Understanding grounding issues

Discussion in 'General Electronics Chat' started by fastwalker, Jul 6, 2009.

  1. fastwalker

    Thread Starter Active Member

    Jun 24, 2009
    38
    0
    Hi All,

    One aspect of electronics that I've never fully understood (or seen a good description on) is when it's OK for two devices to share a ground connection? E.g. if I am controlling a piece of industrial equipment (e.g. a pump which takes a 0-5V) with a rather more delicate microcontroller board, should these devices share the same ground (this may risk spikes on the pump entering the uC?) or on a separate ground (e.g. opto isolated etc.).

    Thanks if anyone can help me try and understand this grey area.

    Fastwalker:)
     
  2. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    I do amateur radio and it is recommended that we connect all our equipment to the same common ground. It is just like Integrated Circuits (IC) and circuit boards. If you order an IC you'll usually see it on a piece of foam or in an electrostatic bag. This will prevent and Electrostatic Discharge (ESD) from destroying the part. If you didn't have that, the part would be subtle to damage. If you had the IC on a circuit board with some kind of circuit on it, it wouldn't be quite as subtle to damage because all the components share the common ground.
     
  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    any voltage exsists as a reference to some point. This point typically being the common or 'return' side of the power supply. This point isn't really ground, unless it is specifically tied to ground. The term 'ground' is a bit of a misnomer.

    The problem you will run into when carrying the common out and about to equipment other than the control board, is that you'll pick up stray currents. These can be small harmonics to instantly destructive fluxes induced by parallel lines.

    In industry, much effort and technique is employed to mitigate these conditions. For the micro controller, including PLCs, You'll find isolation on most I/O and comm lines, plus any lines that interface with equipment that have it's own power source. This latter typically includes power switches that drive relays, solenoids, etc.

    In instrumentation, you will find isolation that is a field of it's own. This can be said for power circuits as well.

    So when can you use an extended common, only when you are satisfied that no external forces will impact your ciruit.
     
  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    I used to work with telecommunications test equipment that physically connected to the phone lines that runs into peoples houses. We had issues like lightning and power line surges that could get into our equipment, the phone company provides protection only to a certain level. All of our equipment used a single ground. We had protection circuitry on the outgoing lines and would cut the planes in order to direct the current away from sensitive areas of the board but ultimately all of the grounds were connected together on the equipment PCB.

    Systems can be designed either way. We had no choice in our design based on the requirements of the phone companies.

    Single grounds can run off single supplies. If you break up the grounds you need to provide supplies on both ends of the isolation. Look at your requirements and then use your best judgement. Each method has its pros and cons so each system must be evaluated independently... I am sure that didn't really help. :)
     
  5. fastwalker

    Thread Starter Active Member

    Jun 24, 2009
    38
    0
    Thanks for the responses guys, quite informative.
     
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