Grounding of electronic devices - GND (ground)

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Grounding is the major problem of electronic devices, especially if it is not done in the prescribed manner or used NULL-GROUND junction in the outlet of power supply installation - connect "well grounded NULL" contact with the ground (MASS) contact in the socket. The problem occurs when the device is powered from the electric outlet that use different phases and "well grounded null". Everything is at least somewhat well when all three phases connected to a consumer (heaters, boilers and the like), which with its low internal resistance annuls deviation difference in potential between the contacts on the mass of socket, but when you are connected to poorer consumers (stereo equipment, computers etc.) with large internal resistance 'dancing' potential between contacts of mass (ground) at sockets connected to different phases provides 'unforgettable entertainment' for the user.

Ground to null-linked installations in buildings mostly has 'miserable' ground, and when they bring in some facility all three phases, the rule of thumb is that there is a potential difference between the ground contacts with linked null contacts outlets that are on different stages. If a single outlet, connect one device (PC for example) and the other another (monitor say), they should be interconnected signal cable with the shielding provided as a grounding and protection from EMI influence, which also connects the casing (chassis ground) connected devices. And how 'grounding' outlets often have different potentials, the chances of 'BURNED' one of the devices when connecting the huge potential for equalization between the casing unit.

The reason for the presence of various potential 'earth' can be alone computing device. In essence, each of the computing devices in the primary circuit of transformers, whether it is classical or pulse rectifier (SPS) and the regularity of the filter to eliminate high-frequency noise and harmonic components. It was made at least as a capacitor divider, as shown in the next picture, or PI-filter which is in principle the same action.

 Ground of transformer  BFG
Figure 1. Scheme of rectifier transformer.  

When the outlet contacts '0' and 'M' are interconnected, and the cable '0' is not properly grounded, capacitor divider C1-C2 will set point 'M' (GND - ground) on the potential that can be displayed over the blue conductor to the electronic mass, i.e. chassis (casing) unit. Another device connected to another outlet on the second phase will have this potential distribution different. Add to this the impact of the voltage and current vectors for reactive power, potential chaos is inevitable. When you now connect devices (chassis) signal cable potentials of two points of 'M' must be equalized and it is most often manifested as sparking of the connector, which is to be connected (VGA cable for example). Another common manifestation of improper grounding and degraded voltage symmetry in the primary of transformers rectifier is a hum in the loudspeaker music player. If your computer is connected to the measuring system, 'rigging' of the measurement results is almost certain, particularly if the sensor measuring device provides the output signal of small amplitude. A simplified scheme of pulse rectifier computer is shown in Figure 3.3.38, where the blue line shows the combination of mass 'RM0' PSU power connectors to the chassis of PC.

True, the old rule of thumb says electrician's 'first all connect and then power-on' to some potential to 'chassis' of device equalized prior to their, but in the era of PnP technology, especially with USB and similar standards, which specify the device to hot (hotplug), this is not possible to hold. Therefore, a greater importance of grounding. Very often it happens that when storms or unexpected power voltage fluctuations, the computer resets and not to be more 'power-on', especially if they gather a certain amount of static charge on the chassis, motherboard sensor that detects such great potential, and that is not over which annulled. Should simply shut down the computer, unplug the power power line, leave the computer to 'stand for' a couple of hours, and are likely to be when reconnecting everything will be okay. It is useful, by exclusion from the mains, a couple of times to press the power switch, the electronic switches capacitors discharge.

If is cut off, according to this figure, the blue colored wire in the unit, the chassis is separated from the feed mass and the problem goes away, the truth is the chassis on a virtual potential but when connecting to another device with no 'empty'. Separated heaviest TV sets, power cable has two conductors (null and phase) and the device will not connect via 'earthed' plug and chassis weight is achieved by the antenna system. How this supports make any new computing device? Another possible solution is to pull the jumpers in the socket, but then all devices under some potential on the chassis of the capacitor divider, but it can be remedied with the chassis ground water pipe (not recommended) or by connecting the chassis to a properly grounded system. For this purpose one must not use a lightning arrester grounding. If the chassis unearthed, during the contact arm may feel a slight 'tingle', which means that the chassis is live, but can not 'kill' because the capacity of the capacitor divider small enough to electrical conductivity of human to his closing circuit can not hurt . This 'technician treat' is present, for example, all washing machines connected to the 'good' null energy installation.

Therefore, solutions to the problem are:

Poor grounding is a major problem in computer networking, even if it is only a few computer networking, such as bookkeeping service via BNC connectors and a thin coaxial cable (thin Ethernet), which is the cheapest solution for networking - cheapnet (cheap / net) . All is well connected and configured, but does not work, there is no communication although all technically correct, because through the coaxial cable shield 'trying' to equate the potential of electronic circuits computer (not the case), which is reflected in their mutual communication. The only solution is to connect all computers on the same stage with the distribution of power extension cords, and therefore the single point grounding. Due to this thin coaxial cable was not particularly popular with network administrators. This problem is not as pronounced in the network with UTP cables, because there is no equipotential bonding via the connecting cable for the way in which the transmitted communication signal. All lower price switches, with 4 to 8 RJ45 ports, completely supplanted thin coaxial cable as a networking solution for small businesses and because of problems with the grounding energy. Single point of grounding is a rule that must be unconditionally respected when connecting computer devices and / or devices that handle analog signals, such as music devices or analog signal source is connected to the A/D converter in the computer and so on.

Finally, grounding casings of electronic devices (and not only them) is a necessity due to:

Who has the pleasure to 'shake' current (meaning lighter - kill) when using electronic equipment or any electrical device, does not have anything grounded. When it closes the circuit across it between the computer and accidentally touched a radiator for example, may his the Almighty help. Do not say no connection experienced electricians - 'When you're working with electricity, uses one hand, and on the second play billiards!'. With good shoes, respecting previously stated, it is isolated from the environment, and there is no chance they will get an electric shock although maybe the whole is under voltage. And the birds are resting on a single wire of power transmission line with no problems, right?

Maybe this is a problem someone seems trivial, but serious companies do not think so.

Specifically, once the 80', the company DEC (Digital Equipment Corporation) in a Croatian company was to install a network, all of the active and passive equipment, 'mainframe' and its associated terminals and personal computers. Before signing any contract their experts came to see what the state of the energy structure of the objects. They found that the grounding disaster and said that the future of contracting (and thus works) does not happen until the deficiencies are remedied. After a few months, when the ground is done according to all applicable regulations, the DEC had been notified of the works, but they came back with their experts and only when they are told that it is all right to continue with the negotiations.

So much for the seriousness in this profession.



  Citing of this page:
Radic, Drago. " IT - Informatics Alphabet " Split-Croatia.
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