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Author Topic: poynt99's Testing of Rose's Circuit 2013-06  (Read 32583 times)
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.99,

The Google+ thingy did jam my computer totally, using up 100% of my CPUs. So I left the Google+
and did look at the live Youtube link instead. http://www.youtube.com/watch?feature=player_embedded&v=zDsc-UAHHAQ
The video quality was crappy at best, the audio did drop out a times. The camera was NOT if focus all the time.

GL.
   
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.99,

The Google+ thingy did jam my computer totally, using up 100% of my CPUs. So I left the Google+
and did look at the live Youtube link instead. http://www.youtube.com/watch?feature=player_embedded&v=zDsc-UAHHAQ
The video quality was crappy at best, the audio did drop out a times. The camera was NOT if focus all the time.

GL.
Yes,two minutes was enough for me. How anyone will get any usful info,and a close look at that setup is beyond me C.C
   

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Buy me a beer
Nothing but problems with the link, in end watched on youtube

Mike 8)


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"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."
Arthur Schopenhauer, Philosopher, 1788-1860

As a general rule, the most successful person in life is the person that has the best information.
   

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It's not as complicated as it may seem...
As pretty much expected, we did not see a faithful reproduction of the Fig. 3 scope shot presented in Rose's first paper.

The key fail was when +12V (or less) Gate voltage was present, there was a significant current flow as shown by the shunt voltage. Fig. 3 in the paper shows pretty much zero current with at least +12V Gate voltage.

[youtube]http://www.youtube.com/watch?feature=player_embedded&v=zDsc-UAHHAQ[/youtube]
   

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It's not as complicated as it may seem...
The following video clearly demonstrates how parasitic circuit inductance can and will skew the battery power measurement "Pbat" when taken using a DSO oscilloscope.

Of note to remember for the video:

-  A "positive" indicated Pbat  tells us that the battery energy is depleting.

-  A "negative" indicated Pbat  tells us that the battery energy is increasing.

[youtube]http://www.youtube.com/watch?v=pnZLwA2Uohs[/youtube]
   
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It's good if we can show some zoom in current waveform

When Power is negative (probes far apart)

When Power is positive (probes moves closer)

Replace the resistor with pure inductance

Of course this is for the electrodynamics crowd and not the OU crowd.   

   

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Nice vid .99.  Distributed inductance in wiring
can be a real bugaboo in certain cases such
as you've demonstrated.

Has anyone determined how the stray inductance
causes the error you've demonstrated?  It would
seem that sufficient kickback is produced in the
wiring which is superimposed upon the desired
signal at the precision resistor to create some
sort of "phantom" in the measurement/calculation
process when the scope leads are improperly
placed.

A scope display of that signal would reveal the
kickback spikes which cause the error?

Gibbs comments above seem to be directed at
the same question.  Perhaps a followup would
be helpful in conveying more understanding?


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"The best teachers are those who show you where to look, but don't tell you what to see." - Alexandra k. Trenfor.
   

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It's not as complicated as it may seem...
The following segment "4" video illustrates essentially the same as segment 3 did, in that parasitic inductance between CSR probe tip and probe ref will significantly skew the Pbat measurement. There was concern expressed that I did not have the Vbat probe reference connected, and therefore it is connected in this redo. In this segment I only compare the CSR probe measurement in two positions rather than 5. The variance is dramatic still and changes from roughly -1.02 to +0.91 by simply moving the probe tip and ref 1" away on either side of the CSR body.

Video Link: http://www.youtube.com/watch?v=SietCns2r-M

The two attached pictures relate to those two probe positions and their resulting Pbat values.
   
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The current amplitude drop as the probes moves close together.  This means the inductive effect is reduced.  It seems like the battery also subjects to parasitic inductance since the voltage observed spiked up much higher than its normal voltage. 

It is questioned that can the current in this circuit reverse (or cross the zero reference).  It seems that even if the current is reversed, there won't be much compare to the battery direction (unless it uses its own capacitance to resonate).  So the negative portion of the current waveform could be a near complete result of inductive kickback while there is little reverse current.

The resistor true value should be IR and the inductive effect is Ldi/dt and L is the parasitic inductance.  We can see that IR is highest when I is highest, but Ldi/dt is highest when di/dt is highest.  di/dt is highest when current begins to flow and when it is cut off.  Furthermore, the polarity for begin and end is opposite.  It is possible that that the true current waveform does not have a negative portion.   

   

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It's not as complicated as it may seem...
Here is one more video showing the negative/positive mean battery power; this time with 20 cycles showing on the scope screen.

http://www.youtube.com/watch?v=CGDzic26qQs
   

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Your vids are helpful in understanding
the importance of measuring device
lead placement to exclude spurious
signals which will affect calculated
levels.

It also helps to understand why in
radio frequency circuits and most
switching circuits good design practices
demand the shortest possible lead
length between critical circuit components.

It stands to reason that the inductive
discharge transient of the circuit wiring
would generate a substantial negative
impulse as that voltage is developed
across a relatively high impedance.

I'm wondering whether anyone has
captured a scope shot which actually
shows the offending transients?  As
in a single pulse close-up?

It would be very interesting to see the
amplitude, polarity and time duration
of the offending spurious pulse compared
to the desired signal pulse.


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"The best teachers are those who show you where to look, but don't tell you what to see." - Alexandra k. Trenfor.
   

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It's not as complicated as it may seem...
I'm not sure why you fellows are talking about inductive discharges; they are not the cause of the negative mean battery power computation. The measurement skew is caused by the phase change of the oscillation portion of the wave form. In theory they should amount to almost zero power, but when parasitic inductance is allowed in between the csr probe locations, this phase change happens and the result is an erroneous computation.
   

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That may be; increasing the inductive component
in series with the Current Measurement Resistor
would introduce both a phase change in the
measured waveshape and a change in amplitude.

So you're saying then that the negative error is
dependent upon oscillation?  With simple pulsing
the error would not exist?

Granted, at the higher frequency of the oscillation
the effect would be more pronounced and possibly
easier to detect with digital sampling over the long
term.


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"The best teachers are those who show you where to look, but don't tell you what to see." - Alexandra k. Trenfor.
   

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It's not as complicated as it may seem...
If there were no oscillation component, the error would be non-existent yes.

But since there is an inductive resistor and plenty of wire, there is going to be at minimum a lot of ringing. In this case because of the miswiring of the MOSFETs, there is oscillation.
« Last Edit: 2013-07-08, 14:49:50 by poynt99 »
   
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So you're saying then that the negative error is
dependent upon oscillation?  With simple pulsing
the error would not exist?


It's a good point.  I've designed a circuit to demonstrate this.  I could not access falstad to test it but it looks pretty straight forward. 

The circuit does not have any capacitance so we can say the current cannot reverse.  R1 is the current sensing resistor and L3 is the inductance that cause the measurement error.  When switch S is closed, current increases because it bypassing R2.  When S is opened, circuit energy stored in inductance release through R2.  This simulates a pulse. 

We can measure Pbat by multiplying its voltage with the current waveform.  To simulate inductance error, the current waveform can be taken between L3.  I think there will be a Pbat difference because R1 waveform and L3 waveform are different through out this pulse transient.
   
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