Schonstedt Instrument GA.22 User manual

INSTRUCTION MANUAL
FOR
MODEL GA.22
MAGNETIC LOCATOR
SCHONSTEDT
INSTRUMENT
COMPANY

M"giibtic
Locator
MODEL GA-22
SCHONSTEDT INSTRUMENT COMPANY
1775 WIEHLE AVENUE, RESTON, VIRGINIA 22090
Telephone [phone]

PREFACE
The Model GA-22 Magnetic Locator is a product of over twenty
years of experience in producing the world's finest flux-gate magneto-
meters and magnetic detectors for aerospace, military and civilian
applications. The GA-22 incorporates the knowledge gleaned from
manufacturing under the most rigid quality control standards.
The heart of the GA-22 is i'ts patented Schonstedt HeliFtux@
magnetic field sensors. These sensors, acknowledged to be the world's
finest, make possible the unequalted performance of the locator.
TABLE OF CONTENTS
OPERATION
I ntroducrron
Turn-On and Range Setting
Search
Low Range
Extended Range
APPLICATION 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
SPECIF ICATIONS
WARRANTY
1-3
1
1
2
J
3
4-9
4
b
7
8
9
10-1 1
10
't1
12
13
14

OPERATION
INTRODUCTION
The Model GA-22 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 amplitude (volume) of a tone signal in the head-
phones.
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 illustra-
tion, the magnetic field of the iron marker is stronger at sensor A than
it is at sensor B. As a result, a 1000 Hz tone signal appears in the head-
phones. The tone increases in intensity as the locator is moved closer
to the marker.
Magnetic field of an iron marker.
TURN.ON AND RANGE SETTING
Connect the headphones to the jack 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 instrument for what is refer-
red to as NORMAL range, the
locator can be oriented in any
direction without producing any
significant tone signal. In cold
weather it may be necessary to turn
the knob slightly counterclockwise
beyond the dot to achieve normal
range. The converse may be
required for operation during hot
weather. Other range settings are
discussed in later paragraphs.
Control setting
for normal range.
SEARCH
Grasp the locator just below the large end as illustrated below.
Because the upper sensor is located near where the locator is usually
held, wrist watches may produce unwanted tone signals. 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 tone will appear in the headphones when the locator
is within range of an iron marker.
Searching with the locator.
oo

OPERATION (cont.l
LOW RANGE
Unwanted background signals
due to nearby magnetic objects
may require that the range of the
locator be reduced. To reduce the
range, turn the knob in the clock-
wise direction from the reference
dot. Reduced range is useful in
pinpointing the location of a
strongly magnetized marker.
Control setting for low range.
EXTENDED RANGE
The range of the locator can
be increased by turning the range
control knob counterclockwise
from the reference dot. The added
range imposes some constraint on
operating methods. The locator
will produce a tone which varies in
amplitude depending on the instru-
ment's orientation in the earth's
magnetic f ield. Control setting
for extended range
When searching using extended range, keep the locator in a f ixed
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, either an
increase or decrease.
@06
o0'6

n
L# SIGNAL FOR A
| | VERTCALLY
ll oRTENTED
I I TARGET GREATESI
II+ OVERTOP
ll
ll /-\
U/
SIGNAL FOR A
HOR IZONTA L LY
ORIENTED TARGET
GREATEST OVER ENDS
APPLICATION NOTES
BASIC SEARCH PATTERNS
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 taroet.
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 /r" 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
f rom a rusty bolt or other sma ll ite m will drop much f aster with distance
than the signal from a larger target such as a corner marker.
SIGNAL ABOVE GROUND
SIGNAL AT GROUND
E
e$
SMALL BOLT CORNER MARKER

APPLICATION NOTES (cont.l
STRONG LY MAGNETIZED MAR KE RS
Strongly magnetized markers at or near the surface may give
misleading information as to the location of the markers. The mao-
netic f ield of such a marker is illustrated below.
The heavy line in the figure represents the variation in tone ampli-
tude when passing the locator over the marker. In moving the instru-
ment from A to B, the tone increases and then suddenly decreases at
B. From just beyond B the tone 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 might be assumed to
be between A and B or C and D.
The phenomenon is explained by the fact that the locator 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 tone is
produced at these points.

APPLICATION NOTES (cont.l
MANHOLES, SEPTIC TANKS, WELLS, PIPES
The magnetic field is strongest
at the edges of manhole covers.
Under a resurfaced road, the man-
hole covers produce a very strong
f ield. Turn the sensitivity down all
the way, and you can easily trace
the edges of the cover.
The great length of a well casing
provides a strong f ield at the su rface
that permits easy location.
lron water and gas lines near n
the surface can be traced in some lf
cases. Greater signals are obtained ll
at the ioints, ends and bends in the ll
pipe ll
3'""'^T U
The locator can be used to precisely locate the
metal handles or reinforcing bars on septic tank covers.

APPLICATION NOTES (cont.l
BARBED-WI R E, WATER, SNOW
Examine trees for bench marks
and embedded barbed wire of old
f ence I ines. Ho ld the locator para l-
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 - lust
thrust the locator into the snow as
deeply as necessary to locate the
ta rget.
7

APPLICATION NOTES (cont.l
ALONG FENCES
Search in the vicinity of an iron-wire fence requires not only
reduced range but also some control over the orientation of the loca-
tor' Position the locator substantially horizontal with its long axis
approximately perpendicular to the fence. This orientation assures
that the upper sensor is kept away from the fence.
Search by moving the locator along the fence, keeping the end
a constant distance from the fence. When a point 1-5/g,, from the end
of the locator is directly over the stake, the signal will drop abruptly
as shown below. Any variation in position will produce an abrupt rise
in the intensity of the tone.
SIGNAL NULL WITH
LOCATOR AS SHOWN

1
t.
2.
3.
4.
APPLICATION NOTES (cont.l
VALVE BOXES
Both the valve and its casing,
when iron, provide strong magnetic
fields which make them easy to
locate. Plastic enclosures con-
taining magnets are easily located
at depths of 3 feet or more.
OTHER NOTES
Operation under power lines may introduce a garbling of the tone
signal. The garbling generally does not significantly affect the
detection capabilities of the instrument.
The GA-22 is ideal for locating water meters and utility shut-off
va tves.
The locator is useful in many instances for detecting the presence
of reinforcing bars in concrete.
The instrument will not detect nonmagnetic materials such as
gold, silver. copper. brass, aluminum, snow. water, ice, etc.

MAINTENANCE
REPLACEMENT OF BATTER IES
The GA-22 is designed and built to give trouble free operation.
Normally, maintenance is limited to occasional replacement of the
batteries. In the event that your locator does malfunction. we ask that
you refer to the troubleshooting guide on the next page. This lists a
few possible problems that can generally be corrected in the field so
that you will be able to continue using the locator without interruption.
The GA-22 is powered by four C-cell batteries carried in clios
illustrated in the exploded view of the electronic assembly below.
Access to the batteries is obtained by removing the nut at the end of
the electronic unit followed by the case. The battery keeper is removed
by sliding towards the end.
The four batteries are connected in series. The proper polarities
for the batteries are shown on the clip assemblies. Occasionally oppo-
site contacls must be pressed toward each other to insure sufficient
pressure bdtween the contacts and the batteries.
laru:n'([Phb,l3*)
L33;i"'
Exploded view of the electronic unit case
Headset Plugged ln
CONTACT
SOLDER LUGS BENT --====fu,
O--_ilililTi-"
t=!€#HrIr
>?
Headset Out
10

MAINTENANCE (cont.l
GA-22 TROUBLE SHOOTING GUIDE
Symptom Possible Cause How to Check How to Fix
Dead Dead Batteries
Headset
Batteries Not Making
Good Contact
Power Switch Not
Making Good Con-
Replace
Try replacement (one
half of a stereo set
will work)
Inspect visually, try
increasing pressure
of terminals by hand.
With electronics cover
removed and headset
plugged in unit will
operate if you press
contacts closed by
hand.
Replace
Replace with cor-
rect monaurat set.
Bend battery holder
so batteries will fit
tight. lf corroded,
clean terminals with
sa nopaper.
Bend power switch
blade so that firm
contact is made with
headset plug inserted.
8e sure contacts open
when headset plug is
removed. See f igure
on opposite page.
Inter mittent H eadset
Batteries Not Making
Good Contact
Power Switch Not
Making Good Con-
Range Control
Try replacement (one
half of a stereo set
will work)
I nspect visual ly, try
increasing pressure
of terminals by hand.
With electronics cover
removed and headset
plugged in unit will
operate if you press
contacts closed by
hand.
Tone will sound noisy
or will change abrupt-
ly when range control
is adjusted.
Replace with correct
monaural set.
Bend battery holder
so batteries will f it
tight. lf corroded,
clean terminals with
sanopaper.
Bend power switch
blade so that firm
contact as mad€. with
headset plug inserted.
8e su/,e contacts open
when headset plug is
removed. See f igure
on opposite page.
Replace range control
potentiometer.
Short Battery
Life
Power Switch Con-
tacts Remain Closed
Battery Case Ter-
minals Shorted to
Battery Case
Inspect to be sure con-
tacts open when head-
phone plug is removed
Inspect visually
Bend power switch
blade so contacts open
when headset plug is
removed. Contacts
must close when plug
is inserted. See figure
on oppostte page.
Bend battery terminal
lugs away from bat-
tery case, See figure
on opposite page.
11

SiEVEFIALWAYS
Tcl USE THE SiTFIAP
WITHTHE MLC-1
MAGiNETIC LclCATc'FT CASE
WEAR ACROSS
T}IE GHEST
LIKE THIS
TO OPEN CASE
TURN WINGNUTS COUNTER.
CLOCKWISE 18OO PLACE THUMB
IN HOLE AND PRESS.
TO LOCK CASE
CLOSE CASE AND TUBN WING.
NUTS CLOCKWISE UNTIL YOU
HEAR LOCK SNAP INTO POSI.
TION.
SHIPPING
IF CASE IS TO BE USED AS SHIPPING
CONTAINER CLEAN AREA WHERE
SHIPPING LABEL IS TO BE ATTACHED
WITH ISOPROPYL (RUBBING) ALCO-
HOL.
clFl
WEAR
AGROSS
THE CHEST
LIKE THIS
oFl
SHORTEN STRAP
BY FORMING A SECOND
IOOP AT EAGH END
AND
WEAR
ACROSS
THE SHOUTDER
IIKE THIS

SPECIFICATIONS
(Specifications subiect to change without notice.)
lnput Power: Supplied by four C-cell batteries (1% Veach).
Battery Life: 50 hours of intermittent operation.
Output: Approximately 1000 Hz tone in headphones.
Amplitude increases with gradient field in-
tensity.
Power Switch: Power is turned on when the headphone jack
is plugged in.
Weight: Approximately 3 pounds including head-
ohones.
Operating Temperature: 0o to 1f:OoF.
Length: 42 inches.
Waterproof Length: 34% inches.
Nominal Sensor
-Spacing: 20 inches.
Construction: Rugged, all solid state.
PATENTS
Manufacture licensed under the following Patents: United States: 2,916,696;
2,981,885; 3,894,283; 3,909,7O4; 3,961 ,245 and 3,977,Q72. Canada: 637,963;
673,375 and 1,006,915. British: 1,446,741 and 1,446,742. France: 2,205,671.
Other United States and foreign patents pending.
13

STANDARD WARRANTY
The Schonstedt Instrument Company warrants each instrument
of its manufacture to be free from defects in material and workman-
ship. our liability under this warranty is limited to servicing or adjust-
ing any instrument returned to the factory for this purpose and to
replace any defective part thereof. Electron tubes, batteries, lamps
and fuses are specifically excluded under this warranrv.
This warranty is effective for one year after delivery to the orig-
inal purchaser. As a condition of the warranty, the instrument must
be returned by the original purchaser. transportation charges prepaid,
and prove to our satisfaction to be defective. lf fault has been caused
by misuse or abnormal conditions of operation, repairs will be billed
at cost. Prior to repair in this instance, a cost estimate will be sub-
mitted.
Service or shipping information will be furnished upon notification
of the diff iculty encountered. Model and serial number must be supplied.
14

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s-242-7837