Velleman CS102 - Manual (Page 4)

CS102
19/04/2010 © 2008 Velleman Components nv 4
metal detector G extension shaft
A arm rest H cable
B control shaft with handle I spring-loaded button
C control box J locking nut
D battery compartment K lower shaft
E target indicator L nut
F 5-pin input jack M search coil
control box + indicator
1 DISC/TONE discrimination control: to eliminate (notch) undesired metals
Note: this setting influences the sensitivity
2 GND BAL ground balance control: to eliminate background signals caused by
mineralized soils
3 VOL volume button: set speaker or headphone volume to normal or low
4 TRACE trace button: to keep the detector in tune
5 PHONE headphone jack: to connect an external headphone (not incl.)
6 SENS sensitivity control: to control the depth of detection
7 THRESHOLD threshold control: adjust the level of the received signal
8 LOW BAT low battery indication: lights up when voltage drops below 8.8V
9 DISC - TONE 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
10 analogue meter needle indicates signal intensity (ALL METAL mode) or metal type (DISC
mode)
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 Electrical
conductivity (S/m)
Material Electrical
conductivity (S/m)
silver 63.01 × 10 6 nickel 14.3 × 10 6
copper 59.6 × 10 6 iron 9.93 × 10 6
gold 45.2 × 10 6 platinum 9.66 × 10 6
aluminium 37.8 × 10 6 tin 9.17 × 10 6
calcium 29.8 × 10 6 sea water 4.788
zinc 16.6 × 10 6 drinking water 0.0005 ~ 0.05