TEFLON MULTI STRAND WIRE

[daverave]

i saw on youtube a person making a star coil...whats the difference in proformance between basket and star coil ???? can these coils give us several inches more depth detection ????

[daverave]

you have general area of all wires 16*3,14*0,2^2/4=0,5mm^2. then, for one wire, you have D^2=0,5*4/3,14=... D=0,8mm.
its enough.

hello kt315....are you saying single wire coil is the best rather than say multi strand ????

[kt315]

hello kt315....are you saying single wire coil is the best rather than say multi strand ????

multi strand is better, but you will get advance if your coil would not be a basket because you get only low sheet copper conductance but not distributed capacitance reducing. also you I do not know why fully ignored a notice of Quaozhi to change one stage preamp to two stage preamp. if you do not remake this way you will not be able to reduce PRIMARY SAMPLE DELAY length, the depth does not grow.

[daverave]

multi strand is better, but you will get advance if your coil would not be a basket because you get only low sheet copper conductance but not distributed capacitance reducing. also you I do not know why fully ignored a notice of Quaozhi to change one stage preamp to two stage preamp. if you do not remake this way you will not be able to reduce PRIMARY SAMPLE DELAY length, the depth does not grow.

i didnt mean to ignore quaozhi but i got so much going on in my head trying to learn all about this technology....maybe i just missed what he wrote about pre amps...why two preamps do they share the overall gain ??? when you say about sample delay length are you talking about sample delay (width) or (position) near to the decay curve ????

[bbsailor]

multi strand is better, but you will get advance if your coil would not be a basket because you get only low sheet copper conductance but not distributed capacitance reducing. also you I do not know why fully ignored a notice of Quaozhi to change one stage preamp to two stage preamp. if you do not remake this way you will not be able to reduce PRIMARY SAMPLE DELAY length, the depth does not grow.

Fast coils only work if the PI has the potential to sample at a lower delay for more sensitivity to smaller targets. On a salt water beach, a 10us delay is about as low as you can go before you start picking up the wet sand as a target. That is why many commercial PI machines that target rings and coins only go down to 15us delay to be minimally affected by salt wet beaches. Up in the dryer sand you can use a delay closer to 10us.

On Carl's Hammerhead design he made almost every parameter variable for educational purposes. The main PPS (Pulses Per Second) rate is variable from 900HZ to 2300 HZ; Pulse Width (PW) is variable from 10us to 75us. The main delay can even be modified down to 8us by altering the value of R42a from 1.5K ohms to 1K ohm. Changing the pulse width has the effect of changing the peak flyback voltage. See his Hammerhead Article figure 22 that a 10us PW produces 120V peak flyback while increasing the PW to 50us produces a 320V peak flyback voltage. The damping resistor value must be optimized for a narrow range of flyback voltage peaks.

To squeeze the most performance, least delay, out of your PI machine, the coil and damping resistor value must be optimized for a very small range of frequency adjustment and PW adjustment. Then the preamp must come out of saturation fast. As KT315 mentioned, making a 2 stage preamp with a gain of 33 in each stage produces a total of 1000 gain but comes out of saturation faster than a single preamp stage of 1000 gain.

Eric Foster made his PI machines operate in the 3000 PPS range with short Pulse Widths so he could damp the flyback pulse very early. Eric also used his high PPS rate to his advantage by integrating about 1000 samples to separate the target signal from random noise by sampling the target in the same place on each pulse cycle. For those interested in learning more about this look up "Lock-in Amplifier" on the web. A function similar to a lock-in amplifier is built into many PI designs that use an integration stage. Instead of using high power pulses, Eric choose to use a lower power pulse that damps earlier but integrated many samples to make up for the lower TX power.

If you have a PI design and use it for seeking the smallest gold targets, you need to sample at the earliest possible time because the eddy currents in small nuggets die off very quickly. Then, you want to eliminate as much capacitance in the TX coil circuit (for mono coils) which included winding wire-to-wire capacitance (Teflon Insulation vice PVC); coil-to-shield capacitance (spacer between coil and shield), coax cable capaitance and length do the damping resistor (need an oscilloscope to optimize this) can be a high as possible to allow the flyback voltage to be damped as quickly as possible. Ideally it should cut off vertically but that is impossible, so making it as close to vertical is based on how much capacitance you can eliminate from the coil and TX circuit which forms a network. Another area to look at is to make sure that the wire itself does not look like a small target with eddy currents being generated in it. That is why stranded wire with strands smaller than AWG32 are important to use in fast coils. Tin-plated stranded wire puts a small resistance between strands and helps prevent eddy currents from being generated in the wire cross section. Litz wire also works but you need to clean the insulation off all the strands on each end of the coil so all strands operate in parallel and operate like the equivalent AWG wire size.

Bottom Line...there are many variables but you need to adjust or alter them to push your design in the same direction if you want to optimize your PI parameters and coil for particular target types.

I hope this helps?

bbsailor

[kt315]

seems you are do not reading all topics in forum and do now wish to use Advanced Seach knob ignoring all possibilities of the forum engine... it is a problem... I mean... look in attach diagram.

http://www.geotech1.com/forums/showt...t=stage+preamp

altra told (By The Way, all geotechers are ABSOLIUTELY in course of Moreland's hammerhead new project, but somebody are yet sleeping. its very grievously)

The key to this design is the amps don't go into hard saturation. Therefore faster settling time and recovery.

The schematic you are looking for is here-
http://www.geotech1.com/forums/showthread.php?t=15732

[daverave]

Fast coils only work if the PI has the potential to sample at a lower delay for more sensitivity to smaller targets. On a salt water beach, a 10us delay is about as low as you can go before you start picking up the wet sand as a target. That is why many commercial PI machines that target rings and coins only go down to 15us delay to be minimally affected by salt wet beaches. Up in the dryer sand you can use a delay closer to 10us.

On Carl's Hammerhead design he made almost every parameter variable for educational purposes. The main PPS (Pulses Per Second) rate is variable from 900HZ to 2300 HZ; Pulse Width (PW) is variable from 10us to 75us. The main delay can even be modified down to 8us by altering the value of R42a from 1.5K ohms to 1K ohm. Changing the pulse width has the effect of changing the peak flyback voltage. See his Hammerhead Article figure 22 that a 10us PW produces 120V peak flyback while increasing the PW to 50us produces a 320V peak flyback voltage. The damping resistor value must be optimized for a narrow range of flyback voltage peaks.

To squeeze the most performance, least delay, out of your PI machine, the coil and damping resistor value must be optimized for a very small range of frequency adjustment and PW adjustment. Then the preamp must come out of saturation fast. As KT315 mentioned, making a 2 stage preamp with a gain of 33 in each stage produces a total of 1000 gain but comes out of saturation faster than a single preamp stage of 1000 gain.

Eric Foster made his PI machines operate in the 3000 PPS range with short Pulse Widths so he could damp the flyback pulse very early. Eric also used his high PPS rate to his advantage by integrating about 1000 samples to separate the target signal from random noise by sampling the target in the same place on each pulse cycle. For those interested in learning more about this look up "Lock-in Amplifier" on the web. A function similar to a lock-in amplifier is built into many PI designs that use an integration stage. Instead of using high power pulses, Eric choose to use a lower power pulse that damps earlier but integrated many samples to make up for the lower TX power.

If you have a PI design and use it for seeking the smallest gold targets, you need to sample at the earliest possible time because the eddy currents in small nuggets die off very quickly. Then, you want to eliminate as much capacitance in the TX coil circuit (for mono coils) which included winding wire-to-wire capacitance (Teflon Insulation vice PVC); coil-to-shield capacitance (spacer between coil and shield), coax cable capaitance and length do the damping resistor (need an oscilloscope to optimize this) can be a high as possible to allow the flyback voltage to be damped as quickly as possible. Ideally it should cut off vertically but that is impossible, so making it as close to vertical is based on how much capacitance you can eliminate from the coil and TX circuit which forms a network. Another area to look at is to make sure that the wire itself does not look like a small target with eddy currents being generated in it. That is why stranded wire with strands smaller than AWG32 are important to use in fast coils. Tin-plated stranded wire puts a small resistance between strands and helps prevent eddy currents from being generated in the wire cross section. Litz wire also works but you need to clean the insulation off all the strands on each end of the coil so all strands operate in parallel and operate like the equivalent AWG wire size.

Bottom Line...there are many variables but you need to adjust or alter them to push your design in the same direction if you want to optimize your PI parameters and coil for particular target types.

I hope this helps?

bbsailor

Yes thats a great help to me...gives me alot to think about...tell me does the (sample pulse width make much difference to depth) ???? the 2 amp design mentioned by the other guys makes great sense but to do that i would have to design my own circuit board...as i dont think any of silver dog's pcb's are designed for that 2 amp modification....just got to get all your information into my head so i can understand.

[daverave]

ive been trying to find out about this lock in amplifier...is it a simple circuit or difficult to make...can you show any sort of diagram that shows this in a pi detector...has anyone on this forum incorporated this into a pi design ??? it sounds interesting if noise levels can be reduced by this lock in amplifier.

[bbsailor]

Dave,

The TX current is based on the coil inductance divided by its total TX circuit resistance which gives the coil Time Constant (TC). This includes the DC resistance of the coil; the coax resistance of both conductors; the MOSFET on-resistance. This number forms the coil circuit Time Constant and shows you how much of the total potential coil current is allowed to rise with one, two or three time constants. A 300Uh coil that has 5 ohms total TX circuit resistance has a 60us TC so that in one TC pulse width (PW) the current rises to 63% of the total maximum which is 12V divided by 5 ohms or 2.4 X .63 or 1.512A. Increase the PW to 2TCs or 120 us and the current in the TX pulse rises to 85% of maximum current or 2.04A and if you let the PW reach 3TCs or 180us, the current reaches 95% of maximum current or 2.28A. Web search on "inductor time constants" to grasp this concept which is very good to know about how PW affects various target type responses.

Typically, coins respond best to longer TX pulses in about the 180us range. Remember that longer pulses generate more current in the TX pulse, a higher flyback voltage and require a lower damping resistor value to damp the energy in the flyback pluse. Make sure that you use about a 2W to 5W damping resistor to absorb the energy being damped. Some targets like small/medium gold nuggets only need 30us to 50us of TX pulse width to fully stimulate them. Any excess PW is a waste of energy as far as these gold targets are concerned.

Coil designs (inductance and DC resistance) and TX pulse widths, optimum damping resistor values and PI operational parameters should be optimized for specific target types.

This should get you going in the right direction.

bbsailor

[daverave]

is this the type of circuit that you would use in a pulse detector ?????

[bbsailor]

ive been trying to find out about this lock in amplifier...is it a simple circuit or difficult to make...can you show any sort of diagram that shows this in a pi detector...has anyone on this forum incorporated this into a pi design ??? it sounds interesting if noise levels can be reduced by this lock in amplifier.

The concept of a lock-in amplifier is already incorporated in the integration circuit of the Hammerhead (and similar circuits with an integration IC) and many of Eric Foster's designs. This allows lower current TX pulses to be used at higher frequencies and respond about as well as higher power TX pulses operating at lower frequencies.

Coil size and sweep speed determine how many of the PPS rate samples are being integrated when the coil is over a target.

bbsailor

[daverave]

does this lock in amplifier circuit need a dedicated phase chip ?????

[daverave]

i have hammerhead revision D...is this incorporated in this revision ????

[daverave]

my first project that ive completed is the surf pi...i have modified it to work at 1500 hz at 100 ma tx current....my coil is 30 swg single strand copper wire at 5 ohms and 400 uH and ive adjusted it to get the max proformance by trail and error...as im not mathmatically minded and find calculations difficult to work out...i have the hammerhead revision D which ive completed but not done anything with so far.

[bbsailor]

does this lock in amplifier circuit need a dedicated phase chip ?????

Dave,

The function of a Lock-in Amplifier works by having the sample time tied to the TX pulse as it always samples the pulse in the same place and feeds the integrator circuit along with the longer delay to eliminate the Earth's magnetic field. See Carl's explaination in the initial Hammerhead article.

Lock-in amplifiers separate a signal burried in noise because noise is random but by sampling the response of a target in the same window many times, a better signal to noise ratio can be had. However, coils move over the target and have limited time over a target so the TX frequency needs to be high in the 3000PPS range to be effective. A microprocessor controlled PI may already have an integrator circuit which functions like a lock-in amplifier. I mentioned the Lock-in amplifier to show how these signal recovery methods have been incorporated into PI designs to allow better detection of weak signals.

Joseph Rogowski

I hope this helps