Schonstedt Instrument GA.32 User manual

INSTRUCTION MANUAL
FOR
MODEL GA.32
MAGNETIC LOCATOR
SCHONSTEDT
INSTRUMENT
COMPANY

HelrFlux'
Locator
MODEL GA.32
SCHONSTEDT INSTRUMENT COMPANY
1775 WIEHLE AVENUE, RESTON, VIRGINIA 22090
Telephone [phone]

PREFACE
The Model GA-32 Magnetic Locator is a product of over twenty
years of experience in producing the world's finest flux-gate magnet-
ometers and magnetic detectors for aerospace, military and civilian
applications. The GA-32 incorporates the knowledge gleaned from
manufacturing under the most rigid quality control standards.
The heart of the GA-32 is its patented Schonstedt HeliFlux@
magnetic field sensors. These sensors, acknowledged to be the world's
finest, make possible the unequalled performance of the locator-
TABLE OF CONTENTS
OPERATION
I ntroduction
Turn-On and Range Setting
Search
Low Range
Extended Range
APPLlCATION NOTES
Basic Search Patterns
Strongly Magnetized Markers
Manholes, Septic Tanks, Wells, Pipes
Barbed Wire, Water, Snow
Along Fences
Valve Boxes
MAINTENANCE
Replacement of Batteries
Trouble Shooting Guide
CASE AND STRAP
SPECIFICATIONS
WARRANTY
1-3
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OPERATION
INTRODUCTION
The Model GA-32 Magnetic Locator detects the magnetic field
of a ferromagnetic object. lt responds to the difference in magnetic
field between two sensors spaced about 20 inches apart. The response
consists of a change in frequency of a tone signal that is normally
present in the headphones.
The figure below illustrates an application of the locator in which it
is used to detect an iron marker for a property corner. In the illustration,
the magnetic field of the iron marker is stronger at sensor A than it is
at sensor B. As a result, the tone signal in the headphone has a higher
pitch than its normal idling frequency of approximately 65 pulses per
second.
Magnetic field of an iron marker.
TURN.ON AND RANGE SETTING
Connect the headphones to the iack on the underside of the
electronic unit. This turns the instrument on. Set the range control
knob on the underside of the electronic unit so the dot on the knob

OPERATION (cont.l
lines up with the dot on the case.
This position of the knob adjusts
the instru ment f or what is refer-
red to as NORMAL range, the
locator can be oriented in any
direction without producing a sig-
nificant change in frequency of
the tone signal from its idling rate.
In cold weather it may be neces-
sary to turn the knob slightly coun-
terclockwise bevond the dot to
achieve normal range. The converse
may be required for operation dur-
ing hot weather. Other range set-
tings are discussed in later para-
graphs.
Control setting
for normal range.
SEARCH
Grasp the locator just below the large end as illustrated be-
low. Because the upper sensor is located near where the locator
is usually held, wrist watches may produce unwanted tone frequency
changes. To avoid such problems either remove the wrist watch or
use the other hand. The earphones are magnetic so the locator should
not be operated closer than 24 inches from the headset.
To obtain maximum area coverage, the locator should be swept
from side to side with the small end of the instrument kept close to
the ground. A higher frequency tone will appear in the headphones
when the locator is within range of an iron marker.
ood
Searching with the locator.

OPERATION (cont.l
LOW RANGE
Unwanted backgrou nd signals due
to nearby magnetic objects may re-
quire that the range of the locator
be reduced. To reduce the range,
turn the knob in the clockwise direc-
tion from the reference dot. Reduced
range is useful in pinpointing the
location of a strongly magnetized
marker.
Control setting for low range.
o06'
EXTENDED RANGE
The range of the locator can be
increased by turning the range con-
trol knob counterclockwise from the
reference dot. The added range
imposes some constraint on oper-
ating methods. The locator tone
will vary in frequency depending
on the instrument's orientation in
the earth's magnetic f ield.
Control setting
for extended range
When searching using extended range, keep the locator in a fixed
orientation, preferably vertical and away from the headphones. Avoid
turning the locator about its long axis as this may produce signal vari-
ations arising from misalignment of the sensors. The presence of a
ferromagnetic object will be indicated by a change in tone frequency.
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APPLICATION NOTES
BASIC SEARCH PATTERNS
SIGNAL FOR A
VERTICALLY
ORIENTED
TARGET. GREATEST
OVER TOP
SIGNAL FOR A
HORIZONTALLY
OBIENTED TARGET,
GBEATEST OVER ENDS
After you have detected a signal,
you can precisely locate the target
to save digging over a wide area.
Simply hold the locator vertically
while moving it in an "X" pattern.
The peak signal occurs directly over
a vertical target, and over the ends
of a horizontal target.
Using the "X" pattern while
holding the locator vertically allows
precise location of small objects.
A P-K nail marker can be located so
it can be uncovered using a 1/2" star
drill.
A trick that helps if you find more than one signal, when you
should find only one, is to raise the locator a few inches. Any signal
that disappears is probably not the one you are looking for. The signal
from a rusty boltor other small item will drop much faster with distance
than the signal from a larger target such as a corner marker.
SIGNAL ABOVE GROUND
SIGNAL AT GROUND
CORNER MARKER

APPLICATION NOTES (cont.l
STRONG LY MAGNETIZED MAR KERS
Strongly magnetized markers at or near the surface may give
misleading information as to the location of the markers. The mag-
netic field of such a marker is illustrated below.
The heavy line in the figure represents the variation in tone fre-
quency obtained when passing the locator over the marker. In moving
the instrument from A to B, the tone frequency increases and then
suddenly decreases at B. From just beyond B the tone frequency in-
creases sharply, becomes very high over the marker and decreases just
before reaching C. From C to D, the pattern is the reverse of that
from A to B. lt is ovbious that the locator must enter the B-C region.
Otherwise the marker might be assumed to be between A and B or C
and D.
The phenomenon is explained by the fact that the loca-
tor is sensitive to the magnetic field components parallel to its
long axis. At points B and C, the field is perpendicular to the locator
so no high frequency is produced at these points.

APPLTCATION NOTES (cont.l
MANHOLES. SEPTIC TANKS, WELLS, PIPES
The magnetic field is strongest
at the edges of manhole @vers.
Under a resurfaced road, the man-
hole covers produce a very strong
field. Turn the sensitivity down all
the way, and you can easily trace
the edges of the cover.
The great length of a wellcasing
providesa strong field at the surface
that permits easy location.
The locator can be used to precisely locate the
metal handles or reinforcing bars on septic tank covers.
lron water and gas lines near
the surface can be traced in some
cases. Greater signals are obtained
at the joints, ends and bends in the
pipe.
--t
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APPLICATION NOTES (cont.l
BARBED-WI R E, WATE R, SNOW
Examine trees for bench marks
and embedded barbed wire of old
fence lines. Hold the locator paral-
lel with the direction of the wire.
You may use the locator in
flooded areas - just keep the elec-
tronic unit out of the water.
You can often trace barbed wire
(of old fence lines) beneath the
surface. Even if the wire is only a
trail of rust, it can be detected near
the surface. Tip the locator a little
lower than usual - but not parallel
with the ground.
Snow poses no problem - just
thrust the locator into the snow as
deeply as necessary to locate the
target.
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