PHASE RESPONSE - The duration of time between target surface eddy current generation and resultant secondary electromagnetic field effect on the search coil's receive windings. Also called phase lag or phase angle and is directly related to target conductivity. Ok in other words.... when your tx coil creates a parabolic bowl of electromagnetic detection field and it induces an eddy current on say a weatie.
For anyone who I have lost.. look up the theory of Induction to understand the process
ps look at a test of eddy currents on a flat coin vs a ring... interesting.
Anyways.. so here we are creating a series of eddy currents from the sine.. sorry modified block wave for you v3 guys.. the phase response can change based on the conductivity of the metal on which the eddy current. Up to 180 degrees if the metal is a perfect conductivity. Pure silver is pretty close. So your filter and processor on your MD recognizes this phase change as a characteristic of silver and alerts the user of the pending silver that could be buried 8 inches in the soil.
oh gotta take a break.. brain hurting.. oh sorry that is my gut.. Mmm food!
Posted on: July 02, 2012, 08:06:05 PM
So now how do police lights meld with metal detecting...
easy.. remember what I was talking about wavelength and red an blue lights... OK here we go with the elementary my dear Watson. Lower frequency like that of say 5kHz has a wavelength long enough that it allows it to travel around the matrix of the soil.. very much like that of the red light and particles in the air. So silver is then charged with an eddy current which then sends a phase shift of the original frequency back to be detected and because it is a longer wavelength it can make it back.. So why do you ask why not gold a greater depths.. ok look at the chart of conductivity.. you have to make the signal back in order to detect it.. silver is highly conductive and can create an eddy current easily... Gold.. not so much. So as the frequency can charge the metal and induce it with an eddy current, the silver is the only one that has enough power in the eddy current to send it back at great depths because of it's higher conductivity rating.
ok now for the gold issue.. why is it detected easily with higher frequency.. say 22kHz and not so much as the 5kHz especially small gold.. well not a great depths but at least4-5 inches or small nuggets on or close to the surface. Remember at the scene of the crime?.. mostly blue light.. because of the reflection refraction and dispersal of the higher frequency being bounced around. (More chances of the target being hit if its bouncing around a shallow detection pool produced by a higher frequency field. ) More chance of eddy currents being generated because of the greater saturation of the magnetic field at that frequency. The red light/ lower frequency energizes the small gold nugget less because most of it runs right around the object and goes right past it... A big gold piece it can find because there is enough surface area to energize.. but the gold backing of a diamond stud earring.... right on by!
Now that you know this... The truth about coils and what the manufacturers are not telling you...
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