Operation (Figure 242). When the mine is laid, both detecting devices (D 102 U/UR/KS and D 102 M1) are exposed to water, and the pressure is equalized for the depth at which the mine plants. Upon impact, the bomb fuze causes the master switch HS to close contact and break its safey shunt. If the water temperature is between -5° Centigrade and +35° Centigrade, temperature switch KTSE is closed and battery B ener-gizes fuse delay switch S1. When S1 has operated (with a delay) it cuts in switch S2, which renders the circuit alive. At this point, if the mine is in less than 15 feet of water, hydrostatic switch WDS will energizes S3 and fire the detonator. (There is a slight delay in firing, due to the making of switch S3 and the passing of current through thermistor UW.) Under normal operating condition, WDS is open and the mine is alive.

Pressure-detecting device D is normally on its pressure contact (UR). a negative pres-sure differential will cause D to break the passive contact UR and make contact U (pro-vided that the pressure differental has a magnitude of from 1.5 to 2 cm water). When D closes to contact U, battery B will operate relay R1 with a delay of six to nine seconds, due to C1. Condenser C1 is assured of being totally discharged, since it is connected across W3 in the normal passive state. When r1 contact closes, the resultant surge to charge condenser C2 allows relay R2 to operate, closing r2 which give R2 a self-holding circuit. Closure of r2 also energizes the microphone M in series with the primary winding of the microphone transformer T. If sound is now present, the resultant alternating cur-rents in T are rectified, operating relay R3 to close r3, and the battery fires the detona-tor through the U contact of D, r2, and r3 with a delay due to thermistor UW.

If pressure reaction takes place, but no sound is present, re-opening of the U contact of B will de-energize R1 and R2, and r1 and r2 will reopen. C1 will discharge quickly through W3. C2 however, may discharge only through W7, which has a resistance of 10 megaohms. Until C2 is fully discharged, closure of D to the U contact will not cause suffi-cient surge of current through R2 to operate it to close r2. Thus, the unit is passive to pressure actuation for five minutes. Therefore, during periods of rough weather, it may be expected that the pressure differentials incident on D will keep C2 charged continu-ously. long enough to prevent the mine from firing when a ship passes overhead.

Figure 242 – DA 102 Unit Circuit