This article explains the general differences between the most common and popular type of metal detectors used in present days.
The article is based on scientific facts, but it is intentionally not written in academic manner, to enable as many metal detector
users as possible to understand some of the basic principals on which the functionality of all metal detectors are based.
So how can any common detector user make realistic assessment about the real capabilities of his/her metal detector vs all
others?
What are the most important factors defining which metal detector is best?
Firstly, BEST is a very relative term when talking about metal detectors. It is almost impossible to define which detector is really
the best, unless some criteria is set first and then the particular unit is judged according to that criteria.
TO ALL READERS. Please note that the term BEST in this article is related to the following criteria;
All information in this article is meant only for basic educational purpose and not to define which metal detectors trade mark or
unit offered on the market is best. That conclusion will be left for all readers of this article to decide for them selves after carefully
considering all information.
How does a metal detector work?
The most common of detectors used in present days are Induction Balance (IB) type. In the basic version their search head
consist of two loops (coils). One is for transmitting signals (TX) and the other is for receiving signals (RX).n
Another very popular metal detector type is the Pulse Induction (PI). This type of detector utilises in most designs search coil
consisting of only one loop used for both transmitting and receiving signals. There is some PI designs utilising search coils with
more than one loop.
This article does not comment on other basic topologies upon which metal detectors are build for a reason that the IB and PI
detectors are the most efficient and powerful commonly used metal detectors to date.
There is one most common believe that the receiving coils in the search head of all metal detectors are actually receiving signals
reflected by the metal targets buried under the ground. The pure scientific fact how ever is this:
IB Detectors
In IB detectors the two loops forming the search head are supposedly in perfect induction balance, meaning that the residual
signal (offset voltage) in the receiving coil is as close as possible to 0.
When a piece of metal comes across the electro-magnetic field transmitted by the TX loop some amount of Eddy currents will
occur in the moment of crossing the transmitted field. The Eddy currents in the metal piece will cause an electro- magnetic field to
form around the metal piece. That electro- magnetic field then will cause the TX and the RX loops to get out of balance within a
certain amount. Out of balance will mean that some amount of offset voltage signal will occur in the RX loop. This offset voltage
signal is not a signal reflected or returned by the metal piece, but a signal transmitted by the TX loop. The presence of a metal
piece in front of the search head will result in the new offset voltage signal in the RX exhibiting a bit different characteristics than
the original offset voltage signal remaining after the factory balance procedures on the search head. The difference of the new
offset signal to the original can be measured in both phase and amplitude.
Exactly on this changes of the phase and the amplitude of the residual offset voltage signal all IB metal detectors are reacting, not
on reflected or returned signals.
Another way of explaining this process is to say that the presence of any, external to the search head, metal targets will alter to
some degree the electro-magnetic properties of the TX and the RX loops, which will result in a different balance situation
between the TX and the RX loops.
The electronic circuits of all IB metal detectors are actually measuring this very change in the balance between the two loops in
the search head.
From this point of view it will be safe to state that the sensitivity of any IB metal detector will depend mostly on the electro-
magnetic properties of the search head loops. The most important of those properties is the Q, quality factor.
This article will not get any further in to the academic aspect of the Q ,but wish to tell that the Q is the main of all factors which
could influence the performance of any search head or single loop.
The Q is of equal importance when PI metal detectors are concerned.
The article is based on scientific facts, but it is intentionally not written in academic manner, to enable as many metal detector
users as possible to understand some of the basic principals on which the functionality of all metal detectors are based.
So how can any common detector user make realistic assessment about the real capabilities of his/her metal detector vs all
others?
What are the most important factors defining which metal detector is best?
Firstly, BEST is a very relative term when talking about metal detectors. It is almost impossible to define which detector is really
the best, unless some criteria is set first and then the particular unit is judged according to that criteria.
TO ALL READERS. Please note that the term BEST in this article is related to the following criteria;
- Depth penetration capabilities.
- Accuracy in discrimination analysis.
- Any other aspect regarding practical qualities of any metal detector will be set aside, considering that it is not covered by
any claim made by Nexus Metal Detectors.
All information in this article is meant only for basic educational purpose and not to define which metal detectors trade mark or
unit offered on the market is best. That conclusion will be left for all readers of this article to decide for them selves after carefully
considering all information.
How does a metal detector work?
The most common of detectors used in present days are Induction Balance (IB) type. In the basic version their search head
consist of two loops (coils). One is for transmitting signals (TX) and the other is for receiving signals (RX).n
Another very popular metal detector type is the Pulse Induction (PI). This type of detector utilises in most designs search coil
consisting of only one loop used for both transmitting and receiving signals. There is some PI designs utilising search coils with
more than one loop.
This article does not comment on other basic topologies upon which metal detectors are build for a reason that the IB and PI
detectors are the most efficient and powerful commonly used metal detectors to date.
There is one most common believe that the receiving coils in the search head of all metal detectors are actually receiving signals
reflected by the metal targets buried under the ground. The pure scientific fact how ever is this:
IB Detectors
In IB detectors the two loops forming the search head are supposedly in perfect induction balance, meaning that the residual
signal (offset voltage) in the receiving coil is as close as possible to 0.
When a piece of metal comes across the electro-magnetic field transmitted by the TX loop some amount of Eddy currents will
occur in the moment of crossing the transmitted field. The Eddy currents in the metal piece will cause an electro- magnetic field to
form around the metal piece. That electro- magnetic field then will cause the TX and the RX loops to get out of balance within a
certain amount. Out of balance will mean that some amount of offset voltage signal will occur in the RX loop. This offset voltage
signal is not a signal reflected or returned by the metal piece, but a signal transmitted by the TX loop. The presence of a metal
piece in front of the search head will result in the new offset voltage signal in the RX exhibiting a bit different characteristics than
the original offset voltage signal remaining after the factory balance procedures on the search head. The difference of the new
offset signal to the original can be measured in both phase and amplitude.
Exactly on this changes of the phase and the amplitude of the residual offset voltage signal all IB metal detectors are reacting, not
on reflected or returned signals.
Another way of explaining this process is to say that the presence of any, external to the search head, metal targets will alter to
some degree the electro-magnetic properties of the TX and the RX loops, which will result in a different balance situation
between the TX and the RX loops.
The electronic circuits of all IB metal detectors are actually measuring this very change in the balance between the two loops in
the search head.
From this point of view it will be safe to state that the sensitivity of any IB metal detector will depend mostly on the electro-
magnetic properties of the search head loops. The most important of those properties is the Q, quality factor.
This article will not get any further in to the academic aspect of the Q ,but wish to tell that the Q is the main of all factors which
could influence the performance of any search head or single loop.
The Q is of equal importance when PI metal detectors are concerned.
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