Elevator Cables and Electrical Interference

Make sure signal cable shields are correctly grounded, avoiding "pigtail" shortcuts at terminals. Also make sure that the power cables are shielded, generally they are not (cheaper not to) and if not shielded, then you will have to separate the RG11 cable from the power cable as far as possible.

Fast surge pulses sent through power cables can cause capacitive coupled noise currents into adjacent cables.The longer the cable, the greater is the effect. Combining both power and signal cable into the one bundle is a shortcut and not a smart one.

Hi Craz, thx for ur prompt reply

what does pigtail" ..shortcuts.. mean? i am not quite understd how this capacitive coupled noise produce. Is this what d industrial so call electro-magnetic field interference? its not easy to separate this Rg cable @ 70 storey high.

thks

I agree with the "proper shield termination". I would disagree with the "separating the cables has nothing to do with it" bit

If the RG ground is separated from the (what I believe to be currently) shared ground of the power cables and the termials of the RG properly shielded and not exposed to interference, the problem experienced by the OP should be fixed. If not, seperation of the RG cable from the bundled power cables is clearly required

Separation clearly won't hurt. But if the coax is grounded to structure at both ends and has ground currents flowing on it, no amount of separation will help. And if the coax ground is lifted at one end, for instance if the camera case is plastic and isolated, then no separation will be necessary.

I suggest a fiber line. permanent immunity to noise

https://www.westlake-electronic.com/search/items/GEF10538/index.htm

lots more, dig here

http://www.google.ca/search?hl=en&q=video+%2B%22fiber+optic+link%22+%2Belevator&btnG=Google+Search&meta=&aq=f&oq=

Assuming the camera puts out standard video, a fiber line requires an extra interface at both ends. That is extra cost, and an added source of unreliability. Coax, properly done, is more than sufficient to the stated need.

I advocate the use of high resolution video as well as a fiber interfae. You can now het an integrated component that costs very little to be placed on the camera. In terms of the overall cost of en elevator in a high rise building this is an inconsequential cost in exchange for long term reliability and immunity to RFI. Fiber lines do not fatigue fail the same way copper does with flexure.

Agreed

seems kinda weird that everything was bundled together without a thought.

well.. save cost of coz .. then again problem surface. Do u think a Rg11 multi- strength cable separated from the bundle can handle a speed of 360m/min elevator speed? Thou d "multi-strength" may sound too good to be true..

Quote"You can check this by removing the coax connection at the camera end, and checking continuity to ground; then connecting the coax to the camera, disconnecting at the other end and rechecking. You had better see an open circuit during one of these two checks."

yeah.. i will check on that, mean time freaking management has given me a hard time not letting me do troubleshooting. imagine 70 storey high, 1flr 8-11 units, average 3 ppl per unit.....darn... Thks all :)

emc c,

You have a great answer here and a likely part of the problem. One thing that I think may have been overlooked though is metal fatigue. Elevator cabling must be constantly flexed. If the video cable was originally constructed with a solid center conductor or very few discrete strands, the center might have several breaks in it acting as switches. As the elevator moves these switches can briefly open and re-close looking like noise on the monitor. If this is the root of the problem then replacement is the only option.

One can't argue that if the cable is breaking, it needs replacing. The original post cited noise issues. If the cable center conductor were breaking, I would expect intermittent loss of signal, not a noisy signal.The OP stated that there was a snowy and jumpy signal. Snowy means low signal-to-noise ratio; jumpy may mean loss of sync - now that points to your diagnosis. If the problem were intermittent connections, I would expect the jumpy signal, so maybe more than one thing is going on here at the same time. Good catch.

That being said, a good troubleshoot to lay this to rest would be to measure end-to-end center pin continuity, through several top-to-bottom and bottom-to-top excursions of the elevator car, looking for either solid continuity, or the lack thereof.

Much easier continuity check can be done by terminating one end of the cable with a fixed resistive load, say a nominal 75 ohms resistance. Measure the cable and resistor resistance at the other end of the cable while operating the elevator. If the resistance does not stay a consistent 75 ohms but bounces to 0 or ∞, then either the shield or center conductor is damaged and the cable needs a replacement.

Right again - much easier!

Yes, Cable flexure in a stranded core is possible, In addition, the same flexure occurs in the stranded insilator, especially after time as the wire get oxidized. It occurred to me to think there might be cables made for this job.

a search founds hundreds, here is one,

http://www.draka-ep.com/index-en.html

and here is the search

http://www.google.ca/search?hl=en&q=elevator+%2B%22coaxial+cable%22&btnG=Google+Search&meta=&aq=f&oq=

Hi guys

I have measured both end of the terminal RG11 cable using multimeter, firstly, i measured the ohmage of both ends, one end to the ground n the other end to the shielded Multi-strength wires, it was found '0' ohm.

When i turned the meter to Ac volt reading, both end were found to have a voltage of 64Volts, i was shorted by it when i touched the wires. I suspected this were EMF leakage.

The termination were checked n done properly, no additional ground. there is no way i can separate this cable, it just too big n bundled with cables...

Is magnetic emf absorber(this thingy look like a current transformer ring core) capable of reducing emf? Any instrument to measure emf leakage?

Thks for the help guys

Need more info here. You say you got an electrical shock? You would not get a shock from simple crosstalk. A shock implies a high resistance short to ac mains. When you say you measured 64 Vac, what was the reference to which that measurement was made (to where were the two meter leads connected)?

yes, i got a shock when i removed the RG11 screw terminal, i measured by pointing one red probe at the RG shielded multi strength wires(centre wire) and another probe(black) to the ground. Hence the 64vac. both terminal end has already been removed then measurement are taken. Thks for the reply :)

Shocking news

I would check the power cables for leakage and continuity with respect to the metal frame and also measure against the RG cable causing you problems and an electrifying experience. Maybe that a cable/s is damaged during pulling through structure?

You mention that the cables are near an elevator. This is a classic cause of what I call spiking.

I mentioned earlier without much detail added,

"Fast surge pulses sent through power cables can cause capacitive coupled noise currents into adjacent cables.The longer the cable, the greater is the effect. Combining both power and signal cable into the one bundle is a shortcut and not a smart one."

Surge pulses are generally caused by motor interference and this is the cause of half of your problem. Contrary to opposing opinions, I still have the view that you will have to relocate the RG cable from the power cable that I assume is at least driving the elevator.

The other half of your problem (and possibly the full problem if my previous opinion is incorrect) is that you have to check the continuity etcetera I mentioned with respect to the power cables.

i have checked the continuity, it was A ok, no leakage found either. as i mentioned, the Rg11 cable is within the bundle, so the only way to isolate this is to buy a standalone RG11 n fix the issue. Again this elevator travel at a speed of 360m/min, i doubt standalone RG11 can handle such speed.

Correct me if i'm wrong, what if both terminal end of the RG11 connector were grounded ,, what will happen?

oops .. i miss this quote

"Separation clearly won't hurt. But if the coax is grounded to structure at both ends and has ground currents flowing on it, no amount of separation will help. "

Let says i do this, will this damage the LCD?

And if the coax ground is lifted at one end, for instance if the camera case is plastic and isolated, then no separation will be necessary. - I don't quite understand this..