GB_Amateur Posted September 5, 2022 Share Posted September 5, 2022 8 hours ago, steveg said: 1. That "rusty tin infestation" seems to be a "western" thing, more than an "eastern" thing, and so -- with 99% of my detecting of 1800s sites being "back East," I'm not nearly as familiar with that "rusty tin" issue you mention. I think this somewhat west vs. east disparity is due to the types of containers that food, and other such necessities, were packed into, for folks traveling long distances (often westward) back in the 1800s. The only time I experienced any of what you are talking about, in terms of that rusty tin issue, has been during the few times I've hunted old miner's camps/cabins, etc. in Colorado. And when there, I was using a Gold Bug Pro, not FBS. But, yes, I did experience how those pieces would ID as conductive, and were very "troublesome." In my limited experience in Western ghost towns it's not just the rusty cans (and worse, pieces of them), although those do play a roll. Even worse in some places are the pieces of sheet metal (iron composition but possibly originally zinc coated by the galvanizing method). Sheet metal was quite common in construction, particularly for roofs. (Sometimes copper was used, but that seems less frequent.) In some ways these are similar to old crown caps, except for the dimensionality (flat or 2-d for sheet metal and unless severely decomposed, 3-d for crown caps with that raised rim). Also it seems that rust preferentially attacks edges and maybe this is where a ferrous+non-ferrous readout can really help. Small pieces have a higher percentage of edge compared to large pieces. 8 hours ago, steveg said: ...My nemesis when hunting 1800s sites "back East" is not the "tin" issue, but the "square nails" issue. (Note: The following paragraph is just my impressions; not carefully studied so may be way off.) For me often the modern rusty nails are worse and I think those might be easier to distinguish. There seems to be a misconception among many that 'ferrous' and 'iron' are equivalent. From an historical (and chemical) standpoint that is understandable. But in metal detecting (as in many pursuits) the lingo that develops and becomes standard isn't particularly conforming to historical or scientific usage. I think 'ferrous' refers to the magnetic properties if ferromagetic materials. Iron (and its common alloy -- steel) also has conductive properties and those can dominate the response of a detector. Where we win is for thin, rusty materials when the ferromagnetic part of the signal can dominate the conductive part. My hope is that with rusty bits of sheet metal (as found scattered thickly in many Western ghost towns) will give a 'tell' on the new ML Manticore. As far as the Manticore being an improvement over FBS/FBS2, one possibility is that its better separation when combined with the ferrous+non-ferrous readout (which those earlier detectors perfected) will give it the edge. Again, just wishful thinking at this time AFAIC. The Equinox has better separation (from what I've been told -- never had an FBS) but lacks the ferrous discrimination properites of those earlier models. Link to comment Share on other sites More sharing options...
Geotech Posted September 5, 2022 Share Posted September 5, 2022 21 hours ago, scoopjohnb said: FBS2 is VLF with a bit of PI for ferrous discrimination thrown in. FBS2 is VLF with time-domain sampling & processing. There is no PI going on. 2 Link to comment Share on other sites More sharing options...
la torche Posted September 5, 2022 Share Posted September 5, 2022 1 hour ago, Johnnysalami1957 said: Aurait pu le nommer Equinox 1000. Ou 1500 selon son prix. So it would rather be Equinox 2000 given the price. 1 1 Link to comment Share on other sites More sharing options...
steveg Posted September 5, 2022 Share Posted September 5, 2022 15 minutes ago, Geotech said: FBS2 is VLF with time-domain sampling & processing. There is no PI going on. Carl, Would it be possible for you to help me understand a bit more. My simplistic, non electrical-engineering-trained mind thinks in terms of VLF being "frequency domain" and PI being "time domain." And I THINK that is correct, right? And I have a very basic understand of the "trasmit, wait while hysteresis occurs, and then receive" idea of how PI units function... BUT -- what I have a hard time understanding is if FBS2 utilizes "time-domain sampling and processing," why is that not considered at least "PI-like?" I would really like to understand this better... Steve Link to comment Share on other sites More sharing options...
palzynski Posted September 5, 2022 Share Posted September 5, 2022 47 minutes ago, la torche said: So it would rather be Equinox 2000 given the price. Or Equinox1999 ... ? 1 1 Link to comment Share on other sites More sharing options...
Popular Post Steve Herschbach Posted September 5, 2022 Popular Post Share Posted September 5, 2022 1 hour ago, steveg said: Carl, Would it be possible for you to help me understand a bit more. My simplistic, non electrical-engineering-trained mind thinks in terms of VLF being "frequency domain" and PI being "time domain." And I THINK that is correct, right? And I have a very basic understand of the "trasmit, wait while hysteresis occurs, and then receive" idea of how PI units function... BUT -- what I have a hard time understanding is if FBS2 utilizes "time-domain sampling and processing," why is that not considered at least "PI-like?" I would really like to understand this better... Steve VLF just means Very Low Frequency and is not the real technology involved. That would be Induction Balance (IB) where current flow to the coil is continuous. It is also therefore called Continuous Wave by some companies. The detector constantly transmits and receives, and the phase based processing involved is called frequency domain processing. Pulse Induction (PI) is where the current to the coil shuts off periodically. There is a transmit portion, then a receive portion. The short time in between allows for induced currents to decay. They do so at different rates, and when this is measured, we call it time domain processing. Whether a detector is Induction Balance or Pulse Induction is a function of the electronics and how the current is flowing, continuously, or intermittently. It has nothing to do with processing. It is possible to do time measurements, time domain type processing, with an Induction Balance detector. As far as I know, it is not possible to do the reverse, to do phase type processing with a PI. This timed processing however does not make an Induction Balance detector into some kind of IB/PI hybrid. There are things inherent in a true PI, the high power pulse, followed by actual decay of eddy currents, that can't be duplicated in a continuous wave device, where the ground and targets are constantly illuminated. It may be a form of hybrid processing, but it is not a true melding of a PI with a IB detector, which is what people seem to think. This idea you will have a VLF with PI depths is just nonsense, and largely marketing BS aimed at people who do not know better. What is does offer is another way to get more information out of the IB signal, which in general means better discrimination at VLF type depths. Since the disc returns usually become less accurate before the actual full depth of a VLF (IB) machine is reached, any improvement in disc at depth is perceived by the end user as "more depth" in relative, but not absolute terms. The following document should be read and fully understood by everyone who wants to put these questions of what is what when it comes to the two basic techs we commonly deal with, IB or PI. How Metal Detectors Work by Mark Rowan & William Lahr - Originally published by White's Electronics as a booklet P/N 621-0395. Basic but rather technical information on how induction balance and pulse induction metal detectors work. 11 5 Link to comment Share on other sites More sharing options...
jasong Posted September 5, 2022 Share Posted September 5, 2022 1 hour ago, Geotech said: FBS2 is VLF with time-domain sampling & processing. There is no PI going on. Do you mean they are doing something like using an inverse Fourier Transform to construct a new time domain waveform out of a number of multiple additive VLF frequencies broadcasted by the coil, and then sample for the target response after the new FFT "pulse" is decaying? But still also sampling in the frequency domain too with the multiple VLF frequencies individually? Or are you talking about something more basic here? I get confused between the way physics/mathematics terminology is used sometimes in the detector world in ways that don't mean what I would interpret them to mean outside the detector realm. Link to comment Share on other sites More sharing options...
Steve Herschbach Posted September 5, 2022 Share Posted September 5, 2022 8 minutes ago, jasong said: Do you mean they are doing something like using an inverse Fourier Transform to construct a new time domain waveform out of a number of multiple additive VLF frequencies broadcasted by the coil, and then sample for the target response after the new FFT "pulse" is decaying? But still also sampling in the frequency domain too with the multiple VLF frequencies individually? Or are you talking about something more basic here? I get confused between the way physics/mathematics terminology is used sometimes in the detector world in ways that don't mean what I would interpret them to mean outside the detector realm. Read what I just posted before you did Jason. Carl means it literally - there is no PI going on here. Link to comment Share on other sites More sharing options...
Geotech Posted September 5, 2022 Share Posted September 5, 2022 1 hour ago, steveg said: Would it be possible for you to help me understand a bit more. My simplistic, non electrical-engineering-trained mind thinks in terms of VLF being "frequency domain" and PI being "time domain." And I THINK that is correct, right? And I have a very basic understand of the "trasmit, wait while hysteresis occurs, and then receive" idea of how PI units function... BUT -- what I have a hard time understanding is if FBS2 utilizes "time-domain sampling and processing," why is that not considered at least "PI-like?" It's a fairly complicated topic that really requires a whole book chapter and a lot of diagrams to explain*. In the old days all VLF designs were frequency domain (or, more accurately, phase domain) and all PI designs were time domain. But BBS/FBS/FBS2 (all really the same basic tech) created sequentially-transmitted frequencies where freq-domain processing doesn't work because the dead time between frequencies would screw up the channel filters. So ML used time-domain processing which, honestly, looks somewhat similar to normal freq-domain sampling. But it's done on ramped-exponential decays instead of sinusoids. From the time-domain sampling you can still get the equivalent of a target phase. PI is also time-domain (and always will be) and also samples a decaying exponential but it does so during a TX "quiet time" where the TX signal is not changing. With FBS the TX signal is always changing, just like VLF. And with PI, you can never extract a target phase. 26 minutes ago, Steve Herschbach said: Whether a detector is Induction Balance or Pulse Induction is a function of the electronics and how the current is flowing, continuously, or intermittently. It has nothing to do with processing. This was a good differentiator until the GPZ came along. In traditional PI the TX current is turned completely off during the RX sampling. In the GPZ it is not, but it is also not changing (the TX current is a bipolar square wave) so the result is exactly the same: there is no changing TX field during RX sampling. So now my definition of PI is a system that receives during a TX dead time, whether current is zero or a DC value. Put another way, during sampling there is no reactive signal. *Inside the Metal Detector, 3rd ed, Ch 2; pub. 2023 (I hope) 7 Link to comment Share on other sites More sharing options...
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