@ #12: Is this really your opinion?

From dexter´s (the questioner) various questions I deduce that he had problems to understand the meaning of the term "virtual ground". And I have tried to give some explanations. I have shown why and under which conditions the diff. voltage has a very small value and that we normally can neglect this voltage which then leads to the term "virtual ground". Was anything wrong?
I think I didn´t overstrain dexters intelligence and that I didn´t expect too much from him.
How can you say that I didn´t adjust my "delivery to fit the audience"?

Do you really think that your (wrong) answer "the inverting input actually HAS zero volts on it" is more appropriate?

 

A virtual ground (at 10 to 50 uvolts) will show zero volts in any measuring range you can choose on a $300 Fluke DVM.

You are free to explain why Dexter can't measure anything except zero volts at a virtual ground, regardless of how he places his test leads.

 

#12: Perhaps you have overlooked that I didn`t speak about "how to measure".
Quotes dexter:
* How can it amplify zero volts on the input pin?
* The input pin has millivolts? , microvolts? or nanovolts?
* Zero volts = Zero current . That doesn't make sense to me

I´ve got the impression that there was some confusion about the opamp´s input diff. voltage on dexters side - and it was my intention to give him some help and some (theoretical) background information. That´s all.
What is the problem you have with that?

 

Expounding a great long explanation of minute differences that the OP could not measure, even if he knew how attach a DVM to the circuit. It is my opinion that beginners need to learn the basic fundamentals, like, "what does ground mean" and, "how can a point named ground have any current flowing through it" before they delve into the tiny error terms that happen in op-amps.

Still, it's your time and fingers that are getting used up. Go ahead and tell people that can barely put batteries in a flashlight that there are unmeasurable (to them) errors on the inputs of an op-amp or to use an Arduino on their Christmas lights. Don't worry about my opinion. The beginners need to know when to bow to a higher intellect, even if they don't understand a word you're saying and can't measure the difference.

 

Go ahead and tell people .... that there are unmeasurable (to them) errors on the inputs of an op-amp .......

The input diff.voltage is not an "error on the input". It is simply necessary to get an output.

The beginners need to know when to bow to a higher intellect, even if they don't understand a word you're saying and can't measure the difference.

Are you sure that the OP Dexter didn`t "understand a word" I was saying?

Sorry to say - but did you realize that it was you who has caused some confusion on Dexter´s side? See his answers in post#26 and #28 to your former statements (..input pin HAS zero volts,...it is amplifying the current).
Perhaps it was just a "floppy" formulation from you, but a voltage input opamp amplifies no current.
Regards
LvW

 

@ #12 and LvW, this is how the infamous ETO debacle started. With the same OP.

 

@ #12 and LvW, this is how the infamous ETO debacle started. With the same OP.

Shortbus, can you please explain in more detail?
What is the "infamous ETO debacle"?

EDIT: Just now I have decided not to further continue this thread. Perhaps, this is best.

 

I have participated in public threads with the moderators at this site wherein I observed at least one of them posting the idea that intentionally telling a beginner things that will not help him understand is frowned upon. I constantly try to communicate with posters in a way they can understand. Sometimes I fail, but it's not because I'm telling them about things that have little to no bearing on what they are trying to do.

"Why can't I measure any voltage on a virtual ground?"
"Oh, it does have voltage
Here's a technically correct explanation that proves it is not zero."
"So why can't I measure it?"

Because there is a high probability that the voltage is less than half a significant digit on the most sensitive range of your best meter.
Besides that, of the 12,207 operational amplifiers that Mouser sells, only 75 of them have an input offset voltage of 50 uV or less. That means that there is a 99.4 percent chance that, whichever op-amp you have been trying to measure, the input offset voltage will be greater than the microvolts of error.

I need a vacation. When I start caring whether the beginners are being taken on a Nantucket Sleigh Ride I've been on this site too much.

 

So what kind of meter or o scope will measure the virtual ground voltage?

 

I tried to explain but my post was deleted a few weeks ago. The OP caused non stop arguments like this, in the end it led to the massive blow up over there with alot of people leaving over it.
Far from being a newbie the op has had over 20 jobs as a tech (his words over there), in various guises he has been asking these questions for around 4-5 years. Most electronics forums that he isnt banned from will have the same kind of posts.
For more info look at ETO and a user Billy Mayo (the op here)
But yes short bus is correct, this is exactly how it all started! over there

 

A very big Thanks, Shortbus and LG.
I was already beginning to suspect something wrong when a third of the chat forum threads were the questions of one person. Now I can understand why someone would take him on the aforementioned sleigh ride.

I still don't think it's nice to misdirect beginners to aspects so small they can't be readily measured or separated from other error terms, but I'm going to stop trying to protect this one.

 

So what kind of meter or o scope will measure the virtual ground voltage?

What do you expect it to tell you if you do measure it? Say it measures 3uV. What are you going to do with that information?

Bob

 

A very big Thanks, Shortbus and LG.
I was already beginning to suspect something wrong when a third of the chat forum threads were the questions of one person. Now I can understand why someone would take him on the aforementioned sleigh ride.

I still don't think it's nice to misdirect beginners to aspects so small they can't be readily measured or separated from other error terms, but I'm going to stop trying to protect this one.

That is a really tough call isnt it! butt thats were you guy's with experience come in, Not every newbie is the same.
Example, newbie wanting to learning electronics from ground up, wants the theory etc, then the 'Truth', detail or whatever matters, same way as conventional and electron doo dah matter.

Newbie, just wants to get x y z working, dosnt need/want debate on string theory or how many electrons you can balance on a 3miltrace.

The hard bit sometime is working out what kind of newbie your dealing with!

 

I'm trying to find the input voltage that it' amplifying, mostly on summing mixer op amp circuits or for op amps circuits that don't have an input resistor

 

I want to take this opportunity to apologize for interrupting a good trolling and a personal apology to LvW for calling him a show-off...if he was just trolling the troll.

If LvW still thinks a beginner can learn the basic theory of op-amps by trying to measure 50 microvolts that is often mixed in with a millivolt (or more) of offset, then we're going to have to conclude that we disagree.

 

The hard bit sometime is working out what kind of newbie your dealing with!

For me, it's always about trying to find the right level of communication, at least in the first couple of exchanges, and sometimes I fail. Nobody can please all the people all the time. Some people just whip out their PhD level thinking and ramble on like it's the OP's problem if he doesn't understand Differential Calculus, or have laboratory grade equipment to use for measurements, or even understand how to connect a DVM to measure ohms.

I don't like that. It doesn't serve the OP and it doesn't make this site look good.
Still,it seems I have my foot squarely in my mouth on this one.

 

Shortbus, can you please explain in more detail?
What is the "infamous ETO debacle"?

EDIT: Just now I have decided not to further continue this thread. Perhaps, this is best.

Every time I try, the mods delete. Little Ghostman and Eric also have tried.

 

Maybe I'm totally off base on my way of Trouble shooting something like this, but... Wouldn't it make more sense to give the boards the input voltage they want (it's on the print), and check that the outputs are correct? Instead of nitpicking each and every component? What do you care what is going on, component by component, if the signals are doing what they are supposed to?

If there is no output, you then back track from the output pin to find the 'dead' component.

 

If LvW still thinks a beginner can learn the basic theory of op-amps by trying to measure 50 microvolts that is often mixed in with a millivolt (or more) of offset, then we're going to have to conclude that we disagree.

I know, I am breaking my own rule not to continue this thread.
Nevertheless, as you adress the above sentence personally to me:

Even for a beginner (no - especially, for a beginner) I think it is very important
a) to know if at one particular node the voltage is zero or not (and WHY !)
b) to know why he perhaps fails to MEASURE it correctly.

This can be of great help to learn
a) how to apply basic rules to calculate node voltages,
b) how to perform measurements (and to learn why some measurements cannot reveal the whole truth).

According to my experience, it is a rather important engineering task not to trust blindly all measurements (and/or simulation results) but to know
a) what could be roughly expected (theoretically), and
b) why it perhaps cannot be verified by measurements.

Final remark: The subject of the whole discussion in this thread (as far as it was a technical discussion) and my explanations were based on one of the most important principles in the field of analog electronics:
The principle of negative feedback.
And it would be a great surprise to me if my attempt to explain why there must be a finite opamp input voltage was not a "delivery to fit the audience" (Quote #40).

 

As a veteran newbie this is my opinion, you both completely miss the point. One of you gives a answer that will suite one type, the other gives an answer that will suite someone else. Now a smart person would look at that and think, Hmmm we have the bases covered. For us newbies its pretty funny when you guy's with experience get into technical debates, personally I love it. Deeper and deeper down the rabbit hole it goes, more and more technical jargon and formulae come out and before anyone knows it you have a thread rich in information.
So just in case you miss my point.. To us newbs its important you both post and express things in the way you feel is correct, in this case what has a newb learnt??
Yes there is something there but he dosnt have a hope in hell of measuring it with normal newb Chinese equipment, superb information. I now know that technicaly a virtual ground isnt exactly 0V but 1. in most cases that wont matter to newb, 2. if it does matter then I have to up my game and learn a bit more and buy some decent equipment.
3. it matters to me but I am skint therefore wasting my time at present trying to measure it.
Thanks guy's you managed a perfect example of team work without even knowing

AND they call us NEWBS lol (joking)