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Originally posted by 1843
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Ivconic detects a 1Lt paint can at 1.4m with a 75cm coil.
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I don't remember right but my coil 60x60 has 22..23 turns. Ivconic 75 cm coil has 18 turns. Original coil 1.1 x 1.1 m has 16 turns. Try everythink you want. R6 ir better to be 680Ohm. The Dumper R5 don't make differences at 100Hz. If you want to see if the schematic is the original make a coil 1.1 x 1.1m with 16 turns and try it.
Ivconic detects a 1Lt paint can at 1.4m with a 75cm coil. -
what happen whit your baby d.p?
[quote=1843;48160]Hi,
I read the BANDITO-IMPULSE manual.
My 70x70 coil has 13 turns of 0.7mm wire. What coil-inductance is best for the DP?(between 300-500 uH) For the 70x70 coil how many turns is necessary?
If my DP be able to detect a large object at 3m, it is the best detector for me!
But it doesn't work correctly.
[/quote]
jejejejeejeje
detectomanComment
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Electromagnetic field tester
Hi, yesterday i worked on my Clone PI coil to get full power from it.
For that i used an electronagnetic field tester to measure the field intensity from my coil. I started with more turns than usual and then i made a step by step measure with my EMF, then i took turns by turns off from the coil until, i got the bigger value from the coil.
Now for the people who has made more experiments with coils, what do you think about this way to get the best from the coil.
If this really work, i will do thw same with my Delta Pulse when i get it finish.
regards
Nelson
[QUOTE=detectoman;48234]Originally posted by 1843 View PostHi,
I read the BANDITO-IMPULSE manual.
My 70x70 coil has 13 turns of 0.7mm wire. What coil-inductance is best for the DP?(between 300-500 uH) For the 70x70 coil how many turns is necessary?
If my DP be able to detect a large object at 3m, it is the best detector for me!
But it doesn't work correctly.[/quote]
jejejejeejeje
detectomanComment
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Experimenting is a good way to learn
Nelson,When you do your field strength tests, keep good notes about the results you get with each number of coil turns.A few more factors come into play. Post your results and also post the following additional information.Type of targets that you are seeking (metal type and size)?Distance that your coil can currently detect your desired target? Inside diameter of your PI coil? AWG wire size? Outside diameter of wire, including insulation? Number of turns? DC resistance of coil? MOSFET used to drive the coil? Pulse width range of your TX pulse? TX pulse frequency? Range of sample delay for RX signal (sample time after pulse turns off)? Amplitude of the back EMF spike at both ends of the pulse width range? Length and type of coil lead to control box (example: 6 ft of RG XXX)? Doubling the coil current will only increase the detection range about 10 to 12percent on a PI mono coil. To double the range requires 64 times the amount of current. This means that you will not see a very large difference in detection distance, but you can optimize it somewhat for specific types of targets with coils of various diameters.Experimenting is a good way to learn. bbsailorComment
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EMF detector to measure coil energy field
Hi bbsailor.
Well i agree with you about taking notes of my experiments, so i ll do that next time when i build the delta pulse coil.
My first try with EMF tester was yesterday. I began with a few more turns than normaly used and then i took off turns one by one, measure the EMF and read the field strengh. I really forgot to take notes of this, because it was my first try to see if this way to measure the coils strengh was the righ way to do it.
In conclusion if you said that this is ok, i ll keep trying my experiments with my new coils and of course i ll post my results.
regards
Nelson
Originally posted by bbsailor View PostComment
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Removing Turns: A few things will change
Nelson,When you remove coil turns, a few things wil happen.1. The coil resistance will drop slightly as each turn is removed.2. The coil current will increase slightly as each turn is removed.3. The peak back EMF spike will be less as each turn is removed.4. The induatance will be less as each turn is removed.5. The current ramp up Time Constant (TC) will change as both Inductance and Resistance is changed, TC=L/R (L in uh and R in ohms = TC in us). A pulse width that is 3 TC long will achieve 95 percent of maximum current. You should measure the things I suggested to better understand how your coil is working. Most improvements occur when a few things are changed. Coil turns, coil diameter, pulse width, TX frequency and coil current need to be balanced to achieve good detection depth, a good response from your coil sweep speed and a reasonable battery life.bbsailorComment
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HI Bbsailor !
Give a more dept If increase a amplitude of the back EMF spike at both ends of the pulse width range from 400V to 800 V ???
Give a more dept if PI detector work whit bipolar transmited pulses???Comment
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The amplitude of the back EMF pulse is based on the inductance of the coil (number of turns) and the current at the time of pulse turn off. The TC of a coil is calculated by dividing L in uH by R in ohms. Thus, a 500 uH coil that is 2.5 ohms has a 200 us TC. If the TX pulse width were variable between 200 to 600 us, the current would grow from 63.2 percent of maximum current to 95 percent of maximum current. The amplitude of the back EMF spike depends where on the curve the pulse is trurned off. Longer pulse widths allow the current to grow more and produce a higher amplitude back EMF pulse. You don't want the back EMF spike to go too much higher than the MOSFET voltage rating because the MOSFET is conducting/clamping the spike and the MOSFET will get hot.
The graph below is universal and applies to the current growth of all PI coils. Just measure your coil's inductance and resistance to find your coil's time constant and apply it to the curve below. You must also add the MOSFET on-resistance to the total coil resistance and any series resistors in the coil circuit. You must know the pulse width of your TX pulse to see exactly where on the curve your coil fits.
The Hammerhead 10 inch coil uses 26 turns of AWG 26 wire. The total wire length is 68.06 Ft. which is 2.788 ohms plus the .5 ohms on-resistance of the MOSFET (IRF740) for a total resistance of about 3.3 ohms. 500 uH divided by 3.3 ohms equals about 152 us. The Hammerhead pulse width of 10 to 75 us places the max current at about .5 TC or about 40 percent of max at 75 us. Carl designed the Hammerhead this way to keep the maximum EMF voltage spike below the MOSFET voltage while being sensitive (26 turns) to small targets.
You can see that there is room for some coil inductance and resistance changes to try to get the coil to operate higher on the TC curve for low conductivity targets (like small gold) along with lower delay settings. Make the coil with 300 uH (19 to 20 turns) of inductance (which reduces the EMF spike) and use thinner wire (wire wrap wire with thicker insulation), AWG 30 (5.5 ohms) with a MOSFET that has about 2.5 ohms on-resistance and you have a coil TC of about 37 us. At 75 us the current has almost reached 2 TC of about 86.5 percent of maximum. You can add a series resistor of a few ohms to get the same effect as using thinner wire using the same wire that you have. The only difference will be coil weight.
Where you want to operate on the curve is based on what types of targets you seek. Some types of metal can be fully saturated with eddy currents at lower TX pulse widths (lower TC), while other targets need longer pulse widths (longer TC) to obtain maximum target response.
Do some research on the time constant or decay time for the size and types of metal you seek so you can reverse engineer the coil and pulse width range to be optimum for you desired targets. Remember, one design cannot be optimized for all targets.
I hope this helps.
bbsailorComment
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Hi bbsailor. Very good analysis but i believe that at detectors with large coil and low frequency as Delta Pulse there is not needing so critical timing and coil construction. All that you say are Very Important at small objects (as gold nudget ) where small times are needing . From my experience with different coils and medium objects (always the smaller object for test is a 25 mm coin and the bigger a pc box) there is not big diference if we will change the turns of a coil at 20%.
OK you will tell that the fine tuning makes the difference, but not at big objects.
Regards
Comment
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Delta pulse not working good
Hi Geo.
I finish my delta pulse from Mikron Schematics. I used the same PCB that you and Ivconic used. When i try to run the DP, a tone sound comes from the coil, and nothing from the speaker. Noice control meda some tone changes and intensity on the coil. I measure it with my EMD, and changes of intesity are show and also when i turn noise control to the maximun, damping resistor is getting very hot to the point it get smoke from it. Coil is 406 mH with 5 ohms damping resistor. VD17 led turns on a few seconds after turning the unit off, and then turns off.
No detection at all
What can be wrong?
I ll check diodes if the polarity is ok, dont know what else to check.
In advance many thanks
Regards
NelsonComment
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Hi Nelson. The sound from coil means that 556 works, the oscillator works. Please tell me if you have oscilloscope to tell you what to looking forOriginally posted by nelson View PostComment
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Hi,
My DP sound is like the canary sound and its detection is poor.
The frequency pot influences in that sound.
What is the problem?Comment
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5 Ohm Damping Resistor?????
Nelson,
A 5 ohm damping resistor is wrong! 5 ohms for coil resistance is OK but the damping resistor should be a value between 500 ohms and 1K ohms (depending on the coil, coax length and MOSFET capacitance). Try making this change first...use a 1 watt 1K damping resistor.
bbsailorComment
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Delta pulse not working
Ok Geo and bbsailor.
Yes i do have a small osciloscope (radio shack that connects to PC).
I forgot, the DP has no sound when is on, and when i turn it off, i can hear a very low decresing tone.
I have an anmeter but not conected jet. I dont know if this could show me any signal stength instead the sound that for know is not working fine.
Regards and best Chrismas wishes to everyone on the forum.
Nelson
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QUOTE=Geo;48391]Hi Nelson. The sound from coil means that 556 works, the oscillator works. Please tell me if you have oscilloscope to tell you what to looking for[/QUOTE]Comment
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Problem in stability
Hi bbsailor & Geo,
In my DP when I put the gain pot at the middle or lower
It works stability, But when I increase the gain,it works instability and makes the canary sound.
I checked the pin1 of the IC5 with scope:
when the gain pot is at the mid:
When is higher:
Where is the problem?:confused:Comment
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