PI running on lower voltage/current

[mickstv]

Hi All, I've been doing some more experiments with a basic PI frontend and comparing using different voltages etc. The tests revolve around 7.2volt and 12volt. I've seen that in air the difference in voltage only shows a minimal difference in detection distance.

My line of thinking is the more power you use the more ground noise/mineralization is going to swamp the frontend and make detecting of small nuggets harder. Or would more power be needed to get through the mineralization ?

Just wondering what other users think about this.




Cheers
Mick

[hdphilip]

Mick

it would be insteresting to use a microprocessor to adjust TX pulse current relative to signal strength, and record the findings to a sd card, import it to excel, and plot the findings.


Philip

[moodz]

There is no voltage term in the coil time constant ....

Tc = L / R

Minelab and others use comparatively low voltages to drive the coil TX.

The UNIPI chip is easily driven through its serial port where you can set the pulse timings and read the SAT values.

moodz

[Carl-NC]

For a given coil, voltage determines the max TX current which affects depth. Doubling the current results in a typical depth increase of 8% or so. Ground signal also increases and whether that matters depends on the ground and the detector circuitry. Increasing the TX current will also increase the decay recovery so you cannot sample as early.

[porkluvr]

Hi All, I've been doing some more experiments with a basic PI frontend and comparing using different voltages etc. The tests revolve around 7.2volt and 12volt. I've seen that in air the difference in voltage only shows a minimal difference in detection distance.

My line of thinking is the more power you use the more ground noise/mineralization is going to swamp the frontend and make detecting of small nuggets harder. Or would more power be needed to get through the mineralization ?

Just wondering what other users think about this.

Cheers
Mick

Expanding on what Carl said you could use less powerful pulses but increase the pulse rate.

[Tinkerer]

For a given coil, voltage determines the max TX current which affects depth. Doubling the current results in a typical depth increase of 8% or so. Ground signal also increases and whether that matters depends on the ground and the detector circuitry. Increasing the TX current will also increase the decay recovery so you cannot sample as early.

The power brick wall.

With traditional PI, the Flyback quickly hits the maximum Mosfet voltage and this is the great limiting factor.
Using the avalanche diode of the Mosfet to clip the Flyback has not produced any good results that I have heard of.
A small damping resistor can reduce the Flyback a little, but extends the decay very much.
With a long decay curve, only larger targets can be detected.

There is a possibility to push the brick wall a bit further, but I have not tried it yet.

This would be as follows:

Use a switched damping resistor. That is, the damping resistor is switched out of the circuit during the TX. At switch off, the damping resistor is switched in. It is a relatively low Ohm resistor that greatly over-damps the Flyback, thus making it possible to increase power.

This will generate a long decay curve.

Sample on this decay curve.

Since the decay current is still considerable, a ferrous target will produce a response of opposite polarity from a non ferrous target. We would therefore have a ferrous/non ferrous target indication.

I have not tried it, but think it is worth a try.

Tinkerer