Measuring magnetic fields Will motors and metal frame interfere?

[engi845]

Hello all, thanks for reading. I'm in the process of designing a machine that will move a hall effect sensor in 3 dimensions through a magnetic field and record readings. Before I started the design however, I wanted to see if there would be huge problems in how I envision this machine.

If I were to use medium sized dc or stepper motors ~30cm away from the test magnet and use aluminum or ss for the support structure, is this going to warp my magnetic field or cause too much noise? Would it be necessary to use as little metal as possible in this machine or move the motors as far away as possible? I basically want to design it so I'm dealing with as little noise as possible. I don't have many details on how machines like this operate so I'm mainly going off of how 3d printers function, I just don't want to make a huge mistake that will render the machine useless. Thanks for your time, I'd appreciate any input you guys have for me.

 

[berkeman]

Hello all, thanks for reading. I'm in the process of designing a machine that will move a hall effect sensor in 3 dimensions through a magnetic field and record readings. Before I started the design however, I wanted to see if there would be huge problems in how I envision this machine.

If I were to use medium sized dc or stepper motors ~30cm away from the test magnet and use aluminum or ss for the support structure, is this going to warp my magnetic field or cause too much noise? Would it be necessary to use as little metal as possible in this machine or move the motors as far away as possible? I basically want to design it so I'm dealing with as little noise as possible. I don't have many details on how machines like this operate so I'm mainly going off of how 3d printers function, I just don't want to make a huge mistake that will render the machine useless. Thanks for your time, I'd appreciate any input you guys have for me.

Welcome to the PF.

Good questions! Yes, you need to keep ferrous metals away from your test volume. I'd initially estimate that you should keep ferrous metals at least 2x away from the test volume (2x each linear dimension). Simulations could provide a better estimate.

 

[meBigGuy]

Doesn't it depend on the magnitude of the measurable fields and the accuracy desired? If what you are measuring is a very weak field, then a stepper motor 30cm away could be an issue. Or not. Same goes for ferrous materials. Some back of the envelope calculations (at least) are probably in order.

 

[jim hardy]

And some experiments.

Most of the flux stays in the motor
but if you are measuring Earth's field, nearby structures affect it more than you'd think.

Differential magnetometer (two sets of sensors separated by a few feet) can be quite sensitive. I built one that saw cars going down the street in front of my house, and knew whether refrigerator door was open or my kids had moved stereo speakers in next room.

 

[engi845]

Ok I agree, I will definitely be doing some experiments beforehand with comparable metals and motors. I do plan on testing fairly small magnets so I'm hoping I won't need to move the motors too far away to reduce noise. I also figured doing a control run before each test with no magnet would help with background fields.

Hm I never thought about using two sensors, that could be interesting. Does any type of magnetic shield material exist? Thanks for the input

 

[Jon B]

Mu Metal Co-Netic, supermalloy, supermumetal, nilomag, sanbold, Molybdenum permalloy, Sendust, M-1040, Hipernom, HyMu-80 and Amumetal.