Home > Instructions > Ground loop signals

Ground loop signals

Ground loop problems and how to get rid of them Written and copyright by Tomi Engdahl NOTE: The information presented here is believed to be correct and is made available here by the author. The author of this document is not liable for any effect this information or any use thereof may have. The documents have been used and recommended by many people and are belived to be accurate. Basics The dilemma is that solving "noise" problems is an art within itself.


We are searching data for your request:

Ground loop signals

Schemes, reference books, datasheets:
Price lists, prices:
Discussions, articles, manuals:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.
Content:
WATCH RELATED VIDEO: Ground Loops: Grounding Series (Part 6)

Ground Loops and AV Equipment


A ground loop is a complete circuit of low-impedance grounding conductors which has no load to slow down current flow. It acts as a loop antenna, which picks up power line hum and other electromagnetic noise, including radio signals. The source of electromagnetic waves induces a current in the ground loop through electromagnetic induction. Because the loop is a circuit of low-impedance conductors, a very large current can be induced from a very small electromagnetic field.

Actually, it doesn't. The current flowing in the ground lines makes the ground potential at one or more devices CHANGE, relative to the ground potential at other devices. The signal going from one of these devices to another is then seen by the receiving device as having this ground differential superimposed upon it.

That's exactly right. Since the ground is supposed to be the reference, the device compares the signal line to the ground line to get the signal.

It sees hum voltages between the signal line and the ground line, so it thinks it's part of the signal. The currents induced in both the shield and the center conductor are identical, as long as a ground loop does not exist.

In illustration A, the hum appears on both the signal line and the shield, so the device does NOT see it as part of the signal. Look in illustration A: The signal line connects the ground between the two devices, but only the receiving device has a safety ground in the power cord. The sending device is double-insulated instead. In illustration B, both devices have safety grounds in their power cords. The shield of the signal cable, plus the two power cords, complete the ground loop.

You are risking your own life, or the lives of others. All it takes is a coke spilled into a device, and somebody is toast! It is much better to deal with ground loops in the signal lines. There is also another serious problem. Disconnecting any of the other cables that comprised the former ground loop will now produce a very LOUD hum, as one device becomes totally ungrounded. This can blow out speakers or ears. The resistor works by loading down the ground loop current.

The huge currents cannot flow, and so the hum is not induced. But if more than one cable in the loop has a resistor, then a weak hum can occur due to a lack of solid grounding. Look for any place where signal cables form a circle, or where signal cables and power line safety grounds form a circle. See second panel at right. Computer and digital audio cables can become part of ground loops. Sometimes the computer monitor can form a path.

MIDI is usually immune from ground loops because the coupling is optoisolated. I have also seen ground loops in permanent wiring cause a digital stage lighting control system to go nuts.

And all of those ground connections were required by the electrical code to be there, so there was no cure! Middle: Multiple monitor selection arrangements often produce ground loops. Here, more than one ground loop is formed. What is a ground loop? How does a ground loop pick up the noise? Why does the ground loop cause noise in the signal lines, when the current is flowing in the ground lines? So the ground loop really tricks the device into thinking the hum is on the signal line?

Why don't other cables pick up the hum? Why is it that sometimes I have ground loops, and sometimes I don't? So should I remove the safety ground, or use a 3-prong to 2-prong adaptor, to break the safety ground? NEVER interrupt the safety ground of a device that was designed to have one. So how DO you get rid of ground loops? There are several methods: The quickest method is to cut the shield of one signal cable in the loop, at the load end.

This is shown in illustration D. This forces the ground return current to flow through the other half of the former ground loop. This does have a disadvantage, as the cable can no longer be used for anything else except to break ground loops.

Be sure to label it as such. You could also make up a set of short ground loop breaker cables, with the shield disconnected at one end. Put one male and one female connector on each cable, and insert it into the cable run every place you find a ground loop. But beware, because disconnecting other cables can still produce the very loud hum. A better trick is to put a 10 ohm resistor into the ground leg, instead of just cutting the shield, as in illustration C.

This keeps the loud hum from happening if one of the other cables in the former ground loop is disconnected. The resistor can also be put in the short ground loop breaker cable for the same purpose.

Grouping the ground loop cables into a snake prevents the hum, even though the ground loop still exists. This is because gathering both legs of the loop into one cable causes both legs to have equal but opposite currents induced. The currents cancel each other out.

Likewise, you can bundle cables in the ground loop together with cable ties, provided they are the same length. The best way to break a ground loop is to use a ground loop isolation transformer, as in illustration E. This passes signal, and keeps everything grounded, but will not pass ground loop currents at all. Disconnecting other cables also produces no hum. How can I recognize the ground loop? Can other cables also form ground loops?

Links: More on grounding and noise: Banish noise from your studio. The difference between an insert and an effects loop. The two kinds of effects. My mixing page: Mixing your own sound. My home page Home "Look for any place where signal cables form a circle, or where signal cables and power line safety grounds form a circle.

B - Ground loop through power safety grounds causes hum. C - Breaking ground loop with Ohm resistor. D - Breaking shield to get rid of ground loop. E - Ground loop isolation transformer. Ground Loop Situations: Top: Ground loops often show up in effects loops and insert loops.

Bottom: Ground loops can be formed through the computer too.


Ground rules: earth, chassis, and signal ground

In analog design, the relationship of a signal to ground is of fundamental concern and can create issues in digital designs, too. All three indicate connecting to a point of theoretically zero voltage , but within a different context: chassis ground for a device, signal ground for very low voltage signals within a device, and earth ground for a power system. But ground as zero voltage is theoretical; only a conductor with zero impedance will have zero voltage. In reality, a ground plane or rail will usually have varying voltages at negligible levels. This is most likely if the circuit or device happens to operate with high amperage draws, or in cases where the ground plane, conductor, or rail has a high impedance i. Current flow I through any material with resistance R will have a voltage V other than zero.

In reality, the signal is recorded at finite time intervals; we change our notation to reflect this.

Ground loops


Ground loops can be a real nuisance in HVAC data acquisition systems because they are hard to spot. Most of the time they do no harm but they can cause unpredictable problems years after the installation! The conductive loop forms a large loop antenna that picks up interference currents easily. The resistance in the ground wires turns the interference currents into voltage fluctuations in the ground system. The ground is no longer stable; therefore the signals you are trying to measure which are referenced to that ground are also unstable and inaccurate. A perfect ground, however, is a laboratory abstraction and does not exist in the real world. Real grounds are conductors, so there is a certain amount of resistance to electrical current between all grounding points. This resistance can change with humidity, temperature, connected equipment and many other variables. The resistance can always allow an electrical voltage to exist across it.

WTF Are Ground Loops?

ground loop signals

These magical creatures crop up out of nowhere and fry your electronics or annoy your ear holes. Understanding them will doubtless save you money and hassle. The ground loop in a nutshell is what happens when two separate devices A and B are connected to ground separately, and then also connected to each other through some kind of communication cable with a ground, creating a loop. This is particularly noticeable in analog AV setups, where the result is audio hum or visible bars in a picture, but is also sometimes the cause of unexplained equipment failures. One example is your cable TV.

In a process control loop, a ground loop circuit can develop when each device's ground is tied to a different earth potential thereby allowing current to flow between the grounds by way of the process loop Figure 1. Ground loops cause problems by adding or subtracting current or voltage from the process loop.

Ground loops: Causes and cures


Vibration controllers are very sensitive to electrical noise and that noise is often visible in testing signals plots. It comes from two different sources of noise in vibration testing systems, ground loop noise, and Electromagnetic Interference EMI. Both of these can cause a variety of problems. It can be caused by a communication system, such as a CB radio, but more often by operating electronic devices, virtually anything from an electric drill to a garage door opener to fluorescent light ballasts; EMI can even be caused by electric power lines. EMI can have a significant effect on a vibration testing system when the surrounding environment is electrically noisy. Long cables, poorly shielded cables, and components and certain amplifiers can, at times, act as antennae, pick up the EMI, and introduce it into the system.

PCB Design & Analysis

Ground Loops Radio Equipment. Ground Loops Vehicles. Vehicle Grounds and Grounding. Ground loop problems usually occur when interconnecting ports are grounded to points operating with voltage differences. The voltages differences are generally created by high currents in another grounded path. The problematic voltage differences are commonly created by voltage drop along a high current conductor that is ground at both ends to a common ground. This can create a potential difference along a signal wire ground path, and that voltage is transferred into the sensitive circuit.

In turn, resistance changes these currents into voltage fluctuations which cause signal noise due to the instability of the system's grounding, which corrupts.

Ground Loops Explained

Few things can be more frustrating than having a recording system plagued by hum. Individually, your effects processors, mixers, recorders and MIDI instruments may function perfectly, but connect them together and the chances are you'll hear at least some background hum. If you're lucky, this will be quiet enough to live with, but at worst, it may be so intrusive as to make your system unusable. Those unfortunate enough to be bothered by this problem often start disconnecting the earth cables from various mains plugs, in the hope that the hum will go away.

Subscribe to RSS

RELATED VIDEO: Eliminating RFI and Ground Loops - Sound Speeds

Thus, an interference signal to the useful signal is added. The interference can be transmitted over a common impedance with an interference circuit or inductively by magnetic field coupling in utilizing circuit. The effect manifests itself in the sound as annoying buzzing sound, often at twice the frequency of the power supply network, which can then connect to the usual rectification Graetz bridge or rectification. The interference signal can express, for example, in audio engineering equipment as unwanted, annoying buzzing noise.

In an unbalanced interface video and consumer audio , this ground voltage difference directly adds to the signal. This generally produces hum or buzz in audio and hum bars in video.

In an electrical system, a ground loop or earth loop occurs when two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them. Current may be produced in a circular ground connection ground loop by electromagnetic induction. Ground loops are a major cause of noise , hum, and interference in audio, video, and computer systems. Wiring practices that protect against ground loops include ensuring that all vulnerable signal circuits are referenced to one point as ground. The use of differential signaling can provide rejection of ground-induced interference. Removal of safety ground connections to equipment in an effort to eliminate ground loops also eliminates the protection the safety ground connection is intended to provide. A ground loop is caused by the interconnection of electrical equipment that results in there being multiple paths to ground, so a closed conductive loop is formed.

Ideally, all grounded points of an electrical system should be at the same potential. However different points of the same grounding system may have different potentials due to:. Ground loop is mostly formed in equipment installations consisting of multiple peripherals and devices connected to different power sources, and using the data lines, video or audio wires to communicate. If there is a difference between the various ground reference voltages, a current will flow from the higher reference ground point to a lower one through a circular path that uses the data line.




Comments: 5
Thanks! Your comment will appear after verification.
Add a comment

  1. Destan

    It is remarkable, very good information

  2. Momuro

    I would like to encourage you to visit the site where there are many articles on the topic that interests you.

  3. Lenard

    We urgently sell Second-hand R-50, R-65 rails, wear group 1, wear up to 3mm, for re-laying on the road. NOT A CROWBAR!

  4. Yojas

    I apologize for interrupting you, but, in my opinion, this topic is no longer relevant.

  5. Yomi

    Maybe I'm wrong.