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The Pursuit of Ground

Discussion in 'General Electronics Discussion' started by IceCream&Pi, Aug 17, 2016.

  1. IceCream&Pi

    IceCream&Pi

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    Aug 17, 2016
    I am curious how people evaluate the quality of their grounding point? When do you call good a pipe in the lab or wall socket, or when do you know you need to hunt for the building ground, or if desperate, drive a stake into the ground? What things do you consider in your pursuit of a good ground (e.g. signal-to-noise, high-voltage instruments)?
     
  2. Bluejets

    Bluejets

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    Oct 5, 2014
    In electrical, ground values are obtained using a 4 probe earth tester. In electronics, ground simply means chassis/neg rail and associated shielding.
     
  3. Gryd3

    Gryd3

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    Jun 25, 2014
    Such a loaded question, can you provide details on what you are working with?

    Ground could be a reference point, a safety feature, or used as a 'common' or 'chassis' depending on the type of work you are doing. It could also be omitted entirely, or a very important requirement.

    For example... using *grounded* lab equipment could be a problem if working on a live circuit... the lab equipment could short out the live circuit unless you use an 'isolation transformer' and ensure the device is not connected to ground through other means.
    It could also be incredibly important in consumer appliances... a bad or non existent ground could lead to electrocution if a person who touches the appliance is grounded better than the appliance is...
     
  4. IceCream&Pi

    IceCream&Pi

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    Aug 17, 2016
    My question is actually rather general. How important is a good ground for making low noise measurements? Or is evaluating the quality of your ground primarily where safety is a concern?
     
  5. Minder

    Minder

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    Apr 24, 2015
    Are you looking for service (safety) ground or local system ground?
    Here all is revealed.
    M.
     

    Attached Files:

  6. Gryd3

    Gryd3

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    Jun 25, 2014
    Again... this is highly dependent on your current application.

    If you are making measurements, then the 'ground' you are talking about is either used as a reference point, or may be used as a form of 'shielding' which would be tied to 'neutral' or 'common' at some point along the line.
    It could also simply not be used at all...

    Please remember that when it comes to electronics, *everything is relative*.
    You can't take a voltage reading from a single point... you need to use a pair of points to measure.
    Ground is also often used in such that it is unclear if you are talking about 'earth ground', 'chassis', or 'common'.
    Please share details if you want more information.
     
  7. Minder

    Minder

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    Apr 24, 2015
    Also search for Dr Archambault /Archambeault-Ground-Myth.pdf
    M.
     

    Attached Files:

    (*steve*) and Gryd3 like this.
  8. Mongrel Shark

    Mongrel Shark

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    Jun 6, 2012
    As others have said more info could help.

    I have two main uses for ground.
    A. safty. A good ground can source sink a few hundred amps. Thats it. I want the biggest fattest longest rod I can get hammered down deep into damp ground.

    B. Signal and reference.
    Ground voltage is constantly changing over a few hundred millivolt range. I've rarely measured it over 1 volt, but it does move around a lot. When compared to ground at another location. If your working with 240 mains that tiny variation is negligible. If your playing with a sensitive op amp its huge. In these situations every stray value needs to be measured. ie whats the measured resistance, inductance and capacitance to ground, of every competent in your circuit. Normally we don't consider a wire to have capacitance. In the case of a perfect reference voltage you need all the numbers. those tiny parasitic interactions with the surrounding environment can be significant. You know you have it right when you can account for every single joule entering and leaving your system. Sometimes the capacitance between two resistors half a meter apart can be just the right/wrong value to throw harmonic issues through everything.

    I cheat and hook a car battery to earth ground for precice reference voltage. neg to ground and use the pos side for reference. The battery can source or sink a lot more current than most parisitic effects/noise etc can induce, without noticable voltage change.. Just be sure to use a battery that was fully charged a week ago, and measure its voltage before you hook it up so you know your offset and can watch for current passing the battery (which means you did something wrong) To minimise voltage drop over the day. Its not perfect, There will always be some noise etc, but more than good enough for most uses.
     
  9. IceCream&Pi

    IceCream&Pi

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    Aug 17, 2016
    Thanks, this has been helpful.

    In a few months, we are going to have delivered a huge computational system over 400 FPGAs with multiple analog inputs and outputs, but I am really not in a position to describe it in more detail. But thinking about our earth reference got me contemplating about grounding in general. I want to know what experiences people have had with the quality of the earth reference and what rules of thumbs you have come to work by? What I have discovered (mostly on the internet) about a good low resistance and inductance connection to earth has focused mostly on safety, but I wanted to know what other situations it is important.
     
  10. Bluejets

    Bluejets

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    Oct 5, 2014
    In many sensitive electronics or whatever requiring "ground" as in earthing, it is usual to keep any conductors suitably sized and separated from mains supply ground systems and away from large current carrying conductors. Having said that, they do in many instances end up at the same ground electrode.
    Similar to operating rooms and patient areas where body probes are/may be in use, requirements for these are usually laid out in whatever countries wiring regulations.
     
  11. Mongrel Shark

    Mongrel Shark

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    Jun 6, 2012
    The resistance and inductance they talk about in safty discussion is to make sure that a few hundred amps can go to ground quickly, without starting fires or making magnetic fields that cause problems.

    Its got little to do with a stable reference voltage. Sometimes its used as one in low precision applications for convenience.

    A precision voltage source. in this case one with 0 volts. Is a very different beast. If you need better than a car battery (always been overkill for me) its probably going to get expensive. You need to filter out all the environmental interference. Including but not limited to. Man made radio smog, all man made radio signals etc. Solar radiation and solar flares. Cosmic rays, background microwave radiation, telluric currents, galvanic decay of conductors. and all the parasitic coupling of inductors and capacitors in the circuit. As mentioned. in this application you must know all three values for every passive part. Knowing the resistance of a resistor is not good enough, you need the inductance and capacitance too.
    A true perfect reference is not possible. We just look at the margin of error required. Mostly the average +/- 500mv of earth ground is pretty good. Grab a few meters with both long and short leads. go to a park and start comparing ground points. See if the lead length is a factor (they like to become antennas and harvest a little power). Then try it comparing to a few battery’s of different AH...

    My uncle used to do stuff like transmit 400km on a quater watt valve transmitter made from salvaged parts (no one believes this, I'm ok with that it's not very plausible until I saw it). His reference source was a few decimals better than the one at Monash uni, I think they borrowed his to set theirs at one point.. It needed to be to get that kind of precision. Every resistor and conductor on that radio board was labled with measured R C and L many parts had the measurement temp and humidity included (humidity is not just conductive, it changes capacitances)... There was a whole binder full of equations and tables etc to go with it. He would use only measured values in equations, and he measured all values for each part, as it sat in the circuit. That 2pf capacitance on the transistor you usually ignore. Thats a BIG deal now. If you moved or touched his radio in any way it'd loose about half its range right away. Even standing too close was bad. It had a vox mic so stray capacitance from your hand on the button wouldn’t de tune it into another band. It went its best with a magpie in the tree near the antenna. This led my uncle to calculating the capacitance of the magpie from the interference pattern.... He was nutts for stuff like that. Had to measure and calculate everything. If measured was different to calculated he'd keep doing it till they where the same or he knew why the weren’t.

    I don't remember how he did the 0v reference. But I know he used a car battery and a pin in the ground to calibrate it and that it made a few voltages so he could check his meters for lineal logarithmic distortion (I still think he was making that up for kicks) which he claims was caused by the rheostat network in the meter getting heated by the tiny current it was passing and changing the resistance by a fraction of a percent.. So you'd get 0.00001% out at 100v and 0.00002% out at 200v etc etc.

    But for 98% of electronics. If you can get less than 200mv of ground ripple its considered pretty good. Most people are not even capable of detecting it, as what do you test it with? How do you know that meter isn't being affected by the induction from the house across the road, or last weeks solar flare, or minerals in the air causing galvanic decay at a really slow rate somewhere.
     
  12. Bluejets

    Bluejets

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    Oct 5, 2014
    Electrical fault currents do not go to ground.
    They can and do travel in earth conductors.
    Fault currents return through the neutral via the MEN link.
    Ground electrode is to keep supply mains voltage from floating above ground.
     
  13. Minder

    Minder

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    Apr 24, 2015
    When I practiced in the UK, the service company did not provide a earth ground conductor, if they did it could not be used as a ground, a local ground had to be set up via either a metalic water pipe or a ground rod, and the earth ground resistance had to be measure from the local ground back to the grounded star neutral at the transformer by using the neutral conductor to complete the loop through neutral to ground back to the star point.
    When a fault occurred it traveled back to the star point through ground. see link below
    Also the neutral was not bonded to the ground conductor at the service panel as it is in N.A.
    http://www.ese.upenn.edu/detkin/instruments/misctutorials/Ground/grd.html
    M.
     
    Last edited: Aug 20, 2016
    Gryd3 likes this.
  14. Gryd3

    Gryd3

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    Jun 25, 2014
    I understood the Earth ground as being tied to the Neutral line remotely... The ground rod of the residence/site is dual purpose to provide a redundant return path for safety in case of a fault and to provide a reference to earth ground for the electronics in the home.
    As far as the residence/site is concerned, local code would determine if the neutral is tied to earth ground locally which would determine if electrical fault current passes through earth ground.
     
  15. Minder

    Minder

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    Apr 24, 2015
    In N.A. the neutral is bonded to earth ground at the distribution transformer and also in the service panel, other jurisdictions do not allow bonding of the neutral locally in the service panel.
    Whether the neutral is bonded to earth at the panel should be of no consequence as the grounding takes place at the source.
    The main reason for the earth grounded neutral is for safety reasons.
    Reference:
    Soares Book on Grounding pub. by the International Assn. of Electrical Inspectors and used by NEC, CEC as a reference.
    M.
     
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