Easy Adding of Iron Recognition in PI MD

[Detectorist#1]

Hi eduardo,
Thank you for this information. My asking is concerned with possible using of this coil for iron discriminating in simple PI detectors. The difference in the inductance of two coils is too big and this coil is not suitable for this purpose. Tomorrow, I will buy MINELAB 10"x5" DD Commander coil and will make tests.

[Detectorist#1]

Hi eduardo,
Unfortunately, no chance to use "Minelab 10"x5" DD Commander Coiл" for easy Fe recognition in simple PI detectors. I measured the inductance of the two sides and the result is: 310iH 0.4oHms for TX coil and 620uH and 16.6oHm for RX coil. In this case, only good variant for passive Fe recognition is to make DIY DD coil with equal two side coils. I have two very fast mono 8" 300uH 2oHm SFR 1MHz coils. I will try to make OO configuration from these two coils and to test this variant with and without balancing. Also, I will try to make balanced DD configuration from these two coils. Interesting tests are coming!

[eduardo1979]

Hello Detectorist 1.
So I realized that the inductances of my coil are somewhat similar to those of yours. I'll have to try homemade coils to see the results.

[Detectorist#1]

Hello Eduardo,
Yes, we have to test home made symmetrical coils for this type of MD. The smaller sizes of the coils (6-8") maybe will be close to your dream for very sensitive PI MD for small nuggets simultaneously with Fe discrimination capabilities.

[pechkata]

Hi eduardo1979,
Please measure the DC resistance and inductance on both sides of the MINELAB 11" DD coil. For good Fe/non-Fe separation, MINELAB recommends using Commander type DD coils and include a size of DD 15"x12" semi-elliptical and DD 18" round. I am sure that these coils should have equal resistance and inductance on both sides.

[Carl-NC]

For good Fe/non-Fe separation, MINELAB recommends using Commander type DD coils and include a size of DD 15"x12" semi-elliptical and DD 18" round. I am sure that these coils should have equal resistance and inductance on both sides.

Minelab iron disc is done by looking at the TX on-time target response. It does not require equal inductances and all the DD coils I've seen have an RX coil with a higher inductance & resistance.

[Detectorist#1]

Hi Carl,
Thanks a lot for this information! Yes, I learned this the hard way. However, passive Fe detection from two closely spaced identical coils provides a very easy and reliable way to determine whether a target is Fe or not. Of course, the sensitivity in this passive mode is reduced, but this should reduce the digging effort in many cases.

[Altair]

Hi,
Is it necessary for the two coils to be nulled or can they just be close together and perhaps not even overlapping?

[Detectorist#1]

Hi Altair,
Nulling of the coils allows faster reading of the RX signal (more short first delay). This is useful for discovering of smaller targets in "ALL" mode.

[Detectorist#1]

The next "natural step" for improving of this project after using of two equal coils, is to use both coils as TX and RX. Thus, in practice repeats the idea of "Twin Loop Treasure Seeker" from 1989 year. At first look this is very good idea - very simple, no need of EFE pulse and GB channel. Also good immunity from electromagnetic fields. This idea gives excellent results in the home laboratory. At practice it is very difficult to use this detector. The terrain have to be very flat and this detector is very sensitive to left-right tilt when real soil is under the coils. Using of only one RX coil and additional GB channel is more good solution. As I mentioned in #7, the using of "Fe" mode with two equal RX coils have to be careful - without left-right tilt and similar to pin-pointing AFTER the receiving of a signal from a target in "ALL" mode.