Bosch GMS 120 Professional User manual

Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
All instructions must be read and observed. The safeguards in-
tegrated into the measuring tool may be compromised if the
measuring tool is not used in accordance with these instructions.
STORE THESE INSTRUCTIONS IN A SAFE PLACE.
English
Safety Instructions

Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
u Have the measuring tool serviced only by a qualified specialist using only ori-
ginal replacement parts. This will ensure that the safety of the measuring tool is
maintained.
u Do not use the measuring tool in explosive atmospheres which contain flam-
mable liquids, gases or dust. Sparks may be produced inside the measuring tool,
which can ignite dust or fumes.
u The measuring tool may not be 100 % accurate for technological reasons. To
eliminate hazards, familiarise yourself with further sources of information, such
as building plans and photographs taken during construction, etc. before carry-
ing out any drilling, sawing or routing work on walls, ceilings or floors. The accur-
acy of the measuring tool may be affected by environmental influences, such the level
of humidity or there being other electronic devices nearby. The structure and condi-
tion of the walls (e.g. damp, building materials containing metal, electrically conduct-
ive wallpaper, insulating materials, tiles) and the number, type, size and position of
the objects may distort the measuring results.
u Make sure that you are properly earthed when taking measurements. If you are
not properly earthed (e.g. by wearing insulating footwear or by standing on a ladder),
it will not be possible to locate live cables.
u If there are gas pipes in the building, check to ensure that none of them have
been damaged after completing any work on walls, ceilings or floors.
u Live wires can be detected more easily when power consumers (e.g. lamps, appli-
ances) are connected to the wire being sought and switched on. Switch off power
consumers and make sure that live cables are de-energised before drilling, saw-
ing or milling into walls, ceilings or floors. After performing any kind of work,
check to ensure that objects placed on the base material are not live.
u When attaching objects to dry walls, and in particular when attaching them to
the substructure, check to ensure that both the wall and the fastening materials
have a sufficient load-bearing capacity.
Product Description and Specifications
Please observe the illustrations at the beginning of this operating manual.
Intended Use
The measuring tool is intended for the detection of metal (ferrous and non-ferrous
metals, e.g. reinforcing steel), wooden beams and live wires in walls, ceilings and floors.
The measuring tool is suitable for indoor and outdoor use.

Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
Product features
The numbering of the product features shown refers to the illustration of the measuring
tool on the graphic page.
(1) Light-up ring
(2) Marking hole
(3) Display
(4) Operating mode indicator
(5) On/off button
(6) Display illumination button
(7) Audio signal button
(8) Gripping surface
(9) Power cable operating mode button
(10) Metal operating mode button
(11) Drywall operating mode button
(12) Contact pads
(13) Sensor area
(14) Serial number
(15) Battery compartment cover
(16) Battery compartment cover locking mechanism
(17) Carrying strap lug
(18) Carrying strap
(19) Protective bag
Display elements (see figure A)
(a) Audio signal indicator
(b) Warning indicator
(c) Non-metallic object indicator
(d) Non-magnetic metal indicator
(e) Magnetic metal indicator
(f) Live wire indicator
(g) Temperature monitoring indicator
(h) Battery indicator

Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
Digital Detector GMS 120
(i) Measuring indicator
(j) Fine scale
(k) Object centre indicator CENTER
Technical data
Article number 3 601 K81 0..
Max. detection depth
A)
– Ferrous metals
120 mm
– Non-ferrous metals (copper)
80 mm
–Live wires 110−230 V (with voltage applied)
B)
50 mm
–Wood
38 mm
Operating temperature
–10 °C to +50 °C
Storage temperature
–20 °C to +70 °C
Inductive sensor
– Operating frequency range
5 ± 0.2 kHz
– Max. magnetic field strength (at 10 m)
72 dBµA/m
Capacitive sensor
– Operating frequency range
20 ± 1 kHz
– Max. electric field strength (at 10 m)
24 dBµV/m
Max. altitude
2000 m
Relative air humidity max.
90 %
Pollution degree according to IEC 61010-1
2C)
Battery
1 × 9 V 6LR61
Approx. operating time
5 h
Weight according to EPTA-Procedure 01:2014
0.27 kg

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Protection rating IP 54 (dust and splash-proof)
A) Depends on operating mode, material and size of the objects, as well as material and condition
of the base material
B) Lower detection depth with non-live wires
C) Only non-conductive deposits occur, whereby occasional temporary conductivity caused by
condensation is expected.
The serial number (14) on the type plate is used to clearly identify your measuring tool.
u The accuracy and detection depth of the measuring result may be negatively af-
fected if the condition of the substrate is unfavorable.
Assembly
Inserting/Changing the Battery
It is recommended that you use alkaline manganese batteries to operate the measuring
tool.
To open the battery compartment cover (15) , push the locking mechanism (16) in the
direction of the arrow and lift the battery compartment cover. Insert the battery.
When inserting the batteries, ensure that the polarity is correct according to the illustra-
tion on the inside of the battery compartment.
u Take the battery out of the measuring tool if you do not intend to use the tool for
a long time. When it is stored in the measuring tool for longer periods, the battery can
corrode and discharge itself.
Battery indicator
The battery indicator (h) on the display always indicates the current battery status:
Display
Capacity
60−100 %
30−60 %
5−30 %
0−5 %
Operation
u Protect the measuring tool from moisture and direct sunlight.
Digital Detector GMS 120

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Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
u Do not expose the measuring tool to any extreme temperatures or variations in
temperature. In case of large variations in temperature, leave the measuring tool
to adjust to the ambient temperature before switching it on. The accuracy of the
measuring tool and the functionality of the display may be compromised if exposed to
extreme temperatures or variations in temperature.
u Avoid hard knocks to the measuring tool or dropping it. After severe external influ-
ences and in the event of abnormalities in the functionality, you should have the
measuring tool checked by an authorised Bosch after-sales service agent.
u Certain ambient conditions fundamentally impair the measuring results. These
include, e.g. the proximity of devices that generate strong electric, magnetic or
electromagnetic fields, moisture, metal building materials, foil-laminated insula-
tion materials or conductive wallpaper or tiles. Therefore, also refer to other in-
formation sources (e.g. construction plans) before drilling, sawing or routing into
walls, ceilings or floors.
u Hold the measuring tool by the intended gripping surface (8) only, so as not to
influence the measurement.
u Do not attach any stickers or labels to the sensor area (13) on the rear of the
measuring tool. Metal labels in particular will affect measuring results.
Do not wear gloves when taking measurements and make sure that you
are properly earthed. If you are not properly earthed, the identification of live
wires may be impaired.
When taking measurements, avoid devices that emit strong electric, mag-
netic or electromagnetic fields. If possible, deactivate all tools whose radi-
ation could interfere with the measurement and switch off the corresponding
functions or tools.
Starting Operation
Switching on/off
u Before switching on the measuring tool, ensure that the sensor area (13) is dry.
If necessary, use a cloth to dry the measuring tool.
u If the measuring tool has been exposed to a significant change in temperature,
leave it to adjust to the ambient temperature before switching it on.
To switch on the measuring tool, press the on/off button (5) .
To switch off the measuring tool, press the on/off button (5) again.
If no button on the measuring tool is pressed for approx. 5 mins, and no objects are de-
tected, the measuring tool will automatically switch itself off to preserve battery life.

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Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
Switching the display illumination on and off
The display illumination can be switched on or off with the display illumination
button (6).
Switching audio signal on/off
The audio signal can be switched on/off with the audio signal button (7) . When the audio
signal is switched off, the audio signal indicator (a) appears on the display.
How it works (see figure B)
The measuring tool checks the base material of the sensor area (13) in the measurement
direction A up to the maximum detection depth. Objects that are different from the ma-
terial of the wall are detected.
Move the measuring tool in a straight line in direction B over the wall.
Always move the measuring tool over the base material applying light pressure, without
lifting it off or changing the pressure.
During the measurement, the contact pads (12) must always remain in contact with the
surface.
Measuring process
Place the measuring tool on the surface to be examined and move it in direction B .
– When the measuring tool approaches an object, the amplitude in the measuring
indicator (i) increases and the light-up ring (1) lights up yellow.
– The amplitude decreases when the measuring tool moves away from the object.
– Above the centre of an object, the measuring indicator will indicate maximum amp-
litude; the light-up ring (1) will light up red and an audio signal will sound.
For small or deep-lying objects, the light-up ring (1) can continue to light up yellow
without the audio signal sounding.
u Wide objects are not indicated by the light-up ring or the audio signal throughout
their complete width.
In order to locate an object more precisely, move the measuring tool repeatedly (3×)
back and forth over the object. The fine scale (j) is activated automatically in all operat-
ing modes. The fine scale indicates a full amplitude when the object is below the centre
of the sensor or when the maximum amplitude of the measuring indicator (i) is reached.
In Drywall and Metal operating modes, the object centre indicator CENTER (k) also lights
up.
Wider objects in the base material can be identified by a continuous high amplitude of
the measuring indicator (i) and fine scale (j) . The light-up ring (1) will light up yellow.
The duration of the high amplitude corresponds approximately with the object width.

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Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
If very small or deep-lying objects are being sought and the measuring indicator (i) reacts
only slightly, move the measuring tool repeatedly over the object in a horizontal and ver-
tical direction. Pay attention to the amplitude of the fine scale (j) and, when in Drywall
and Metal operating modes, to the object centre indicator CENTER (k) as well, which will
then allow for precise detection.
u Before drilling, sawing or routing into walls, refer to other sources of informa-
tion to ensure that you eliminate hazards. As the measuring results can be influ-
enced through ambient conditions or the nature of the wall, there may be a hazard
even though the measuring indicator (i) does not indicate an object in the sensor
area, no audio signal sounds and the light-up ring (1) lights up green.
Operating Modes
You can achieve the best possible measuring results by selecting the correct operating
mode. You can achieve the maximum detection depth for metal objects in the Metal op-
erating mode. You can achieve the maximum detection depth for live wires in the Power
cable operating mode.
The selected operating mode is always shown by the green operating mode
indicator (4).
Drywall operating mode
Drywall operating mode is designed for detecting wooden and metal objects in dry walls.
To activate Drywall operating mode, press the Drywall operating mode button (11) . The
operating mode indicator (4) above the Drywall operating mode button will light up
green.
As soon the measuring tool is positioned on the surface to be examined, the light-up
ring (1) will light up green, indicating readiness to measure.
In Drywall operating mode, all available objects will be detected and displayed:
(c) Non-metallic, e.g. wooden beams
(d) Non-magnetic, but metal, e.g. copper pipe
(e) Magnetic, e.g. reinforcing steel
(f) Live, e.g. power lines
Note: In the Drywall operating mode, other objects, e.g.water-filled plastic pipes, will be
also displayed in addition to wooden and metal objects and live wires. For these objects,
the Non-metallic object indicator (c) will appear in the display.
Nails and screws in the base material may result in wooden beams being identified as
metal objects.

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Bosch Power Tools
1 609 92A 7ZF | (21.06.2022)
If the display indicates a continuously high amplitude of the measuring indicator (i) and
the fine scale (j) , re-start the measuring process again by placing the measuring tool
elsewhere on the surface.
If the light-up ring (1) does not indicate readiness to measure when positioned on the
surface to be examined, the measuring tool has not been able to detect the base material
correctly.
– Press and hold the Drywall operating mode button (11) until the light-up ring (1)
lights up green. Take the measurement as normal.
If, after having completed this measurement, you want to start a new measuring pro-
cess on another wall, briefly press the Drywall operating mode button (11) in order to
reset the measuring tool.
– In rare cases, the measuring tool is not able to detect the base material because the
sensor area (13) on the rear side is dirty. Clean the measuring tool with a soft, dry
cloth and re-start the measuring process.
Metal operating mode
Metal operating mode is particularly suited to detecting magnetic and non-magnetic ob-
jects, regardless of the nature of the wall.
To activate Metal operating mode, press the Metal operating mode button (10) . The
light-up ring (1) and the operating mode indicator (4) above the Metal operating mode
button will light up green.
If the measuring tool passes over a metal object (the light-up ring (1) will light up red),
the type of metal will be shown in the display. For magnetic metals (e.g. iron) the Mag-
netic metal indicator (e) will appear, for non-magnetic metals (e.g. copper) the Non-
magnetic metal indicator (d) will appear.
Note: For reinforcement steel mesh and reinforcements in the examined based material,
an amplitude is indicated over the entire surface in the measuring indicator (i) . For rein-
forcement steel mesh, it is typical that the magnetic metal indicator (e) appears directly
above the iron rods, whereas the non-magnetic metal indicator (d) will appear between
the iron rods.
Power cable operating mode
Power cable operating mode is only suitable for detecting live wires (110−230 V).
To activate Power cable operating mode, press the Power cable operating mode
button (9) . The light-up ring (1) and the operating mode indicator (4) above the Power
cable operating mode button will light up green.
When a live wire is detected, the indicator for live wires (f) will appear on the display.
Move the measuring tool over the surface again in order to locate the live wire more pre-
cisely. After moving the measuring tool over the surface multiple times, the live wire can

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1 609 92A 7ZF | (21.06.2022)
be detected very precisely. If the measuring tool is very close to the wire, the light-up
ring (1) will flash red and the audio signal will sound at a faster rate.
Notes:
– Live wires are detected in every operating mode.
– Live wires can be detected more easily when power consumers (e.g. lamps, appli-
ances) are connected to the wire being sought and switched on. Switch off electricity
consumers before drilling, sawing or milling into the wall.
– In certain conditions (such as behind metal surfaces or behind surfaces with high
water content), live wires cannot always be detected. The signal strength of a live
wire depends on the position of the cable. Therefore, take further measurements in
close proximity or use other information sources to check if a live wire is present.
– You can detect non-live wires as metal objects in the Metal operating mode. Solid-wire
cables are not detected (as opposed to stranded-wire cables).
– Static electricity can cause wires to be detected inaccurately (e.g. over a large area)
or prevent them from being detected at all. To improve the detection, place your free
hand flat on the wall next to the measuring tool, in order to remove the static electri-
city.
Working Advice
Marking objects
If required, detected objects can be marked. Perform a measurement as usual.
Once you have found the boundaries or the centre of an object, mark its position through
the marking hole (2).
Temperature monitoring
The measuring tool features temperature monitoring, as an exact measurement is only
possible as long as the temperature inside the measuring tool remains constant.
If the temperature monitoring indicator (g) lights up, the measuring tool is outside of the
operating temperature range, or has been subjected to large fluctuations in temperature.
Switch the measuring tool off and allow it to adjust to the ambient temperature
switching it back on.
Warning function
If the warning indicator (b) lights up on the display and the operating mode indicator (4)
above the Drywall operating mode button (11) flashes, you must re-start the measure-
ment. Remove the measuring tool from the wall and place it elsewhere on the surface.
If the warning indicator (b) flashes on the display, send the measuring tool in its protect-
ive bag (19) to an authorised Bosch after-sales service centre.