# Measuring magnetic field in a solenoid

I have to measure the magnetic field created by a solenoid. My attempt would be using a commercial Axial Hall Probe, or a Hall Sensor with some electronics. It has got an active (sensing) area with a diameter <1 mm. My coil is 12 mm long and has an inner diameter of 9 mm-s.

My problem is that the radial magnetic field distribution inside the coil is too high. My measurement accuracy should be 1/2000 FS. The magnetic field along the active area of the probe changes by 0.2 % however. It is stronger in the middle and weaker at the sides.

The product sheet tells me that the probes measure an average B field but with this accuracy I don't know if I should choose this sensor.

Thanks

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I strongly doubt that 1/2000 accuracy is reasonable for magnetic fields. Are the 9mm accurate to 5µm?

You are right, I don't have the 5 μm accuracy, but I don't need it. It seems I wasn't accurate, because, what I have to measure, is the strength of the magnetic field in the "center" (the area is as big as the Hall element) of the solenoid with the given resolution. It's just that I think the field gradient along the Hall element is too high.

But I found this and I think there won't be any problem :
http://www.esrf.eu/events/conferences/IMMW12/present/Berkes.pdf

Thanks

Can you wiggle the probe around in a controlled way in order to measure the field as a function of displacement? You can use this measured gradient to calibrate out the gradient error in the center.

Well, I used a simulation program to simulate the field gradient, then used this data to calculate the errors caused by it with the equations from the above mentioned paper. That should be OK now.
On the other hand, wiggling the probe would be a mechanical challenge, I suppose...

Which simulator do you use?

Integral
Staff Emeritus
Gold Member
Why do you suspect a high field gradient inside the solenoid? What do you suspect the field inside is?

What control do you have on the field strength?

I'm simulating with MagNet Trial Edition 7.1.3. The field strength at the end of the armature is about 0,5 mT. The field is PWM controlled with 0.85 A rms. I suppose, the gradient is high because the inner diameter of the solenoid is almost as high a the length.

But I think there won't be any problem because of that, because the sensor should give an average of the field strength.

Interesting,

Does MagNet have a built in calculator that you can use to model the probe averaging? (Ansoft Maxwell has this capability). If so, then you can compare your measurement with your simulation directly.

Also, are you running the PWM during your measurements? You may want to run DC through your device for measurement since MagNet is magnetostatic.

I has got a field line graph but no more options as far as I know. It's a 30 day evaluation version...

Yes, I must use PWM for the measurements. That's why I am using the rms.

Oh, and I have a a laical question: for determining the field distribution from this solenoid, I can use 2 D simulation, right? I mean I don't have to multiply the results by 2*PI or something?