(P49) Ferrous and Conductivity

[Cody]

(P40) There is an illustration on page 40 with some explanations that need to be checked closely. At the bottom of the page we are told that

 

[Anonymous]

Excellent post, Cody, and certainly not too long or drawn out.

What, if anything, can we use to discern between conductance and conductivity (i.e., break the conductance down into its size and conductivity components)? Is it possible for a detector to have a third dimension? I suppose that's what you mean by the 1024-notch capability; if so, I look forward to your discussion of how to implement it.

BTW, do you work mostly in the Smartfind or the Digital display?

Jim

 

[Cody]

Jim, good questions; we really cannot read conductivity with the Explorer. To measure conductivity we would need to have a power source connected to a load and measure it that way or with a test device that connects to the material. Here is an idea of what happens. A target is can be very accurately represented by a power source connected to an inductor in series with a resistor. The power source charges the inductor through the resistor. If the power source has an alternating or pulsating voltage then the inductor will charge and discharge. If we connected an oscilloscope across the resistor we would see a graph of the voltage that would look almost identical to the voltage of the power source. We could then measure, calculate, and predict and lot of electronic and other parameters of the circuit. That is what is done as a target such as a coin has and inductance and resistance. The parameters are predicted based on how an actual silver coin responds. A prediction that is very useful is how long does it take for the inductance to charge and discharge through the resistance of a silver coin. Since the actual conductivity of silver is the same not matter how large the sample we know what the inductance and resistance values are. This data is stored in the electronics in a lookup table as a time constant which is the ratio of L/R, L=inductance and R=resistance. I think I read where Minelab has somewhere around a thousand TCs stored.

When we say conductivity and ferrous it is not the actual measured parameters but the predicted value based on the signal in the receiver coil and electronics. When we see a reading such as 0/30 it is because the process signal compares best to the TC for 0/30. Since we know that 0/30 is silver, know the conductivity of silver and the inductance, then circuits to drive the display and cause a tone generator to sound the appropriate tone is activated. We don

 

[Captain Kirk]

Cody,

You stated:
"The screen has 1024 pixels with each one representing a combination of conductivity/size and ferrous characteristics. (There are good reason for some of the digital numbers we see. As an example 1024 is a natural binary counter which is an electronic circuit. It counts like this. 1, 2, 4, 8, 16, 32, 64, 128, 256, 1024 and is represented by ones and zeros. The digits for 10 would be like this. We would use counters 1, 2, 3, and 8 of the above 1024 counter so the bits would be 0101= 10 since the 2 and 8 counter are a high bit and the 1 and 4 counter are low bits.)"

I think you mean 1,2,4,8

HH,
Glenn

 

[Captain Kirk]

Jim

The term "conductivity" relates to the number of electrons per cubic centimeter. The term conductance relates to how you shape that cubic centimeter. For example, if you take a cubic centimeter of copper and shape it into a long thin wire, then the wire will have much lower conductance (higher resistance) than the cube that it was made from.

HH,
Glenn

 

[Cody]

Yes, I think I did that early in the morning with lights off. I did mean 1, 2, 4, 8 and thanks for your great input and comments.