T.O. 33B-1-1Figure 3-40. Deleted3.6.9.2CompassIndicator.A compass is sometimes used for indicating the presence of external leakage fields. A compass can be placedupon a nonmagnetic surface and a magnetized part (aligned due east and west) moved slowly toward the eastor west side of the compass case. The presence of an external leakage field from the part can cause thecompass needle to deviate from its normal north-south alignment. However, demagnetized parts will causethe needle to deviate from its normal position if the compass case is not approached from an easterly orwesterly direction. The theory of operation is very similar to that for the field indicator since the compassneedle is a permanent bar magnet.3.6.9.3SteelWireIndicator.A piece of iron or steel wire can be fashioned into a fair detector when nothing else is available. By forming aloop at one end of a piece of tag wire approximately 6 inches long, it can be suspended from a second wiresupported in the horizontal plane. The part in question is then brought into contact, near the free end of thevertically suspended wire. The presence of leakage fields will cause the wire to deviate from its normalvertical position as the part is slowly withdrawn in a horizontal direction. Care must be taken todemagnetize the vertically suspended wire between each test. Small pieces of tag wire about 1 inch long canalso be used to indicate the presence of leakage fields. The piece of demagnetized wire is placed upon ahorizontal nonmagnetic surface, and the part in question is placed on top of it. If the piece of tag wire can belifted off the surface as the part is slowly raised, the leakage fields are excessive.3.6.9.4OtherDetectionMethods.Another method of testing for demagnetization is to use a piece of steel feeler stock in a few thousandths of aninch thick and test if the feeler stock is attracted by the part. A small piece of iron or steel, such as aferromagnetic paper clip, can be suspended on a string near the test part to determine if it is attracted to thepart.Change 33-87
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