# Solenoid Magnetic Field Testing

1. Mar 8, 2015

### inversquare

Any recommendations for getting an accurate reading of a magnetic field in a solenoid coil?

They're ferrite cores wrapped with magnetic copper wire. Would putting a Hall sensor at the end of the ferrite be a reasonable way to do this? Or will the field have already diverged? (The coil stops before the end of the ferrite).

One technique we tried was to measure the inductance, use that to calculate permeability of our core

$u=\frac{Ll}{N^{2}A}$

... and use that to calculate our B field.

$B = u\frac{N}{l}I = \frac{LI}{NA}$

Any other ideas??? Thanks!

2. Mar 10, 2015

### tech99

There will always be flux leakage, and the flux diverges as you describe. Measurements with a Hall sensor will relate to the actual solenoid, which is imperfect. Ferrite rods have an effective permeability which is less than that of the material and is dependent on the type of winding. Measuring inductance will give you the effective permeability. It is possible that the the permeability may vary with frequency and you also need to avoid saturation of the core material.