Floating grounds? how do u find them?

[danny davis]

How do u find floating grounds on a circuit?

The schematic of a circuit doesn't tell you where the floating grounds are , its just a ground symbol

Because each section, stage and IC chip has a floating ground

How would u find them?

When measuring with a DVM and putting the black probe not on the right ground will not give you a voltage reading , so how do u find the floating ground?

example: If a circuit PCB board design had 10 different floating grounds how would u find them?

 

[barry]

First of all,'ground' is a pretty arbitrary term. What do you mean by a "floating ground"? Do you mean a net that is not connected to some OTHER net that you've named "ground"? If that's the case, set your DVM to measure ohms, put your 'black probe' on your 'ground' and measure the resistance to the other points. If you measure other than zero ohms, that OTHER point is not ground.

 

[danny davis]

Floating Ground, I mean that its isolated from the other grounds

There is 12 different grounds that are isolated from each other

Some of the Isolated grounds have either positive or negative DC offset

The problem I'm having is on the schematics it shows only the ground symbol , but it doesn't say which ground it is and if it has a DC offset voltage

So how do u find the ground of each IC chip or stage? because the ground symbol on the schematics all look the same but the schematic doesn't tell you which isolated ground it is

So how do u find out?

How can you make multiple isolated grounds without using a multiple isolated outputs on a transformer?

 

[Audioguru]

All grounds on a schematic are connected together so there is no DC offset voltage between them.
A ground does not float because it is a common reference voltage that is usually 0V.

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All grounds on a schematic are connected together so there is no DC offset voltage between them.
A ground does not float because it is a common reference voltage that is usually 0V.

 

[danny davis]

All grounds on a schematic are connected together

No they are not connected together

This circuit im testing at work has 16 different grounds and the schematic doesn't tell you which ground is which ground because the ground symbol is the same on the schematic

If i put my DVM meters black probe on a ground, I don't get any voltage reading on my meter because its not the right ground for the IC chip or stage of circuit

These grounds are not connected together they are all isolated from eachother

 

[barry]

There is something wrong with your use and understanding of "grounds". If you use the SAME symbol on your schematic for ground, then they are,by definition, all connected together. If they are not connected, then you are NOT using the SAME symbol on your schematic. You can call those points 'floating ground', but THEY ARE NOT GROUND, they are simply nets like any other net on your schematic. There is obviously some disconnect between your schematic and your pcb. You need to go back and verify your schematic and netlist.

 

[danny davis]

How do u find floating grounds when the schematic doesnt tell u?

ccan floating grounds have a dc offset voltage?

 

[godfreyl]

Floating Ground, I mean that its isolated from the other grounds

There is 12 different grounds that are isolated from each other

"Floating Ground" is an oxymoron. If it's floating then it's not grounded, by definition.

If you've got "grounds" on your PCB that are isolated from each other, then there's something wrong with your PCB (or your understanding of the circuit).

As Audioguru said in post 4:

All grounds on a schematic are connected together so there is no DC offset voltage between them.

 

[danny davis]

Well I continuity checked the grounds and they don't make continuity with each other at all

 

[barry]

Well I continuity checked the grounds and they don't make continuity with each other at all

THEN THEY ARE NOT GROUNDS!!

Why are you resistant to accepting what people here are telling you?

1) As godfrey points out, there is no such thing as a floating ground. Either it's ground, or it's not.

2) If something you expect to be ground isn't, then you've got two choices: Your schematic is wrong or your PCB is wrong.

 

[danny davis]

Well the schematic has ground symbols so its a reference for sure

 

[Audioguru]

Please attach your schematic for us to see the "16 floating grounds".

 

[FvM]

This circuit im testing at work has 16 different grounds and the schematic doesn't tell you which ground is which ground because the ground symbol is the same on the schematic.

With most CAD tools, "different grounds" would get an unique net designator along with it. Needless to say, that it's absolutely required for readability of a schematic. But there are surely ways to cheat a tool if you want to make mysterious schematics intentionally.

If the "circuit" involves multiple boards, theres a certain risk that they use different unconnected ground nets without descriptive names. But in this case, looking at connectors and wiring diagrams should clarify things.

 

[danny davis]

The grounds don't connect together because i continuity check them on my DVM meter and it doesn't beep. The grounds are isolated, but my main question is how do u find these ground nets? Because the schematic just shows a ground symbol but it can be of or which one out of 16 different ground nets?

 

[Tunelabguy]

The grounds don't connect together because i continuity check them on my DVM meter and it doesn't beep. The grounds are isolated, but my main question is how do u find these ground nets? Because the schematic just shows a ground symbol but it can be of or which one out of 16 different ground nets?

If the schematic uses the same symbol for all the grounds then they are supposed to be connected together. The fact that you checked continuity with the DVM just shows that the physical circuit does not conform to the schematic. It is the same as saying the schematic shows Q1 is a NPN transistor, but in the circuit board Q1 is a PNP transistor. Obviously the schematic is lying.

 

[danny davis]

right, thats my whole point is that how do u find out which ic chips or components are referenced to which net or ground? the hard part is finding the reference point, how would u guys find the reference or net? if i measure at the wrong reference or net it won't give me a voltage reading on my DVM meter

 

[barry]

You need to find out why the schematic is different than the PCB. Do you have the original schematic file?(What tool is it?) You are going to have to go through the schematic and click each ground symbol and determine what net it's connected to. You could also use the netlist file and search for each IC ground pin and find what net it is on.

 

[danny davis]

HOw can i find each netlist without using the schematic just using the pcb?

to find each IC chips Vee and ground is easy, the hard part is finding where that ground is netlist to

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I Dont have the netlist file, so how can u find the ground netlist with just the pcb and a DVM meter?

 

[barry]

Good luck. You've got a schematic that doesn't match your pcb and you don't have a netlist. I suppose you don't have the original PCB file and layout software, either. Well, then you've only go one choice: measure every point on your pcb with your meter.

 

[FvM]

Reviewing the discussion, I think the "wrong schematic" is just a (plausible) guess, made due to lack of information. We don't know about the kind of circuit or what the OP want to achieve. At the end of day, things may turn out to be different. I wonder if the OP's other threads are somehow related to this topic?