how metal detectors find CAVITY

[okantex]

some detector producers claims their detectors finds cavity and light the led which is on control panel.
how can a detector do this
can anybody explain this to me
thanks

[Carl-NC]

Most soil has some amount of mineralization, i.e., ferrous particles. Mineralized soil produces a "ground signal" in detectors, which is why many of them have a ground balance control. When the detector goes over a void, there is less mineralization, and the ground signal is reduced. Detectors can be tuned to signal this decrease.

[okantex]

Hi CArl
in delta pulse there are pots called.

sens noise trshold gain signal

is noise the pot used to tune the ground balance

and if it beeps because of cavity .how can we differ it from metal

[Carl-NC]

I haven't kept up with the Delta Pulse, so I don't know. But in most cases, PI detectors don't see ground mineralization as well as VLF, so PI is not a good choice for a cavity detector.

[okantex]

the dedector at this links claims to differ
gold ,metals and cavity.
http://www.noktadedektor.com/ing/index.asp
but does not give tecnical information.
and claims it can detect up to 8 meters without any problem because of it's tank circuit.
what do you think about this unit.
is it vlf.

[okantex]

talking about model 106 P.S

[okantex]

here you can see search coil
http://www.noktadedektor.com/yenireklam.asp?id=0

it looks like there is only one winding.but 5 wire pin in cable socket.
but at coil 3:1 pr 3:2 coil ratio can not be seen.
may be DD coil.

[okantex]

and it has only one coil.
it 's diameter is likely 50cm .
claims 8 meters dept with this coil?

[Carl-NC]

the dedector at this links claims to differ
gold ,metals and cavity.
http://www.noktadedektor.com/ing/index.asp
but does not give tecnical information.
and claims it can detect up to 8 meters without any problem because of it's tank circuit.
what do you think about this unit.
is it vlf.

I have no idea...

[Qiaozhi]

What's this XA-1 detector that they're showing on their website?

[okantex]

have not you seen something like that before?
it a long range locator.
you must have seen four rod system.this is energized four rods.
http://www.sismikelektronik.com/trm44omnitron.asp
you can see another version here
http://www.sismikelektronik.com/urunler.asp

[okantex]

I have a question
vlf and bfo detectors are effected from minerals
PI do not .
who can consider bfo and PI for me.
both have one coil winding .think that we we wind them in same sizes and turns.
what will happen.why you say PI s do not effected.

[Qiaozhi]

have not you seen something like that before?
it a long range locator.
you must have seen four rod system.this is energized four rods.
http://www.sismikelektronik.com/trm44omnitron.asp
you can see another version here
http://www.sismikelektronik.com/urunler.asp

So these are just rubbish claims then? :confused:

[Qiaozhi]

I have a question
vlf and bfo detectors are effected from minerals
PI do not .
who can consider bfo and PI for me.
both have one coil winding .think that we we wind them in same sizes and turns.
what will happen.why you say PI s do not effected.

BFO and PI detectors work on different principles. The BFO looks for a change in inductance by monitoring the frequency of the oscillator, and is therefore more sensitive to ground minerals. The PI looks for a change in the decay time of the transmitted pulse. In this case the ground matrix is not good at supporting eddy currents, so effectively the ground is ignored.

[okantex]

so we can say if a company insist on finding cavity,it can not penetrate deep like PI.
can we say if soil mineral is low even this machines can not find cavity?