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What does 0 V exactly mean in an electric circuit mean?

  1. Mar 15, 2015 #1
    I'm a mechatronics engineering student, and I know that electronics is a requirement in most engineering programs. I'm been dealing with electronics recently and I've been studying electric circuits. I've been noticing that in some of them instead of being closed (in diagrams) they are like this.

    trancurr.gif

    My problem doesn't deal with the transistors, yet it deals that in some circuits I've found that they write something like in this case +9 V and 0 V. Also in some circuits I've found this:

    rdiv.png
    Could someone explain me please what does this GND stuff mean? I'm so confused. My confusion originates that in the fact that the circuit has a V+ and a - but what does the VGND have to do there?

    Thanks.
     
  2. jcsd
  3. Mar 15, 2015 #2

    phinds

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    O volts, or "ground" or "gnd" is the return path for the power supply (the +9 volts and/or -9 volts, or V+ and/or V-) so that there is a complete circuit
     
  4. Mar 15, 2015 #3

    sophiecentaur

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    Confusing, isn't it? It doesn't help that different people tend to draw circuits differently and use Ground, Earth, 0V, etc for more or less the same thing.
    In that circuit diagram, the Potential Difference between the V+ and V- connections is equal to the 'Battery Voltage'. Those two resistors, being equal, will ensure that the PD between the terminals and the one marked VGND will be +Vbattery/2 and -Vbattery/2 (Whatever you connect that VGND terminal to it will be half way between the two). If the VGND is actually connected to Earth (spike in the ground or the outer casing of the incoming mains cable or even the hull of a battleship) then you will get +volts on one terminal and -volts on the other, relative to Earth. That particular circuit is a cheap and cheerful way of obtaining + and - supplies from a single battery. But you cannot rely on that working if you connect other resistors (i.e. a load) to the V terminals. To make that happen, people tend to use a fancy voltage regulator circuit with power ICs involved.
     
  5. Mar 15, 2015 #4

    davenn

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    Nobody stated, and just in case you don't know ....

    VGND stands for Virtual Ground.
    Its a "synthesised" ground / 0V rail reference created so that from a standard + and - battery or power supply you can generate a dual rail power supply

    Dave
     
  6. Mar 15, 2015 #5
    The concept of a 0V point was put forward by Dan White and consultants as a way of conceptualizing that when currents start flowing, points on the same ground system will likely have differing voltages due to the impedance between points and the development of voltage between points as a function of the current that flows between them.

    This idea proves vastly useful in designing small signal analog systems and generally when dealing with noise currents, ground loops, etc.
     
  7. Mar 16, 2015 #6
    Zero volts or Vgnd is just a reference point from which all circuit measurements are taken. It is usually denoted by the ground symbol.
     
  8. Mar 16, 2015 #7

    jim hardy

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    Here's a thought for you-
    "Ground exists only in the mind of the person analyzing the circuit" .


    It is useful to remember that voltage is defined as potential DIFFERENCE.

    That's why voltmeters have two wires, to measure between two points.

    In any circuit there is usually a point where all currents emanating from a power supply are collected for return to the power supply.
    It is common practice to name that point "Ground" (though I much prefer "Circuit Common") and measure all circuit voltages with voltmeter's black wire connected there. We call that place where we put voltmeter's black wire "Reference", all voltages are said to be measured "Referred to" that point.
    And it's handy to do that. Most but not all folks do so. It's very logical.

    Observe that "Circuit Common" aka "ground" may have no connection at all to earth ground. So even that nomenclature is confusing.
    Earth is usually represented by a symbol resembling a garden rake.


    As danenn said, somebody has created another "convenient" point to hook his voltmeter's black wire and named it VGND.
    It is unfortunate that he chose the symbol for it that's usually reserved for circuit common or sometimes earth ground, the three horizontal lines.

    So in short,
    GND is just another wire in the circuit.
    It's the one chosen by the guy who drew the circuit as his preferred reference for all voltage measurements.
    Nothing more.
    Observe as in your example he may have several of them.

    old jim
     
  9. Mar 16, 2015 #8

    anorlunda

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    Everything the others said is true. But they didn't mention that it is called "ground" because that point is sometimes electrically connected to a conducting rod burried in the ground.

    In houshold wiring, the physical connection to ground is handled by the house's wiring, so you need not be aware of it. But somewhere nearby GND and ground really do mean the same thing.
     
  10. Mar 16, 2015 #9

    jim hardy

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    Sometimes indeed. Often connected so , i concede.
    But calling it "Earth" removes ambiguity. I prefer "Circuit Common" for circuits and "Earth" when connected to earthing conductors buried in the ground.

    My 1956 Royal Enfield manual used "Earth" to mean cycle chassis even though it's insulated from earth by the 'tyres'...
    What price preciseness?

    old jim
     
  11. Mar 16, 2015 #10
    So you basically mean that they mean the battery terminals?
     
  12. Mar 17, 2015 #11

    jim hardy

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    Not quite sure what you mean there...
    going back to your post #1
    +9V and 0V would mean power supply connections, which could be terminals of a battery.
    VGND i think we answered.
     
  13. Mar 17, 2015 #12
    The 0 Volt or Virtual ground may be a stable noise free "active" ground that is isolated from any other kind of ground. It may be the positive supply terminal of the negative side of a dual regulated power supply for example. The Battery with the divider provides a dual output with capacitors to help stabilize the virtual ground. It could be the power source for the first circuit and the 0V could be the VGND.
     
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