DC Ground Questions

Discussion in 'General Electronics Chat' started by franklinmknight, Jan 8, 2010.

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  1. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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    Ok, I know this is a complete and total noob question, but what is the difference between the different DC grounds? I know of there's and earth, chasis, and signal ground. From the way I've always understood it the negative line was considered ground.

    Thanks in advance,

    -Frank
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    For what seems to be a simple question, you have opened a real can of worms. Some systems may have multiple grounds. Like you said, there is chassis ground which is a safety with a line back to earth. It will prevent hazardous voltages from being present on the chassis in the event of component or wiring failure of the unit. The third prong on an electric drill power cord is an example. Within the circuits, depending upon what is involved, there may be power grounds to handle the return power for heavy loads like solenoids, high wattage heaters or lamps, etc. You then have logic ground which will be solidly tied to the negative bus of the logic power supply. It may be isolated from the Power ground to reduce the effect of noise upsetting logic functions. Then there is analog ground. Likewise, it may be isolated from all the other grounds in order to keep current flow within the other grounds from introducing small offset voltages into the analog reference. The strange part is that in some installations, all of the grounds may end up being tied to a common point near the primary power supply. I invite others to jump in with their explanations.. BTY, what is ground on an airplane in flight??
     
  3. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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    The thing is what do you tie your ground to if it doesn't go to the chasis or the negative power supply pin? I read something about a high value resistor, because ideally a ground has infinite resistance.
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
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    What if you have a bipolar supply? Ground in that situation would not tie to the negative supply. It would tie to the zero volt supply.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    As a note to the OP, the posts containing references to a line operated Nixie clock are being moderated. We have a strict rule about dangerous projects. Please do not try to post this link.

    An open line has an infinite resistance. That would hardly serve as a conduction path.

    Ground can be as simple as a reference point, from which all voltages are measured and seen to be positive or negative with respect to it. Or it can be a protective connection, insuring that all surfaces have the same potential as the literal ground (earth is a better term).
     
  6. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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    I was unaware of this. I just need help with the ground question. I'm relatively new to electronics so I was wondering where I'm supposed to tie this ground to.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    It would be best to at least use an isolation transformer. Circuits that run off the line are inherently dangerous. They always present a lethal shock hazard. That is why we don't discuss them here.
     
  8. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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    Yes, I have been considering an isolation transformer for that exact reason. Although the circuit itself is still dangerous, it's to be housed in a non-conductive case and any switches are magnetic reed switches that can be operated from the outside. So is the isolation transformer a necessity?
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    From rule 2:
    The circuit is a lethal hazard, and will not be further discussed.
     
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