The AT205 loop spec'd in MIL-STD-461 (basic and rev. A) is 13.3 cm in diameter. It is rather inefficient at the low end (20 Hz). The Electrometrics MFM-11, which began life in the '60s as a magnetic anomaly detector (MAD) has a sensor wand that easily fits in the palm of your hand. it has a narrowband frequency independent sensitivity of 13 dBpT, and a broadband sensitivity (20 Hz - 50 kHz) of 60 dBpT. The obsolete RE04 limit was written to protect this meter. The Walker VLF-80D covers the same range of 20 Hz - 50 kHz with a sensor wand the size and shape of your pinky.
Ken Javor ---------- >From: "Robert Macy" <[email protected]> >To: "Ken Javor" <[email protected]>, "Jim Bacher" <[email protected]>, "Mirko Matejic" <[email protected]>, <[email protected]> >Cc: "Mothish" <[email protected]> >Subject: Re: Re[2]: assist me >Date: Wed, Jan 3, 2001, 1:30 PM > > The accurate volume is about 1/3 by 1/3 of the outside dimensions. At least > that's my "measured" experience. > > Just means one has to make a rather large Helmholtz for a large sensing > coil. And my recollection of most sensing coils in that range are that > they're over 1/2 meter in diameter. I've seen almost 1 meter in diameter. > > There is another way. That is to use a "calibrating" coil. Whose field is > very well known (in free space) along its axis. Then, at a fixed distance > the sensing coil should give a standard reading. [ Be at least 3 diameters > of the largest coil dimension away from the driving coil, the further, the > more accurate. Also, be a long ways away from magnetic materials like rebar > in concrete under you ]] > > There is one more way to make a field for calibrating a loop that > has a much larger accurate internal volume than Helmholtz. It is > approximated with 5 loops spaced appropriately. It is my understanding that > the "useable" volume inside that coil is around 70% Don't know where I put > the information on that coil, but if people are interested, will try to > find. > > - Robert - > > Robert A. Macy, PE [email protected] > 408 286 3985 fx 408 297 9121 > AJM International Electronics Consultants > 619 North First St, San Jose, CA 95112 > > > > -----Original Message----- > From: Ken Javor <[email protected]> > To: Jim Bacher <[email protected]>; Mirko Matejic > <[email protected]>; [email protected] <[email protected]> > Cc: Mothish <[email protected]> > Date: Wednesday, January 03, 2001 7:11 AM > Subject: Re: Re[2]: assist me > > >> >>The easiest to way to calibrate a magnetic field sensor in the audio >>frequency range is with a Helmholtz coil or a solenoidal coil. A Helmholtz >>coil is two coils of radius r with the planes of the loops also separated > by >>distance r. The magnetic field between the coils and at the center of >>either type coil is very uniform and solely a function of coil current and >>geometry (frequency independent). If you monitor coil current with an >>ammeter of sufficient bandwidth (any handheld DVM like a Fluke will likely >>do) that is the only measurement you need to determine the field. >> >>You can find all the equations at: >> >>http://www.geocities.com/CapeCanaveral/Hall/6153/ >> >>Have fun! >> >>Ken Javor >> >>---------- >>>From: [email protected] (Jim Bacher) >>>To: Mirko Matejic <[email protected]>, [email protected] >>>Cc: Mothish <[email protected]> >>>Subject: Re[2]: assist me >>>Date: Wed, Jan 3, 2001, 9:45 AM >>> >> >>> >>> Forwarding for Mothish, please keep him on your cc list as you respond. >>> >>> ____________________Reply Separator____________________ >>> >>> --- Mothish <[email protected]> wrote: >>>> >>>> > >>>> > ---------- >>>> > From: Mothish[SMTP:[email protected]] >>>> > Sent: Monday, January 01, 2001 10:24:56 AM >>>> > To: [email protected] >>>> > Subject: assist me >>>> > Auto forwarded by a Rule >>>> > >>>> helo sir, >>>> i got ur email id from iric.com. >>>> iam doing my project work for my engineering >>>> studies.(chennai,tamil >>>> nadu, INDIA) >>>> i have selected magnetic field sensor,for radiated >>>> emmision testing. >>>> i seek ur help for me to know the necessity of loop >>>> calibration(we are >>>> using loop ant. for 20Hz-50KHz range. >>>> plz provide me with the information iam in need of. >>>> or give me some contacts to whom i can clarify my >>>> doubts in future. >>>> >>>> seeking ur help barely. >>>> expecting ur reply. >>>> bye >>>> >>>> SINCERLY, >>>> MOTHISH BABU >>>> > > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
