GERMAN UNDERWATERS ORDNANCE MINES |
Chapter 12 - CLOCKS AND ASSOCIATED DEVICES |
AUTOMATIC LATITUDE-ADJUSTMENT DEVICES (A.L.A.) |
ELECTROMAGNETIC A.L.A. (Figure 301) |
The needle consists of an aluminum drum, mounted horizontally and fitted with a mag-netic belt which is magnetized diametrically. It is placed between two sets of vertical pole pieces which conduct the vertical component of the earth's field thoruh the needle. The needle G thus tends to rotate counter-clockwise as a result of the RED field effect. |
A separate local magnet J, would with a coil, is also fitted to the unit. Its polarity is such that it puts out a BLUE magnetic field which tends to rotate the needle clockwise. This BLUE field is stronger than the earth's field; and, as a result, the needle rotates clockwose to its limit stop. |
A contact K is mounted on the drum, and two vertical wires are placed in such a po-sition that clockwise or counterclockwise rotation of the drum causes K to make contact No. 2 or No. 1 respectively. Thus, contact No. 1 becomes the RED contact and contact No. 2, the BLUE contact; and, since the field of the local magnet is stronger than that of the earth, the needle will make contact K2 when the mine is laid. |
When the unit is energized by the battery, current through fuse R (figure 302) ener-gizes the latitude-adjuster coil S and thermistor M. S is wound on the local magnet and is energized so that the field produced will be opposite to that of its core (i.e. the local magnet). The field produced by energizing S is stron enough to overcome the BLUE field of a local magnet, causing the needle to break contact K2, thereby breaking the electro-magnetic field of S. Since the residual magnetism of the local magnet is strong enough to swing the needle back again, contact K2 is again made and S re-energized. |
This pulsing, or deperming, continues until the residual magnetism of the local magnet is no longer capable of making switch K2. The process is assisted by the heating of ther-mistor M, whose decreasing resistance allows it to pass more current, thereby decreas-ing the pulsing current through S. |
Figure 301– Electromagnetic A.L.A. Component Parts |
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Figure 302 – Electric A.L.A. Circuit |
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