Rolling Lines HDVCI

Hello, we just installed an HDCVI system from Dahua.

About 5 cameras have a "rolling line" going up the picture.

Its not real bad... but you can see the slightly dark rolling line that continuously moves up the picture.

We have checked for any power etc wire crossing the camera wire etc etc.

Any ideas?

Is there any type of filter we can put on the lines to stop this?


Sounds like a ground loop. Is it a metal building?

Or it could also be a lighting issue. Is it in an area that has fluorescent lighting?

What type of wire are you using? Is it pure copper or CCA/CCS? Baluns?

Dahua advertise their own ground loop isolators on their website, model number PFM791.

Sounds like a ground loop. Are all the cameras on the same outlet as the recorder?

You can get a ground loop isolator, this one says its for HD, but ive never used it.

Agreed with the above. It likely is a ground loop. When your cameras are powered from a different 120vac circuit than your recording device, there can be a slight difference in the voltage. Not much, .5 to 2 volts (sometimes more). That is a difference in potential. That one or two volts will travel up the ground wire of the video camera to the recording device and cause the roll (black bars or lines that roll up the screen) you describe. The greater the difference in potential, the heavier the black bars will look on your screen.

The cleanest way to eliminate it is the ground loop isolator U1 mentions.

You can check by installing a cheater plug (2 prong to three prong adapter on the camera power supply and recorder (you are "floating" the system), removing ground for a test. If the bars go away, you have found your problem. The plugs cost about dollar each. If they don't, you may have to look for other sources - lighting etc.

Mark, I would only add to mention that cheater plugs aren't a solution. They are fine for testing and diagnosis, but should never be left in service. Also, for an easy cheater, I just bust the ground prong off a 12" extension cord. I keep them in my truck for when you can't fit a large wall wart int an outlet/power strip/UPS.

They are fine for test and diagnosis, but should never left in service.

To be fair to Mark, he does say to do it 'for a test', though reiterating the warning can't hurt.

Also, for an easy cheater, I just bust the ground prong off a 12" extension cord.

I would only add to mention that this is inviting someone plugging in a normally chassis grounded device, like a power tool, at the female connector of the extension cord, unaware that it is not grounded at the source.

Skip the cheaper cheater and ALWAYS use the adapter at the device end for clarity.

I never said Mark was wrong in anything he said. I was just adding to his comment.

Also, if you read my post, I said a 12 INCH cord. I highly doubt anyone would add that to any device for a 1 foot extension. It would never be left onsite anyways.

Also, if you read my post, I said a 12 INCH cord.

I read your post, did you read mine? :)

The problem isn't about the length, it's the fact that the ungrounded nature of the cord is obscured when a homemade cheater is used, (because of the way it dovetails into the female, unlike a real cheater, which are distinctive and have an external tab or wire at the plug.

I highly doubt anyone would add that to any device for a 1 foot extension.

Probably not, but would someone *remove* it before using it is the question.

The danger is that you have the your cheater plugged in to a longer extension, (because it's short, right?), let's say at a job site.

Some other contractor plugs a tool in to your cord at some point when you have stepped away... How would they know it's ungrounded?

Or if the cord isn't broken down after use and the next guy grabs it.

IMHO, its an added liability not worth saving $1 for.

There is no extension cord involved, the way you are describing. It isn't something I would leave on site, or walk away from. It would be in my hand for testing purposes. I don't know what axe you have to grind here. It is effectively the exact same thing as a cheater plug, I just didn't have to run to a store to buy one.

No ax to grind.

Peace, brother.