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: I need to build a current sensor and am using a coil wrapped ferrite ring.
: The question I have is how to focus the flux concentration best on the
: sensor. I have several questions I need more knowledge on.
: 1) If I have a larger ferrite band, that means i will have a larger
: concentration of flux within the ferrite band?
: In order to place the sensor within the field, I need to embed it in the
: ferrite. so given (A) a ferrite band of 2in diameter with a thickness of
: 1/4in and a height of 1/2in and (B) a small transistor sized hall effect
: sensor, which of the following will yield the highest field density
: crossing the sensor?
: a) drilling a tiny hole in the middle of the ferrite band
: b) cutting a slit cleanly through the ferrite band
: c) cutting a slit as in (b) but shaping the ends in an angular fashion to
: focus the ferrite ends at the sensor
: Thank you in advance!
: Hello David,
: The larger the cross sectional area of the ferrite, the greater the amount
: of flux that can be handled within the core without saturation and
: (potentially) the greater the degree of flux concentration. The cross
: sectional area of the core should be at least as large as the sensor and
: up to about 2X the area of the sensor if tapering the core. Example A
: (above) should not be used since most of the flux will bypass the sensor
: and you'll also get highly nonlinear performance.
: Because ferrite is quite brittle and hard to machine, most ferrite-based
: hall effect sensors simply use a slotted ferrite core (your example B
: above). If you really need to further concentrate flux, then the ends of
: the ferrite should be tapered to channel the flux down to the area
: occupied by the sensor - your example C above. You can use a simple
: conical taper or a more complex taper. An example of a more complex
: geometry can be seen here (using a steel alloy, not a ferrite):
: The degree of further flux concentration by shaping the slot faces is
: limited by increased flux leakage in the tapered region. For linear
: characteristics, the reduced core area (adjacent to the sensor) should be
: no less than half that of the main core area. Following is some additional
: information that may help you with your design:
: Allegro also has a number of other publications dealing with Hall Effect
: applications that may be useful for you:
: Good luck,
I just found an article that shows the slotted and tapered core technique being used on a ferrite core on a Hall Effect current sensor - see:
And some more design information you may find useful from Allegro Microsystems: