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Grounding in electronic circuits

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MPYC

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Hi dears.
I have questions about grounding in electronic circuits. plz help me know that:
1- does electronic circuits that working with signals need to grounding?if yes. may you make me some examples?
2- which parts of every electronic system(power supply, ac driver, etc) must be connect to ground and how?

my purpose in this forum is obtaining knowledge for better design. I faced with some problem that I will bring it up in other post.

Thanks a lot.


 

deepsetan

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Hi,

1. yes
2. What do you mean by 'part' and 'how'? It is too general. Maybe you should come with schematic then you'll more understand.
 

KlausST

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Hi,

What do you mean with grounding?

More an EARTH connection, or the use of a "signal ground".

If "signal ground" then this is very basic. Signal ground acts as a reference to all voltages that are related to this potential.
On PCBs you often see signal ground as a ground plane (copper plane, filled copper area). And it is recommended to do so.

Especially with power, digital switching, high speed signals, analog signals ... it is mandatory to use a ground plane.


Klaus
 

chuckey

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The most important earth (or ground) is the PE, protective earth. This is so if insulation fails somewhere in the circuit, the exterior metalwork cannot become live with respect to the actual earth, i.e. adjacent metalwork, plumbing etc. This only applies to mains powered equipment. The theory being that if the insulation fails in a mains transformer, the current flowing from the mains live through the fault will be directed to earth so blowing the mains fuse and making sure that the external metalwork does not become live.
Signal circuits normally need a ground because they are single ended, i.e. the signal voltages are measured with respect to a common line, which is normally connected to the chassis. The chassis or earth plane in a PCB is then meant to act as a low impedance path for all the signals. Because of all the signal currents that can flow through the earth, often special layouts are needed so that the high current path does not also include the path for a low level signal.
Frank
 
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MPYC

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thank you. it was usable.
according to your note generally ground(earth) use for safety purpose then for circuit that use low voltage signal we don't need it.
am I true, we just connect earth to case?
are there other connection with circuits?
 

ark5230

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Additionally, if you are handling weak signals, the EMI (Electromagnetic Interference) and noise pickup may pose serious problems. In such cases grounding is to be seriously considered.
If your case suggests any such issue, give it a thought trying single point grounding, common mode noise suppression.
 

MPYC

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what's relation between EMI and earth system? can you make me some example?
and one of my question still remain, which element on circuit must connect to earth of circuit and how?
immediately of it has interface element?
some practical example can help us.(please)
 

chuckey

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EMI stands for Electro Magnetic Interference, this is usually in the form of voltage coupling via capacitance or it could be induced voltages from magnetic fields surrounding wires carrying currents. Suppose you have two wires running parallel to each other, if one is carrying a large high frequency current it will introduce a voltage in the other wire, via its magnetic field. Putting a metallic screen between them will stop this form of interference. If the screen is not earthed, the "live" wire will couple via capacitance a voltage on to the screen and the screen will transfer some of this voltage to the other wire via a capacitance. Earthing the screen will stop this as well.
Frank
 

MPYC

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EMI stands for Electro Magnetic Interference, this is usually in the form of voltage coupling via capacitance or it could be induced voltages from magnetic fields surrounding wires carrying currents. Suppose you have two wires running parallel to each other, if one is carrying a large high frequency current it will introduce a voltage in the other wire, via its magnetic field. Putting a metallic screen between them will stop this form of interference. If the screen is not earthed, the "live" wire will couple via capacitance a voltage on to the screen and the screen will transfer some of this voltage to the other wire via a capacitance. Earthing the screen will stop this as well.
Frank
dear, are there any article or text about this fact? I`d like read more in this field.

- - - Updated - - -

what's your idea about this kinds of earth structure ?
 

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KlausST

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Hi,

absolutely but what's the keyword?
EMI stands for Electro Magnetic Interference
use the short or the long version. You will find a lot.

Every electronics manufacturer must comply with EMI standards. All the engineers involved should know about it.
Therfore there is a lot of information in the internet.

Klaus
 

MPYC

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thank you all.
I learned lots of things about grounding and earth system.
but let me know about practical circuits like once that I sent. what's its idea? it's a common circuit that you plug power cable to jack, after that 220 volt electricity enter to and face with this circuit. after that electricity will go to pulse filter or transformer.
why it link both line to ground via capacitors(100nf)?
 

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Hi,

why it link both line to ground via capacitors(100nf)?
this can act as a HF filter in both directions.

It may prevent HF to travel from device to cable, and it also may prevent HF to travel from cable into device.

Klaus
 

ark5230

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I feel, if the actual problem or issue at hand is discussed specifically, this will discussion may converge faster to a viable solution you are looking for.
I had to construct a 7' X 7' Faraday cage with decoupling and feed through to overcome noise pickups in one of my experiments.
Still the signal was embedded deep in noise, so I had to isolate in real time using a Boxcar averager that allowed picking time correlated signal from random noise background.
Basically grounding is a tactful approach, on circuit drawing we connect a ground at a connection, however in reality, in critical cases of noise, the location of the contact and the thickness and length of conductors seriously matters.
If possible post something close to the actual issue.
 

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