The "Seismik" was an experimantal attempt to produce a mine-firing unit wich opera-tes on very low frequencies. It was in the developmental stage, and was intended to be used in combination with firing units operating on other principles.

The "Seismik" (Seismograph Microphone) is used in a system which the Germans call the "S-Systeme". The system consists of a special microphone and a simple electrical circuit designed to be used as a low-frequency component for a combination mine unit. It was intended to combine the Seismik with M 4, A 4, and D 2. The last was to have been designated DS 1, but never went beyond the idea stage. The Seismik microphone is designed for frequencies of the 1 to 10 cps. range, but has been applied in development only to a circuit whose optimum frequency was 5 to 8 cps.

The Circuit. The circuit of the Seismik is shown in the upper half of figure 249. The microphone is fed by a battery in a transformer circuit. Introduction of the transformer is connected, unrectified, to the operating coil of relay F, which must oscillate with the al-ternating-current output, thus eliminating the high frequencies, depending upon the de-gree of damping (f) alternately charges condenser C1 from battery B2 and discharges it through the operating coil of relay R on the other half-cycle. Closure of contact (r) cau-ses charging of C2 through W1 and the charge on condensor C2 occurs in a manner simi-lar to that shown in the lower half of figure 249, with W2 causing the small discharges. When C2 is charged sufficiently to operate relay Fu, contact (fu) closes and B2 fires the detonator, or permits another influence firing component to do so.

Figure 249 – Seismik Unit Circuit

Frequency Response. The optimum frequency response of the system described is reported to be 5 to 8 cps. The microphone itself, however, is reported to have an essen-tially flat response down to one cycle per second. The lower frequencies are eliminated partially by the microphone transformer, and partially by the values of W2 and C2. The higher frequencies are eliminated by the unrectified signal current on the relay coil. This microphone might be used for other purposes where a pressure-equalized diaphragm type is necessary, but SVK considered that, because of its mounting, the response would start to fall off a about 15-20 cps., with possibly a peak at 30 cps. due to the fact that the rubber bag resonates at that requency.

Figure 250 – D 1/A Seismik Unit