How It Works - Velleman ED21102 Notice D'emploi

metal detector
A arm rest
B control shaft with handle
C control box
D battery compartment
E target indicator
F 5-pin input jack
control box + indicator
1 DISC/TONE
2 GND BAL
3 VOL
4 TRACE
5 PHONE
6 SENS
7 THRESHOLD
8 LOW BAT
9 DISC - TONE
10 analogue meter

6. How it works

• A (low frequency) metal detector basically consists of a transmitter, a receiver and a
microprocessor (control box) which handles the signals.
Transmitter
• The transmitter is a coil of wire located inside the search coil. By sending an alternating current
through this coil a magnetic field is generated, having a polarity pointing either into or out of the
ground. This magnetic field will induce a flow of current inside nearby metallic objects. These
objects in turn will create a magnetic field with a polarity which is usually opposite to that of the
magnetic field of the transmitter.
Receiver
• The receiver is another coil of wire that is located inside the search coil and which is constructed
in such a way that the magnetic field of the transmitting coil does not induce current in it.
Magnetic fields from nearby metallic objects however will produce an electric current in the
receiver coil.
Phase shift
• The signal received from the receiving coil will usually be delayed versus the transmitted signal
due to the tendency of conductors to impede changes in the flow of current, the so called
inductance. The delay is referred to as phase shift. Metal objects that are primarily inductive
e.g. large thick objects made of good conductors (gold, silver, copper...) will result in large phase
shifts, whereas metal objects that are primarily resistive e.g. smaller thin objects made of less
conductive materials will result only in minor phase shifts. Refer to the table below for a short
overview of the electrical conductivity of some materials.
Material
silver
copper
gold
aluminium
calcium
zinc
23/03/2009
discrimination control: to eliminate (notch) undesired metals
Note: this setting influences the sensitivity
ground balance control: to eliminate background signals caused by
mineralized soils
volume button: set speaker or headphone volume to normal or low
trace button: to keep the detector in tune
headphone jack: to connect an external headphone (not incl.)
sensitivity control: to control the depth of detection
threshold control: adjust the level of the received signal
low battery indication: lights up when voltage drops below 8.8V
discrimination mode selector: in DISC mode, type of metal is indicated by
tone length; in TONE mode it is indicated using high or low tones
needle indicates signal intensity (ALL METAL mode) or metal type (DISC
mode)
Electrical
conductivity (S/m)
63.01 × 10
59.6 × 10
45.2 × 10
37.8 × 10
29.8 × 10
16.6 × 10
CS102
G extension shaft
H cable
I spring-loaded button
J locking nut
K lower shaft
L nut
M search coil
Material
6
nickel
6
iron
6
platinum
6
tin
6
sea water
6
drinking water
4
Electrical
conductivity (S/m)
6
14.3 × 10
6
9.93 × 10
6
9.66 × 10
6
9.17 × 10
4.788
0.0005 ~ 0.05
© 2008 Velleman Components nv