Xergix said:
I do not know if the topic has already been discussed,I compared my MXT300 with a MXTpro with 10DD, ...
Did you compare BOTH the MXT 300 and MXT Pro with the 10" Double-D coil, or did you compare the 10" DD to a Concentric coil on different models with different settings?
The MXT 300 was simply a designation of an MXT that came standard with the 300 mm or 12" Concentric coil. The MXT Pro was available with either a 12" Concentric or the 950 Concentric coil, so by their titles these models could have had one of several 'standard' search coils. The current MXT All-Pro [size=small](which is just an MXT Pro with an 'All' sticker on the side)[/size] comes with a 10" D2 Double-D coil or the 950 Concentric coil.
So, the first thing to know for sure is which search coils you were comparing?
Xergix said:
... the configuration is on Relic with discrimination fully open and trigger forward, ...
With the MXT, if the Discrimination is set at the minimum point [size=small](fully open)[/size] and the trigger toggle is locked in the forward position, that is the Iron ID setting. No rejection and most ferrous targets will respond with a low audio tone, and non-ferrous [size=small](or any target with a conductivity higher than '0' VDI)[/size] will produce a higher-pitched tone.
Xergix said:
... also MXTpro with two tones,
The MXT Pro, can produce two tones based on the 2-tone option and the Discrimination level setting ...
OR ... you can select the Iron ID tone setting. Iron ID will be similar to the setting you described for the basic MXT, with no rejection and targets producing a low iron audio, if the VDI is a negative reading, and a higher-pitched audio for positive-reading VDI's.
So, what specific settings were you using for the MXT Pro?
Xergix said:
i have this difference: with a ferrous target (5 vdi),
If the target produces '5' VDI, that is a positive response. A '-5' VDI would suggest a ferrous target, in most cases.
Will ALL ferrous targets produce a negative VDI read-out? Generally YES, but only if they are of a size and shape that doesn't enhance their conductivity when swept directly across the center axis of the search coil. If an iron-based target produces a positive reading VDI, then that suggests it is of a particular shape that enhances its conductivity. Often the VDI read-out of those types of ferrous-based targets will be more radical and not as 'tight' a reading as a similar size and shape non-ferrous target.
Generally, you can use ATC [size=small](Audio Target Classification)[/size] on those kinds of questionable responses by using
'Quick-Out' or EPR [size=small](Edge-Pass Rejection)[/size] techniques to help audibly quality or classify the target. This is done audibly and visually with today's modern display models. I have been using those methods, even just audibly, since I discovered the technique with my early '70s era Compass TR's, and have instructed the techniques to customers since '77, and in my seminars I conduct since 1981.
The reference to "Edge-Pass" doesn't mean the exact 'edge' of the search coil because it can vary somewhat based upon the coil size, coil type [size=small](Concentric vs Double-D)[/size] and the detector's electronic design. Usually, it will be just in from the outer-edge of a Concentric search coil, but sometime just barely beyond the outer-edge of a search coil with a Double-D design. I explain some of the ATC methods under Tips & Techniques on the AHRPS org website.
Nothing is 100% and there's no such thing as a 'perfect' metal detector or 'perfect' performance because we don't have control over the ground mineral make-up, the presence of nearby masking targets, or the size, shape, position and alloy make-up of the unseen targets we sweep a coil over. One example we all know about are those annoying crimp-on Bottle Caps which often produce a 'good' sounding audio response and can 'read' similar to a penny/dime or quarter on TID and VDI displays.
They will be attracted to a magnet and are magnetic-based targets, but their man-made
shape causes them to give a high visual and audio [size=small](if using Tone ID)[/size] response. In my seminars or other demonstrations I grab four sample targets out of my jug of 'stuff.' Two are paper clips. The plain ol' metal paper clips we use. One is in its natural shape or I can bend it open into a straight piece of metal or forum a 'U' shape out of it.
Swept across the center axis of a search coil it will produce an 'Iron' visual response and VDI number, and a Tone ID reports it with the low Iron Tone audio. Then I use the second paper clip. It is an identical ferrous based target, but I have opened it up and formed it into a circular shape and hooked the two ends to make contact. The result of this ferrous target when swept across the center axis of the search coil is a higher-tone and high-reading TID & VDI response.
Same size and type of metal, just re-shaped in a form that makes it more conductive. Can I still get an Iron display reading and a low-tone audio response to tell me it's iron? Yes, by using EPR. The other two items are a fairly thick rusty nail, and s similar thickness old rusty bottle opener. The nail produces an Iron audio and display reading, but the bottle opener, if held in a position that is 'flat-to-the-coil,' gives me the high-tone and good positive VDI response. Why? Man shaped that ferrous object into a form that enhanced it's conductivity. EPR can help 'classify' that target as well.
So, a few things need qualification, and that is what, specifically, was the "ferrous object" and it's size and shape. Also, what orientation was it held and presented to the search coils, AND was it moved across the center-axis of the coil in both cases using Concentric and Double-D coils.
Xergix said:
... with MXT300 I have a good low tone, with MXTpro, I have a torn and dirty tone as if the target were to be discriminated against,
Could be differences in the settings used not being the same for each of the wo detector models. Other than that ... the Dealer might well be correct.
Xergix said:
my impression is that the calibration of the discrimination of MXTpro is too high,
What do you mean by "calibration?" If both are set up the same, then performance will be similar, as in very close to identical. MXT w/trigger toggle forward and Disc. at the minimum will be
similar to the MXT Pro with Iron ID tone selected.
Xergix said:
my dealer says it is the fault of the DD coil, that with the concentric should not do...for me it's a stupid thing...
Double-D coils do not discriminate as cleanly as do similar-size Concentric coils. Also, DD coils have more challenges rejecting iron than do Concentric coils. Personally I only have one, and sometimes two, DD coils in my personal detector/coil inventory because I hunt a lot of brushy sites, those with building rubble, and many with ample old trash that is mainly ferrous type, such as iron nails or rusty tin. It is due to the coil size and internal design that I prefer a Concentric to a Double-D, and their better handling of iron junk or working close to metal structures.
Xergix said:
Has anyone ever had this problem?
Tanks.
Sure have, but I deal with it by using the best type of coil, size of coil, and settings, as well as having the best detector for my needs in-hand.
For more open areas with sparse targets more scattered, I keep the 9" Concentric spider coil mounted on my MXT All-Pro. For denser trash environment, especially iron junk, I have a 6
