bman4523

Hi all, love the site, this is my first post so here gos. Did an installation of a 300KVA UPS system last year in an existing medical imaging clinic. All the feeders in the building were run in PVC and I followed suit when I ran the feeder for the UPS. Clinic has had a problem ever since the UPS went on line with the Ultra sound machine (ultra sound room is located across a hallway from the UPS room) When the tech uses the color mode for ultra sounds he gets a lot of artifacts (interference) on the screen. IF we put the UPS in bypass and shut the inverter down no more interference. IF we use an extension cord and roll the Ultra sound out the room and down the corridor 15' no more interference. The UPS reps have been on site and claim the problem is because the feeders are not in metal conduit. We are not convinced as the interference occurs when the ultra sound is placed near the UPS room but has no effect other wise. Thoughts?

Billy_Bob

First off, I have no idea how an ultra sound machine works!

But if the problem is in fact "interference" coming through the "air" like a radio signal, then there are options.

To me the best thing would be the easiest and least expensive fix. I think this would be a "Faraday cage" or a partial Faraday cage to block the interference coming through the wall.

A faraday cage is a metal wall/ceiling/floor which is grounded. This blocks signals from entering the room. If the ultra sound machine is this sensitive to outside interference, then a faraday cage might be the best idea because it would block other interference as well = like radio/TV stations, cell phones, private radio communications, etc.

A faraday cage does not need to be solid metal. Fine mesh copper screen like for a screen door will work as well.

Maybe just one wall of copper screen on the "UPS wall" would do the trick? But they might want to go ahead and do the other walls and ceiling as well if this works. (I wouldn't bother with the floor.) If it is necessary to cover the door, you could use one of those burglar alarm wires to connect the ground to the door screen.

The screen can be painted over once it is installed.

I would discuss this idea with the ultra sound company engineering types and see what they think. Also you could just hang copper screen on the wall with tacks and ground it, then see what happens.

More about Faraday cages...
http://en.wikipedia.org/wiki/Faraday_cage

goose134

I agree with Billie Bob. We installed something like he was describing at a radio station broadcast booth. Everything was in EMT, but they didn't want ANY noise affecting their system. Sounds like this equipment is based on sensitive waveforms that could be altered by EMF's. In fact, if they were so inclined, you could drywall over the screen like they did at the station.

electrician1957

I know this thread is almost a month old, but this problem seems to be an RF problem. An RF tech with a spectrum analyzer should be able to pinpoint the problem...

bman4523

I wouldnt know where to begin to find such a person, ghost busters?!
bman

brian john

It is very possible you have a SDS, or not an SDS (the UPS that is) improperly grounded and you have set up a ground loop, neutrals grounded downstream from the main neutral ground connection. Then you have ground current on the metallic components of the building. This sets up an EMF field and this messes with displays.

I am no ghost buster but I resolve electrical related anomalies.

nick

Well the reps maybe have a point but there is one thing i can point out to them ultrasound is what it says , sound waves it is not radio waves ,but sound waves at high frequency like around 1 mhz to 5mhz and the probe they used just sends out the sound waves and these sound waves return back as a echo to the same probe that sends them . there is no magnetic fields or radio waves thats a fact . its like sonar sound waves . but the inverter on your ups can trash the line meaning if near a ac power line close by or it can as a freq drive back feed you system chopping you 60 cycle ac lines . use a line reactor which is nothing more than a filter on you input ac power line that feeds the ultrasound equipment or as[ Brian has stated grounding/ connections is most important] . but pvc is not your problem . that extension cord may have enough resistance in it to or limit some line chop. hope nobody has a pace maker in that hallway if the emf is that high ? just dont see emf that strong from across the hallway ? electronic stuff is very touchy so the faraday cage might be correct but i really dont think so , i would try a[ line reactor filter] . i maybe out of line or incorrect comments .take care best to ya

JTPBOY

New to the forum, experienced in UPS service. Those power conductors in PVC are giant broadcasting antenna's emitting frequencies at 60 hertz and in multiples of 60 hertz. The reason the UPS manufacture indicates a requirement in their installation manuals for the input and output power wiring to be run in metal conduit is to create that faraday cage around that antenna to reduce the emissions for those cables. No doubt that the further you get from the UPS the less it will effect the load.