I was asked a question today which may not be exactly electrical in nature but here goes.
The parking meter guy has had problems with the electronics in the parking meters going bad. I believe they run on batteries (no power supply from an external source.) About a year ago an MRI office opened across the street from the meters and since then the problems have been occuring. (No problems before this to my understanding.) Is it possible that magnetic fields from the MRI machines are causing problems with the electronics of the meters?
The distance is a typical two-way street, a sidewalk and whatever the distance inside the building the machine is. I'd say roughly 50 to 75 feet.
I haven't done any real investigation, I was just posed the question today.
As an interesting side note, This link came up in discussion that started off requesting information on known effects of electric wheelchair EMI on multiple sclerosis patients. Someone touched breifly on how the wheelchairs themselves have to be tested for effects from EMI
I also found it interesting that the manual specifically stated that the wheelchair also was compliant with a 20 V/M field from (IIRC) 30 MHz to 1000 MHz. That's nice, since personal electronic emitters (cell phones, PCS, handheld CB sets) typically generate about 5 to 10 V/M at about 1 to 2 meters distance. That increases the chances that the wheelchair user can safely use a cell phone without spinning in circles (or worse).
I hope that you don't mind this slight tangent.
[This message has been edited by Bill Addiss (edited 06-06-2001).]
Re: Parking Meters#1894 06/06/0108:00 AM06/06/0108:00 AM
We had to have $3500 worth of shielding put around the service in a building we did for IEEE. The grounded service enclosure didn't stop the EMI, and it was causing monitors to act up. I'd really like to learn more about this, as I don't quite understand why all the high $ steel would make so much difference, and certainly don't want to go through the same drill again elsewhere.
Re: Parking Meters#1895 06/06/0108:21 AM06/06/0108:21 AM
You bring up an interesting point. I don't know much about it but a place where I once worked had a room built of copper screening all around that I thought was sheilding something. ?? One of the products they made or tested was microwave antennas or something like that.