Virtual Ground or floating ground on input of an op amp reads zero voltages why?

[pplus]

That`s what I told him already in post#3.

Yes, of course. This is just another way of explanation.

 

[danny davis]

Why is the Op amps input pins in the microvolts? Its because why?

 

[LvW]

Why is the Op amps input pins in the microvolts? Its because why?

See my post#9, last line.
Danny, do you read all the answers you get?

 

[danny davis]

Its a formula, but i still don't get why its in microvolts. Are u saying that every input pin on an opamp will always be in microvolts or is it just for diffential opamps?

is the opamps input pin in microvolts because why?

 

[LvW]

Its a formula, but i still don't get why its in microvolts. Are u saying that every input pin on an opamp will always be in microvolts or is it just for diffential opamps?
is the opamps input pin in microvolts because why?

OK - Danny, the primary function of an opamp is to amplify a differential voltage Vd (available between both inputs).
The gain Ao without feedback is very large (1E4....1E6).
Thus, we have the equation

Vout=Vd*Ao.

When Vout is within the linear operating range (several volts), for example Vout=5V we have

Vd=5/Ao=5/1E6=5µV (assumption: Ao=1E6).

Do you agree?

 

[danny davis]

Yes i understand what an Opamp does as far as amplify a small voltage or waveform into a bigger one, and the feedback resistor adjusts how much gain its going to be

What I don't understand is that, When I put my DVM probes on the input pins why is it zero volts or microvolts?

Are you saying that when you guys use an DVM meter and put your probes on the inputs of any op amp circuit it won't read because the DVM meter can't read microvolts so it say zero volts?

Is the inputs of any op amp circuit always like this? is this normal

My DVM meter can't measure microvolts, it can measure millivolts but when I put the DVM meter to millivolts setting it still read zero volts

Example:
When troubleshooting multiple op-amp stages lets say,
1.) Would the input pins always measure zero volts , microvolts?
2.) How would a Troubleshooting Tech, Know if the inputs were working or not?
3.) Because for me I can't tell if the inputs are normal/working because my DVM meter won't measure microvolts

Do u see my problem i'm having?

 

[pplus]

Yes i understand what an Opamp does as far as amplify a small voltage or waveform into a bigger one, and the feedback resistor adjusts how much gain its going to be

Hallelujah!

What I don't understand is that, When I put my DVM probes on the input pins why is it zero volts or microvolts?

Oh My ***!

Are you saying that when you guys use an DVM meter and put your probes on the inputs of any op amp circuit it won't read because the DVM meter can't read microvolts so it say zero volts?

YES!

Is the inputs of any op amp circuit always like this? is this normal

This is normal if opamp is in linear mode.

My DVM meter can't measure microvolts, it can measure millivolts but when I put the DVM meter to millivolts setting it still read zero volts
Example:
When troubleshooting multiple op-amp stages lets say,
1.) Would the input pins always measure zero volts , microvolts?

If opamp is in linear mode. If the op amp is in not linear mode, it is such a comparator is not true.

2.) How would a Troubleshooting Tech, Know if the inputs were working or not?

Based on the logic of the scheme. Linear / non-linear mode, open / closed feedback, positive / negative feedback.

3.) Because for me I can't tell if the inputs are normal/working because my DVM meter won't measure microvolts

You can tell whether or not the circuit operates.
You would do well to get yourself a bit of theoretical knowledge. At least in the amount of Wikipedia.
https://en.wikipedia.org/wiki/Operational_amplifier

 

[godfreyl]

1.) Would the input pins always measure zero volts , microvolts?

Zero volts between the two inputs. However there is often an easily measured voltage between the inputs and ground.
e.g. Both inputs are at +2V, so there is 0V between them.

2.) How would a Troubleshooting Tech, Know if the inputs were working or not?

You don't check if individual pins are working. You want to know if the opamp as a whole is working, so you apply a signal to the input of the circuit and check the output to make sure it's correct.

Example:
In the circuit below, if I apply +1V at the input, I expect to see +4V at the output, so that's what I would check.

At the same time, both opamp inputs will be at +1V and there will be almost zero volts between them. I would not bother to check that though unless the circuit is not working and I'm trying to troubleshoot it.

 

[danny davis]

So you don't check the input pins on the op amp , you just check Vin and the output of the Op amp?

 

[godfreyl]

Yes, that's right.

 

[danny davis]

So it doesn't matter is the Opamp is Linear / non-linear mode, open / closed feedback, positive / negative feedback
The input pins will be in the micro volts for DC and AC signals or just DC volts?

You always measure the V input and V output not on the Input pins right? either its DC or AC voltages

 

[pplus]

So it doesn't matter is the Opamp is Linear / non-linear mode, open / closed feedback, positive / negative feedback
The input pins will be in the micro volts for DC and AC signals or just DC volts?

In linear+closed feedback+negative feedback mode only

You always measure the V input and V output not on the Input pins right? either its DC or AC voltages

Yes, the voltages is measured relative to the ground, not differential voltage.