seismometer new

7/28/2019 Seismometer New

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INSTRUMENTATION & CONTROL SYSTEM

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Seismometer is a device that is made to measure and

record the motions of the ground.

It also help seismologist to locate and measure the size

of these different seismic waves.

Seismometer converts ‘Ground Motion’ into an

electric output signal.



Two basic types of seismometer

Inertia seismometer

Strain meters seismometer

Seismometer are the instruments with very low

natural frequency. Due to this seismometer are often

in very large size.

Seismometer will store the vibrations measured on

some kind of storage device know as seismograph.



In AD 132, Zhang Heng of china’s Han dynasty invented thefirst seismoscope, which was called Houfeng Didong Yi.

After 1880,most seismometer were descended from the team

John Milne. They invented the seismometer using damped

horizontal pendulum. The basic damped horizontal pendulum swing like a gate of a

fence.



A seismograph consists of a ground motion detectionsensor called seismometer which is connected to arecording system.

A simple seismometer consists of a weight hanging ona spring. This spring and weight are a part of a framewhich moves alongside earths surface.

There is a pen attached to the mass which helps recorda history of motion called seismogram. Seismographswork on the principle of inertia.

Modern seismometers are electronic.



Modern instruments use electronic sensors,amplifiers, and recording devices. Most are

broadband covering a wide range of frequencies.

Modern sensitive's come in three broad ranges:

Long Period Seismometer

An instrument in which the resonant frequency is very low.



Short Period Seismometer

Is constructed to have a very short natural frequency & a

correspondingly high resonant frequency which is higher

than most frequencies in a seismic wave.

Strong motion seismometer

Are not as sensitive to ground motion as teleseimic

instrument but they stay on the scale during the strongest

seismic shaking. The data is essential to understand how anearthquake affects manmade structures.



Broadband seismometer

As an inertial pendulum design with a force feedback

mechanism. The feedback force is applied is determined by using

an electrical transducer to convert the motion of the mass into anelectrical signal.



Is use to measure the movement in the Earth’s

crust



Short period OBSs

Record high frequency motions. It can record small

and short period earthquake.

Long period OBSs

Records much broader range of motion. It is use for

recording mid-sized earthquake and seismic activity.



The OBS data is not quite as high quality as land data

because OBS cannot be carefully placed. It will be

drop off and are located wherever it settle down.

It has noisier signal due to current along the ocean

bottom, and the timing accuracy is not as good.

The OBS data is nearly as good as land data and it provides essential observation from location where we

cannot place land sensor.



It contain sensor that listen for sonar signals in the

water.

It will send a certain code and then the lead weight isrelease, the rest of the OBS is buoyant and it will rise

up. It takes about 2 hours.



Very stable clocks make comparable readings frommany far flung seismometers.

Data can be recovered easily with the help of a datacable. This feature helps in saving task of carefullydisassembling the instrument casing on a movingship.

With the help of this method data is available instantlyfor usage which is very useful for geologists torespond to a major earthquake



Ocean Bottom Seismometers are very difficult toinstall at a specific place with a pinpoint accuracy.

Usually they are lowered into place through thousandof meters of water.

Short period seismometers have short battery life andmust be changed repeatedly.

Sometime OBSs fails to rise to the surface and arelost.



What we learn from this research is, seismometer is use

to measure the movement of the earth and it also help to

record seismic waves that allow seismologists to map

the interior of the earth. Most seismometer areelectronic operated now days, and there are a few types

of seismometer used by the seismologists.

seismometer new

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