Ground loop - what is it and what effects can it have on the operation of systems?
In the previous episode, you will find information about galvanic separation .
Before about the ground loop, it would first be worth explaining what ground is. In electronic systems, it is a node (that is, where different branches of the circuit connect) that is said to have zero potential. In general, the mass is a very wide path or even a plane of copper on the plate so that the currents between the branches can flow freely. At the same time, the track width is large or large conductor cross-section it helps to reduce the resistance, which is also advisable. Flowing currents cause formation voltage drops so our theoretically "zero" potential of the ground line may not be zero in some places ...
A ground loop is created when circuits connect to each other by more than one ground path. And I do not necessarily mean PCB tracks - we can as well talk about combining the masses of two separate devices, e.g. a CD player and an audio amplifier. In this case, the ground loop is formed by the connections between them: one connection is the protective conductor of the network installation, and the other is the shield of the signal cable.
Why is the ground loop so bad? Theoretically, it is very good because two connections will always have a lower resultant resistance than either of them, which is what we want. However, the reality is less perfect and there is a precise cause here.
Such a ground loop has its surface: if they are two tracks located in different places on the board, we are talking about the area of the figure that they delimit. If they are wired connections, we mean the area of the entire area between them. In the case of stage equipment, they can be even hundreds of square meters.
According to Faraday's law of induction, an alternating magnetic field (you should bear in mind, first of all, the 50 Hz electromagnetic field that all power cables emit) induces voltage in such a loop. So if we "add" a component with a frequency of 50 Hz to the signal path, it is not difficult to predict what the effect will be. Humming, humming, buzzing - listening effects vary. Nevertheless, we treat ourselves in this way with an elegant source of interference to the useful signal.
The second issue is the voltage drops on the conductors and potential differences depending on the power consumption of the devices, these unwanted signals via ground loops may overlap the useful signal.
Interestingly, not only audio equipment is susceptible to the influence of the ground loop, although its effects are most visible (or rather audible) in audio equipment. With sufficiently long connections, interference may appear even in the digital transmission, e.g. between the sensor and the computer.
The solution is simple (in theory): you have to cut a closed path for the current. If we sayon wire connections, it usually boils down to disconnecting the ground connection in the signal cable so that the devices are only short-circuited by the protective conductor. In some audio equipment you will find a "ground / lift" switch, which breaks the ground loop. It can be worse on the PCB as it may require a complete redesign of the track layout. However, the ground loop does not make itself felt in every situation and you need to be aware of it.
What can we do?
Use appropriate wire sizes and paths, minimizing voltage drops.
Run loops as tightly as possible, we will limit the field covered by signal paths and wires as well as conducting operating currents.
Loop avoidance through star topology.
The use of digital transmissions that are more resistant to interference.
The use of a medium providing galvanic separation, e.g. optical fiber, toslink, signal transformers, wireless transmission.
Have you had problems with the ground loop?
"Author: Michał Kurzela / Futrzaczek"
"Correction and photos: stabilizer"
In the previous episode, you will find information about galvanic separation .
Before about the ground loop, it would first be worth explaining what ground is. In electronic systems, it is a node (that is, where different branches of the circuit connect) that is said to have zero potential. In general, the mass is a very wide path or even a plane of copper on the plate so that the currents between the branches can flow freely. At the same time, the track width is large or large conductor cross-section it helps to reduce the resistance, which is also advisable. Flowing currents cause formation voltage drops so our theoretically "zero" potential of the ground line may not be zero in some places ...
A ground loop is created when circuits connect to each other by more than one ground path. And I do not necessarily mean PCB tracks - we can as well talk about combining the masses of two separate devices, e.g. a CD player and an audio amplifier. In this case, the ground loop is formed by the connections between them: one connection is the protective conductor of the network installation, and the other is the shield of the signal cable.
Why is the ground loop so bad? Theoretically, it is very good because two connections will always have a lower resultant resistance than either of them, which is what we want. However, the reality is less perfect and there is a precise cause here.
Such a ground loop has its surface: if they are two tracks located in different places on the board, we are talking about the area of the figure that they delimit. If they are wired connections, we mean the area of the entire area between them. In the case of stage equipment, they can be even hundreds of square meters.
According to Faraday's law of induction, an alternating magnetic field (you should bear in mind, first of all, the 50 Hz electromagnetic field that all power cables emit) induces voltage in such a loop. So if we "add" a component with a frequency of 50 Hz to the signal path, it is not difficult to predict what the effect will be. Humming, humming, buzzing - listening effects vary. Nevertheless, we treat ourselves in this way with an elegant source of interference to the useful signal.
The second issue is the voltage drops on the conductors and potential differences depending on the power consumption of the devices, these unwanted signals via ground loops may overlap the useful signal.
Interestingly, not only audio equipment is susceptible to the influence of the ground loop, although its effects are most visible (or rather audible) in audio equipment. With sufficiently long connections, interference may appear even in the digital transmission, e.g. between the sensor and the computer.
The solution is simple (in theory): you have to cut a closed path for the current. If we sayon wire connections, it usually boils down to disconnecting the ground connection in the signal cable so that the devices are only short-circuited by the protective conductor. In some audio equipment you will find a "ground / lift" switch, which breaks the ground loop. It can be worse on the PCB as it may require a complete redesign of the track layout. However, the ground loop does not make itself felt in every situation and you need to be aware of it.
What can we do?
Use appropriate wire sizes and paths, minimizing voltage drops.
Run loops as tightly as possible, we will limit the field covered by signal paths and wires as well as conducting operating currents.
Loop avoidance through star topology.
The use of digital transmissions that are more resistant to interference.
The use of a medium providing galvanic separation, e.g. optical fiber, toslink, signal transformers, wireless transmission.
Have you had problems with the ground loop?
"Author: Michał Kurzela / Futrzaczek"
"Correction and photos: stabilizer"
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