GB2254701A - Thunderbolt sensor - Google Patents

Description

225 47',l l 1 - 1 ka) TIl.'IT'LEE. OF THE INVENTION rnw -E 1HUNDER ALARM

DEVICE

(b) BACKGROUND OF THE INVENTION

Th i s invention relates to a thunder alarm device L developed for;the purposes of lessening the possibility ofE the occurrence of accidents, such as death and injury, caused by thunderbolts in a limited area which accommodates a number of visitors, an audiences, players, etc., and reducing accidental damages in a place where numerous computers are L0 used, by means of forecasting the approach of thunderclouds from a long distance and judging lightning activities correctly.

In recent years, automation in factories, research laboratories, and offices has develooed remarkably and employment of computers i n such locations nas become wide-soread, and such Llend continues. At the same time, comnutler troubles caused by thunderbolts have remarkably increased.

Factories and off- E ices using many computers urgently need proper thunder alarms that can foretell the outbreak of thunder in an early stage and issue an adequate warning in good time, so that operators in such factories and offices can take effective counter-measures beforehand, such as switching 'L-,he power of computers over to an installed power aenerator or to remove floppy disks from the computers so C is 2 memories can be saved. -e, heref-o. many peopl-e Ihunder alarm device.

As to conventional techniques relating to methods of li--h4-ni,,icr forecast, there are a radar method, a radio wave recepzion method, an electric field measurement method, etc.

1. Radar Method (Meteorological Radar):

A radio wave of a wavelength of 3 - 10c.m is used, and groups of precipitation particles (rain drops, snow pellets, ice pellets, hail, etc.) which fall through clouds owing to -v are detected as echo. As convective clouds become gravit thunderclouds when the preci-r)itat-Lon area grows h-4,clrher than 7k.-n in summer and higher than 3km in winter, thunderclouds can be detected with -reference to these facts. The advantages and disadvantages of 1Che radar method are as follows; i. ihe oosition and the scale of the orec-initat;.on area are measured accurately from 'Lime to time.

htn-ina is indirectly judged (2) As an outbreak of limg m i-rom the height of the precipitation area, reliability is rather limited.

(3) The radar system is expensive specially-trained technicians to operate it 2. Radio Wave Reception Method:

This method is to receive desire to obtain a reliable and requires elect.ro-magnetic waves 3 ' gene rat ed by lightning discharges and judge lightning ac.ivitki-e-s, as to whether the activities are vigorous or not, and/or as to whether the 1L.Cchtning is approaching or not, W based on the intensity and frequency of the received signals.

However, Ithis method has the following disadvantages.

(1) As it catches radio waves generated by lightning - lightning before its discharges, it is impossible to forecast outbreak.

(2) Some -probability exists that radio waves generated by artificial noise sources are taken as an outbreak of L li,ghtning.

(3) A correct estimation lightning discharges is difficult.

(4) It is difficult to distinguish a weak radio wave is from near thunderclouds and a strong radio wave from distant thunderclouds.

(5) A similar forecast can be obtained by ncise radio receiver.

reception, using an ordinary 16) 111, - L, L is impossible to -ell the difference between -s and cl.oud discharges.

thunderbolt As seen from the above, radio wave reception, using only one receiver, is not very effective, and thus, recently it is not widely used.

However, recently a similar but more sophisticated system called "Lightning Location and Positioning System", of the distance to the 1 4 has been developed. The main features cf- this system are as consists of more than -hree stat-lons The system -- 1 L - t, each of which receives electro-magnetkic waves z.rom lightning discharges, determines their propagation directions and analyzes their wave-forms to distinguish thunderbolts from cloud discharges. The obtained results are gathered at a main station and promptly processed by computer, and oositions of thunderbolts are located.

This system can cover a wide area, such as one with a radius 0 L' about 40Okm, wi th relatively high accuracy.

However, as it uses radio waves, errors associated with Furthermore, inst direction 4.Lnding are unavoidable. Lal 1 aticn of expensive equipment is required and a large number of exoerts are also required for operation and management.

is 3. Electric Field Measurement Method n addition to the above-.mentLi4ene,-J mez-.ods 1 and 2, -ric '-e".d measurement me- 'n elec4 L Lhis mezhod there is an 11 hod.

is intended to measure -he surface ellectric f-feld and issues ---ic f -4eld an e, J ective all arm when the elect- exceeds a certain value. order to-measure the surface electric field, there t are Lhe following three met-hods (1) ROTARY ELECTRIC FIELD METER (2) CORONA CURRENT METER (3) DETECTOR OF ELECTRIC FIELD-CHANGES Although the rotary electric field meter is capable of is measuring the surface electric f--;eld in a consecut:Lve manner, -ating mechanical parts and needs careful and eGr.ta4ins rot expens ve malnzenance.

The corona current meter has the shortcoming of the -i eld current measurement becoming unstable in the critical - onset. it is imooss4 11o measure corona for corona current t, - Lble ' -han 1Okm, and in current unless thunderclouds come closer t order to forecast the aooroach of thunderclouds from a long distance, it is required that many corona currenu meters be ns-ailed over a wide area. At the same ±4me, a como14cated L, J. - communication system connecting them with each other is also requred.

n Ihis device is intended to measure the surface electric -h -feld which has the mos- i.,i--ma- Ll- Le relat4onship wi+ nearby 'or knowing tIhunde rb o 1 t s. Although the device is sui4able f local t - -z is diff -,o accurazely ,he risk of I hunderbolts, tIne occurrence of closet-,unde.-bol.-:,-s merely by the 4n-cens--;-!,y of the surface electricc Lield, because it is also aEe c - tled above t f led by space charge accumulat ght he "r - sDace surface. In order. to avoid the eftect of such grounds charge, corona current needles for measuring corona current must be set up so high as to penetrate through the layer- of surface space charge. Therefore, in order to monitor a wide area properly by such devices, large construction expense is required, since a considerable number of L-he supporting posts 6 "he needles should be constructed and communication f or -111 cables must be laid down for them.

ric field-changes is designed to

The detector of elect.

I detect and count the electric field-changes caused by liohtn-ing discharges by measuring voltage change induced on a metal electrode fixed on a holder above the ground surface, but connected to the ground through a high register. The counted number of the electric field changes is integrated for the predetermined time interval, and when this number exceeds a present value, an alarm is issued. According to th.1s method, an alarm can be issued when thunderclouds are aenerated within a radius of about 3Okm. However, in order -0 the preset value J s to issue the above alarm, adjustment of L. rather difficult and the judgement as to whether generated is thunderclouds will approach or not, is also difficult.

in the case when convective clouds develoo right ion of elec- overhead, the dezect Iric field-changes begins only after lightning discharges start and, consequently, the alarm will not be issued in tirle.

SUMMARY OF THE -INVENTION

Jonal methods and Among the above-mentioned three conventways, a comparatively reliable one is the electric field measurement method.

-udy4 Firstly, the present invention proposes, by st Mg and developing the function of the said (2) corona current meter, a method for predicting the approach of close thunderbolts which may cause fatal and serious disaster.

Secondly, by combining the said (3) detection technique of the electric-., f'ield changes with the (2) corona current meter, the present invention provides a multi-purpose thunder alarm device, based on the information on the total lightning activity covering a range from a long distance of about 30km in radius to a very short distance right overhead. The present invention util.izes the following nature of the electric field and the electric fileld-change. The minimum amplifi-cation of the electric fieldchange detector for distant lightning discharges is proportional to the distances of discharges, in case they are even in discharge scale. The corona current caused by surface electric field, varies in accordance with the square of the electric field.

The multi-purpose thunder alarm device of the Present MventLon is simple and ye- cacable of providing the user --he information whether lightning discharges break out in a long distance or not, they will approach or not and whether overhead convective. clouds are growing into thunderclouds or not. All this information is essential to avoid fatal lightning accidents and to protect property and electronic instruments against lightning damage.

The usage of the present invention may be more practical than the installation of such exDensive systems as radar sets 8, or so-called liahtnina location systems. The simultaneous C= L, - t, use of the present invention with such systems will immensely the whole syst increase the effectiveness ol Uem.

Two important features of the present invention will be described hereafter. 1. DETECTION OF CLOSE THUNDERBOLTS in the present invention, when sudden polarity change of corona current is caused by a thunderbolt, the measured currents right before and after the sudden change provide very valuable information. The larger the difference between the pre-change current and the post-chanae current is, the I= c= greater the charge consumed by the thunderbolt is. Also, the larcrer the ratio of the ore-chanae current over the -he greater the effect of the space post-change current is, 41--- L, - char.ie near the around surface is. Since this snac-- charae is formed stroncres'll: right under the center of the C'-arg_ed cloud, the larger ratio indicates that the space e'.,iarae density is stronger and therefore, the cloud center is closer to the observation site. The user of the present invention can notice the close approach of thunderbolts by looking at a graph drawn on the connected chartrecorder, or by adjusting the positions of posiltive and negative preset relay pointers -he operation of the logic attached to the meter relay, or by 4.1 circuit, which automatically issues a close thunderbolt warning.

is 9 2. NEW ELECTRODE ARRANGEMENTS FOR MEASURING CORONA CURRENT AND DETECTING ELECTRIC FIELD CHANGES

Regarding corona needle electrodes and electric -ill remaine field-change detection electrodes, there S t several problems. For the problems of the corona current varying irregularly at the critical electric field for corona current onset, the number of corona needle electrodes is increased to equalize the irregularity, in the present invention. For this purpose, five groups of six insulated corona needle electrodes are installed radially on a hemispherical electrode.

Under a strong electric field, a pulse corona current flows from the electric field-change detection electrode and disturbs the field change detection. When rain drops or snow flakes hit the electric field-change detection electrode under the same condition, disturbing pulse current -:^lows also. In order to avoid malfunction due to pulse currents, some arrangement is necessary by which the field-chancr ge detecting electrode is not exposed to a very strong electric field. In the present invention, this problem has been successfully solved by adopting a synthesized electrode system, i.e., groups of corona needle electrodes are installed radially on a hemispherical electric field-change detecting electrode which detects electric field-change, and reduce the electric field imposed on a hemispherical electrode. (d) BRILEFF DESCRIPTION OF 1.11111E FIGURES

Fig. 1 is an illustration showing the relation between a model thundercloud and a surface electric field.

Fia. 2 shows temporal changes of the surface electric field recorded at a point (A) of Fig. 1 when the thundercloud moves in the direction as shown by an arrow.

Fig. 3 is an illustration showing the relation between ace, needle electrodes and the space charge above around sur-.i under usual thundercloud.

Fig. 4 is an illustration showing the distribution of Lhe space charge at the periphery of the needle electrodes right after a thunderbolt.

Fig. 5 is an i 1 lus t rat i on showing the charge is distribution in a thundercloud, space charge above the cry-ound surface and the distribution of lines of electric farce whi= indicates --ric the main elect L Fig. 6 is an illusitrazion right after a thunderbolt (cloud-to-Pround d-iscl."a.-ge). it. shows how the electric fixed of Fig. 5 has chang-ed.

Figs. 7(a) and 7(b) are examples of records of sudden changes of the surface elect.ric field caused by close thunderbolts.

Fig. 8 is a block diagram showing a system of a detector of electric field-changes.

-11 Fig. 9 is a view showing a microammeter with two preset pointers of re- lay contacts which is fitted on both sides of the zero point. The zero point preset is set at the center of the ammeter.

Fig. 10 is a side view showin a synthesized lightning 9 detection sensor which consists of a hemispherical metal electrode for field-change detection and of groups of corona needle electrodes installed radially on the hemispherical field-change detecting electrode.

Fig. 11 is a diagram of the invented thunder alarm device in which the close thunderbolt detection circuit is connected to the synthesized lightning detection sensor of Fig. 10.

Fig. 12 is a block diagram of the invented thunder alarm device that issues multi-purpose thunder alarm.

(e) FUNCT-LONS OF THE PRESENT INVENTION Fic.. 1 shows a model of thundercloud and its electric -F'i e 1 d. In the f igure, the observation site indicated by (A) is a fine weather region where the surface electric field is

C) directed downward. - The site indicated by (B) is right under a thundercloud where the surface electric field is directed upward, and the site indicated by (C) is a site where the surface electric field changes its direction. Fig. 2 is a temporal record of the surface electric field observed initially at site (A) in Fig. 1 and continuously during the

1? perriod when the ithunde rcloud moves in the direction as shown by the arrow. The elect.ric field changes suddenly and reduces its absolute value, as shown by the small arrows, cur.

every time when lightning discharges oc- C) The detection circuit of the close thunderbolts the sudden changes of the surface electric field on of a chart-recorder connected to the microammeter sudden changes of very large amplitudes as shown by 2, and judges whether thunderbolts are approaching the observation site.

The way each part of the present invent-lion works willnow be described. 1. DETECTION OF CLOSE THUNDERBOLTS under a cloud base (usually t,-.e it is well known that lower part of clouds in negatively charged), space charge J - tIhe is for-ned having an opposite polar lly of cloud charge above the around surface. iers. 3 and 4 show t-e distribution of space charae in the vie-;nitv of a synthesized lightning detection sensor before and af ter thunderbolts.

Fig. 5 is a typical example of the electric charge distribution of a thundercloud and electric field right- -1 c before thunderbolts. Due to the lower negative electr charge in the cloud, space charge represented by (D is formed m 4= under the cloud base. The electric field becomes strongest at the lower edge of the negative electric charge in the monitors the graph r> - picks up P i n F J. =--,.

-o close G 13.

cloud and a leader of thunderbolt starts "from this position.

The -ield is directed upward at observation site A j elec tric in the Lgure. The electric field is about 5 - 1OkWm due to the effect of the space charge. Fig. 6 shows a state right after a thunderbolt. Though most of negative charge in a cloud is discharged down to the ground by the thunderbolt, the space charge remains as it was. Accordingly, the surface electric field changes its direction as indicated by the lines of force in the ficure and the absolute value of the he same or becomes a surface electric field remains about 'L". little larger than the one right before the thunderbolt.

Since the surface electric field is recorded conti.nuously on a chart, its sudden change caused by the thunderbolt can be treated numerically. The absolute value of the surface electric field measured right before -s at the observation s4 thunderbolt -te A in Fig. 5 i S the represented by Xa and the one measured rierht a4LUer CD thunderbolts at the same site by Xb. The absolute value of I- electric field tIhe same

L.he right before thunderbolts at - point, presuming that no space charge exists, is represented by X. This electric field X is obtained by subtracting the electric field Xb caused by space charge from the electric field Va, namely:

X =)(a - ( - Xb Xa + Xb On the otherhand, according to the present results of 14 lightning study, it is estimated that the electric potential C; -1 LI U L, - of tlie center of tne negative chlarge in thunderclouds is 10 8 V 3 and its height above the ground is S x 10 m. Therefore, the following relation can be outlined. 10 8 = 2 X 10 4 V/m = 20kV/m x 10 3 Therefore, even when a correct reduction factor for absolute measurement is not'. obtained by the present system, an aDuroximate absolute value of the surface electric field can be estimated. For example, if Xa and Xb are equal be±ore and after the thunderbolt as shown in Fig. 7 (a and b), the following approximate estimation can be obtained.

)(a + Xb X = 20kV/m, Xa = VAb Xa and Xb -is dii 11hus, Xa Xb = lOkV/m and recteed upward and downward respectively.

if Xib is about two times Xa in absolute value as shown -ions can be obtaJ in Fig. 7(b), the following relat, Lned.

Xa + Xb = 20kV/m, Xb = 2 Xa Thus, Xa = 7kV/m and Xb = 13kV/m hold approximaltely.

Similarly, Xa and Xb are directed unward and downward.

The foregoing is an approximate numerical e S14 Jon for _mati - ±hat the amplitude of the a typical thundercloud. The f act - sudden change of electric field, Xa + Xb = X is large,

CD means that the quantity of the electric charge consumed by a thunderbolt is larae. Likewise, the fact that ratio Xb/ Xa is large.

i s la ae means that the o f the e f J'."e ct space charge Because the space charge is formed strongest right under the center of the thundercloud, it can be judged that the larger Xb/)(a is, the closer the center of thundercloud is to the observation site. For example, if the amplitudes AX, in Figs. 7(a) and (b), are about the same and the value of Xb/Xa in Fig. 7(b), is twice that in Fig. 7(a), it is judged that the center of the thundercloud i s far closer to the observation site at the situation of Fig. 7(b) compared with that of Fig. 7(a).

In this way, the fact that the above-mentioned two quantities are gradually increasing indicates that a powerful thundercloud is approaching overnead.

Also, according to the present invention, the approach of thunderbolts can be automatically detected either by both -th U e positive and negative preset relay pointers of a microammeter with relay contacts or by using a logic circuit of a semiconductor.

2. MULTI-PURPOSE THUNDER ALARM DEVICE It includes a hemispherical metal electrode for field change detection fixed to the ground's surface and a corona current needle electrode, the elect.rode being integrally mounted on the hemispherical metal electrode through an insulator. The detection of close thunderbolts has the added 16 function of issuing a first warning when either a detector of electric field-change connected to the i-,e.-,i-ischer-ical metal electrode for f-ield-change detection or a detection circuit of corona current directly connected to the corona current needles are separately activated, and issuing a second warning when they are activated simultaneously.

Since both the surface electric field value and the value of sudden changes thereof are large enough J_ 1 in the range indicated by K in Figs. 1 and 2, the detector of electric - of corona current field-changes and the detection circuit connected to the microammeter function almost simultaneously.

As already mentioned, the present invention also contains the detection circuit of close thunderbolts and issues "close thunderbolt warningall as the final emergency alarm.

mult -ourpose t ce Accordingly, t i- - - thunder alarm dev4 o:

tulne present invention can easily judge whether a tl,-.understor.m is approaching, whether the risk of thunderbolts is increased thunderbolts, and whether the as a result of the approach of thunderstorm is going away.

3. SENSITIVITY ADJUSTMENT OF DETECTOR OF ELECTRIC FIELD-CHANGES

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18 There will be described a synthesized lightning detection sensor formed of an integral combination of a hemispherical metal electrode for fieldchange detection with a group of corona needle electrodes installed radially on a hemispherical electrode through an insulator with reference to Fig. 10.

An umbrella-shaped insulator is mounted on an upper part of each of metal pipes 55, radially installed on a hem-is-iherical metal electrode for field-change detection 59.

A plurality of tapered bosses 52 are arranged on an upper surface of a metal base 51 of round shape mounted on the tip of the insulator. Corona needle electrodes 53 having a sharp tin somewhat point-led are detachably and radially mounted on the metal base 51 at suitable intervals. These corona needle is electrodes are all electrically and integrally connected through a conductor wire at the inner side - of the ".eld-change de±- Ln hemispherical metal el--ct.-ode for f-.-ction, a state insulated from the corona needle electrodes.The corona needle electrodes 53, the metal base 51 of round shape, etc. stainless steel. Ho ever are made of a conductive material such as 9 the present invention is not limited in material. The number of needles is set such that six corona needle electrodes 53 are provided to one unit of metal pipe 55. Since the hemispherical metal electrode for field-change detection 59 is provided with five units of

19 tal 30 pieces of corona needle electrodes 53 metal pipes, a tot aree radially scattered to detect corona current. Medical needles or similar needle electrodes (hereinafter simply referred to as the "injection needles") may be used as the needles of the corona needle electrodes.

The numeral 51 denotes a metal base of round shape which is a genuine circular ball. The metal base 51 of round shape need not necessarily be a genuine circular ball; it may be a C ball of any similar configuration or of an elliptic shape as is formed in- --a configuration making it difl-icult long as it E- for corona current to break out.

The numeral 52 denotes tapered bosses which are radially erected on an upper surface of the metal base 51 at suitable intervals. An injection needle 53 for the corona needle electrodes is replaceably mounted on each of the bosses 52 by means of engagement etc.

D In the figures, the numeral 1554 denotes umbrella shaped -al pipes, 56 insulators, 57 shaft insulators, 55 met i lls, 58 connecting terminals, and 59 a hemispherical metal electrode P for field-change detection. If too many corona needle electrodes 53 are provided to one unit, the corona current is saturated and thus undesirable. As such crouiD of corona needle electrodes 53 installed radially on a hemispherical electrode is normally located outdoors, they are subjected to harm from birds and insects. However, as a plurality of

1 corona needle electrodes 53 are provided, it does not result in substantial damage even i f several corona needle electrodes are damaged. Corona current generated by the outbreak of a thunderstorm varies a great deal in current value at the outbreak. However, in this case, as many needles are used, discharges of corona current are averaged. Also, there may be a possibility of the electric field being ---1 on demendina on acted upon from a diagonal direct- However, no substantial difference occurs to the sensitiVitV 0'^ the device of the present invention, by virtue of its construction.

When the device is installed in a high place tlInat is susceptible to strong rain from a side direction, the is configuration of the hemispherical metal electrode for fieid-change de- .---.'-on 59 need not necessarily be a hemispherical shape. _Tnstead, one very close to a ball may be used. Also, when the installation place is a high mountain where thunder approaches from a lower alt-ltude, a plurality of metal pipes 55, attached to the metal base 51 of -he c o r- round shaDe orovided at the -i'l-io thereof with t ona needle electrodes 53, are sometimes radially installed in such a manner as to face downward.

When thunderclouds approach, a large amount of corona current flows out Lrom the group of corona needle electrodes creocrrar)hical conditions and the installation clace C= 21 installed radially on a hemispherical electrode. As a result, when a large amount of negative charge stays at the cloud base, as depicted in Figs. 3 and 4, a weak corona breaks out from grass, trees, rocks, or other projecting substances in the vicinity of the ground surface, and positive ions are discharged. large number of ions are generated at the top of the elect.rode of the synthesized electrode of the present invention, because of its structure, the sensitivity of the improved and extremely detection of close thunderbolts is effective.

In general, when pulse current flows to the electrode tecting electric field changes, the detector of for det ions.

electric field-changes sometimes malLunct. One of the causes for such malfunction is that corona current --:'lows to -he U, electrode (because corona current is a pulsewave), rain drons or snow flakes colilide wJ...

ano -Ikl-her cause is -1111at 4-1, or ail-tach to it (in this case, pulse current also flows). in any case, a large amount of electric Lield acts on the electrode for detecting electric field changes. However, thehemispherical metal electrode for field-change detection 59 of the present invention is round in shape and the head portion of each of the metal pipes 55 is also covered with a round umbrella-shaped insulator. In addition, the tip portions of a plurality of the corona needle elect.rodes 53 However since a particularly 22 a e -.)oslt-ored on the upper part oiLi, L l, ' the hemispherical metal electrode for.'-ield-change detecticn 59. Accordingly, electric field is concentrated on the tins of the needles of the ggroup of corona needle electrodes installed radially on a hemispherical electrode right under the thunderclouds. As a result, the hemispherical metal electrode for field-change detection 59 does not receive a large amount of electric field directly and there is no fear that the detector of electric f-ield-changes will malfunction.

Also, abnormal current sometimes flows into the corona current needles, causing malfunction. That is, when electrified rain drops hit the hemispherical metal electrode for f.-jield-change detection 59 portion, the charge of the rain drops is transferred to t-he hemispherical metal electrode for is field-change detection 59 and the charge accumulates in the electrode 59, though -for a short period of t-lme. Even -4f zl-,e state of t-he elec-cric --,-"-4e'-.d is nor such that corona current flows therefrom, it happens that current flows from tinle hemispherical metal electrode f-or -f-ield-.change -;e±--ct.4on to the corona needle electrodes, causing -malfunction. However, as insulation S perfectly accomiDlished by the f e c of - umbrella-shaDed insulator 54, the ef Inle charge of the rain drops cannot be a cause for malfunction.

5. EMBODIMENT SYNTHESIZED FROM THE FOREGOING Fig. 11 shows one embodiment of a thunder alarm device 23 connected wi th a close thunderbolt detection circuit utilizing the detection of close thunderbolts of the present invention. A resistor 20 of a high value is connected between the hemispherical metal electrode for f-ield-change detection 59 and an earth electrode 2. The numeral 53 denotes corona needle electrodes, 54 umbrella-shaped insulators, 7 a DC current amplifier, 81 microammeter with relay contacts, the center of which is zero and both sides of which are provided with preset relay pointers, as shown in Fig. 9, and 10 a relay circuit annexed to 81, 81 and 10 being connected to the DC current amplifier 7. A contact for positive current of the relay circuit 10 annexed to a microammeter 81 is connected to the relay 11, and a contact for negative current is likewise connected to the relay 12.

-urning is The numerals 13 and 14 denote auxiliary circuits (ret d' when 'th ULme: 0. 1 - 0. 5 sec.), 15 a relay which is actuated L-e fo.

contact - - positive current and the contact for negative current are simultaneously operated, and 19 an alarm c-4----u-it for issuing a "close thunderbolt warning".

In this embodiment, the sudden polarity changes of corona current is detected using the microammeter with relay -h a logic contacts. However, this part can be replaced will circuit of a semiconductor.

Lastly, one embodiment of a thunder alarm device using a multi-purpose thunder alarm device of the present invention 24 i s --es a hemispherical shown in Fi a. 12. The numeral 59 denou metal elect-rode for electric field-c.h.ancre detection, 2 an earth terminal, and 4 a detector of electric field-changes for outputting signals for a predetermined time (about 30 sec.). The numeral 53 denotes corona needle electrodes, 54 umbrella-shaped insulators, 7 a DC current amplifier capable of adjusting sensitivity, 8 and 81 microammeters (see Fig. 9) with relay contacts, the center of which is zero and both sides of which are provided with preset pointers, and 9 and

10 relay circuits annexed to 8 and 81, 8 and 9, and 81 and 10 being connected to the DC current amplifier 7. The relay circuit 9 annexed to a microamme-Ier 8 is actuated in - of both posit accordance with the amount Uive and negative t- current by the preset pointers. On the other hand, a contac -1 for positive current', of the relay circuit 1-0 annexed to the -ed - microammeter 81 is connect o the relay 11, and -a contlac-_ or negative The numerals current is likewise conneczed to zhe relay 12.

13 and 14 denote auxiliary circuits (returning t tlime: 0.1 0.5 sec.), 15 a relay which is actuated when the contact f-Por positi've electric current and the contact for negative electric current are actuated almosu simultaneously, -or issuing a Ilfirst warninC, 18 a circuit for 17 a circuit L.1 issuing a "second warning" and 19 a circuit for issuing a "close thunderbolt warning".

When the detector of electric field-changes -4 is -ed to output a signal, or when corona current flows ac t u at U L, -- J nzo. the corona needi-e electrodes 5533 and the relay c--.-cuit 9 annexed to the microammeter 8 is actuated exceedingthe ways) of the preset pointers (both in positive and negative 9 m microammeter 8 to issue a warnin signal, the warning circuit 17 of the Il irst warning" is aclua-ced provided that either one of the warning signals is output. above---nent ione d si-inals are out-ut When both of -11,--- t almost simultaneously, the warning ciz-cu4-', 1-8 of the "second "ua-d.

warning" is act -s, for example, a thunder in case of close thunderbolt cloud is close, and corona current already exceeded the t - negative preset Pointer ot the microammet-r 81. And when thunderbolts occur r c. ext, the polari ty of the corona current is suddenly changed and positLve corona current sometimes --lows out, he oos-'-4-. o 'Jowever, as ex c e e d in a t, 4ve prese ive charcre at .he r.eaat- -loud base is Mcreased with the time, the current value ol. Ihe microammeter 4 passage o fr s e reduced and the point-r returns to the position wher it was before the thunderbolts occurred.

The value of the corona current rght before -his change is represented by II= and the value of the corona current right after this change is represented by lxb. The poinzers -o Ixb due of -he microammeter is suddenly changed from Ixa t t -hunderbolts. When both the relays 11 and 12 are actuated 4 0 L L, - 26 almost simultaneously exceedina the positive and necative "ak-ing into preset pointers which are de-.'-e.--n4S-ned t consideration the values of ixb - ixa and Ixb/Ixa, the relay circuit 15 is actuated by the auxiliary circuits 13 and 14 to actuate the warning circuit 19 of the "close thunderbolt warning".

If the preset pointers of the microammeter 81 are set - Ixb - Ixa and the taking into consideration of the value oL L, value of Ixb/Ixa so that Ixa and Ixb can be compared, a warning can be issued when the probability of a close direct thunderbolt is increased. Also, the meter relay portion can be replaced with a logic circuit using a semiconductor.

Even in case a thunderbolt strikes an iron tower of cower transmission lines located az a far distance, there is a possibility that factories and offices having a ccmouter-controlled system using many computers suffer from tremendous damage because of inzerruption of service or instantaneous voltage drop. According to a thunder alarm device of the present invention, the detector of electric -field changes is able to detect comparatively distant and middle-distant lightning activities, and lightning activity rapidly developed overhead is -immediately caught bythe corona current detector, and the corresponding warnings can be issued.

The approach of a close thunderbolt point can also be 27 detected by the detection circuit of close thunderbolts before stated and a close thunderbolt alarm will be issued.

In this way, by forecasting the possibilities of significant thundercaused damages in large scale compute r-c ontro 1 led factories and offices by a thunder alarm device of the present invention based on the mult.L-purpose thunder alarm, disaster can be prevented by means of an effective countermeasure such as switching to a private power generation.

Furthermore, as the thunder alarm device of the present invention is capable of correctly issuing a timely warning of the outbreak of a thunderstorm in a limited area, such as a football ground, baseball ground or construction sites which people, it can be of great help accomodates a large number of in preventing a thunderbolt accident resulting in the injury or death of many people.

-i on 0 the present invent- Also, the thunder alarm device to-l 1 can be used for forecasting thunderbolts and the accompanying abnormal air-stream endangering the take-off and landing of aircraft and for locating tornados by suitably adjusting its sensitivity.

As apparent from the foregoing description, the present invention makes it possible to issue a warning signal at an early stage by correctly forecasting thunderbolt-Is regardless of whether the thunderbolts are those entering into a 28 monitored area or are an outbreak of lightning overhead.

Since the thunder alarm device of the present invention does not require a large installation space or place and tall supporting posts are not required because it takes advantage of the phenomenon of space charge, maintenance is easy. This invention is most suitably applicable to such places as airports where tall obstacles are not welcome. Furthermore, if the invention is used together with information obtained by radar at an airport, a forecast af- very high probability can be obtained. Since the device is inexpensive and installation costs are low, the thunder alarm device of the present invention is economical. -Tr. addition, since even an amateur can use it with ease and t-he invention is hardly susceptible to trouble, maintenance is low, which is a significant advantage.

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Claims (5)

1. CLAIMS is 1. A thunder alarm device comprising a close thunderbolt

   detection circuit that measures corona current of corona needle electrodes and compares a corona current value Ixa immediately before sudden polarity changes due to thunderbolt with a corona current value Ixb immediately after the sudden polarity change that indicates a presence of a thunderbolt, and automatically issues a close thunderbolt warning when it exceeds a present value decided by taking into consideration values of Ixb - Ixa and Ixb/Ixa beforehand.
2. 2. A thunder alarm device as claimed in claim 1 including a close thunderbolt detection circuit for measuring corona current by a group of corona needle electrodes installed radially on a hemispherical electrode and automatically issuing a "close thunderbolt warning".
3. 3. A thunder alarm device as claimed in claim 1 20 further including a synthesized lightning detection sensor integrally formed of a group of corona needle electrodes installed radially on a hemispherical electrode comprising a hemispherical metal electrode for field-change detection, metal pipes radially installed on said metal electrode, umbrella-shaped insulators mounted on upper parts of said metal pipes, a plurality of tapered bosses radially projecting from an upper surface of a metal base of round shape mounted on each of said insulators, and corona current needles each of which is detachably mounted to each of said tapered bosses, said group of corona current needles installed radially on a hemispherical electrode being connected to said close thunderbolt detection circuit and to a detection circuit of corona current, said hemispherical metal electrode for field-change detection being connected to a detector of electric field-changes, a "first warning" being issued when said detector of electric field-changes and said detection circuit of corona current are separately activated, a "second warning" being issued when said detector of electric field-changes and said detection circuit of corona current are simultaneously activated, a "close thunderbolt warning" being issued when said close thunderbolt detection circuit is activated.
4. 4. A thunder alarm device as claimed in claim 3, which includes a detector of electric field-changes formed of a combination of multistage changeover switches capable of adjusting gains of an amplifier, count number of an integrator of sudden changes-of electric field, a timing circuit, etc. among circuits for integrating the frequency of sudden changes of 31 electric field for a predetermined time.
5. 5. A thunder alarm device substantially a hereinbefore described with reference to and as illustrated in the accompanying drawings.