Harmonic Interference What can I do?

[bigcatbobcat 0]

I've got an installation, 16 cameras, 2 out in a detached garage. It's 160 feet away from the DVR. We noticed there are waves or just a general distortion and thought it was the 277v conduit in the garage that was in the same area (sometimes touching) our cable. Then the owner said "No I think it's your power supply" It wasn't. So we figured it out. I was messing with it and talking to my partner on the phone, as I separated the cable from the conduit, he noticed every time he heard a noise the picture began to distort. It turns out it was the air compressor they used to fill tires or whatever. I switched the outlet that was plugged into, same issue. I talked to our most experienced installer and he said, "Yep, harmonic distortion." He knew what it was but didn't have much of an answer for how to fix it. What do you guys think? I could have sworn I saw there was something you could do to even out the picture, some sort of accessory or something? Any help is appreciated.

[Nimrod 0]

The problem you have is called inductive coupling, harmonic distortion is simply a distorted waveform and has no transmission effect.

 

You should never run low voltage lines such as camera, network, telephone etc, close and parallel to power wiring. If you have no other way to run it, be at least 12 inches away from each other, or put your low voltage wire in metal conduit for shielding.

 

In your case with an air compressor you may have to be even farther away. Air compressors draw a lot of amps and put out a lot of interference. The more amps there are the stronger the magnetic field is and the more inductive coupling.

[bigcatbobcat 0]

I'm back on this job. Customer was OK with temporary interference and actually started using a different compressor but the cameras have gone out. We replaced the cameras and the issue immediately came back. Is placing the cable in metal conduit my only option?

[Birdman Adam 0]

Yea, that will do it. Ground the conduit!!

 

It is totally possible for the EMF put out by big electric motors like those in compressors to distort you cameras. I would first try to keep the compressor farther away from the camera+video cable, and keep the cable away from power wires (only cross them at 90 degree angles).

[bigcatbobcat 0]

What about supplying the power locally. Currently have the usual siamese cable coming from the main building, approx 175 feet away. If we use a power supply out in the garage would that eliminate the issues?

[Soundy 1]

Depends whether the noise is getting into the system through the power or signal lines, or both. If it's being picked up by the RG59, then moving the power won't help.

 

Won't hurt to test it, though... it might help some, even if it doesn't clear it up entirely.

[bigcatbobcat 0]

Yeah, it helped a little but didn't clear it up. I'm not sure what else to do here. It is a metal building, metal housings, metal screws of course, might put them on a plastic box? I have no idea...

[Soundy 1]

You can remove a camera from the building and let it hang from its wire to determine pretty quickly if it's a ground-loop issue... if it's EMI, then lifting the ground likely won't help.

 

As has already been stated, it's probably a factor of your signal line running too near to other power: when the compressors start, the lines supplying them carry a lot of current, which creates a pretty substantial electromagnetic field around the wire. That in turn induces a current in another wire running close to it... in this case, your RG59.

[bigcatbobcat 0]

I meant to update, it does it all the time now. I don't know if they've added any more appliances out there that pull significant power. The issue I'm having is that I've sort of resigned myself to saying "Ok we have to put it in conduit." and I don't want to bear that cost and I'm sure the customer won't either, I had a hard enough time getting him to pay for the system.

[Soundy 1]

While it's most common to have problems with signal lines running parallel to power lines for long stretches, it only takes some part of your system to be near the source of the noise for it to get in and potentially affect everything. You could try filtering the power to the DVR by plugging it into a UPS and then unplugging the UPS from the AC source, leaving it to run on battery only. You could do the same for the camera power (or if they're 12VDC cameras, try powering them off batteries - if you have 12V or even 14V cordless tools, those batteries will work for testing).

 

I've seen even a line crossing power at a right angle cause problems: when I was doing IT support at a digital-arts school, we had a set of computers on one wall that 80% of the time would not pull an IP from the DHCP server. They had a link, the runs tested fine on the cable tester, and the rare times the machines did get an IP, they would communicate on the network. Stranger still, they would get an IP probably 90% of the time when booting from a network-attaching boot CD, but then fail 4 out of 5 times under Windows.

 

The problem was limited to only the computers on that one wall, so I traced the conduit that the runs were in, up the wall, and across the ceiling. It crossed a conduit with the power run to the light switch at one point, and they'd used the "best practice" of crossing the two at right angles, so that didn't seem likely... but after testing several other things unsuccessfully, I came back to that point, and pried the network conduit further away from the power conduit, increasing the gap from maybe 1/4" to about a full inch... and magically, the computers all started getting their IPs properly. Just that small distance was all it took to reduce the interference enough for things to work.

[bigcatbobcat 0]

Yeah, thanks soundy. I'm just going to have to go out there and try things. The only issue is the owner follows me around whenever I'm doing anything like a lost puppy asking questions and thinking of places I can move the cameras he has to and adjusting the ones we've adjusted 20-30 times. Anyway, I'll test it and reply here once we find a solution.

[bigcatbobcat 0]

Took the camera off the wall, it instantly stopped. We put them on PVC outdoor J-Boxes, so they have the gasket between the camera and the box, they're indoors so not too worried about water getting on the connections any so we didn't completely seal the boxes, like leaving a gap and the pictures are perfect. Must be some grounding issue or something in the steel walls of the building.