TESORO GOLDEN SABRE

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It depends on which side of the null that the loops are balanced.
On one side a non-ferrous target may cause an increase in amplitude at a 20 degree offset, whereas on the other side it may cause a decrease. In the latter case you would have to sample at a point which is effectively 180 + 20 degrees (i.e. 200 degrees) otherwise discrimination would work opposite to what you want.

How can a coil like this work? And yet it works perfectly, even though it is balanced where tx is leading by app. 200 degrees. Won't the phase detectors sample at the wrong intervals? Wouldn't they be off by some 180 degrees?

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Above, zero crossing at 2π is implied for adjacent waveform comparison.

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In comparing two sinus waves. I measure from the Rising ZERO Crossing of the 'reference' wave forward in time to the rising Zero crossing to the other.
Phase difference in my mind can go from 0 to 360 (which is back to zero) degrees.

Yes, zero crossing is the right way, but not the only way, especially if the sinusoids aren't perfect.
But for the code guys, it's probably the easiest way to extract phase angle by formulaic means.

Surely a waveform can be shifted by up to 360 degrees along the x Axis in the time Domain, this is for a single waveform being shifted computationally or by means of a circuit, and compared to it's original position, in other words, you assume a zero crossing of T=0. On the scope, you are comparing the same signal but at two different points in the circuit. There is no ambiguity about which one is leading, and it will end up having a negative phase angle.( It's zero crossing will be behind the zero crossing of its phase shifted counterpart, hence leading)
But my assertion is when comparing two separate sinusoids (same frequency) but of different origins on a scope screen, one cannot say for sure who is leading vs who is lagging. It's all relative. T=0 is merely an abstraction. The two closest adjacent zero crossing points will always be less than 180 degrees apart. That's my point. But if you were writing code for DSP, then I imagine you can compute all the way to 360. Or even 720 and beyond. That's software.

[waltr]

In comparing two sinus waves. I measure from the Rising ZERO Crossing of the 'reference' wave forward in time to the rising Zero crossing to the other.
Phase difference in my mind can go from 0 to 360 (which is back to zero) degrees.

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You did not quite understand me correctly --- there cannot be a phase difference of 200 degrees, maximum 180. Show me an oscillogram with such a phase)))

SWL, now I am understanding your point on this matter. I think you are right. Practically speaking, phase should be measured from the two closest adjacent peaks of the two sinus waveforms of identical frequency, in which case there would never be more than 180 degrees phase shift. In addition, the phase difference could the be described as minus( lagging) or plus( leading).
So if I say, for example, the TX has a minus 20 degrees phase shift relative to the RX, then it's obvious to everyone that the TX is lagging the RX by 20 degrees.
I should intuitively measure the two closest adjacent peaks, in which case I will always get less than 180. Minus and plus ( lagging or leading) is simply who is relative to who.

[dbanner]

It depends on which side of the null that the loops are balanced.
On one side a non-ferrous target may cause an increase in amplitude at a 20 degree offset, whereas on the other side it may cause a decrease. In the latter case you would have to sample at a point which is effectively 180 + 20 degrees (i.e. 200 degrees) otherwise discrimination would work opposite to what you want.

All well and good, however...
Sometime ago, was it not you who measured and described the phase balance of a stock tesoro concentric coil at 200 degrees? I seem to recall a relevant thread on this matter. If not, l apologise.

[Qiaozhi]

It depends on which side of the null that the loops are balanced.
On one side a non-ferrous target may cause an increase in amplitude at a 20 degree offset, whereas on the other side it may cause a decrease. In the latter case you would have to sample at a point which is effectively 180 + 20 degrees (i.e. 200 degrees) otherwise discrimination would work opposite to what you want.

[dbanner]

Now here is a question.
Start off with two in phase sinus waveforms. Phase shift one of them to the right. Now the one shifted to the right can now be described as leading. Now continue shifting it to the right, at what point can it be said to be lagging. After 180 degrees? How would you know if it were leading or lagging merely by a snapshot of the oscilloscope screen? How would you know where to take the reference. From the two closest adjacent peaks? Two cursors merely give an angle, one relative to another. But leading, lagging?
Someone explain. Could it be for the sake of nomenclature, a waveform should never be described as leading or lagging more than 179.99..... degrees. At 180 degrees it would be ambiguous?
I shall try to find the thread where Qiaozhi measured the phase of a Tesoro concentric. I hope I remembered correctly, if not, I apologise.

[dbanner]

I think in a concentric, the tx should lag the RX by around 20 (tgsl). The opposite for the DD ( lead by 20).
But I do remember 200 being measured on an original tesoro concentric. There is a thread somewhere.

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Here is Tesoro brown concentric measured at around 20

https://www.geotech1.com/forums/showthread.php?24864-Tesoro-Brown-Concentric&highlight=Tesoro+brown+concentric

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Factory Tesoro concentric coil ( golden sabre type) was measured to be balanced at around 200 degrees phase difference between TX and RX. That's the concentric.
Now if you were to add 180 to 200 you'd get 20. But what about the synchronized demods, won't they be sampling the negative going RX waveform with such a balanced coil(@200)
But how can this be? Summing two negatives becomes a positive at the end?. Someone can explain.

Now in addition,what if one were to balance a DD coil @200 or conversely, a concentric coil @ 20?
No difference? someone explain.

[waltr]

You did not quite understand me correctly --- there cannot be a phase difference of 200 degrees, maximum 180. Show me an oscillogram with such a phase)))

Mathematically yes, only 0 to 180 degree using Sin functions.
But in a Real Circuit. the Phase can increase through 180 degrees (Inverted) all the way to 360 degree.

DSP operations do 0-360 phase shifts.

Excel spreadsheet plot showing a sine at 0, 20, 180 & 200 degrees phase.

[SWL]

You did not quite understand me correctly --- there cannot be a phase difference of 200 degrees, maximum 180. Show me an oscillogram with such a phase)))

[waltr]

It was often mentioned here that when nulling the coil, you must adhere to a phase shift of 200 degrees.I guess I don't understand something, but how can there be an angle of 200 degrees between TX and PX? This turns out to be a complete phase reversal .. Isn't that so?Probably it means either +20 or -20 degrees ...

Yes, I go for about 20 degree phase shift with RX lagging (later in time) then the TX.
This is the typical phase shift for a DD coil.

I have built coils that nulled with a 200 degree phase shift and they worked fine with proper GB and Disc.

Study the sample periods of the GB & Disc relative to the waveform phase. Then realize that the discrimination circuits (op-amp
filters) are AC coupled and only response to a Change.

This is explained in the book "Inside the Metal Detector".

[SWL]

It was often mentioned here that when nulling the coil, you must adhere to a phase shift of 200 degrees.I guess I don't understand something, but how can there be an angle of 200 degrees between TX and RX? This turns out to be a complete phase reversal .. Isn't that so?Probably it means either +20 or -20 degrees ...