Discuss the interference of magnetic field on PCB board

[Benjam]

I am a high school student from Texas. I am very interested in electromagnetics. I found that the best magnetic encoder is from Renishaw, and when I was learning about his product, I found this product: https://www.rls.si/eng/aksim-2-off-axis-rotary-absolute-encoder I have a very big doubt. It interacts with the magnet below it through the PCB board. When the magnet rotates, will it generate a magnetic field? The book says, isn't the PCB board to avoid magnetic interference? The changing magnetic field will interfere with the circuit board. The higher the frequency of change, the stronger the interference (because the changing magnetic field will induce current inside the conductor); more than a certain degree, the circuit board may be burned (the principle of the EMP bomb). So does this conflict? ? I am very confused. 

[Manul]

Yes, it is true that changing magnetic field induces electric current. But something being true does not necessarily make it a huge factor. For example, does light from your computer screen heats up your eye retina because of photon absorbtion? Answer is: yes it does. But your eyes does not start boiling and burning, because in this case the heating is absolutely negligible, not even worth talking.

It is true, that a precision circuit might be disturbed by changes in magnetic flux. Special PCB layout techniques or magnetic shielding (like mu metal) might be needed. Likely not in this case. Interference is very small.

[Terry Bites]

emf=NABω

A track of say 1mm is one turn (n=1). A is one mm2, B say 10mT, ω=1000rad/s (10000rpm)

1*0.0000001*.01*1000= 1uV into an open curcuit. Less than an ant fart.