Hello, I am an engineering student doing my first real engineering project with a group of other engineering students. To give a background of my issue, I am charged with the task of designing a system which is able to detect when a rotating shaft spins too fast and send an appropriate signal to a device that will disengage this shaft from its driving source. I've decided to use the rotating shaft to generate a small emf using a wire loop in a constant magnetic field, or at least am using this model, as a voltage source to a circuit which will then interpret the signal and detect when the signal gets too large. I've already simulated the circuit, but what's getting me is how to actually build the voltage source when it comes to prototype building time: The area I have to work with isn't all that small - maybe a cubic foot or so around this rotating shaft - so I have some leeway on how big I can make the wire loop or how large the magnets can be, but I can't seem to get good info on how to determine what magnetic field my wire loop will be seeing if I place opposite poles on either side of my wire loop. My electromagnetic fields book says that the field can be treated as constant, but I'm not so sure. With that being said, the only listings on websites regarding magnetic field are measurements taken at the surface of the magnet. If I place a wire loop between two similar magnets spaced say half a foot apart, I infer from my book that on a direct path between the two surfaces of the magnets the field will be the same as on the surface of either, but this seems very wrong to me. I think the book may be assuming the surface area of the magnets is much greater than the length between them, and I will not have that sort of convenience. Am I just going to have to do calculus on each length of wire based on the surface shape of my magnets, or can I do something easier with the information given on websites that I'm looking at to purchase magnets from?