WHAT KICKS THE TARGET

[Tinkerer]

A traditional PI provides only a small fraction of the information available in the response of the target.
An IB-PI can give much more information. This is what I have been working on with the TINKERERS IB-PI.
A picture is worth a thousand words, so I will show some scope shots.

The first pix shows the DD coil, sitting on some red clay bricks. On the coil is a transparent plastic box and on the box a steel lug.

The second pix shows the scope with the TX and RX and no target. The TX is about 90uS. The response appears during TX and after TX off. Observe how different the response is to the different targets.

The third pix shows the response of the steel lug.
The fourth pix shows the response of a 0.55gram silver ring.
The fifth pix shows the response of the steel ring.
The last pix shows the response of a 0.5gram gold ring.

The silver and gold rings are nearly the same weight, but, since gold has a specific gravity of about 19 and silver has about 11, the size is different.

The hight of the plastic box is about 30mm, so the targets are close to the coil to make the signal amplitude visible to the eye.

Tinkerer

[Tinkerer]

About the relationship of the Pulse Induction Time Constant TC to VLF frequency

About the relationship of the Pulse Induction Time Constant TC to VLF frequency
What kicks the target, or what triggers the response of the target.
With both types of detectors it is the rate of change in the coil current (di/dt) that generates the response of the target.
With a VLF, the current changes in a continuous manner, but the rate of change is not linear.
The rate of change is equal on the up and down slope of the sine wave, but on the peak and the trough of the wave, the rate of change is minimal.
This means that the target gets excited on the two slopes of the sine wave. The excitation changes polarity each time. The VLF receives the response of the target at the very moment that it is generated in the target.
Attached are 2 pictures of a sine wave of about 3700Hz, a frequency that would be used for deep penetration but not very small targets, and a sine wave of about 10,000Hz, that would give less penetration but make the detector more sensitive to very small targets.
Look at the slope of the sine wave, the rate of change is nearly linear for a good part of the slope. Is the current the same all along the slope?
Now let’s look at the TX pulse of the Pulse Induction detector PI. With each picture I only show one pulse, because of power saving, we place the pulses relatively far apart.
Then you notice that the pulse is not a square pulse. Usually people look at the voltage pulse. However, it is not the voltage that we are interested in, but the rate of change of the current in the coil. (di/dt) The Amps times the amount of turns in the coil, determine the strength of the magnetic field.
The pulses shown is the current wave form. You can see that the rate of change or the slope of the pulse has some similarity with the slope of the sine waves. However, this does not tell the whole story.
The rate of change is highest at the beginning of the pulse, but the Amps are highest at the end of the pulse, just at the point where the current is cut off.
Both pulses have the same duration of about 90uS. One pulse has a time constant of about 150uS, the other one has a time constant of about 16uS. The short time constant reaches maximum current early and then stays there. This is sometimes called a “flat top”.
With the TINKERERS, we take samples during the TX pulse. This means that we sample the response of the target at the same time it is happening, just like the VLF does.
This makes it possible to discriminate iron targets just like the VLF does.
There are other features too. I will try to describe them in days to come.
Tinkerer

[Tinkerer]

WHAT KICKS THE TARGET PART 2

The next 3 pictures show:

The time scale is the same for these 3 pictures, 20uS/div. but the voltage scale varies, so that I can show both channels at once.

#1 The VOLTAGE TX pulse and the Flyback with the RX at the output of the preamp.
#2 The CURRENT TX pulse and the RX
#3 The Mosfet gate TX pulse and the RX

So far we have looked at the total TX time and about 100uS of the time after TX switch off.

This is the time when things happen with a PI.

There is a lot happening during the Flyback, but it happens in nano seconds and will take me some time to find a way to show it in pictures.

So let's first look at what happens DURING THE TX TIME.

Tinkerer

[Tinkerer]

WHAT KICKS THE TARGET PART 3

Let's look at what happens during the transmit time.
The TX pulse has about 12 V and a duration of 90uS.
The DC resistance of the Mosfet, the cable and TX coil is about 2.5 Ohm.
The coil has an inductance of 375uH, that means 375/2.5= a TC of 150uS

At 35uS, the coil current has reached about 1A, about 9.6W into the coil.

At 90uS, the coil current has reached about 2.15A and 14W into the coil.

The pictures show the response of different targets when exposed to the changing magnetic field.

I have changed the time scale to 10uS/div, so now the Tx or Transmit Time takes nearly the whole screen.

#1 No target
#2 A piece of half inch square alu foil is the target. It has a TC of about 5uS
#3 A piece of one inch square alo foil, about 10uS
#4 A Nickel ($0.5 coin) about 15uS
#5 A Penny ($0.1 coin) about 70uS
#6 A Quarter ($0.25 coin) this one has a TC of more than 90uS
#7 the last one is our steel lug again. It has a TC of more than 90uS and its response is negative, (saturating the preamp) while all the non ferrous targets gave a positive response.

The distance of the targets varies, to avoid saturation of the preamp, while still making it possible for the naked eye to see the responses of the different targets during TX.

Tinkerer

[Alexismex]

Hello tinkerer,
More i see your pictures ...more i know you are inside of something big for the progress of discrimination ...Keep cool working

[ZED]

Tinkerer why am i seeing a signal when there is no target present,i imagine you are using an IB coil.

Zed

[Tinkerer]

Tinkerer why am i seeing a signal when there is no target present,i imagine you are using an IB coil.

Zed

Hi Zed,

The scope shots show the TX pulse with a duration of about 90uS, of the TINKERERS_V1 with a DD coil.
The coil is sitting on red clay bricks to simulate magnetic soil, therefore there is the response of the clay bricks as the basic "no target" picture.

Any signal thereafter is the change produced by a target, while under the influence of the magnetic response of the clay bricks.

Tinkerer