Focus coil as magnetometer polarisation coil

[spacer76]

Hi all,

Last week I salvaged a focus coil's from a scrap klystron.
My intention is to use it as the polarisation coil for a proton magnetometer.

The dimensions from this coil are :

Inner diameter : 25.5cm
Outer diameter : 37cm
Height : 3.5cm
Layers stacked on each other : 36
Weight : +/- 14kg
DC Resistance with an ohm meter is about 0.2 ohm

The problem I have is that the 'wire' is not round but rectangular. (about 4mm (height) x 1mm)

a) I can't find formulas to calculate the inductance where the wire is rectangular, so if anyody can help calculating inductance that would be great.
b) would such thing work as a polarisation coil for a proton precession magnetometer ?

I've made some pics to clarify things up :

[Qiaozhi]

I presume you do not have an inductance meter?

[spacer76]

No, not at the moment and frankly i want to know the theoretical point of view from not round wires in coils also

[Qiaozhi]

No, not at the moment and frankly i want to know the theoretical point of view from not round wires in coils also

I would expect the effect of square versus round wires would be an increase in inductance. Using my own coil calculator, I get an estimated inductance in excess of 1H.
My assumption is that there are 2088 turns on the coil.

I do not have a formula for square cross-section wires.

[Fred]

that´s strange, my guess is 280 turns ...is that a typo?
There is surely an increase in capacitance anyway, so resonant frequency will be diferent from round wire.

[Qiaozhi]

that´s strange, my guess is 280 turns ...is that a typo?
There is surely an increase in capacitance anyway, so resonant frequency will be diferent from round wire.

height of coil winding = 35mm
number of vertical layers = 36
wire thickness = 35/36 = 0.97mm
width of coil winding = (outer diameter - inner diameter)/2 = 57.5mm
number of horizontal layers = 57.5/0.97 = 59.3 (let's say 59)
total number of windings = 36 x 59 = 2124

Last time I rounded the numbers earlier in the calculation.
If there were 280 total turns, then you would only have about 8 turns in the horizontal layer.

[Qiaozhi]

OK - I see the problem.

The 36 layers are vertical, not horizontal. In that case:

width of coil winding = (outer diameter - inner diameter)/2 = 57.5mm
wire thickness = 57.5/36 = 1.6mm
number of horizontal layers = 35/1.6 = 22
total number of windings = 36 x 22 = 792

approximate inductance = 272mH

That probably makes more sense.

[Fred]

That probably makes more sense.

not really:





36X8=288

where is the mistake ?

Edit: i see , you assumed round (or square) wire

[Qiaozhi]

not really:

[ATTACH]9185[/ATTACH]

[ATTACH]9186[/ATTACH]

36X8=288

where is the mistake ?

Edit: i see , you assumed round (or square) wire

Yes - I agree. It looks like 36 x 8 from the photos.

I think the mistake is assuming that the wire is square, when in fact it is rectangular. In other words, it's a flat cross-section.