CA2032165A1 - Electric field detection system - Google Patents
Electric field detection systemInfo
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- CA2032165A1 CA2032165A1 CA 2032165 CA2032165A CA2032165A1 CA 2032165 A1 CA2032165 A1 CA 2032165A1 CA 2032165 CA2032165 CA 2032165 CA 2032165 A CA2032165 A CA 2032165A CA 2032165 A1 CA2032165 A1 CA 2032165A1
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- Prior art keywords
- electric field
- signal
- field signal
- aircraft
- antenna
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
- G01R29/08—Measuring electromagnetic field characteristics
- G01R29/0807—Measuring electromagnetic field characteristics characterised by the application
- G01R29/0814—Field measurements related to measuring influence on or from apparatus, components or humans, e.g. in ESD, EMI, EMC, EMP testing, measuring radiation leakage; detecting presence of micro- or radiowave emitters; dosimetry; testing shielding; measurements related to lightning
- G01R29/085—Field measurements related to measuring influence on or from apparatus, components or humans, e.g. in ESD, EMI, EMC, EMP testing, measuring radiation leakage; detecting presence of micro- or radiowave emitters; dosimetry; testing shielding; measurements related to lightning for detecting presence or location of electric lines or cables
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Traffic Control Systems (AREA)
- Geophysics And Detection Of Objects (AREA)
Abstract
ELECTRIC FIELD DETECTION SYSTEM
Abstract A detector for use on board an aircraft (A) traveling along a path of movement to detect a power line (P) comprises an antenna (32) for sensing the electric field associated with the power line and producing an electric field signal (EH', EV'), and a signal processor (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the aircraft to reach the power line if it continues on its path of movement. Sensors (30, 34 180, 182) are used to determine the direction of the power line.
Abstract A detector for use on board an aircraft (A) traveling along a path of movement to detect a power line (P) comprises an antenna (32) for sensing the electric field associated with the power line and producing an electric field signal (EH', EV'), and a signal processor (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the aircraft to reach the power line if it continues on its path of movement. Sensors (30, 34 180, 182) are used to determine the direction of the power line.
Description
2 ~
ELECTRIC ~IELD DET~CTION SYSTEM
Background of the Invention The present invention relates generally to a system for detecting an electrical power line, and more specifically to an improved detector and method for use on board an aircraft for providing an indication of the time-to-impact with the power line if the aircraft remains on course.
Other devices have been proposed in the past for detecting the distance of a power transmission line or cable. Such devices generally fall within two categories, one being those that detect power lines by sensing the magnetic field associated with a conductor having an alternating current (AC) flowing therethrough, and the other type of device sensing the electric field associated with such power lines. From electromagnetic field theory, it is well known that an infinitely long conductor carrying a current will have an associated magnetic field H in a circular pattern concentric about the conductor, and an electric field directed radially away from the conductor. From this, it is apparent that the means for sensing an electric and a magnetic field would be different, as well as the circuitry for interpreting the sensed ; electric and magnetic fields.
A system and method for detecting the direction of power lines from a helicopter by detecting an alternating magnetic field associated with the power lines is disclosed in United States Patent No.
4,362,992 to Young et al. The magnetic field is detected by two vertical loop antennas, with each antenna defining a planar area and receiving a hori-zontal component of the magnetic field. The antennas are preferably positioned perpendicular to one ,"f',, another. A signal processor is provided to receive and interpret the magnetic field which is sensed by the vertical pair of antennas, and determines there-from the direction of the power line emitting the magnetic field relative to the helicopter.
The Young et al power line detector also includes a third loop antenna which defines a horizontal planar area and detects the vertical component of the magnetic field. The detected vertical component is used to determine the magnitude of the magnetic field and to provide an early warning of the presence of power lines when the magnitude exceeds a predetermi'ned level.
The Young et al power line detector compensates for the extraneous magnetic fields from sources other than the power line. For example, the effects of any static magnetic fields surrounding the antennas are cancelled by using three pairs of Helmholtz coils. A
flux valve is used to cancel the earth's magnetic field, and a latitude selector or attitude data unit compensates for the latitude or attitude of the helicopter. Compensation for local variations in the earth's magnetic field is provided by a unit programmed with known data supplied from tables.
Such a cumbersome scheme of multiple compensation inputs renders such a magnetic field detector highly susceptible to errors.
Thus, the Young et al detection system merely indicates the relative direction of a power line from a helicopter, and provides an early warning of the presence of power lines. It does not provide or even suggest such useful outputs as the distance or range of the helicopter from the power line, or the time remaining until the helicopter would impact the power line.
2 ~ ' . ' , j1 ~ , ~
- Another magnetometer device for use on board an aircraft to detect the position of a magnetic source, such as a submarine, relative to the aircraft is disclosed in United States Patent No. 4,309,6;9 to Yoshii. As shown, four magnetometer units A, B, C and D are positioned at the aircraft nose, tail and wing tips, respectively. The magnetometer units measure components of the magnetic field in two and in three mutually perpendicular directions. These components, along with a gyroscope signal, are inputs provided to a signal processor.
Magnetometer systems, such as that of Yoshii, typically detect variations in the earth's magnetic field caused by the presence of large magnetic bodies, such as a submarine. From this variation, the position of the magnetic body is computed rela-tive to the position of the magnetometer system. The - signal processor computes the distance, direction, attitude and magnetic moment to locate the magnetic source being sought. Typically, aircraft equipped with magnetometers for determining the location of a magnetic source are flown with wings level, even while making turns, otherwise pitch and roll compen-sation must be included in the magnetometer system.
Other magnetic field detectors are disclosed in U. S. Patent Nos. 2,996,663; 3,582,932;
ELECTRIC ~IELD DET~CTION SYSTEM
Background of the Invention The present invention relates generally to a system for detecting an electrical power line, and more specifically to an improved detector and method for use on board an aircraft for providing an indication of the time-to-impact with the power line if the aircraft remains on course.
Other devices have been proposed in the past for detecting the distance of a power transmission line or cable. Such devices generally fall within two categories, one being those that detect power lines by sensing the magnetic field associated with a conductor having an alternating current (AC) flowing therethrough, and the other type of device sensing the electric field associated with such power lines. From electromagnetic field theory, it is well known that an infinitely long conductor carrying a current will have an associated magnetic field H in a circular pattern concentric about the conductor, and an electric field directed radially away from the conductor. From this, it is apparent that the means for sensing an electric and a magnetic field would be different, as well as the circuitry for interpreting the sensed ; electric and magnetic fields.
A system and method for detecting the direction of power lines from a helicopter by detecting an alternating magnetic field associated with the power lines is disclosed in United States Patent No.
4,362,992 to Young et al. The magnetic field is detected by two vertical loop antennas, with each antenna defining a planar area and receiving a hori-zontal component of the magnetic field. The antennas are preferably positioned perpendicular to one ,"f',, another. A signal processor is provided to receive and interpret the magnetic field which is sensed by the vertical pair of antennas, and determines there-from the direction of the power line emitting the magnetic field relative to the helicopter.
The Young et al power line detector also includes a third loop antenna which defines a horizontal planar area and detects the vertical component of the magnetic field. The detected vertical component is used to determine the magnitude of the magnetic field and to provide an early warning of the presence of power lines when the magnitude exceeds a predetermi'ned level.
The Young et al power line detector compensates for the extraneous magnetic fields from sources other than the power line. For example, the effects of any static magnetic fields surrounding the antennas are cancelled by using three pairs of Helmholtz coils. A
flux valve is used to cancel the earth's magnetic field, and a latitude selector or attitude data unit compensates for the latitude or attitude of the helicopter. Compensation for local variations in the earth's magnetic field is provided by a unit programmed with known data supplied from tables.
Such a cumbersome scheme of multiple compensation inputs renders such a magnetic field detector highly susceptible to errors.
Thus, the Young et al detection system merely indicates the relative direction of a power line from a helicopter, and provides an early warning of the presence of power lines. It does not provide or even suggest such useful outputs as the distance or range of the helicopter from the power line, or the time remaining until the helicopter would impact the power line.
2 ~ ' . ' , j1 ~ , ~
- Another magnetometer device for use on board an aircraft to detect the position of a magnetic source, such as a submarine, relative to the aircraft is disclosed in United States Patent No. 4,309,6;9 to Yoshii. As shown, four magnetometer units A, B, C and D are positioned at the aircraft nose, tail and wing tips, respectively. The magnetometer units measure components of the magnetic field in two and in three mutually perpendicular directions. These components, along with a gyroscope signal, are inputs provided to a signal processor.
Magnetometer systems, such as that of Yoshii, typically detect variations in the earth's magnetic field caused by the presence of large magnetic bodies, such as a submarine. From this variation, the position of the magnetic body is computed rela-tive to the position of the magnetometer system. The - signal processor computes the distance, direction, attitude and magnetic moment to locate the magnetic source being sought. Typically, aircraft equipped with magnetometers for determining the location of a magnetic source are flown with wings level, even while making turns, otherwise pitch and roll compen-sation must be included in the magnetometer system.
Other magnetic field detectors are disclosed in U. S. Patent Nos. 2,996,663; 3,582,932;
3,909,704; and 3,983,475.
There are a variety of proximity alarms for warning a heavy equipment operator, such as a crane operator, that the boom of the crane is approaching an energized power line. One such device is disclosed in United States Patent No. 3,745,549 to Jepperson et al, which detects the proximity of the power line by detecting the electrostatic field associated therewith.
An antenna is mounted to the heavy equipment extre-2~?~3 ~,~
mity, such as the boom of a crane, the forks of a forklift truck, or the ladder portion of a ladder truck. A switching and control circuit includes antenna sensitivity controls, test circuitry and alarm circuitry. The alarm may be either a light or an audible signal which merely warns the operator when the equipment extremity enters the electrostatic field associated with an energized power line.
Further useful information is not provided by the Jepperson et al device, such as the direction of the power line relative to the equipment extremity, the distance therefrom, or the time before an impact of the equipment extremity with the power line would occur. The Jepperson et al device also requires calibration. If the sensitivity is adjusted to screen out electrostatic fields from nearby extraneous sources, such as high voltage transmission lines, the danger exists that a lower voltage line in the proximity of the equipment may go undetected. Addi~ionally, such sensitivity controls may become misadjusted due to their being accidentally bumped or to the vibration - of the heavy equipment during operation.
A proximity detector for warning the operator of a backhoe that the backhoe bucket is approaching an underground conduit is disclosed in United States Patent No. 3,907,136 to Christides et al.
This device detects conduit or pipe by transmitting an oscillating electric signal in the region where the backhoe is working, with such transmitters preferably being located on the backhoe support or stabilizer pads. The transmitters induce a small current in any buried electrically conductive conduit in the region. The induced current is detected by sensors mounted within the bucket 2 ~ 3 -~1 teeth. Such transmitters may consume a great deal of e lectrical power in generating the e lectric field-inducing current. Also, the range of such transmitters would be limited by their power consumption, and are apparently only useful for detecting power lines or conduits within the immediate vicinity of the transmitters.
Other examples of devices used on heavy equipment to detect the presence of power lines are disclosed in U. S. Patent Nos. 2,615,969;
3,168,729; 3,833,898; 4,064,997; 4,649,375;
There are a variety of proximity alarms for warning a heavy equipment operator, such as a crane operator, that the boom of the crane is approaching an energized power line. One such device is disclosed in United States Patent No. 3,745,549 to Jepperson et al, which detects the proximity of the power line by detecting the electrostatic field associated therewith.
An antenna is mounted to the heavy equipment extre-2~?~3 ~,~
mity, such as the boom of a crane, the forks of a forklift truck, or the ladder portion of a ladder truck. A switching and control circuit includes antenna sensitivity controls, test circuitry and alarm circuitry. The alarm may be either a light or an audible signal which merely warns the operator when the equipment extremity enters the electrostatic field associated with an energized power line.
Further useful information is not provided by the Jepperson et al device, such as the direction of the power line relative to the equipment extremity, the distance therefrom, or the time before an impact of the equipment extremity with the power line would occur. The Jepperson et al device also requires calibration. If the sensitivity is adjusted to screen out electrostatic fields from nearby extraneous sources, such as high voltage transmission lines, the danger exists that a lower voltage line in the proximity of the equipment may go undetected. Addi~ionally, such sensitivity controls may become misadjusted due to their being accidentally bumped or to the vibration - of the heavy equipment during operation.
A proximity detector for warning the operator of a backhoe that the backhoe bucket is approaching an underground conduit is disclosed in United States Patent No. 3,907,136 to Christides et al.
This device detects conduit or pipe by transmitting an oscillating electric signal in the region where the backhoe is working, with such transmitters preferably being located on the backhoe support or stabilizer pads. The transmitters induce a small current in any buried electrically conductive conduit in the region. The induced current is detected by sensors mounted within the bucket 2 ~ 3 -~1 teeth. Such transmitters may consume a great deal of e lectrical power in generating the e lectric field-inducing current. Also, the range of such transmitters would be limited by their power consumption, and are apparently only useful for detecting power lines or conduits within the immediate vicinity of the transmitters.
Other examples of devices used on heavy equipment to detect the presence of power lines are disclosed in U. S. Patent Nos. 2,615,969;
3,168,729; 3,833,898; 4,064,997; 4,649,375;
4,675,664; and 4,727,447.
Several types of portable detection devices for locating buried metallic pipes have been proposed, which sense an electromagnetic field emitted from the pipe. United States Patent No.
3,988,663 to Slough et al detects the location and - depth of buried metallic pipes which carry AC
signals impressed thereon as a result of various industrial activities in the vicinity.
United States Patent No. 3,889,179 to Cutler discloses a portable buried pipe locator. External excitation of the pipe by an external power supply is required to provide an emission source to generate an electric field which is detected by the locator.
Such a locator first requires that an external loca-tion of the pipe be known and the connection be made.
The depth of the buried pipe is computed by a trian-gulation method using multiple readings in the devices of both Slough et al and Cutler.
Another electromagnetic field detecting device for locating buried pipe is disclosed in United States Patent No. 3,893,025 to Humphreys, which also requires external excitation of the buried pipe. The external excitation is provided by trans~itters which impre~s radio frequency signals upon the buried cable or pipe, Two ver~ically displaced ant~nnas are us~d to detect the emitted electzic field; ~he dif~ere~ce in the electric f ie ld detected by each antenna and the fixed dist3nce between the ancennas are used to determine the depth of the oipe. Ot~e devices for locating buried conductors are disclosed in U, S. Patent Nos. 4,~95,095 and 4,672,321.
Thus, a need exists ~o~ an improved apparat~s ~or detecting the presence, range and direction relative to an aircra~t o~ an electric power line, as well as ~or de~e~inin~ the ti~e remaini~g for a pilot oE the 3iroraft to make a Course correction to avoid an impact with the power line.
- According to the present invention, a detector or use on board an aircra~t to detect an zo electri~ po~er line comp~ises antenna means for sensing the electric ~ie}d associated with the powe~ line and producing an electric field signal, and signal processing means foc ~eceivin~ the electric ield signal and generating a time-to-impact signal representative of the time for the a~tcraft ~c reach the power line i~ it continues on its p~th o moVe~ent .
ef Descri~tion of tlle Drawinqs B r 1 For a better un~erstanding of the invention, ~nd to show ho~ the same may be car r ied into eect, refe~ence will now be made, by way o~
ex~mple, to the accompanying dra~ings in which:
PIG, ~ is an unscaled perspective view of an 3~ aircraft and illustra~es an elect~ic ~ield detectcr h' ? ~
em~odying the present invention, FIGS. 2, 3 and 4 are diaseams and gr~phs illustratinq the theo~y o~ operation of the p~esent invention, including in FIG. 4 A pl ot of ex~erimen-tal teQt data, F~G. ~ is a circuit diagram of one fo~m of a signal conditioning ~eans that orms p~t o~ the on-board electric field detee~or, FIG. 6 is a block di~gram of one ~orm o~ a signal p~ocessing ~eans and output means that form part of the on-board elec~ic field detector, FIGS, lA and 7B ill~steate apparatus u~ed to dete~t the electric field in the vicinity of an electric power line, lS FIG~ 8 shows a detail of ~IG. 1 in order to illustrate how the di~ection of a power line can be de te rmined, FIG. 9 illustrates how a~paratus similar to that shown in FIG. 7B might be used on an aircraft to determine the direct~on of a powe~ line rela~ive ~o the heading of the aircraft, and F~G. 10 illustrates another apparatus for detecting the di~ec~ion of a power line rela~ive to the heading of an a i ~cr a~ t .
Detailed Description FIG. 1 illustrates an on-boaed electric field detector sy~tem 20 for use on board an aircra~t to detect an ele~trical power line P, having an elec-tric field associated the~ewith.
~e~ore discussing ~he operation of the electric fie~d detector, it will be use~ul to desc~ibe the theoretical ~ac~round o the invention and some experimental observations.
3~ Refe~ring to FIG. 2, the three ph2se power line P
~f FIG. 1 is ~cdeled as a Line eo~nprising t~ree spaced conductoes labeled as I=l, I-2 and I=3. (The distance and direction o~ the sensor from ~he three phase power line is indicated as the vector S quantity ~ he conducto~s are spaced apart a distance ZS and located a linear distance 2L above an electeical ground plane whiCh may be located ne~r the earth's s~rface.
The voltage on the three phase power line is assumed to be sinusoidal, that is of the form ~i =
vmaxsin ~t ~ 0i), where the phase between the : lines differs by 2~/3. Although this analysis is fo~
three p~ase lines, it is apDa~en~ that the ~ethod would be similar ~or single .phase and two phase lines. ~he energized lines create images of them-selves, indi~ted in ~IG. ~ as image lines la~eled I~4, I~5 and I=6. The image li~es are s~aced ~?art a distance ZS ~nd l~cated beneath the ground plane the same linear distance ZL as the real lines are 2~ above the gro~nd plane. The polarity o the image lines is opposite to that o~ ~he real lines.
~he electric field at a distance R from a sin~le linear cond~ctor can be c~p~ted from the following eq~a~ion:
~5 2~oR
where p = the charqe density, 3~ ~0 = the per~itti~i~y of free s~ace, and R - the radial distance from t~e line to the sensor.
~Halliday and Resnick, "Physics", John Wiley sons, 675 ~lg66) ) __.
Without any loss of generality, relative field strengths may be calculated from the geometry of the model by summing the contributions of each conductor, insertin~ range values and setting the constants for a given power line, i.e. P/(2~Eo), equal to one.
As mentioned earlier, the electric field E is directed radially away from the power line. The net electric field at any point of interest is tne vector sum of the electric fields from the real three phase power line plus the electric fields from the three image conductors. The fields can be reduced to vertical and horizontal components relative to the earth's surface and the components summed to obtain the net electric field. The net horizontal component is generally different in magnitude from the net vertical co~ponent.
FIG. 2 illustrates the horizontal and vertical components EH and EV of the electric field El, measured at a point Pl, which is a vertical distance ZA above the ground plane and a radial distance Rl from the real power line conductor labeled I=l. For the real power line conduc~ors, where I equals one, two or three, the total field may be computed as:
sin (I x 2~/3j EI
[(R + (I _ l)z5)2 + (ZA ~ ZL)2]l/2 sin (I x 2~/3) From this, the vertical component may be expressed as:
EVI = EI x (ZA ~ ZL)/RI
And the horizontal component may be expressed as:
. EHI = EI X ~R + ~I - 1) ZS]/RI' .
The total field for the image conductors located beneath the ground plane, where I equals , four, five or six, may~be expressed as:
-sin [~I - 3) x 2~/3]
E
[(R + ~I _ 4~Z5)2 + tZA + ZL)2]l/2 - -sin t(I - 3) x 2~/3]
RI' ' From this, the vertical component may be expressed as:
EVI - EI x (ZA + ZL)/RI
And the horizon~al component may be expressed as:
EHI ' EI x tR + ~I ~ 4)ZS)]/RI''.
From the above, the total horizontal an~
vertical fields are the summation o~ the respective horizontal and vertical contributions of the real conductors and the image conductors, that is from the variable I equals one through ~ equals six.
:, :
. ~ - ' '~ ' .' ':
~ario~s ~ange values were subs~ituted in~o the abo~e e~uations and the res~lts are graphed in FI~.
3.
From evaluating the plots in FIG. 3 llsing a curve-~itting analys~s, i~ was concluded thae the elect~ic field decreases as a high orde~ ~unc~ion o~ distance, whi~h in this case is approximately l/R3 at la~ge distances, such as greate~ than 100 mete~s, Thu~, ~or large values o~ R the relationship between the elec~ric ield S and the distance R is gi~en by ~ = K/R3, where K is a proportionalit~ constant. ~ence, ~2 ~ El - K~ R2) whe~e E2 is the field strength at a point P2, which is ~t a distance R2 from the powe~ line. If the pointa Pl a~d P2 are close together, SO that is much,' much less than the value of R2, it follows that ~E = 3K(R2/~R)2, where ~E = E2 ~ ~1' ~e~er~ing again :o FIG. 1, detec~or 20 comp~ises sensor means 2~ including on-~ard an~enna means, such as antenna 32, ~or sensing t~ç
elect~ac ~ield produced by the electrical power ~5 lines P and for pcoducing an ~lectric ~ield signal co~responding co ~he sensed electric field. Signal processin~ means ~4 ace provided for recei~in~ and proce~sing ~he electric ield signal and ~o~
p~oducing t~e~efrom an output signal~ The out~u~
~ignal is received by output means ~6 for providing an output to an operator of the ai~c~Et, such as an air~raft pilot or an autopilo~ ~ontrol system, indicative o~ ~actors conce~ning the approaoh o~
the aircraft to~ard the power line P, such a~ the time-~o-i~pact.
12 ~ 3 The antenna means may comprise one or more of a variety of different antenna arrangements capable of detecting an electric field. For example, an antenna means.placed upon a vehicle having a nonconductive body, such as of fiberglass, may comprise metallic strips adhered to the body of the vehicle. In such applications, the antenna means may be mounted on eithec the interior or the exterior of the vehicle body. Dipole antennas projecting outwardly from the vehicle exterior may also be used.
For a vehicle having a body of an electrically conductive material, such as steel, aluminum or another metal, which acts as a shield to an - 15 electric field, antennas may be mounted to the exterior of the vehicle body. In this case, it is necessary to insulate the antenna from the body, for example by use of an electrically insulating mounting means.
The following nomenclature will be used in describing the si~nals generated by the illustrated embodiment of the emission source detector 20 of the present invention. The subscript letter "Hn refers to a horizontal component of the electric field, while the subscript letter "V" reers to a vertical component of the electric ~ield. The letter "E" is used to denote an electric field voltage signal which corresponds to the electric field. The prime symbol (') indicates a sensed voltage representing the composite electric field seen by an antenna means. A double prime symbol (") or an unprimed variable denotes a signal produced by the signal processing means.
One particularly useful antenna means comprises means for sensing two mutually ~ r ~ ~
i3 per~endicular componenes o the electric ~ield, such as the horizontal and vertical components, and producing two elect~ic field ~ignals in resp~nse thereto, For example, in FIG. 1 for aircra~t R
S having a body o~ a~ elec~rically shielding m~te~ial, su~h as alu~inum, t~e sensor means 22 comprises the cross-polarize~ antenna 32, mounted to the exterior of the body by an electrically insulaeing me~ns (~0~ shown).
Electri~al coupling means, such as a ooaxial ~able~ intecConnect the an~en~a 32 with the signal p~ocessing ~eans 24. An electrical ~o~pling means aLso inte~connect the signal processing means 24 with the outp~ means 26.
F~G. 5 illusr~ates an add,itiQnal po~tion o~
the sensoe means 22 compr ising sisnal condi tionin~
means 60 ~o~ producing a cond~icned electrical ~ield ~eignal output of ~H' ' or Evl ' f~om the hocizontal or vectical an~enna signal E~' or The signal conditioning mesns 60 have a high i~pu~
itnpedance operational ampli~ie~ 62 which receives and amplieLes an antenna signal, such as E~ he amplif iet antenna si~nal is iltered by a ~ilter 64 to re~nove E~e~}uency ~omponents otHer than the powec 2~ line f~eq~ency and ~o produce co~ditioned antenna si~nals E~
Re~er~ing again to F~G. 2, i~ we assume that . the aircraft i5 traveling at a constant ground speed towards ~he power line and pa~ses ~he point Pl at time el and the point P2 at time t2, then ~he time-to-imp~ct T, measu~ed rom ehe time t2, is eq~al to ~2~tl - t~ R, whece AR = R~ ~ Rl.
SubS~ituting for ~2/ ~ f~,om the e~pression ~or into the expression for ~E, ~E = 3K(~/~T)2, or 3~
I~E
T = ~T¦ -~ 3K
For points P1 and P2 that are close together, EH and EV are each linearly related to E.
Therefoce, T = CH
and T = CV~T ~
- ; 15 where CH and Cv are constants, ~E~ is the difference between the values of the horizontal com?onent of E at points P2 and Pl and ~EV is the - difference between the values of the vertical component of E at points P2 and Pl. The values of - 20 CH and Cv can be calculated from measured values of E and R. Thus, if ~T is known and ~EH or ~EV is measured, the value of T can be calculated. For example, the signal EH'', which represents the horizontal component of E, is sampled at predetermined intervals (10 ms, say) and two consecutive sample values of EH'' are subtracted to return a value for ~EH. Since the sampling interval (which is equal to ~T) is known, and CH
has been calculated, the value of T c~n then be calculated. Separate values of T may be calculated based on the horizontal and vertical field components respectively, to provide verification.
The necessary calculation can be carried out using a general purpose digital computer, or a simple analog computer could be designed to solve the equation for T, given the values of T and ~.
From the graphs, such as that shown in FIG. 3, it is apparent that a component electric field signal value may be compared with a reference value which is known and correlates a given component electric field signal with a range value. From the graph shown in FIG. 3, it is also apparent that the relative strength of the horizontal and vertical component curves approach one another as the aircraft A approaches the power line P. Thus, by comparing the ratio of the vertical to the horizontal electric field signals with a reference value, a range value can be determined.
From the graphs, it is apparent that the vertical component of the electric field is larger than the horizontal component until the moving ~ vehicle reaches a certain distance from the line during approach. At distances closer than lO0 meters or so, the slope of the vertical component curve begins to change, as does the slope of the horizontal curve at a slightly closer distance to the power line. Due to these changing slopes, the calculations ~et forth above predict that the horizontal and vertical components of the electric field intersect at a range of approximately 50 meters. By detecting the cross-over point, a discrete warning can be given to the aircraft pilot that the power line is very close and that he should take steps to avoid impact with the power line.
The existence of the curve cross-over phenomenon was confirmed by experiments conducted on electric fields emitted from a power transmission line and detected by a hand-held l6 sensor. Readings were taken while moving the sensor along a ridge of land extending away from the power transmission line. The detector was a simple high input impedance ampli~ier having an output to a digital voltmeter. The sensor was a dipole antenna, which was held in horizontal and vertical orientations to detect the respective horizontal and vertical components of the electric field at various distances from the power transmission line. This experimental data is shown in FIG. 4, with the cross over of the horizontal and vertical components occurring at a range of approximately 90 meters from the power line. The vertical scale on the graph of FIG. 4 is in volts, as read from the digital voltmeter.
Depending upon the particular application, the sensor means 22 comprising the antenna means and - the signal conditioning means 60 may be physically concentrated within one area of the aircraft or dispersed in several locations throughout the aircraft. For example, the signal conditioning means 60 may be physically located within the aircraft adjacent the signal processing means 24.
Alternatively, the signal conditioning means 60 may be located near the antenna 32.
Although the expression for T has been derived on the assumption that the aircraft heading is directly towards the power line, the aircraft heading is not relevant to the time-to-impact calculation since the time-to-impact is dependent only on the range R and the component of the aircraft's ground velocity that is perpendicular to the path of the power line. However, the heading relative to the direction of the power line is important to a pilot determining in which direction ^,f ' ~
to make a course correction. (In this specifica-tion, the term "direction of a power line," means the direction of the shortest line from the aircraft to the power line.) The direction of the power line relative to the aircraft heading may be determined by use of sensors 30 and 34. Sensors 30 and 34 are mounted at the left and right respec-tively of the aircraft.
In order to aid in understanding the operation of the system includin~ sensors 30, 34, reference is made to FIG. 7A, which shows two hollow, rectan-gular metal shells 120 and 122. Shells 120 and 122 are identical. The end faces of the shells are parallel and the shells are attached together by a plate 124 of electrically insulating material, such as the synthetic plastic material sold under the trademark DELRIN. The four side faces of shell 122 are coplanar with respective faces of shell 120.
Referring to the coordinate axes shown in FIG. 7A, the X, Y and Z dimensions of each shell are about 12.5 cm, 5 cm and 18 cm respectively, and the shells are spaced apart in the X direction by about 6.4 cm. An ammeter 126 is connected to the two shells. Although the ammeter is shown outside the shells, this is purely for ease of illustration.
In fact, the ammeter is inside one of the shells, so that it is shielded from external fields, and its display is observed through a small hole in a face of that shell. The apparatus shown in FIG. 7A
is similar to apparatus currently used for detecting electric field in the vicinity of an electric power line.
The apparatus shown in FI~. 7A was supported above the ground in the vicinity of a three-phase, high voltage electric power line. The apparatus s~
was suppo~ted at a heigh~ of about 4 m above the ground, in order to minimize g~ound ~lane efSects.
The shells were disposed with the XZ plane horizontal and the power line extendin~ parallel ~o the ~ axis and spaced from the shells along the X
axis by a distance o~ abc-lt 50-100 m. The ammeter, which is o~ very low impedance, pr~vides the only path fo~ cur~ent to flow between the two shells and the cha~ges on th~ two shells are redis~ributed throuqh the amme~er. The ammeter provided a measurable current readLng. The appa~atus was then rocsted th~oug~ 180 deqrees about a vertical axis, so that the posi~ions o~ ~he shells relative to th~
p~wer line ~ere reversed, b~ the two shells stayed in ~he same positions relative to each other. The ammeter reading was found not to be significantly diee~ent from the previous am~eter reading.
A si~ilar expeciment to that described with ref e~enc:e ~o F~. 7A ~as conduc_ed using the apparatus sho~n in FIG. 7B. The apparatus showrl in F~G. 7B i~ the same as that shown in ~IG. 7~, except that the Z dimension o~ one o the shel~c is ahout 36 cm instead of about la cm. I~ was found that when the smalle~ shell was closer to the power line, tbe ~mmeter r~ading ~a3 a~ou~ twice th~t when the la~ge~ shell was close~ to the powee line, Refer~in~ again to FIG. 1, each of the sensors 3a and 34 is a rectan~ular shell.
Sensors 30 and 34 are mounted to opposite res~ec-tive sides o~ the central pl3ne of the aircraf t ,i.e., the plane th~ough the central axis of the airc~t and a~out ~hich the aircraft is subs~an-tially symmetrical, with the YZ plane (FIG. 7A) parallel to the central plane of the ai~craft.
Sensors 3~, 34 are mour,ted by use of insulating 19 ~ ~ c~ ~ '3 ' ~., '' >~
material and a~e electrically connected to the metal aircrat body through raspecti~e ammeters 128, 130 ~IG. 8). The metal ~ircraft body then unction3 as ~ larg~ shell ~elative to the smaller shells of sensors 30, 34.
Based on the results of the experiments desc~ ibed with ~e~erence ~o FIG~. 7A ar.d ~B, the current between sensor 30 ar~d the aircraft body will be larger than the current between sensor 34 and the airc~a~t body i~ the direc~ion o~ the power line is t~ the le~t o~ ~che ai~cra~t, and vice ve~sa when the di ~ect ion of the powe~ line i s to the right of the ai~c~a~t, Ammeters 128, 130 generate ~oltage signals proportional ~o the respec~ive current ~lues, these signals are applied to a comparator 132 and the result of the compae i50n iS
used to indic~te the direction ~ the power l~ne~
ReEer~ing again to the arrangement described wi~h reference ~o FIG5. 1 and 5, FIG, 6 illust~ ates ~0 ha!dwa~e 70 used to process ~he cor~ditioned antenna signals. ~he conditi,oned antenna sign~l outputs Erom fllter 64 o the senso~ means 22 are supplied as the conditioned analog E f ie ld sensoc inputs to an analcg-to-digital converter 72. ~he voltage signal~ ~epsesentative of the cur~ents measured by ammeters 128, 130 a~e applied to analog-to-disital con~rerte~ 7 2 instead of to compara~or 132. Conver-ter 72 con~rerts its input signals into digital signals which ~re supplied to a cen~ral bus 14.
~he signal p~ocessing means 24 includes a central processo~ unit ~CPUl 80, men~ory n~eans 82, data input device sl~ch as a touch pad 84, and visual output device such as a CR~r moni~or 86. Each oi~ the ~ignal proces-ing means components 8û, 82, 84 and 86 communic:ates with the cent~al bus ?4.
__.
\
The central pcocessor unit 80 includes inter-acting bus control means 88, arithmetic means such as an arithmetic unit 90, flags 92, a stack pointer 94, a program counter 96, and storage registers 98.
The memory means includes various memory units, such as random access memory (RAM), read-only memory (ROM), and electrically erasable and programmable read-only memory (EEPROM). The visual output device 86 and the data input device 84, such as a keyboard, may be of the type typically used with personal computers.
The output means 26 in communication with central bus 74 include an audible warninq device 100 and a visual line location indicator 102, which communicates with central bus 74 through a digital-to-analog (D/A) converter 104. The audible warning device 100, which may include a speech synthesizer, provides an output to a loudspeaker or other elec-troacoustic transducer 106 to alert the pilot of an upcoming power line. The visual line indicator 102 provides an output to the pilot which indica~es the direction of an upcoming power line relative to the aircraft heading. The visual line indicator may take on any form, such as three lights or light-emitting diodes (LEDs) 108. For example, for a power line detected to the left of aircraft A, light 108a turns on to indicate this, while lights 108b and 108c, indicating the respective front and right side directions, remain off (see FIG. 6).
The visual output device 86 provides a legible readout of the result of the time-~o-impact calcu-lation.
It will be appreciated that there is a danger of a spurious indication of time-to-impact being given if the altitude of the aircraft is consi-derably greater than the height of the power line.
This possibility may be guarded against by providing additional sensors, similar to sensors 30 and 34, on the top and bottom of the aircraft body:
if the current between the aircraft body and the sensor on top of the aircraft body is substantially greater than that between the aircraft body and the sensor on the bottom of the aircraft body, it implies that the aircraft's altitude is such that it will not impact the power line. If the currents are substantially the same, the pilot should gain altitude.
It will be appreciated that it is not necessary to know the aircraft's ground speed in order to calculate the time-to-impact. This is a considerable advantage, because it is often diffi-cult to obtain an accurate measure of ground speed.
Slight variations in ground speed, for example due to gusts of wind, do not affect the accuracy of the calculation of the time-to-impact, because the samples of the electric field signal are taken at intervals that are much shorter than any short-term fluctuations in ground speed, and in any event the current value of the ground speed is implicitly used in calculating time-to-impact.
FIG. 9 illustrates an aircraft having a bubble 140 of insulating material projecting beneath the aircraft body, which is typically metal. Inside the bubble 140 is apparatus 142 for detecting the direction of a power line. This apparatus is simi-lar to the apparatus described with reference to FIG. 7B, and comprises two different-sized metal shells 144, 146 connected to an ammeter 148 and - mounted on an insulating plate 150 so that the only current path between the shells is through the ammeter. The shells are supported so that they can be rotated continually relative to the aircraft about an axis perpendicular to the open ends of the shells without changing the orien~ation of the shells relative to each other. This is accom-plished by use of a motor 152 connected to plate 150 through a shaft 154. The shaft is provided with an angle encoder 156 which indicates the angu-lar position of the shells relative to the central axis of the aircraft. Both the ammeter and the angle encoder are connected to a computer 160.
When the aircraft is in the vicinity of a power line, and is at a height such that the horizontal component of the electric field from the power line induces charge on the shells, the current flowing through the ammeter will vary with a frequency equal to the rotational frequency of shaft 154.
The computer detects the positive and negative peaks of the periodic variation in the current and relates it to the azimuth signal provided by the angle encoder. The computer then provides an output signal indicating the direction of the power line relative to the central axis of the aircraft so as to enable the pilot to change the heading of the aircraft in a manner that will avoid impact with the power line.
FIG. 10 illustrates in plan view another form of apparatus for detecting the direction of a power line.
The apparatus shown in FIG. 10 comprises a pair of identical sensors 180, 182 mounted at oppo-site respective wing tips of an aircraft. In a typical light aircraft, the antennas are about 7-10 m apart. Each sensor is composed of a metal shell similar to shell 144 and is mounted on the aircraft 23 2 ~ ~, wing, if it is made of metal, in electrically insu-lating ~ashion and in an orientation such that the X axis is parallel to the central axis of the aircraft. Respective ammeters are connected between the sensors and the respective aircraft wings, to measure the redistribution of charge between each sensor and the aircraft body, in simi-lar fashion to that described with reference to FIG. 8. If the aircraft heading is directly towards the power line, the currents measured by the two ammeters will be equal, whereas if the aircraft is not heading directly towards the power line, the current measured by the ammeter connected to the sensor that is closer to the power line will be larger than the current measured by the other ammeter~ The values of the currents measured by the respective ammeters are compared in order to provide an indication as to the direction of the power line relative to the aircraft heading, i.e., whether the power line is straight ahead of the aircraft, to the left or to the right.
It will be appreciated that the present invention is not restricted to the embodiments that have been shown and described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof. For example, although the invention has been described with reference to voltage signals, current signals may also be used. Further, the invention is not applicable only to fixed wing aircraft but may be used with helicopters also. The fact that it is not necessary to measure ground speed is particularly important in the case of a helicopter, since a helicopter may have a very low air speed 24 ~ ; ' f .' J
and a gust of wind might then have a large ef~ect on the helicopter's ground speed. The cross-over phenomenon described with reference to FIGS. 3 and 4 is a use~ul safety measure for use with a helicopter, because a helicopter traveling at low speed towards a power line might have a long time to impact, yet still be dangerously close to the power line. The embodiment described with reference to FIG. 9 may be applied to a helicopter by mounting the sensors on the rotor tips.
.
Several types of portable detection devices for locating buried metallic pipes have been proposed, which sense an electromagnetic field emitted from the pipe. United States Patent No.
3,988,663 to Slough et al detects the location and - depth of buried metallic pipes which carry AC
signals impressed thereon as a result of various industrial activities in the vicinity.
United States Patent No. 3,889,179 to Cutler discloses a portable buried pipe locator. External excitation of the pipe by an external power supply is required to provide an emission source to generate an electric field which is detected by the locator.
Such a locator first requires that an external loca-tion of the pipe be known and the connection be made.
The depth of the buried pipe is computed by a trian-gulation method using multiple readings in the devices of both Slough et al and Cutler.
Another electromagnetic field detecting device for locating buried pipe is disclosed in United States Patent No. 3,893,025 to Humphreys, which also requires external excitation of the buried pipe. The external excitation is provided by trans~itters which impre~s radio frequency signals upon the buried cable or pipe, Two ver~ically displaced ant~nnas are us~d to detect the emitted electzic field; ~he dif~ere~ce in the electric f ie ld detected by each antenna and the fixed dist3nce between the ancennas are used to determine the depth of the oipe. Ot~e devices for locating buried conductors are disclosed in U, S. Patent Nos. 4,~95,095 and 4,672,321.
Thus, a need exists ~o~ an improved apparat~s ~or detecting the presence, range and direction relative to an aircra~t o~ an electric power line, as well as ~or de~e~inin~ the ti~e remaini~g for a pilot oE the 3iroraft to make a Course correction to avoid an impact with the power line.
- According to the present invention, a detector or use on board an aircra~t to detect an zo electri~ po~er line comp~ises antenna means for sensing the electric ~ie}d associated with the powe~ line and producing an electric field signal, and signal processing means foc ~eceivin~ the electric ield signal and generating a time-to-impact signal representative of the time for the a~tcraft ~c reach the power line i~ it continues on its p~th o moVe~ent .
ef Descri~tion of tlle Drawinqs B r 1 For a better un~erstanding of the invention, ~nd to show ho~ the same may be car r ied into eect, refe~ence will now be made, by way o~
ex~mple, to the accompanying dra~ings in which:
PIG, ~ is an unscaled perspective view of an 3~ aircraft and illustra~es an elect~ic ~ield detectcr h' ? ~
em~odying the present invention, FIGS. 2, 3 and 4 are diaseams and gr~phs illustratinq the theo~y o~ operation of the p~esent invention, including in FIG. 4 A pl ot of ex~erimen-tal teQt data, F~G. ~ is a circuit diagram of one fo~m of a signal conditioning ~eans that orms p~t o~ the on-board electric field detee~or, FIG. 6 is a block di~gram of one ~orm o~ a signal p~ocessing ~eans and output means that form part of the on-board elec~ic field detector, FIGS, lA and 7B ill~steate apparatus u~ed to dete~t the electric field in the vicinity of an electric power line, lS FIG~ 8 shows a detail of ~IG. 1 in order to illustrate how the di~ection of a power line can be de te rmined, FIG. 9 illustrates how a~paratus similar to that shown in FIG. 7B might be used on an aircraft to determine the direct~on of a powe~ line rela~ive ~o the heading of the aircraft, and F~G. 10 illustrates another apparatus for detecting the di~ec~ion of a power line rela~ive to the heading of an a i ~cr a~ t .
Detailed Description FIG. 1 illustrates an on-boaed electric field detector sy~tem 20 for use on board an aircra~t to detect an ele~trical power line P, having an elec-tric field associated the~ewith.
~e~ore discussing ~he operation of the electric fie~d detector, it will be use~ul to desc~ibe the theoretical ~ac~round o the invention and some experimental observations.
3~ Refe~ring to FIG. 2, the three ph2se power line P
~f FIG. 1 is ~cdeled as a Line eo~nprising t~ree spaced conductoes labeled as I=l, I-2 and I=3. (The distance and direction o~ the sensor from ~he three phase power line is indicated as the vector S quantity ~ he conducto~s are spaced apart a distance ZS and located a linear distance 2L above an electeical ground plane whiCh may be located ne~r the earth's s~rface.
The voltage on the three phase power line is assumed to be sinusoidal, that is of the form ~i =
vmaxsin ~t ~ 0i), where the phase between the : lines differs by 2~/3. Although this analysis is fo~
three p~ase lines, it is apDa~en~ that the ~ethod would be similar ~or single .phase and two phase lines. ~he energized lines create images of them-selves, indi~ted in ~IG. ~ as image lines la~eled I~4, I~5 and I=6. The image li~es are s~aced ~?art a distance ZS ~nd l~cated beneath the ground plane the same linear distance ZL as the real lines are 2~ above the gro~nd plane. The polarity o the image lines is opposite to that o~ ~he real lines.
~he electric field at a distance R from a sin~le linear cond~ctor can be c~p~ted from the following eq~a~ion:
~5 2~oR
where p = the charqe density, 3~ ~0 = the per~itti~i~y of free s~ace, and R - the radial distance from t~e line to the sensor.
~Halliday and Resnick, "Physics", John Wiley sons, 675 ~lg66) ) __.
Without any loss of generality, relative field strengths may be calculated from the geometry of the model by summing the contributions of each conductor, insertin~ range values and setting the constants for a given power line, i.e. P/(2~Eo), equal to one.
As mentioned earlier, the electric field E is directed radially away from the power line. The net electric field at any point of interest is tne vector sum of the electric fields from the real three phase power line plus the electric fields from the three image conductors. The fields can be reduced to vertical and horizontal components relative to the earth's surface and the components summed to obtain the net electric field. The net horizontal component is generally different in magnitude from the net vertical co~ponent.
FIG. 2 illustrates the horizontal and vertical components EH and EV of the electric field El, measured at a point Pl, which is a vertical distance ZA above the ground plane and a radial distance Rl from the real power line conductor labeled I=l. For the real power line conduc~ors, where I equals one, two or three, the total field may be computed as:
sin (I x 2~/3j EI
[(R + (I _ l)z5)2 + (ZA ~ ZL)2]l/2 sin (I x 2~/3) From this, the vertical component may be expressed as:
EVI = EI x (ZA ~ ZL)/RI
And the horizontal component may be expressed as:
. EHI = EI X ~R + ~I - 1) ZS]/RI' .
The total field for the image conductors located beneath the ground plane, where I equals , four, five or six, may~be expressed as:
-sin [~I - 3) x 2~/3]
E
[(R + ~I _ 4~Z5)2 + tZA + ZL)2]l/2 - -sin t(I - 3) x 2~/3]
RI' ' From this, the vertical component may be expressed as:
EVI - EI x (ZA + ZL)/RI
And the horizon~al component may be expressed as:
EHI ' EI x tR + ~I ~ 4)ZS)]/RI''.
From the above, the total horizontal an~
vertical fields are the summation o~ the respective horizontal and vertical contributions of the real conductors and the image conductors, that is from the variable I equals one through ~ equals six.
:, :
. ~ - ' '~ ' .' ':
~ario~s ~ange values were subs~ituted in~o the abo~e e~uations and the res~lts are graphed in FI~.
3.
From evaluating the plots in FIG. 3 llsing a curve-~itting analys~s, i~ was concluded thae the elect~ic field decreases as a high orde~ ~unc~ion o~ distance, whi~h in this case is approximately l/R3 at la~ge distances, such as greate~ than 100 mete~s, Thu~, ~or large values o~ R the relationship between the elec~ric ield S and the distance R is gi~en by ~ = K/R3, where K is a proportionalit~ constant. ~ence, ~2 ~ El - K~ R2) whe~e E2 is the field strength at a point P2, which is ~t a distance R2 from the powe~ line. If the pointa Pl a~d P2 are close together, SO that is much,' much less than the value of R2, it follows that ~E = 3K(R2/~R)2, where ~E = E2 ~ ~1' ~e~er~ing again :o FIG. 1, detec~or 20 comp~ises sensor means 2~ including on-~ard an~enna means, such as antenna 32, ~or sensing t~ç
elect~ac ~ield produced by the electrical power ~5 lines P and for pcoducing an ~lectric ~ield signal co~responding co ~he sensed electric field. Signal processin~ means ~4 ace provided for recei~in~ and proce~sing ~he electric ield signal and ~o~
p~oducing t~e~efrom an output signal~ The out~u~
~ignal is received by output means ~6 for providing an output to an operator of the ai~c~Et, such as an air~raft pilot or an autopilo~ ~ontrol system, indicative o~ ~actors conce~ning the approaoh o~
the aircraft to~ard the power line P, such a~ the time-~o-i~pact.
12 ~ 3 The antenna means may comprise one or more of a variety of different antenna arrangements capable of detecting an electric field. For example, an antenna means.placed upon a vehicle having a nonconductive body, such as of fiberglass, may comprise metallic strips adhered to the body of the vehicle. In such applications, the antenna means may be mounted on eithec the interior or the exterior of the vehicle body. Dipole antennas projecting outwardly from the vehicle exterior may also be used.
For a vehicle having a body of an electrically conductive material, such as steel, aluminum or another metal, which acts as a shield to an - 15 electric field, antennas may be mounted to the exterior of the vehicle body. In this case, it is necessary to insulate the antenna from the body, for example by use of an electrically insulating mounting means.
The following nomenclature will be used in describing the si~nals generated by the illustrated embodiment of the emission source detector 20 of the present invention. The subscript letter "Hn refers to a horizontal component of the electric field, while the subscript letter "V" reers to a vertical component of the electric ~ield. The letter "E" is used to denote an electric field voltage signal which corresponds to the electric field. The prime symbol (') indicates a sensed voltage representing the composite electric field seen by an antenna means. A double prime symbol (") or an unprimed variable denotes a signal produced by the signal processing means.
One particularly useful antenna means comprises means for sensing two mutually ~ r ~ ~
i3 per~endicular componenes o the electric ~ield, such as the horizontal and vertical components, and producing two elect~ic field ~ignals in resp~nse thereto, For example, in FIG. 1 for aircra~t R
S having a body o~ a~ elec~rically shielding m~te~ial, su~h as alu~inum, t~e sensor means 22 comprises the cross-polarize~ antenna 32, mounted to the exterior of the body by an electrically insulaeing me~ns (~0~ shown).
Electri~al coupling means, such as a ooaxial ~able~ intecConnect the an~en~a 32 with the signal p~ocessing ~eans 24. An electrical ~o~pling means aLso inte~connect the signal processing means 24 with the outp~ means 26.
F~G. 5 illusr~ates an add,itiQnal po~tion o~
the sensoe means 22 compr ising sisnal condi tionin~
means 60 ~o~ producing a cond~icned electrical ~ield ~eignal output of ~H' ' or Evl ' f~om the hocizontal or vectical an~enna signal E~' or The signal conditioning mesns 60 have a high i~pu~
itnpedance operational ampli~ie~ 62 which receives and amplieLes an antenna signal, such as E~ he amplif iet antenna si~nal is iltered by a ~ilter 64 to re~nove E~e~}uency ~omponents otHer than the powec 2~ line f~eq~ency and ~o produce co~ditioned antenna si~nals E~
Re~er~ing again to F~G. 2, i~ we assume that . the aircraft i5 traveling at a constant ground speed towards ~he power line and pa~ses ~he point Pl at time el and the point P2 at time t2, then ~he time-to-imp~ct T, measu~ed rom ehe time t2, is eq~al to ~2~tl - t~ R, whece AR = R~ ~ Rl.
SubS~ituting for ~2/ ~ f~,om the e~pression ~or into the expression for ~E, ~E = 3K(~/~T)2, or 3~
I~E
T = ~T¦ -~ 3K
For points P1 and P2 that are close together, EH and EV are each linearly related to E.
Therefoce, T = CH
and T = CV~T ~
- ; 15 where CH and Cv are constants, ~E~ is the difference between the values of the horizontal com?onent of E at points P2 and Pl and ~EV is the - difference between the values of the vertical component of E at points P2 and Pl. The values of - 20 CH and Cv can be calculated from measured values of E and R. Thus, if ~T is known and ~EH or ~EV is measured, the value of T can be calculated. For example, the signal EH'', which represents the horizontal component of E, is sampled at predetermined intervals (10 ms, say) and two consecutive sample values of EH'' are subtracted to return a value for ~EH. Since the sampling interval (which is equal to ~T) is known, and CH
has been calculated, the value of T c~n then be calculated. Separate values of T may be calculated based on the horizontal and vertical field components respectively, to provide verification.
The necessary calculation can be carried out using a general purpose digital computer, or a simple analog computer could be designed to solve the equation for T, given the values of T and ~.
From the graphs, such as that shown in FIG. 3, it is apparent that a component electric field signal value may be compared with a reference value which is known and correlates a given component electric field signal with a range value. From the graph shown in FIG. 3, it is also apparent that the relative strength of the horizontal and vertical component curves approach one another as the aircraft A approaches the power line P. Thus, by comparing the ratio of the vertical to the horizontal electric field signals with a reference value, a range value can be determined.
From the graphs, it is apparent that the vertical component of the electric field is larger than the horizontal component until the moving ~ vehicle reaches a certain distance from the line during approach. At distances closer than lO0 meters or so, the slope of the vertical component curve begins to change, as does the slope of the horizontal curve at a slightly closer distance to the power line. Due to these changing slopes, the calculations ~et forth above predict that the horizontal and vertical components of the electric field intersect at a range of approximately 50 meters. By detecting the cross-over point, a discrete warning can be given to the aircraft pilot that the power line is very close and that he should take steps to avoid impact with the power line.
The existence of the curve cross-over phenomenon was confirmed by experiments conducted on electric fields emitted from a power transmission line and detected by a hand-held l6 sensor. Readings were taken while moving the sensor along a ridge of land extending away from the power transmission line. The detector was a simple high input impedance ampli~ier having an output to a digital voltmeter. The sensor was a dipole antenna, which was held in horizontal and vertical orientations to detect the respective horizontal and vertical components of the electric field at various distances from the power transmission line. This experimental data is shown in FIG. 4, with the cross over of the horizontal and vertical components occurring at a range of approximately 90 meters from the power line. The vertical scale on the graph of FIG. 4 is in volts, as read from the digital voltmeter.
Depending upon the particular application, the sensor means 22 comprising the antenna means and - the signal conditioning means 60 may be physically concentrated within one area of the aircraft or dispersed in several locations throughout the aircraft. For example, the signal conditioning means 60 may be physically located within the aircraft adjacent the signal processing means 24.
Alternatively, the signal conditioning means 60 may be located near the antenna 32.
Although the expression for T has been derived on the assumption that the aircraft heading is directly towards the power line, the aircraft heading is not relevant to the time-to-impact calculation since the time-to-impact is dependent only on the range R and the component of the aircraft's ground velocity that is perpendicular to the path of the power line. However, the heading relative to the direction of the power line is important to a pilot determining in which direction ^,f ' ~
to make a course correction. (In this specifica-tion, the term "direction of a power line," means the direction of the shortest line from the aircraft to the power line.) The direction of the power line relative to the aircraft heading may be determined by use of sensors 30 and 34. Sensors 30 and 34 are mounted at the left and right respec-tively of the aircraft.
In order to aid in understanding the operation of the system includin~ sensors 30, 34, reference is made to FIG. 7A, which shows two hollow, rectan-gular metal shells 120 and 122. Shells 120 and 122 are identical. The end faces of the shells are parallel and the shells are attached together by a plate 124 of electrically insulating material, such as the synthetic plastic material sold under the trademark DELRIN. The four side faces of shell 122 are coplanar with respective faces of shell 120.
Referring to the coordinate axes shown in FIG. 7A, the X, Y and Z dimensions of each shell are about 12.5 cm, 5 cm and 18 cm respectively, and the shells are spaced apart in the X direction by about 6.4 cm. An ammeter 126 is connected to the two shells. Although the ammeter is shown outside the shells, this is purely for ease of illustration.
In fact, the ammeter is inside one of the shells, so that it is shielded from external fields, and its display is observed through a small hole in a face of that shell. The apparatus shown in FIG. 7A
is similar to apparatus currently used for detecting electric field in the vicinity of an electric power line.
The apparatus shown in FI~. 7A was supported above the ground in the vicinity of a three-phase, high voltage electric power line. The apparatus s~
was suppo~ted at a heigh~ of about 4 m above the ground, in order to minimize g~ound ~lane efSects.
The shells were disposed with the XZ plane horizontal and the power line extendin~ parallel ~o the ~ axis and spaced from the shells along the X
axis by a distance o~ abc-lt 50-100 m. The ammeter, which is o~ very low impedance, pr~vides the only path fo~ cur~ent to flow between the two shells and the cha~ges on th~ two shells are redis~ributed throuqh the amme~er. The ammeter provided a measurable current readLng. The appa~atus was then rocsted th~oug~ 180 deqrees about a vertical axis, so that the posi~ions o~ ~he shells relative to th~
p~wer line ~ere reversed, b~ the two shells stayed in ~he same positions relative to each other. The ammeter reading was found not to be significantly diee~ent from the previous am~eter reading.
A si~ilar expeciment to that described with ref e~enc:e ~o F~. 7A ~as conduc_ed using the apparatus sho~n in FIG. 7B. The apparatus showrl in F~G. 7B i~ the same as that shown in ~IG. 7~, except that the Z dimension o~ one o the shel~c is ahout 36 cm instead of about la cm. I~ was found that when the smalle~ shell was closer to the power line, tbe ~mmeter r~ading ~a3 a~ou~ twice th~t when the la~ge~ shell was close~ to the powee line, Refer~in~ again to FIG. 1, each of the sensors 3a and 34 is a rectan~ular shell.
Sensors 30 and 34 are mounted to opposite res~ec-tive sides o~ the central pl3ne of the aircraf t ,i.e., the plane th~ough the central axis of the airc~t and a~out ~hich the aircraft is subs~an-tially symmetrical, with the YZ plane (FIG. 7A) parallel to the central plane of the ai~craft.
Sensors 3~, 34 are mour,ted by use of insulating 19 ~ ~ c~ ~ '3 ' ~., '' >~
material and a~e electrically connected to the metal aircrat body through raspecti~e ammeters 128, 130 ~IG. 8). The metal ~ircraft body then unction3 as ~ larg~ shell ~elative to the smaller shells of sensors 30, 34.
Based on the results of the experiments desc~ ibed with ~e~erence ~o FIG~. 7A ar.d ~B, the current between sensor 30 ar~d the aircraft body will be larger than the current between sensor 34 and the airc~a~t body i~ the direc~ion o~ the power line is t~ the le~t o~ ~che ai~cra~t, and vice ve~sa when the di ~ect ion of the powe~ line i s to the right of the ai~c~a~t, Ammeters 128, 130 generate ~oltage signals proportional ~o the respec~ive current ~lues, these signals are applied to a comparator 132 and the result of the compae i50n iS
used to indic~te the direction ~ the power l~ne~
ReEer~ing again to the arrangement described wi~h reference ~o FIG5. 1 and 5, FIG, 6 illust~ ates ~0 ha!dwa~e 70 used to process ~he cor~ditioned antenna signals. ~he conditi,oned antenna sign~l outputs Erom fllter 64 o the senso~ means 22 are supplied as the conditioned analog E f ie ld sensoc inputs to an analcg-to-digital converter 72. ~he voltage signal~ ~epsesentative of the cur~ents measured by ammeters 128, 130 a~e applied to analog-to-disital con~rerte~ 7 2 instead of to compara~or 132. Conver-ter 72 con~rerts its input signals into digital signals which ~re supplied to a cen~ral bus 14.
~he signal p~ocessing means 24 includes a central processo~ unit ~CPUl 80, men~ory n~eans 82, data input device sl~ch as a touch pad 84, and visual output device such as a CR~r moni~or 86. Each oi~ the ~ignal proces-ing means components 8û, 82, 84 and 86 communic:ates with the cent~al bus ?4.
__.
\
The central pcocessor unit 80 includes inter-acting bus control means 88, arithmetic means such as an arithmetic unit 90, flags 92, a stack pointer 94, a program counter 96, and storage registers 98.
The memory means includes various memory units, such as random access memory (RAM), read-only memory (ROM), and electrically erasable and programmable read-only memory (EEPROM). The visual output device 86 and the data input device 84, such as a keyboard, may be of the type typically used with personal computers.
The output means 26 in communication with central bus 74 include an audible warninq device 100 and a visual line location indicator 102, which communicates with central bus 74 through a digital-to-analog (D/A) converter 104. The audible warning device 100, which may include a speech synthesizer, provides an output to a loudspeaker or other elec-troacoustic transducer 106 to alert the pilot of an upcoming power line. The visual line indicator 102 provides an output to the pilot which indica~es the direction of an upcoming power line relative to the aircraft heading. The visual line indicator may take on any form, such as three lights or light-emitting diodes (LEDs) 108. For example, for a power line detected to the left of aircraft A, light 108a turns on to indicate this, while lights 108b and 108c, indicating the respective front and right side directions, remain off (see FIG. 6).
The visual output device 86 provides a legible readout of the result of the time-~o-impact calcu-lation.
It will be appreciated that there is a danger of a spurious indication of time-to-impact being given if the altitude of the aircraft is consi-derably greater than the height of the power line.
This possibility may be guarded against by providing additional sensors, similar to sensors 30 and 34, on the top and bottom of the aircraft body:
if the current between the aircraft body and the sensor on top of the aircraft body is substantially greater than that between the aircraft body and the sensor on the bottom of the aircraft body, it implies that the aircraft's altitude is such that it will not impact the power line. If the currents are substantially the same, the pilot should gain altitude.
It will be appreciated that it is not necessary to know the aircraft's ground speed in order to calculate the time-to-impact. This is a considerable advantage, because it is often diffi-cult to obtain an accurate measure of ground speed.
Slight variations in ground speed, for example due to gusts of wind, do not affect the accuracy of the calculation of the time-to-impact, because the samples of the electric field signal are taken at intervals that are much shorter than any short-term fluctuations in ground speed, and in any event the current value of the ground speed is implicitly used in calculating time-to-impact.
FIG. 9 illustrates an aircraft having a bubble 140 of insulating material projecting beneath the aircraft body, which is typically metal. Inside the bubble 140 is apparatus 142 for detecting the direction of a power line. This apparatus is simi-lar to the apparatus described with reference to FIG. 7B, and comprises two different-sized metal shells 144, 146 connected to an ammeter 148 and - mounted on an insulating plate 150 so that the only current path between the shells is through the ammeter. The shells are supported so that they can be rotated continually relative to the aircraft about an axis perpendicular to the open ends of the shells without changing the orien~ation of the shells relative to each other. This is accom-plished by use of a motor 152 connected to plate 150 through a shaft 154. The shaft is provided with an angle encoder 156 which indicates the angu-lar position of the shells relative to the central axis of the aircraft. Both the ammeter and the angle encoder are connected to a computer 160.
When the aircraft is in the vicinity of a power line, and is at a height such that the horizontal component of the electric field from the power line induces charge on the shells, the current flowing through the ammeter will vary with a frequency equal to the rotational frequency of shaft 154.
The computer detects the positive and negative peaks of the periodic variation in the current and relates it to the azimuth signal provided by the angle encoder. The computer then provides an output signal indicating the direction of the power line relative to the central axis of the aircraft so as to enable the pilot to change the heading of the aircraft in a manner that will avoid impact with the power line.
FIG. 10 illustrates in plan view another form of apparatus for detecting the direction of a power line.
The apparatus shown in FIG. 10 comprises a pair of identical sensors 180, 182 mounted at oppo-site respective wing tips of an aircraft. In a typical light aircraft, the antennas are about 7-10 m apart. Each sensor is composed of a metal shell similar to shell 144 and is mounted on the aircraft 23 2 ~ ~, wing, if it is made of metal, in electrically insu-lating ~ashion and in an orientation such that the X axis is parallel to the central axis of the aircraft. Respective ammeters are connected between the sensors and the respective aircraft wings, to measure the redistribution of charge between each sensor and the aircraft body, in simi-lar fashion to that described with reference to FIG. 8. If the aircraft heading is directly towards the power line, the currents measured by the two ammeters will be equal, whereas if the aircraft is not heading directly towards the power line, the current measured by the ammeter connected to the sensor that is closer to the power line will be larger than the current measured by the other ammeter~ The values of the currents measured by the respective ammeters are compared in order to provide an indication as to the direction of the power line relative to the aircraft heading, i.e., whether the power line is straight ahead of the aircraft, to the left or to the right.
It will be appreciated that the present invention is not restricted to the embodiments that have been shown and described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof. For example, although the invention has been described with reference to voltage signals, current signals may also be used. Further, the invention is not applicable only to fixed wing aircraft but may be used with helicopters also. The fact that it is not necessary to measure ground speed is particularly important in the case of a helicopter, since a helicopter may have a very low air speed 24 ~ ; ' f .' J
and a gust of wind might then have a large ef~ect on the helicopter's ground speed. The cross-over phenomenon described with reference to FIGS. 3 and 4 is a use~ul safety measure for use with a helicopter, because a helicopter traveling at low speed towards a power line might have a long time to impact, yet still be dangerously close to the power line. The embodiment described with reference to FIG. 9 may be applied to a helicopter by mounting the sensors on the rotor tips.
.
Claims (24)
1. A detector for use on board an aircraft (A) traveling along a path of movement to detect an electric power line (P), comprising:
antenna means (32) for sensing the electric field associated with the power line and producing an electric field signal, and signal processing means (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the aircraft to reach the power line if it continues on its path of movement.
antenna means (32) for sensing the electric field associated with the power line and producing an electric field signal, and signal processing means (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the aircraft to reach the power line if it continues on its path of movement.
2. A detector according to claim 1, wherein the antenna means comprise a first antenna for sensing the horizontal component of the electric field and producing a horizontal component electric field signal and a second antenna for sensing the vertical component of the electric field and producing a vertical component electric field signal.
3. A detector according to claim 2, wherein the signal processing means receive both the horizontal component electric field signal and the vertical component electric field signal and generate respective time-to-impact signals therefrom.
4. A detector according to claim 1, wherein the signal processing means sample the electric field signal and generate the time to impact signal based on the difference between successive samples of the electric field signal.
5. A detector according to claim 1, for use on board an aircraft having first and second opposite sides and including conductive material between the first and second sides, further comprising a first conductive element (30, 180) at the first side of the aircraft, a second conductive element (34, 182) at the second side of the aircraft, and means (128, 130) for measuring current between said conductive material and the first and second conductive elements respectively and generating a signal representing the direction of the power line from the aircraft.
6. A detector according to claim 1, wherein the signal processing means generate the time-to-impact signal by evaluating the equation:
where T represents time to impact, .DELTA.E represents change in the electric field signal over an interval T, and C is a constant.
where T represents time to impact, .DELTA.E represents change in the electric field signal over an interval T, and C is a constant.
7. A method for determining the direction of an electric power line relative to an aircraft's heading, comprising the steps of:
(a) positioning two dissimilar conductive elements (144, 146) in capacitively coupled relationship with the power line and in a first orientation relative to the aircraft heading, (b) observing the difference in charge induced on the two conductive elements in the first orientation, (c) positioning the conductive elements in a second orientation relative to the aircraft heading without changing their positions relative to each other, (d) observing the difference in charge induced on the two conductive elements in the second orientation, and (e) comparing the difference observed in step (b) with the difference observed in step (d).
(a) positioning two dissimilar conductive elements (144, 146) in capacitively coupled relationship with the power line and in a first orientation relative to the aircraft heading, (b) observing the difference in charge induced on the two conductive elements in the first orientation, (c) positioning the conductive elements in a second orientation relative to the aircraft heading without changing their positions relative to each other, (d) observing the difference in charge induced on the two conductive elements in the second orientation, and (e) comparing the difference observed in step (b) with the difference observed in step (d).
8. A detector for use on board an aircraft (A) for detecting the direction of an electric power line (P), comprising:
two dissimilar conductive elements (144, 146), means (150, 152, 154) for mounting the conductive elements aboard the aircraft so that the orientation of the conductive elements relative to the aircraft can be changed without changing the positions of the conductive elements relative to each other, and means (148) for observing the difference in charge induced on the conductive elements in at least two different orientations relative to the aircraft.
two dissimilar conductive elements (144, 146), means (150, 152, 154) for mounting the conductive elements aboard the aircraft so that the orientation of the conductive elements relative to the aircraft can be changed without changing the positions of the conductive elements relative to each other, and means (148) for observing the difference in charge induced on the conductive elements in at least two different orientations relative to the aircraft.
9. A method for determining the direction of an electric power line relative to the heading of an aircraft having a metal body, comprising the steps of:
(a) positioning first and second conductive elements (30, 34; 180, 182) at opposite respective sides of the central plane of the aircraft, (b) observing the difference between the charge induced on the aircraft body and the charge induced on the first conductive element, (c) observing the difference between the charge induced on the aircraft body and the charge induced on the second conductive element, and (d) comparing the difference observed in step (b) with the difference observed in step (c).
(a) positioning first and second conductive elements (30, 34; 180, 182) at opposite respective sides of the central plane of the aircraft, (b) observing the difference between the charge induced on the aircraft body and the charge induced on the first conductive element, (c) observing the difference between the charge induced on the aircraft body and the charge induced on the second conductive element, and (d) comparing the difference observed in step (b) with the difference observed in step (c).
10. Apparatus for determining the direction of an electric power line relative to the heading of an aircraft having a metal body, comprising:
first and second conductive elements (30, 34; 180, 182) mounted on the aircraft at opposite respective sides of the the central plane of the aircraft, means (128) for sensing the difference between the charge induced on the aircraft body and the charge induced on the first conductive element, means (130) for sensing the difference between the charge induced on the aircraft body and the charge induced on the second conductive element, and means (132) for comparing the difference between the charge induced on the first conductive element and the charge induced on the aircraft body with the difference between the charge induced on the second conductive element and the charge induced on the aircraft body.
first and second conductive elements (30, 34; 180, 182) mounted on the aircraft at opposite respective sides of the the central plane of the aircraft, means (128) for sensing the difference between the charge induced on the aircraft body and the charge induced on the first conductive element, means (130) for sensing the difference between the charge induced on the aircraft body and the charge induced on the second conductive element, and means (132) for comparing the difference between the charge induced on the first conductive element and the charge induced on the aircraft body with the difference between the charge induced on the second conductive element and the charge induced on the aircraft body.
11. A detector for use on board a vehicle traveling relative to the earth along a path of movement to detect an object that is stationary relative to the earth and has an electric field associated therewith, comprising:
sensor means (32) including antenna means for sensing the electric field and producing an electric field signal, and signal processing means (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the vehicle to reach the object if it continues on its path of movement.
sensor means (32) including antenna means for sensing the electric field and producing an electric field signal, and signal processing means (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the vehicle to reach the object if it continues on its path of movement.
12. A detector according to claim 11, wherein the antenna means comprise a first antenna far sensing the horizontal component of the electric field and producing a horizontal component electric field signal and a second antenna for sensing the vertical component of the electric field and producing a vertical component electric field signal, and wherein the signal processing means receive both the horizontal component electric field signal and the vertical component electric field signal and generate respective time-to-impact signals therefrom.
13. A detector according to claim 11, wherein the signal processing means sample the electric field signal and generate the time to impact signal based on the difference between successive samples of the electric field signal.
14. A detector according to claim 11, wherein the signal processing means generate the time-to-impact signal by evaluating the equation:
where T represents time to impact, .DELTA.E represents change in the electric field signal over an interval .DELTA.T, and C is a constant.
where T represents time to impact, .DELTA.E represents change in the electric field signal over an interval .DELTA.T, and C is a constant.
15. A detector according to claim 11, wherein the antenna means comprise a first antenna for sensing the horizontal component of the electric field and producing a horizontal component electric field signal and a second antenna for sensing the vertical component of the electric field and producing a vertical component electric field signal, and wherein the signal processing means receive both the horizontal component electric field signal and the vertical component electric field signal, compare the horizontal component electric field signal with the vertical component electric field signal, and provide a warning signal when the vertical component electric field signal is equal to or greater than the horizontal component electric field signal.
16. A detector according to claim 11, wherein the signal processing means sample the electric field signal at predetermined intervals and generate the time-to-impact signal based on the difference between successive samples of the electric field signal and the duration of the predetermined interval.
17. A detector for use on board a vehicle traveling along a path of movement to detect an object having an electric field associated therewith, comprising:
sensor means (32) including antenna means for sensing the electric field and producing an electric field signal, and signal processing means (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the vehicle to reach the object if it continues on its path of movement, the signal processing means generating the time-to-impact signal by evaluating the equation:
where T represents time to impact, .DELTA.E represents change in the electric field signal over an interval .DELTA.T, and C is a constant.
sensor means (32) including antenna means for sensing the electric field and producing an electric field signal, and signal processing means (24) for receiving the electric field signal and generating a time-to-impact signal representative of the time for the vehicle to reach the object if it continues on its path of movement, the signal processing means generating the time-to-impact signal by evaluating the equation:
where T represents time to impact, .DELTA.E represents change in the electric field signal over an interval .DELTA.T, and C is a constant.
18. A detector according to claim 17, wherein the antenna means comprise a first antenna for sensing the horizontal component of the electric field and producing a horizontal component electric field signal and a second antenna for sensing the vertical component of the electric field and producing a vertical component electric field signal, and wherein the signal processing means receive both the horizontal component electric field signal and the vertical component electric field signal, compare the horizontal component electric field signal with the vertical component electric field signal, and provide a warning signal when the vertical component electric field signal is equal to or greater than the horizontal component electric field signal.
19. A detector for use on board an aircraft traveling along a path of movement to detect a power line having an electric field associated therewith, comprising:
sensor means (32) including antenna means for sensing the instantaneous electric field and producing an instantaneous electric field signal, and signal processing means (24) for receiving the instantaneous electric field signal and generating a time-to-impact signal representative of the time for the aircraft to reach the power line if it continues on its path of movement.
sensor means (32) including antenna means for sensing the instantaneous electric field and producing an instantaneous electric field signal, and signal processing means (24) for receiving the instantaneous electric field signal and generating a time-to-impact signal representative of the time for the aircraft to reach the power line if it continues on its path of movement.
20. A detector according to claim 19, wherein the antenna means comprise a first antenna for sensing the horizontal component of the electric field and producing a horizontal component electric field signal and a second antenna for sensing the vertical component of the electric field and producing a vertical component electric field signal, and wherein the signal processing means receive both the horizontal component electric field signal and the vertical component electric field signal and generate respective time-to-impact signals therefrom.
21. A detector according to claim 19, wherein the signal processing means sample the instantaneous electric field signal and generate the time-to-impact signal based on the difference between successive samples of the electric field signal.
22. A detector according to claim 19, wherein the signal processing means generate the time-to-impact signal by evaluating the equation:
where T represents time to impact, .DELTA.E represents change in the instantaneous electric field signal over an interval .DELTA.T, and C is constant.
where T represents time to impact, .DELTA.E represents change in the instantaneous electric field signal over an interval .DELTA.T, and C is constant.
23. A detector according to claim 19, wherein the antenna means comprise a first antenna for sensing the horizontal component of the electric field and producing a horizontal component electric field signal and a second antenna for sensing the vertical component of the electric field and producing a vertical component electric field signal, and wherein the signal processing means receive both the horizontal component electric field signal and the vertical component electric field signal, compare the horizontal component electric field signal with the vertical component electric field signal, and provide a warning signal when the vertical component electric field signal is equal to or greater than the horizontal component electric field signal.
24. A detector according to claim 19, wherein the signal processing means sample the instantaneous electric field signal at predetermined intervals and generate the time-to-impact signal based on the difference between successive samples of the instantaneous electric field signal and the duration of the predetermined interval.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US373,805 | 1982-04-30 | ||
| US37380589A | 1989-06-28 | 1989-06-28 | |
| US47854790A | 1990-02-12 | 1990-02-12 | |
| US478,547 | 1990-02-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2032165A1 true CA2032165A1 (en) | 1990-12-29 |
Family
ID=27006315
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2032165 Abandoned CA2032165A1 (en) | 1989-06-28 | 1990-06-13 | Electric field detection system |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU6043990A (en) |
| CA (1) | CA2032165A1 (en) |
| WO (1) | WO1991000525A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2676824B1 (en) * | 1991-05-23 | 1993-09-24 | Asept Applic Securite Positive | DETECTOR FOR PROXIMITY OF AERIAL ELECTRIC LINES. |
| GB2343956B (en) * | 1998-09-18 | 2003-09-03 | Safe Flight Instrument | In-flight aid for detecting power lines |
| US7248054B2 (en) * | 2004-12-23 | 2007-07-24 | Power Survey Company | Apparatus and method for detecting an electric field |
| DK2016371T3 (en) * | 2005-10-19 | 2020-09-14 | Osmose Utilities Services Inc | DEVICE AND METHOD FOR MONITORING AND CONTROLLING THE DETECTION OF VAGA BONDING VOLTAGE ANOMALS |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2454630A (en) * | 1945-01-08 | 1948-11-23 | United Air Lines Inc | Method and apparatus for indicating potential gradients |
| US2969539A (en) * | 1958-03-28 | 1961-01-24 | Bosch Arma Corp | Proximity warning and collision avoidance system |
| US4199715A (en) * | 1974-11-15 | 1980-04-22 | The Johns Hopkins University | Method and apparatus for defining an equipotential line or _surface in the earth's atmosphere and measuring the misalignment of a _selected line or plane relative to an equipotential line or surface |
| US4013955A (en) * | 1975-07-02 | 1977-03-22 | The United States Of America As Represented By The Secretary Of The Navy | Analog signal processor |
-
1990
- 1990-06-13 AU AU60439/90A patent/AU6043990A/en not_active Abandoned
- 1990-06-13 WO PCT/US1990/003374 patent/WO1991000525A1/en active Application Filing
- 1990-06-13 CA CA 2032165 patent/CA2032165A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| AU6043990A (en) | 1991-01-17 |
| WO1991000525A1 (en) | 1991-01-10 |
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