Ralph:
The field within a solenoid coil is very uniform and predictable (it’s a expansion of the Biot-Savart equation). I built my own 3-axis sensor using a magnetoresistive chip sensor similar to this Honeywell design: http://www51.honeywell.com/aero/common/documents/myaerospacecatalog-documents/Defense_Brochures-documents/HMC5883L_3-Axis_Digital_Compass_IC.pdf You can find similar systems in the “maker” marketplace for under $20; IIRC, Adafruit provides these mounted to boards that mate with Arduinos and other microcomputers. https://learn.adafruit.com/adafruit-hmc5883l-breakout-triple-axis-magnetometer-compass-sensor/overview I’m a bit hazy on what I did a decade ago; I seem to have lost my entire notes for that part of the project. Anyway, the Honeywell sensor can measure up to 8 Oersteds, so you can prove the “coil factor” to yourself with 1% accuracy. (Remember that H-field scales directly with current.) You can also move this sensor around inside the coil volume to check the field uniformity. I just downloaded a free ap from the Apple Store, called “TeslaBot” and it’s now running on my iPhone. It turns the iPhone’s 3-axis magnetoresistive sensor into a magnetometer, displaying each axis simultaneosuly in µT plus solving and displaying sum of all three axes. (The point being, why not? I’m sure somebody will ask me about magnetic field sensing at the next party I attend!) My desktop ambient is 38µT, and if I move my old wireless phone near it, it shoots up to over 500µT. Of course, I have no idea of the absolute accuracy of that reading, but it would be interesting for someone with a coil to verify how accurate the iPhone sensor really is. At the very least, TeslaBot makes a good demonstrator for convincing upper management that EMI is real and they shouldn’t fire you. Ed Price WB6WSN Chula Vista, CA USA -----Original Message----- From: Ralph McDiarmid [mailto:[email protected]] Sent: Tuesday, June 21, 2016 9:28 AM To: [email protected] Subject: Re: [PSES] Magnetic Field at 400 A/m But how to calibrate such a thing, to know how much magnetizing force is really being applied to the DUT ? Ralph McDiarmid Product Compliance Engineering Solar Business Schneider Electric From: Manny Barron [ <mailto:[email protected]> mailto:[email protected]] Sent: Monday, June 20, 2016 7:54 PM To: <mailto:[email protected]> [email protected] Subject: Re: [PSES] Magnetic Field at 400 A/m Back in 1996 when I managed a 3rd party EMC test lab and when the IEC 1000-4-8 test became mandatory, I built my first magnetic field test setup using a "hula hoop" from Toys-R-Us. I wound the appropriate amount of insulated wire loops inside it, and added an appropriate power supply/transformer and some low resistance high wattage resistors. It worked great for small products and the 3 or 10 A/m test levels. Today there are more aesthetically appealing test setups available from various suppliers. Manny Barron Sr. EMC Engineer From: Ed Price [ <mailto:[email protected]> mailto:[email protected]] Sent: Monday, June 20, 2016 7:01 PM To: <mailto:[email protected]> mailto:[email protected] Subject: Re: [PSES] Magnetic Field at 400 A/m Grace: I used to regularly test equipment to MIL-STD-1399, which had a DC magnetic field strength exposure requirement of 20 Oersteds, applied for 60 seconds. Since 1 Oersted is about 79.5 Amps/meter, that was equivalent to a 1600 Amp/meter field exposure. I did that with a Sorensen 50 ADC power supply, a 0.001 Ohm sense resistor, a DMM and a custom solenoid coil. The coil was wound with 163 turns of #12 solid wire, with a coil length of 711mm and a diameter of 590mm. This was adequate to expose a several unit high 19” rack-mount EUT. FYI, this antenna had an “antenna factor” of 2.217 Oersteds/Amp or 175.8 Amps/meter per DC applied Amp, with about 1.6 Ohms resistance. I built the solenoid coil using a “hazardous chemical disposal carboy” (think big strong plastic garbage can) with a cheap Harbor Freight appliance dolly bolted to one end. (Not only does this make the antenna easy to move, but it also greatly aids you winding that 1000 feet of #12 wire onto the carboy during several hours of Zen meditation.) Of course, if your EUT is smaller, then you don’t need such a large solenoid; I have a spreadsheet describing the design and performance characteristics of six solenoid coils I have built over the years. If anyone is interested, I have a description of the coil and the spreadsheet which I can send off-list. Ed Price WB6WSN Chula Vista, CA USA 1961 Amphicar 770 2001 Fleetwood Storm 31W 2008 Ford Explorer From: Grace Lin [ <mailto:[email protected]> mailto:[email protected]] Sent: Monday, June 20, 2016 4:18 PM To: <mailto:[email protected]> mailto:[email protected] Subject: [PSES] Magnetic Field at 400 A/m Dear Members, Does anyone know which standard requires to have magnetic field evaluated at 400 A/m? Is there any commercial available instrument (loop) for the purpose? Thank you very much for your time and I look forward to hearing from you. Best regards, Grace Lin - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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