Loop Xmit Power for the TM/TP

[SC Dirt Fisher]

Does anyone know how the TM/TP detectors transmit enough power in the soil to actually detect anything? I'm not electronics geek BUT it must be done by some type of step up transformer? The V3i transmits 10v from the coil, but it has a 12 V battery pack. The treasure pro only has (2) 1.5V batteries, which only adds up to 3V.

 

[Larry (IL)]

Once upon a year I would have answered your question but it is so easy to just Google "How do metal detectors work" and you will get a couple dozen perspectives on the process and learn so much more. BTW, voltages are not transmitted into the ground and the coil voltage can be boosted to 30 volts on the V3i but that seldom results in more depth for most users. (The bright lights in a fog theory) It IS a great tool to help with EMI though.

 

[SC Dirt Fisher]

Larry,
Thanks for the response. I had worded that incorrectly. I did know that the voltage is not xmitted directly in the ground but the strength of the signal is a result of the voltage sent to the coil. Per Carl's writings about the V3, the additional 20v will get you about another inch of depth.

 

[Hightone]

CMOS technology. Micro-circuitry can operate on micro amps. Kind of like the old CB radios needing 12V to send/receive. Yet an iPhone working on micro-power can be a computer plus a phone at the same time. Isn't (digital) technology great?

 

[SC Dirt Fisher]

CMOS technology. Micro-circuitry can operate on micro amps. Kind of like the old CB radios needing 12V to send/receive. Yet an iPhone working on micro-power can be a computer plus a phone at the same time. Isn't (digital) technology great?

Understood that the internal circuitry is microamp. I'm trying to understand how the performance of a coil operating @ 3v. max. can detect any where nearly as deep as a coil operating @ 10 v. Especially in high mineralized soil. I know that more is not always better, but in this instance it seams that the strength of the xmit field would have a direct bearing on detection depth. What am I overlooking here?

 

[Larry (IL)]

Dirt Fisher, you are overlooking dozens of factors and seem to be fixated on the magnetic field voltage of the coil which is probably one of the lesser important items of a metal detector. Applying a voltage to a coil of wire to create a magnetic field is pretty simplistic compared to the receiver side of the metal detector. Detecting and processing the eddy current info generated by the electromagnetic field is doing most of the work of detecting a target.

If you really want to know what you are overlooking I would suggest reading "Inside the Metal Detector" by George Overton and Carl Moreland.

 

[thebeatmachine]

Its not so much how strong the field is that is sent out, but the detectors ability to detect changes in the field from metal objects and not noise.

 

[SC Dirt Fisher]

Thanks Larry, but I already had a copy. I think if you had read it you would know that this book's focus is on building a hobby detector and not explaining why useful power to the coil is limited by the physics involved with the interaction of the ground and the target.
I thought my question to be fair and relatively simple to the point that it had probably already been answered, and as it turns out, it had.
Using the search term "coil transmit wattage" ( instead of voltage) found several well explained answers, one of the best being answered here on this forum 5 years ago.
Here is the link. It not only answers my question but also corrects some incorrect answers and debunks some myths also.

http://www.findmall.com/read.php?34,273955,280816#msg-280816

 

[Larry (IL)]

I'm glad you found your answers Dirt Fisher and I DO have, and read his book. I know Carl and I worked with him on the V3 project, BTW, a lot of my time was spent on coil testing and compatibility.

"useful power to the coil is limited by the physics involved with the interaction of the ground and the target."

The coils power is measured by taking the operating voltage times the current (inductive reactance) P=I*E

Power (Watts) is electrical energy used by the coil making a magnetic field, heat losses and such, it has little, if anything to do with interaction with the ground and target.

 

[Larry (IL)]

I shouldn't write before my first cup of coffee, (inductive reactance) should not be there, that is the resistance of the coil, not part of Ohms law for power. Sorry about the error.

 

[SC Dirt Fisher]

That's OK Larry. I think we both were a little over our heads on this one. Myself especially! We've probably both learned a lot by trying to discredit the other's statements.
I have learned some things but at this time will still disagree with anyone who states that for a given detector and coil that the amount of power emitted by the coil does not matter. There probably is a point of dimishing returns, or let me say "there is a point of diminishing returns or negative returns" but for each different detector/coil design, the power that is provided or emitted either varies or is designed to a proven "standard" to perform at a maximum depth. If this is not true how could the Whites V3 possibly give an inch more depth just by boosting the X-mit voltage from 10v to 30v? Carl states this in the Advanced Users Guide on the Whites V3 forum.
I don't know if this is the same Carl (Overton) that wrote the book? If not, they need to talk! I think. LOL