PI and VLF combo detector

[Twapster]

Hi Guys, just throwing it out there...why is there not a combo detector? A VLF weighs bugger all, why would it not be possible to attach the mechanics of a VLF on say for eg: an older SD series and then have a good dual purpose machine that can discriminate and pinpoint, and nail deep gold nuggets?

Is the coil mechanism different or are they the same type coils. You could just switch between machines. Must be a reason why this is not a common modification. Would love to know if there's a reason why its not done? Anyone know..

 

[Ben78]

Coils are very different

Minelab FBS is a hybrid VLF with PI elements although users don't get to make a choice between the two.

A VLF weighs bugger all, just take one with you!

 

[Twapster]

Sorry Ben, but swinging 2 detectors is not my cup of tea, and i'm not about to walk 4km back to the car to get "the other detector"

The 6 inch DD coil on my Xterra isn't that big, must be a coil maker out there that can incorporate both. Unless you say the metal in one coil affects the workings of the other coil if u put both together...no idea but that's prob the only reason why you couldn't run a VLF and a PI with one "supercoil" so to speak.

 

[joe]

Sorry Ben, but swinging 2 detectors is not my cup of tea, and i'm not about to walk 4km back to the car to get "the other detector"

The 6 inch DD coil on my Xterra isn't that big, must be a coil maker out there that can incorporate both. Unless you say the metal in one coil affects the workings of the other coil if u put both together...no idea but that's prob the only reason why you couldn't run a VLF and a PI with one "supercoil" so to speak.

Hi mate, as Ben said two different technologies. PI uses 100 cycles per second and VLF close to 1000 per second.

 

[Twapster]

Joe i'm not saying they aren't different. A switch to go from one to the other would fix that?

 

[joe]

As a multifunction next generation detector its certainly doable. Technology is constantly changing with more capability/functionality/application and size. It has to do with market share and demand just like smart phones these days that have more power/capability than your 3 year old desktop. What would be the return on investment of this next gen detector since we already have very capable machines out there?

 

[KarlS]

From electronics point of view there is no technical reasons why such a dual detector could not be designed and produced. But you would probably pay double for it. Mind you, the PCB and the electronics on 5K detector are worth less then 50 dollars.
Karl

 

[Twapster]

That's what I mean, One could put together an old exterra and an sd series, and come away with an Under 2k machine that can do pretty much anything. Or lets say a GPX 5000 and a switch to "VLF" mode. No need for the "second detector"

Of course manufacturers will be reluctant to combine them as they can sell 2 separate products. In terms of capable machines, how does the GPX 5000 discriminate...I didn't think it did. The VLF will give me a -8 signal on iron and a +10 for gold. Anyway just throwing it out there as it would be a good mod on two older PI and VLF detectors if it was possible, combining the best of both technologies.

 

[KarlS]

What I meant was it would not be difficult for manufacturer to do it from the scratch. Actually quite easy as they got VLF and PI old design are hand. But to DIY would be very difficult, mainly because of coil.
Karl

 

[Twapster]

Hey Karl, yes ive heard about the DIY detectors. Might be an interesting project for me. I've also seen the DIY coils. Just electronics not my strong point but ill give anything a go. Thought it might be easier to buy an old SD and add my Exterra to it somehow!

 

[KarlS]

Yes, you can forget about kit detector, even the cheap Chinese one work better. I know, I build one long time ago. Your idea of marriage SD and Xterra is interesting one and could be doable. But and big but is the coil. You see the XTERRA uses microprocessor in the coil that acts as preamplifier for received signal and also sends code to the main processor in the control box. Without the correct code your XTERRA will not recognize the coil. I'm not sure about SD I think it works in similar fashion. Even if you design coil that would be suitable for both detectors, it would not work.
So you would have to keep swapping the coils and the would defeat the purpose of whole exercise.
Karl

 

[Twapster]

Sounds like its all down to the coil. Anyone out there build coils? I will check with a friend who may be able to advise.

 

[GOLD Billyen]

Hi Guys, just throwing it out there...why is there not a combo detector? .

Thanks Twapster. What a great question! Seriously, I was just about to ask it myself. I think me being a newbie means I'll ask the "dumb" question that's actually smart. I try to re-read the forums so I don't ask a question that's been answered but, this is a good one.

I've read a ton on detectors and I'm watching every video out there. If the PI and VLF don't mess up each others signal than it makes sense. Do they? Everyone says PI is the way to go but VLF sometimes picks up something a PI may have missed.

I saw a video were the Eureka got a signal and the 5000 missed it. I don't know if it was a set-up but, that scared me a bit off a 5000 purchase. I'm seeing a lot of videos that are done by pro "this brand" and seem to ALWAYS do better against the other brands they are testing. I assume it just staff or re-sellers doing them.

I don't see why I need to carry 2 detectors around when some guy in a lab can make 1 that does both.

If we can put a man on the moon they can make a lightweight, nicely designed PI/VLF detector. I'd pay more for that. I just don't want to walk over gold.

 

[loamer]

This excellent article by White's may be of assistance. http://www.whiteselectronics.com/the-hobby/knowledge-base/field-reports/how-metal-detectors-work

You have asked a good question but the answers I am getting are no, it can't be done because of the two differing types of technology, including the VLF coils are different from the PI coils. As an example, my Minelab Xterra 70 cannot run the coils I run on my Minelab 4500 and visa versa. Also, most manufacturers PI coils are interchangeable between brands (the TDIs are an example), don't know if the same is true with VLFs.

As for home made coils - there are a few people who make them, I don't of any who advertise - the good ones are quite expensive given they are hand-made (wiring, fibre glassing etc) The great thing with good quality home-made coils is the toughness of the coil (open a broken manufacturers coil one day and see how actually flimsy they are inside) and the high level of balance - that is the centre is very accurate which if you are digging through ironstone/calcrete you need to know where the centre is to avoid digging bigger holes than you need.

 

[joe]

DIY - Hybrid VLF/PI Technology.

http://australianelectronicgoldpros...tector/working-on-an-hybrid-vlfpi-technology/

 

[Twapster]

Tks for the links guys, Joe....the electronic forum a little over my head! However I guess people are trying to develop a Hybrid. Good info on PI vs VLF Loamer so tks for that. Ill try read it 5 times so it sinks in. My bet is that either someone will do it one day, or someone else will invent a Gold only detector. Wouldn't that be nice! Its bound to be available in the future...hopefully in my lifetime.

 

[Ben78]

PI uses 100 cycles per second and VLF close to 1000 per second.

Very inaccurate information although not particularly harmful.

Current marketed VLF detectors operate at 2500 cycles per second to 71000 cycles per second and use a Sine wave to transmit signal. The coils typically have a much higher number of finer gauge windings than a PI coil and also must be balanced on an individual basis. On a DD this is done by moving the two coils in relation to each other and in a concentric coil it is done by adding a third small coil to balance the two coils against each other.

PI Detectors run maybe as low as 100 pulses per second and as high as ~3200 pulses per second (Whites TDI). I am not sure what the GPX runs at but I have seen figures as high as 5000 although I personally have not scoped my GPX. PI detectors transmit a square wave pulse and then wait a set period or multiple set periods to take a reading/s of the residual current in the coil (a coil will 'hold' onto a current when it is switched off). Coils on PI machines are much less sensitive to variances in inductance and balance in the case of DD coils. Whites 'Dual Field' coil, although it looks like a concentric is actually a dual mono.

I think it is possible to incorporate a Induction Balanced VLF detector and a PI detector into one machine and one coil but there is going to be a massive tradeoff. Lets put it this way, would you be happy if your new top of the line dual mode detector costing many thousands of dollars was about effective as a chinese knockoff VLF or as a 100us delay PI machine? Not to quote hard numbers but I think that would be a starting point for the crossover of efficiency.

That thread Joe leaves a funny aftertaste... a lot of it is very interestingly anti-minelabesque I'd be taking it with a large grain of salt.

 

[joe]

PI uses 100 cycles per second and VLF close to 1000 per second.

Very inaccurate information although not particularly harmful.

Current marketed VLF detectors operate at 2500 cycles per second to 71000 cycles per second and use a Sine wave to transmit signal. The coils typically have a much higher number of finer gauge windings than a PI coil and also must be balanced on an individual basis. On a DD this is done by moving the two coils in relation to each other and in a concentric coil it is done by adding a third small coil to balance the two coils against each other.

PI Detectors run maybe as low as 100 pulses per second and as high as ~3200 pulses per second (Whites TDI). I am not sure what the GPX runs at but I have seen figures as high as 5000 although I personally have not scoped my GPX. PI detectors transmit a square wave pulse and then wait a set period or multiple set periods to take a reading/s of the residual current in the coil (a coil will 'hold' onto a current when it is switched off). Coils on PI machines are much less sensitive to variances in inductance and balance in the case of DD coils. Whites 'Dual Field' coil, although it looks like a concentric is actually a dual mono.

I think it is possible to incorporate a Induction Balanced VLF detector and a PI detector into one machine and one coil but there is going to be a massive tradeoff. Lets put it this way, would you be happy if your new top of the line dual mode detector costing many thousands of dollars was about effective as a chinese knockoff VLF or as a 100us delay PI machine? Not to quote hard numbers but I think that would be a starting point for the crossover of efficiency.

That thread Joe leaves a funny aftertaste... a lot of it is very interestingly anti-minelabesque I'd be taking it with a large grain of salt.

True Ben, hypothetical comparison to highlight they are two completely different technologies , thanks mate

 

[the duck]

some info that may help

http://www.whiteselectronics.com/the-hobby/knowledge-base/field-reports/how-metal-detectors-work

 

[GOLD Billyen]

This excellent article by White's may be of assistance. http://www.whiteselectronics.com/the-hobby/knowledge-base/field-reports/how-metal-detectors-work

Thanks Loamer,
(a good read)

I think what the OP and me were thinking is a bit simpler. Think of 2 designs.

1.
Dumb-ass Design-You duck tape a VLF and a PI detector together. (I'm still to have some tell me if the 2 detectors will interfere with each other.)

2.
Smart design- You have 1 rod with a 2 pronged folk at the end. Like this -----< . (Nice drawing eh?). with x amount of space between the coils. Then you have 2 separate read out boxes on top or 1 that cleverly shows what you are looking at.

If designed well, you could even get the 2 machines to talk to each other. PI says.. "Look what I found at 7 cm?" VLF says "Ya..me too, looks good...lets tell the boss." or VLF says... "I found this at 5 cm but it's small." The PI says.."Ya, I saw that too but, I think it's a piece of rusted copper. Don't worry about it." . Crude but, do you get the idea?

I'm sorry but it doesn't seem hard to me to make one-if we can put a man on the moon etc. I can go buy a VLF and a PI now and do it with both arms. Why should I have to?