threshold question

[kevinslack]

every now and then when detection i will lose the threshold sound over a small spot. using ttf there will be no sound of iron. could that be a very deep target that i don't get a sound for and just lose the threshold sound because its trying to spot a real deep target. i thought the next time it did it, i would pull a plug out and go over the hole to see if a sound would appear.

 

[marchas45]

If I think what you mean I would say it's nulling because your going over iron.

 

[Jason in Enid]

I'm confused also. Are you using a COMPLETELY open screen? If you have any of the FE lines blocked out, you will null over iron.

 

[kevinslack]

heres what my screen looks like, it does not null like iron. the threshold sound will go quit every now and then on some spots of the ground. it dont happen alot. i was just thinking maybe the threshold sound was trying to hit on something to deep.

 

[Digger]

TTF has no effect on whether a target will make a sound or not. What TTF does is allow the user to hear one of two tones associated with the ferrous properties, opposed to the tones associated with a target's conductive properties. However, I have also encountered what you describe. When running with the screen "wide open", I still occassionally get a brief nulling of the Threshold. When I was digging everything to get the hang of my ETRAC, I never dug anything of value when this happened. As such, I have elected to simply pass them off as being a deeply buried object with a high ferrous content. JMHO HH Randy

 

[etracjoe]

The threshhold sound will go away "or null" when you hit a target in the blacked out area of your screen. Im guessing the way you have it set it would either be iron or foil. Unless your in real heavy iron and are tired of hearing all the low grunts I would open up the screen other than the very top line the way you have it. You will hear a grunt for iron and high tone for "good" stuff. Good luck and hope this helps.

 

[kevinslack]

ok, thanks for the replys

 

[coinnut]

What Jason said is correct. You are probably nulling over the iron your pattern chose to reject. Now if you had a completely clear screen and still got nulling, then it might be what I have encountered. When running a high sensitivity, in an area that should not have it that high, I have gotten nulling as the detector read the concentrated mineralisation in the Basalt rocks we have here. In other words, because the sensitivity was cranked, it nulled on the fast change in minerals. When I went to auto+3, and the sensitivity almost matched the manual setting I had, I got no nulling.

 

[Ray-Mo.]

if it is iron disced out which is very likely with your settings pictured.Even in a wide open all metal set up you can get nulls at high man. sens. from heavy concentrations of coal slag/cinders.

 

[AL KS]

just pop it over there and then you can tell.

 

[tippyhound]

Your screen is showing blacked out areas (discriminated areas) if your target falls inside those blacked out areas you will receive a null as you pass over it.

 

[david.di]

You're spot on and I agree with what you and many others that suggest the most obvious cause in this case.

Take note of Ray-Mo's response where he's said that:

"Even in a wide open all metal set up you can get nulls at high man. sens. from heavy concentrations of coal slag/cinders".

I've encountered the same problem on a few of occasions where it was fine and the threshold prevails, when using auto sens +3
but
same target in man.high sense without a tone of any sort, in a wide open screen, there is a loss of the threshold null.?????

In all cases, I dug and found a mass of cinders, devoid of any solid metals.

If it can't be pinpointed, chances are , it is not a whole metal but rather an oxide or mineral concentration that a setting of man. high sense is detecting but in the cases I encountered, auto it does not


daviddi

 

[tippyhound]

In the early days of VLF- Ground Balanced machines we lived with what we called Hot Rocks (they are still around today) which would give you a target but when you tried to pin point that target it would null out (disappear) on you.

It was very flustering at first but we soon learned what caused it and learned to identify the problem and live with it. As we got better at ground balancing our machines we lived less and less with the problem. Coal slag / cinders gave very much the same response especially if there was large amounts of them.

Here in the Mid West / Coal Country where people used coal to heat with it was a very big problem. The manual Ground Balance machines were much better at handling this problem. I have actually dug coins right out of the middle of cinders and wasn't even aware they were there till I dug.

There is a park in Springfield IL that has a back fill of coal cinders. The concentration of cinders is so large you can not ground balance your machine period. Making it almost impossible to operate a metal detector there.

Being new to the detector I'm not really to sure about the way the E-Trac handles ground balance, but have experienced few problems with Hot Rocks or Cinders. I did dig a Mercury Dime one day and experienced a condition like we sometimes have with iron in the area of the coin causing a one sided / broken signal, my Quick Mask showed the target was good so I dug and found the Mercury laying up against cinders (blackened on one side). These ciders often contain iron slag which could create that problem.

I hope this might help you understand why Cinders cause these problems and maybe clear up the picture for you a little. Rick (IL)

 

[minelabgeek]

i dont like any threshold