CA2298789C - Electric arc monitoring systems - Google Patents

Abstract

Electric arc monitoring is effected by exploiting the discovery that electri c arcs are fractal phenomena with all essential information that signifies "arc" contained in each fractal subset. These fractal subsets are logarithmically distributed over the arc spectrum. Monitoring of arcs is most advantageously effected on a fractal subset of low logarithm ic order where the amplitude is higher pursuant to the 1/f characteristic of electric arcs (22), where cross-induction among neighborin g circuits is lower, and where travel between the arc and the arc signature pickup (23) is longer than at the high frequencies customary for a rc detection. Fractal subset transformation reduces the danger of false alarms. Arc signature portions may be processed in out of phase pat hs or treated as modulated carriers.

Description

2 Technical Field 3 The technical field of the invention includes methods and 4 apparatus for monitoring, detecting, indicating, evaluating and signaling electric arcs or sparks.
6 Background 7 The chaotic electromagnetic emanations manifesting 8 themselves as electric arcs or sparks are closely linked to 9 matter, wherein electromagnetic interactions bind electrons to nuclei in atoms and molecules and wherein the fundamental unit 1l of electromagnetic r~~diation is the photon.
12 Indeed, spectra of electric arcs and sparks extend 13 practically from DC through the entire radio-frequency spectrum 14 and through microwaves, infrared and light spectra.
Useful exploitations of the electric arc and spark 16 phenomenon include the electric arc lamp, electric weldi~xg, the 17 electric-arc-type of metallurgical furnace, the arc t.ppe of ion 18 generator in satellite thrusters and for propulsion in outer 19 space, the spark-plug-type of ignition in internal combustion engines, and electric spark ignition in gas appliance;3.
21 Unfortunately, the same quality of the electric arc oc spark 22 that led to electric lighting, electric arc welding and 23 metallurgy, and ignition of internal combustion, has catastrophic 24 effects in electrical faults that cause explosions or devastating fires through chaotic:: arcing or sparking.
26 By way of example, electric arc monitors would be useful in 27 garages, automobile or motorcar repair facilities, gasoline 28 (British "petrol" ) storage or dispensing facilities an~i in other 29 areas where accidental electric arcing can cause disastrous explosions.
31 Moreover, fuses and circuit breakers are c~ipable of 32 preventing serious overload conditions, but they are generally 33 ineffective to prevent electrical fires and other d~maQe from 1 accidental arcs and sparks which typically generate enough heat for a fire at electric current 2 levels below the level at which the fuse will blow or the circuit breaker will trip. Reliable arc 3 monitoring would thus be highly desirable in a large number and variety of electrical circuits.
4 These are, of course, only representative examples of fields where reliable arc or spark monitoring could be useful.
6 A major stagnating problem in this respect has been that prior-art development has 7 run its course in its fear of false alarms. Of course, false alarms are the bane of alarm 8 systems, as frequent occurrence of false alarms can nullify the utility of an alarm system.
9 Accordingly, in an effort to reduce the possibility of false alarms arising from radio broadcast and radio frequency security system signals, the arc detection system as disclosed 11 in the International Patent Publication W090/04278, by HAMPSHIRE, Michael John, rejects 12 frequencies below about 160 kHz and above some 180 kHz of the arc signal signature, 13 leaving for electrical fault detection only a narrow 20 kHz band at some 170 kHz center 14 frequency. This, however, left a sample for arc detection that was dozens of times too small 1 S in the 100 kHz range for reliably detecting the occurrence of an arc signature while at the 16 same time preventing the occurrence of false alarms equally reliably.
17 An arc detection system which avoids that drawback is apparent from 18 PCT/US90/06113, filed 24 October 1990 and published as W092/08143, by Hendry 19 Mechanical Works, inventors HAM, Jr., Howard M., and KEENAN, James J., and in its corresponding US Patents 5,373,241, issued 13 December 1994, and 5,477,150, issued 19 21 December 1995. Reference should also be had to their corresponding EPO 507 22 (90917578.8) and resulting European national patents, and to their corresponding Australian 23 Patent 656128, Canadian Patent 2,093,420, Chinese Patent 1077031, Japanese Patent 24 6504113T, Korean Patent 212020, and Mexican Patent 178914 (9201530). That system avoids false alarms by converting instantaneous arc signature frequencies into a combination 26 frequency from which arc-indicative signals are detected in contradistinction to extraneous 27 narrow-band signals that could cause false alarms.
28 Against this background, a frequency selective arc detection system appears as a 29 typical representative of the prior -art approach to arc detection. It accordingly presents a variety of approaches to arc detection that mainly look at frequencies in the upper kilohertz 31 range, such as from 100kHz to one megahertz. This, however, covers not only major 32 portions of the public A.M. radio broadcast band, also known as "longwave"
and "medium-33 wave" broadcast bands in some countries, but also the 1 kind of control or security systenos radio frequency barut refewed to in the above mentioned 2 W090/04278 reference. Depending on location, one thus had to contend with dozens of 3 extraneous signal interferences.
4 The same in essence applies to another embodiment in that prior-art proposal that suggests using a comb filter ar7-an~emont campo;~ed of four handpass tilters each of which O has a 50 kHz passband, and thref; csi' which have ~a c.mter l~reep~ncy oi~225 kHz, 525 kHz, and 7 825 kHz, respectively. In the A.IL9. broadcast arid above mentioned control and security 8 systems radio frequency hand pardon of that spccarum, 50 kHtz samples can only represent 9 minor fragments of the chaotic arc; signature, raising the danger of false alarms from coincidental extraneous signals. hhis also affecrs the el~fiecrcy of the ~5 kI
Iz bandpass, filter in 1 1 that comb tilter awangement, inasmuch as that prior-art pr-<>posal continuously rotates its I 2 detectic>n process among the four filter components of that comb filter arrangement.
13 A prior effort at arc detectic>n that ventured into low Frequency regions effected 14 monitoring in various low frequc;ncy bands that were too narrow for reliable arc detection as I S apparent from articles by B. D. h:ussell et al., cntitl~°d "An Arcing FaGrlt Detection ~Tec;hnique l6 Using I.ow Frequency Current ( on~ponents- Performance lvaluation lJsing Recorded Field 17 Data " and "Behaviour Ih 1 of Low Frequency Spectra During Arcing Fault and Switching 2 Events" (IEEE Transactions on Power Deliverlr, Vol. 3, No. 4, 3 October 1988, pp. 1485 - 1500) indicating lack of success.
4 These developments in retrospect appear largely as a reaction to the perception of electric arcs as highly random 6 phenomena borne out of the chaotic nature of arc signatures.
7 This prior-art perception, however, ignores the fact that chaotic 8 systems have a deterministic quality, and can be successfully 9 dealt with, if one is able to discover What the underlying principles are and how they can be put to effective use.
11 Indeed, even chaotic electric lightning displays some self-12 similarity among its arboresque nocturnal discharges and within 13 the branched configuration of its lightning bolts.
14 In this respect, pioneering work done by Benjamin Franklin and by Georg Christoph Lichtenberg back in the 18th Century casts 16 a long shadow all the way to the subject invention.
17 Ia particular, Franklin through his famous kite experiment 18 in a thunderstorm proved that lightning is an electrical 19 phenomenon. Lichtenberg thereafter created his famous ~Lichteaberg figures" in 1777 by dusting fine powder, such as 21 sulfur, over insulating surfaces over which electrical discharges 22 had taken place. Many of these Lichtenberg figures of electrical 23 discharge resemble lightning in appearance and otherwise display 24 a striking self-similarity in their patterns of branching lines and within such branching lines themselves. Manfred Schroeder 26 compared this to diffusion-limited aggregation (DLA) in his book 27 entitled "FRACTALS, CHAOS, POWER LAWS" (W. H. Freeman and Company, 28 1991), pp. 196, 197, 215 and 216. Kenneth Falconer, in his book 29 entitled "FRACTAL GEOMETRY" (John Wiley & Sons, 1990), pp. 270 to 273, also applied the DLA model to electrical discharges in 31 gas.
32 By way of background, fractals are phenomena in the fractal 33 geometry conceived, named and first explained by Benoit 34 Maadelbrot in 1975. Fractal geometry in eff~:ct is a manifestation of the fact that the natural world does not coafornn 36 to an Euclidean type of geometry. Euclidean geometry is based 37 on characteristic sizes and scaling. The natural world is not *rB

1 limited to specific size or scaling. Euclidean geometry suits 2 man-made objects, but cannot realistically express natural 3 configurations. Euclidean geometry is described by formulas, 4 whereas the mathematical language of natural phenomena is 5 recursive algorithms.

6 Such recursiveness is an expression of~nature throughout 7 destructive if not chaotic influences, manifesting itself, for 8 instance, in a persistent invariance against changes in size and 9 scaling, called self-similarity or self-affinity. Fractals are self-similar in that each of various small portions of a fractal 11 represents a miniature replica of the whole. Such small portions 12 are herein called "fractal subsets".
13 Electric arc or spark monitoring generally addresses itself 14 to so-called arc signatures which are part of the electromagnetic spectrum of arcs or sparks situated in frequency bands way below 16 light, heat radiation and microwave spectra.
17 Problems in this area include false alarms from mutual 18 induction among neighboring monitored circuits. In this respect, 19 reference may be had to a standard equation for mutual induction, such as between a monitored circuit in which an arc is occurring, 21 and a neighboring monitored circuit in which no arc is occurring 22 at the time:

24 In -_ 2~rfMI=./Z~ (1) 26 wherein: I" = arc signature current flowing in the monitored 27 circuit where an electric arc occurs at the 2 8 mome:a t , 29 In = current induced by the arc signature in a moni-tored neighboring circuit where no arc has 31 occurred at the moment, 32 M - mutual inductance, 33 Zn = impedance of said neighboring circuit, and 34 f - frequency.
36 As between neighboring circuits, the current I" inct~uced in 37 a neighboring monitored circuit by current I" flowing in the 1 monitored circuit where an arc is occurring, decreases with 2 decreasing frequency of that primary current I". However, 3 electromagnetic arc signatures are characterized by a special 4 shape approximating an inverse frequency (1/f) progression of their amplitude. If this is put into the above Equation (i) one 6 gets $ In = (2'~fMI"/f) /Zn (2) 9 in which "f" would cancel out, so that one gets 11 I" = 2rMI"/Z" ( 3 13 that is, a mutual inductance and a secondary current, I", that 14 are independent of frequency. Such considerations have led to the prior-art conclusion that lowering the frequency of arc 16 signature bands in which arcs are monitored would not effectively 17 reduce cross-induction and false arc alarms therefrom.

1 Summary of Invention 2 It is a general object of the invention to provide improved 3 electric arc monitoring systems that employ novel circuitry 4 and/or take advantage of properties of electric arc signatures not heretofore utilized.
6 It is a related object of embodiments of the invention to 7 permit reliable arc monitoring at distances from electric arcs 8 longer and with less cross-talk or induction than heretofore.
9 In this respect and in general, the expression "monitoring"
is herein used in a broad sense, including monitoring, detecting, 11 indicating, evaluating and/or signaling electric arcs or sparks, 12 whereas the word "arc" is herein used generically to cover 13 electric arcs and sparks interchangeably as being essentially the 14 same phenomenon.
From one aspect thereof, the subject invention exploits the 16 discovery that electric arcs are fractal phenomena not only in 17 the visible luminous portion of their electromagnetic radiation, 18 as heretofore thought, but in fact are fractal phenomena all the 19 way down to the extremely low frequency band of their electromagnetic emanation into space or along wires of the 21 circuit where the particular arc occurs. Since all essential 22 information that signifies "arc" is thus contained in each 23 fractal subset, it is sufficient for arc monitoring purposes to 24 monitor a fractai subset of the arc's electromagnetic emanation.
The realization according to the subject invention that the 26 fractai nature of the arc is not limited to its visible region, 27 but in fact extends all the way down to a few cycles per second 28 of its signature, adds to the previously known characteristics 29 of electric arcs at least one fundamental characteristic and at least one criterion; namely, that:
31 1. All essential information for effective eleci~ric 32 arc monitoring is contained in any fractal subset 33 of the arc signature; whereby 34 2. the selection of the monitoring frequency band for 1 each purpose is liberated from prior-art con-2 straints and can truly be the result of an optimum 3 tradeoff in sensitivity, speed of detection, 4 prevention or rejection of false signals, desired length of travel and mode of transmission of the 6 arc signature from the arc to the monitoring 7 circuit in different environments.
8 Pursuant to these principles, the subject invention resides 9 in a system of monitoring an electric arc having an arc signature typified by a wideband range of frequencies of a chaotic nature 11 in a monitored circuit, and, more specifically, resides in 12 selecting a fractal subset of the arc signature characterized by 13 relatively long travel along the monitored cir:;uit, and 14 monitoring that fractal subset of the arc signature.
The expression "relatively" in this context refers to the 16 fact that the length of possible travel of the arc signal is 17 inversely proportional to the frequency of the arc fiignature.
18 In this respect, reference may be had to the familiar algebraic 19 equation for electric current:
I = E/ [R2 + (2~rfL - 1/2nfC) z] ~' (4 ) 21 wherein: I = electric current, 22 E = voltage or potential, 23 R = resistance, 24 f = frequency, L = inductance, and 26 C = capacitance of the electric circuit.
27 From this equation a related benefit of an embodiment of the 28 invention can be seen; namely, that a selection of t:he lowest 29 frequency or longest wavelength fractal in effect amounts to a selection of the longest survivor of the different fractals of 31 the arc signature traveling along the monitored circuit. Up to 32 a point, one can say that the monitored circuit itself thus 33 performs the function of a low-pass filter for the arc detection 1 monitor. Accordingly, embodiments of the invention permit arc 2 monitoring at considerable distances from the occurrence of arcs 3 in the circuit, which is useful in practice for several reasons, 4 including the capability of surveying large circuits, and the convenience of providing central arc detection monitoring 6 stations for several different circuits.
7 At any rate, at low arc signature frequencies, the possible 8 travel of the arc signal along the monitored circuit is long, 9 relative to higher arc signature frequencies.
It also turns out that false alarms from mutual induction 11 among neighboring monitored circuits is lowest at low arc 12 signature frequencies, quite contrary to what the prior art would 13 have indicated pursuant to Equations (1) to (3) set forth above, 14 wherein the frequency factor "f" in the denominator would cancel out the "f" in the numerator in Equation (2).
16 However, the fallacy of that conclusion becomes apparent if 17 certain possible radiation effects are considered. In this 18 respect, it is well known that ~/2 and ~/4 antennas constitute 19 excellent Hertzian and Marconi-type electromagnetic radiators.
The wiring in many~telephone exchange, electric power supply and 21 other installations in effect often forms such antennas at the 22 kind of radio frequencies selected by the prior art for electric 23 arc detection purposes. Even where the length of some wiring in 24 an installation in insufficient to constitute a quarter-wave-length antenna, certain reactances in the circuit can provide the 26 lumped-impedance kind of tuning or "loading" that renders even 27 relatively short conductors effective radiators.
28 In consequence, picked-up electromagnetic arc signatures are 29 transmitted among neighboring circuits, resulting in false alarms, unless the segment of the arc signature picked up for 31 monitoring is of a very low frequency (VLF) according to one 32 aspect of the invention.
33 Accordingly, lower frequency fractals pursuant to 34 embodiments of the invention induce less spurious signals through cross-induction in neighboring circuits than arc signatures 36 having higher frequencies. Low frequency fractals more 37 effectively avoid false alarms from mutual inductance among 1 neighboring circuits than arc signatures at higher frequencies.
2 In consequence, embodiments of the invention not anly permit 3 arc monitoring at considerable distances from the occurrence of 4 arcs in a monitored circuit, but also avoid false alarms in 5 aeighboring monitored circuits.
6 According to a related embodiment of the invention, the 7 electric arc is detected from a fractal subset of the arc 8 signature at frequencies below 30 kHz. According to The New IEEE
9 Staadard Dictionary of Electrical and Electronics Terms, Fifth 10 Edition (The Institute of Electrical and Electronics Engineers, 11 1993), this is the upper limit of the very low frequency (VLF) 12 band.
I3 A presently preferred embodiment of the invention restricts I4 fractal subsets from which the electric arc is detected to the ELF (extremely low frequency) band which in that IEEE Standard 16 Dictionary is defined as extending from 3 Hz to 3 kHz.
17 Another embodiment of the invention restricts monitored 18 fractals to arc signature frequencies below the voice frequency 19 band (vf) defined in that IEEE Standard Dictionary as extending from 200 Hz to 3500 Hz.
21 In that vein, a further embodiment of the invention 22 restricts monitored fractal subsets to arc signature frequencies 23 below a first harmonic of a standard line frequency in 24 alternating-current power supply systems.
An embodiment of the invention even selects the monitored 26 arc signature fractal subset from a frequency band on the order 27 of a standard line frequency in alternating-current power supply 28 systems.
29 According to a related aspect of the invention, an apparatus for monitoring an electric arc having an arc signaturA typified 31 by a wideband range of frequencies of a chaotic nature in a 32 monitored circuit, comprises, in combination, an electric filter 33 having an input coupled to that arc, having a passband 34 corresponding to a fractal subset of the arc signature characterized by relatively long travel along the monitored 36 circuit, and having an output for that fractal subset of arc 37 signature. Such ap~raratus includes a chaotic wideband signal 1 detector having a detector input for that fractal subset of the 2 arc signature coupled to the output of the electric fa.ltEr.
3 From another aspect thereof, the invention resides in a 4 method of monitoring an electric arc having-an arc signature extending over a wideband range of frequencies of a chaotic 6 nature in a monitored circuit. The invention according to this 7 aspect resides, more specifically, in the improvement comprising, 8 in combiaation, processing portions of the arc signature in two 9 paths out of phase with each other, and monitoring thc~ electric arc from such out of phase portions of the arc signature.
11 From a related aspect thereof, the invention wesides in 12 apparatus for monitoring an electric arc having an arc signature 13 typified by a wideband range of frequencies of a chaotic nature 14 in a monitored circuit. The invention according to this aspect resides, more specifically, in the improvement comprising, in 16 combination, an electric filter having an input coupled to the 17 arc. having a passband corresponding to portions of the arc 18 signature, and havi~~g an output for such portions of arc 19 signature, an invertvng amplifier having an input connected to the output of the electric filter, and having an amplifier 21 output, a non-invert:i.ng amplifier having an input connected to 22 the output of the electric filter, and having an amplifier 23 output, and a chaotic wideband signal detector having :,. detector 24 input coupled to the amplifier outputs of the inverting and non-inverting amplifiers.
26 From another aspect thereof, the invention res:~des in a 27 method of monitoring an electric arc having an arc signature 28 extending over a wideband range of frequencies of a chaotic 29 nature in a monitored circuit, and, more specifically, :resides in the improvement comprising, in combination, treati:ag the arc 31 signature as a modulated carrier having a modulation indicative 32 of the electric or" and monitoring the electric =arc by 33 monitoring a modulatioa of the modulated carrier.

1 From a related aspect thereof, the invention resides in 2 apparatus for monitoring an electric arc haviag an arc signature 3 typified by a wideband range of frequencies of a chaoi:ic nature 4 in a monitored circuit, and, more specifically, resides in the improvement comprising, in combination, a modulated carrier 6 detector having an arc signature input and a carrier modulation 7 output.
8 From a similar aspect thereof, the invention resides in 9 apparatus for monitoring an electric arc having an arc signature typified by a wideband range of frequencies of a chaotic nature 11 in a monitored circuit, aad, more specifically, resides in the 12 improvement comprising, in combination, combined modulated 13 carrier detectors having arc signature inputs and a combined 14 carrier modulation output.

1 Brief Description of the Drawing's 2 The subject invention and its various aspects and objects 3 will become more readily apparent from the following detailed 4 description of preferred embodiments thereof, illustrated by way of example in the accompanying drawings which also constitute a 6 written description of the invention, wherein like reference 7 numerals designate like or equivalent parts, and in which:
8 Fig. 1 is a polar coordinate representation of na electric 9 arc signature spectrum in terms of Wavelength and illustrates selection of a fractal subset for arc monitoring pursuant to an 11 embodiment of the ixivention;
12 Fig. 2 is a block diagram of an electric arc monitoring 13 system pursuant to an embodiment of the invention;
14 Fig. 3 shows gain vs. frequency graphs illustrating a presently preferred embodiment of the invention;
16 Fig. 4 is a schematic of circuitry that may be used in the 17 system of Fig. 2 or rtherwise for monitoring an arc according to 18 an embodiment of the invention;
19 Fig. 5 is a schematic of another circuitry that may be used in the system of Fig. 2 or otherwise for monitoring an arc 21 according to an embodiment of the invention;
22 Fig. 6 is a schematic of a further circuitry that may be 23 used in the system of Fig. 2 or otherwise for monitor~.ng the arc 24 also according to an embodiment of the invention; anc.
Fig. 7 is a circuit diagram of an optical indicator of 26 possible or actual arcing that can be used at various stages in 27 the systems of Figs. 2, 4, 5 and 6, according to a further 28 embodiment of the invention.
29 The accompanying Fig. 1 is copyright ~ as an original creation under the Berne Convention and all corresponding 31 national laws, with Hendry Mechanical Works, cf Goleta, 32 California, United States of America, beiag the copyright 33 proprietor which understands that this figure will be published 34 by the World Intellectual Property Organization and thereafter by patent offices throughout the World.

WO 99/09424 ' PCT/US97/14497 1 Modes of Carrying' Out the Irwention 2 The drawings ilyustrate some basic modes and also preferred 3 modes of carrying oui: an aspect of the invention. Since yractal 4 geometry is a visual art as much as a mathematical science, Fig.
1 shows the workings of the invention in terms of a logarithmic 6 spiral. This is a novel aspect, since arc signature spectra 7 traditionally have been plotted in Cartesian coordinates and in 8 terms of frequency. To a large extent, thinking and plotting in 9 terms of frequency was justified, since the frequency of the arc signature is largely independent of the medium throug:~ which it 11 travels, while the wavelength of the arc signature de~~~ends more 12 directly on the traversed medium.
13 The traditional focus of the prior art on frequency ab 14 initio obstructed visualization of arc .signatures as a i5 logarithmic phenomenon of fractal nature, whereas thinking and 16 plotting in terms of wavelength according to the currently 17 discussed aspect of the invention, leads to visu~ili:~ation, 18 graphic representation and beneficial exploitation of that 19 phenomenon.
In this vein, the polar coordinate representation of Fig.
21 1 arises from the basic equation 2 2 r = exp ( q~") ( 5 ) 23 wherein: r = radius, 24 q = growth factor larger than 1, and ~" = polar angle in terms of wavelength in the particTilar 26 medium, such as monitored circuit wires.
27 The polar coordinate plot of Fig. 1 represents a logarithmic 28 growth spiral occurring in innumerable natural objects, including 29 the spiral ammonite-.: that appeared on the earth during the Devonian period which also brought forth algae and the first 31 terestial plants soma 380 million years ago. These developed in 32 the subsequent Carbc.~niferous period some 260 million years ago 33 to ferns that have very pronounced fractal structur~a wherein 34 each leaf structure is a miniature replica of the branch structure, and wherein each branch is a replica of the fern plant 36 or bush. Ammonites became extinct at the end of the ~~retaceous 1 period some 65 million years ago, but ferns are very much alive 2 along with millions of natural objects of fractal structure.
3 Fortunately for the insight needed in the subject invention, 4 the area where the pioneering mathematician Jacob Bernoulli lived 5 until 1705, had been a marine environment millions of years 6 earlier. This provided that region with an abundance of 7 petrified ammonites, along with a plethora of other 8 petrifications.
9 Bernoulli was so fascinated by the logarithmic spiral that 10 he devoted his famous treaty entitled "Spira Mirabilis"
11 (Wonderful Spiral) to the same. One of such wondrous properties 12 is that the logarithmic spiral is the perfect f racial in that it 13 persists through various changes. To magnification and reduction 14 it responds elegantly by rotational displacement, thereby 15 preserving its shape unaffected. This and other well-known 16 properties of logarithmic spirals reveals them as truly fractal 17 phenomena to which the electric arc signature seems akin, if 18 viewed in polar coordinates in terms of wavelength, such as in 19 Fig. 1.
In this respect, the ammonite shell had a chambered 21 structure wherein internal chambers were partitioned off by 22 septa, which were a series of spaced plates which were spaced 23 most closely at the center of the shell and the spacing of which 24 increased logarithmically along the growth spiral of the shell.
Accordingly, the size of the chambers between adjacent septa 26 increased logarithmically along the growth spiral.
27 In analogy to asnnonite shell chambers, the size of frequency 28 or wavelength intervals 12 between indicated wavelengths or 29 frequencies 13 also increases logarithmically in terms of wavelength in the electric arc signature or spectrum 10.
31 The core of tt~e electromagnetic arc emanation has been 32 labelled as <~. at the pole of Fig. 1, indicating wavelengths of 33 less than one micron; that is, signifying the familiar visible 34 light emitted by the arc. In the subsequent logarithmic turn, the symbol >~, has been shown to indicate infrared radiation and 36 microwaves that can be responsible for the utility of electric 37 arcs in electric welding, metallurgical furnaces, and internal 1 combustion engine ignition, and contrariwise in the sparking of 2 explosions and startup of devastating fires by electric arcs.
3 Thereafter, Fig. 1 indicates specific portions c:f the 4 electromagnetic arc signature in terms of frequency, including the following frequency bands with increasing progression:
6 GHz = gigahertz, 7 ~z = megahertz range wherein arc signature detection has 8 been conducted by the prior art and wherein extraneous 9 signals from television broadcasts and rad:~.a signals abound, 11 100 kHz - the one-hundred kilohertz range wherein ar~~

12 signature detection also has been conducted 13 extensively by the prior art and wherein radio 14 broadcast signals abound, 30 kHz = a lower limit of prior-art arc detection, 16 VLF = "very low frequency" defined as extending frorx 3 kHz 17 to 30 kHz by the above mentioned IEEE Dictionary.

18 ELF = "extremel~~~ low frequency" defined as extending from 19 3 Hz to ,4 kIiz by that IEEE Dictionary, of = "voice fr~:quency" within the range of 200 to 3500 Hz 21 according to that IEEE Dictionary, and 22 ef = "line frequency", i.e. 50 Hz in European Systems, or 23 60 Hz in American systems.

24 Of course, no patent drawing can actually depict tile chaotic nature of electric arcs. Rather, Fig. 1 as a minimum has to be 26 viewed in terms of an instantaneous moment in the chaotic 27 occurrence of an arc signature. Nevertheless, Fig. 1 shows the 28 statistical self-similarity of logarithmic fractal subsets of the 29 depicted arc signature.
Summarizing the ammonite analogy, the logarithmic nature of 31 the depicted arc spectrum is seen not only in the evc~lutian of 32 the growth spiral 10, but also to the logarithmically progressing 33 length of frequency intervals 12 in terms of ws.velength, 34 individually delimited by what corresponds to the above mentioned septa of the amanonite shell. In terms of the electric arc 1 signature, such septa correspond to radial lines 13 denoting 2 certain frequencies so that the intervals 12 between such 3 frequency points are logarithmically distributed along the arc 4 signature in terms of increasing wavelength or decreasing frequency.
6 Fig. 1 also depicts the inverse frequency or 1/f dependency 7 of electric arc signatures in terms of amplitude. In the case 8 of Fig. l, this shows as an amplitude increasing with wavelength 9 to a value of am.x~ This is another indication of the fractal nature of electric arcs.
1i On the subject of 1/f-noise. Dres. rer. nat. Heinz-Otto 12 Peitgen and Dietmar Saupe, have pointed out in their work 13 entitled "THE SCIENCE OF FRACTAL IMAGES" (Springer-Verlag, New 14 York, 1988) pp. 39 to 44, that there are no simple mathematical models that produce such noise, other than the tautological 16 assumption of a specific distribution of time constants.
17 This quite unlike to white naise on the one hand and 18 Brownian motion on the other hand. In this respect, they relate 19 the discovery that almost all musical melodies mimic 1./f-noise.
This to those serious researchers suggests "that music is 21 imitating the characteristic way our world changes in time".
22 Indeed, music with its numerous variations on a theme is replete 23 with fractals.
24 Dres. Peitgen and Saupe also point out that both music and 1/f noise are intermediate between randomness and predictability.
26 Even the smallest phrase reflects the whole. And so it is with 27 electric arc signatures, with such smallest phrase called herein 28 a "fractal subset".
Z9 As the Leitmotif in music, such fractal subset may have the nature of an attractor as a limit figure of fractal iteration, 31 as more fully described below.
32 In terms of indications in Fig. 1, a preferred embodiment 33 of the invention detects the electric arc from a fraci:al subset 34 below 30 kHz of the wideband range of arc signature frequencies.
This includes the above mentioned VLF (very low frequency) range 36 and frequencies below that range.
37 More specifically, an embodiment of the invention restricts 1 fractal subsets from which the electric arc is detected or in 2 which the electric arc is monitored to the ELF (extremely low 3 frequency) band which according to The New IEEE Standard 4 Dictionary of Electrical and Electronics Terms, Fifth Edition (The Institute of Electrical and Electronics Engineers, 1993) is 6 defined as extending from 3 Hz to 3 kHz.
7 Another embodiment of the invention restricts monitored 8 fractals to arc signature frequencies below the voice frequency 9 band (vf) defined in that IEEE Standard Dictionary as extending from 200 Hz to 3500 Hz. In that vein, a further embodiment of 11 the invention restricts monitored fractal subsets to arc 12 signature frequencies below a first harmonic of a sta~c:dard line 13 frequency in alternating-current power supply systems. An 14 embodiment of the invention even selects the monitored arc signature fractal subset from a frequency band on the order of 16 a standard line frequency (8f) in alternating-current power 17 supply systems.
18 In this manner, the invention in its embodiments can select 19 the fractal that will give the best overall performance in a given situation, all the way to the maximum arc signature 21 amplitude of a,~x for optimum signal-to-noise ratio; with the 22 signal in such case being the 1/f-noise of the arc which we have 23 designated above as ~" - noise. The noise in the expression 24 "signal-to-noise ratio", on the other hand, includes white noise and Brownian noise, such as produced by the electronic: circuits 26 of the arc monitoring apparatus, and extraneous signals that 27 could engender false alarms or readings.
28 Of course, depending on application, there may be goals 29 other than reaching a~,x, but as Fig. 1 depicts, arc signature amplitudes at various frequency fractals selected pursuant to the 31 subject invention in the larger.portion of the outer turn of the 32 growth spiral 10 still are significantly better than what the 33 prior art had to work with.
34 In this respect, selecting from the arc signature a fractal that yields an amplitude of a,~,X or an amplitude comparable 36 thereto according to an embodiment of the invention has another 37 advantage where cross-induction of arc signatures could be a *rB

1 problem. Take for example the case where several electric 2 circuits are monitored for electric arcs by several corresponding 3 arc detectors. and assume that an arc occurs in one of these 4 circuits and that the arc detector pertaining to that circuit is to respond thereto.
6 Pursuant to what has been said above at and of ter Equations 7 (1) to (4), by selecting a high-amplitude (i.e. long-wavelength 8 or low-frequency) fractal subset for the arc monitoring process, 9 a preferred embodiment of the invention minimizes if not practically eliminates the prior-art danger of false alarms from 11 cross-induction among independently monitored neighboring 12 circuits.
13 Fig. 2 shows an electric conductor 20 of electric circuitry 14 21 wherein an electric arc 22 occurs.
By way of example, the circuitry 21 may be part of a 16 telephone exchange or may be another one of a large variety of 17 electric circuits or loads, including the following examples:
18 In internal combustion engine research, develo~merrt, and 19 maintenance, it is important to establish and to maintain the optimum spark in each cylinder. A reliable spark monitoring 21 system is therefore highly desirable, if not putentially 22 indispensably in cutting-edge internal combustion engine 23 technology.
24 In a similar vein, electric welding is becoming increasingly robotized and reliable monitoring of the welding arc oz spark 26 would greatly benefit research, development and assembly-line 27 quality control and assurance in automated electric arc welding.
28 Moreover, many modern electric spot welding processes rely on 29 immediate application of electric energy to the work pieces to be joined, Without intervention of an electric arc. In fact, the 31 occurrence of an electric arc, such as by imperfect contact 32 between the work pieces, degrades the resulting weld in such 33 Joule-effect welding processes. Accordingly, the load at 21 may 34 for instance be a robotic or other spot welding apparatus. In that case, the electric arc monitor could supervise the spot 36 welding process and could signal when substandard welds are being 37 produced by intervening arcing. This, in turn, would signal the 1 need for remedial action, such as including better cleaning of 2 work pieces prior to welding or better compression of the work 3 pieces during welding for more intimate contact.
4 Also, modern descendants of the original electric arc lamp, 5 such as mercury or sodium vapor lamps, could beneøit as to 6 research and development and in the maintenance of high-quality 7 performance from reliable arc monitoring systems, as could 8 electric-arc-types of metallurgical and other furnaces.
9 Similarly, arc and spark monitoring systems would be useful 10 to detect and if necessary eliminate faults in electric circuitry 11 and equipment creating radio interference through excessive 12 sparking or arcing.
13 As a further example, some gas heating appliances have 14 gaseous fuel ignitors that work with an electric spark. In such 15 cases, it is often important to know whether the desired spark 16 has occurred for proper ignition, especially if the thermostat 17 is remote from the heating unit. Also, an electric spark monitor 18 would indicate when the igniter is in need for replacement, 19 before breakdown and costly outage occur.

20 Moreover, electric arcs are used in ionizers: such as 21 ammonia arc and other ion generators that are coming intc use in 22 satellite thrusters and in propulsion systems in outer space, 23 such as for restabilizing satellites in geostationary orbits or 24 for propelling satellites and space probes on their journey. In such cases, an electric arc monitor would be useful in research, 26 development, maintenance and operation of such ion generators.
27 Alternatively, machinery, circuitry or apparatus at 21 that 28 produces normal sparks in its operation could be monitored for 29 detrimental arcing. One of many examples concerns cummutators of electric motors that are often damaged when th~:ir carbon 31 brushes wear out, as the rotating commutator then rubs against 32 the metallic brush holder springs. Siace such Wear is 33 accompanied by heavy arcing, an early detection of ;such heavy 34 arcing, as distinguished from regular commutator spar~:ing, would signal the need for preventive action and could save the 36 equipment from breakdown and severe damage. The same applies to 37 relays and contactors that generate sparks and arcs in their *rB

1 normal operation, but are subject to excessive arcing in case of 2 malfunction or excessive wear.
3 Similarly, the recurrence of the electric automobile as an 4 environmentally friendlier vehicle than, the gasoline-drives automobile or petrol-driven motorcar, renders reliable arc 6 monitoring even more important. In particular, such electric 7 vehicles carry large storage batteries that have to be recharged, 8 typically overnight, and that generate combustible gases, such 9 as oxygen and hydrogen, during such recharging. Electric arcing obviously could be disastrous in such as atmosphere. Accordingly, 11 monitoring that environment for electric arcing sad shutting down 12 the charging process and giving an alarm immediately upon 13 detection of arcing, could prevent disaster.
14 In all these cases, the invention selects a fractal subset 16 of the signature of the electric arc 22 for the purpose of arc 16 detection. In such selection the invention aims for a relatively 17 long travel of arc signature along the monitored circuit 20 18 (distance between arc 22 and pickup 23), and for low cross-19 induction among neighboring circuits, including the monitored circuit 20.
21 According to a preferred embodiment of the invention, the 22 fractal subset of arc signature is selected in a frequency band 23 below 30 kHz, where arc signature amplitudes are higher, arc 24 signature travel along wires (20) is longer, and arc signal cross-induction among separately monitored neighboring circuits 26 (21, 30) is lower, than at higher frequencies.
27 The invention then detects the electric arc 22 from the 28 fractal subset 16 of the arc signature. A preferred embodiment 29 of the invention detects the electric arc 22 from a fractal subset of the arc signature below 30 kHz, such as is the ELF
31 (extremely low frequency) band. defined above~as exte;ading from 32 3 Hz to 3 kHz, or even below the voice frequency band (vf) 33 defined above as extending from 200 Hz.
34 By Way of example Fig. 3 shows such a fractal subset of the arc signature at 16 within a band 15 illustrated on a logarithmic 36 scale. In practice, selection of such a low-frequency fractal 37 subset 16 avoids false alarms by cross-induction, such as between 1 the circuit 20 where an arc 22 does occur, and any separately 2 monitored neighboring circuits 30, etc., wherein no arc occurs 3 at the moment or, conversely, between any neighboring circuit 4 where an electric arc does occur and is monitored by another monitoring circuit 19, and the circuit 20 when no arc occurs at 6 that point.
7 Selection of such low-frequency fractai subset 16 also 8 pezmits detection of the arc 22 from a remote location along 9 wires 20 over longer distances than would be possible at high frequencies. Selectian of such a low frequency band also yields 11 a high amplitude input signal for the detection process according I2 to the above mentioned 1/f or ~" characterist:ic of the arc for 13 highest signal-to-noise ratio with lowest exposure to false 14 alarms.
Sensitivity to switching transients in telephone exchanges, 16 to multiplexed audio and otherwise. and to harmonics of alterna-17 ting-current supply frequencies may be practically eliminated, 18 and the permissible travel distance of arc signals between the 19 arc 22 and the pickup 23 may be multiplied as compared to high-frequency detection systems, by selecting the narrower frequency 21 band 15 on the order of a standard line frequency in public 22 alternating-current power supply systems. Preferably, according 23 to that embodiment, the selected narrower frequency band is below 24 the first-order harm~~nic of that standard line frequency.
According to the embodiment illustrated with the aid of Fig.
26 3, the selected arc signature fractal subset may be a filter 27 passband 15, below line frequency, such as below 50 Hz for 28 European-type systems and below 60 Hz for American-type systems.
29 Accordingly, it may be said that arc monitoring according to a preferred embodiment of the invention concentrates on the 31 low end of the arc signature spectrum.
32 The fractal subset of the arc signature 16 or the passband 33 15 from which detection of an arc 22 takes place, covers at least 34 a quarter of a logarithmic decade of the wideband range of frequencies of the electric arc 22.
36 This overcomes a drawback of the prior-art approach 37 manifestation in the above mentioned W090/04278 that missed the 1 point by limiting the band of detection to within some 20 kHz at 2 some 170 kHz center frequency. this, however, left only a few 3 percent of the arc signature information in the particular 4 logarithmic decade available for detection, considering that a range of 20 kHz in the 170 kHz area is but a small fragment of 6 the particular logarithmic decade that contains the information 7 signifying "arc" as distinguished from other signals.
8 The situation is not much better in the case of most 9 bandpass filter components of the comb filter disclosed in W090/0427$. All but the first bandpass filter component have 11 center frequencies belonging in effect to the fifth logarithmic 12 decade covering from 140 kHz to one hertz less than 1 MHz.
13 Since all these components have a 50 kHz bandwidth, they can 14 only pass a small percentage of the arc signature information in the particular logarithmic decade for detection of an arc as 16 distinguished from other error signals or from picked-up 17 extraneous signals. By rotating detection among the components 18 of its comb filter arrangement, that prior-art proposal even 19 misses an opportunity of making best use of its lowest frequency component in the 55 kHz area.
21 By way of example, the invention may be practiced with the 22 circuitry shown in Fig. 2. In that circuitry, an electric arc 23 22 having an arc signature typified by a wideband range of 24 frequencies of a chaotic nature, is detected with the aid of an electric filter 25 having an input 26 coupled to that arc, 26 having a passband corresponding to a fractal subset 16 of the 27 arc signature characterized by relatively long travel along the 28 monitored circuit and low cross-induction among neighboring 29 circuits, and having an output 27 of that fractal subset of arc signature. Chaotic wideband signal detector circuitry having a 31 detector input for that fractal subset 16 of the arc signature 32 may be coupled to that output of the electric filter, such as 33 disclosed in the further course of Fig. 2.
34 The arc signature pickup 23 may be of a conventional kind, such as a clamp-on current transformer terminating into an 36 impedance 24 that may be symbolic of a conventional peak-to-peak 1 limiter for clipping unusually large input transients, such as 2 with the aid of two high-speed diodes connected back to back with 3 one side to ground and a series current limiting resistor.
4 The pickup or transformer 23 may for instance be wound to be sensitive to frequencies in the 25 Hz to 50 Hz range with a 6 minimum of insertion loss. Such transformer 23 may be clamped 7 around the line 20 to be monitored. Hall effect sensors present 8 another example of arc signal pick-ups that may be employed in 9 the practice of the invention, which extends to the use of other sensors of a wired or wireless type. Other monitored circuits 11 30, etc., may be provided with like or similar pickups 123 and 12 monitoring circuitry 19.
13 The picked-up arc signature signal or fractal subset 16 is 14 passed through a lowpass filter 25 having an input 26 connected to the arc signature pickup 13. In a prototype of this 16 embodiment, the configuration of this filter is that of two 17 cascaded 3rd order Butterworth filters; but other configurations 18 and other kinds of filters may be selected within the scope of 19 the invention.
The gain vs. frequency plot of Fig. 3 shows a typical 21 response characteristic 41 of such a filter, having little 22 attenuation in the selected narrower frequency band 15.
23 Within the scope of the invention, the passband 15 could 24 cover an entire logarithmic decade, such as from 10 Hz to 100 Hz .
According to an embodiment of the invention the monitored arc 26 signature fractal 16 or passband 15 covers not more than a 27 logarithmic decade of the wideband range of frequencies of the 28 electric arc 22, inasmuch as the decade of from D.C. to 10 Hz is 29 rather a regular decade than a logarithmic decade.
In this respect, Fig. 3 shows only about half of a 31 logarithmic decade for the upper portion of the filter 32 characteristic 41 at passband 15. This demonstrably has provided 33 reliable arc detection with the illustrated embodiment of the 34 inventiozl. Depending on circumstances, the fractal of arc signature 16 may be even less than as illustrated in Fig. 3, but 36 should cover at least a quarter of a logarithmic decade of the 37 wideband .range of frequencies of the electric arc, far reliable 1 arc detection with simultaneous exclusion ~f false alarms.
2 In principle. aspects of the invention herein disclosed can 3 be applied to frequency bands other than the preferred ELF
4 (extremel~r low frequency) band, and the subject applicants have 5 built models of the circuitry shown in Fig. 2 not only for the 6 ELF band, but also for operation at several kilohertz, as well 7 as in the 10 to 20 kHz region.
8 According to a preferred embodiment, the narrower frequency 9 band 15 0:: fractal subset 16 is selected where there are less 10 extraneous signals than in a remainder of the wideband range of 11 frequencies of the arc signature. In this respect, the 12 embodiment illustrated in Fig. 3 shows the narrow frequency band 13 15 as covering from about 10 Hz to less t~:an 50 Hz where there 14 are no significant switching transients in telephone exchanges, 15 effects of multiplexed audio signals, harmonics of alternating-16 current supply frequencies, signals from control or security 17 systems and radio broadcast signals. However, not all 18 embodiments of the invention are intended to be limited to 19 operation within and below the very low frequency range.
20 According to Fig. 2, the output 27 of the filter 25 is 21 applied to nonlinear processing in what is herein called a non-22 linear processor 42. Hg way of example, such non-linear 23 processor may comprise a demodulator also called "modulated 24 carrier diatector" that demodulates signals passed by the filter 25 25, including picked-up electric arc signature segments with 26 chaotically varying amplitudes and frequencies. This and other 27 aspects c~f the invention treat a fractal subset of the arc 28 signature as a modulated carrier having a modulation indicative 29 of an electric arc 22, and monitor the electric arc by monitoring one or mcxe modulations on such modulated carrier.
31 Apparatus for monitoring an electric arc having an arc 32 signature. typified by a wideband range of frequencies of a 33 chaotic nature in a monitored circuit, include a demodulator or 34 modulate2. carrier detector such as in the non-linear processor 42 having an arc signature input 27 and a carrier modulation 36 output 43.
37 Fey ~~ay of example, the fractal subset of an arc signature 1 may be treated as an amplitude-modulated carrier, and the 2 electric arc may then be monitored by monitoring a modulation of 3 such amplitude-modulated carrier, such as by recovering the 4 modulatio~a on such amplitude-modulated carrier, aad by then detecting the amplitude from such recovered modulation.
6 Acco:rdingiy, the non-linear processor 42 may be an Abt 7 detector or demodulator that in response to chaotically varying 8 amplitudes at 27 produces an AC signal at 43 as a function of 9 such chaotically varying amplitudes. More steady signals erroneously picked up by the circuitry 23 to 27, on the other 1l hand, produce no such AC signal. The non-linear processor 42 12 thus is a .first stage that distinguishes picked-up arc signatures 13 from signals stemming from radio or television broadcasts, radio 14 frequency security systems or other sources except electric arcs.
The non-linear processor 42 thus in effect treats the 16 picked-up arc signature as an amplitude-modulated or AM carrier 17 whose modulation can be monitored by monitoring a modulation or 18 amplitude of such monitored carrier, such as for detection of an 19 electr:i.c arc 22. At least in the case of AM detection, such 'modulation' still includes its 'carrier'. Such carrier may be 21 stripped from its modulation by such means as a bandpass filter 22 44 connected to the output 43 of the non-linear processor or AM
23 detector 42. By way of example, the bandpass filter 44 may 24 comprise a 3rd order Butterworth filter, or a filter with a similar zesponse. A preferred responsF: of such filter in 26 principle may follow the characteristic 41 shown in Fig. 3, 27 except that the gain may be adjusted as desired or necessary.
28 By way of example, the filter 44 may pass alternating-current 29 signals of frequencies below 20 or 30 Hz and reject spikes and other fait signals that might be produced or occur within the 31 circuitry up to that point.
32 The recovered modulation signifying "arc" appears at the 33 output 45 of bandpass filter 44.
34 According to an embodiment of this aspect of the invention, combined modulated carrier detectors having arc signature inputs 36 and a combined carrier modulation output may be used in 37 monitoring electric arcs.

1 In this respect such combined modulated carrier detectors 2 may be like kind modulated carrier detectors; such as both AM
3 detectors or both FM detectors. An example of this is shown in 4 Fig. 2 ac~:.:ording to which like kind modulated carrier detectors are series connected.
6 In ~uarticular, the output 45 of bandpass filter 44 is 7 connected to a second demodulator 46 which, for instance, may be 8 an AM demodulator or detector for producing at its output 47 a 9 signal level varying as a function of picked-up arc signature.
With:i.n the scope of the invention, like-kind modulated 11 carrier detectors may be parallel connected, such as within non-12 linear processor 42.
13 Within the broad aspect of the invention, it should be 14 understood that other types or kinds of demodulation techniques may be used, such as those developed for frequency modulation, 16 phase modulation or carrier-suppressed or single-sideband 17 modulation, for example.
18 Accordingly, the non-linear processor 42 may, for instance, 19 include an FM demodulator which at output 43 produces a signal in response to such chaotic variations of phase or frequency as 21 occurring in an electric arc signature. In this respect, the 22 combined modulated carrier detectors may include different kinds 23 of modulated carrier detectors, such as an FM detector at 42 and 24 an AM detector at 46 connected in series.
According to an embodiment of the currently discussed aspect 26 of the invention, an arc signature is treated as a carrier 27 modulated both in a first manner and in a different second 28 manner, and its electric arc is monitored by monitoring first and 29 second modulations of said carrier modulated both in said first manner. anal in said second manner.
31 By ~~ay of example, different kinds of modulated carrier 32 detectors include an AM detector and an FM detector, and such AM
33 detector and FM detector are connected in parallel.
34 By way of example, the non-linear processor 42 may include parallel-connected AM and FM demodulators 412 and 413 having 27 36 as their common input, and having individual outputs connected 37 to an ANh-element 414, such as shown in Fig. 4.

1 AND-element 414 only provides an output signal at 43 if both 2 ~ the AM demodulator 412 responds to chaotic amplitude variations 3 of the picked-up signal at 27 and the FM demodulator 413 responds 4 to chaotic phase or frequency variations of that signal at 27.
This, then, provides a further safeguard against false 6 alarms from such extraneous signals as AM broadcast or control 7 signals and FM broadcast or control signals, and assures that 8 picked-up signals are only signified as stemming from electric 9 arcs if they display not only the chaotic amplitude variation, but also the chaotic phase or frequency variation, that 11 characterize electric arc signatures.
12 Preferrably, full-wave rectification or detection is used 13 at 42 and 46 instead of a half-wave rectification or detection, 14 in order to improve the speed of detection. Such increased speed, in turn, permits selection of a lower frequency band, such 16 as 15 shown in Fig. 3, where signal-to-noise ratio is at a 17 maximum with extraneous signals 52 being at a minimum, even in 18 the deliberately exaggerated showing of Fig. 3. In other words, 19 selection of full-wave rectification or detection alleviates the tradeoff of lower detection speed at lower detection frequencies.
21 The above mentioned higher and less error-affected sensitivity 22 of detection is thus realized without objectionable delays in 23 detection.
24 The arc-indicative signal resulting at an output 47 from the detection process at 46, is timed and level sensed at 48.
26 Conventional RC-type or other timing circuitry and conventional 27 comparator circuitry may be employed at 47 to prevent the arc 28 detector from responding to switching transients, contact 29 bouncing, ordinary commutator arcing and other transient, harmless arcs, such as more fully discussed herein with respect 31 to Fig. 6. Alarm circuitry 50 thus responds only to arcs that 32 sustain themselves for a given, dangerous period of time.
33 The circuitry 47 may include a conventional resettable 34 latching arrangement for latching in an alarm condition if an arc 22 occurs and all detection criteria are met as herein described.
36 Various control circuits may be energized at this point, such as 37 for providing an audible alarm, a remote fire alarm, etc., or for 1 shutting down power is the affected line 20. Since circuits of 2 this kind are known per ~, only a block 50 has been shown to 3 signify the possible presence of such control and alarm circuits .
4 The embodiment of Fig. 2 elegantly avoids false alarms from extraaeou;~ signals, without narrowing the bandwidths of picked-up 6 arc signals to significantly leas than a fractal subset 7 containing sufficient arc information. Such avoided extraneous 8 signals fir instance include television signals, radio broadcast 9 signals, ~~arious control signals, harmonics and other signals that ante relatively narrow in bandwidths as compared to the wide 11 band of chaotic arc signals.
12 Some extraneous signals, such as those which are of a 13 chaotic nature themselves, may have to be subjected to some 14 common-mode rejection or other processing in order to avoid confusion thereof with chaotic arc signatures. Such rejection 16 of extraneous signals elegantly comes about when picked-up 17 signals are beat against themselves, such as in the context of 18 the following embodiments of the invention.
19 In this respect, refinements pursuant to embodiments of the invention derive from the arc 22 a fractal arc signature subset 21 16 Within a frequency band 15, and convert that fractal arc 22 signature subset 16 to an arc signal 17 in a frequency band 18 23 distinct from that fractal subset or frequency band 15, such as 24 shown in Fig. 3, and detect in that arc signal 17 a chaotic wideband characteristic typical of an electric arc. A preferred 26 embodiment of the invention subjects the fractal subset 16 to a 27 frequency transformation, such as shown at 17 in Fig. 3, and then 28 detects the electric arc 22 from that fractal subset after 29 frequency transformation. By way of example and not by way of limitation, the fractal subset 16 may be added to itself and the 31 electric arc 22 may be detected from the fractal subset added to 32 itself, such as in the manner disclosed in Figs. 3 and 5.
33 In particular, a component 142 of the circuitry shown in 34 Fig. 5 prEVents extraneous signals that do occur in the monitored frequency band from affecting the arc detection process.
36 According to that technique, narrow-band extraneous signals in 37 the monitored fractal subset 16 of the arc signature are *rB

1 diminished in energy relative to a remainder of that fractal 2 before detection of the electric arc from that fractal. Such 3 component may be a frequency converter 142 that has converter 4 inputs 127 and 227 for the arc signature fractal subset 16 5 coupled. to an output 27 of electric filter circuitry 25, and has 6 a converter output 43 for an arc signature segment 17 in a 7 frequency band 18 distinct from the pasabaad 15 of the filter 8 circuitry 25. A chaotic wideband characteristic typical of an 9 electric arc is then detected from such converted arc signal 17, 10 such as w:~th a chaotic wideband signal detector.
11 By way of example and not by way of limitation, the input 12 and output terminals 26 and 45 may be the same in Figs. 2 and 5, 13 whereby the remainder of the circuit may be the same for Fig. 5 14 as in the apparatus of Fig. 2 more fully described above.
15 The ~.llustrated embodiment of the invention even alleviates 16 the inherent tradeoff of slower detection speed at lower 17 frequenci~a. In particular, by converting the selected arc 18 signal fractal subset 16 from the lower frequency band 15 to a 19 higher frequency band 18 such as shown in Fig. 3 or higher, the 20 currently discussed embodiment of the invention realizes the 21 detection Speed corresponding to the higher frequency band 18 for 22 an arc signature fractal subset i6 stemming from the lower 23 frequency band 15 where there are less extraneous signals and 24 where cross-coupling among circuits is lower and actual travel 25 distance of picked-up arc signals is higher than at frequencies 26 above the band 15. At the same time, the illustrated pref erred 27 embodimen~c of the invention realizes for the higher detection 28 speed associated with the higher frequency band 18 the lower 29 cross-coupling among circuits and the longer possible travel 30 distance along the affected line 20 that are associated with the 31 lower frequency band 15. An arc 22 occurring in line 20 thus may 32 be picked up from such line 20 at a considerable distance from 33 that arc, without a release of nay arc alarm condition in 34 neighbori~.~.g lines that are individually equipped with arc pickups 123 and a,.rc monitoring circuits 19 which correspond to the 36 circuitry of Figs. 2, 4, 5 or 6, but in which no arcs are 37 occurring at the time.
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1 As a3.ready indicated, the passband of the filter circuitry 2 25 may be located where there are less extraneous signals than 3 is a remainder of said wideband range of frequencies. Such 4 passbaad may be in the ELF (extremely low frequency) band, or even belong the of (voice frequency) band, or below a first 6 harmon:.c of a standard line frequency in alternating-current 7 power supply systems, or may even be on the order of a standard 8 line frequency in alternating-current power supply systems, 9 and/or ma~~ cover at least a quarter of a logarithmic decade of the wideb~~nd range of frequencies of the electric arc, so as to 11 provide sufficient information for a reliable detection of the 12 arc sigaa:~ from that logarithmic decade.
13 The frequency converter 142 of Fig. 5 may constitute the 14 son-linear: processor 42 of Fig. 2. By way of example, the component 142 may include a multiplier having first and second 16 inputs 12~ sad 227 connected to a single line 27 for receiving 17 the filtered picked-up arc signal. This has the net effect of 18 mixing the signal with itself, creating sum and difference 19 products at its output 43. Hy way of example, the component 142 may be a four-quadrant multiplier of the type AD633. However, 21 within the scope of the invention, a diode or non-linear circuit 22 may be us~:d for intermodulation of the selected fractal subset 23 16 with itself.
24 By way of example, Fig. 5 in effect adds the arc signature fractal subset 16 to itself in mixer 142 so as to double the 26 frequency band 15 of that fractal subset as the distinct 27 frequency band 18 of the arc signal 17 which may be somewhat 28 truncated,. such as by a subsequent filter 144 at the lower end 29 at that higher band 18. That filter may be similar to the above mentioned filter 44 in the circuit of Fig. 2, but may have a 31 narrower bandpass characteristic, such as shown at 51 in Fig. 3.
32 In apparatus terms, a frequency converter, such as component 33 142, has two converter inputs, such as 127 and 227, for the arc 34 signat~.xre fractal subset 16 coupled to the output 27 of the electric Filter circuitry 25, and has a converter output 43 of 36 the arc ;.ignature signal in a frequency band 18 double or 37 otherwise higher than the frequency band 15 of the arc signature 1 fractal subset.
2 The component 142 in effect dilutes re~,gular, man-made, non-3 chaotic signals that, if picked up and not diluted, might produce 4 false alarms. The multiplier or similar stage 142 does more than simply double the frequencies of the input. It also beats all 6 the frequencies occurring at one input 127 against all the 7 frequencies occurring at the other input 227. This causes the 8 output to display a summation of all the individual frequencies 9 at one input added and subtracted from all the frequencies at the other ia~ut. Since both inputs contain a continuum of 11 frequencies, the result is a very rich mix of frequencies at even 12 higher and lower frequencies than those contained at the inputs.
13 Because a man-made signal is usually a discrete single frequency 14 or at wor:~t a narrow spread of frequencies, such signal does not have the breadth of spectrum to contribute strongly to the output 16 at 43. Such man-made signal constitutes a narrow source beating 17 against the broader naise or arc signature continuum, and the 18 result is a very weak component at the output.
19 In this manner, the relative strength of the continuum spectrum from the arc is enhanced compared to the strength of any 21 discreet ~r man-made components that are passed by the limiter, 22 such as at; 24, or by the filter circuitry. This is the essence 23 of this embodiment's ability to reject signals that would produce 24 false alarms. However, a fluctuating carrier with no noise at the input could still be misidentified as an arc if it has 26 sufficient strength, because even though the relative sensitivity 27 to chaotic noise is greater than to modulated carriers, the 28 latter can still reach the output if they are of sufficient 29 strength, and thus can produce a level that may be mistaken as an arc.
31 Accordingly, the output of the converter or multiplier 142 32 is fed to the input of a bandpass filter 144, that may have a 33 response characteristic 51 as shown in Pig. 3. Response 34 characteristics of the type shown in Fig. 3 at 51 may, for instance, be realized by operational amplifier type of bandpass 36 filters, quartz filters, LC resonance filters, and other 37 circuitry accomplishing such kind of function.

1 As can be seen, the characteristic 51 displays minimal 2 response to any fundamental frequency passed by the lowpass 3 filter 25, such as in the band 15, and, in our example, displays 4 response only to frequencies of the picked-up arc signature fractal subset 16 whose sum or other modulation product falls in 6 the passband range 18 of the frequency-converted arc signature 7 signal 17.
8 Baadpass filter 144 will pass only frequency components that 9 are within a few hertz on either side of the passband, such as 80 Hz, fir instance. This delivers a sample of the higher 11 frequencies in the output of the multiplier 142 to the next stage 12 46. Because the passband is above the 50 8z or other selected 13 cutoff of the first filter 25, this stage 144 is only going to 14 pass signals which have been boosted in the mixing process to frequencies higher than such cutoff. This i.n effect prevents 16 non-chaotic signals from passing this stage.
17 In principle, the multiplier or stage 142 should not pass 18 any of the original input frequencies (e. g. below 50 8z) if there 19 is no direct-current at either input 127 and 227, and if such multiplier or stage 142 is perfectly efficient. However, neither 21 assumption is always correct in practice. Accordingly, use of 22 the higher frequency passband filter 144 provides effective 23 rejection. of the unprocessed or unmixed original frequencies.
24 If a higher band of detection frequencies had been selected within the scope of the invention, such as a band limited between 26 10 and 20 kHz, as an example, an alternate choice for bandpass 27 center frequency would be at some much lower frequency (i.e. 500 28 8z.) detecting a difference component in the output 43 of 29 multiplier 142. This would permit a much wider separation in the responses of the different filters employed in the circuitry, 31 such as filters 25 and 144.
32 In either case, the frequency conversion or intermodulation 33 at 142 greatly reduces the energy of picked-up extraneous signals 34 52 in the: arc signature segment 16, by intensive common-mode or similar rejection.
36 The output 43 of the multiplier 142 represents a chaotic 37 frequency sum or difference signal version of the picked-up and 1 filtered chaotic arc signature fractal subset 16.
2 Within the scope of the invention, the component 142 may 3 also include the above mentioned AM or FM detector or the 4 combined AM and FM~detectors 412 and 413 of Fig. 4, for instance.
In such cases, the detector or detectors detect the amplitude 6 aad/or frequency or other type of modulation in the converted arc 7 sigaature, such as iadicated at 17, for arc monitoring purposes .
8 Fig. 6 shows aaother embodiment of the invention where the 9 energy of extraneous signals is subjected to effective common-mode or similar rejection by pairing inverting and non-inverting 11 amplifiers 242 and 342 with each other. By way of example, the 12 inverting amplifier 242 has an input 327 connected to the output 13 27 of bandpass filter 25, and the non-inverting amplifier 342 has 14 an input 427 connected to that output 27 of the above mentioned baadpass filter 25 through which the picked-up arc signal is 16 processed.
17 The inverting amplifier 242 has an output 421 connected to 18 a mixer 442, and the non-inverting amplifier 342 has an output 19 422 connected to that mixer 442.
The electric filter 25 in the embodiment of Fig. 6 may be 21 the same txs the electric filter 25 in the embodiments of Figs.
22 2 to 5. Such a filter may be split in two, providing between the 23 terminal 26 a first filter for the inverting amplifier 242 and 24 a second filter for the non-inverting amplifier 342. Filter 25 may be similarly split in or for the embodiment of Figs. 4 and 26 5 to provide separate filter paths from the input terminal 26 to 27 detectors 412 and 413 or multiplier or frequency converter inputs 28 127 and 227.
29 By way of example, the mixer 442 may be composed of conventional components, such as of two diodes interconnected in 31 an OR-element configuration between input terminals at 421 and 32 422 and the previously mentioned output terminal 43. Within the 33 scope of that embodiment, the component 442 may, however, include 34 a modulator, such as the above mentioned modulator 142. In this respect and in geaeral, the circuitry in Fig. 6 between the 36 filtered arc signature portion or segment at 27 and the terminal 37 43 may correspond to the non-linear processor 42 shown in Fig.
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1 2. The output of such processor 42 or 242, 342, and 442 at 43 2 may be filtered or otherwise processed at 244. For example, the 3 circuit 244 may include a baadpass filter corresponding to the 4 bandpass filter 4426 or 144 mentioned above with respect to 5 Figs. 2 to 5. Alternatively or additionally, the component 244 6 in Fig. 6 may include a standard IF amplifier, such as the 7 commercially available 440 Hz IF amplifier to name an example.
8 In method terms, the embodiment of Fig. 6 processes a 9 fractal segment, such as shown at 16, or a higher frequency 10 segment of the arc signature in the two paths 327 and 427 out of 11 phase with each other, and detects the electric arc 22 from such 12 out-of-phase segments or portions of the arc signature.
13 In F:pparatus terms, the embodiment shown in Fig. 6 has an 14 input 327 of a first phase processor, herein called "inverting 15 amplifier" 242 connected to the electric filter output 27 in a 16 first signal path 327 - 421, and has an input 427 of a second 17 phase processor, herein called "non-inverting amplifier" 342, 18 connected to the electric filter output 27 in a second signal 19 path 427 ~~ 422; with such first and second phase processors being 20 180° or otherwise out of phase with each other.
21 The more the outputs 421 and 422 are out of phase with each 22 other, the greater is the common-mode or similar rejection of 23 extraneor~s narrow-band signals 52 in the embodiment of Fig. 6.
24 The embo~',imeats of Figs. 2 to 5 thus share with each other a 25 feature according to which the narrow-band extraneous signals, 26 such a.s mentioned above or shown in Fig. 3 at 52 in a fractal 27 subset 1G or other fractal of the arc signature are diminished 28 in energ3~ relative to a remainder of such fractal subset portion 29 before detection of an electric arc 22 from such fractal subset.
30 At least in the embodiments shown in Figs. 3 and 5, the 31 fractal subset 16 is subjected to a frequency transformation, 32 such as shown in'Fig. 3, and an electric arc 22 is detected from 33 such fractal subset after such frequency transformation. By way 34 of example, a fractal subset 16 may be cross-modulated or may be 35 added to itself, such as disclosed above with respect to Fig. 5 36 or as mentioned with respect to Fig. 6, and the electric arc is 37 detected from such crass-modulated or added-to-itself fractal 1 subset. '.~'he embodiment of Fig. 4 adds the variant of parallel 2 different kind detection or demodulation, and the embodiment of 3 Fig. 6 adds the variant of out-of-phase prr~cessing.
4 In either case, a fractal subset o~: the arc signature portion may be treated as a modulated carrier having a modulation 6 indicative of any electric arc 22, and such electric arc may be 7 detected from such modulated carrier for further rejections of 8 extraneous signals. The demodulator system disca.osed above with 9 respect tc~ Fig. 2 can also be used in the embodiment of Fig. 6, the terminal 47 of which may be the same as the input terminal 11 47 of the time sad level sensing and alarm circuitry 48 - 50 in 12 Fig. 2, With respect to which various systems of modulation have 13 been mentioned above.
14 Of course, a wideband signal is not an arc signature unless it disvla~rs chaotic frequency changes. ~~~ccordingly, a stage 16 including comparator 55, may be provided such as shown in Fig.
17 7 to detect and to display a pickup of a disturbance or signal 18 that is not only wideband in the region of interest, but that is 19 also c~ixaotic in nature as an arc signature is, and that is sustained for a period of time, such as determined by the RC
21 component 58.
22 Fig. 7 is a circuit diagram of an optical indicator of 23 possible c:c actual arcing that can be used at various stages in 24 the systems of Figs. 2, 4, 5 and 6, according to a further embodiment of the invention.
26 By waif of example, indications of the progress of the signal 27 through ax~~ monitoring circuitry may be accomplished with three 28 similar functional blocks or differential indicators of which a 29 prototype is shown in Fig. 7 at 54.
Such circuit 54 includes an operationa:!_ amplifier 55 having 31 its nou-inverting input 56 connected to a circuit input 57 32 through a lowpass filter and RC timing component 58 to prevent 33 response to short-term transients. The inverting input 60 of 34 that op amj~ is connected to comparator level resistors 61 and 62.
That op ar~.p 55 has a feedback circuit 64 which may include a 36 feedbaclc c.3pacitor or other impedance 65 and a unidirectional 1 current. conducting device, such as shown at 66, for such purposes 2 as noise reduction, prevention of premature or excessive 3 switching. Hy way of example, the op amp 55 may be of the type 4 LM35BAN.
The indicator circuit 54 includes light-emitting diodes or 6 LEDs 68 and 69 switched by transistors 71 and 72 biased through 7 resistors. including series resistors 73 and 74 and a pair of 8 resistc~ars 75 and 76. Transistors 71 and 72 may, for instance, 9 be of the type 2N2222.
A re:;istor 78 connects transistor 72 to the output of the 11 comparatow op amp 55. Transistor 71 is normally biased ON
12 through tt.se series-connected resistors 75 and 76. This turns ON
13 the fixst LED 68 which, for instance, may be a green LED.
14 Conversel~r, the second LED 69 may be a red LED. However, the second trxnsiator 72 and thus the red LED 69 are biased off at 16 that point.
17 As signals having frequencies in the monitored fractal 18 subset or other band of interest occur at the output 43 of the 19 non-linear processor 42 or modulator 142 or mixer 442 in the embodiments of Figs. 2, 4 and 5, and thereby at the input 57 of 21 the circuit 54 connected thereto, the output of the comparator 22 55 goes positive, turning the transistor 72 ON, and shutting the 23 transi:~tor~ 71 OFF. This turns the red LED 69 ON and turns the 24 green LED 68 OFF, thereby indicating to an observer that frequenciE:s in the band of interest for arc detection are 26 occurring, such as through a disturbance that may be, but not 27 necessarily is indicative of an electric arc 22. The gain of the 28 circuit 5~ may be adjusted to avoid sharp transitions in 29 switching states. This helps a user gain a 'qualitative feel' for the amplitude of the signal at that point by gauging the 31 mixture of red and green LED colors. The unidirectional current 32 conducting device 66 may be omitted, if the circuit of Fig. 7 is 33 so used in. any of the circuits of Figs. 2, 4, 5 and 6.
34 Alternatively, the terminal 57 of the display circuit 54 may be connected to the terminal 45 in Figs. 2, 5 or 6, or a 36 duplicate of the circuit shown in Fig. 7 may be so connected to 37 that terminal 45 and thereby to the output of the bandpass filter 1 or IF amplifier 44, 144 or 244.
2 Such display stage 54 then indicates through its red LED an 3 occurrence of wideband signals in a bandwidth of interest, such 4 as in the monitored fractal subset; a well-known criterium of arc signatures. Gain adjustments in such circuit 54 again may give 6 a user a 'qualitative feel' With respect to picked-up wideband 7 signals at that point by gauging the mixture the red and green 8 LSD colors.
9 However, a wideband signal is not an arc signature unless it displays chaotic frequency changes. Accordingly, the 11 circuitry shown in Fig. 7 may be used as a final display stage 12 is the monitoring circuits shown in Figs. 2, 4, 5 and 6. For 13 instance, the input terminal 57 of the circuit 54 may be 14 connected to the alarm output terminal 49 shown in Fig. 2. In fact, the circuitry of Fig. 7 from terminal 57 through op amp 55 16 may be used as liming circuit 58 and as comparator 55 in the 17 above mentioned timing and level sensing circuitry 48 shown in 18 Fig. 2.
19 The circuitry 54 may thus be used to detect and to display a pickup of a disturbance or signal that is not only wideband in 21 the region of interest, but that is also chaotic in nature as an 22 arc signature is,. and that is sustained for a period of time, 23 such as determined by the RC component 58.
24 As disturbances or signals at wideband frequencies in the range of interest occur and vary chaotically, the output of the 26 comparator 55 at circuitry 48 and terminal 49 goes positive, 27 turning ON the transistor 72, and shutting OFF the transistor 71.
2 8 Thi s turns ON the red LED 6 9 and turns OFF the green LED 6 8 , 29 thereby indicating to an observer the occurrence of an arc 22 in line 20.
31 The embodiment shown with the aid of Fig. 7 thus provides 32 a prewarning of a possible electric arcs preferably in two or 33 three stages, culminating in a display of an occurrence of a 34 chaotic wideband signal in a bandwidth of the monitored fractal subset, or otherwise in a bandwidth of interest such as described 36 above in connection with these Figs. 2, 4, 5, 6 and 7.
37 Principles and circuitry herein disclosed may be employed 1 in various arc monitoring functions, such as mentioned above.
2 In the case of such uses as research, development, and 3 maintenance in such areas as internal combustion engines or 4 electric ignition, electric welding, and electric lightiag, such as mentioned above, circuitry of the type shown in Fig. 2 may be 6 employed up to the termiaal 47, with and without circuitry of the 7 type shown in Figs. 4, 5 and 6. The kind of signal display 8 stages shown in Fig. 7 aad more sophisticated signal display and 9 evaluation stages may be used in such cases.
This extensive disclosure will render apparent or suggest 11 to those skilled in the art various modifications and variations 12 within the spirit and scope of the invention.

Claims (58)

WE CLAIM

1. A method of monitoring an electric arc having an electromagnetic arc signature typified by a wideband range of frequencies of a chaotic nature in a monitored circuit, comprising the steps of:
selecting a fractal subset of said arc signature that is consistent with a relatively long electrical distance along the monitored circuit between a pickup and the electric arc; and monitoring said electric arc from said fractal subset of said arc signature.

2. A method as in a claim 1, wherein:
said fractal subset is selected from a logarithmic decade of said wideband range of frequencies.

3. A method as in claim 1, wherein:
said fractal subset covers at least a quarter of a logarithmic decade of said wideband range of frequencies of the electric arc.

4. A method as in claim 1, wherein:
said fractal subset is selected from a frequency band below 30 kHz.

5. A method as in claim 1, wherein:
said selection of said fractal subset is restricted in frequency to an ELF
(extremely low frequency) band.

6. A method as in claim 1, wherein:
said selection of said fractal subset is restricted in frequency to below a of (voice frequency) band.

7. A method as in claim 1, wherein said fractal subset is selected below a first harmonic of a standard line frequency in alternating-current. power supply systems.

8. A method as in claim 1, wherein:
said fractal subset is selected from a frequency band on the order of a standard line frequency in alternating-current power supply systems.

9. A method as in claim 1, wherein:
narrow-band extraneous signals in said fractal subset of said arc signature are diminished in energy relative to a remainder of said fractal subset before:
detection of said electric arc from said fractal subset.

10. A method as in claim 1, wherein:
said fractal subset is processed in two paths out of phase with each other;
and said electric arc is monitored from the fractal subset processed in said two paths out of phase with each other.

11. A method as in claim 1, including:
providing a prewarning of a possible electric arc.

12. A method as in claim 1, including:
displaying an occurrence of signals having frequencies in a bandwidth of said fractal subset.

13. A method as in claim 1, including:
displaying an occurrence of wideband signals in a bandwidth of said fractal subset.

14. A method as in claim 1, including:
displaying an occurrence of a chaotic wideband signal in a bandwidth of said fractal subset.

15. A method as in claim 1, wherein:
said fractal subset is subjected to a frequency transformation;
and said electric arc is detected from said fractal subset after said frequency transformation.

16. A method as in claim 15, wherein:
said fractal subset is added to itself; and said electric arc is detected from the fractal subset added to itself.

17. A method as in claim 1, wherein:
said fractal subset is treated as a modulated carrier having a modulation indicative of said electric arc; and said electric are is monitored by monitoring a modulation of said modulated carrier.

18. A method as in claim 17, wherein:
said fractal subset is treated as a carrier modulated both in a first manner and in a different second manner; and said electric arc is monitored by monitoring first and second modulations of said carrier modulated both in said first manner and in said second manner.

19. A method as in claim 17, wherein:
said fractal subset is treated as an amplitude-modulated carrier; and said electric arc is monitored by monitoring a modulation of said amplitude-modulated carrier.

20. A method as in claim 19, wherein:
said electric arc is monitored by recovering the modulation on said amplitude-modulated carrier, and by then detecting an amplitude from the recovered modulation.

21. A method as in claim 17, wherein:
said fractal subset is treated as a frequency-modulated carrier; and said electric arc is monitored by monitoring a modulation of said frequency-modulated carrier.

22. A method as in claim 21, wherein:
a prewarning is provided in stages.

23. An apparatus for monitoring an electric are having an arc signature typified by a wideband range of frequencies of a chaotic nature in a monitored circuit, comprising:

an electric filter having an input coupled to said arc at a monitoring point, said monitoring point located a relatively ,along distance along the monitored circuit from the arc;
said filter having a passband corresponding to a fractal subset of said arc signature that is consistent with a relatively long electrical distance along said monitored circuit from said arc to said monitoring point and low cross-induction between said monitored circuit and neighboring circuits, said filter also raving an output for said tractal subset of arc signature;
and a chaotic wideband signal detector having a detector input coupled to said output of said electric filter for detecting said fractal subset of said arc signature.

24. Apparatus as in claim 23, wherein:
said passband is in a logarithmic decade of said wideband range of frequencies.

25. Apparatus as in claim 23, wherein:
said passband is below 30 kHz.

26. Apparatus as in claim 23, wherein:
said passband is where there are less extraneous signals than in a remainder of said wideband range of frequencies.

27. Apparatus as in claim 23, wherein:
said passband is in an ELF (extremely low frequency) band.

28. Apparatus as in claim 23, wherein:
said passband is below a vf (voice frequency) band.

29. Apparatus as in claim 23, wherein:
said passband is below a first harmonic of a standard line frequency in alternating-current power supply systems.

30. Apparatus as in claim 23, wherein:
said passband is on an order of a standard line frequency in alternating-current power supply systems.

31. Apparatus as in claim 23, wherein:
said passband covers at least a quarter of a logarithmic decade of said wideband range of frequencies of the electric arc.

32. Apparatus as in claim 23, wherein:
said passband covers not more than a logarithmic decade of said wideband range of frequencies of the electric arc.

33. Apparatus as in claim 23, including:
an inverting amplifier having an input connected to said output of said electric filter, and having an amplifier output connected to said detector input; and a non-inverting amplifier having an input connected to said output of said electric filter, and having an amplifier output connected to said detector input.

34. Apparatus as in claim 23, wherein said chaotic wideband signal detector includes a modulated carrier detector coupled to said output of the electric filter.

35. Apparatus as in claim 34, wherein:
said modulated carrier detector is an AM detector.

36. Apparatus as in claim 23, including:
an energy converter having a converter input for said fractal subset and for narrow-band extraneous signals in said arc signature coupled to said output of the electric filter, and having a converter output for said arc signature and for narrow-band extraneous signals of diminished energy relative to the fractal subset and being connected to said chaotic wideband signal detector.

37. Apparatus as in claim 23, including:
a frequency converter having a converter input for said fractal subset coupled to said output of the electric filter, and having a converter output for said fractal subset in a frequency band distinct from said passband and being connected to said chaotic wideband signal detector.

38. Apparatus as in claim 23, including:
a frequency converter having two converter inputs for said fractal subset coupled to said output of the electric filter, and having a converter output for said fractal subset in a frequency band double the frequency band of said fractal subset as a distinct frequency band of said arc signal and being connected to said chaotic wideband signal detector.

39. Apparatus as in claim 23, including:
a modulator having a modulator input for said fractal subset coupled to said output of the electric filter, and having modulator output for a modulated carrier having a modulation indicative of said electric are connected to said chaotic wideband signal detector:
said chaotic wideband signal detector including a modulation detector.

40. Apparatus as in claim 23, including:
an electric arc prewarning indicator coupled to said electric filter.

41. Apparatus as in claim 23, including:
an electric arc prewarning indicator coupled to said chaotic wideband signal detector.

42. Apparatus as in claim 23, including:
a modulator having a modulator input for said fractal subset coupled to said output of the electric filter, and having a modulator output for an amplitude-modulated carrier having an amplitude modulation indicative of said electric arc connected to said chaotic wideband signal detector:
said chaotic wideband signal detector including an amplitude-modulation detector.

43. Apparatus as in claim 42, wherein:
said amplitude-modulation detector includes a first stage recovering the modulation on said amplitude-modulated carrier, and a second stage detecting from the recovered modulation an amplitude indicative of said arc signature.

44. Apparatus as in claim 23, including:
a wideband signal indicator coupled to said chaotic wideband signal detector.

45. Apparatus as in claim 44, wherein:
said indicator is a wideband chaotic signal indicator coupled to said chaotic wideband signal detector.

46. Apparatus as in claim 23, wherein:
said chaotic wideband signal detector includes a modulated carrier detector coupled to said output of the electric filter.

47. Apparatus as in claim 46, wherein:
said modulated carrier detector is an FM detector.

48. Apparatus as in claim 46, wherein:
said chaotic wideband signal detector includes combined modulated carrier detectors.

49. In a method of monitoring an electric arc having an arc signature extending over a wideband range of frequencies of a chaotic nature in a monitored circuit, the improvement comprising in combination:
monitoring a subset arc signature frequency range of said wideband range of frequencies for said arc signature;
treating said subset arc signature frequency range as a modulated carrier having a modulation indicative of said electric arc; and monitoring said electric arc by monitoring a modulation of said modulated carrier.

50. A method as in claim 49, wherein:
said subset arc signature frequency range is treated as an amplitude-modulated carrier: and said electric arc is monitored by monitoring a modulation of said amplitude-modulated carrier.

51. A method as in claim 50, wherein:
said electric arc is monitored by recovering a modulation on said amplitude-modulated carrier, and by then detecting an amplitude from the recovered modulation.

52. A method as in claim 49, wherein:
said subset arc signature; frequency range is treated as a frequency-modulated carrier; and said electric arc is monitored by monitoring a modulation of said frequency-modulated carrier.

53. A method as in claim 49, wherein:
said subset arc signature frequency range is treated as a carrier modulated both in a first manner and in a different second manner; and said electric arc is monitored by monitoring first and second modulations of said carrier modulated both in said first manner and in said second manner.

54. An apparatus for monitoring an electric arc having an arc signature typified by a wideband range of frequencies of a chaotic nature in a monitored circuit, the improvement comprising in combination:
an electric filter arranged to accept an arc signature and provide a subset arc signature frequency range; and a modulated carrier detector having an input arranged to accept said subset arc signature range and provide a carrier modulation output.

55. Apparatus as in claim 54, wherein:
said modulated carrier detector is an AM detector.

56. Apparatus as in claim 54, wherein:
said modulated carrier defector is an FM detector.

57. An apparatus for monitoring an electric arc having an arc signature typified by a wideband range of frequencies of a chaotic nature in a monitored circuit, the improvement comprising in combination:
combined modulated carrier detectors having arc signature inputs and a combined carrier modulation output, wherein said combined modulated carrier detectors include different kinds of modulated carrier detectors, said different kinds of modulated carrier detectors include an AM and FM detector, said AM and FM detector connected in parallel.

58. An apparatus for monitoring an electric arc having an arc signature typified by a wideband range of frequencies of a chaotic nature in a monitored circuit, the improvement comprising in combination:
combined modulated carrier detectors having arc signature inputs and a combined carrier modulation output, wherein said combined modulated carrier detectors include different kinds of modulated carrier detectors, said different kinds of modulated carrier detectors include an AM and FM detector, said AM and FM detector connected in parallel, the apparatus further comprising an AND-element having inputs connected to said AM
detector and said FM detector, and having an output as said combined carrier modulation output.