the coil and around to the bottom of the anvil through
30 the anvil's top, then u~w~rd through the bottom of the h~mmer and out through its
top. Because the h~mmer and anvil are separated, each will have a North and South
pole. As this unipolar energization is repeated, the North and South poles of both the
h~mmer and anvil become stronger until they retain their magnetic orientation. As
stated by Lenz's Law, this induced magnetic effect is proportional to the amount of
35 energy used to create it and will, therefore, oppose it with like force. On successive
energizations, therefore, this residual magnetization will oppose lifting the hammer
to its desired level. This is particularly true when the hamrner rests on the anvil.
WO 91/06372 ,2 ~ '7 2 129 PCI/US90/03748
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The result of this residual magneti_ation is that the anvil and h~mmer are of
different poles and are therefore attracted to each other and may not lift at all when
the enel~i~Lion is at a low level. The length of time and amplitude of the ener~i~ation
are varied to adjust the intensity of the rapper.
s In practice, numerous operational problems associated with the cleaning
process may be experienced. FYres~ive rapping results in the particulate billowing
from the plate into the gas stream where it is re-entrained in gas flow and must be
recaptured. Other~vise, the re-entrained dust will be discharged from the eYh~l-st
stack, resulting in unacceptable emissions into the atmosphere. Insufficient rapping
0 ~ clll~ the particulate from falling from the surfaces to be cleaned. In either case,
collection efficiency of the preci~ ator is reduced which reduces the gas volumes that
can be treated by the precipitator. In most industrial applications there is a direct
correlation between precipitator capacity and production capacity. Therefore, there
are significant monetary benefits to be derived from m~imi7in~ rapper efficiency.
5 Also, grossly inefficient precipitators which allow an excessive amount of particulate
emissions into the atmosphere can ~lOlllpt the Environmental Protection Agency to
shut a particular process down indefinitely.
In the prior art, rapper control has been limited to m~n~-~lly controlling and
adjusting the ~;Ul 1 ellt level to an entire group of rappers, rather than individual rapper
20 control. However, rappers in dirrerent locations within the group may operate more
efficiently with different current levels. Since the number of rapper groups, as well as
the number of rappers within each group, may vary and prior art rapper control only
allows for intensity adjustment of an entire group, a colll,ololllise in control standards
therefore prevails. The result is often rapper inefficiencies that reduce precipitator
25 and production capacity as well as increase emission levels.
Similarly, open and short trip values must be set for the rappers as a unit. Since
rappers at different locations may have different current protection requirements, the
prior art represents yet another co,ll~urolllise. To protect the rappers as a unit the least
sensitive rapper must de energize when a circuit condition occurs that is threatening
30 to the most sell~iLive rapper. This is inefficient since some rappers will at times be
de-energized unnecessarily even though their particular operating parameters are not
exceeded.
With respect to circuit protection, the prior art uses fuse or relay technology
to detect and isolate fault conditions. This technology is slow in that the devices
35 require up to several full cycles before electrical protection can be assured. Within
several full cycles of a fault condition significant damage can occur to rapper circuitry.
Some commercial rapper control systems purport to incorporate solid state fault
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detection, but the trip level is set high because all rappers are required to have the
same trip level. The trip level cannot be individually adjusted to a specific single
rapper within these systems and a colll~loll.ise in control standards results.
Another drawback of the prior art is that rapper control technology is an open
s looped system. The current level is set at a particular point in time, considering the
present rapper conditions in the electrostatic preci~ alor. But, rapper conditions are
not static. Numerous things can change rapping conditions which often affect current
flow to the rappers. For in~t~nce, the precipitator may operate at elevated tempera-
tures which change the ambient temperature of the rapper. Rapper slugs as they
0 energize travel through a sleeve which often gets dirty and sticky. Numerous influen-
ces change the rappers characteristics but the prior art requires control just as if the
conditions are constant. This again results in inefficiencies.
The prior art does not provide an easy or economical way to check the present
operating conditions of rappers in large precipitators. Presently, technicians must
15 personally walk near each prc~ i~lor while w~tchin~ and listening to determine
whether a specific rapper is operating. To determine the present current flow to a
rapper, or to determine what current a particular style of rapper draws, a technician
must personally measure each rapper input with a meter. In large precipitators (for
instance, 250 rappers or more) it becomes cost prohibitive to personally check the
20 efficiency of each rapper.
Similarly, the prior art is unable to provide trending information for specific
rappers, which can be very important in troubleshooting, calcul~tin~ overall operating
efficiencies, as well as calc~ ting the useful life expectancies of specific rappers.
In addition, the prior art does not provide a means by which the undesirable,
2~ residual magnetism created within rapper components can be elimin~te-l
A long felt need in the air pollution control industry remains for improvements
in rapper control for electrostatic pre.;i~ a~o,~ to alleviate the many operational and
maintenance difficulties which have been encountered in the past. The primary goal
of this invention is to fulfill this need.
The present invention provides an hll~roved way to control power to a rapper
within an electrostatic precipi~alor.
Since m~nu~lly adjusting current to rappers as a unit is inherently inefficient,an important object of this invention is to provide a means for individually pre-setting
electrical operating conditions for each rapper within a multiple rapper precipitator.
Another object of this invention is to provide a means for individually setting
short and open trip conditions for each rapper within a multiple rapper precipitator.
~ ~ 1Z'~
61316-771
This wlll eliminate the compromise required in the prior art and
increase rapper efficiency.
Still another ob~ect of this lnventlon is to provide
fault protectlon which assures detectlng and lsolating a fault
conditlon within 1/2 cycle from the moment a fault occurs. Reduc-
ing fault trip response times from several full cycles to 1\2
cycle will greatly lncrease clrcuit protection and increase the
useful life expectancy of the rappers and preclpltator as a whole.
Another ob~ect of thls invention is to provide a closed-
loop control means for a rapper. Enabling the rapper currentcontrol to sense, measure and ad~ust the input current in the
event the actual current is not substantially similar to the pre-
set electrical lnput current wlll greatly ald rapper efflclency.
Yet another lmportant ob~ect of thls invention is to
provide a source of rapper energlzatlon that wlll reverse polarlty
every tlme an lndlvldual rapper ls energlzed. Further, the polar-
lty of energlzatlon wlll be remembered so that lt can be reversed
on the occurrence of each energization.
It is also an ob~ect of this invention to de-magnetize
those rappers that have become magnetized wlth prlor art controls.
Also, it is a further ob~ect of this invention to more
accurately control rapper lift and thereby rapper intenslty by
ellmlnatlng the detrlmental and lnconslstent effect~ of resldual
magnetlsm on predicting conslstent rapper llft.
Another important ob~ect of this invention ls to provlde
present operating condltlons for each rapper wlthln a preclpitator
and to store the rapper operating condltions. This will provide
an economical way to check the actual operatlng condltions of each
5a ~ 61316-771
rapper as well as provide lnformation for troubleshootlng and
trendlng.
The lnventlon may be summarized, accordlng to a flrst
broad aspect, as a multlple rapper control for an electrostatic
preclpltator, said rapper control for controlllng the energlzatlon
of a plurality of rapper types, said rapper control comprislng: a
plurality of electrostatlc precipltator rappers, sald plurallty of
rappers lncludlng a plurality of rapper types; means for switchlng
havlng a plurality of switches whereln each said rapper ls connec-
ted to at least one of said switches~ means for controlllng powerwith an output connected to said switch means to vary power to
each said rapper, said power control means includlng a pair of
SCRs connected ln a predetermlned conflguratlon; and loglc means
to control power to said plurallty of rappers lncluding a plur-
allty of rapper type~ ln a preselected log~c sequence.
According to another aspect, the lnvention provldes the
method of detecting and curlng open and short current fault condl-
tlons ln a plurallty of rappers, lncludlng a plurality of rapper
types, in an electrostatic precipitator, sald method comprlslng
the steps of: storlng ln a memory means predetermlned current
values lndlcatlve of open and short current fault conditions
associated with each said rapper type; senslng and measurlng the
peak electrlcal current at each said rapper; comparlng sald mea-
sured peak electrlcal current of the rapper belng sensed wlth sald
predetermlned open and short current fault conditlons associated
with the rapper belng sensed; de-energlzlng the rapper that ls
belng sensed lf sald comparison indlcates the presence of an open
or short current fault condltlon; and automatically re-energlzlng
A
~=~ ~
~ 20721 29
5b 61316-771
the de-energlzed rapper once sald open or short fault condltlon ls
extingulshed.
According to yet another aspect, the lnvention provides
the method of controlllng a plurallty of rappers in an electro-
statlc preclpltator, said method comprlslng the steps of: provl-
ding a plurallty of electrostatlc preclpltator rappers, whereln
sald plurallty of rappers ls comprlsed of a plurallty of rapper
types; supplylng power to each sald rapper through a pair of SCRs
whlch are connected in a predetermlned conflguratlon; senslng and
measurlng the peak electrlcal current at each sald rapper; compar-
lng sald measured peak current of the rapper belng sensed wlth a
preset, deslred peak current value assoclated with the rapper
belng sensed; ad~usting said measured peak current to substan-
tlally the preset, deslred value lf said measured peak current
departs from sald preset value, thereby maintaining said rapper
operation at a desired level, and provlding a unltary rapper con-
trol system for controlllng the power to a plurallty of rappers
includlng a plurallty of rapper types.
Accordlng to a further aspect, the lnventlon provldes
the method of controlllng the power to a plurallty of rappers ln
an electrostatlc preclpltator; sald method comprlslngs energlzlng
a flrst predetermined group of a plurallty of said rappers; and
energlzlng a second predetermlned group of a plurallty of said
rappers, whereln at least one of sald rappers ln sald flrst
predetermlned rapper group ls one of sald rappers ln sald second
predetermlned rapper group.
5c ' 20721 29 61316-771
Description of the Drawlnqs
In the accompanying drawlngs whlch form a part of the
speclflcatlon and are to be read ln con~unctlon therewlth, and ln
whlch llke reference numerals are used to lndlcate llke parts in
the varlous views:
Flg. 1 ls a block dlagram lllustratlng a multlple rapper
control constructed ln accordance wlth a preferred embodlment of
the lnventlon;
Fig. 2 is a block diagram showing the power source and
power control means of the multiple rapper control ln more detail 7
Fig. 3 is a block diagram showing the current detectlng
means of the multlple rapper control ln greater detail;
~`.
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W O 91/06372 - ~ 2 i ~ 9 PC~r/US90/03748
Fig. 4 is a block diagram showing the power source and power control means,
along with an optional voltage selection relay and the AC/DC relay of the multiple
rapper control;
Fig. S is the block diagram of Fig. 4 in~ tli ng an additional and optional polarity
5 reversal means; and
Fig.6 is a block diagram showing the polarity reversal means of Fig.5 in greaterdetail.
This invention specific~lly contemplates the control of a plurality of rappers
for an ele~lr~ lic ~recipilalor. This description uses two rappers for illu~LlaLi~e
0 purposes and not as a limitation on the number of rappers to be used in practicing the
invention.
A multiple rapper control embodying the principles of this invention is $hown
in Fig. 1 of the drawings with the control block ~lesign~te~l generally by the reference
numeral 10. Control block 10 is connected to a central co,ll~uLer 12, a power source
5 18 and a plurality of rappers as schem~tic~lly in~liç~ted by Rapper 1 and Rapper 2
blocks. More specifically, central co"l~uLer 12 is bi-directionally connected to a
microco",lluLer 14 which in turn is connected to both a power control means 16 and
a TRIAC switch device 20. Power control means 16 is connected between a power
source 18 and TRIAC switch device 20. A current detecting means æ senses and
20 m e~ lles the ~;Ul 1 Gll~ between power control means 16 and TRIAC switch device 20.
Current detecting means 22 is connected to the output of power control means 16 and
is bi-directionally connected to microcomputer 14. Rapper 1 and Rapper 2 are each
individually connected to a TRIAC within the TRIAC switch device 20. In other
words, each rapper is connected to only one TRL~C andj conversely, each TRIAC is25 connected to only one rapper. The TRIAC may be typically characterized as a silicon
bi-directional triode thyristor, such as T6420M of Motorola clçcign~3ted for a 600 volt
rating for 40 amps.
The power control means 16 and power source 18 are illustrated in Fig. 2.
Power control means 16 comprises an SCR firing circuit 28, a full-wave rectifier 30,
30 an SCR 1 and an SCR 2. Power source 18 co~ ises a L.all~ro~lller 26 and two input
terminals 24 to which power is applied. The input terminals 24 are connected to the
primary of L~ ro, ---er 26. One side of the secondary of Ll allsrol ll~er 26 is connected
to an inverse parallel SCR 1 and SCR 2 which connects, along with the other side of
the secondary of L,ansro"ner 26, to full-wave rectifier 30. SCR firing circuit 28 is
35 connected seriallybetween microcol~uLer 14 and the inverse parallel SCR 1 and SCR
2~
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, ~. ~, i
The current detecting means æ is best illustrated in Fig.3. One sense resistor
32 is connected serially between power control means 16 and TRIAC switch device
20. The sense resistor 32 is also connected across a conventional input protection
circuit 43 and then to an isolation amplifier 34 connected serially with a precision
S rectifier 36. Precision rectifier 36 is connected with a peak detector 41 which bi-direc-
tionally connects to microco,l,~uter 14. Isolation amplifier 34 may typically comprise
an AD202JN chip sucll as l"~.l..ri1~tured by Analog Devices of Norwood, Mas-
s~chncetts. Precision rectifier 36 colllp-ises two operational amplifiers and two high
speed switching diodes (such as lN4148 diodes) ap~,r~liately biased to rectify the
10 input characteristic to a DC level that is independent of the voltage drop across the
diodes. The two operational amplifiers may comprise TL032CP operational
amplifiers characterized as an enhanced JFET (iunction field effect transistor), low
power, low offset, analog operational amplifier such as m~mlf~ct~lred by Texas Instru-
ments of Dallas, Texas. The peak detector 41 may typically comprise a PKDOlFP chip
such as m~nl1f~ct~lred by Precision Monolithics Inc. of Santa Clara, California and
characterized as a monolithic peak detector with reset and hold mode.
The components which allow a rapper to receive either an AC or DC signal at
120 volts or 240 volts are best illustrated in Fig.4. Microcoll"~uler 14 is connected to
both a voltage selection relay 40 and an AC/DC relay 42. Voltage selection relay 40
20 is connected to a normally open contact 44 and a normally closed contact 46. Normally
closed cont~ct 46 is connected to the 240 volt lead of power source 18, and normally
open contact 44 is connected to the 120 volt lead of power source 18. Both contacts
44 and 46 are connected to the inverse parallel SCR1 and SCR2. The AC/DC relay
42 is connected to two normally open contacts 48 and 50 and two normally closed
25 contacts 52 and 54. Normally open contact 48 is connected to the inverse parallel
SCR1 and SCR2 while normally open contact 50 is connected directly to the power
source 18. Both normally open contacts 48 and 50 are connected to TRIAC switch
device 20. Normally closed contacts 52 and 54 are connected to the positive and
negative output of bridge rectifier 30, respectfully. Both normally closed contacts 52
30 and 54 connect with TRIAC switch device 20.
In operation, a look-up table inclll~ling characteristics for each individual
rapper is determined, entered and stored in central computer 12. The look-up table
parameters comprise the location of each rapper, the rapper type (i.e., AC or DCvoltage), the voltage level, the pre-set current characteristic of each rapper, open and
3~ short trip conditions for each rapper, the IIIAX;III~IIII duration of enelgi;calion and the
mi"i",."" time delay between ene~ tion cycles for each rapper. Microcoln~uler 14is a slave to central colllpwler 12 in that the microcomputer 14 waits for instruction
wO 91/06372 2 0 7 ~ ` Pcr/usso/o3748
from the central con.puler 12 before be~innin~ operation. Upon receiving instruction
from central colllpuler 12 to energize Rapper 1, the microco~ uler receives the
location of Rapper 1, the voltage type and level of Rapper 1, the pre-set ~;ullent
characteristic for Rapper 1, the time duration of energization and the open and short
5 trip conditions for Rapper 1. The pre-set current characteristic is stored in local
memory at microcolll~uler 14 and then ll~ ",il(ed to power control means 16. Theduration of ener~,i~lion is COllvt;l led into a time equivalent number of frequency half
cycles and fractional half cycles. This number of half cycles is Ll~ led to power
control means 16. The open and short trip conditions are also stored in local memory
0 at the microcom~uler 14. The location of Rapper 1 is tr~n~l~ted at microcol--puler 14
into a specific TRIAC switch and information to energize the a~ l iate TRIAC is
."~",illed to TRIAC switch device 20.
SCR firing circuit 28 of the power control means 16 receives the pre-set Rapper
1 ~;ullelll characteristic, and duration of energization in terms of half cycles and
15 fractional half cycles, from microcol~l~uler 14. The SCR ~lring circuit 28 tr~n~l~tes
the pre-set ~;ulle~ll characteristic for Rapper 1 into a firing angle, Theta, which is sent
to SCR 1 and SCR 2. Power is applied to the rapper in terms of SCR ffring angle
degrees. The ~iml~oi(l~l electrical cycle con~aills 360 degrees, and consists of a positive
half cycle and a negative half cycle with respect to polarity. Each SCR can be fired
20 anywhere from 0 degrees to 180 degrees in the electrical cycle, 0 degrees being full
power and 180 degrees being 0 power. When an SCR is fired at 45 degrees, for
example, it will conduct from 45 degrees to 180 degrees. Therefore, a difference in
firing angles can be represented as a distance along the abscissa of the sine wave. Due
to polarity reversal, the SCR stops conducting when the ~;Ul I ent p~c~ing through the
2s SCR falls below a specified holding current for the device.
The normal operating state of SCR 1 and SCR 2 is 180 degrees which allows 0
power from l~ansrol",er 26 to pass through to the rappers. After SCR firing circuit
28 tr~n~l~tes the pre-set current characteristic into the a~ro~riate firing pulse, it fires
SCR 1 and SCR 2 which begins allowing the al,~lo~,iate current to pass through to
30 full-wave rectifier 30. SCR firing circuit 28 also counts the number of half cycles and
fractional half cycles that pass through the SCR combination. SCR 1 and SCR 2
remain energized until the number of half cycles counted equals the number of half
cycles L~ "li~led from microco"~uler 14. At this point SCR firing circuit 28 sends
SCR 1 and SCR 2 a firing angle of 180 degrees, in effect ce~in~ power flow.
Full-wave rectifier 30 COIlVt;l ~ the AC signal which passes through SCR 1 and
SCR 2 into a p~ tin~ DC signal. As the pnl~tin~ DC signal exits full-wave rectifier
30, it also exits power control means 16. From power control means 16 the p~ ting
WO 91/06372 Pcr/US9O/03748
20721 29
DC signal enters TRIAC switch device 20. The TRIAC, a multi-layered solid-state
device, acts as an AC switch. There is one TRIAC per rapper. When a rapper is
energized, its associated TRIAC is energized. Microcomputer 14, having tr~n~l~ted
the location of Rapper 1 into Rapper 1's corresponding switch and llal~ll~illed this
5 information to TRIAC switch device 20, the appropriate switch is energized to allow
the DC p~ ting signal to pass to Rapper 1.
TRIAC switch device 20 may consists of a number of circuit boards with up to
16 TRIACs per board. Microcollll)uler 14 can typically accommodate a total of 16circuit boards with 16 TRIACs per board. Thus, one microconlputer could charac-
0 teristically accommodate a total of 256 TRIACs and 256 rappers. For a precipitatorwith more than 256 rappers, another control block 10 (including a second microcom-
puter, ~;U[l ellt ~letecting means, power control means and TRIAC switch means) could
be added as required to replicate the system illustrated in Fig. 1. The central computer
12 and power source 18 would be connected to any additional control block 10 added
5 to the basic arrangement.
The plll~ing DC signal exiting power control means 16 is sensed and
measured by .;ùllelll del:ecting means æ. This actual rapper input cullent is sensed
and converted to a voltage by external sense resistors 32. This voltage passes through
isolation amplifier 34, the output of which is an AC voltage proportional to the ~,Ul 1 e111
20 flowing to Rapper 1. The output of isolation amplifier 34 is routed to precision
rectifier 36 which rectifies an analog input to a DC level that is proportional to the
sensed rapper input current. The DC level is independent of the voltage drop across
the diodes within precision rectifier 36.
The output of precision rectifier 36 is routed to a peak detector 41. The peak
2s detector 41 upon a co.~ d from microcomputer 14 will detect the peak value of the
wave form at its input. This is a sample and hold device which, on comm~nll, will store
the peak value. Current detecting means 22 provides an electrically isolated rectified
peak detection of the input current for selected Rapper 1.
While Rapper 1 is being energized, microcoll,~uter 14 instructs peak detector
30 41 to detect peak ;ullent. The microcomputer 14 takes the output of peak detector
41 and CO11Vel 1~ it to a digital word. This digital word is then colll~ared by microcom-
puter 14 to previously stored short and open trip conditions and the pre-set input
-ullelll characteristics for Rapper 1. At this point the speed of colll~ ation is very
important. Once SCR 1 and SCR 2 of power control means 16 are energized, they
35 cannot be turned off until the current passing through them falls below a specified
holding ~;ullenl for the device. The current through these SCRs drops below the
specified holding current a~,ro,~ tely every 8.33 milliseconds. During that 8.33
Wo 91/06372 ; Pcr/US9O/03748
07~i29
millisecond time period current detecting means 22 must sense and measure the actual
peak current entering Rapper 1; microcolllpuLer 14 must take that information,
CO11Ve1 L it to a digital word, colll~are it to the stored short and open trip conditions,
determine that a trip condition is met, and ~ SIIIit information to SCR firing circuit
s 28 to ~ gn~te a firing angle of 180 degrees before the SCRs are fired a second time.
Fl t;vel~lhlg the SCRs from firing a second time in the event of a short or open condition
is a significant illlprovelllent over the prior art and can be best accomplished by
tili7ing the speed inherent in microcolll~ulers.
In the event a trip con~lition is not present, the same digital word is colllpared
0 within microcolllpuler 14 to the previously stored pre-set input current characteristic
for Rapper 1. Based on that comparison, inrollllation is ll~ lllitted to power control
means 16 to perform any adjustments required to have the actual ~;ullenl entering
Rapper 1 be subst~n~i~lly similar to the stored input current characteristic for Rapper
1.
L5 Each time microcolllpuler 14 collvel l~ the output of peak detector 41 into a
digital word, this same h~rollllation is IlA.~ ed to central colllpuler 12 and stored.
This hlfollllalion is stored according to its colles~onding rapper and is available for
present operating conditions and trending purposes.
At the end of the rapping cycle, if there are no short or open contlition~, all
20 TRLACs are shut off and the microcolll~uler 14 waits for the next instruction. Central
computer 12 at this time determines when the next rapper should be energized. When
that time is reached the above process is repeated for the appropriate rapper. If a
short or open condition does occur, the fault condition is sent to the central computer
and that rapper's energization cycle is passed over in the filture.
2s The embodiment of Fig. 4 is used to allow the rappers within a precipitator to
operate at different voltage levels and with different signal types (AC or DC). When
central computer 12 downloads the operating characteristics for a rapper to
microcolllpuier 14, the rapper type (AC or DC) and voltage level is included.
Microcolllpuler 14 transll~its to voltage selection relay 40 the required voltage level.
30 If 240 volts is needed, the normally closed contact 46 remains closed, and normally
open contact 44 remains open, allowing all 240 volts available from power source 18
to pass. If 120 volts is needed, voltage selection relay 40 causes normally closed contact
46 to open and normally open contact 44 to close, which allows only 120 volts to pass
from power source 18. Further, microco...l,uter 14 Lr~ to AC/DC relay 42 which
3s voltage type the energized rapper requires. If DC voltage is needed, normally closed
contacts 52 and 54 remain closed and normally open contacts 48 and 50 remain open.
This connects TRIAC switch device 20 to the output of full wave bridge rectifier 30,
WO 9l/06372 ~ Pcr/usso/o3748
20721 29
.-
11
which will in effect supply a DC signal to the rapper. If ACvoltage is required, AC/DC
relay 42 causes normally open cont~ctc 48 and 50 to close and normally closed contacts
52 and 54 to open. This allows the AC signal leaving the inverse parallel SCR1 and
SCR2 to bypass bridge rectifier 30, which in effect supplies the rapper with an AC
s signal. It should be noted that the relay contacts in Fig. 4 were illustrative as one
embodiment and that solid state devices or co~ ble variations are understood to
be included within this disclosure.
Turning to FIG. 5, an alte,llalive embodiment of the present invention is
shown. Operation of this circuit is the same as described with refere"ce to the original
0 embodiment of the present invention with the addition of the polarity reversal of the
supply to rapper 1 and 2 to ~,e~nl u~w~ ed magnetic orientation of the rapper
components. Preferably, SCR firing circuit 28, SCR 1 and SCR 2, bridge rectifier 30,
damper diode bridge 38, ~ enl detector 22 and polarity reversal circuit 37 are placed
on one circuit board and col"prise power module 35.
Normally closed contacts 52 and 54 are connected to output terminals 70 and
72, respectively, of polarity reversal circuit 37. In general, circuit 37 reverses the
polarity of the supply to rapper 1 and rapper 2 each time they are energized. This
velll5 an llndecirable magnetic orientation at the rappers. Input terminal 80 of
polarity reversal circuit 37 is connected to positive output 31 of bridge rectifier 30 and
20 a positive output 39 of damper diode bridge 38. Bridge rectifier 30 and damper diode
bridge 38 may be referred to as bridge combination 33 and serves as an input supply
means for circuit 37. To assure proper polarity rt;vel~al at output terminals 70 and 72
of circuit 37, the signal to input terminal 80 must remain positive and the signal to
input terminal 82 must remain negative. This is called the input integrity of circuit 37
25 and remains col~Lall~ due to the selected arrangement of the bridge combination 33.
A rapper in operation causes transient electrical characteristics to flow back
into the control circuitIy. This wash-back may damage circuit components and
decrease system operating efficiency. Damper diode bridge 38 protects the circuit
components by absorbing and dissi~alh~g any transient electrical characteristics that
30 have washed back from the rapper.
FIG. 6 illustrates the polarity reversal circuit 37. Circuit 37 is colllplised of
four identical TRIAC circuits Tl through T4 which are connected as a double pole,
double throw switch. Since each TRIAC circuit is identical, only circuits T3 and T4
show the preferred configuration while circuits T1 and T2 are shown in block form for
3s simplicity. ATRIAC, often called a bilateral thyristor can be switched to a conducting
state when properly triggered.
WO9l/06372 t~ ~ 2~0~7~?12~ Pcr/usso/o3748
Each TRL~C circuit is interfaced with microcoll~uler 14 through an accom-
panying optolectronic coupling device (optocoupler) U1 through U4 such as the MOC
3021 as made by Motorola Corporation, Phoenix, Arizona. Each optocoupler U1
through U4 has a five volt DC power supply and an input resistor configuration
5 colnpl ised of resistors R1 and R2.
Leads from positive input terminal 80 connect to TRIAC circuits T1 and T3.
Leads from negative input terminal 82 connect to TRLAC circuits T2 and T4. The
oull,u~ from circuits T3 and T4 are conn~cte~ to output terminal 70. Outputs from
circuits T1 and T2 are connected to output terminal 72. Output terminals 70 and 72
10 act as supply means for providing polarity reversal to the rappers.
In operation, every time microcolll~uler 14 is instructed to energize a rapper,
the rapper location and the polarity used is stored in memory of microcomputer 14.
When the next ene~gi~lion occurs, the last polarity is obtained from memory and
complimented to provide polarity reversal. The memory is then updated with this new
~5 value. This provides for polarity reversal each time the rapper is energized.When polarity circuit 37 is energized, only two of the four TRIACs T1 through
T4 will conduct, and the rem~ining two will not conduct, or will be off. When circuit
T1 and T4 are conducting, the output polarity is negative. In this state, T2 and T3 are
off, or not conducting. When T2 and T3 are conducting the output polarity is positive
20 and T1 and T4 are off, or not con~hl- ting~ As a result, each time a rapper is energized,
it will have the opposite polarity that it had on the immediately procee-ling energiza-
tion. This polarity reversal 1,l evenls undesirable magnetization of the rapper com-
ponents as a result of conlilluous uni-directional flow of electromagnetic flux.The foregoing ~ s~ion describes the operation, results, and advantages of
2s the polarity reversal circuit in accordance with the present invention. The following
example is presented to clarify the prefelled configuration of polarity reversal circuit
37 as described herein. Substitute devices may accomplish the same result and the
following example should be understood to be an illustration, and not a limit~tion, of
preferred circuit components and operation.
The output polarity of circuit 37 is in an initial or present state. For purposes
of this example, the initial state is to be positive. Microcolllpuler 14 has the rapper
location and this positive polarity stored in memory. Circuits T2 and T3 are conducting
and circuits T1 and T4 are off. Accordingly, output terminal 70 is positive with respect
to output terrninal 72.
Next, central colllpuler 12 instructs microcomputer 14 to again energize the
rapper. Microcollllluler 14 obtains the polarity from memory, compliments it, and
stores the new polarity back in memory. To illustrate, an &~pro~liate bit (or word)
WO 9l/06372 ~ 72i 2 9 Pcr/US90~03,48
13
representing the polarity of a COI ,esponding rapper location may be set. When a bit
is set, it is represented as a one (1) and has an associated direct current (DC) voltage
(SV). This is called a "high state". By contrast, a cleared bit is represented as a zero
(0) and has an associated "low state" voltage of zero volts. The compliment of a one
5 (1) is a zero (0) and visa versa. It should be understood that numerous combinations
of bits, words, and voltage variations may be employed to represent the polarity of an
accoll~allying rapper location. In the present ex~mple, a positive polarity is repre-
sented by a set bit (i.e., a one (1)). Microcol"~u~er 14, having obtained the polarity
(positive polarity represented by a one), complimented it (to a negative polarity
0 represented by a zero), and stored the new polarity back in memory sends this new
"low state" signal to polarity reversal circuit 37.
The low state (zero volt) signal is inverted to high state.(5 volts) at invertor 60.
This inverted high state signal serves to turn off TRI~C circuits T2 and T3 through
optocoupler U2 and U3. Referring solely to U3, this occurs because a high voltage at
15 node 64 stops ~url t;n~ flow through optocoupler U3. TRIAC 68 is now off and is in a
high impedance nonconducting state. A similar analysis applies to optocoupler U1.
Simultaneously, the inverted high state signal is again inverted (back to low
state) at i"ve, lor 62 and sent to optocouplers U1 and U4. Referring solely to op-
tocoupler U4 (the same analysis applies to U1), low voltage at node 66 causes ~u" e"~
20 to flow. This activates optocoupler U4 thereby interfacing circuit T4 with microcom-
puter 14. This places the device in a highly conductive state, and therefore it is on.
The conducting on state TRL~C circuits T1 and T4 supply negative polarity to thera~l,e,~. ;
When the next energization of the rappers occurs, the process is repeated.
25 However, on the next ene~ lion, circuits T2 and T3 will conduct, and circuits T1 and
T4 will not conduct. This will result in a positive polarity since T3 is connected to
positive input terminal 80 and T2 is connected to negative input terminal 82.
From the forégoing it will be seen that this invention is one well adapted to
attain all end an~ objects hereinabove set forth together with the other advantages
30 which are obvious and which are inherent to the structure.
It will be understood that certain features and subcombinations are of utility
and may be employed without reference to other features and subcombinations. This
is contemplated by and is within the scope of the claims.
Since many possible embodiments may be made of the invention without
35 departing from the scope thereof, it is to be understood that all matter herein set forth
or shown in the accompanying drawings is to be interpreted as illustrative and not in
a limiting sense.
