Coil current vs size

[AK48]

hello, a question that bothers me after seeing a video where a guy had a test with the DEUS 2 he used the 22 cm disc and the 28 cm disc on the same targets and the targets were all found with the 22 cm but sounded worse with the 28 cm disc, my question is: if the detector is optimized for the standard 22 cm disc, does fitting a larger disc not require more current? because by changing the discs of the detector, the current supplied is the same and in my opinion, the more the disc connected to the detector grown, the more the detector should supply current to the disc n am I right?
thank you
regards
AK48

[Carl-NC]

Different size coils are usually matched for inductance which means their coil currents should be the same. This also means that the larger coil will have fewer turns so the "ampere-turns" will be lower than the small coil. This seems to suggest that a small coil will always be better because it has a stronger field but the field drops off quicker than for the large coil. This is why the small coil wins on smaller shallower targets but the large coil can win on larger deeper targets. In the video the targets were probably more suited to the small coil than the large.

[Carl-NC]

green has made a graph that illustrates this:

https://www.geotech1.com/forums/attachment.php?attachmentid=56840&d=1646527293

[AK48]

thanks for the explanation carl
regards

[Skippy]

It's worth pointing out that the graph of signal strengths shown above is for a PI mono-coil, so is not identical to that of a DD coil on a VLF ( like the Deus2 ) , particulary when the target is close to the coil. However, the basic physics effects are still the same.

But ... more importantly: You're forgetting the Deus2 has a great deal of the electronics inside the coil. Almost the entire machine, by some interpretations. Which means changing the coil size can come along with MANY other changes. Coil inductance does not have to be the same. Transmit voltage may well be identical. But receive gain ( analogue pre-amplifiers, and/or software sensitivity changes ) may be different. So comparing one coil with another has to be done cautiously.

( this also applies to machines like the Equinox. Not only is there a pre-amp inside the coil, which could have different gains for different coil sizes, but there's also an 'identifier' chip, which among other functions, will tell the control-box what size/shape the coil is. This info could then be used to tailor the machine's performance, such as by changing gain/sensitivity, recovery-speeds etc. All of which make comparing one coil to another difficult.)

[AK48]

you are right, pulse induction and VLF are two
differents technologies but the basic principle
is quite similar, on the other hand looking
more closely at the DEUS coil, we see that it
has a whole host of components embedded on coil
board and I wonder how is it that these
components are not detected? as for the nulling
of a head with two coils or by acting on the
discri to find an accuracy balance between the
detection of targets and the rejection of the
on-board electronics?
thank you
regards

[Carl-NC]

Skippy: those are really good points.

AK48: as long as the embedded PCB does not move it won't normally be detected and nulling can still be achieved. However, hot rocks can induce eddy currents even in static metal so it is possible for the PCB to cause problems.

[AK48]

right , as long as the embedded PCB does not move , it will be not detected but if the detector is a non motion ? and everyone know that no-motion detector don't need the target to move to be detecteable ?

[Skippy]

Non-motion modes look for target changes AFTER you select that mode, for example when you press Pinpoint button.
( when I say 'changes' I mean 'increases' , so if you press pinpoint, then raise your coil 1 metre, the drop in signal won't give an audio indication. )

[Carl-NC]

right , as long as the embedded PCB does not move , it will be not detected but if the detector is a non motion ? and everyone know that no-motion detector don't need the target to move to be detecteable ?

Even a non-motion detector will not detect a static target if that target has been tuned/nulled out. Tape a coin to the coil, then turn on the detector and tune it as normal. If you can get to a normal tuning threshold with the coin attached then you will not be able to detect the coin.

[AK48]

perfect , it's perfect tha's what i was expected , thank you and good night
regards