Gordon, the May 2002 issue of Conformity magazine had an excellent article on Helmholtz coils. I checked their website but didn't see how to access old issues. If you can't get a copy online I will be glad to FAX you a copy of the article. To put things in perspective we can think about the field around an infinite length wire. Say the wire has a current of 1 ampere and the point of measurement is 1 meter away. The field H is (1A)/(2Pi meters)= 0.16 A/m. Now B=uH and u = 1.256uH/m. So, B= (1.256uH)(0.16A/m) = 200nT. To obtain 5mT one would need 25,000 amps with this arrangement! Let's do a Helmholtz: H = 1.43(nI/d) where d is the diameter of the circular coil. The coils are spaced one diameter. For coils with a diameter of 1 meter, one turn, and one ampere the field H is 1.43 A/m. You need about 4000 A/m for 5mT. Lots of amps. How about 200 turns at 20 amps? That will do it. So, two 1-meter coils with 200 turns of #12 AWG wire with 20 amps flowing. The resistance at 100 deg C is about 10 ohms, so 200 VDC is needed. 2000 watts. Smokin!!
Dave Cuthbert Micron Technology From: Gordon,Ian [mailto:[email protected]] Sent: Thursday, January 23, 2003 8:15 AM To: 'IEEE EMC-PSTC GROUP' Subject: CALIBRATION AND CONSTRUCTION OF HELMHOLTZ COILS All I would like to construct a Helmholtz coil to perform magnetic field immunity testing at DC frequencies and thus simulate the effect of a permanent magnet. There are some details on construction in EN61000-4-8 which details power frequency magnetic field immunity testing within the scope of the EMC directive. However the fields referred to are measured in A/m, whereas I need a field of, for example, 5mTesla. Can anybody advise me as to how to construct such a coil with a test volume of 0.5 x 0.5 x 0.5m and a field of 5mTesla? Thanks Ian Gordon _____________________________________________________________________ This e-mail has been scanned for viruses by the WorldCom Internet Managed Scanning Service - powered by MessageLabs. For further information visit http://www.worldcom.com This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
