Confusion about Analog Signal Wiring and The Term " ground"

Thread Starter

alexfrey

Joined Feb 23, 2019
22
I am a new engineer in automation industry.

For a while, I have tried to understand analog input & output signals and (differential , single ended wiring etc). I think , the reason of my being confused about these subjects is the usage of word " ground " for everything. I mean some says ground for both earth ground and common and I think it makes me confused.
For example, while I was learning about single ended and differential wiring. I saw that in single ended wiring measuring is made relative to ground. is this ground earth ground or common of power supply ? I attached an example photo taken from this website. As I know, the symbol used for "ground" in that photo is earth ground symbol but from my knowledge, it shows here common of power supply (I know depends on desire, it can tie or not tie to earth ground)
A friend of mine told me that "-" of analog input module is always tied to chassis ground inside module. Is it really "always" or it depends on choice ?

Thanks.
 

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MaxHeadRoom

Joined Jul 18, 2013
21,227
I am a new engineer in automation industry.

For a while, I have tried to understand analog input & output signals and (differential , single ended wiring etc). I think , the reason of my being confused about these subjects is the usage of word " ground " for everything. I mean some says ground for both earth ground and common and I think it makes me confused.
Thanks.
Not only that, but the earth ground symbol is routinely used for chassis ground.!
Including popular works on Electronics theory.
Unfortunately the way it is, you have to analyze any schematic or article that you may be interested in and decipher from the circuit itself what the originator intended when the earth symbol is used..
Sad to say.:confused:
Max.
Dr Archambeault had a rant video on this.
 

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MrChips

Joined Oct 2, 2009
21,666
Welcome to the crazy world of electronics. Ground means different things to different people. Tell your friend that the boyz at All About Circuits say that he is wrong.

upload_2019-2-23_16-48-15.jpeg

Edit: Max beats me to it.
 

nsaspook

Joined Aug 27, 2009
7,476
I am a new engineer in automation industry.

For a while, I have tried to understand analog input & output signals and (differential , single ended wiring etc). I think , the reason of my being confused about these subjects is the usage of word " ground " for everything. I mean some says ground for both earth ground and common and I think it makes me confused.
For example, while I was learning about single ended and differential wiring. I saw that in single ended wiring measuring is made relative to ground. is this ground earth ground or common of power supply ? I attached an example photo taken from this website. As I know, the symbol used for "ground" in that photo is earth ground symbol but from my knowledge, it shows here common of power supply (I know depends on desire, it can tie or not tie to earth ground)
A friend of mine told me that "-" of analog input module is always tied to chassis ground inside module. Is it really "always" or it depends on choice ?

Thanks.
Take a look at this:

https://www.analog.com/media/en/technical-documentation/application-notes/41727248an_347.pdf
 

MrChips

Joined Oct 2, 2009
21,666
Your device does not have to be "grounded". It can also be "floating".

Think of an automobile or aircraft. There is no "earth ground" in either case.

Earth ground means that your device is referenced to "earth" at "earth potential". This is also referred to as "safety ground".

In electronics, when someone refers to ground they really mean "circuit common" or sometimes "chassis ground". We can understand what "chassis ground" means on an automobile and airplane. Yet this does not have to be the same as "circuit common".

"Circuit common" refers to a point or node on the circuit that we choose to call our "zero volt reference". I can build an audio amplifier using a 12V battery or power supply. My circuit might need +6V and -6V. Hence I can select a point in the circuit at +6V and call this "COMMON". All my voltage measurements are made with reference to this 0V point. Hence my test meter will indicate +6V and -6V in various parts of my circuit even though the circuit might be "floating" at 1000V.

Hence connecting the negative terminal to ground is not always the case. There are times when one may elect to connect the positive terminal to ground.
 

Thread Starter

alexfrey

Joined Feb 23, 2019
22
I am a new engineer in automation industry.

For a while, I have tried to understand analog input & output signals and (differential , single ended wiring etc). I think , the reason of my being confused about these subjects is the usage of word " ground " for everything. I mean some says ground for both earth ground and common and I think it makes me confused.
For example, while I was learning about single ended and differential wiring. I saw that in single ended wiring measuring is made relative to ground. is this ground earth ground or common of power supply ? I attached an example photo taken from this website. As I know, the symbol used for "ground" in that photo is earth ground symbol but from my knowledge, it shows here common of power supply (I know depends on desire, it can tie or not tie to earth ground)
A friend of mine told me that "-" of analog input module is always tied to chassis ground inside module. Is it really "always" or it depends on choice ?

Thanks.
Thanks for answers, As I understood, respond of question above highlighted in black is that it is power supply "-" not earth ground and the earth symbol is in attached photo is used wrong. Am I right ?
 

MaxHeadRoom

Joined Jul 18, 2013
21,227
Thanks for answers, As I understood, respond of question above highlighted in black is that it is power supply "-" not earth ground and the earth symbol is in attached photo is used wrong. Am I right ?
In light of the current (mis)useage, I would say that all of the earth symbols were common to the battery -ve .
But I could be wrong!:confused:
Max.
 

BobTPH

Joined Jun 5, 2013
2,503
Usually, what is meant by ground is the circuit node that all signals are referenced to. Thus, ground is 0V and signals may be positive or negative with respect to that ground. In order to a signal to go from one device to another, they must share a common signal ground. Consider two battery operated devices, neither has an actual earth ground. If we try to send a signal over one wire from one to the other, nothing happens. This is because current must flow in order to detect a signal. So we use two wires, one for the signal, and the other for ground. In a battery operated device with a single voltage source, the ground is typically connected to the negative terminal of the battery, though this is not necessary as long as both sides know it.

All of the above is for devices and signals that are connected electrically, i.e, there are wires between them. There are other methods of transferring signals, eg. optically or magnetically, that do not require a common ground. In these cases no current flows directly from one device to the other.

Bob
 

crutschow

Joined Mar 14, 2008
25,265
In summary, in most electronic applications "ground" is the same as the circuit "common" or the point to which all voltages are measured (edit: irrespective of the ground symbol used).
If it's actually earth ground, it's usually apparent from the circuit design or the discussion.
Usually (but not always) earth ground is used for the safety ground, and not the circuit ground (common).
 
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MaxHeadRoom

Joined Jul 18, 2013
21,227
But the bottom line is, as is shown by the OP's example, the Earth symbol is used for circuit common, I am not surprised he is confused.!!
IF the correct symbols were used in the example, we would not be having this discussion!
This is assuming that the originator did not really mean Earth for common.:rolleyes:
Max.
 

kubeek

Joined Sep 20, 2005
5,731
A friend of mine told me that "-" of analog input module is always tied to chassis ground inside module. Is it really "always" or it depends on choice?
That is generally not true. Yes, in installations the minus pole of the power supply is tied to PE at some point, but modules don´t do this connection on their own. Right now I am working on an AI module, and the measurement circuitry is floating relative to the power supply anyway, and the only components that are connected between anything and PE are some capacitors for emc compatibility.
 

MrChips

Joined Oct 2, 2009
21,666
Back in the early days of transistor radios, it was common to use a battery with PNP transistors. Guess what? The positive terminal of the battery was commonly the "zero voltage" ground connection.
 

MaxHeadRoom

Joined Jul 18, 2013
21,227
Back in the early days of transistor radios, it was common to use a battery with PNP transistors. Guess what? The positive terminal of the battery was commonly the "zero voltage" ground connection.
So was the first vehicle I owned, DC generator/battery with body frame connected to +ve. ;)
Max.
 
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Thread Starter

alexfrey

Joined Feb 23, 2019
22
In light of the current (mis)useage, I would say that all of the earth symbols were common to the battery -ve .
But I could be wrong!:confused:
Max.
Thanks for respond. Reading the answers here also making some search on web, I am trying to get over confusions in my head.
But on some websites, it says in single ended wiring (signal is always references to EARTH ground) but I really don’t understand it. why they emphasize the earth. I think it can be earth grounded but without Earth connection just circuit ground is also be fine.
What do you think about this ? Thanks in advance (I hope I could explain my question well)
 

MaxHeadRoom

Joined Jul 18, 2013
21,227
Circuit ground and earth ground is two different definitions, although they can also be connected in some cases, the confusion arises when the terms are incorrectly used and the wrong symbol(s) are used, especially when the earth symbol is commonly used for any power supply common, as it often is.
Earth grounded implies it is actually referenced to an actual earthed conductor.
Max..
 
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