Zero Potential is not ground, How do you tell the difference?

[danny davis]

How do you tell the difference between a ZERO potential and a ground that is zero volts?

They both are Zero Volts

My Manager gave me an example , when you hook up two different power supplies and set them to the same voltage and measure with your DVM. The potential difference between them is ZERO

So is this an open or short?

If you're bench checking a circuit board and you get NO output from that stage that has a failure, is it a short, open or a Zero potential?

1.) Short has a voltage Potential?
2.) Open has a voltage Potential?
3.) Zero Potential

At work I have a BAD board that has NO output, the output Components are Referenced going to a DC ground, all the other components went to a Signal Ground. I had to Remove each component one by one that was tied going to the DC ground to chase this short. After Removing IC after IC after lifted up components to isolate them for different stages and branches , etc. etc. it still has no output.

Is this the best way to track down a Ground Short? is to remove one component at a time?

My Manager said since there is No output that doesn't mean there is a short because there is Zero volts on the output. It could be it's at a zero potential. What does he mean by this?

I think it has something to do when you have isolated grounds, Digital grounds and Signal Grounds that when you measure between them using a Volt meter it will measure zero potential since they are the same voltage which is ZERO since its ground. The continuity tester on my DVM will measure an OPEN tho between the two isolated grounds

Now if the Digital ground and the Signal Ground are SHORTED , what happens? the Potential is at ZERO volts but you have a SHORT. So the continuity tester on my DVM will measure a SHORT between the two isolated grounds

 

[dick_freebird]

Force current relative to "real" ground and see what voltage
you get. Any driven ("virtual ground") zero-potential node
will deflect against driver resistance (to the extent that a
feedback scheme doesn't fight it, and all of those have a
limit somewhere). A perfect ground-ground will not.

Using some other power supply as your measurement
return is a good way to distinguish open from grounded.
Uses the meter impedance as a "pull".

 

[danny davis]

why a circuit may have zero volts on its output
1.) Component Open or shorted before the output pin = Zero volts on output pin = Zero Potential
2.) Using a volt meter , with zero volts on the output pin because of a SHORT before the output pin will measure Zero volts on the volt meter referenced to ground = Zero potential between the output pin zero volts and reference ground
3.) A Zero volts node doesn't mean its a ground, its a zero potential, It's confusing because when you use a Volt meter , it will measure Zero volts and you will think its a ground or reference when really is a zero potential. So how do you tell the difference?

- - - Updated - - -

Force current relative to "real" ground and see what voltage
you get. Any driven ("virtual ground") zero-potential node
will deflect against driver resistance (to the extent that a
feedback scheme doesn't fight it, and all of those have a
limit somewhere). A perfect ground-ground will not.

How do I put a Force current on the ground node? using an external power supply?

Using some other power supply as your measurement
return is a good way to distinguish open from grounded.

How can this distinguish an open from ground?

Uses the meter impedance as a "pull".

How do I use my meter impedance as a pull? what u mean by pull?

 

[danny davis]

How can you test if an OP-amp or a digital 7400 family is shorting from VCC to ground or it shorting to ground?

Can I use my Ohm meter?, Diode checker? or continuity checker?

I can put my DVM fluke meter from IC pin VCC to IC pin Ground and measuring if there is a short?

What tests can I do to tell if the Op amp or Digital IC chip is shorting to ground?

 

[FvM]

Somehow I feel reminded to Joseph Weizenbaum's Eliza :smile:

 

[godfreyl]

Can Eliza find SHORTS? If an IC is SHORTED to ground, how can we use ELISA to find the SHORT? I can use elisa to find if the opamp or digital ic is SHORTED to ground?

 

[nick703]

sorry godfreyl i didn't get it What is Eliza ?

 

[Tunelabguy]

sorry godfreyl i didn't get it What is Eliza ?

Eliza was a computer program in the 1960's that tried to simulate human interaction by generating plausible looking responses to whatever you typed in to it. I tried it once back then. It was like talking to a inane psychiatrist. It was like a very primitive form of Siri, but without voice recognition and without any real usefulness.

 

[FvM]

I think the resemblance is the method of changing any answer into a new question - without thinking.

 

[danny davis]

Can you please help me out, i don't if this would work or not

How can you test if an OP-amp or a digital 7400 family is shorting from VCC to ground or it shorting to ground?

Can I use my Ohm meter?, Diode checker? or continuity checker?

I can put my DVM fluke meter from IC pin VCC to IC pin Ground and measuring if there is a short?

What tests can I do to tell if the Op amp or Digital IC chip is shorting to ground?

 

[dick_freebird]

What answer could we give that does not yield a dozen
more?

 

[danny davis]

Easy stop going in my threads , that will fix your problem

Your first name represents you very well

Stay out of my threads