another small breakthrough on our NERD technology.

[picowatt]

I KNOW that the offset has nothing to do with peak to peak.  It has everything to do with that AC coupled value.  And the AC coupled value relates to PEAK TO PEAK.  It is applicable to the gate voltage.  You insisted on reading it as DC.  My advices were that you should be applying AC.  In which case the actual voltage across the gate is LESS THAN the value displayed as DC.  And we never apply any ajustments once the coupling has been chosen.  Therefore there is NO ADJUSTMENT made to the traces anywhere at all that is not determined by the machine.  And it is well able to determine zero.

Isn't the object here to determine the actual voltage across the gate?  Wasn't that the point of your question in the first instance?  Has this NOT been answered to your satisfaction?  Are you still implying that the voltage on the DC Coupled value is correct?  If so - and if you're satisfied that the DC voltage has been misrepresented - then I have run out of answers.  Because that's the best advice that I have been given.  By an IMPARTIAL EXPERT.  It may well be that I have not understood that answer sufficiently.  But overall and what I most certainly have had explained - is that the VALUE IS CORRECT - provided that you take the voltage reading as an AC value and NOT a DC value.  Because that incorporates the offset value.  I'm afraid that's the best I can do.

Again
Rosie Pose

Rosemary,

Referring to FIG 3 of your first paper, during the portion of the cycle wherein the output of the function generator is a positive voltage, what is the voltage indicated on channel 3 by the scope capture?

I see it at 1.25 major divisions above the zero volt reference, which is the little line with the number 3 above it to the left of the screen.  Channel 3 is set to indicate 10volts per division.  1.25 divisions times 10volts represents 12.5volts.  That is telling me that during the portion of the cycle wherein the generator swings positive, it is attaining a positive voltage of 12.5 volts.

What voltage do you read that point in the cycle as being?

PW   

[Rosemary Ainslie]

Rosemary,

Referring to FIG 3 of your first paper, during the portion of the cycle wherein the output of the function generator is a positive voltage, what is the voltage indicated on channel 3 by the scope capture?

I see it at 1.25 major divisions above the zero volt reference, which is the little line with the number 3 above it to the left of the screen.  Channel 3 is set to indicate 10volts per division.  1.25 divisions times 10volts represents 12.5volts.  That is telling me that during the portion of the cycle wherein the generator swings positive, it is attainging a positive voltage of 12.5 volts.

What voltage do you read that point in the cycle as being?

PW

In the first instance that display was to determine the applied frequency.  Not the voltage.  In the second instance - the DC voltage is NOT applicable.  Therefore - the voltage across the gate should be read as an AC voltage.  That's the advices that I was given.  Left to my own devices then I would say that the zero crossing line is midway between the peaks of the voltages displayed and the voltage should be read accordingly.  Therefore the value is something less than 6 volts.  And this adjustment because the signal from the generator is NOT DC but AC. 

Now - PicoWatt - let me know something from you.  I'd like to see it again - in black and white.  You have advised us that actually the offset as displayed needs to be applied to ALL values.  Let me know what you mean?  Are you suggesting that we must adjust the battery voltage from the mean average voltage displayed as DC to that -170 odd volts shown in the ofs display number?  And equally - are we to determine the voltage across the shunt to be offset by some 4 volts positive as displayed in that offset box?  Let me know.  Then I'll take your argument straight to my expert for comment.  It will be most entertaining.

Again,
Rosemary

I had to scroll back 8 pages to find this file reference.  That's how long it's been that this has been discussed.  Which says much about the value of discussion on this matter.  It's circular and going nowhere.

[TinselKoala]

You've exceeded her math capability with that question.
That's why her answer is word salad and refers to her "expert". She cannot read an oscilloscope unless it has numbers in boxes. I know this is hard for you to believe, but by now you must realize it is true. Else, why can't she just come out and say, 1 and a quarter divisions, at 10 volts per division, equals 12.5 volts. It's because she doesn't understand what a division on the screen means, or even what a "tick mark" is.

[picowatt]

In the first instance that display was to determine the applied frequency.  Not the voltage.  In the second instance - the DC voltage is NOT applicable.  Therefore - the voltage across the gate should be read as an AC voltage.  That's the advices that I was given.  Left to my own devices then I would say that the zero crossing line is midway between the peaks of the voltages displayed and the voltage should be read accordingly.  Therefore the value is something less than 6 volts.  And this adjustment because the signal from the generator is NOT DC but AC. 

Now - PicoWatt - let me know something from you.  I'd like to see it again - in black and white.  You have advised us that actually the offset as displayed needs to be applied to ALL values.  Let me know what you mean?  Are you suggesting that we must adjust the battery voltage from the mean average voltage displayed as DC to that -170 odd volts shown in the ofs display number?  And equally - are we to determine the voltage across the shunt to be offset by some 4 volts positive as displayed in that offset box?  Let me know.  Then I'll take your argument straight to my expert for comment.  It will be most entertaining.

Again,
Rosemary

Rosemary,

I must respectfully disagree with the answer you have given.  The voltage indicated on the FIG 3 capture for channel 3 during the portion of the cycle wherein the function generator output is a positive value is shown as approximately +12.5 volts.

I would like to see as well where I said that the offset value must be added to anything.  I did no such thing.  I believe it was you that stated I must somehow use the "ofs" numbers to measure or correct my values from the screen.

Regarding the -172volt offset indicated for channel 2 in that same FIG 3 scope capture, the -172volts is merely telling us how far down the position of the channel 2 zero volts line is from the center of the screen.

Referring again to FIG 3, the zero volt reference indicator to the left of the screen for channel 2 is 1.72 major divisions below the center of the screen.  The vertical sensitivity of channel 2 is set to 100volts per division.  1.72 divisions times 100volts per division is -172volts.  Therefore the zero volts reference line (and indicator) has been positioned (via the offset control) at -172volts below the center of the screen.  And that is what and all the "ofs" numbers are saying.

As to what the indicated battery voltage is.  During the portion of the cycle wherein the function generator is a positive voltage, I see the battery voltage trace (channel 2) as being approximately 2.5 minor divisions above the channel 2 zero volt reference line (again, the indicator to the left of the screen).  Channel 2 is set to 100volts per division.  There are four minor divisions per major division so each minor division equals one fourth of 100volts, which is 25volts.  2.5 minor divisions times 25 volts equals 62.5 volts, which is in close agreeent with the indicated 65volt mean value.

No where in estimating the voltages from optically reading the traces on the screen did I need, use, or require the "ofs" number.

All that is required to read a value off the screen is the "zero reference line" indicated to the left of the screen and the "volts per division" setting for the channel I am measuring. 

PW

[TinselKoala]

Here, PicoWatt. Maybe this will help you explain the offset to Rosemary. Maybe not.

Rosemary, do you realise that the Tek oscilloscope doesn't even display the offset value in a box on the screen, because it is generally of no use or interest to the user? The Zero levels are indicated, of course, but it is up to the user to count the tick marks from the scope's center line to the channel marker if the offset value is, for some strange reason, needed.

In the LeCroy diagram below, from the demo, the offset of the GREEN channel, the common mosfet drains, is explained. The offset value read in the channel settings box is nothing more than the "distance" that the channel's zero marker has been moved from SCREEN CENTER. It has nothing to do with what is traced on the channel. This number will be the SAME no matter what the waveform in the trace is, flatline or the most complex you can imagine... because all it is telling you is how far down or up the trace has been moved-- with the vertical position knob-- from the screen's exact centerline. It has NOTHING to do with the waveform or the values of the waveform's parameters.
You can see that the distance in volts, using that channel's scale, down from center, is the offset value given in the box.

You can prove this for yourself, Rosemary, if you have the scope handy. Just turn it on , don't give it any input, and wiggle the channel position knobs. You will see that the offset value given in the box depends only on where that little zero marker under the channel number on the left side of the screen is, relative to the center of the screen, and scaled by the channel volts per division setting. It has nothing whatever to do with the waveform at all.