Is this a ground loop problem?

[ccolvard 0]

We have just installed a system (Cat5/Baluns) using Pro-Video CVC-695AM cameras at the pedestrian gates and Samsung SCC-131AN for overhead. The Samsung's are powered by 24v AC and Pro-Video's 12v DC. Transformers were installed at buildings closest to camera location, but located on different buildings and the control room (DVR) is in a different building.

 

The Samsung's are working perfectly, but I've got what appears to be a ground loop problem with 12v DC Pro-Video cams. All of the Pro-Video cameras have vertical scroll that is the same on each of the cameras. (The Samsung’s have built-in ground fault isolation.)

 

Is this a ground loop problem with 12v DC power?

 

If not, what should I be looking for?

 

If so, can I isolate the ground at the DVR & monitor to resolve the problem or do I have to use a blocker in between the Pro-Video’s and the DVR.

 

Does the ground carry through the DVR & monitor if I use an isolation transformer on both of them?

 

Thanks,

[rory 0]

first plug in a monitor where the camera is powered and then see what you have. If there is no problem there, then yes its probably a ground loop problem.

 

Since you are using Cat5, I would suggest some good active UTP transceivers/transmitters such as NVT.

 

(eg: http://www.nvt.com/products/NV_652R.html) The active ones have Built-in Transient protection & ground lifting. How many or what type you need will depend on the number of cameras: http://www.nvt.com/products.html

 

Rory

[Cooperman 0]

Hi ccolvard

 

Interesting little problem you have there. Here's a few 'if's' to be going on with....

 

If you have a battery powered test monitor, have you checked the picture straight out of the Pro-Video cameras? Picture o.k. or not?

 

If not, you have a local problem, perhaps with the cameras (or power supply units).

 

If the pictures are o.k., check the image quality at the other end of the camera cable, again using a battery test monitor.

If the problem appears, it's probably down to a signal transmission issue.

 

If it doesn't, connect the camera signal directly to a mains powered monitor (or TV with video input).

If the problem appears, it's almost certainly an Earth (ground) loop hum, but almost certainly nothing to do with 12v DC.

 

I don't know the cameras you're using, but if the camera case / weatherproof housing are metal, what are they bolted on to? If any part of the camera/ housing (and that includes mounting bolts or screws) is in contact with a metal clad building (for example), that can set up a problem.

 

Maybe you could do a few more tests, and in the meantime, no doubt other guys will be along with some more suggestions.

[ccolvard 0]

Hi Again:

 

Thanks for the quick replies!

 

I have tested each run (at camera & termination) with hand held monitor and images are good.

 

I know PV cameras are grounded because they are mounted on wrought iron security gates. I thought it was a ground loop problem because all of the PV cams were scrolling at the same rate and frequency.

 

Transmitters/recievers will cost me about $800.00 (US) before labor for the 4 cameras. I'm looking for a solution that is much cheaper.

 

It's not clear to me why isolating the ground (at the DVR & monitor) and terminating the run at the DVR, wouldn't break the ground loop. This would be accomplished by installing Tripp Lite Isolation Transformer that costs about $90.00 (US). ( http://www.tripplite.com/products/product.cfm?productID=226 ) Am I off base here?

 

If that's not possible has anyone used GB60-UTP (by FM Systems)? The cost for 4 channels is only $350.00 (US).

 

Any advice or comments would really be helpful.

 

Thanks,

[Cooperman 0]

The simplest and cheapest thing to do (certainly to confirm whether it is an earth loop) is to 'insulate' the cameras from any contact with external metal.

 

Maybe the first thing to try is, detach all the P.V. cameras from any physical contact with metal, and see if the problem has disappeared.

 

I don't know these cameras, so forgive me if my guesses are wide of the mark. If the cameras have metal cases, or a metal retaining bolt is going into the internal chassis, and making contact with either a metal or grounded plate, or the housing itself, consider how to place an insulating barrier between the camera and whatever it's touching. Something as simple as a thick PVC tape (or lane marking tape) as a cushion, then maybe use heavy duty nylon cable ties to secure the camera.

 

If it works, you've avoided the cost of an "engineering" solution.

 

Incidentally, being low voltage, there is no requirement to ground them here in the U.K. I would assume the rules are similar Stateside.

[AVCONSULTING 0]

Go to your local distributor and borrow a ground loop isolation transformer.

Vicon and Pelco make them. That is the easiest way to check if you have a ground loop.

[rory 0]

while we are on this subject, I have a similar issue, but its RG59.

 

There are 7 cameras, 4 of them GE Kalatel Traditional Cameras with AI VF lenses, they are great. However, the domes, all 3 of them, or at least 2. didnt look too clear at the other one, have a ghosting effect. I know this is an easy one, but 1 hour sleep a night for a few days and just got in from a long day of meetings, any quick ideas? Im moving at least one of the Domes anyway and putting it outside, in another building about 100 feet away, will get into that in another thread to get some ideas..

 

thanks

rory

[ccolvard 0]

Solution Found:

 

1. My installer removed the rubber screw brackets and grounded the cameras to the wrought iron gates.

 

2. The building electrical system (upon inspection) had the main ground wire to the panel disconnected.

 

All ground for the entire control center building was running through the earth ground established by ignorant installer at 3 camera locations.

 

After, help from you guys and several other resources was able to isolate one camera without ground and it worked perfectly.

 

Later I had the project manager have his electricial connect a new ground (6' solid copper to electrical system) and entire issue was resolved today.

 

Moral: Learn from any reasouce, then use common sense to work through the issue.

 

Thanks for your help!

[rory 0]

Are you talking about Electrical Ground? (High Voltage)

[ccolvard 0]

Yes, the main ground to the building was disconnected.

 

I explained the problem and told the project manger what had to be done.

 

This enabled me to charge a change order to solve the problem and earn some $$ for my time.

 

Not all problems have to be a crisis. Some time we just have to be creative.

 

Thanks again for your help!

[rory 0]

Darn, i imagine thats dangerous, probably could get a fine for that in the US? Here its like that all the time, well dont know about the ground, but you should see some attics I have been in, live exposed wire everywhere ...

There are no laws for that here ... or they are / will never be enforced.

[Cooperman 0]

Shocking isn't it

 

Pleased to hear you got it sorted ccolvard; it's often the little things ....

 

Rory,

Are you sure the dome covers are o.k? cable terminnations? I've had three hours sleep so I'm not far behind you

[rory 0]

hi,. just stopped in from that job, just took down the dome to put it over in the next building, where i just mounted all the alarm parts. Anyway, the GE KTC-840E Traditional Exview Camara i put up in its place, took 2 minutes, perfect picture no lines. I think GE's vandal resist domes just suck!! Everyone I have used have been like this. They look cool though, at least they have that going for them. No problems with their indoor domes so far. Could still be a termination issue, I checked the power supply box and everything there is okay. All the cameras are 24VAC. Maybe I will try powering them off of their own Power Supplies and see what happens also. I have a spare 4 channel Altronix 24VAC power box.