Schonstedt Instrument GA-52B User manual

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ModelGA-528
MagneticLocator
MANUFACTURED BY
Schonstedt Instrument Company
1775 Wiehle Avenue
Reston, Virginia 2ZO}O
(703) 471_1050
TWX: 710-833-9880
FAX: [phone]
Printed May 1989

PREFACE
The Model GA-528 Magnetic Locator is a product of thirtylive years of
experience in producing the woild's finestflux-gate magnetometers and mag-
netic detecfors for aerospace, military and civilian applications. The GA-528
incorporates the knowledge gleaned f rom manufacturing under the most rigid
qual ity control sfandards.
The heart of the GA-528 is ifs patented Schonstedt HeliFluxa magnetic
field sensors. Ihese sensors, acknowledged to be the world's finest, make
possib/e the unequalled performance of the locator.
TABLE OF CONTENTS
OPERATION
lntroduction
TurnOn, Volume and Sensitivity Settings
Low Sensitivity
High Sensitivity
Search
APPLICATION NOTES
Basic Search Patterns
Strongly Magnetized Marke rs
Manholes, Septic Tanks, Wel ls
Barbed Wire, Water, Snow
Along Fences
Valve Boxes
Cast lron Pipes
Other Notes
MAINTENANCE
Replacement of Batteries
Trouble Shooting Guide
Service Information
SPECIFICATIONS
GA-528 REPAIR PARTS
WARRANTY/SH I PPI NG I N FORMATION
1-3
1
2
2
3
3
4-10
4
F
6
7
8
I
U
10
10-12
10
12
12
12
13
14

Operation
INTRODUCTION
The Model GA-528 Magnetic Locator detects the magnetic field of a fer-
romagnetic object. lt responds to the difference in magnetic field between two
sensors spaced about 20 inches apart. The response consists of a change in
the frequency of a signal that is emitted by a loudspeaker.
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 mag-
netic field of the iron marker is stronger at sensor A than it is at sensor B. As a
result, the f requency of the signal on the loudspeaker is higher than the idling
frequency,40Hz, which exists when the field is the same at both sensors.
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Magnetic field of an iron marker.

Operation (cont.)
TURN-ON, VOLUME AND SENSITIVITY SETTINGS
SENSITIVITY
Contro ls ( N ormal Settings)
LOW SENSITIVITY
Turn on the Model GA-528
and adjust the volume level by ro-
tating the ON-OFF/VOLUME con-
trol in a clockwise direction untll
the idling tone reaches the level
desired. Position the SENSITIVITY
(range) control as shown in the
figure. With the knob in this posi-
tion, the sensitivity is set for what
is referred to as NORMAL RANGE.
The locator can be oriented in any
direction without producing a sig-
nif icant change in frequency of the
tone from its idling rate.
When headphones are used,
no variation in sound volume is
provided by turning the VOLUME
Control.
Unwanted background signals
due to nearby magnetic objects
may require that the range of the
locator be reduced. To reduce the
range, turn the sensitivity knob in a
counterclockwise direction. Re-
duced range is useful in pinpointing
the location of a strongly magnetized
marker.
Setting for Low Sensitivity
INCREASE
DECREASE
OFF POSITION
ON-OFF/VOLUME
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Operation (cont.)
HIGH SENSITIVITY The sensitivity of the locator
is increased by turn ing the sensitivity
knob in a clockwise direction. A
h igh sensitivity setting imposes
some constraint on operating meth-
ods. The locator tone will vary in
frequency depending on the instru-
ment's orientation in the earth's
magnetic f ield.
Control Setting for High Sensitivity
SEARCH
Set the sensitivity control for normal operation and grasp the locator
just below the large end as illustrated. Because the upper sensor is located
near where the locator is usually held, wrist watches may produce unwant-
ed tone frequency changes. To avoid such problems either remove the
wrist watch or use the other hand. Also, avoid bringing the locator close
to your shoes, since they might contain magnetic material.
To obtain maximum area coverage, the locator should be swept from
side to side with the smallend of the instrument kept close to the ground.
A higher frequency tone will be heard from the loudspeaker when the
locator is within range of an iron marker.
When searching using extend-
ed range, avoid turning the locator
about its long axis as this may pro-
duce signal variations arising from
misalignment of the sensors.
The presence of a ferromag-
netic object will be indicated by a
change in tone frequency.
Searching With the Locator

Application Notes
BASIC SEARCH PATTERNS
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VERTICALLY
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TARGET GREATEST
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SIGNAL FOR A
HORIZONTALLY
ORIENTED TABGET
GREAIEST OVER ENDS
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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
t t'X" pattern. The peak signal occurs
.\r directly over a vertical target, and over
the ends of a horizontal tarqet.
Using the "X" pattern allows
precise location of small objects. A
1-114" P-K nail marker can be located
at depths from 4" to 8". lt can be un-
covered by using a 112" 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 dis-
appears is probably not the one you are looking for. The signal from a
rusty bolt or other small item willdrop much faster with distance than the
signal from a larger target such as a corner marker. An 1B-inch length of
3/4 inch pipe can be located up to 7 feet.
SIGNAL ABOVE GROUND
SIGNAL AT GROUND
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Application Notes (cont.)
STRONG LY MAGNET IZED MAR KERS
Strongly magnetized markers at or near the surface may give mis-
leading information as to the location of the markers. The magnetic field
of such a marker is illustrated below.
The heavy line in the f igure represents the variation in tone f requency
obtained when passing the locator over the marker. In moving the instru-
ment from A to B, the tone frequency increases and then suddenly de-
creases at B. From just beyond B the tone frequency increases 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 obvious
that the locator must enter the B-C region. Otherwise the marker miqht
be assumed to be between A and B or C and D.
The phenomenon is explained by the fact that the locator is sensi-
tive 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.
SIGNAL PATTERN
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The magnetic f ield is strong-
est at the edges of a shallow
manhole cover. Turn the sensi-
tivity down all the way and you
can easily trace the edges of
covers near the surface. Locating
depth ranges up to B feet.
Application Notes (cont.)
MANHOLES, SEPTIC TANKS, WELLS
The locator can be used to precisely locate the metal handles or re-
inforcing bars on septic tank covers buried up to 4 feet.
The great length of a well
casing provides a strong f ield at
the surface that permits easy
locating of casings buried up to
1 5 feet.
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Application Notes (cont.)
BARBED-WI RE, WATER, SNOW
You may use the locator in
f looded areas - just keep the elec-
tron ic un it out of the water.
Snow poses no problem
just thrust the locator into the
snow as deeply as necessary to lo-
cate the target.
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Examine trees for bench
marks and embedded barbed rnrire
of old fence lines. Hold the locator
parallel with the direction of the
wire.
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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 de-
tected near the surface. Tip the
locator a little lower than usual -
but not parallel with the ground.
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