any AC signals that is RIDING ontop of a DC offset voltage is "Floating" then right?

NO! Not neccessarily. If both signals are referenced to GROUND then neither is considered "floating". It's when you can NOT measure a signal or voltage relative to ground but rather relative to some other point, it would then be considered floating.

 

Take a look at my X-ray tube head schematic in a previous post of mine. That is an excellent example of a floating voltage. The filament circuit is isolated from Ground via a special transformer and all of the high voltage components and wiring and the X-ray tube are all totally immersed in insulating oil.

 

I had to post when I saw this thread, to the OP, don't worry, this concept confuses the so called "professionals" too! We had a situation at work where a well known company which sent out quite a few EE's and programmers were mistakenly measuring a "differential" signal and claiming that both signals were going high, and it resulted in countless arguments and blame. There was another case at work where an EE PE was trying to measure TTL signals and didn't reference the common side properly and it caused endless confusion...

 

I heard of designers putting Relays coil voltages on a Floating reference voltage so its above or below the ground

I'm trying to find out what circuits or network would use floating reference voltages and why

 

The voltage that operates a relay coil isn't a reference voltage. If you are running a relay logic tree, it can't float, either. It has to be referenced to ground if DC, or AC neutral if AC.

I think this has been mentioned in an earlier posting, but a 9 volt battery is a great example of a floating voltage. Put a meter across the terminals and read 9 volts. Measure from either terminal to ground and read just about anything. Since the terminal is not referenced to ground, it is floating, and cannot be measured with respect to ground.

Put the negative terminal to ground, and the other terminal is still 9 volts away from it, but it is also 9 volts positive with respect to ground. Tie it to positive 9 KVDC, and the battery now measures 9,009 volts with respect to ground. But still 9 volts terminal to terminal.

You can float any reference voltage as long as the absolute voltage difference between the terminals is all that is needed.

 

Thanks for the information and help

From a EE designers point of view

Whats the difference between 12 voltages referenced to ground VS floating ( absolute voltage difference) from node to node equals 12 volts also?

Why would a EE desinger choose the Floating voltage ?

What does having a reference above or below ground do in circuit or design?

 

Thanks for the information and help

From a EE designers point of view

Whats the difference between 12 voltages referenced to ground VS floating ( absolute voltage difference) from node to node equals 12 volts also?

Why would a EE desinger choose the Floating voltage ?

What does having a reference above or below ground do in circuit or design?

It depends on the system you're talking about, there might be some case where one of the wires is always the return or common, then you could say that that signal is the "ground" since you can measure all other signals with reference to it, even though it is not necessarily connected to earth. Or if there are 2 wires that are switched upstream (for example) both of them might be able to go high with reference to "ground" but also there could also be a voltage between them, one could go to 0 V and the other xx V, or vice versa, it's hard to explain in words. I work with transit vehicles and you see both of these methods a lot in that application, thus the confusion in measuring some of the signals even for the most seasoned "professionals" when they don't necessarliy understand the circuits they are testing.

 

this concept confuses the so called "professionals" too!

Confusion indeed.

The term ‘floating potential' was originally tightly defined by Electrical Engineers, Physicists and Mathematicians before there was a science of Electronics.

A science dictionary definition is

“The potential appearing on a single electrode, when all other potentials on other electrodes are held constant”

With this definition it is essential that the electrode in question is connected to the other electrodes and the potential appearing on it is the result of the impedances between the electrodes and their potential differences.

Electrical engineers use the reciprocal of impedance, called admittance, in the matrix circuit equation (network analysis - method of node currents)

I=YV

Where I is the vector of all currents, Y is the admittance matrix and V the vector of all voltages at circuit nodes.

All nodes are considered floating.

Given a table of the network admittances (impedances) the equation may be solved
for the voltages in terms of the currents or vice versa.

This definition simply means that a circuit node that is floating may take on any value that is dictated by the circuit parameters.


Unfortunately electronic engineers began using the term floating in what seems to be the opposite sense – That of ‘disconnected’.
Alternatively the term is used when the node voltage is not referenced to ground.

Most of the examples offered have been in these categories.

Thus memory makers use the floating-gate MOSFET transistor which has an extra gate not connected to any other part of the circuit.

Thus a battery or transformer supply is called floating if neither side is connected to ground.

 

Are you saying a floating potential= admittance

 

Are you saying a floating potential= admittance

Definitely not.
I said potential (=voltage) is found by solving the matrix equation

I=YV

I did say that the admittance is the reciprocal of impedance.

 

Is a resistor to ground on the input jack going to FLOAT the AC signal between VCC + volts to the other end of the resistor?

example

9volts VCC

AC signal of 5 volts P/P into input jack

1K resistor goes from input jack to the ground

If you measure with your DVM meter from input jack to VCC its going to have a voltage that is not 9volts but inbetween , so its a Floating reference it seems , its put DC offset on the AC signal

So my main point is that any LOAD resistor or a resistor to ground is adding DC offset which will be a FLOATING reference between VCC to Ground

 

That's why real world equipment has blocking capacitors connecting input jacks to the rest of the circuit.

 

The neutral lead no longer has AC as you think of it, and the hot lead is the powered wire.

This confuses me. In AC the "hot" and "neutral" wires are the same wire inside the generator or turbine or whatever. The only difference is that one side (neutral) has been earth referenced and so it is color coded different so we humans know which one was earthed.

I'm new to these things, but AC to me doesn't mean the black wire swings 120v rms above and 120v rms below ground (I know it does from "ground's" point of view), but instead conventional current comes out on "black" and returns on "white" and then comes out on "white" and returns on "black" 60 times a second. Is that right or am I just way off beam here?

Thanks for any help you can offer because I read things like, "The white wire is the return. It carries current, but has no voltage."

I know they must mean "no voltage relative to ground", but they never say that and to call the white the return only, makes me think that I don't understand AC at all,

Thanks again.

 

I think you understand AC correctly. The hot voltage on the hot wire swings back and forth, and if you have some resistive load connected between hot and neutral, then the conventional current behaves the way you described.

I don´t quite understand that last sentence, but the white is simply return in the sense that current regardless of polarity is "sourced" from the hot wire and should return through the neutral, but the current can as well close the circuit through anything else that is somehow connected to earth potential, like the safety earth wire or a person standing on floor.

 

Thanks for your response.

I understand how most, if not all, people refer to the hot vs neutral wire (they see it as in reference to ground), but my "misunderstanding" is that I believe that this is a convenient way to look at AC, but not reality and since your respond still said that current is sourced from the hot and returns on the neutral, it sounds like you're still speaking in terms of this construct.

I will try to say what I understand and would very much appreciate if you could tell me where I am wrong:

Theoretically, there is a spinning wire in a magnetic field that emerges from some turbine as two ends of the same wire (no load connected). These two ends alternate in a push-pull of electric potential. If neither of these ends were grounded then they would indistinguishable, but a load could be put across them and current would flow back and forth with neither one considered the source or return or better yet, one is the source and one the return and then they switch roles. Now, in our AC system, one is earth grounded for safety and so it is color coded white, but that doesn't change the fact that it is a source 60 times per second just as the black wire is.

Is that right? And if it is, why do people always say the hot wire is sourcing positive and then negative current? I understand there is nothing wrong with saying this in reference to ground, but I though most people are taught to follow conventional current, which would be the flow of positive charge, which to me means seeing it come from one side of the turbine and the coming from the other side.

I hope you can shed some light on this, because I think I am starting to obsess.

Thanks again

 

Now, in our AC system, one is earth grounded for safety and so it is color coded white, but that doesn't change the fact that it is a source 60 times per second just as the black wire is.

This depends how you look at it. From the electron point of view, the wires alternate as sources of electrons.
But since we use the concept of ground as a common reference point, you can look at it in the way that ground (I dont explicitly mean protection earth potential, but rather neutral wire since it is tied to protection earth-the "true" ground potential, so in simplified descriptions we treat it as ground too) stays where it is, and the hot wire is sourcing negative and positive voltage with respect to ground. It is called source in the way that it simply provides current (even though with alternating polarity), not in the way that it sources electrons.

The reason why it is treated like this I think is that when people are sort-of used to solving simple DC circuits, it is easier to look at the AC circuit the same way as a DC one - i.e. one "positive" voltage and one ground, and only keep the fact that the current changes direction 120 times a second somwewhere in the back of their heads, because it really is not needed for lots of things.

 

Phew, that sounds right and makes me feel better. Thanks for your explanation.

 

How can access/read your ESD article.
We are contemplating over floating vs grounded PCB board designs.Where do I get adv dis of both the schemes