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Publication numberUS2310786 A
Publication typeGrant
Publication dateFeb 9, 1943
Filing dateMay 21, 1941
Priority dateMay 21, 1941
Publication numberUS 2310786 A, US 2310786A, US-A-2310786, US2310786 A, US2310786A
InventorsHildebrand Ralph L
Original AssigneeWestinghouse Electric & Mfg Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrical dust-precipitator indicating system
US 2310786 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)


ATTORNEY Patented `l" `eb.'9, '19437 ELECTRICAL DUST-PRECIPITATOR l. INPICATING SYSTEM Ralph L. Hildebrand, lnkewwd, ohio, signor to Westinghouse, Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application May zi, 1941, serial n. 394.459

7 claims. (ci. 1st-v) K My invention relates generally to indicating and alarm `systems applied to electrostatic gascleaning precipitator installations, and more particularly relates to convenient signalling systems high to beA dangerous, being in the order of 12,000 to ,14,000 volts, more or less, in the ionizing zones, and in the order of up to 6,000 volts and sometimes above, in the precipitating zones. This entor indicating the operating condition of separate ergizing means is usually in the form of a relasubdivisions of a. large precipitator installation, -with individual subdivision indications neareach subdivision, and combined indications for all of the subdivisions located at a remote central panel or station.

More specically, my invention relates,v to the multi-zone type of gas-purifying precipitator assembly which comprises gas-cleaning means inj which the gas is first blown or drawn through an nating-current power distribution system generally available into the required supply 0f limited- 10 venergy high-voltage power; and in'practical application. the parts for such a voltage-conversion means are mounted in a suitable grounded metal casing. forming a power supply casing-unit fo the precipitatorinstallation or assembly.

ionizing zone where the gas-borne dust particles l5 For practical application. the voltage-converare electrically charged, and then blown or drawn through a separate precipitating zone or zones where the charged dust particles are electrically acted upon for precipitation. Preferred forms of such precipitators, are shown and described in G. W. Penney Patent No. 2,129,783, granted September 13, 1938, and the E. H. R. Pegg Patent No.'2,215,298, granted September 17, 1940.

In such electrical multi-zone precipitators the v sion casing-umts are built in'selected sizes capavble of suitably energizing a certain number of precipitatox'units; and'ior large gas-purifying precipitator installations. requiring a large number of precipitator-units. more than one voltageconversion casing-unit is employed, each supplying power to a subdivision of the total number of precipitator-units.

The relatively high voltages at the output of ionizing zones usually comprise spaced curved. 25 the casing-units are dangerous, and to reduce ground electrodes between which ionizing wires are insulatedly-supported, the ground electrodes being relatively large in comparison to the ionizing wires which are relatively line, being less than 3 2 milsin thickness, and in practice being as fine as mechanical limitations will permit, 5 mil tungthe accompanying hazards, each casing-unit is duits so that the necessary power for the precipltator-units can besupplied through short unexposed well-insulated high-voltage leads .or co'nnections which pass directly through a wall of ,cipitatorplates adjacent ones of which are relathe casing-unit and the abutting .wall ct the gasconduit.` Since the precipitator-units are ven- 354 cased in the gas-conduit the voltage-conzones usually comprise a plurality of spaced pre- .tivelv insulated. the plates having dust-collecting surfaces or provisions for collecting the dustl particles previously charged-in the ionizing zone. V The?- plates may be at as shown, for example,

in theaforesaid patents, or they may be bent as shown; for example, in the Pound et al. Patent multi-zone precipitators are built in housing units or cells, each of a certain limited capacity, i'or cleaning precipitator installations, and more parcipitator-units are arranged side by side in vertctal capacity required for a particular gas-cleaning installation. a large number o! precipitates'- units generally being necessary for large instal-1 v lstions o! high capacity.

' above that generally available and sumciently version means are encased in the metal casing# unit, it is desirable to provide signal means. 'which heretofore have been' incorporated in the casing-l unit, iorthe voltage-conversion'means, these s18- A 4o nal means being operated upon the occurrence No..'2,2l2,885, granted August 27, 1940. Suchv o t the known types of possible electrical faults or operation-conditions in the precipitata-units, by which the resulting effects oisuch faults or operation-conditions express themselves in the voltv age-conversion means-the signal means being ticaior horizontal rows, or both.- to make up the incorporatedinsuchmsnuerthsttheirsignsl .In the form of the sppsrsh herein described 's green light. when visible, indicates that the precipitata-assembly subdivision, comprising the voltage-conversion means and the particular pref cipitator-unit or -units energized thereby, is operating properly: 'a visible redlight alone indi. cafes an excess-current drain'by the particular precipitator-assembly subdivision, which may be v variously caused, as, for example, by shorting between precipitator plates, a broken energized ionizing wire falling on a grounded element, a defective rectier in the voltage-conversion means passing more current than it should,V or other faults causing an excess-current drain from the available low-voltage supply lines or causing a lowering of the output voltage of the limited-energy voltage-conversion means; and visible combined red and green lights indicate an open circuit, which also may be variously caused, as, for example, by a broken ionizing wire hanging loosely out of contact with metals at other potentials. a burned-out transformer secondary winding, or other faults causing insuiilcient current-drain by the precipitator-assembly subdivision, or overvoltage at thehigh-voltage output of the voltage-conversion means.

As aforementioned, the high voltage delivered by the voltage-conversion casing units makes it necessary to .mount them against or at the gasconduit encasing the precipitator-assembly. Such locations, however, frequently are in awk- Ward and, perhaps, almost inaccessible places. so that the signal indications can only be observed with extreme diiiiculty or with great inconvenience; and it is an object of this invention to provide a low-voltage signalling system for apparatus such as hereinbefore described which includes a convenient, readily observable arrangement calling attention to a faulty operation-condition of the precipitator-assembly.

Pegg patents illustrate and describe dliferent forms of self-contained units. Such units are housed in a metal housing or casing 2, and each includes an ionizing chamber or zone 3 followed, in the direction of gas or air-flow, by a precipitating zone or chamber I. The ionizing chamber of each precipitator-unit comprises cooperating ionizing-electrodes disposed transversely with respect'to the air-flow, but for simplicity of illustration, only a. few of these ionizing-electrodes are illustrated, and these shown somewhat, schematically. In this` ionizing chamber, the air first passes between two spaced parallel tubular ground electrodes 5 which are grounded to the gas-conduit l through metal casing 2 which supports the ground electrodes. Between each pair of ground electrodes a ne ionizing wire 6 -is supported of the type whose characteristics are more particularly described in the aforesaid Penney patent.

Each precipitator-unit also comprises a precipitating chamber including a relatively large number of precipitator-electrodes comprising alternately insulated and non-insulated plates `no'tch'ed metal bars I2 which are grounded on It is an additional object of my invention to lncorporate in the system as hereinbefore described duplicate signals, conveniently located, which will enable an operator to observe and determine the operating conditions of the precipitating-assembly, the central or remote signals being preferably arranged on a central panelboard and duplicating the signals of the power-supplying voltage-conversion casing-units for the different-subdivisions of the precipitator-assembly, so that an operator or maintenance man can tell at a glance how the respective subdivisions are operating.

It is a more particular object of my invention to provide a signalling system utilizable'with an electrical precipitator which will indicate at a convenient remote location faulty operation-condtions thereof, the signalling system starting an alarm upon the occurrence of a fault, but having operable means operable by an operator for canceling the alarm without disturbing the conditioning of the signalling system for subsequent operation of the alarm. Consequently, when the operator seeks to remedy the faulty operationcondition at the precipitator subdivision or assembly where it occurs, the alarm will again immediately sound if the fault has not been removed or a second fault occurs.

The foregoing and other features. objects and advantages of my invention will be apparent from the following description thereof which is to be taken in conjunction with the accompanying drawing, the single figure of which is' a diagrammatic view of circuits and apparatus schematiifzally illustrating my invention in its preferred orm. 4

4In the illustrated embodiment of my invention.

air to be cleaned is forced through a metal gasconduit` I which encases a number of precipitatorassembly subdivisions such as M and N, each sub- Y division. comprising a plurality of precipitatorunits. Each precipitator-unit may take any suitable form, and the aforesaid Pound et al. and

the metal housing 2 for the precipitator-unit.

other, and certain or all of them in direct contact with the metal gas-conduit. Electrical energy for each vsubdivision oi? precipitator-units is supplied to one or more of these precipitatorunits by means of a power unit, which derives its' energyy from a customary 110-volt alternating-current power line, such as a single-phase power line having power conductors I3 and I4. The power unit may comprise a specially deysigned step-up transformer I5 having a magnetizable circuit including a primary portion Ii, a secondary portion I1, and a magnetic-leakage path I8 therebetween, which includes an airgap I9 or its equivalent, by means of which the leakage is initially regulated. The prlmaryiportion I6 of this transformer carries a low-voltage primary winding 2|, and may have two separately insulated auxiliary windings 22 and 23 for supplying a very low voltage for energizing filaments of tube rectiilers to be later described. The secondary portion Il of the magnetizable circuit carries a high-voltage secondary winding 24 provided with an intermediate tap 25 near one end. A separate low-voltage tertiary winding 26 is also carried by this secondary portion I1.

For rectifying the high voltage supplied by the secondary winding 24, two rectifier tubes 3| and 32 are utilized in the illustrated embodiment, having lamentary cathodes which are energized from the auxiliary transformers 22 and 23, respectively. The rectiiler tubes are designed to withstand a high inverse peak-voltage of about 20,000 volts, and are capable of carrying a continuous load of about 20 milliamperes of rectied direct current. 'Ihese rectifier tubes are connected to the transformer and tov two seriallyconnected capacitors 33 and 3l in such manner as to cumulatively charge the capacitors, the charges being indicated byplusv and minus signs on the drawing. The size of the capacitors is such that they act to smooth, or reduce the ripple of, the pulsating rec'tlned current-output of the tubes. The capacitors 33 and may be shunted by discharging-resistors '35 and 3i, respectively.

for dissipating the charge on the capacitors after thepower is'turned oil. The foregoing elements ofthe limited energy voltage-conversion means,-

comprising the transformer and windings,the tubes, the capacitors and resistors are -conveniently arranged in a metal casing, such as X or Y, which is mounted at or on the gas-conduit as schematicallyillustrated inthe drawing. Each of these casing-units is capable of supplying energy to a limited number of precipitator-- umts through output leads P for the insulated precipitating-electrodes and I for the ionizingelectx'odes, these circuits being completed through grounds g, including the gas-conduit. VThe leads P and I are made very short and are well insulated, passing throughv suitable small holes in the metal casings X and Y and the gas-conduit I, the periphery of the holes preferably being protected and closed as far as possible by rubber washers. In practice, the leads Pand I are connected only to one precipitator-unit, theother precipitator-umts energiaed by the particular voltage-conversion means being energized by metal bridging bars or jumpers suitably interconnecting the corresponding insulatedA elements of the precipitator-units of a precipiy tator-assembly subdivision, as well known to the art. Y,

The casing-unit X supplies energy to a limited number of precipitator-'units associated with M, in accordance with the capacity. of the casingunit; and where the precipitator-assembly includes a greater number of precipitator-units, additional casing-units are utilized to energize the additional precipitator-units arranged in subdivisions. each subdivision having no more precipitator-umts than the associated casingunit is rated to suitably and safely energize.

The casing-units of the particular embodiment casing-unit. y Y v y o In order to indicate the Adifferent operation-- conditions of a precipitating subdivision, a volt-.-V

age 4relay 4| is vconnected across the tertiary winding 26, and a current relay 42 is connected in series with the primary winding 2|, the enery gizing circuit for this winding being completed. through leads 43 and 44,' including a disconnect switch 45, a thermal-responsive protective switch 46, and one or more series-connected door switches 41 in the main line I4, each doorswitch automatically opening the energy supply to all of the voltage-conversionmeans creasing-units when a door, or the equivalent, ofv the gasconduit means is opened for access to any of the precipitator-units.

. The voltage relay 4| is designed to attract its movable contact 48 when the voltage across it,

and consequently the voltage across the tertiary winding 26, is at or above' a predetermined voltage indicative of normaler proper operating are basically alike, so that the description of one will sumce for all.

Brieilyjthe actual connections are such that "the negative terminal of the capacitor 34 is voltages on the electrodes of the precipitatorunits, and completes alcircuit, including a contact terminal 49, to a green light G'mounted in.

the casing-unit and shining through an appropriate bulls-eye lens. Upon the occurrence of I an undervoltage, the relay drops its contact 43 to deenergize the green light, and energize a red signal light R.

" The relay 42 attracts its movabie'contact 5 when the primary winding draws aV current of a value equivalent to or above the transformed value of the current drawn by the precipitator subdivision under normal or proper operationconditions'I and when the current falls below this value, vthe relay releases this contact to energize the same red signal light R by means of a branch circuit 5|, including a contact terminal'x52.

The .equipment within the casing-unit is schematically indicated in. the illustration by an venveloping broken line 53 indicative of the metal casing-unit X, and by the broken line 54 indicative of the metal casing-unit Y, each casing-unit being provided in practice with a suitable door to permit access to the encased parts.

plate of the tube 32 isalso grounded while the plate of the tube 3| connects to one terminal of the secondary winding 24, the other terminal being common to the output terminal `ior thel lead P. The intermediate tap 25 of the secondary windingv is conductively connected to the illament of the tube 32, while the filament 'of the tube 3| is conductively connected to the terminal for the output lead I. A y A As a, result of the foregoing construction it is possible,'in a particular embodiment, to supply a'voltage in the order oi.' 5000 to 6000 `volts between the relatively insulated precipitator-electrodeslx1-and 8,7and a voltage in. the orderA oi."

12,000 to 14,000 volts'jbetween the ionizing-wires 6 and ground electrodes 5".- f

mi the illustrated entament, the prcipitators-nnit` M representsa'isubdivision energizedv by one casing-uni@andtheprecipitato-unit N The operation of the signals under the diiIerent fault operation-conditions of the' precipitator apparatus is more particularly described in Patent No. 2,217,481,9granted October 8, 1940, to I. A. Yost and myself. Y

In general, an excess-current condition in a precipitator subdivision will lowex` the voltage across its relay 4|, causing the green light G to l'go out and the red light R to'go on. If the fault should be an open circuit, then the primary current drops, causing the relay 42 to release its contact 50 and'thereby energize the red signal R I through the branch circuit 5|. However, the

lcontact 48 of the relay 4| is still in its attracted position, because of the higher voltage across the .tertiary winding 20 so'that this faulty operationcondition of the precipitating-subdivision is indicated -by the combined During normal operation, the movable contacts 48 `and l0 are in their up positions so that only the green lig-ht is energized. It should be noted that during excess-current conditions the'primary is drawing excess current so that the contact 50 is in its up position during suclra faulty operation-condition.

, Since the high-voltage output ofthe voltageconversion means forces each casing-unit to be placed at locations as near to the precipitatorrepresents a. subdivision energized by a 'second 'display of the red and units it supplies as is practically possible. and such locations may be diiilcult to 'reach and inconveniently located, it is desirable, in such instances, to augment the local casing-unit signals by additional remotely-located signals more conveniently located, and to this end I provide i a central panel, indicated by the broken lines 55,

upon which the signals indicated by each of the voltage-conversion casing-units are duplicated.

The signals G and R' are arranged on the central panel 55 in the same manner as the signals G and R of the casing-unit X, and the signals G" and R" are arranged in the same manner as the signals for the casing-unit Y, and as many additional similar signals may be provided on the panel 55 as there are casing-units in the particular gas-purifying precipitator-assembly. 1n order to suitably energize each set of signals, the signal G' is connected between a power-conductor extension 56 of the powerconductor H and a lead 51 to the conductor between the green light G and the contact terminal I9, and the signal R is connected between the extension 56 and a lead 58 between the red light R and the contact terminal 52, so that the illumination of the signal G alone indicates normal or proper operation of the precipitatorsubdivision, illumination of the signal R' alone indicates an excess-current operation-condition in the precipitator subdivision, which may be variously caused, and a combination of the two signals G' and R' indicates an overvoltage operation-condition in the precipitator subdivision, which may be also variously, caused. Similar connections are provided for'the different respective sets of signals on the central panelfor the other voltage-conversion casing-units, the broken lines in the connecting conductors being indicative of length.

The central panel signalling system further includes a relay 50, for each casing-unit, each relay 50 being connected across, or in parallel with, the red signal light of the casing-unit with which it is associated, so that it is energized simultaneously with its associated red light. Each relay 60 has a movable contact 6I, the respective contacts being connected in parallel between power-conductor extension 56 and alwire for energizing a time delay relay 62, so that whenever any red light indication responds this time delay relay 62 is also energized, its circuit being cleaning equipment, such fiashovers frequently occurring, for example, when large particles of dust are trapped which momentarily bridge the precipitator plates. These short-circuiting ii'asliovers or arcs quickly disappear'when the particles are burned out by the excess-current through them.

-In order to prevent this alarm from `continuouslysounding while at the same time maintaining the signalling system in operating condition for indicating a fault in any precipitator.

subdivision, an operator at the remote point at which the central panel 55 is located may deasiofzse press a normally spring-opened circuit maker 6l which completes the circuit to the coil of the vrelay 61 when the contact of the time delay relay is in its up or circuit closing position. Consequently, the contact 66 will be raised, interrupting the energizing circuit to the alarm 65 and establishing an obvious holding circuit for the coil of the relay 61 in the raised position of its contactor.

However, any red light indication R or R" is not disturbed so that the operator is fully informed f which precipitating subdivision requires attention. Accordingly, he may attend to the matter at the location of the faulty precipitator subdivision, andin order to do this he must open a door of a casing-unit or a door of the gas-conduit, all of which are provided with Adoor operated switches, such as 41, or other expedients assuring disconnection of the power supply, for deenergizing the equipment, the gas-conduit door switch or switches 41 preferably deenergizing all of the casing-units. Upon deenergization of the precipitating-apparatus, the signal lights, both at the local casing-units X and Y and at the remote panel 65 will go out and the different relays 60 will become deenergized, thereby deenergizing the time delay relay 62, which is of the quick release type. The deenergization of the time delay relay 62 releases its contact, thereby interrupting the holdingfcircuit of the relay 61 which drops its contact 56 to prepare the alarm circuit for subsequent operation without any further manual operation on thel part of the operator.

If a'double fault has occurred, and only one remedied, the alarm will resound when the energy is restored. It should be noted that when all of the lights at the central panel go out, this itself is an indication that thexprecipitator installation is deenergized. I

From the foregoing, it is apparent that I have extended the present available signalling systems for electrical precipitators of the type described, so that remote indications and an alarm will inform an operator of the operation-condition of large precipitator apparatus, the alarm being continuously primed to respond to any kind of fault in any subdivision of the precipitator apparatus.

I claim as my invention:

1. The'combination with a gas-purifyirm precipitator-assembly comprising gas-duct means having therein electrostatic gas-cleaning means for charging foreign particles -in the gas, and for electrostatically precipitating said charged particles, means for energizing said gas-cleaning means comprising relatively high-voltage voltage-conversion means comprising step-up transformer means, rectifying means and capacit'or voltage-smoothing means having output terminals adapted to supply rectiiied voltages, insulated short-lead electrical connections for connectlng said output terminals to said gas-cleaning means; of low-voltage signal means cooperating with said transformer rneans, comprising a signal and a remote alarm for actively indicating a faulty operation-condition of said precipitator-assembly as reected in said transformer means, normally-inactive means operable for cancelling said 'alarm operation but retaining said signal operation during said faulty operation-condition, said gas-duct means comprising ,door means for controlling the venergization of said gas-cleaning means by s/aid high-voltage voltage-conversion means, and for automatically restoring said normally-inactive means and alarm to inactive but operable condition for subsequent operation in accordance with their operations as aforesaid, upon deenergizatlon of said gas-cleaning means. Y

- 2. The `combination with a gas-purifying precipitator-assembly comprisingelectrostatic gascleaning means for charging foreign particles in the gas, and for electrostatically precipitating said charged particles, means for energizing said gas-cleaning means comprising relatively highvoltage voltage-conversion means comprising step-up transformer means, rectifying means and capacitor voltage-smoothing means having output terminals adapted to supply rectified voltages, insulated electrical connections for connecting said output terminals to said gas-cleaning means; of remotely located low-voltage signalmeans cooperating with said transformer means, compris- -ing a signal and an alarm for actively indicating a faulty operation-condition of said precipitatorassembly as reflected in said transformer means, normally-inactive means operable for cancelling said alarm operation but retaining said signal operation during said faulty operation-condition, and means whereby said normally-inactive means and alarm are automatically restored to inactive age means for causing an indication for indicating a faulty operation-condition of said gas-purifying precipitator-assembly as reflected in said voltageconversion` relatively high-voltage means; of remote signal means including alarm means. operableby said circuit means after said faulty operation-condition persists for a predetermined time.

5. The Acombination with a gas-purifying' precipitator-assembly comprising electrostatic gascleaning'means having relatively insulated ionizingv electrodes for charging foreign particles in the gas, and having relatively insulated precipitator-electrodes. for electrostatically precipitating the charged particles, and relatively high-voltage voltage-conversion means for supplying electrical energy to said gas-cleaning means; of low-voltage signal means cooperating with said voltageconversion means, having a signal with aresponse to excess-current operation-conditions in said gas-purifying precipitator-assembly, and an alarm operable with said signal but after said excess-current operation-conditions have persisted but operable condition for subsequent operation for a predetermined time, so that there will be no c alarm response to momentary flashes in said precipitator-electrodes.

6. In combination: a gas-purifying precipitator-assembly comprising a plurality of precipitator-iinits,.eacl1 precipitator-.unit comprising a plurality of current-consuming relatively insulated electrode-means; a pluralityY of high voltage energizing means, each for supplying energy to an associated selected number.. of -said precipitatorunits; a plurality of responsive means, each 4ass ociated with a one" of said energizing means, and

each responsively operative one manner to t .condition of excess current-consumptionby the electrode-means of the precipitator-units which are associated therewith lthrough the associated energizing said gas-cleaning means,` insulated A electrical connection means passing through said lgas-conduit for connecting said capacitor volt-v age-smoothing means to supply a rectified voltage to said ionizing electrodes and to supply a rectified voltage to said precipitator electrodes:

low-voltage signal means cooperating with said voltage-conversion relatively high-voltage means,

having a signal for indicating a normal or proper operation-condition of said gas-purifying precipitator-assembly, and'having a second signal for indicating one type of a faulty operation-condition of said gas-purifying precipitator-assembly, said signal means indicating a second type of a faulty operation-condition of said gas-purifying precipitator-assembly by the combination of 'both of said signals, said signal means being operated by the effect of s'aid operation-conditions on said transformer means, and single alarm means operable a predetermined time after operation of said second signal, either alone or in combination with the i'lrst said signal. v 4. The combination with a gas-purifying precipitator-assembly comprising electrostatic gascleaning means-for charging foreign particles in the gas, and for electrostatically attracting said ocharged particles; voltage-conversion relatively high-voltage means having output means for sup-v y plying rectified electrical energy forV saidv gascleaning means; insulated short-lead electrical connection means for connecting said output --=`fmeansntog`shaid gas-cleaning means: and s181181' means havinE`ci'rcuit-means locally associated energizing means, and responsively operative in another manner to a condition of inadequate cul'- rent-consumption by such electrode-means; a signal means associated with cach of said responsive means for indicating, at a plurality of places, in which of said manners the associated responsive .means is responsively operative; remote alarm 'means; means for causing said remote alarm means to operate with an indication by any of said signal means of either of said current-consumption conditions if such current-consumption A' condition persists for a predetermined time; and normally-inactive means manually momentarily operable for' causing discontinuance of the operation of said alarm means, said manually-operable normally-inactive means being automatically restored to normally-inactive but operable condi- 4' tion when the last said current-consumption condition ceases.

7. In combination; a gas-conduit means; a gaspurifyig precipitator-assembly in said gas-conduit means, comprising a plurality of precipitatorunits, each precipitator-unit comprising a pllrrality of current-consuming relatively insulated electrode-means; a plurality of power-supply means, comprising high-voltage energizing means outside said gas-conduit means, a power-supply means being provided forenergizing an associated selected number of said precipitator-units; a plurality of responsive means, each associated with a one of said power-supply means, andv each responsively operative in one manner to afaulty condition of current-consumption by the electrode-means ofthe precipitator-units which are associated therewith through the associated with said voltage-conversion relativelyhigh-volt-y 75 power-supply means, andresponsively operative in another manner to a normal condition of current-consumption by such electrode-means: a signal means for each of said responsive means, for indicating to which of said conditions the associated responsive means is responsively operative; alarm means for producing a remote alarm indication with a faulty condition indication by any of said signal means, which persists for a predetermined time; and normally-inactive means means without disturbing the last said faulty condition indication, said manually-operable normally-inactive means being automatically restored to normally-inactive but operable condition when such faulty condition indication ceases.


Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2566597 *Aug 5, 1949Sep 4, 1951Cass George JPower failure alarm
US2632522 *Oct 28, 1950Mar 24, 1953Westinghouse Electric CorpElectrostatic precipitator
US3266222 *Nov 29, 1963Aug 16, 1966American Air Filter CoVoltage indicator arrangement for electrostatic precipitators
US4533368 *Sep 30, 1982Aug 6, 1985Black & Decker, Inc.Apparatus for removing respirable aerosols from air
US5688308 *May 30, 1995Nov 18, 1997Trion, Inc.Electrostatic air cleaning system with air flow sensor
U.S. Classification96/26, 340/524, 96/82, 340/635, 340/327
International ClassificationB03C3/68, B03C3/66
Cooperative ClassificationB03C3/68
European ClassificationB03C3/68