Induction Balance - to what extent?

[Teleno]

What attenuation ratio is to be expected from a commercial DD coil? 1:10? 1:100? 1:1000?

I'd be building a DD coil and, although Pulse Induction does not require extreme attenuations, would like to achieve the best possible balance.

I'd appreciate any pointers on how to do it, guys. Thanks in advance!

[green]

What attenuation ratio is to be expected from a commercial DD coil? 1:10? 1:100? 1:1000?

I'd be building a DD coil and, although Pulse Induction does not require extreme attenuations, would like to achieve the best possible balance.

I'd appreciate any pointers on how to do it, guys. Thanks in advance!

Hi Teleno
I'll reply with what I do for IB coils for PI detector to get it started. Maybe good, maybe not. Works for me. Used ITMD as a starting guide. Position Rx coil for minimum signal while monitoring amplifier out with an oscilloscope during coil charging. I use a piece of 2mm craft foam between Tx and Rx coils where they overlap. Glue in place. Use a small ferrite bead to adjust final null after coil is finished if desired. I wind the coils spider web(flat basket) and use a graphite shield above and below spaced at least 2mm from coils. The wire from the coil OD for common.

[Teleno]

Hi Teleno
I'll reply with what I do for IB coils for PI detector to get it started. Maybe good, maybe not. Works for me. Used ITMD as a starting guide. Position Rx coil for minimum signal while monitoring amplifier out with an oscilloscope during coil charging. I use a piece of 2mm craft foam between Tx and Rx coils where they overlap. Glue in place. Use a small ferrite bead to adjust final null after coil is finished if desired. I wind the coils spider web(flat basket) and use a graphite shield above and below spaced at least 2mm from coils. The wire from the coil OD for common.

Thanks for answering. Some questions:

- what is the craft foam for?
- waht graphite shield? I have graphite spray, how should I apply it and connect it electrically?

[Carl-NC]

Typical VLF null is 60dB, or 1000:1. A PI coil is trying to null a broadband pulse so you will likely not get 60dB for the high-frequency content.

Craft foam is probably used to space the TX & RX coils to minimize capacitive coupling.

[green]

Thanks for answering. Some questions:

- what is the craft foam for?
- waht graphite shield? I have graphite spray, how should I apply it and connect it electrically?

http://www.geotech1.com/forums/showt...555#post203555

Some instructions I posted awhile back. Been using poster board instead of the cardboard to paint with the graphite after attaching the drain wires. Using 1/2 inch spacing for the tooth picks, better spacing especially when wrapping around sharper corners(DD). Think I would try a flat spiral instead of the flat basket if I had a form to wind it on. I tried painting the outer rim of the coil with graphite also, think it had a negative effect on the coil. With the outer winding going to common, painting the outer rim doesn't seem to be necessary. It's not a fast way to make a coil. Best way I've found so far to make a fast coil with solid enamel coated wire. I'm always trying to learn so it's away to start.

The foam spaces the graphite from the coil. Been using a piece of the foam between the Tx and Rx coils for spacing, not sure it's needed.

[Sean_Goddard]

6dB per inch of original signal. OR you Rx 1/2 of 1/2 what you put out as a Tx signal (rule of thumb). This is from experiments I have conducted.

Example, 100V Tx would give you a maximum of 25V at the Rx coil (50% of 50V) at 2 inches that would be 6.25V, at 3 inches it will be 1.5625V etc.

You can see how machines like Tesoro which Tx 7 volts dont go very deep, event their HOT output like the Tejon (15V) do not give much increase in depth. It is basically the old square law thing again.

[green]

What attenuation ratio is to be expected from a commercial DD coil? 1:10? 1:100? 1:1000?

I'd be building a DD coil and, although Pulse Induction does not require extreme attenuations, would like to achieve the best possible balance.

I'd appreciate any pointers on how to do it, guys. Thanks in advance!

Hi Teleno

Connected my 8 inch DD coil to the bench circuit and performed some tests. Scope pictures amplifier gain 450, unbalanced(coil balance, one of the first attempts at IB coils, not very good) balanced(used a ferrite bead to balance) unbalanced, opposite(used the ferrite bead to unbalance opposite polarity). Looks like could sample the balanced coil a little sooner. Channel 1(amplifier out) Channel 2(probe near mosfet to show decay shape) I haven't been able to prevent the amplifier from saturating during the decay, would be interested if you can.

(DD coil) Charted integrator out vs target distance while offsetting target from center of coil, inline and 90 degrees from DD coil overlap. Couple observations,(a DD coil is usually drawn to have a narrow detection range) charted a narrow range with 90 degree offset with the target at 2 inches. The amplitude at 3 and 4 inch 90 degree offset reversed polarity(added value to chart because log plot can't chart minus values). At larger target distances not so narrow.

Interested in your DD coil tests.

Carl's reply #4 about the spacing between the coils was the reason for adding them. Haven't experimented with different spacing. Maybe has something to do with the amplifier saturating during decay.