New Rigol DS1054Z oscilloscope

[Fungus]

voltage is a difference of two potentials between two points in the space.

Of course.

zero is and can only be arbitrary

I disagree. I think that two people at opposite ends of the universe could create an object and when those objects are brought together there will be 0V difference between them.

Edit: ... although that value of 'zero' would have no practical use for engineers.

[JPortici]

difference
that's the key word. voltage, difference of potentials, is a result of an integral which is always a difference between two quantities. "Zero Volts" only means that the two points you are measuring are at the same potential.
Always two.

100 Voltage means that the difference between two points is 100. one could be 100 and the other 0.. or one 0 and the other -100... or 150 and 50, referred to a third point

[Fungus]

difference
that's the key word. voltage, difference of potentials, is a result of an integral which is always a difference between two quantities. "Zero Volts" only means that the two points you are measuring are at the same potential.

Yes of course, but they numbers aren't "arbitrary".

eg. I could (theoretically) examine two objects in complete isolation and tell you the voltage difference between them when they are brought together.

[tggzzz]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

After reading that, I felt like asking if there is such a thing as a standard voltage (or standard ground), kinda like we have a GPS frequency standard and some way of determining absolute power (dBm). But then what you are saying suggests that V is merely relative, like dB. Yet, V seems to be a fundamental component of power.

If such thing was needed, the earth is the absolute 0.

If only that was true, it would make engineering certain systems much simpler.

Start by considering why, in a thunderstorm, you are advised to keep your two feet together (amongst other advice). Consider what happens when there is a lightning strike nearby and large currents flow through the ground you are standing on. Hint: you don't want sufficient potential difference between your feet that some current goes throught your body.

If you don't like high current engineering, then consider antennas. Start by considering the physical processes by which monopole antennas "appear" to be twice their physical length. Hint: it is because currents flowing in the earth create a virtual image of the real physical antenna.

[ebastler]

eg. I could (theoretically) examine two objects in complete isolation and tell you the voltage difference between them when they are brought together.

Huh? You mean, without having a common reference potential to refer to in you examination of the individual objects? And you could tell the potential difference between them before you bring them together to compare them? How would you do that?

[canibalimao]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

After reading that, I felt like asking if there is such a thing as a standard voltage (or standard ground), kinda like we have a GPS frequency standard and some way of determining absolute power (dBm). But then what you are saying suggests that V is merely relative, like dB. Yet, V seems to be a fundamental component of power.

If such thing was needed, the earth is the absolute 0.

If only that was true, it would make engineering certain systems much simpler.

Start by considering why, in a thunderstorm, you are advised to keep your two feet together (amongst other advice). Consider what happens when there is a lightning strike nearby and large currents flow through the ground you are standing on. Hint: you don't want sufficient potential difference between your feet that some current goes throught your body.

If you don't like high current engineering, then consider antennas. Start by considering the physical processes by which monopole antennas "appear" to be twice their physical length. Hint: it is because currents flowing in the earth create a virtual image of the real physical antenna.

You are considering extreme conditions. But even in that conditions, the lightning strike just flows to the phisical ground because the earth doesn't have any potential and the current allways flows to the lowest potential possible with less resistence. So I don't see your point...
And also, I don't see any significan simplicity considering earth as the absolute 0V. Like some guys said here, voltage is just a matter of potential difference and the earth potential is a bit irrelevant.

[Fungus]

Huh? You mean, without having a common reference potential to refer to in you examination of the individual objects?

No, I mean with a common reference potential.

(or by counting the ratio of protons to electrons in the objects)

[bitseeker]

As far as standards go, there's the Josephson voltage standard. Interesting stuff.

[Fungus]

As far as standards go, there's the Josephson voltage standard. Interesting stuff.

"....is the basis for voltage standards around the World".

So there you go, voltages have an international reference standard. 

(you doubters!)

The next step is to build one and use my DS1054Z in math mode to measure true voltages.

[tggzzz]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

After reading that, I felt like asking if there is such a thing as a standard voltage (or standard ground), kinda like we have a GPS frequency standard and some way of determining absolute power (dBm). But then what you are saying suggests that V is merely relative, like dB. Yet, V seems to be a fundamental component of power.

If such thing was needed, the earth is the absolute 0.

If only that was true, it would make engineering certain systems much simpler.

Start by considering why, in a thunderstorm, you are advised to keep your two feet together (amongst other advice). Consider what happens when there is a lightning strike nearby and large currents flow through the ground you are standing on. Hint: you don't want sufficient potential difference between your feet that some current goes throught your body.

If you don't like high current engineering, then consider antennas. Start by considering the physical processes by which monopole antennas "appear" to be twice their physical length. Hint: it is because currents flowing in the earth create a virtual image of the real physical antenna.

You are considering extreme conditions. But even in that conditions, the lightning strike just flows to the phisical ground because the earth doesn't have any potential and the current allways flows to the lowest potential possible with less resistence. So I don't see your point...
And also, I don't see any significan simplicity considering earth as the absolute 0V. Like some guys said here, voltage is just a matter of potential difference and the earth potential is a bit irrelevant.

In what way, exactly, do antennas represent "extreme conditions"?

If you want something "closer to home", consider the current flows in ground planes on PCBs. The naive think that, because copper is a good conductor, a PCB everywhere on a ground plane is at the same potential. Unfortunately not, and the more experienced hardware engineers know it. Start by realising that if there is a signal conductor between a transmitter and receiver, then the return current doesn't go back directly from the receiver to the transmitter. Instead, at high frequencies, it is concentrated underneath and follows the signal conductor. And current flow is intimitely related to potential differences, and vice versa.

Exactly analogous phenomena occur in electrical distribution networks, except that the frequencies tend to be lower and the currents higher.

So no, the phenomena I allude to are real and important, not theoretial and esoteric.

[David Hess]

The whole "how much bandwidth is necessary to display a square wave" issue is why I prefer to think of oscilloscope performance in terms of rise and fall time.  And "peak detect glitch capture" when discussing DSOs.

[metrologist]

The whole "how much bandwidth is necessary to display a square wave" issue is why I prefer to think of oscilloscope performance in terms of rise and fall time.  And "peak detect glitch capture" when discussing DSOs.

Has anyone actually characterized this in the DS1xx4Z? I'd like to see that. I think I saw a topic here about that, or something similar. Rise time was one of my first questions about this scope as I was comparing it to my (defunct) Tek 2230A.

[ebastler]

Huh? You mean, without having a common reference potential to refer to in you examination of the individual objects?

No, I mean with a common reference potential.

OK, that I can understand, thanks for clarifying. I would not call that "examining them in complete isolation", though, since you need the reference "connection" between them.

[Fungus]

OK, that I can understand, thanks for clarifying. I would not call that "examining them in complete isolation", though, since you need the reference "connection" between them.

The 'connection' can be an agreed-upon voltage standard, it doesn't have to be the same physical object.

[ebastler]

OK, that I can understand, thanks for clarifying. I would not call that "examining them in complete isolation", though, since you need the reference "connection" between them.

The 'connection' can be an agreed-upon voltage standard, it doesn't have to be the same physical object.

Hmm, we are still not on the same page here. My take is that a "voltage standard" can give you a common scale, but you also need a common reference potential if you want to determine the relative voltage between two separate objects. Say you have one charged object on the moon and one on earth, and a calibrated voltmeter next to each object. How do you measure the potential of each object and predict what the relative voltage between the two will be when you bring them together?

You could use two "reference objects", which you have brought together and brought to the same potential at some point in the past, and then carried one to the moon. But again, that does not count as "measuring in isolation" in my book ;-)

Considering the thread title, we may be drifting ever-so-slightly off topic here... Apologies to everyone else reading this!

[Fungus]

You could use two "reference objects", which you have brought together and brought to the same potential at some point in the past, and then carried one to the moon.

OK, I see the confusion: The point is that you can create those two reference objects in complete isolation.

(using a universal standard for voltage reference objects)

[JPortici]

Hmm, we are still not on the same page here.

good luck
have fun

[ebastler]

You could use two "reference objects", which you have brought together and brought to the same potential at some point in the past, and then carried one to the moon.

OK, I see the confusion: The point is that you can create those two reference objects in complete isolation.

(using a universal standard for voltage reference objects)

Gridlock... 
So how do you obtain a "universal standard for voltage reference objects" without moving a reference object aross the universe, or running a wire across the universe?

[bitseeker]

I pasted a link earlier about the method used to establish a voltage standard. However, it would be best to move this discussion to its own thread. Perhaps create it in the metrology forum? It's a good topic and deserves to be fully explored.

[ebastler]

I pasted a link earlier about the method used to establish a voltage standard. However, it would be best to move this discussion to its own thread. Perhaps create it in the metrology forum? It's a good topic and deserves to be fully explored.

But, again - the Josephson standard only establishes a scale (the "slope") for measuring voltage, not an absolute reference potential, doesn't it?

Anyway, you are right that we are derailing this thread, and it seems that we are going round in circles; so I'm giving up. At least we have successfully demonstrated the difficulty of establishing "common ground" across a distance 

[canibalimao]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

After reading that, I felt like asking if there is such a thing as a standard voltage (or standard ground), kinda like we have a GPS frequency standard and some way of determining absolute power (dBm). But then what you are saying suggests that V is merely relative, like dB. Yet, V seems to be a fundamental component of power.

If such thing was needed, the earth is the absolute 0.

If only that was true, it would make engineering certain systems much simpler.

Start by considering why, in a thunderstorm, you are advised to keep your two feet together (amongst other advice). Consider what happens when there is a lightning strike nearby and large currents flow through the ground you are standing on. Hint: you don't want sufficient potential difference between your feet that some current goes throught your body.

If you don't like high current engineering, then consider antennas. Start by considering the physical processes by which monopole antennas "appear" to be twice their physical length. Hint: it is because currents flowing in the earth create a virtual image of the real physical antenna.

You are considering extreme conditions. But even in that conditions, the lightning strike just flows to the phisical ground because the earth doesn't have any potential and the current allways flows to the lowest potential possible with less resistence. So I don't see your point...
And also, I don't see any significan simplicity considering earth as the absolute 0V. Like some guys said here, voltage is just a matter of potential difference and the earth potential is a bit irrelevant.

In what way, exactly, do antennas represent "extreme conditions"?

If you want something "closer to home", consider the current flows in ground planes on PCBs. The naive think that, because copper is a good conductor, a PCB everywhere on a ground plane is at the same potential. Unfortunately not, and the more experienced hardware engineers know it. Start by realising that if there is a signal conductor between a transmitter and receiver, then the return current doesn't go back directly from the receiver to the transmitter. Instead, at high frequencies, it is concentrated underneath and follows the signal conductor. And current flow is intimitely related to potential differences, and vice versa.

Exactly analogous phenomena occur in electrical distribution networks, except that the frequencies tend to be lower and the currents higher.

So no, the phenomena I allude to are real and important, not theoretial and esoteric.

That's true. But you also must know that a ground plane on a PCB isn't the same as an earth connection.
That occours on a ground plane due to copper resistence and due to high frequencies (you don't give time to the copper potential balances).
In a thunderstorm you don't have that high currents for too long, I think... I live in a place where there's lightning strikes once or twice in a year, so I'm not used to it. But I think that a lightning strike only affects a small portion of the earth, and not the entire earth potential...

[tggzzz]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

After reading that, I felt like asking if there is such a thing as a standard voltage (or standard ground), kinda like we have a GPS frequency standard and some way of determining absolute power (dBm). But then what you are saying suggests that V is merely relative, like dB. Yet, V seems to be a fundamental component of power.

If such thing was needed, the earth is the absolute 0.

If only that was true, it would make engineering certain systems much simpler.

Start by considering why, in a thunderstorm, you are advised to keep your two feet together (amongst other advice). Consider what happens when there is a lightning strike nearby and large currents flow through the ground you are standing on. Hint: you don't want sufficient potential difference between your feet that some current goes throught your body.

If you don't like high current engineering, then consider antennas. Start by considering the physical processes by which monopole antennas "appear" to be twice their physical length. Hint: it is because currents flowing in the earth create a virtual image of the real physical antenna.

You are considering extreme conditions. But even in that conditions, the lightning strike just flows to the phisical ground because the earth doesn't have any potential and the current allways flows to the lowest potential possible with less resistence. So I don't see your point...
And also, I don't see any significan simplicity considering earth as the absolute 0V. Like some guys said here, voltage is just a matter of potential difference and the earth potential is a bit irrelevant.

In what way, exactly, do antennas represent "extreme conditions"?

If you want something "closer to home", consider the current flows in ground planes on PCBs. The naive think that, because copper is a good conductor, a PCB everywhere on a ground plane is at the same potential. Unfortunately not, and the more experienced hardware engineers know it. Start by realising that if there is a signal conductor between a transmitter and receiver, then the return current doesn't go back directly from the receiver to the transmitter. Instead, at high frequencies, it is concentrated underneath and follows the signal conductor. And current flow is intimitely related to potential differences, and vice versa.

Exactly analogous phenomena occur in electrical distribution networks, except that the frequencies tend to be lower and the currents higher.

So no, the phenomena I allude to are real and important, not theoretial and esoteric.

That's true. But you also must know that a ground plane on a PCB isn't the same as an earth connection.
That occours on a ground plane due to copper resistence and due to high frequencies (you don't give time to the copper potential balances).

The analogy is still valid; the speed of light and distance are the relevant parameters. As I explicitly stated, with electrical distribution networks the relevant frequencies are lower. Obviously you realise that lower frequencies imply longer time periods.

In a thunderstorm you don't have that high currents for too long, I think...

True, but that doesn't affect the point under discussion.

But I think that a lightning strike only affects a small portion of the earth, and not the entire earth potential...

And how, exactly, are you going to measure "the entire earth potential"? Your answer should take account of the speed of light.

You really, really should have a look at the precautions taken in industrial systems to take account of differing "earth" potentials.

[JPortici]

you should check the legislation in your country and what it says on the subject.. oh if it is a fun subject.
besides lightning, during a short to ground of an home appliance the earthing system resistance bust be lower than X mOhm because the ground potential around your house mustn't rise above Y volts or else the safety measures could not function properly and remove the short

and X depends mainly on the kind of soil under/around your house, which will also vary with temperature and humidity

sorry for being so vague, i studied as an electrical technician in high school but i never wanted to go on with that career so i forgot all the numbers but the concept is there

[JPortici]

oh and about the "derailing"
it itsn't the first in this topic, it won't be the last.

rule 25.

[canibalimao]

That's true. But you also must know that a ground plane on a PCB isn't the same as an earth connection.
That occours on a ground plane due to copper resistence and due to high frequencies (you don't give time to the copper potential balances).

The analogy is still valid; the speed of light and distance are the relevant parameters. As I explicitly stated, with electrical distribution networks the relevant frequencies are lower. Obviously you realise that lower frequencies imply longer time periods.

In a thunderstorm you don't have that high currents for too long, I think...

True, but that doesn't affect the point under discussion.

But I think that a lightning strike only affects a small portion of the earth, and not the entire earth potential...

And how, exactly, are you going to measure "the entire earth potential"? Your answer should take account of the speed of light.

You really, really should have a look at the precautions taken in industrial systems to take account of differing "earth" potentials.

You don't need to measure the entire earth potential. You just need to try to "send" the lightning strike to another earth connection than the one used by you, no?

I don't know almost anything of the industrial protection systems and how they deppend on earth connections, what I know is that the earth plane created in each build (house, factory, High voltage line supports, whatever) has a lot of testing in order to reach a regulated resistance value (in the order of mOhm). With this I just want to make clear that an earth point is virtually isolated from another point few meter away. If you just put a wire on the ground you won't have (it just won't work, believe me) an earth point.