Here is a post awaiting Stefan's approval and publication over at "the other forum" where Poynt's arduous and patient teachings are starting to get through to Stefan on some critical issues. I thought I should post it here at my "home forum" as well. It typically takes Stefan a day or two to release my posts, so Rosemary may well see it here first. She reads here fastidiously by her own admission.
I should note, to the full credit of (and my improving opinion of) Stefan's personal integrity, he has eventually cleared 100% of my posts since putting me on "censorship" status. I, in return, have avoided all personal remarks, ad hominem attacks, sarcasm and ridicule (although it has been hard at times). Years ago, Stefan "perma-banned" me for repeatedly attacking lies told by Ashtweth, so this is no trivial achievement.
It is no secret to him or to anyone reading that Humbugger and cHeeseburger are one and the same.
Re: Rosemary Ainslie circuit demonstration on Saturday March 12th 2011
« Reply #373 on: Today at 12:37:20 AM »Quote
Note:
This message is awaiting approval by a moderator. Now, Stefan and Poynt, we are converging on the truth finally. The battery is a fixed DC potential with millivolts of actual ripple due to its internal resistance. The battery voltage does not actually have the 150VAC 1.5MHz signal Rosemary is feeding the 'scope.
The importance is now properly focused on the shunt and the actual current flow there.
This demonstration shows the difference between the waveforms obtained across the inductive shunt and the resistive portion of same shunt. The scale factors are identical (1V per division) on both traces. Notice three super-important things:
1) The amplitude when we include the inductance is way higher and does not agree at all with the actual current measured just across the resistor. The inductance allows a much larger voltage swing, fooling us into thinking the current is much larger than it really is.
2) Look at the areas above and below zero. In the larger (inductance included) trace, by eyeball, it looks like the areas are close to even or maybe even slightly more negative. But in the real current trace it is clear that the area above zero is easily greater than that below zero.
3) There is significant phase skew between the two waveforms and this will ruin the accuracy of any multiplied samples. The true current (across just the resistive part of the shunt) does not peaqk at the same time as the false, inductor-polluted "current" trace and is in fact not always the same polarity at a given instant in time. Notice the inductive shunt trace is approximately at its peak at the zero-crossings of the real current: almost 90 degrees phase shift. Basic fundamentls when the L vastly dominates the R of shunt!
So, the amplitude, waveshape and phase angle of the "current" signal Rosemary is feeding into the scope is by no means an accurate picture of the true current flowing in the circuit. When the "battery" voltage also has an enormous misrepresentation due to series inductance inside the measuring points, and we multiply the data samples point by point, the numbers are so far from any believable reality that it boggles the mind and the results could come out anywhere and are totally meaningless, sorry to say.
Here is a challenge for Rosemary: Submit this post to your favorite Tektronix Applications Engineer. He or she is a certified oscilloscope measurement expert and is called on all the time to sort out these kinds of measurement questions. Ask him or her to write a paragraph about it, agreeing or disagreeing with what I have wriiten here, attach his or her name to it, and publish it here for us.
Cheeseburger
So the truth is laid bare and Rosemary has been challenged to take the matter to a fully qualified and very available (at no cost) expert who is a disinterested party. Let's see how she responds to this.
Humbugger
P.S. For those just learning about inductance, notice how the inductive trace voltage amplitude corresponds to the
rate of change of the actual current through it as seen on the pure resistance. This explains why the inductive voltage trace can go negative while the actual current is still positive but rapidly declining. While the real current is rising rapidly, the inductive voltage is at peak positive. The voltage across an inductor is a pure function of the rate of change of current through the inductor. The polarity of the voltage has nothing to do with the polarity of the current, but rather whether is is rising or declining.
Author
Topic: The Rosemary Ainslie Circuit (Read 459841 times)
