other ground loops
other ground loops
Ground loops have a different meaning in the audio / TV / CCTV world. In a large installation a security camera may be located in one area and locally grounded where as its TV monitor may be a thousand feet away and grounded to its local ground.
The two grounds may be at different potentials however the coax cable will now be joining them together forming a loop. The video voltage on the cable is typically less than 1 volt so it does not take much of a ground difference to swamp the signal altogether. This is displayed as a thick horizontal bar moving up or down the picture.
In audio systems the signal levels can be much smaller and the ground loop will cause a 60Hz or 180Hz (50Hz / 150Hz) hum to be on the sound.
From an installation point of view the best solution is to have a single place where all technical equipment is grounded and make sure cameras are insulated from local metalwork and any local DC supplies do not pass a ground through to the camera.
There are electronic solutions to reduce the effect of ground loops however the single technical ground and ensuring no cables are grounded on their way is always a good starting point
In a perfect world all grounds would be at the same potential however these days many items of electronics have input power filters each of which will leak a mA or more to the ground and this all adds up. Another problem is where the ground and neutral conductors are connected at multiple locations ? sometimes intentionally. This forces the local ground voltage to be the same as the neutral voltage which will rise with load due to the cable resistance.
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other ground loops
Ground loops have a different meaning in the audio / TV / CCTV world. In a large installation a security camera may be located in one area and locally grounded where as its TV monitor may be a thousand feet away and grounded to its local ground.
The two grounds may be at different potentials however the coax cable will now be joining them together forming a loop. The video voltage on the cable is typically less than 1 volt so it does not take much of a ground difference to swamp the signal altogether. This is displayed as a thick horizontal bar moving up or down the picture.
In audio systems the signal levels can be much smaller and the ground loop will cause a 60Hz or 180Hz (50Hz / 150Hz) hum to be on the sound.
From an installation point of view the best solution is to have a single place where all technical equipment is grounded and make sure cameras are insulated from local metalwork and any local DC supplies do not pass a ground through to the camera.
There are electronic solutions to reduce the effect of ground loops however the single technical ground and ensuring no cables are grounded on their way is always a good starting point
In a perfect world all grounds would be at the same potential however these days many items of electronics have input power filters each of which will leak a mA or more to the ground and this all adds up. Another problem is where the ground and neutral conductors are connected at multiple locations ? sometimes intentionally. This forces the local ground voltage to be the same as the neutral voltage which will rise with load due to the cable resistance.
G