直視記録方式による長周期地震計 第2報
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概要
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In order to add long period seismographs to our radio tele-recording seismograph system we are developing a long period seismograph system as shown in Table 1. In this paper, we report on the long period seismograph designated as No. 2 in Table 1. The maximum magnification of the seismograph is approximately 1000 at the period of 30 sec. The response curve covers the period range 10 to 100 sec. The design of the pendulum is shown in Fig. 1. The brass boom is 45 cm long and the mass is 5000 .gr. The axis of rotation is obtained by a knife edge at the point (5) and a steel ribbon at the point (13) as shown in Fig. 1. The pendulum period is adjustable for a range of 10 to 65 sec with good stabilty. The transducer of the seismograph is a moving coil which has a winding of 100,000 turns with a mean diameter of 4.2cm and a resistance of 1 Megaohms. The magnet is made of MK-5 with pole pieces arranged to produce a radial magnetic field of 3500 .gauss. A shunt capacitance is used to lengthen the period of pendulum. The theory for the period lengthener was given by Coulomb (1952). The output of transducer is then put into an integrator with the time constant of 63 sec (2πRC). The function of this network is that of a double integrator having identical time constant. (See Fig. 2 and 3) The D. C. amplifier which is used to amplify the output of the integrator is the chopper type. Its amplification is 20 Volts per 100 micro-volts at the load resistance of 4 Kilo-ohms and the drift is less than ±20 micro-volts in 24 hours. The recorder is an ink-writing galvanometer with period of 0.03 sec and sensitivity of 5 mm per 1 m amp. The seismograph was constructed in February 1962, and has been operated at Yasuda Hall in the campus of Tokyo University. A typical record is shown in Fig. 8, where the upper traces 1 and 2 are the record of Press-Ewing seismograph (To = 30 sec. Tg = 90 sec 3) and the lower trace is that of our seismograph.
- 1963-03-10
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