I am designing a PCB and am using a 3mH air core inductor which is physically large (about 6cm diameter, 3cm depth) so i was intending on mounting it underneath the board with other components above it. One of those components will be a hall effect sensor... i was wondering if the magnetic field of the inductor would affect the field in the hall effect device and result in erroneous current readings? The maximum current will be ~3A and the hall effect device is planned to be located in the centre of the inductor coil (right in the path of the magnetic flux argh!)

*edit: not sure if its relevant but the hall effect sensor is the Allegro ACS712.

 

At first guess, I'd say it is guaranteed to interfere.
Then again, Hall sensors have a "most sensitive axis" which might be used to your advantage.

 

The Hall-effect sensor will do a very good job of reporting the strength of the magnetic field in the center of the inductor. If you planned on doing something other than that, well ... go fish.

Only other thing that comes to mind is perhaps using mu-metal to block the field, but that will get expensive and labor intensive in a big hurry.

 

Thanks for the replies, i tested how bad the effects were, just sat it on top of the sensor and watched the output... it is affected quite badly when in the centre, but is unnoticeable when its placed beside the inductor. looks like my PCB is going to have to be twice as big .

 

It may not really be a good idea, but in theory you could put the sensor under the edge of the inductor and it wouldn't be affected by the field produced by the coil, which would be horizontal at that point. You'd need to shove things around experimentally to find the right location. But if your product generates large amounts of something that has to be measured accurately, I would say you're starting with a handicap.

 

Did you read THIS?
I also used THESE in extremely noisy environments without affecting them. I never used them INSIDE a coil, though.