Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Reexamination Certificate
1998-08-19
2002-06-18
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
Reexamination Certificate
active
06407550
ABSTRACT:
CROSS REFERENCE TO MICROFICHE APPENDIX
Appendix A, which is a part of the present disclosure, is a microfiche appendix consisting of 5 sheets of microfiche having 400 frames. Microfiche appendix A includes a software program operable in a microprocessor controller of a left/right line locator as described below.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
This and other embodiments are further described below.
BACKGROUND
1. Field of the Invention
The invention relates to a line locator for locating concealed conductors and, more specifically, to line locators having the capability of determining the lateral location of the line locator relative to the concealed conductor.
2. Background
It is often necessary to locate buried conduits, which are employed by numerous utility companies, in order to repair or replace them. In addition, it is important to locate conduit lines in order not to disturb them when excavating for other purposes (such as, for example, addition of new conduits). Examples of buried conduits include pipelines for water, gas or sewage and cables for telephone, power or television. Many of the conduits are conductors, such as metallic pipelines or cables. In other applications, it is often useful to locate concealed elongated conductors, such as power lines or copper water lines, concealed in the walls of buildings. It is well known to locate concealed elongated conductors (“lines”) by detecting electromagnetic emissions from them.
A conducting conduit (a line) may be induced to radiate electromagnetically by being directly connected to an external transmitter or by being inductively coupled to an external transmitter. In some instances, such as with power lines, the line may radiate without an external transmitter.
A line locator detects the electromagnetic radiation emanating from the line. Early line locators included a single sensor that detects a maximum signal or a minimum signal, depending on the orientation of the sensor, when the line locator is passed over the line. Later line locators have included two sensors to provide information regarding proximity to the line.
FIG. 1
shows a line
4
, beneath surface
7
, that is radiating a magnetic field
5
. Magnetic field
5
is generally directed in a circular fashion around line
4
. Line locator
1
is held by operator
6
over line
4
. Line locator
1
includes sensor
3
that detects magnetic field
5
and displays a signal on a display
2
that is indicative of the magnetic field strength at sensor
3
. Depending on the orientation of sensor
3
(i.e., whether it is sensitive to horizontal or vertical components of the magnetic field), display
2
will indicate a maximum signal or a minimum signal when line locator
1
is held directly above line
4
(where the magnetic field
5
is directed horizontally).
For purposes of this description, a horizontal magnetic field refers to a magnetic field directed parallel with surface
7
, even if surface
7
happens to be a wall. A vertical magnetic field refers to a magnetic field that is directed perpendicular to surface
7
. Similarly, a horizontally oriented sensor is arranged to detect horizontal components of the magnetic field while a vertically oriented sensor is arranged to detect vertical components of the magnetic field.
FIG. 2A
shows a line locator
200
having a left sensor
201
, a right sensor
202
, and a center sensor
203
, each of the sensors being vertically oriented. Left sensor
201
and right sensor
202
are positioned at equal elevation above surface
7
and have substantially identical responses to magnetic fields. Center sensor
203
is disposed equidistant from left sensor
201
and right sensor
202
and can have an elevation above surface
7
that is different from the elevation of left sensor
201
and right sensor
202
. Center sensor
203
is a compensating field sensor that is used to correct for ambient magnetic fields (i.e., magnetic fields that do not originate from line
4
) in the vicinity of left sensor
201
and right sensor
202
. As indicated by the dots drawn adjacent each sensor, center sensor
203
is arranged such that, given the same magnetic field, the output signals from center sensor
203
will have the opposite polarity of the output signals from left sensor
201
and right sensor
202
.
In general, a transmitter
205
is electrically coupled to line
4
so that line
4
will radiate with a frequency determined by transmitter
205
. Line locator
200
is capable of detecting whether line
4
is to the left or the right of center sensor
203
by comparing the magnetic field
5
at left sensor
201
with the magnetic field
5
at right sensor
202
. U.S. Pat. No. 4,639,674, entitled “Apparatus and Method Employing Extraneous Field Compensation for Locating Current-Carrying Objects,” issued Jan. 27, 1987, to Rippingale, describes such a line locator.
FIG. 2B
shows detection circuitry for line locator
200
of FIG.
2
A. The output signal from center sensor
203
is added to each of the output signals from left sensor
201
and right sensor
202
such that a correction is made for ambient magnetic fields not associated with line
4
(see FIG.
2
A). The corrected output signal from left sensor
201
is processed through a channel comprising, in series, a pre-amplifier
204
, a mixer
205
, an IF filter/amplifier
207
, and a phase detector
210
. The corrected output signal from right sensor
202
is processed through a substantially identical channel.
In each channel, mixer
205
combines the output signals from pre-amplifier
204
with a LO FREQ signal from local oscillator
206
. The LO FREQ signal is the frequency of transmitter
205
(see
FIG. 2A
) plus a center frequency. IF Filter
207
is a band pass filter and amplifier that passes signals at the center frequency. The combination of mixer
205
and IF filter
207
provides some filtering of the signal being processed through each channel. The gain of IF filter
207
is set by set-point
208
.
The phase reference for phase detectors
210
is determined from the channel containing left sensor
201
by phase-lock-loop
209
. The output signals from the two channels are summed, after being independently processed, in adder
211
. The output signal from adder
211
is the left/right signal. The polarity of the left/right signal indicates whether center sensor
203
is laterally displaced to the left or right of line
4
.
This method of line detection, however, is subject to phase instability. Because of the difficulty inherent in insuring that the output signals from left sensor
201
and right sensor
202
remain comparable over the full range of input signal strength, as is required by this method of signal processing, little signal filtering can be accomplished in the two channels. Additionally, because the phase reference is determined using the output signal from left sensor
201
, line locator
200
is incapable of left/right location if left sensor
201
and right sensor
202
are both displaced to one side of line
4
where the output signals from both sensors have the same polarity.
Other line locators, such as U.S. Pat. No. 5,001,430 to Peterman et al., having a left/right detection capability include a left sensor, a right sensor and a central sensor where the left sensor and the right sensor have an orientation of between 0° and 90° from the horizontal, but specifically not 0° or 90°. In addition, because the left sensor and the right sensor detect magnetic fields having the same polarities (i.e., primarily the horizontal component of the magnetic field), the output signal used in the circuitry is a difference signal between the magnetic field measured at the left sensor and the magnetic field measured at the right sensor. As
Parakulam Gopalakrishnan R.
Polak Stevan
Edwards Gary J.
Metrotech Corporation
Patidar Jay
Skjerven Morrill & MacPherson LLP
LandOfFree
Line locator with accurate horizontal displacement detection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Line locator with accurate horizontal displacement detection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Line locator with accurate horizontal displacement detection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2973772