A Pen-Writing Long-Period Seismograph Part 1.

We are developing long-period seismographs to add to our radio tele-recording seismograph system. The whole plan for long-period seismograph development is shown in Table 1. A horizotal seismsograph of type No. 1 in the table was designed and constructed. This seismograph has a high sensibility displacement transducer, shunt capacitance for lengthening period of pendulum, and high gain R-C coupled amplifier. The records are made by an ink writing galvanometer of 0.03 sec period. The magnification of seismograph is approximately 500 for a period of 30 sec, while its response covers periods from 1 to 50 sec. (cf. Fig. 5) The appearance of the pendulum is shown in Fig. 1. The free period of the pendulum is 1.5 seconds, and the mass is 200 gr. The boom is 10 cm. long, the weight of both booms is 15 gr., and they are balanced. Characteristics of the displacement transducer are shown in Fig. 2. It is a variable inductance type with high frequency oscillator (4 kc), and acts as a differential transformer (by a secondary winding connected for differential). The sensitivity of this transducer is about 1 v/1 mm when the source signal is supplied with 5 V. The output signal of the transducer is 4kc amplitude modulated wave. Fig. 3 shows characteristics of a pendulum of which period is lengthened by shunt capacitance. Fig. 4 is a diagram of electronic part of the system. Typical seismograms recorded at Tokyo by this seismograph and the Omori Displacement seismograph (lower trace) with constants T0 = 46 sec magnification = 16.5 are shown in Fig. 6. At every 15 mm minute marks are made by a crystal clock