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14:38 Feb-06-2010

Mulianto Sinaga

NDT Inspector, -
Joined Sep 2009
yoke pole spacing

Dear all,

I want to know what's the affect of pole spacing of yoke if I open the pole too close?

14:55 Feb-06-2010

Godfrey Hands

PRI Nadcap,
United Kingdom,
Joined Nov 1998
Re: yoke pole spacing In Reply to Mulianto Sinaga at 14:38 Feb-06-2010 (Opening).

Hi Mulianto,
If you open the poles up too far, then the magnetic field between the poles may not be enough to detect the cracks you need to find.
If you keep them too close together, there are two risks
1. You will get a smaller coverage, so need to test next test much closer
2. You may saturate with magnetism and cause too big a background to see cracks.

That's a very simple explanation. Hope it helps.


17:23 Feb-06-2010

Jim Draper

Consultant, ASNT Level III MT PT RT VT
Draper NDT,
Joined Jul 2009
Re: yoke pole spacing In Reply to Godfrey Hands at 14:55 Feb-06-2010 .


I use a Parker DA 200 probe. My manual recomends 5 to 6 inches between the legs. Here is a link to a PDF of the manual. I hope this helps.


20:28 Feb-06-2010


Other, Retired ex Laboratory Technical Manager
OMECO Research Centre,
Joined Sep 2008
Re: yoke pole spacing In Reply to Mulianto Sinaga at 14:38 Feb-06-2010 (Opening).

You can see the effect with a simple specimen: a plate 50x250x20 mm with a subsurface 1-1,5 mm hole on the side. Good look, ciao, ezio

08:59 Feb-07-2010


NDT Inspector, -
Joined Jan 2010
Re: yoke pole spacing In Reply to Mulianto Sinaga at 14:38 Feb-06-2010 (Opening).

Pole spacing too close means the magnetic field between the the poles will be greater and it leads to non relevant indications named as banding.

11:24 Feb-08-2010


Philippine Nuclear Research Institute (PNRI),
Joined Jul 2005
Re: yoke pole spacing In Reply to rama at 08:59 Feb-07-2010 .

Hi, Mulianto,

Making your Yoke pole spacing too close will create too much sensitivity due to the increase in the magnetic field strenght and that creates unnecessary indications. On the otherhand, making your pole spacing too far would provide lesser magnetic field strenght (lesser sensitivity).
So it is better for you to established your own correct pole spacing by doing some experimentation using same material of the same thickness with a known artificial defect and with that you can make your own appropriate MT procedure.

Renato Banaga


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