phase frequency question

[simonbaker]

Maybe Qiaozhi or anyone interested can answer this:

What is the effect of TX frequency on the range of phases of different metal targets in an IB detector?

For example: Silver has a different phase than nickel. Let's say difference is deltaPhi.

Now if we change the TX frequency, does deltaPhi change? How?

I would guess if lower TX frequency, deltaPhi gets smaller? Increase TX frequency, deltaPhi gets bigger?

I would think it is easier to discriminate at higher frequencies because phases of targets more spread out. Up to a point anyway, maybe they shift too far, wrap around, all confused.

So is there any data on this???

Regards,

-SB

[ivconic]

More popular (dummy) explanation would be:
Silver, Gold etc..etc.. are having weak magnetic features. Let's say inert and poor magnetic features. It is easier to "magnetize" those metals on higher frequencies. Once "magnetized" under em field produced by coil , Silver's and Gold's alternative field will decay very,very fast. Also will be very weak.
To achieve some so so response from it, higher frequency is desireable.
Higher pulse rate per second - less time for alternative field to decay fast.
Under higher pulse rate, decay not reaching zero - it is holding some potential until next pulse. So...it evolves certain "load", enough to disturb balance at IB coil. That "load" and decay time directly affecting phase. Higher frequency = more accurate phase readings.
Phase.... ? Phase is phase!? What about phase? What was the question here!?
This maybe reminds on PI.Looks like i mixed PI with IB. Not at all. It is the same old process. Just different approach later in analyze.
More accurate phase readings are main reason for higher frequencies at newer machines. Multifrequency even better. Todays ultra fast (and ultra cheap) uPC's allowing much datas to be processed fast, so it is almost obligatory (at high end detectors today) to cover more frequencies.

Ok..you may laugh on my explanation. But easiest way to imagine some process is to simplify it to triviallity!

[Qiaozhi]

Maybe Qiaozhi or anyone interested can answer this:

What is the effect of TX frequency on the range of phases of different metal targets in an IB detector?

For example: Silver has a different phase than nickel. Let's say difference is deltaPhi.

Now if we change the TX frequency, does deltaPhi change? How?

I would guess if lower TX frequency, deltaPhi gets smaller? Increase TX frequency, deltaPhi gets bigger?

I would think it is easier to discriminate at higher frequencies because phases of targets more spread out. Up to a point anyway, maybe they shift too far, wrap around, all confused.

So is there any data on this???

Regards,

-SB

The TX frequency has some effect on the phase-shift and also on the amplitude of the received signal. This is the reason that some detector manufacturers use multiple transmit frequencies, as this can provide additional information about the target.

The phase-shift and amplitude of the received signal is also influenced by many other factors, such as coil type and the way it is balanced. This is a very complex subject, and unfortunately I do not have any graphs or charts that could be posted here. However, small changes in TX frequency will have little or no effect on the RX phase-shift in the TGSL. Although, as Ivconic said, a higher frequency is desirable if you're searching for gold. But you need to stay below 100KHz to avoid skin effect.

[simonbaker]

Thanks for the replies, they're good --

What I'm really interested in is more the "spread" in the phase of the targets, not the shift of all the targets. In other words, the phase separation of, for example, nickel and silver. Different coils, etc will affect the phase shift of all the targets, but how do they affect the separation??? In particular, how does TX frequency affect this spread?

I think Ivconic said similar to what I'm thinking -- phase and time delay are sort of same thing. If a target has a particular "time constant", then it has sort of a constant delay. But constant delay means different phase shift for different frequencies.

So I look at TGS discriminator, which shifts detector pulse over 90 deg range. If we used a very different TX frequency, say 20 kHz, then maybe target phases more spread out and 90 deg range not big enough to discriminate all the targets?

Or if change frequency to 4 kHz, then 90 deg range too big, not sensitive enough because target phases packed together???

Is this something commercial detectors pay attention to? What is difference between discriminator circuit on a 4 kHz machine and a 20 kHz machine?

-SB