Sunday, July 10, 2011

Getting rid of Hum Bars within a Video Camera Surveillance System

By Tim Norton

Any time you put in a surveillance camera system, you might on occasion end up with these types of nasty lines across the display. Usually the initial thing you end up doing is return the camera since it has to be defective, only to discover it works perfectly while in the workshop or that the new unit does a similar thing.

The most common cause of it is really an ground loop, in which a voltage variance has developed on one side of the coax cable to the other end, with respect to ground.

They'll occur as various patterns on the screen and even make a DVR to not record due to a distorted sync pulse. Below a few of the visible effects you may see.

There's really no point in accusing anyone for these because they are unforeseen as to when they are likely to occur but they are more prevalent where the surveillance camera is installed in a location that has a different grounding point to the Digital video recorder or display. For example a security camera pole isn't earthed to the same point as the building where the Digital video recorder is. The fact is it is possible to earth loops in lots of other applications like data as corruptions and audio as a buzz.

There are several procedures that should decrease the odds of finding an ground loop but not one will prevent them.

1. Insulate your camera on the bracket. This requires taking away every electrical bond from the video cameras metal case and the mounting bracket but is only required if your mount will be on a conductive area such as a tin shed or a light pole.

2. When ever putting in the coax , be sure there aren't any lacerations in the insulation as a result of pulling it across jagged edges .

3. Where practical, join the earth of both ends with one another. However this is costly as you will have to install extra ground cable to each camera.

4. You can install fiber optic cable connections to your distant security cameras. This is often pricey but does offer additional added advantages. You've also eliminated lightning strikes from flying through your complete system, destroying almost everything. You can put numerous video cameras on one fibre.

Doing at least points 1 & 2 above, in the event you get an ground loop you'll have to purchase a gadget known as a hum bug eliminator and the issue shall magically vanish.

The unit comes in many forms which includes DIN rail or rack mounted but a beneficial one to have in the tool kit is this in-line hum eliminator, which can be put in between the Digital video recorder input and coax heading to the surveillance camera.

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