please suggest DC Magnetic Flux meter - Page 1
Forum section: electronics / testgear

author: wraper
author_rank: Unknown
timestamp: July 20, 2017, 02:29:27 pm
content: In short, I barely know anything about magnetic flux meters. Are there any people here who actually have used them? What I need is to check some small permanent magnets and magnetic flux at certain points while designing a device and later for occasional screening of the incoming batches of magnets. This need came out as a device which I'm designing has multiple hall sensors which are close to each other with flying magnet above them. I need to ensure reliable operaton of intended sensors while preventing nearby sensor unintentional triggering. In certain positions, distance to the magnet and angle (up to around 25ooff perpendicular axis) changes too, which makes it even more important. So I need something to check the actual magnetic field. I see there are some cheap meters that are specified only for AC magnetic field, so, I guess, they won't work for me. Those which have DC is specifications are quiet expensive. As I won't have much use for it, I would like to keep it cheap, below $150 if possible.P.S. Please don't suggest to change mechanics. I know that magnet pole should be perpendicular to the hall sensor. However mechanically there is not much that could be done without unreasonably complicating the thing. And I would like to keep SMT hall sensors on the flat PCB to keep it cheap and simple, and this concept proved itself to work so far. I just want to ensure that it will be reliable with all possible hall sensor and magnet tolerances.

author: cvanc
author_rank: Frequent Contributor
timestamp: July 20, 2017, 02:49:54 pm
content: Do you need to determine actual field strength, or simply tell North from South? For the latter, inexpensive devices exist (such ashttps://www.mcmaster.com/#57255k71/=tzpsop).

author: wraper
author_rank: Unknown
timestamp: July 20, 2017, 02:58:34 pm
content: Quote from: cvanc on July 20, 2017, 02:49:54 pmI need actual field strength. Telling between North/South is easy, hall sensors I use are unipolar. I could simply attach a LED to the hall sensor I already have and it would do the job. Cheapest I found what would probably do the joblinkBut it certainly looks dodgy.Seems there are clones made by different companies.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: July 20, 2017, 04:23:51 pm
content: Well, you can get an app for the iphone to measure magnetic fields. Start with that.From your description I think what you really need to do is model the relevant parameters of your problem. How else are you going to reliably and cheaply ensure the range of magnets and sensors that will actually work? That requirement is far from being satisfied with a measuring device. You need an accurate simulation in which you can plug in different magnets, distances and sensors.Cheap electromagnetic simulators are available, fortunately. Google FEMM 4. If you have a reliable 3D model you should be able to do this.Then what you actually need from the magnetometer is to calibrate your model with reality.Good luck!

author: wraper
author_rank: Unknown
timestamp: July 20, 2017, 06:34:12 pm
content: Quote from: RandallMcRee on July 20, 2017, 04:23:51 pmSimple, with a datasheet with hall sensor specs and a meter. If I measure magnetic field with small probe at each point where sensor is located and compare with figures in the datasheet, I can check if there is large enough margin to reliably activate it or not activate it. Optimal sensor positions can be verified with magnetic viewing film/card. In any case, I'm interested in 6 digital hall sensors and 8 positions of the magnet above them. Actually it's only a half of those, as this thing is basically symmetrical with 2 groups of 3 hall sensors and 4 positions of magnet. At each time only 1 or 2 out of 3 sensors must be activated to resolve 4 total magnet positions. Trying to learn electromagnetic simulator and making a close enough model of the magnets used is too much effort for relatively simple one off job IMO. When I can (and in the end must) measure it in real hardware anyway. I don't have an iphone (guess there are for android) but it won't give me any measurement which is usable for this purpose. Nor I can stick the phone in the device under the magnet.QuoteThat is what I certainly won't have. Most magnets barely have any data on them at all.QuoteThanks

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: July 20, 2017, 10:57:21 pm
content: Hmmm, given your reply I'm still thinking that you do not need a meter....because you are simply going to prototype it and fool around until it works.Nothing wrong with that if everything is super simple.If the magnetic fields interact things are not simple. Hopefully, they don't. The problem with magnetic fields is that you cannot "see" them in the same way that you can get an insight into a circuit using an oscilloscope. A magnetometer gives you a one-dimensional view like a DMM. Imagine trying to design something complicated with only a DMM to check it (and no AC!) That is why I suggested the modeling. I can understand that you might be reluctant but it is the difference between being blind and lucky or sighted and skillful...Magnetic viewing cards are toys IMHO.Insofar as the magnets go they are actually pretty predictable. E.g. N45 rare earth has properties directly proportional to volume and its magnetic alignment.Have you looked at the information at KJ Magnetics? e.g.http://www.kjmagnetics.com/blog.asp?p=gaussmeterLots of useful information there.More good luck...

author: wraper
author_rank: Unknown
timestamp: July 21, 2017, 12:10:08 am
content: Quote from: RandallMcRee on July 20, 2017, 10:57:21 pmI said that it already works. But I need to be sure that it will 100% reliably work on every board with every magnet. I don't wan't to guess how much reliability margin is there, I want to see actual numbers.QuoteExactly what I need, as hall sensor also sensitive only in one dimension.QuoteThat's good and dandy, but how it is supposed to work without accurate model of the magnet? That is not simplified by the fact, that the best working type for this purpose turned out to be pot type magnet. First of all it does not affect nearby hall sensors that much as they are unipolar. And, secondly, even when cup magnet is under angle, I can relatively easy put a sensor under magnetic field which is in perpendicular direction to it. But I want to see actual numbers.QuoteQuiet useful link. I was not aware there are inexpensive factory trimmed hall sensors like Allegro A1301.Anyway, I already ordered this one.http://www.thanksbuyer.com/sj300-digital-gauss-meter-static-magnetic-field-tesla-tester-0-200mt-2000mt-with-adapter-53843#tab-description

author: wraper
author_rank: Unknown
timestamp: July 21, 2017, 09:02:17 am
content: Quote from: RandallMcRee on July 20, 2017, 10:57:21 pmToys or not, they can visualize magnetic field in the plane I'm interested. Much better than just guessing/estimating.