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Why do different gauss meters measure magnetic field strength differently

  1. Oct 6, 2012 #1
    I have used two different Gauss meters to measure the same NdFeB rare earth N45 (45 MGOe) disc magnet (D28X6mm), with a Residual Induction (Br) of 1320-1380 mT.

    The first is a Dr. Steingroever GmbH FH51 Gauss meter.
    It would take readings of up to approximately 1.2 Tesla (12,000 Gauss)

    The other was a DC Magnetometer from AlphaLab (I think this is the right model, as the one I have must be an old model as it's not shown).
    This one will only take readings of up approximately 0.35 Tesla (3,500 Gauss)

    So my questions is why the different readings? Are they measuring the same property of the magnet and is there a standard method for recording such measurements?

    Thank you.
     
  2. jcsd
  3. Oct 6, 2012 #2
    Hi, measurement devices generally have limited precision near the ends of their scales. Make sure this is not the case. Also check whether they are correctly calibrated.
     
  4. Oct 6, 2012 #3

    mfb

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    Are you sure that both measurements were done at the same position(s)?
     
  5. Oct 6, 2012 #4
    Yes, measurements were correctly made and you wouldn't get such a variation from different testing methods or calibration issues, 10-20% maybe but not 300%.

    There are two different ways of measuring magnetic field strength with gauss meters and I am trying to understand why the difference.

    Many websites that sell magnets will sometimes describe magnets using Br and the lower figure as the "Surface Gauss". I am wondering what different properties the gauss meters are measuring to record the different values?

    Thank you.
     
  6. Apr 28, 2013 #5
    The frequency range is different--I wonder whether this might have an impact? One measures objects with a 45-800 hertz and one measures from 20-10kHz.
     
  7. Apr 28, 2013 #6
    Best Gauss or Tesla meter for home and office inspection

    The original question seems a bit old and without answer, but I'm going to hijack this thread to see if anyone can answer my question, as well.

    I'm having trouble determining what would be a trustworthy measurement of gauss/tesla in a residence and office environment . . . my current 2 meters always show different measurements (right now, .2 mG, Trifield, and 40 mG, Cornett, in the same place--a meter in front of the computer screen). The difference is huge, anywhere!

    Of course I'd like to get a lower cost, trustworthy instrument--eventually I plan to get an oscilloscope, as well.

    First, is there an independent ranking of gauss meters?

    Trifield 100XE--Problem!
    So far, I realized that the Trifield model 100XE is frequency weighted and so only measures what is at 60 Hz. With technology hertz just keep increasing, so office equipment might be at 2.5 Gigahertz and so on up. So, the Trifield meter is not including the magnetic field from these instruments.

    Cornet ED75--Question of Gauss Reliability?
    The Cornet Electrosmog ED75 meter (reviewed here: http://www.electricsense.com/3649/ ) is stated to have a larger range, but I haven't the understanding from the specs whether the wider range of hertz applies only to radiofrequency signals or applies also to gauss measurements. Service hasn't responded to my email or picked up the phone, and the specs also ask that it not be used for reference in a court of law, which suggests that it is less than accurate. Still, it seems to work well for RF measurement.

    Alphalabs & Trifield & Specs of other equipment?
    So, I've started looking at other gauss instruments online and am wondering about advice. I thought perhaps I could return my Trifield meter for a credit, and then purchase a meter from the same company, which has a wide selection of meters ( http://www.trifield.com/ ). I looked at the website an am a bit overwhelmed by the number of meters as to what might work. Some of the meters do not go up as far as 40 gauss, and I am curious whether this is necessary--it would be nice to determine the useability of the Cornett as well. If the Cornet's accuracy could be pinpointed, this would be a bonus. I haven't tried calling Alphalab yet, but can put that on my list, since this seems the most sensibly cost-efficient thing to do.

    One thing bothering me is that I can't find a ranking online of the quality of some of this equipment, or how these items compare. Shouldn't there be an independent organization ranking these items? It seems to me, for example, that it is kind of sad that so many people have purchased a Trifield 100XE meter--it's suggested virtually all over the internet as the instrument of choice--but that in reality it is frequency weighted for a very small selection pool of actual magnetism. It would seem to me that Alpha Labs, if it were more ethical, might state upfront that the 100XE is useless for measuring most current technologies, and suggest alternatives . . . This makes me think that AlphaLabs either hasn't thought much about it, or just doesn't care--so why purchase from them? They may not be managing things carefully, then.
    Other alternatives: Bell 4080 and msi 95
    I found an article on the Bell 4080 and msi 95 ( http://www.mikeholt.com/mojonewsarchive/PQ-HTML/HTML/ShouldElectricianHaveGaussmeter~20020326.htm ) and began looking at the specs on this webpage: http://www.magneticsciences.com/HelpChoosingGaussmeter.html . I noted that the Bell 4090 was stated to be the professional model, and so it can be used for home and office inspection, and noted the price tag: $400. I'm a bit lost with some of the specs, as a newbie, but think this might be something that I could learn to use. Two things, though:
    1) I'm guessing that some of these triaxial meters just provide an average of the gauss level, so perhaps this isn't a real assessment?
    2) I wonder whether the Bell 4090 is adequate by itself, requires the msi 95, or whether the msi 95 would be enough on its own.
    I would greatly appreciate some response to this question! I'm a newbie just getting into this due to heavy exposure at work, and would like to insure my residence and workplaces can be arranged or modified accordingly. I'm sure this would help a lot of other people as well, since I haven't seen this critical evaluation posted clearly elsewhere. I'm going to also probably post this question on a physics forum as well, in the hopes of getting a greater or quicker response.
     
  8. Apr 29, 2013 #7

    CWatters

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    Right there in the specification it mentions the frequency range and weighting..

    http://www.trifield.com/content/trifield-meter/

     
  9. Apr 29, 2013 #8

    CWatters

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    For what it's worth it says here the ED75 will measure magnetic fields upto 10kHz which isn't as high as the Trifield.

    http://www.electricsense.com/3649/

     
  10. Apr 29, 2013 #9
    Reason for Gauss Differences & Test

    Thanks for correcting me. I misplaced the specs and hadn't seen them online.

    I ran a test to compare the Cornet ED75 and the Trifield 100XE (the latter purchased from AlphaLabs). Different readings can happen, sure, if the meter sensors are in different places when compared. And the Cornet has one axis, versus the Trifield's 3. After the test, I came up with another reason for a problem.

    I concluded that the Cornet ED75 had a preference for RF readings, so that the RF sensor and software seemed to override the mG function.

    In the test, I set the meters 12 and 6 inches away from a hair dryer, and turned the hair dryer on and off for 2 sets of measurements. With the Cornet being single axis, I turned it different ways: with hairdryer pointing to gauss side, RF side, top (both sensors accessible), and with the Cornet standing up, "back" to hair dryer. Any which way, the RF sensor seemed to override the gauss function, as judged by the fluctuations of the "gauss" measurements.

    The Trifield provided stable, but very different measurements. I do not know if these are accurate. Online at Amazon, a small percentage of people complained about accuracy, but also noted that different manufacturers made the 100XE for Amazon. I purchased mine from AlphaLabs, not Amazon.

    However, I'm positive that the Cornet measurements were invalid. With the hair dryer off, the Cornet ranged (fluctuating) from 20 to 122 mG, just for example. I know when I use the Cornet for RF measurement that it is useful for pinpointing sources, partly because of the single axis. But the mG function was all over the place. The best I could figure out was that the "starting point" appeared to be around 33 or 39 mG.

    In sum, I wish I had purchased, right away, a single purpose gauss measuring tool with high accuracy.
     
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