A 1 Unit - Operation (Figure 163)

Arming. Two minutes after the hydrostatic clock starts, S3 closes, blowing fuse F and starting the delay clock. When the hydrostatic clock runs off its delay period, (17 minu-tes) S4 and S5 close, putting the detonator in the circuit. When the delay clock runs off its period (six days maximum), S1 and S2 close and the unit is alive.

Normal Firing. When sound impinges on the microphone resistance will appear as cur-rent variations on the primary of transformer T and as alternating signal current on the secondary of T. The signal current is then rectified by rectifiers X1 and X2, with direct current then flowing from the secondary through two relays in series, the first, R1 being more sensitive than the second, R2.

If the sound is of suitable intensity for normal firing, the current flowing through R1 and R2 will not be strong enough to operate R2. If the sound persists long enough to charge C1, R1 closes to r1. B3 now sends current through R2, which opposes and is stronger than the induced cuurent from the secondary of T. The direction of this current is such that R2 closes to contact rf, putting the detonator across B4.

Normal Anit-countermining. A loud sound which produces a strong current through R1 and R2 tends to operate both relays. Because of the delay in R1 occasioned by C1, R2 operates first and, because of the direction of the actuating current, closes to rc.

B1 and B2 then apply a locking voltage, preventing R1 from operating, blocking further current from the secondary of T and keeping R2 closed to rc. This condition persists un-til thermal delay heater D heats and opens its switch, d, after about 12 seconds.

R2 then opens, d closes, and the unit returns to normal. If frequent anti-countermin-ing shocks are received, D will heat to the point where the unit's inert period may be as short as three seconds.

Intermediate State. A sound which builds up uniformly and rapidly to a point of consi-derably intensity may produce a current which is strong enough, after R1 operates to cancel out the current from B3 which would ordinarily close R2 to rf. R2 would not then close to either contact, and the unit would neither fire nor be rendered passive. If such a signal ceased abruptly, R1 would open, although the unit would probably fire as a re-sult of discharge from C2 through R2 which would close to rf.

Figure 163 – A 1 Unit Circuit