Impulse AQ Coil Connector False Signals

[Willy]

7 hours ago, Steve Herschbach said:

First off, I want to point out that what I am about to describe is not uncommon with high power detectors that have a coil that can be disconnected. The only way to really eliminate the problem is to hard wire the coil, which is another reason for why this option is chosen by so many manufacturers of underwater metal detectors. The White's TDI Beachhunter is a good example. The problem has its root in coil capacitance and the high voltages involved, and the difficulty of getting good shielding using a removable connector.

If the Impulse AQ is submerged halfway, so that the water level is anywhere in roughly the area indicated in the photo below, you will get continuous false signals. Just holding the unit stationary in the water at this level will cause signals as the water moves around the connection area. If you are not aware of what is happening it is every easy to mistake this for electromagnetic interference (EMI).

The problem is worst in the Tones mode, which I just happen to be using a lot. It is accentuated by a short pulse delay, high sensitivity settings, and low ATS settings. If you want to reduce the false signals, here are some solutions:

1. Use the All Metal or Volcanic modes instead of Tones
2. Increase the Pulse Delay to 9 or higher
3. Reduce the Sensitivity to 4 or lower
4. Increase the ATS to 8 or above

Or some combination of the above.

In practice this only occurs when wading, and only at a certain depth. My solution was simply to stay either deeper or shallower. This does leave a strip or area unhunted. You can either switch the settings as suggested above, or do something to change the height. Like hunt that strip with mask and snorkel, for instance. 

Anyway, hopefully this is put in the manual as it is something inherent in the operation of the detector, and can drive you nuts if you run into it and do not know what is going on. It took me several hours of detecting to put two and two together, and it was then confirmed that yes, that is the way it is.

The high voltage and short pulse delay of the Impulse are requiring a strict shielding of all the parts subjected to the pulses (coil, cable and connector).

That effect is due to the small gap of continuity of the cable shield between the the male and female connectors and the changes of capacitance coming from the conductive  water level variations.

It was for that reason that the coil connector was initially made of metal in order to keep the continuity of the cable shielding up to the inside of the enclosure. (Same supplier, other item)

Field tests in the sea water had shown a bad electrolysis effect on its body giving it a nasty look.

A plastic connector had to be used for the AQ.

The GOLD version will even require more attention to this capacitance effect as it will have a much  shorter pulse delay, it will get an (expensive) stainless steel connector to keep a perfect shielding.

 

[Willy]

5 hours ago, Jim in ma said:

I had the same with my Infinium.

There is a wire that is connected the connector to the mother board, Ground ?  cut it , problem solved.

Yes, you can do that to solve this problem but you then generate a sensitivity to external EMI for the whole system.

[Skull diver]

Feel free to laugh of my try to find a solution ?as it might sound crazy or at least stupid...

Can't be possible to create an outside connector shielding sock with a 3m shield tape? Something like a cable/connector glove to avoid direct saltwater contact with the area? Is it something to be necessarily fully waterproof?

[Willy]

1 minute ago, Skullgolddiver said:

Feel free to laugh of my try to find a solution ?as it might sound crazy or at least stupid...

Can't be possible to create an outside connector shielding sock with a 3m shield tape? Something like a cable/connector glove to avoid direct saltwater contact with the area? Is it something to be necessarily fully waterproof?

 Nothing to laugh at. This is the way to make good  brainstorming.

In order for that to be effective, it would need to be electrically connected to the shield of the cable AND be protected from the sea water contact. Difficult to implement and ugly-looking.?

If you do not mind the consequences of the electrolysis on a metallic connector, you could use one to replace the plastic-based but Quid of the Warranty?

[Skull diver]

6 minutes ago, Willy said:

the consequences of the electrolysis on a metallic connector

I perfectly remember this thing on the Excalibur battery connector, never been a big problem with some good gel grease ...Now...Using a metallic connector installed from the source (FT plant), I think the connector electrolysis phenomenon can be on the outer part of it right ?

So I see a temporary solution : heat shrink tubing right around the end of cable and connector...

[Willy]

2 minutes ago, Skullgolddiver said:

I perfectly remember this thing on the Excalibur battery connector, never been a big problem with some good gel grease ...Now...Using a metallic connector installed from the source (FT plant), I think the connector electrolysis phenomenon can be on the outer part of it right ?

So I see a temporary solution : heat shrink tubing right around the end of cable and connector...

Yes, it stays outside of the connector but that was deemed to be unbearable by the reports of early testers. The change of connector resulted in it sensitivity to local capacitance variations. (You can't have your cake and eat it )

There was even an electrolysis effect on the surface of the metallic upper shaft with a nasty looking result. This was also replaced by the current plastic-made upper shaft.

[Skull diver]

9 minutes ago, Willy said:

The change of connector resulted in it sensitivity to local capacitance variations

Well...I have reached my knowledge limit in this specific field...

Considering that I hunt at a medium to modest high water depth, I'm prepared to live with the machine fully under the surface however...

I'm waiting like a child under Christmas tree for this...

Thanks for your technical explanations!

[okara gold]

Willy.. Thanks for all the information. It sure helps a lot of us with inquiring minds!

[tvr]

7 hours ago, Willy said:

It was for that reason that the coil connector was initially made of metal in order to keep the continuity of the cable shielding up to the inside of the enclosure. (Same supplier, other item)

Field tests in the sea water had shown a bad electrolysis effect on its body giving it a nasty look.

A plastic connector had to be used for the AQ.

The GOLD version will even require more attention to this capacitance effect as it will have a much  shorter pulse delay, it will get an (expensive) stainless steel connector to keep a perfect shielding.

Having read the whole thread, I'll go back to the part quoted. How much more are the expensive stainless steel connectors? I'd think that I'd pay more for a version that would keep the continuity of the shielding, maybe not $1,000 more but certainly $100 more. And if that would mean that it needs to be coated in silicon grease to keep it looking nice, that is OK too.