US 3132330 A
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May 5, 1964 M. DONNER ELECTRIC ALARM SYSTEMS Filed April 30, 1962 REC. l
LOUDSPEAKER- VOLTAGE LIMITING 0 1: V 2/ MEANS VOLTAGE LIMITING MEANS VOLTAGE LIMITING MEANS VOLTAGE LI M I Tl NG MEANS INVENTOR MEIER DONNER trol station, to .modulators in order to produce currents modulated by the signals.
' My copending US. application Sen-No. 117,002, of
June14, 1961, under the title Electric alarm system,
describes a system adapted to detect unauthorized passagesat predetermined points, thedetecting means being constituted by seismographs positioned under ground.
Said prior application describes also a system for processing the electric voltages collected by the seismographs,
'said Voltages acting, whenever they rise above a prede termined threshold, on electronic; multivibrators which act in'their turn on any suitablealarm system. Said prior application further describes various modifications which increase the sensitivity of such multivibrators, under the 7 action of signals having a steep front.
' My present invention more particularly is. directed to improvements in the indicating members incorporated with. detecting systems of the type referred to, said indi- United States Patent eating members being fed by the voltages across the teraninals of the seismographs.v
It covers more particularly embodiments constituted by a complete system adapted to investigate a large area carrying a large number of groups of seisrnog-raphs, which seismog'raphs feed information to a control station, which allows asmall number of operators at said station to investigate the whole'area to' be considered.
My invention has chiefly for its object to further such an investigation together with the discrimination to be obtained between the useful signals and parasitic noises, while it. reduces the probability ofan untimely alarm and improves thus, generally speaking, the efficiency of the j investigation.
According to my invention'and in order to further the investigation operations andto draw immediately the attention of the operators when the seismographsdetect signals of interest, the voltages supplied by the different 'seismographs areapplied to a single loud-speaker However, the insertion in series or in pa fl lel of the voltages fed by theseismographs with a view. to feeding therewith a single loud-speaker, cannot provide usable results, since this would only show thesum of the voltages .(or intensities) corresponding to said signals, which latter would lose their individuality and the indications given out by the'loud-speaker would befmeaningless, as may easily be proved by experience. p
To this end, and in accordance with a first feature of my present invention, and with a view to retaining the individualization of the signals, the voltages collected by the different groups of seismographs, are fed at the concarrier Experience shows that the useful signals serving for the detection of any tentative passage over a predeterminedarea, are constituted by signals of avery low frequency, said frequency being lower than about l00 cycles.- 4, Consequently, a channel adapted to transmitthe signals collected by a group of seismographs, may, without any -drawback, be given a band width limited to about 200 cycles (0 to 200 cycles) and the frequency of the carrier wave used may therefore be selected within the range of audible fiequencies. I
:It is immediately apparent that it is easily possible to obtain within the range of audible frequencies, to wit: 500 to 10,000 cycles, about transmission channels 3,132,330 Patented May 5, 1 964 Ice ferent channels.
According to my invention, the voltages provided by these different channels are merely added and applied to a single loud-speaker. Y The interest of said last feature resides in the fact proved by experience that the human ear readily" detects, among a system of sounds, the characteristic features of those sounds which occupy apredetermined band of fre: quencies. v v
Said property of the human ear allows it to select among all the signals reprodilced in bulk by the loudspeaker, that signal or those signals of a predetermined channel. Said feature of my invention allows an acoustic investigation by a single operator of the whole alarm system, which would be obviously impossible, if it were necessary toprovide as many loud-speakers as; there are groups of seismographs.
This novel feature provides furthermore, a substantial simplification in the equipment of the control station, since it allows reducing to a single loud-sneaker the whole system of acoustic alarm means at'said station.
According to a still further feature of my invention, the control station may also be provided with. optical alarm means constituted for instance, by indicators or by illuminated tubes of the magic eye type, or else by luminous points. J i
In the case of the use of illuminated tubes of the magic eye type, the optical indication supplied is provided by.a luminous surface the shape of which defines the voltage applied to the. indicator. V
'In-the case ,where a luminuous source such as an incandescent bulb is used, the luminous intensity of the source maybe controlled so as to define a function of thesignal voltage applied to the indicator or else, according-to a still further feature of my invention, it is possible to resort to a source of intermittent light having a constant or variable luminosity and the frequency of illumination of which depends on the amplitude of the signals applied to it.
. The voltages fed by the seismog raphs may vary within a very large range; In contradistinctiou, the range of variations of thevoltagesapplicable to the luminous indications between a minim um voltage providing a useful indication and the maximum voltage whichrnay be ap plied, is much more restricted and consequently I'prefer resorting, according to my invention, for each. group, of seismographs, toa system of optical indicators of decreasingsensitivity, said indicators being fed through intensity limiting means with input'voltages the values of which increase preferably in accordance with a geometrical progression; a v H Further features and advantages of my invention will appear, in the readingof the following description, refer,- ence beingmade to thesingle figure. of the accompanying drawings which illustrates the circuits relating to a predetermined channel with a singleldud-speaker and theassociated optic indicators.
' As illustrated, a group of seisrriographsl i siadapted to provide voltages to be added together and the total voltage thus obtained, is. fed by a separate transmission channel 2 to the control station where said voltage is amplified by the amplifier 3. The amplified voltage serves for modulating inthe modulator 4 an audible carrier .wave supplied by the local generator 5/ .As disclosed, the audible frequency of the generator 5 defines the transmission channel considered. 1 17., y I
The modulated Wavepassing 'outof the modulator 4 through the lead 6, reaches a receiver 7 tlieinput into which is also fed through further leads 8 with the moducontrol station.
r a s a lated voltages fed by the other channels controlled by-the other groups of seismographs associated with the same The receiver 7 adds the different voltages supplied by the leads 6 and 8 and feeds them into a single loud-speaker 9 forming the acoustic indicator.
Furthermore, a number of luminous signalling means are associated with each lead 6, that is with each group of seismographs. To this end, between the lead 6 and ground, resistances are inserted in series, the number of which resistances is equal to the number of luminous signalling means to be controlled, say four, in the case illustrated in the figure. 7
These four resistance 10", 1 1, 12 and 13 are mounted in series between the lead 6 and the ground, their values are calculated in a manner such that the voltages between their upper ends and ground may form advantageously a geometrical progression having for 'instance as a ratio e voltage of the connecting point between the resistances 12 and 13 with reference to ground is applied through the voltage limiting system 14 to the indicator 15, while the voltage of the point connecting the resistances 11 and 12 is fed to the indicator 17 through'the voltage limiting means 16-, that of the point connecting the resistances 10 and 11 to a third indicator 19 through the voltage limiting means 18 and lastly, that of the lead 6 to a fourth indicator 21 through the voltage limiting means 20. V r
The voltage limiting means 14, 16, 18, 20 are preferably all identical, and are designed so as to limit their output voltage to the maximum value which may be usefully applied to the luminous indicators 15, 17, 19' and 21 which are also preferably identical with one another.
The operation of the arrangement may be readily explained by assuming that the indicators become luminous as soon as the voltage applied to them reaches the value of 1 volt and they supply their maximum luminosity for a voltage equal to /E=3.2 volts or thereabout.
'It is immediately apparent that, by reason by this arrangement, when the voltage between the lead 6-. and the ground varies for instance between 1 and 3.2 volts or thereabouts, only the indicator 21 subjected to the voltage of the lead is actuated and passes from its lower condition corresponding to no emission of light, to its upper condition corresponding to maximum luminosity, whereas when the voltage rises above 3.2 volts, said .indicator 21' remains in its upper maximum luminositycondition, while the indicator 19 begins being illuminated and so on, the indicator 15 showing its maximum illumination only when the voltage of the lead 6 reaches its maximum.
Preferably, the amplifiers such as 3, are provided with an automatic gain control system, designed so as to give a low gain for signals of a constant intensity or of an intensity which varies slowly. as in the case of those produced for instance by a continuous wind, and a large gain for signals having a steep front. Thus a continuous parasitic movement will produce only a very slight noise in the loud-speaker.
Such automatic gain control means are obviously wellknown in the technique of electric communications and geophysical prospection and it is therefore unnecessary to give any example thereof. 7 7
Obviously as many groups of luminous indicators 15 to 21 are used, as there are groups of seismographs and transmission channels. a
In the case illustrated, the optical signalling means are fed by the voltage at the output of the modulator 4, but
they may be fed directly by the voltage at the output of the amplifier 3 since it is not necessary-for said optical signals to be fed by a voltage which has been subjected to a modification in frequency.
In the case where it is desired to use intermittent sources of light having illuminating frequencies varying as a function of the intensity of the signals, it is sufiicient to insert in series with and beyond the voltage limiting means 14 to 2.0, generators operating at suitable adjustable frequencies, for instance multi-vibrators incorporating transistors or vacuum tubes, the frequencies of such multivibrators or the like generators being controlled by the voltages at the terminals of the resistances 10' to 13.
In the embodiment referred to, the voltages fed by the seisrnographs are applied individually to the control station where they serve for modulating separate carrier waves.
The amplifiers, modulators and local generators 3, 4 and 5 may be placed next to each group of seismographs and the modulators may feed a single transmission channel which conveys 'all the informations as a whole to the control station, said single transmission channel adding the voltages received and feeding them into the loudspeaker. This cuts. out thus any individual transmission channels, but this advantage is partly offset by the fact that it is necessary at the control station to actuate the luminous signalling means through filters so 'as to separate again the individual channels from one another.
It will be noted that my improved arrangements thus disclosed are independent of those described in the abovementioned copending prior patent application and that they may be used simultaneously with the latter, if required.
The use of luminous signals associated with each channel, allows the operators 'Whose attention has been drawn by the loudspeaker to ascertain immediately which channel or channels has produced the alarm signal so that they may appreciate upon inspection of the modifications in the luminosity of the signals, the cause which has sounded the alarm signal.
Experience. shows, as a matter of fact, that certain causes, such-as a gust of Wind progressing along the perimeter of the area to be investigated provide an illumination having a characteristic appearance, and for instance they may produce an apparent sliding movement of light over the board carrying sai d luminous signalling means.
A small amount of experience allows the operators to clearly ascertain the difference between parasitic and interesting signals.
Many details may obviously be modified in the embodiments described without unduly widening thereby the scope of the present invention, as defined in the accompanying claims. t
In particular, it is possible to modify the number of optical indicators corresponding to each group of seismographs while also said indicators may be distributed in any desired manner on a board, or the like.
What I claim is:
1. An alarm system for a plurality of groups of sensitive geophones distributed over a pre-determined ground area for producing signals in accordance with detected disturbances over said area, said alarm system comprising a plurality of amplifying means, each one of said plurality of amplifying means being connected to a respective one of said groups of geophones for amplifying signals from each group of geophones, a plurality of audio frequency carrier wave signal generating means, each having a fixed audio frequency carrier wave signal "different from any other one of said plurality, a plurality of modulator means, each one of said modulator means being connected to a respective one of said plurality of generating means for modulating the respective audio frequency carrier wave signal of said generating means in accordance with modulating signals and each one of said plurality of amplifying means being connected to respective one of said modulator means for providing amplified geophones signals as modulating signals to said modulating means, and a control station including a loudspeaker and means to connect all of said modulated audio frequency carrier wave signals produced by all the modulators to said loudspeaker to simultaneously energize said loudspeaker.
2. 'An optical system as claimed in claim 1 further comprising optical alarm means for each group of geophones for receiving amplified signals therefrom, said optical alarm means for each vgroup of geophones including a" plurality of indicator means each effective for being illuminated at a particular voltage and means connecting together the plurality of indicator means for each group of geophones to successively illuminate the indicator means as a function of theintensity of the received ampli- 3'. An alarm system as claimed in claim 1 comprising an optical alarm system for each group of geophones con- 'nected to the'modulator means for. the particular group of geophones, each said optical alarm system comprising a plurality of series connected resistances, and optical in- .7
dicators connected successively with said resistors for being illuminated in succession and with a luminous in- 15 tensity which is a function of the intensity of the signal received from the modulator means.
4. An alarm system as claimed in claim 3 wherein each said optical alarm system comprises voltage limiting means for each optical indicator connected between the resistances and the respective indicator.
References Cited in the'file of this patent V UNITED STATES PATENTS Italy Mar. 31, 19-36