>-----Original Message----- >From: Gordon,Ian [mailto:ian.gor...@edwards.boc.com] >Sent: Thursday, January 23, 2003 7:15 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 > >
OK, less drama and more numbers. In a Helmholtz, the "sweet spot" or volume, should be limited to 1/3 the distance between the coils. So that means that coil separation should be 150cm to yield a test volume of 50cm. And, the definition of a Helmholtz is two identical flat coils, in plane, and separated by the radius of the coil. So, the radius of the coil is also 150cm. Now, the Helmholtz equation, re-arranged to find necessary current when the field (Gauss), turns (N), radius (a, in cm) and separation (cm) are known. I= [((5)^^(1.5)) x a x 10 x Gauss] / [ 32 x Pi x N ] So, lets try with a 150 cm radius & separation coil, with 50 turns, looking for 50 Gauss (which is equivalent to your 5 milliTeslas). I = [((5)^^(1.5) x 150 x 10 x 50] / [ 32 x Pi x 50] (please don't let me mess this up) I = 838526 / 5026 = 167 Amps The only variables you can work with are number of turns and current. What size power supply have you got? Ed Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military & Avionics EMC Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
