JPS6161610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moving coil type seismometer.

Figure 1 shows a schematic structural diagram of a conventional seismometer. In Figure 1, 1 is a yoke, 3 is a pole piece,
4 is a magnet, 5 is a detection coil, 6 is an output lead wire, 7 is a coil winding frame, 8 is an additional mass body, 9
1 is a spring fixed holder, and 10 is a spring.

Next, the operation will be explained.

In general, seismometers need to detect only seismic vibrations rather than various other vibrations in the ground. Therefore, the detectable band of seismometers is adjusted according to the purpose of measurement. The output characteristics of a moving coil seismometer are generally expressed by the following equation.

h=Bg ²・ι ² /4π・m・f ₀・R ...(3) Here, f ₀ : Natural frequency, S: Stiffness of spring, m: Equivalent mass of vibration system, U: Output value,
f: arbitrary frequency, h: attenuation constant, R: total circuit resistance, Bg: magnetic flux density in the magnetic air gap of the magnetic circuit, ι:
Indicates the moving coil length.

As can be seen from equation (2), when f=f ₀ , the output value U
is the maximum, and the usable band is determined by the value of the attenuation constant h determined by equation (3) (see FIG. 3). In other words, as shown in Figure 3, when f/f ₀ is plotted on the horizontal axis and output is plotted on the vertical axis, the damping constant h
The curve increases in the direction of arrow A, where the value of
The characteristics are C ₁ , C ₂ , and C ₃ , and the used bands are B ₁ , B ₂ , and B ₃ , respectively.

By the way, in a seismometer, in order to match the usable band of the seismometer to the target band, it is necessary to adjust the natural frequency f ₀ and the damping constant h. If one attempts to adjust only the used bandwidth, the attenuation constant h may be adjusted as shown in equation (2). The adjustment of h is based on equation (3) using Bg, ι, m,
You can adjust the constant from either f ₀ or R, but
f ₀ cannot be moved because the band center value will move.
If m is fixed at f ₀ , the value of S must be adjusted at the same time. Since ι and R are related to each other, it is not possible to adjust only one value. Further, the movable coil can only be adjusted in the unwinding direction, and only in the decreasing direction of h. For these reasons, it can be seen that the easiest way to adjust h is to adjust Bg. However, in conventional seismometers, to adjust the Bg value, either disassemble the seismometer and perform magnetization/demagnetization to obtain the desired Bg value, or measure magnetization/demagnetization without disassembling it. A method of repeatedly adjusting to the desired bandwidth was required. It also required expensive equipment for magnetization and demagnetization.

This invention was made in consideration of the above points, and aims to make it possible to adjust Bg easily from the outside even after assembling the seismometer, thereby making it possible to adjust h without expensive equipment or complicated adjustments. The purpose is An embodiment of this invention will be described below.

FIG. 2 shows an embodiment of the present invention. In this figure, 2 is threaded on the outer periphery;
This is a magnetic flux density adjustment plate with a screwdriver groove in the center. Reference numeral 1a denotes a screw hole drilled in a part of the lower magnet attachment surface of the yoke 1. After assembling the magnetic circuit, the magnetic flux density adjusting plate 2 is screwed into this screw hole 1a.

In a seismograph equipped with a magnetic circuit having a magnetic flux density adjustment plate 2 as shown in Fig. 2, in addition to the magnetic gap into which the moving coil is inserted, the magnet 4
A continuously variable magnetic resistance is provided on the bottom surface of the yoke 1 at the bottom of the yoke. This continuously variable magnetic resistance, that is, by rotating the magnetic flux density adjustment plate 2 with a screwdriver, the gap between the magnet 4 and the magnetic flux density adjustment plate 2 changes continuously, and Bg can be continuously changed. can.
Furthermore, if the configuration is as shown in Figure 2, Bg adjustment can be easily made even after the seismometer is assembled.

As explained above, this invention allows Bg to be easily adjusted from the outside in a moving coil seismometer, so even after assembly is completed, h can be easily adjusted without disassembling it, and it is possible to adjust h without disassembling it even after assembly is completed. It has the advantage that it can be easily and efficiently adjusted depending on the situation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional moving coil seismometer, and FIG. 2 is a sectional view showing an embodiment of the present invention.
FIG. 3 is a characteristic diagram showing the relationship between the output of the seismograph and the frequency. In the figure, 1 is a yoke, 1a is a screw hole, 2 is a magnetic flux density adjustment plate, 3 is a pole piece, 4 is a magnet, 5 is a detection coil, 6 is an output lead wire,
7 is a coil winding frame, 8 is an additional mass body, 9 is a spring fixing holder, and 10 is a spring. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An earthquake characterized in that, in a moving coil seismometer, a screw hole is formed in the yoke constituting the magnetic circuit, and a magnetic flux density adjustment plate for adjusting the magnetic flux density of the magnetic gap from the outside is screwed into the screw hole. Total.