Whats the difference bertween BBS, PI etc???

[wreckrat]

Hi,
Im confused with all the technical infprmation on underwater detectors. Of course each claims to be the very best and those who use them also claim the same. Can anyone give me a simple explaination as to the differences between the technology used, in the Minelab and Garrett underwater detectors for example? Or point me to a site with some info on the prosd and cons of the different operating systems.
Or....is it a case of 'they all work' so it doesnt matter what you use
thanks

 

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[steve from ohio]

OK, so I took an E-Trac, a 12" piece of 30 gauge sheet steel, and a silver dollar. I could not detect the silver dollar under the steel. Nor on top of the steel. I tried a 20-ounce silver bar. I still only "see" the steel.

Some other clarification... Minelab introduced MF to hobby detectors, but MF techniques go back to at least 1948. Also, both BBS and FBS are two-frequency only, 3kHz and 24kHz (they are identical). Yes, you can run MF using a single coil.

- Carl

Geesh........can I see a photo of your E-trac? How about a video? Two frequencies? Really? How about calling Minelab on that. There number is 702-891-8809. I bet they will ask you if you are drinking. BTW.....I will do a video of this situation sometime soon. I will show the E-trac's screen, the set up of the metal and the coin and do a test for the video.

Sounds like you do not know too much about what FBS and BBS technology is. Try 28 frequencies between 5 and 100 KHz. with the FBS technology (E trac) and 17 frequencies for the BBS system (Excalibur). I see no there is no information on what you have stated anywhere in Minelabs technical data or anywhere else for that matter. Those frequencies are transmitted simultaneously.

It is possible that a 2 frequency system was developed in 48, but Minelab hold the patents for FBS and BBS technology and White's had to go to Minelab in order to use their technology.

Nice try.

 

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[Arthur-Canada]

OK, so I took an E-Trac, a 12" piece of 30 gauge sheet steel, and a silver dollar. I could not detect the silver dollar under the steel. Nor on top of the steel. I tried a 20-ounce silver bar. I still only "see" the steel.

Some other clarification... Minelab introduced MF to hobby detectors, but MF techniques go back to at least 1948. Also, both BBS and FBS are two-frequency only, 3kHz and 24kHz (they are identical). Yes, you can run MF using a single coil.

- Carl

Geesh........can I see a photo of your E-trac? How about a video? Two frequencies? Really? How about calling Minelab on that. There number is 702-891-8809. I bet they will ask you if you are drinking. BTW.....I will do a video of this situation sometime soon. I will show the E-trac's screen, the set up of the metal and the coin and do a test for the video.

Sounds like you do not know too much about what FBS and BBS technology is. Try 28 frequencies between 5 and 100 KHz. with the FBS technology (E trac) and 17 frequencies for the BBS system (Excalibur). I see no there is no information on what you have stated anywhere in Minelabs technical data or anywhere else for that matter. Those frequencies are transmitted simultaneously.

It is possible that a 2 frequency system was developed in 48, but Minelab hold the patents for FBS and BBS technology and White's had to go to Minelab in order to use their technology.

Nice try.

The water is getting pretty mucky now and common sense is headed for the window in a hurry.

Although it is possible to transmits 28 frequencies at the same time, in this case it is not economically feasible. It would require 28 separate oscillators each working at a different frequency with a separate circuit somehow shielded entirely from the 27 other frequency oscillators. Minelab is good technology, but not that good...nor does it have to be!! It does just fine doing one frequency at a time with a long enough pause in between to see what the reaction is from the target it hits. This is happening so fast that it is actually possible to make a detector this way without too many limitations. The only limitation is speed of your sweep. Anyone who has every become proficient in the use of a Minelab knows that if you swing too fast you will miss targets...more so than with a single frequency machine.

 

[Carl-NC]

Try 28 frequencies between 5 and 100 KHz. with the FBS technology (E trac) and 17 frequencies for the BBS system (Excalibur). I see no there is no information on what you have stated anywhere in Minelabs technical data or anywhere else for that matter. Those frequencies are transmitted simultaneously.

Actually, BBS and FBS transmit way more than 17/28 frequencies. As do Fisher CZ's, White's DFX, and any PI detector you care to name.

You made the statement, "Those frequencies are transmitted simultaneously." I notice did you not say, "Those frequencies are analyzed simultaneously." Or "used". Or "received". Or "processed". Or "detected".

I'm glad you agree with both me and Minelab, that BBS/FBS don't really analyze all those frequencies. Did I say Minelab? Why, yes, I did. Read the advertising! In all the years since the Sovereign was first released, Minelab has never claimed that BBS/FBS analyzed (or used, received, processed, detected...) all those frequencies. They only claim to transmit 17/28 frequencies. They could claim to transmit 43 frequencies if they wanted to. Or 143. So could Fisher & White's. And every PI.

And, yes, there is no difference between BBS and FBS... they use identical transmit waveforms. And the transmit waveform only (realistically) supports 2 frequencies: 3kHz and 24kHz. The same way DFX only supports 3k and 15k. Despite having lots and lots of other frequency byproducts present.

You don't have take my word for it; read the advertising! Better yet, call Minelab and ask them directly: "How many frequencies do you receive & analyze?" Heck, I'll bet they even tell you the truth!

- Carl

 

[Carl-NC]

Although it is possible to transmits 28 frequencies at the same time, in this case it is not economically feasible. It would require 28 separate oscillators each working at a different frequency with a separate circuit somehow shielded entirely from the 27 other frequency oscillators. Minelab is good technology, but not that good...nor does it have to be!! It does just fine doing one frequency at a time with a long enough pause in between to see what the reaction is from the target it hits. This is happening so fast that it is actually possible to make a detector this way without too many limitations. The only limitation is speed of your sweep. Anyone who has every become proficient in the use of a Minelab knows that if you swing too fast you will miss targets...more so than with a single frequency machine.

You can easily transmit multiple frequencies using a digital waveform, which is what Minelab, Fisher, and White's all do. You can easily set up that digital waveform to have 2 or 3 reasonably usable power levels. But as you try to use more & more frequencies, the power levels have to drop. Plus you need a separate receive channel for each frequency. If you ever got to 28, the power levels would be pretty low, and the receive circuitry would be enormous.

- Carl

 

[Carl-NC]

Does Minelab need different coils to produce the same desired effect as a detector that has a switch to chose which one might work best? Of course not. Then would Minelab chose to produce different frequency coils for the same detector? Is it a con? Is it a muse? Is it a trick? Is it ridiculous?

Maybe. Maybe not. But if they could transmit three different frequencies all at the same time through the same searchcoil - then why would they need diffferent coils tuned to different frequencies when one coil with automatic or manual selection would be a lot more practical, you think?

It's just common sense, that's all.

Sometimes when you get into sales and marketing gimmicks, common sense takes a back seat. But you ask a valid question: "[Why] would Minelab chose to produce different frequency coils for the same detector?" There are 2 possibilities: (1) It is necessary, and (2) it is desirable.

Since there are other detectors using multiple (2 so far) frequencies with a single coil, (1) is not the right answer. So why would multiple coils be desirable? It's possible that the coils are better optimized for their individual frequency, but I happen to know that there are ways to do this with one common coil. It's also possible that Minelab wanted to sell lots of coils.

Using a single coil to handle multiple frequencies is no more difficult than using a single antenna to handle 20MHz worth of FM radio stations. You just use filters. And, yes, you could add a second tuner to the same antenna, and receive TWO radio stations at the exact same time. Europeans have been doing that for years.

- Carl

 

[MajorBeep]

LL

"Could you imagine in your wildest dreams a receiver coil that conducts (not radiates) electrons inducing multiple frequencies through a SINGLE winding of copper wire around an axis?"

Well your wildest dreams have come true, some 100 hundred years ago of course. Audio transformers, both of the auto-transformer and isolation types conduct multiple frequencies at the same time. As well as the voice coils of typical loudspeakers & headphones in use today.

Which brings me to my next point. FBS & BBS are NOT frequency domain detectors, they are time domain detectors. All of these posts about multiple oscillators, and multiple receive circuits, is trying to take old "simple" single frequency knowledge base and apply it to time domain processing. It's NOT about frequency, it's about the inverse of frequency, time.

As clearly stated in this white paper:

http://www.minelab.com/consumer/xstandard/files/ML_08_007WhitePaper8.pdf

"Multi-frequency transmitting and receiving metal detectors have a signifi cant advantage in time constant discrimination, and to some extent ferrous discrimination capability, over the most common form of detector, the VLF detector. “VLF” stands for Very Low Frequency, and refers to the frequency of the single-frequency sine-waves that they transmit, usually at high pitched audio frequencies.
There are basically 2 types of “multi-frequency” detectors currently available for coin detection. Some transmit square waves, which is effectively a multi-frequency transmission. Minelab’s Sovereign, Excalibur and Explorer units use a more advanced transmit signal consisting of multi-period rectangular waves, which gives more useful information (more frequencies, in effect) than square waves. The major advantage results from having several different frequency R signals. These can be used to more accurately determine time constants of targets because these different frequency R signals are not contaminated by soil mineralisation X signals, unlike the more common VLF detectors which use R and the mineralisation contaminated X channel to determine the target time constant. In essence, targets with short time constants produce larger high frequency R signals than low frequency R signals, whereas with long time constant targets, the low frequency R signals are larger than the high frequency R signals. Thus, the ratio of the low frequency R component to the high frequency R component gives a measure of the target time constant without interference from the large soil X component. In addition, it is possible to extract a better assessment of the ferrous/non-ferrous nature of a target using multi-period rectangular waves by measuring X when this target component is maximized during a particular period of the multi-period rectangular signal. No equivalent such period occurs in a VLF system. See Chapter 2.9 for more information on Minelab’s BBS and FBS ferrous target processing. This results in greater accuracy of
discrimination at greater depths."

And further:

"As stated, these metal detectors produce many transmit frequencies simultaneously (see fi gure 3). Thus, it is easy to extract high frequency, medium and low frequency components for accurate target time constant discrimination (see 1.1.3)."

Square wave transmission and processing provides a given number of odd harmonics as can be seen here:

http://www.allaboutcircuits.com/vol_2/chpt_7/2.html

Bruce Candy expanded on that capability by using multi-period rectangular waves. Therefore using a frequency domain instrument such as an oscilloscope you "could" measure the time from one rising edge to another of the various rectangular waves being transmitted, and via 1/T derive a frequency. And because there are multi-period rectangular waves you could come up with various "frequencies". But all of this misses the true nature of of how this detection system works. And those who know better are trying to obfuscate how this technology works by stating it only operates on certain frequencies.

It is more of a hybrid system that doesn't fit neatly into either category, a messy marrying of VLF and PI. It is like a PI system that doesn't need to turn off the transmit signal in order to make a measurement. And on top of that it is like a hybrid PI system that simultaneously transmits and processes pulses of various widths at the same time to better identify high & low conductivity targets. But PI's for the most part look at decay times, they haven't to this point been able to extract accurate identification information.

Bottom line, for years reading multiple forums, this system correctly identifies targets at depth in difficult soil better than any other consumer based detector technology available. The reported finds speak for themselves and it's why Explorers/E-tracs command the price they do. The market confirms that this technology is worth the price being paid for it. Otherwise they would sit in the warehouses and stop being manufactured.



MajorBeep

 

[Carl-NC]

Well your wildest dreams have come true, some 100 hundred years ago of course. Audio transformers, both of the auto-transformer and isolation types conduct multiple frequencies at the same time. As well as the voice coils of typical loudspeakers & headphones in use today.

Yes, two excellent examples of a single coil handling multiple frequencies.

Which brings me to my next point. FBS & BBS are NOT frequency domain detectors, they are time domain detectors.

Sorry, this is incorrect... BBS & FBS are frequency domain. So are CZ's, and DFX.

This is why Minelab choses to use only one frequency at a time to induce it into the soil by itself, regardless of the capabilities of the circuitry capacity to examine and isolate the square wave and it's time freq difference.

X-Terras transmit only 1 frequency at a time. Not so with BBS/FBS... they are simultaneous. So are CZ's, and DFX.

If it were possible to isolate all these differing freqs in one coil and use them effectively then there would be no need for different coils operating at different frequencies.

Unless you wanted to sell more coils!

A quick scope hookup of a cz or White's 2-freq or Sov multi quickly dispells the notion that multiple freqs are being administered or transmitted at the same time.

Have you done this? I have. It proves just the opposite, that multiple frequencies are being transmitted at the same time.

And yes, in a rather distorted way even old field coil speakers were capable of carrying multiple freqs, but again not directly.

Oh, yes, very directly!

- Carl

 

[MajorBeep]

Here is the real time capture of a spectrum analyzer of a Fisher CZ, the 5kHz & 15kHz signals are plainly evident.



Next from Bruce Candy's white paper the figure clearly showing that the detectors use time domain analysis, not frequency domain. Also shown in this figure the rectangular waves being transmitted AND how they are processed on the receive side. And let's be clear, an individual who is a professor with a PhD in Physics & Applied Mathematics is NOT going to present a white paper and state something that would leave himself open to professional ridicule.



Lastly, an example of how multiple frequencies are being derived from multi-period rectangular waveforms. The key is to gate the receiver on the rising edge of the waveform. Being that the waveform is being transmitted and received by the same device, it is a completely synchronous process, where the gating times can be changed on the fly depending on results derived from the return signal. I have designs that have been in commercial use for 10+ years, that use just such a transmission technique, but not related to metal detection technology.

Therefore....the technique works, it works well, and I have proven it in my own designs.



MajorBeep