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Post Time: 23/07/2008 22:33:04 |
fshui9
Total Forum Posts: 10 |
Hi Alasdair
I recently prepared what I thought would be agood demonstrating tool for the shielding paint (Yshield). I have alarge piece of hardboard (about 1m2) which I painted with two coats of Yshield and then attached an earth lead (with the sticky conductive tape that Yshield sell) and finished by painting over the top of the tape for good measure. I attached the other end of the earthing cable to the earth pin of a blank plug.
The surprise to me (although I suspect, not to you) is that when I then plugged it into a noraml socket, the electrical field (whatever the position of the baord)rises even higher than when its unplugged!
Can you please advise why it doesn't work and if there's a better method to create a portable demonstrator?
Thanks
Robert Gray |
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Post Time: 28/07/2008 21:25:56 |
alasdairP
Total Forum Posts: 173 |
Robert
Probably because of what I wrote in the reply to your bed question.
Electric fields are attracted to any earthed surface and they often come up through your legs and body and return to the earthed surface (in your case your Y-Shield board).
Gigahertz Solutions get around this by supplying an "earth reference lead" for their meters. The trouble is that is not what a person standing there experiences. They bridge between the floor they are standing on (or the bed they are lying on, etc) and the nearest surface at a lower potential. If you stand on an earthed pad of metal (or metal foil) and do the test, then you will find the electric fields decrease near to your demonstrator board.
Generally, people do not realise that in many buildings, especially upstairs, the floor is a major source of electric fields. That does not mean that we should not try to reduce the fields by making all surfaces vibrate! National Grid live wire workers can hang in a metal cage attached to a 400,000 volt AC transmission line and "be ok" (at least in the short-term!). That doesn't mean it is a good or sensible thing to do. Birds manage in a similar way when they perch on powerlines.
The evidence is that we should minimise electric field exposure. That means under our feet and well and above our heads and to the side of us. That is why the EMFields Pro is calibrated to measure the electric field that the person holding it is being subject to.
Many bau-biologists tend to use a sensitive voltmeter connected between the person and ground. That reads in actual millivolts on the body. personally, I prefere electric field readings as measured by the Pro or a similar meter. The Gigihertz meter is OK without using the Earthing lead.
Best are shielded wires inside an earthed metal conduit (tube). Second, individual wires inside an earthed metal conduit. Thirdly screened wires (with internal screen). Worst are unscreened wires as usually used. In a major London TV studio complex I measured E-fields less than 5 volts per metre almost everywhere because all wires were within metal conduit or trunking. It can be done.
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