Chapter 12 - Clocks and Associated Devices - Period Delay Mechanisms (P.D.M.): Mechanical P.D.M.Chapter 12 - Clocks and Associated Devices - Automatic Latitude-Adjustment Devices (A.L.A.): Mechanical A.L.A.
GERMAN UNDERWATERS ORDNANCE MINES
Chapter 12 - CLOCKS AND ASSOCIATED DEVICES
PERIOD DELAY MECHANISMS (P.D.M.)
ELECTRICAL P.D.M. - FUSE-DELAY SWITCH (Figure 297)

The accompanying diagram shows a typical fuse-delay switch type P.D.M. set to "3". If an actuation is registered on the unit detector, current from the battery flows through fuse-delay switch No. 1 although in some cases a by-pass fuse is used to reduce the resistance of the circuit to a value low enough to allow rapid holding in the detecting circuit. After a short delay period, switch No. 1 switches over, cutting out its own heater coil, opeing the holding circuit, and passing all current through switch No. 2 for a period long enough to allow the detecting circuit to recover.

When switch No. 2 operates, it puts switch No. 3 in the circuit and the unit is alive again. As this process is repeated, switches No. 3 and No. 4 operate in a like manner, with a third actuation firing the detonator. P.D.M.'s of this type may have a many sett-ings as can be fitted to the unit's P.D.M. terminal board, with the P.D.M. setting of any unit being determined as follows:

X equals 2M-2, where X equals the number of fuse-delay switches and N equals the P.D.M. setting.

This device is used with BM 1000 units.

Figure 297– Electrical P.D.M. (Fuse Delay Switch) Circuit

Chapter 12 - Clocks and Associated Devices - Period Delay Mechanisms (P.D.M.): Mechanical P.D.M.Chapter 12 - Clocks and Associated Devices - Automatic Latitude-Adjustment Devices (A.L.A.): Mechanical A.L.A.