The Phantom Signal

[eddiecurrent]

This happens to me on rare occasions while using my Fisher CZ, it might not be model specific, I dunno, but what occurs is weird and unlikely...I'll detect a target at the beach, say a nickel, then dig it out. I'll then pass the coil over the hole again to check for anything missed...and I'll get a "nickel" hit. But there's no nickel...no anything. Pass the coil over the hole again...nothing, no signal.
Mind you, the first phantom hit was repeatable. I almost thought I imagined this when it first happened, but over 3 decades it's happened at least 4 times.
Cue the twilight zone music.

 

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[Jason in Enid]

Every time I have had this happen it was caused by the object sliding to the bottom of the hole after a scoop, and standing up on edge. Every time I have a good target, and then it suddenly disappears after a scoop, I know its coming out on the next scoop.

 

[eddiecurrent]

Ok, but that's not what's happening in my case. I've had the same experience as you, when I get the phantom signal tho', I carefully search the hole, to no result.

 

[rick67]

"Halo"

 

[eddiecurrent]

Wouldn't the act of digging out the coin..disturbing and removing the matrix..disrupt a "halo"?

 

[rick67]

Oxidation is an electrochemical process that acts somewhat like a battery, exchanging small amounts of electricity. Like batteries. Even though you took the nickel away which was fuel to the process. The reaction needed time to peter out in the soil around it.
Or you can just stick with the Twilight Zone theory.

 

[eddiecurrent]

Well, I don't know about the electrification part of that electrolysis theory, but the coins aren't really oxidized. You can see the pitting and oxidation on a sacrificial zinc boat rod. I suppose it's plausible that a microscopic amount might leach into the surrounding soil/sand, we ARE talking about beach sand that probably has a lot of salt, a caustic oxidizer, but that still doesn't explain why the signal remains as a nickel (for a nickel) or a dime for a dime, nor does it explain why the signal might remain after the soil/sand is disrupted. I'm still in the Rod Serling mystified camp.

 

[Jackalope]

It simply could be, that the detector holds an averaged signal that is assigned to registers, which are set to variables within the detector's algorithms, and are held for a period of time as new information is added with each sweep of the coil. Every time you move the coil the thousands of returned voltages and amplitudes are measured, averaged; the phase determined, and various differences and ratios calculated, then stored for use. These registered values are continually averaged, to include ground conditions, as new information is added with more coil movement. Most detectors store the info in what is essentially RAM, and will alert the user with a beep when the measured values, ratios, phase calculations as compared with ground values meet the minimum requirement, as engineered by the software developers.

If the last held values are kept, meaning the detector is undisturbed while you dig out the coin, then the next sweep may appear to hold a voltage value that was held from the previous sweep before you set the detector down. There was nothing in the hole to unbalance the induction-balance - not even the much overworked theory of 'halo' effect, it was still the coin. But this effect would be an artifact of the coin's response - a memory of the past. The registers won't average back to near zero until a couple of swings of the coil happen. It's a theory.

Usually, when setting the coil down the detector ends up resetting as the coil is moved. It probably requires a unique set of stored set values to fool the detector and cause a beep, so it's a rare event, or at least should be (failing to clear previously assigned variables is not good program coding, though this effect is too rare to be bothersome).

 

[eddiecurrent]

That's well thought out. It's plausible, but the signal is repeatable once. I don't think it's a chatter artifact.