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Cartridge dynamic behaviour
Cartridge dynamic behaviour
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Old 10th February 2019, 07:24 AM   #381
Hans Polak is offline Hans Polak  Netherlands
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At last I've managed to reproducing Jackinnj's image.
First step was to reduce the Q significantly, while still keeping the phase going from +90 to -90degrees.
This was possible by splitting the Cap in two pieces and by adding a damping resistor.
See the LTspice model below and the sim |Z|=50*(Vin-Vout)/Vout.
From this I extracted Re and Im.
Treating the Imaginary values as being produced by a coil, I divided its absolute values by 2*Pi.
And voila, there it is, at the end quite a simple minimum phase model with just one SFR (self resonating frequency).


Hans
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File Type: jpg Self Resonance5.jpg (163.1 KB, 100 views)
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Old 10th February 2019, 08:29 AM   #382
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by Hans Polak View Post
At last I've managed to reproducing Jackinnj's image.
First step was to reduce the Q significantly, while still keeping the phase going from +90 to -90degrees.
This was possible by splitting the Cap in two pieces and by adding a damping resistor.
See the LTspice model below and the sim |Z|=50*(Vin-Vout)/Vout.
From this I extracted Re and Im.
Treating the Imaginary values as being produced by a coil, I divided its absolute values by 2*Pi.
And voila, there it is, at the end quite a simple minimum phase model with just one SFR (self resonating frequency).


Hans
Well done, Hans. Although the system is minimum phase, phase plot and |Imag| don't match because that's not the system.

At small levels the challenge is to extract accurate phase info in this method. Also to know with confidence that |Imag| at 10kHz is inductive, which in this system it probably is.

Another method that might be easier at small signals is to examine |Real| at 10kHz. Thesis is that a loss mechanism would be involved in any apparent L reduction, which would show up in |Real|.


A philosophical thought: for a given flux change, does generator output follow |Imag|? I think it does.


LD

Last edited by luckythedog; 10th February 2019 at 08:33 AM.
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Old 10th February 2019, 09:06 AM   #383
Hans Polak is offline Hans Polak  Netherlands
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I could make it even simpler, by just using one cap with a damping resistor in parallel, a somewhat more logical model.
This is as close as I can come to the original HP3577 image.


Hans
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Old 10th February 2019, 09:59 AM   #384
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by luckythedog View Post
Well done, Hans. Although the system is minimum phase, phase plot and |Imag| don't match because that's not the system.
Probably my latest model comes closer to the system.
Quote:
Also to know with confidence that |Imag| at 10kHz is inductive, which in this system it probably is.
That's how it seems to be.
Quote:
Another method that might be easier at small signals is to examine |Real| at 10kHz. Thesis is that a loss mechanism would be involved in any apparent L reduction, which would show up in |Real|.
Could it be that you mean |Z| instead of |Real|?
Zcart=Rload*(Vin-Vout)/(Vout).
Up to 30Khz L calculated from |Z| by dividing it by 2Pi*Freq gives almost the same outcome as when calculated from the true Imaginary.
At 10Khz they are within 1% in my model.

Quote:
A philosophical thought: for a given flux change, does generator output follow |Imag|? I think it does.
So do I, but at 10Khz also |Z|.


Hans
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Old 10th February 2019, 01:04 PM   #385
jackinnj is online now jackinnj  United States
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Cartridge dynamic behaviour
Is this helpful? Screenshot from HP3577, not Bode 100 -- -27dBm with 1Hz bandwidth, 16 averages and a long settling time, Z in of channels A and R 50R:
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Old 10th February 2019, 01:09 PM   #386
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by luckythedog View Post
At small levels the challenge is to extract accurate phase info in this method. Also to know with confidence that |Imag| at 10kHz is inductive, which in this system it probably is.
That was my original point, the network analyzer is measuring transmission loss the rest is maths. If you look at that, due to the loss because of the impedance levels, the signal at channel A is VERY small. At a ref level of -40dBm the signal level at A gets below -80dBm and the instrument specs don't support an accurate phase measurement at that level. The de-Qing in making the model fit probably lumps all loss mechanisms such as eddy current. If a proper sensitivity analysis was done using the specs of the instrument I would suspect that the extracted values have fairly wide error bars.

BTW your notation is confusing, |Imag|, is redundant unless mag is magnetic? In either case the magnitude alone is neither inductive nor capacitive you need the phase (imaginary part).
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Old 10th February 2019, 01:11 PM   #387
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by jackinnj View Post
Is this helpful? Screenshot from HP3577, not Bode 100 -- -27dBm with 1Hz bandwidth, 16 averages and a long settling time, Z in of channels A and R 50R:
It would help even more to know the Magnitude of the Y axis for |Z|.


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Old 10th February 2019, 01:20 PM   #388
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by jackinnj View Post
Is this helpful? Screenshot from HP3577, not Bode 100 -- -27dBm with 1Hz bandwidth, 16 averages and a long settling time, Z in of channels A and R 50R:
Thanks, those are the levels I expected. Since you averaged I assume the lumpy phase at resonance is part of the instrument residual? BTW the Bode 100 supports Python so you have available some powerful (free) model fitting tools.
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Last edited by scott wurcer; 10th February 2019 at 01:36 PM.
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Old 10th February 2019, 01:25 PM   #389
scott wurcer is online now scott wurcer  United States
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Originally Posted by Hans Polak View Post
It would help even more to know the Magnitude of the Y axis for |Z|.
There is no Z on this plot, it's the magnitude of A/R which enters and leaves resonance at 20dB/decade inductive in capacitive out. See post #361 at -27dBm the plots agree (without the damped Q). I can try to add that and see what I get.
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Last edited by scott wurcer; 10th February 2019 at 01:39 PM.
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Old 10th February 2019, 02:23 PM   #390
jackinnj is online now jackinnj  United States
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Cartridge dynamic behaviour
Also on the Bode 100, left y-axis is magnitude of impedance, right y-axis phase. Anyone who wants can get the raw data (real and imaginary) by sending a PM. (I did a calibration before this run.)
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