Testing the TK Tar Baby

[TinselKoala]

So... getting back for a moment to the offset issue...

.99 said,

However, if there is an observable change in the "position" of the trace when changing from AC to DC coupling, then there WILL (or at least should) be an effect on the MATH computation when switching between the two.

So, in the CVR trace there are actually two superposed signals, right? I mean there is usually a bit of DC current in the forward conventional direction as well as the oscillations on top of that, and the oscillations can be of greater amplitude than the DC current. Right? At least this seems to be what's shown in the traces from the Ainslie papers.

So... if one were only interested in the power in the oscillations themselves and wanted to only count the contribution of the oscillations, and not the DC component, to the instantaneous power curve... how would one set up the scope for that?

It seems to me that a DC component in the conventional direction would raise the CVR trace above its baseline by some amount. Would this not then actually also raise up the negative average power value (bringing it closer to zero) computed from the multiplication and averaging?

[picowatt]

So... getting back for a moment to the offset issue...

.99 said,
So, in the CVR trace there are actually two superposed signals, right? I mean there is usually a bit of DC current in the forward conventional direction as well as the oscillations on top of that, and the oscillations can be of greater amplitude than the DC current. Right? At least this seems to be what's shown in the trace below from the Ainslie papers.

So... if one were only interested in the power in the oscillations themselves and wanted to only count the contribution of the oscillations, and not the DC component, to the instantaneous power curve... how would one set up the scope for that?

It seems to me that a DC component in the conventional direction would raise the CVR trace above its baseline by some amount. Would this not then actually also raise up the negative average power value (bringing it closer to zero) computed from the multiplication and averaging?

TK,

I would think that if the CSR trace were AC coupled a small positive offest at the CSR due to DC bias may not be accounted for.  This condition would be similar to connecting the FG or bias supply ground to the batt side of the CSR so that DC current is not accounted for by the CSR trace.  As to the degree of error, it is somewhat difficult to predict.  I would suspect no more than 50mV postive if Ibias were 200ma.  As this current is modulated to some degree by the oscillation, it would likely be slightly less than that amount.  The short answer is that by not including the DC current, the neg mean pwr measurement would be indicated as being greater negative than it actually is (the constant 50mV or so positive DC voltage at the CSR would reduce the neg mean).  If you have an idea as to what your Ibias was at the time, possibly a correction can be applied that reflects that DC current.  As for me, I was convinced that you had a neg mean pwr when you did the "add the dots".   

Also, any asymmetry in the CSR waveform will cause the position of the trace to drift up or down depending on which polarity of the cycle is of greater magnitude.  This effect would likely not affect the math calculations.


PW

[TinselKoala]

Thanks, that is what I figured as well.

So, if all goes well we have another play date on Monday.... if I get my radiator back from the shop tomorrow as scheduled. For that one Tar Baby will have freshly charged batteries, five of them, and I'll be sure to use DC coupling on all traces... as appropriate.

If you could please remind me before then of some of the (short, easy) tests that you suggested I do with that scope, I'd appreciate it, and perhaps I'll be able to perform them, if Tek's momma isn't using it for (redacted) at the time.

Unfortunately, unlike the old LeCroy that I demoed some time ago, this Tek only seems capable of displaying a single math trace, but it can do fairly complex functions and nested algebra on that one trace.  Of course I still haven't read the manual nor have I pushed all the buttons or turned all the knobs, so there might be hidden functionality that I'm not aware of. For example there is this whole "wave inspector" thing that could be useful if someone only understood it.

[Rosemary Ainslie]

picowatt.  This is the post you refer to.

The Lecroy does not have a separate position control.  I read the 300 series manual and it stated to use the offest control to adjust trace position.  As well, the visual calculations from centerline agree very well with the indicated offset, and the observed FG drive during neg osc visually calculates to where it should be within a volt or two.  If necessary, I will call LeCroy.

In the first instance you 'IMPLIED' that your analysis related to the 'offset' reading of the LeCroy was ENTIRELY representative of the the zero point positioning of the signs against the X axes center graticule - as it relates to zero.  And what I TOLD you REPEATEDLY - is that this zero reference needs to be qualified against the 'coupling' that is manually applied to the voltage reading.  Therefore is there no relevance related to representation of the voltage across the Gate of Q1. Remember?  You said either the MOSFET had blown - OR - the Le Croy measurement was wrong. Well that OPINION is wrong.  There is no resulting SKEW that also results in an incorrect math function as you INFERRED.  Nor is there SKEW resulting in a MISREPRESENTATION of the zero crossing line across the current sensing resistor.  Nor is there SKEW resulting in a MISREPRESENTATION of the battery voltage.  Nor does the voltage across the Gate at Q2 represent the entire picture.  It needs 'qualification' against that coupling.  And further qualification against the the offset of the function generator.  And as an 'expert' in the art of reading an oscilloscope - you should have KNOWN this.  Instead of which, let me say this again, you DECLARED that either the MOSFET had blown.  OR that there was a measurement's error.  You were  and are WRONG on both counts.   Where I erred was in my poor efforts to explain this.  But you do and did understand me.  And you are and were pretending not to.  In the same way that you pretend that preschoolers can capably handle a solder iron - or that they can read, write and do THE MATH - at an average and adult level competence.

Then you state...

It seems you are reliably able to obtain the negative pwr figures.  Now that you have that 'scope there, I wonder if you could be troubled to investigate bypassing the batteries with caps and adding wire if needed as discussed.  You might even be able to solder a switch to a batt connector and the caps lead to allow you to bypass the batteries by merely using the switch when desired.  Likely any additional wire added could remain in circuit for either test, and it might also increase the amplitude of the osc.  With the 'scope there, doing the two tests would be pretty quick, none of that "add the dots" needed.

This is like MileHigh's proposal that the best way to evaluate the oscillation is to remove it.  IF you apply a path for that counter electromotive force - away from the battery - then it will not be advantaged by the potential difference of those batteries.  I would refer you to our introduction, discussion and conclusion in the second part of our two-part paper.  You prove NOTHING by taking away the very property that we rely on to generate the oscillation.  The argument is as good as saying water flows downhill.  I can disprove this by putting a mountain in its path.  Then within a certain limited supply of that water - I will PROVE that it no longer flows downhill.

Here is the effective paragraph from that paper that relates to this.
Effectively, therefore, the battery primary supply represents the only component on the circuit that has an intrinsic charge imbalance. Therefore at each zero crossing, which is the point when the current entirely discharges the potential difference across the circuit material, then the voltage across the battery moves to its average voltage which, unlike the circuit components, is always greater than zero. Therefore too, the CEMF will add to or subtract from that battery average depending on the applied voltage and direction of current flow. This, in turn, thereby imposes a greater potential difference at the battery than its rated capacity. [/font]

Which following a logic that is REALLY skewed - you then state...

Yes, it is looking like .99's analysis is correct.  No one moreso than I wish it were not true.  Regardless how small the probability is, or was, I for one truly hoped something unusual or previously unnoticed was occurring.  After all, what is the fun, or reward, in everything behaving "normally"? 

in the hopes of endorsing the 'spin' that you rely on - so heavily.   There is no-one member or reader here, that also reads this thread with any level of impartiality - or even scientific detachment -  that will EVER believe that you'd be 'SORRY' to find reason to dismiss our claim.  I"ll move onto your last post  to me hereafter.   

Kindest regards nonetheless
Rosie Posie

[picowatt]

Rosemary,

I caught up on some reading I must have missed on this thread. 

While discussing with you how Q2 is turned on by the FG, I missed your argument, or did not at the time understand what you were saying, regarding their being no evidence of Q2 being turned on.

I assume by this you mean that no current flow is indicated across the CSR that would indicate Q2 is being turned on.

With regard to DC, Q2 does not turn on fully.  It is being biased into a linear region of operation.  Q2 will regulate the DC current flowing thru it in concert with the FG negative voltage and the FG's internal 50 ohm resistor such that the DC current flowing thru Q2 when it is biased on will be limited to 200 milliamps more or less.  This current is referred to as "Ibias".

This amount of current would produce only +50 millivolts more or less of voltage at the CSR.  At the 'scope settings used, and with the oscillation masking its view, this 50 millivolts would be difficult to see.

Additionlly, if the FG signal ground is connected to the battery side of the CSR, the Q2 DC bias current would not be indicated at all by the CSR trace, as the bias current would not be passing thru the CSR.

PW