Basic Home Testing

[B^C]

Hi Guys,

As Promised,

This is a simple test & can be done by everyone at home with good results & repeatable results which is the most important thing. Later on if anybody wants it i will show how to get some great signal shots from various targets, gold nuggets etc which is a lot more detailed in approach.

I have included a picture of the coil voltage signal from a very basic circuit i put together to demonstrate this home testing proceedure & have compared this to a GPX4500.

The Tests are to show the strength of the magnetic field at the target & where & what creates the strongest magnetic field in realworld conditions.

The tests are done in highly Magnetic Soil as you will see from the Magnet picture & this is the soil used.
These are UNDERGROUND tests & the target is only a piece of 3/8" Ferrite Rod about 3/4" long with 10 turns of small insulated circuit hookup wire Wound on one end with the ends of the wire about 18" long out of the test cell.
For ease of showing the signal strength at the target it is buried only about 3" under the soil, this is bad soil though. The metal detector coil is about 2" above the soil.
The O-scope settings are the same for both shots, Probe Attenuation X1, the probe is connected to the ferrite cored coil wires.

As you will see it is the Flyback that creates the strongest magnetic field & is the reason i have been on about it. This also verifies Aziz's LTspice Sim & what he mentioned about this also.

Where not looking at frequency or anything else just the strength of the magnetic field at the buried target that Induces the small ferrite cored coil & the signal produce by this.

The 4500 is using higher voltage than what i have on this little circuit & hence the target signal is a little under the 4500 but not much & especially considering this basic circuit cost me about $20 & took me 1hr to slap it together & it can take a lot more power which i will do later, it's not to bad.
The secret is getting more from the circuit for less power input, which is another story later & is very doable.

The scope screen has some scratches on it & these look like small spikes, the signals are actually very clean with NO noise filtering at all.

When i get my Main circuit totally finished i will post some pics of how it operates & how it blows the 4500 out of the water--totally different way of going about things than this but it works out of sight & you may be interested..

The first O-Scope picture is the basic circuit coil voltage for the test.

Some comments would be good--good or bad!

[homefire]

I have NO idea what your trying to say here!

[B^C]

Gday homefire,

BASIC HOME TESTING!

Not sure how to write it out any easier?

Basically it is looking at the magnetic field strength "at a Target" underground from a Pulse so you can determine if your detector is any good.
If you can't induce the target to a respectable level then throw it in the trash & start again because you have a fizzer not a detector.
From a std basic setup you can do realworld comparitive testing at depth to see what your detector or circuit is like before & after modifications.
Most detectors besides ML have a pulse as strong as as a 104 year old man so this will test how good your detectors pulse is at punching into the ground & to the targets.

Or you can test in air instead of underground & find what is laying on top of the ground with your detector if you like, there's a big difference.

The GPX4500 is a good benchmark but maybe there not as good as they should be for the money.

[Tinkerer]

It would be interesting to see the difference between the Flyback response with the sensor always at the same distance from the center of the coil and buried at different depths, starting with surface to maybe 10 - 15".
How much difference can you see between the air test and the buried test?
These are pictures of the voltage. How about pictures of the current?

On your picture of the setup, the Flyback is a clean spike. On the pictures in the soil, the spikes do not look the same. Could you post pictures of the Flyback with the scope set at 1 or 2 uS/div. ?

Tinkerer

[WM6]

Gday homefire,

BASIC HOME TESTING!

Not sure how to write it out any easier?

Basically it is looking at the magnetic field strength "at a Target" underground from a Pulse so you can determine if your detector is any good.

As I understand this is only soil penetrating test and say nothing about MD sensitivity? Or I am wrong?

[B^C]

Gday Tinkerer,

Yes, that's what i had in mind, i will add some more shots today of what you mention & more, all this is just a preliminary warm up.

I will not add shots of the GPX4500 current etc though as this is rightfully Mr Candy's business as we can all respect & is the reason i just knocked up a quick basic circuit with similar signals for these tests.
I just added the 4500 signal picture to show we are looking at something very similar for the testing which is a good benchmark seeing they are the best there is.
In saying this i have no wish to copy any of there technology but as an educational tool it's worth looking at, what's there's is there's, best to beat them by being different & rightfully so.
In fact i have never seen a Minelab Circuit board & have no wish to cheat, i like doing things the hard way--the Aussie way!
I have a great ML modification but even that's a Plugin & can be done without even taking the control box apart.

I believe there is a better way which i will get onto later on when i have my main circuit complete. Well i have it complete but i am still having an issue with just one component.

WM6,

Yes & No, best to start at the first step with getting a pulse into the soil & then work from there to have a closer look at things, sensitivity & thought's on what's required will be tested as well. I have found many things that are quite interesting & will share the results as we get to them but first things first.

[moodz]

Hi Guys,

As Promised,

This is a simple test & can be done by everyone at home with good results & repeatable results which is the most important thing. Later on if anybody wants it i will show how to get some great signal shots from various targets, gold nuggets etc which is a lot more detailed in approach.

I have included a picture of the coil voltage signal from a very basic circuit i put together to demonstrate this home testing proceedure & have compared this to a GPX4500.

The Tests are to show the strength of the magnetic field at the target & where & what creates the strongest magnetic field in realworld conditions.

The tests are done in highly Magnetic Soil as you will see from the Magnet picture & this is the soil used.
These are UNDERGROUND tests & the target is only a piece of 3/8" Ferrite Rod about 3/4" long with 10 turns of small insulated circuit hookup wire Wound on one end with the ends of the wire about 18" long out of the test cell.
For ease of showing the signal strength at the target it is buried only about 3" under the soil, this is bad soil though. The metal detector coil is about 2" above the soil.
The O-scope settings are the same for both shots, Probe Attenuation X1, the probe is connected to the ferrite cored coil wires.

As you will see it is the Flyback that creates the strongest magnetic field & is the reason i have been on about it. This also verifies Aziz's LTspice Sim & what he mentioned about this also.

Where not looking at frequency or anything else just the strength of the magnetic field at the buried target that Induces the small ferrite cored coil & the signal produce by this.

The 4500 is using higher voltage than what i have on this little circuit & hence the target signal is a little under the 4500 but not much & especially considering this basic circuit cost me about $20 & took me 1hr to slap it together & it can take a lot more power which i will do later, it's not to bad.
The secret is getting more from the circuit for less power input, which is another story later & is very doable.

The scope screen has some scratches on it & these look like small spikes, the signals are actually very clean with NO noise filtering at all.

When i get my Main circuit totally finished i will post some pics of how it operates & how it blows the 4500 out of the water--totally different way of going about things than this but it works out of sight & you may be interested..

The first O-Scope picture is the basic circuit coil voltage for the test.

Some comments would be good--good or bad!

Hi BC .... I would point out that your sensor does not detect magnetic fields ... it detects changing magnetic fields. You are not detecting some huge magnetic field during the flyback ... it is the rate of change you are detecting. Sit a permanent magnet over your detector ... and of course you will not sense the magnetic field ... spin the magnet with a drill and you will. If you were using a hall effect or squid type detector ... then you would see the actual magnitudes of the magnetic flux.

Regards,

Moodz.

[B^C]

Gday Moodz,

Yes, i was working on the principle that a changing magnetic field is in fact still a magnetic field, if it were not there would be no induction?

I have Hall detectors connected as well & will show some shots with the signals from these as well.
Your comments are appreciated.

[moodz]

Hi BC ... thanks ... try connecting a high intensity LED directly to your sensor coil .... red or orange ... these have a frequency response above 10 Mhz as they are usually made from gallium arsenide doped substrate. An optical PIN diode is used to receive. The optical response gives an approximation of a real target response .... and provides optical isolation from the sensor coil. Some types of optocouplers are suitable also.

Regards,

Moodz.

[B^C]

Hi Moodz,

I have taken a shot of the output directly from one of my hall detectors which is now buried, the pulse is from the basic test circuit above.
It clearly shows the magnetic field, it tells a great story also---well to me it does, hahaha!
See what you think.

[moodz]

Well ... that is interesting ... there seems to be a sudden sharp flux reversal at flyback. Is this your circuit or 4500?

Regards,

moodz.

[B^C]

Gday Moodz,

I thought you would find it as interesting as i have.
The picture is from the basic circuit i put together for the testing purposes.
No other pictures of the 4500 will be added as mentioned previously, just that first 4500 comparison picture at the start of the thread.

The 4500 does however show the same magnetic field characteristics as will anything with a good Transient spike.

There seems to have been a lot of misconceptions about Pulsed Induction, i would hope to be able to clear some of it up by the end of this thread.

[moodz]

doh ...i liked the 4500 videos ..... probably as close as I will ever get to one

[Ray-NM]

It looks like your last image shows some hysteristes by way of the droop of the signal. I am probably wrong but that is wat it looks like to me. storage in the magnetic soil?
RayNM

[wyndham]

BC, I am wondering about the signal from a target where we'll say is a nugget that has the probe attached at 2 point. Is the signal coming from the target the result of the tx pulse or the flyback or the combo of the 2?
If you made a hall effect target where a current was going through the target and monitored on the oscope and a second set of probes attached 90 deg to the current and this was routed to a second oscope screen, would this give a more measurable way of seeing the TX pulse or is this what you are getting from your target.
On a side note is an eddy current in a target a way for the target to dissipate the tx pulse energy and the only way is for to create an orderly field to radiate back the tx pulse.
Just treading in deep water Wyndham