Figure 3-40. Deleted
A compass is sometimes used for indicating the presence of external leakage fields. A compass can be placed
upon a nonmagnetic surface and a magnetized part (aligned due east and west) moved slowly toward the east
or west side of the compass case. The presence of an external leakage field from the part can cause the
compass needle to deviate from its normal north-south alignment. However, demagnetized parts will cause
the needle to deviate from its normal position if the compass case is not approached from an easterly or
westerly direction. The theory of operation is very similar to that for the field indicator since the compass
needle is a permanent bar magnet.
Steel Wire Indicator.
A piece of iron or steel wire can be fashioned into a fair detector when nothing else is available. By forming a
loop at one end of a piece of tag wire approximately 6 inches long, it can be suspended from a second wire
supported in the horizontal plane. The part in question is then brought into contact, near the free end of the
vertically suspended wire. The presence of leakage fields will cause the wire to deviate from its normal
vertical position as the part is slowly withdrawn in a horizontal direction. Care must be taken to
demagnetize the vertically suspended wire between each test. Small pieces of tag wire about 1 inch long can
also be used to indicate the presence of leakage fields. The piece of demagnetized wire is placed upon a
horizontal nonmagnetic surface, and the part in question is placed on top of it. If the piece of tag wire can be
lifted off the surface as the part is slowly raised, the leakage fields are excessive.
Other Detection Methods.
Another method of testing for demagnetization is to use a piece of steel feeler stock in a few thousandths of an
inch thick and test if the feeler stock is attracted by the part. A small piece of iron or steel, such as a
ferromagnetic paper clip, can be suspended on a string near the test part to determine if it is attracted to the