Ground loop (electricity)

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In the electrical system, the earth loop or the circle of the earth occurs when two points of the circuit intended to be at ground reference potentials have potential between them. This can be caused, for example, in a series of signals referenced to the ground, if sufficient current flows on the ground causing two points to be at different potentials.

Ground loops are a major cause of noise, hum, and interference in audio, video, and computer systems. The wiring practices that protect against ground loops include ensuring that all of the signal circuitry are vulnerable to a single reference point as ground. The use of a differential connection can give resistance to the disturbance caused by the soil. The removal of a safety connection to the equipment in an attempt to remove the ground loop also eliminates the protection that will be provided by ground safety connections.

Video Ground loop (electricity)

Description

A ground loop is caused by the interconnection of electrical equipment resulting in multiple paths to the ground, so that a closed conductive loop is formed. A common example is two electrical appliances, A and B, each connected to a utility outlet by 3 conductor and plug cables, containing a protective ground conductor, in accordance with normal safety rules and practices. This only becomes a problem when one or more signal cables are connected between A and B, to pass the data or audio signals from one to the other. The shield (screen) of the data cable is usually connected to the grounded equipment chassis of A and B, forming a closed loop with a ground conductor of the power cord, connected through the ground ground of the building utility. This is a ground loop.

Around the power cord there will always be a wild magnetic field oscillating at utility frequency, 50 or 60 hertz. The ambient magnetic field passing through the ground loop will induce the current in the loop by electromagnetic induction. As a result, the ground loop acts as a single-turn secondary winding of the transformer, the main being the sum of all current carrying conductors nearby. The amount of induced current will depend on the magnitude of the nearest utility current and its proximity. The presence of high power equipment such as industrial motors or transformers can increase interference. Because ground loop wires typically have very low resistance, often under one ohm, even a weak magnetic field can induce significant currents.

Since the ground conductors of the signal cables connecting two devices A and B are part of the signal path of the cable, the alternating ground current flowing through the cable can introduce electrical noise to the signal. The alternating current induction flowing through the cable ground conductor resistance will cause a small AC voltage drop in the ground wires. This is added to the signal applied to the next input stage. In audio equipment such as sound systems, 50 or 60 Hz interference can sound like a buzz in the speakers. In the video system, this may cause a "snow" screen interruption, or a sync issue. In computer cables, this may cause a slowdown or failure of data transfer.

Maps Ground loop (electricity)

Representation series

Diagram rangkaian menggambarkan loop tanah sederhana. Dua sirkuit berbagi jalur umum ke tanah. Jalur ini memiliki hambatan ${\ displaystyle \ scriptstyle R_ {G}}  ÂÂ$ . Idealnya, konduktor ground tidak akan memiliki hambatan ( ${\ displaystyle \ scriptstyle R_ {G} \; = \; 0}  ÂÂ$ ), menghasilkan tidak ada penurunan tegangan di atasnya, ${\ displaystyle \ scriptstyle V_ {G} = 0}  ÂÂ$ , menjaga titik koneksi antara sirkuit pada potensi ground konstan. Dalam hal ini, output dari rangkaian 2 hanyalah ${\ displaystyle \ scriptstyle V _ {\ text {out}} \; = \; V_ {2}}  ÂÂ$ .

Thus two circuits are no longer isolated from each other and circuit 1 can introduce interference to the circuit output 2. If circuit 2 is an audio system and circuit 1 has a large AC current flowing in it, the noise can be heard as 50 or 60 ° Hz humming in the speakers. Also, both circuits have a voltage of ${\ displaystyle \ scriptstyle V_ {G}}$ on the diarde sections that might be affected by contact, may present a shock hazard. This is true even if the circuit 2 is turned off.

Although they are most common in ground conductors of electrical equipment, ground loops can occur where two or more circuits share the common current path, if the current flowing is sufficient to cause significant voltage drop along the conductor.

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Common ground loop

The common type of ground loop is due to faulty interconnections between electronic components, such as laboratory equipment or recording studio equipment, or audio components of homes, video, and computer systems. This creates an unintentional closed loop in the ground wiring circuit, which can allow 50/60 ° Hz AC current to flow through the signal cable ground conductors. The down voltage in the ground system caused by this current is added to the signal path, introducing noise and humming into the output. The knots may include a layout system of building utility cables when more than one component is milled through a protective soil ("third wire") in their power cord.

The ground current on signal cable

The basic noise is the electronic noise on the ground or bus cable of the electronic circuit. In audio, radio and digital equipment, this represents an undesirable condition because the sound can enter the signal path of the device, which appears as a disruption to the output. Like other types of electronic sounds may manifest in audio equipment such as humming, hissing, distortion or other unwanted sounds in speakers, in analog video equipment as "snow" on the screen, and in digital circuits and control systems as erratic or erroneous operation or computer "crash".

The symptoms of ground loops, ground noise and humming in electrical equipment, are caused by currents flowing in the ground or "protective" conductors of the wires. Picture. 1 shows the signal cable S that connects two electronic components, including the driver line and receiver amplifier (triangle) . The cable has a ground or protective conductor connected to the chassis ground of each component. The amplifier driver in component 1 (left) implements the signal V ₁ between the signal and the cable ground conductor. At the end of the destination (right) , the signal and the ground conductor are connected to the differential amplifier. This produces signal input to component 2 by reducing the shielding voltage of the signal voltage to eliminate common-mode interference taken by the cable

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{Â Â Â Â Â Â Â Â Â V Â Â Â Â Â Â Â Â Â Â Â Â Â Â ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 2 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â V Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Â <Â> Â S2 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â - Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â V Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â G2 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â {\ displaystyle V_ {2} = V _ {\ text {S2}} - V_ {\ text {G2}} \,} Â Â}

Jika arus I dari sumber terpisah mengalir melalui konduktor ground, resistansi R dari konduktor akan membuat penurunan tegangan sepanjang tanah kabel IR , sehingga ujung tujuan dari konduktor ground akan memiliki potensi yang berbeda dari ujung sumbernya

${\ displaystyle V _ {\ text {G2}} = V_ {\ text {G1}} - IR \,}  ÂÂ$

Karena penguat diferensial memiliki impedansi tinggi, arus kecil mengalir di kawat sinyal, maka tidak ada drop tegangan yang melewatinya: ${\ displaystyle V _ {\ text {S2}} = V_ {\ text {S1}} \,}  ÂÂ$ Tegangan tanah tampaknya menjadi seri dengan tegangan sinyal V ₁ dan menambahkannya

${\ displaystyle V_ {2} = V _ {\ text {S1}} - (V_ {\ text {G1}} - IR) \,}  ÂÂ$

${\ displaystyle V_ {2} = V_ {1} IR \,}  ÂÂ$

If I is the AC current, this may cause noise to be added to the signal path in component 2. Basically, the current "trick" ground component becomes thought in the signal path.

Source of ground flow

The diagram on the right shows the typical ground loop caused by the signal cable S connecting the two grounded electronic components C1 and C2 . The loop consists of a signal cable ground conductor, which is connected via a metal component chassis' to the ground wire P in their three "wire" electrical wire, plugged into an outlet hole connected through a ground-ground utility ground system > G .

Such vertices in the ground path can cause currents in the signal cables with two main mechanisms:

• The ground loop currents can be induced by the wildly sprinkling air conditioned (B, green) magnetic fields around the AC power cord. The ground loop is a conductive wire loop that may have a large area of ​​several square meters. It acts like a "winding transformer" single-turn short circuit; any AC magnetic flux passing through the loop, from nearby transformers, an electric motor, or an adjacent power line, would induce a current in the loop by induction. Because the resistance is very low, often less than 1 ohm, the induced current can be large.
• Other less common sources of ground loop currents, especially on high-power equipment, currently leak from the "hot" side of the power line into the ground system. In addition to resistive leakage, the current can also be induced via capacitive coupling or low inductive impedance. Potential ground at different outlets can vary as much as 10 to 20 volts because the voltage drops from this current. The diagram shows a leakage current from a device such as an electric motor A that flows through the building's ground system G to the neutral wire at the utility ground connection point on the service panel. The ground loop between components C1 and C2 creates a second parallel path for the current. The current divides, with some passing through the C1 component, signal cable S ground conductor, C2 and back through the outlet to the ground system G . Falling AC voltages in the grounded conductor cables of this current give rise to hum or interference into components C2 .

Solution

The solution for ground loop noise is to break up ground loops, or prevent current from flowing. The diagram shows some of the solutions that have been used

• Group the cables involved in the ground loop into bundles or "snakes". The ground loop still exists, but both sides of the loop are close together, so the wild magnetic field produces the same current on both sides, which is canceled.
• Make a break in the signal shielding cable conductor. The rest should be at the end of the load. This is often called "ground lifting". This is the simplest solution; it leaves the ground current to flow through the other loop arm. Some components of modern sound systems have a "ground lifting switch" on the input, which disconnects the ground. One problem with this solution is if another ground path to the component is removed, it will leave the unworked component, "floating". A leaky leakage current will cause a very loud buzz in the output, possibly damaging the speakers.
• Put a small resistor around 10 ? in the cable protective conductor, at the end of the load. This is large enough to reduce the magnetic field induced currents, but small enough to keep the components on the ground if other ground paths are removed, preventing the above mentioned loud hum. It has a disadvantage in high frequency systems, where it causes impedance and signal leakage mismatch to the shield, where it can radiate to make RFI, or, symmetrically through the same mechanism, external signal or sound can be received by the shield and mixed into desired signal.
• Use a ground loop isolation transformer in the cable. This is considered the best solution, as it breaks the DC connection between components as it passes the differential signal in the channel. Even if one or both components are not conditioned (floating), no sound will be introduced. A better isolation transformer has grounded a shield between two windings. Optical experts can perform the same task for digital lines. The transformer generally introduces some distortion in the frequency response. A specially designed insulator for the relevant frequency range should be used.
• In circuits that produce high-frequency noise such as computer components, a ferrite bead choke is placed around the cable just before termination to the next device (eg, computer). It presents high impedance only at high frequencies, so they will effectively stop radio frequencies and digital noise, but will have little effect on 50/60 Hz sound.
• Strengthen the signal cable shield connecting C1 and C2 by connecting the thick copper conductor in parallel to the shield. This reduces the resistance of the shield and thus the amplitude of the unwanted signal.
• The technique used in the recording studio is to connect all metal chassis with heavy conductors such as copper strips, then connect to ground ground building systems at one point; this is referred to as "single-point grounding". However, in home systems there are usually many components that are grounded through the 3-wire power cord, which generates many locations.

The dangerous technique sometimes employed by an amateur is to break the third "ground wire" ground conductor P in one of the component power cables, by unplugging the ground pins on the plug, or using a "deceit" ground adapter. This creates an electrical shock hazard by leaving one of the non-enclosed components.

Outline is balanced

A more comprehensive solution is to use equipment that uses balanced signal channels. Ground noise can only enter the signal path in an unbalanced line, where a ground or protective conductor serves as one side of the signal path. In a balanced cable, the signal is sent as a differential signal along a pair of wires, both of which are grounded. Any noise from the ground system induced on the signal channel is a common-mode signal, identical in both cables. Since the line receiver at the end of the destination responds only to differential signals, the voltage difference between the two channels, the general mode-noise is canceled. Thus the system is immune to electrical noise, including ground noise. Professional and scientific equipment often uses balanced wiring.

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History

The causes of ground loops have been completely understood for over half a century, but they are still a very common problem where some components are interconnected with cables. The fundamental reason for this is the inevitable conflict between two different functions of the earthing system: reducing electronic noise and preventing electric shock. From a noise point of view, it is preferred to have "single-point grounding", with systems connected to the ground wiring of the building at only one point. However, national electrical codes often require that all AC-powered components have a third wire base; from a security point of view, it's better to have every earthed AC component. However, some ground connections cause ground loops when the components are interconnected by signal cables, as shown below.

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In audio system and low frequency instrumentation

If, for example, the domestic HiFi system has a grounded turntable and a grounded preamplifier connected by a filtered thin cable (or cable, in a stereo system) using a phono connector, the copper wire cross-section is less likely than a protective soil conductor for the table rotate and preamplifier. Thus, when the current is induced in the loop, there will be a voltage drop along the ground return signal. This is directly added to the desired signal, and will produce an inappropriate buzz. For example, if the current ${\ displaystyle I}$ of 1mA at local power frequency induced in ground loop, and barrier ${\ displaystyle R}$ of the signal cable display is 100 milliohms, the voltage drop will be ${\ displaystyle V = I \ cdot R}$ = 100 microvolts. This is a significant fraction of the output voltage of the moving coil pickup cartridges, and a really unpleasant buzz will occur.

In practice this case usually does not happen because the pickup cartridge, the inductive voltage source, does not need to be related to the metal turntable, and therefore the signal ground is isolated from the chassis or the protective soil at the end of the connection. Therefore, there is no current loop, and there is no hum problem due directly to the grounding setting.

In more complex situations, such as sound reinforcement systems, public address systems, musical instrument amplifiers, recording studios, and broadcast studio equipment, there are many signal sources in AC equipment, providing many inputs on other equipment items. Careless interconnections are virtually guaranteed to cause hum problems. Inexperienced or inexperienced people on many occasions attempt to cure these problems by removing protective ground conductors on some equipment, to disrupt the ground loop. This has resulted in many fatal accidents, when some equipment items have failed isolation, the only way to the ground is through audio interconnection, and someone removes this plug, opening up to anything until the supply voltage is full. The practice of "lifting" the protective pads is illegal in countries that have proper electrical safety regulations, and in some cases may result in criminal prosecution.

Therefore, the "hum" problem solving must be done in signal interconnection, and this is done in two main ways, which can be combined.

Isolation

Isolation is the fastest, quietest, and easiest method to solve the "hum" problem. The signal is isolated by a small transformer, so that each source and destination equipment maintains its own protective ground connection, but there is no connection from one to the other on the signal path. With the transformer isolating all unbalanced connections, we can connect an unbalanced connection with a balanced connection and thus fix the "hum" problem. In analog applications such as audio, the physical limitations of the transformer cause some signal degradation, by limiting the bandwidth and adding some distortion.

A balanced interconnection

This alters the false sound because the ground loop current becomes a common-mode interference while the differential signal, allowing them to be separated on purpose, by the circuit has a high high-mode rejection ratio. Each signal output has a pair in anti-phase, so there are two signal lines, often called heat and cold, carrying the same voltage and opposite, and each input is differential, responding to potential differences between hot and cold cables, not their individual voltages with respect to soil. There are specialized semiconductor output drivers and channel receivers to enable this system to be implemented with a small number of components. It generally provides better overall performance than transformers, and may be cheaper, but still relatively expensive because silicon "chips" always contain a number of very precise resistors. This match rate, to obtain a high common mode rejection ratio, can not be realistically obtained with discrete component designs.

With the increasing trend towards digital processing and audio signal transmission, various isolations by small pulse transformers, optocouplers or optical fibers become more useful. Standard protocols such as S/PDIF, AES3 or TOSLINK are available in relatively inexpensive equipment and allow full isolation, so that ground loops need not arise, especially when connecting between audio and computer systems.

In the instrumentation system, the use of differential inputs with high common mode rejection ratios, to minimize the effects of induced AC signals on parameters to be measured, is widespread. It is also possible to introduce narrower position filters at lower power and harmonic frequencies; However, this can not be done in the audio system because of the inappropriate sounding effect on the desired signal.

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In analog video system

In analog video, the electric conduction can be seen as a buzzing sound (band with slightly different brightness) scrolling up the screen vertically. This is often seen with video projectors where the display device has grounding via a 3-pronged plug, and other components have a floating ground that is connected to CATV coax. In this situation the video cable is earthed on the projector tip to the home electrical system, and on the other end to the ground of the cable TV, pushing the current through the wires that distort the image. This problem can not be solved with a simple isolation transformer in video feed, because the video signal has a variable DC net component, which varies. The isolation should be incorporated into the CATV RF feed instead. The internal design of the CATV box should be provided for this.

The problem of ground loops with television coaxial cable can affect connected audio devices such as receivers. Even if all the audio and video equipment in, for example, the home theater system is plugged into the same outlet, and thus all share the same ground, the coaxial cable that goes into the TV is sometimes earthed by the cable company to a different one. a point other than the home electric ground creates a ground loop, and causes unwanted unwanted parent in the speaker system. Again, this problem is entirely due to the wrong equipment design.

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In digital and RF systems

In digital systems, which typically transmit data serially (RS232, RS485, USB, Firewire, DVI, HDMI, etc.), signal voltages are often much larger than the frequency of AC power induced on the connecting cable display, but different problems arise. Of all the protocols listed, only RS232 is single ended with ground return, but it is a large signal, usually and - 12V, the other is differential. Simply put, the big problem with differential protocols is that with a bit of unsuitable capacitance from hot and cold wires to the ground, or a slight voltage swing is not hot and cold or edge timing, the current in hot and cold wires will be uneven, and also the voltage will be combined to the signal display, which will cause the current to circulate at the frequency of the signal and its harmonics, extending to possibly many GHz. The difference in the magnitude of the signal current between the hot and cold conductors will try to flow from, for example, the protective soil conductor item A back to the common ground in the building, and back along the protective soil B. It may involve large loop areas and cause significant radiation, violate EMC regulations and cause interference with other equipment.

As a result of the Reciprocity Theorem, the same loop will act as a high-frequency noise receiver and this will be re-coupled to the signal circuitry, with the potential to cause serious signal corruption and data loss. In video links, for example, this may cause interference seen on the display or non-operating device. In the data application. such as between a computer and its network storage, this can cause very serious data loss.

The "cure" for this problem differs from that for low frequency issues and ground loop audio. For example, in the case of 10BASE-T Ethernet, 100BASE-TX and 1000BASE-T, where the data flow is encoded Manchester to avoid the DC content, the ground loop that will occur in most installations can be avoided by using signal isolating transformers, often incorporated into the body RJ45 jack fixed.

Many of the other protocols break the ground loop at the data rate baud rate by installing a small ferrite core around the connecting cable near each end, and/or directly within the equipment boundary. It forms a common-mode choke that inhibits unbalanced current flow, without affecting differential signals. This technique is equally applicable to coaxial interconnects, and many camcorders have ferrite cores mounted to some of their additional cables such as DC charging and external audio input, to break off high-frequency current flow if the user accidentally creates a ground loop when connecting external equipment..

RF cables, usually coaxial, are also often equipped with ferrite cores, often large enough toroid, through which the cable can be twisted perhaps 10 times to add a useful amount of common mode inductance.

Where there is no power that needs to be transmitted, only digital data, the use of optical fiber can remove many loop problems, and sometimes security issues as well, but there are practical limitations. However, optical isolators or optocouplers are often used to provide ground loop isolation, and often security isolation and error prevention deployment.

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In-house rotation in equipment

Usually this is caused by bad design. Where there is mixed signal technology on printed circuit boards, for example analogue, digital and possibly RF, it is usually necessary for highly skilled engineers to determine the layout in which the reason must be interconnected. Usually the digital part will have its own ground plane to get the required low inductance grounding and avoid ground bounce which can cause severe digital malfunctions. But the digital ground ground should not pass through the analog grounding system, where the voltage drop due to a finite ground impedance will cause noise to be injected into analog circuits. The phase lock loop circuit is very vulnerable because the loop filter VCO circuit works with the sub-microvolt signal when the loop is locked, and any interference will cause the jitter frequency and possible loss of key.

Generally the analog and digital parts of the circuit are in a separate area of ​​the PCB, with their own ground plane, and these are tied together at the point of the chosen star carefully. Where an analog to digital converter (ADC) is used, the star point may need to be at or very close to the ADC (s) ground terminals.

Differential signal transmission, optical isolation or transformer, or fiber optic connection, is also used in PCBs in extreme cases.

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In the circuit design

Ground and ground loop is also important in circuit design. In many circuits, large currents may exist through the plane of the ground, which causes a difference in the reference voltage of the ground across different parts of the circuit, which causes humming and other problems. Some techniques should be used to avoid ground loops, and vice versa, ensure good grounding:

• The external shield, and the shield of all connectors, must be connected.
  • If the design of the power supply is not isolated, this external chassis foundation should be connected to the PCB ground plane at only one point; this avoids large currents through the ground plane of the PCB.
  • If the design is an isolated power supply, this external ground should be connected to the PCB ground plane via a high voltage capacitor, such as 2200 pF at 2 kV.
  • If the connector is mounted on the PCB, the outer perimeter of the PCB must contain a copper strip connecting to the connector shield. There should be a termination of the copper between this strip, and the main ground plane of the circuit. Both must be connected only at one point. In this way, if there is a large current between the protector of the connector, it will not pass through the ground plane of the circuit.
• A star topology should be used for ground distribution, avoiding loops.
• High-power devices should be located closest to the power supply, while low-power devices may be placed farther away.
• The signal, wherever possible, should be different.
• The isolated power supply requires careful inspection of the parasitic aircraft's internal power, component, or PCB capacitance which allows the AC to be present at the input or plug-in power to enter the ground plane, or to other internal signals. AC may find its way back to its source via an I/O signal. Although it can never be eliminated, it should be minimized as much as possible. An acceptable amount is implied by the design.

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See also

• Phantom loop
• Current sheath
• stray voltage
• Telluric stream

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References

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External links

• Sound System Interconnection - from Rane Corporation
• Audio Grounding and Shielding Devices - from Rane Corporation
• Whitlock, Bill. "Signal Purity". Sounds & amp; Video Contractor. Archived from the original on September 17, 2004.
• "Medical Information Technology" (PDF) . Archived from the original (PDF) on March 19, 2009. Ã, Risks and solutions for electrical security in the medical system

This article incorporates public domain material from the General Services Administration "Federal Standard 1037C" document.

Source of the article : Wikipedia