Delta Pulse

[ivconic]

in theory PI mashine is really more sensitive to ferrous metals, not to gold. it is normal. let gurus in this forum to give you more detailed report on this matter... if you so need in the theory and patents... mine english is not so applicable for longest extensive structured cool&hard classified answers you could be hope. i am more a practician than theorist...

good luck

Explanation is quite simple;
metals with better magnetic features are presenting better targets.

[kt315]

Re: depths on various metals


Posted by: Eric Foster (---.ipt.aol.com)
Date: May 26, 2000 01:26PM


Hi Jeff,
It is the characteristics of both the object and the detector that gives this strange result. Dealing with the object first. One of the fundamental laws of electromagnetics is that any change in equilibrium is resisted. If you change a magnetic field, as happens at the end of the TX pulse, then eddy currents will flow to try and maintain the field at its original value. In the absence of a metal object, the coil will produce a very high voltage in an attempt to jump between the ends of the coil and maintain the field. Hence the back emf. If there is a metal object, then a small portion of the field is coupled to the object and on field removal, currents are set up in the object to try and maintain this local field. For a metal with a relatively high resistance (nickel) the emf necessary to set up the current to maintain the field is higher than for a lower resistance metal (quarter). This results in a higher signal initially for the nickel, but which decays quicker due to the resistive losses. For the quarter, the initial signal amplitude is lower but due to the lower resistance, carries on for longer. It’s the same principle that if you have a 1K resistor, you will need 1V to get 1mA current, whereas for 100 ohm resistor, you only need 0.1V. I have tried to illustrate this in the diagram below. The two curves represent the decaying signals from a nickel and a quarter but it would apply to any objects of different conductivities. The hypothetical nickel and quarter are at the same distance from the coil and, for the reasons above, the nickel starts off at a higher amplitude. If your sampling window is at A (say 15uS) then the nickel signal is greater than the quarter, which translates into a bit more range. If you move the sample window to B (say 75uS), then the reverse is the case as the nickel signal is decaying faster. Move the sampling window to C (say 150uS) then you will only detect the quarter, although not at the same range that you would at B or A. On the Deepstar, the sampling window is moved by means of the REJECT control and that is how you can reject pull tabs and bits of foil. You will also lose thin section rings and nickels but at least it gives the user some adjustment for different conditions and objects. Most users will keep the control set at the shortest pulse delay to get maximum sensitivity and range for all objects and this will result in nickels and the majority of rings being detected at greater ranges than copper, or silver coins.
The second factor is the width of the transmitter pulse. I mentioned in an earlier post that the TX pulse should be longer than the object time constant, otherwise maximum signal will not be obtained. Most beach hunters want to find gold rings primarily and coins or silver objects are of secondary interest. Having a longer TX pulse than necessary is wasteful of transmitter current and the 100uS of the Deepstar is about right at the pulse frequency used to give good range on most rings and acceptable battery life. For the more conductive coins and particularly silver ones, the TX pulse is a bit short, hence a further small reduction in range on top of that due to the object characteristics.
Eric.

Identifying Nails


Posted by: Eric Foster (---.ipt.aol.com)
Date: April 1, 2000 04:46PM


Some PI detectors have the capability to identify a proportion of nails, wire and pins, but this depends on several factors. The foremost is the response speed of the detector, with detectors having the faster response performing better. Nails, being ferrous, give a disproportionally large signal for the amount of metal present. This is because the signal is made up of two components, a conductive one which is due to eddy currents generated in the metal, and a magnetic component which is due to the coil field magnetizing the iron and the magnetization decaying relatively slowly at the end of each field pulse. The magnetic component of the signal is greatest when the lines of flux from the coil are parallel to the axis or length of the nail and a minimum when the flux is at right angles to the nail. This can be tested by passing a nail vertically under the centre of a PI search coil. The signal will be a maximum when the nail is under the centre of the coil in the line of the flux. Turn the nail through 90 degrees and pass it under the coil. the signal will now be a minimum under the centre of the coil but there will be a maximum at each edge where the flux is turning and is again parallel to the nail. In this orientation you get a weak signal under the centre of the coil which is due to the conductivity. The majority of nails etc tend to lie horizontally in the ground with the result that this effect can often be used to identify them. Bury a 2in nail horizontally in the ground at a depth of 6in. Scan the search head over it and listen carefully to the signal. If the signal has two peaks, do a second scan at right angles to the first and listen for a single, but much weaker response. Compare this with a coin buried horizontally, where there is just one single peak whichever way you scan across it. This method does rely on most coins and rings lying horizontal, as also do most nails. It falls down when a nail is vertical, when it will sound like a coin and also for a vertical coin which will sound like a nail. If the detectors response time is rather slow, then it may not be possible to distinguish the two peaks as they will blur into one. However, it will be a broad signal spanning the width of the coil in one direction and a weak one in the other, so with care, identification is still possible but it takes much practice. Coins and rings by comparison always have a sharp cut off and a nice localised response under the coil centre. Below is a sketch that illustrates the effect of a horizontal nail.
Eric.

[ivconic]

KT315 you are pointing on very good elaboration! Very good and true.
But essence of the problem is metal magnetic preference. Simply as that.
Better metal magnetic preferences - better response.
Gold is not having good magnetic features - tough to be detected easy and presents tough target. No matter; at PI or I/B.
Rising frequency will rice good chances to better gold detection - but also to even better iron response... Simply can not detect Au without Fe detection in same "package". But than that's good disc circuitry is for - to mark out Iron (and ferromagnetics) from diamagnetics and paramagnetics. Better designed disc circuitry - better repression (rejection) of unwanted components in received signal.
So that's why i said that magnetic preferences and features are usually distinguishing factor.
Regards!

[Belief]

Hi all

Which one is better, delta pulse or pulse strar II ?

are there anybodys to have PCB ?


Thanks....

[kt315]

Hello


I attached 1.zip printable Pcb for delta pulse .

Best Wishes
Erol Ünal

Erol, were your PCB's done by industrial way? how much a price you ask for one?

[ivconic]

Hi all

Which one is better, delta pulse or pulse strar II ?

are there anybodys to have PCB ?


Thanks....

Pulse Star II is generally better. And more expensive.
DP is good cose it can be easy made in homemade arrangement..
You have few nice versions of pcb on these forums. PCB for PS II i haven't seen yet here..

[kt315]

pulse star has TWO levels of protection from coping:
- Black Box way. epoxy-encapsulated block with PCB's you are not able to open without full damage it.
- two PIC chips with code protection.

you even have NOT ABSOLIUTELY a chance to learn pulse star. we say about OPEN project here, DP is of.

[ivconic]

pulse star has TWO levels of protection from coping:
- Black Box way. epoxy-encapsulated block with PCB's you are not able to open without full damage it.
- two PIC chips with code protection.

you even have NOT ABSOLIUTELY a chance to learn pulse star. we say about OPEN project here, DP is of.

I had version without "black box" on service. Not an issue.
But real issue are those 2 PIC's ! Protected!

[kt315]

I suspected PS is without Black Box, PS-II with it. or I am not right?

[ivconic]

No i had PSII Pro. It is without black box.
Wait...i will find some photos...

[ivconic]

Yes it was PSII Pro..

[bilneo]

Hi all !!
First many thanks and regards for you all Geo, Ivnovic, kt315 carl...
I have Build Delta pulse yesterday but it works with a very poor sensibility and it's always making a continues loud sound from head phone though TRSHOLD is at the MINIMUM!! I can't make it silent!! (when TRSHOLD is at maxmimum it sound like a sirene)

When i Disconect disk coil nothing changes, the continues sound is always here (loud sound, a rapide tic tac after what come silence when dicreasing TRSHOLD but in my case TRSHOLD is already at minimum but sound doesn't come silent)

When I tried with a 3V battery the sound is adjusted normally and it become silent but with a 9V or 12V battery adjustment are imbossible in minimum. (i tried 12V/2A 12V/4.5A)

I realy don't know what to do, I'm not an electronicien experiment and a haven't an oscilloscope!

many thanks and respects for who can save me!!

[bilneo]

I forget another thing when power supply is 9V led is ON when 12V the led doesn't lights! (i used double face PCB) hop this helps to fix my problem

Regards

[diminute]

Led only is on when the baterry is about 10.5 volts or lower. Is a indicator for when is necessary recharger the battery;

If you don´t have osciloscope you need to verify all voltages. For example, you need to check if you have the correct values for and E-, is I remenber the correct values is V(-) - 1.2 or 1.3

Thanks,

diminute

[bilneo]

thanks diminute for the led informations!!

I cheked the voltage and the +E/-E is about 3.56 V :s I don't know if my NE556 is working correctely, that's what I suspect

Regards