Analog Seismograph
Previously we have understood the causes of earthquakes, now we will learn how analog Seismograph earthquake work.
The working principle of a Earthquake Analog Seismograph is that if a seismometer detects a vibration, the seismometer will send a signal to an amplifier to amplify the signal. The signal will be amplified by 56,000 times the initial signal.
After that, the signal will be given to a drum recorder device. Inside the drum recorder there are additional electronic devices that can regulate the movement of the recording needle, and the rotation speed of the drum. The diagram blog can be seen in below.
Seismometer Ranger SS-1
Seismometer Ranger SS-1 is a production of the company KINEMETRICS Inc., which is one of the sensor components for Earthquake Analog Seismograph instruments located in the Banda Aceh Climatology and Geophysics Meteorology Agency.
The following physical form of the Ranger SS-1.
Analog Seismograph – Seismometer SS-1 Ranger works on the basis of a “moving coil” to produce electricity based on electromagnetic fields.
The construction of the Ranger SS-1 can be seen in figure below.
Inside the seismometer there are Spring Hanger Rods, Suspension Spring, Flexure, Output Coil, Mass (moving magnet), Period Extending Magnet, and Calibration Coil
Spring Hanger Rod and Suspension Spring are useful for control the mass when used in a vertical or horizontal plane.
Flexure is useful as an adhesive field for the masses.
Coil output is useful as a source of voltage in case of vibrations in the SS ranger 1.
At the output coil there is a Rg resistance coil generator, which is the resistance of the generator coil (coil signal) with Ohms units.
The value of this resistance is 5000 Ohms. Mass is a permanent magnet that can move.
The Exteding Magnet Period is used for expanding the magnetic field to produce a timing.
Calibration Coil is used for the calibration process. Calibration functions as a normal determination of the tool’s work to show the correct value when measuring. This calibration coil has a resistance of 100Ohm.
Ranger SS-1 is a “spring-mass” instrument with electromagnetic transduction.
Permanent magnets are made as seismic “mass” and the output coil as a transducer is attached to a frame or seismometer body.
The mass is supported by two circular flex, located at the top and bottom which functions as a buffer for the mass.
When the seismometer detects a vibration, the mass supported by flex will move perpendicular to the output coil.
As a result of the movement by the mass, so that it will cause an electromagnetic field at the output coil. Due to the electromagnetic arising, it produces a voltage at the output coil.
The relationship between the constant speed from mass to the output coil that can produce this voltage is called the Constant Generator.
Ranger SS-1 has a constant generator that is 340V / ms. This shows that if the mass moves a distance of one meter in one second, the output coil will produce a voltage of 340V.
But in reality, the mass only moves within a range of ± 1 mm so that the resulting voltage is very small, ranging from nanovolts to millivolts.
The voltage generated by the output coil will be supplied to the Amplifier that looks like through the MS 3106E-14S-5S connector.
The amplifier will amplify the voltage by 56,000 times.
In Figure above, shows a 5 pin configuration with the following functions:
- Pin A and B = Output Coil
- Pin D and E = calibration coil
- Pin C = Grounding Casing based on the datasheet, the determination of the polarity of the installation is as follows:
The voltage on pin A is positive with respect to pin B.
When a positive voltage is applied to pin E against pin D, mass moves down which results in a positive voltage on pin A.
Recorder
To be able to record earthquake events, an analog recorder is used that represents one sensor.
There are three recorders used, namely horizontal to record the direction of:
- East-West (EW)
- North-South (NS)
One mounted vertically to record the direction of:
- Up-Down (UD).
Each single recorder has some of the same devices, a drum, Analog Seismograph paper as a data writing medium, as well as several settings namely strengthening, position, drum rotational speed, and recording time.
The recorder basically records earthquake activity on Earthquake Seismograph paper glued to a drum that is rotated at a certain speed using a pen that moves parallel to the drum continuously for the whole amount of recording.
The duration of recording in a drum is 24 hours. The time markers on the seismogram sheet are marked with a break every minute.
Figure above is the recording timing on the seismogram sheet. Timing is limited to once every minute. Recording each line within 15 minutes. The duration of recording is influenced by the rotation of the stepper motor which drives the drum recorder and pen. The motor used is a 12Volt stepper motor with 1/6 RPM.
There are two motors that are used, for transferring the position of the pen (left) and drum rotation (right).
The speed of the two motors can be adjusted by changing the position of the selector at the bottom of the drum recorder.
In figure below there are two selectors, each of which has a different function. Drum speed is used to adjust the rotation speed of the drum. The current setting is 60mm / min.
This states that the 60mm length of recording takes 1 minute or 60 seconds, can be seen in Figure below.
It also means that within 1 mm the time required is 1 second. Selector in Record Length functions to express the length of time used in recording on seismogram sheets.
Current settings show at 1days / record. This states that for one sheet of seismogram paper can record for one day consisting of 24 hours.
Below is a rear view of each recorder.
There appear to be two fuse units (top right black and two round). There are two fuses that are used to function to secure each motor when suddenly there is an excessive voltage source.
The fuse is capable of delivering a maximum current of 5A.
To be able to support the performance of a Earthquake Seismograph, a power supply is used. Figure below can be noted that it takes two power supply units with 220Volt input voltage and 12Volt output (yellow).
This recorder has three input power supplies (+, Ground, and -), which serves to make the waves swing from positive and negative.
In addition to the two power supply units, several 12 volt battery units (white) are also used to maintain the Earthquake Seismograph that can record earthquake vibrations even though the electric current has been cut off.
Seismogram analysis
Earthquake Seismograph analysis is performed on seismogram paper. The results recorded from paper are analyzed based on primary, secondary, maximum amplitude, wavelength, magnitude, distance determination, and origin time determination.
In this practical work, analysis is limited by counting primary, secondary, duration, amplitude, and impulse waves.
After the value is obtained, analysis of magnitude, direction of longitude, latitude, angle, from the location of the earthquake can be determined using existing software.
Determination of P Waves
The P wave is measured based on the time of the first wave. Calculation of time rests on the fault that shows the allocation of hours. In figure below, the analysis is based at 09.00 because the earthquake occurred in the line which is one line below 09.00, this means that the recording of the earthquake occurred in the line 09.15.
Because the earthquake occurred several faults before the fault at 09.15, we can measure the distance of the initial wave using a ruler on the basis of the distance is 1mm / sec.
the P wave can be determined by subtracting the initial value which is 09:15:00 with the value obtained using a ruler which is 00:06:65.
Determining the S Wave
To determine the S wave, you can also use the same method as when determining the P wave.
Determination of Amplitude
To measure the magnitude of the amplitude, the equipment used is the same as determining the P and S waves, the ruler.
Taking the position to get the amplitude is the longest position of the wave either the P or S waves.
Determine the Duration
To determine the duration of an earthquake, measurements can be made using a ruler from the beginning of the P wave to the end of the S wave.
Determination of Impulses
Impulses are determined from P waves based on each of the Z, North-South, and East-West components. These impulses are useful for knowing the direction of an earthquake.
In the yellow circle, it can be seen initially that the P wave is shaking and forming a wave towards the top.
This wave has an amplitude that is 1 mm after being measured using a ruler. This result was written in the format 01.0 mm.
The formula of this result is as follows:
If the impulse obtained data that shocks occur towards the top, then the value is placed in lines U, East and North.
If the initial wave shock occurs downward, the value obtained is placed in the Down, South or West rows.
After the impulse value of the three components is known, the next step is to enter into the software to get the direction from the source of the earthquake.
Use of OpenOffice Software
Look at the software in Figure below, the third column is S-P which is the result of reducing the value of the P wave to the S wave.
The results are obtained as follows:
This value is entered with the letter CNE, because when we analyze impulses, we get the value Up (written in C), North, and South.
From the figure above the results obtained from Longitude (104.51), Latitude (10.00), Derjat (12.54), Magnitude (6.4 Richter) and Direction of the earthquake occurred in the Southwest direction of Banda Aceh City.
Seismometer Location
Seismometer Ranger SS-1 is placed on the rock surface in the mountain and wrapped in a box made of concrete shown in below. This is done with the aim of protecting the sensor from local interference such as direct sliding.
In below there are three seismometers placed in Horizontal and Vertical directions.
Horizontal seismometer to detect East-West (EW) and North-South (NS) directions, and vertically to detect Up-Down (UD) directions.
That is all I can give to you, I hope this Analog Seismograph article is useful.
Source:
- Operating Instructions for Model SS-1 Ranger Seismometer, 1990.
- http://www.sigana.web.id/index.php/gempa-bumi.html
- http://www.kinemetrics.com/uploads/SS-1_Oblique8b.png
- http://info.geonet.org.nz/download/attachments/952083/oturere_general.gif?api=v2
- http://bmkg.go.id/BMKG_Pusat/Profil/Logo_BMKG.bmkg#ixzz3SAkr624Y
- http://earthquake.usgs.gov/learn/topics/seismology/history/part03.php
- http://www.china.org.cn/china/2010-12/03/content_21472907.htm
- http://www.peigenesis.com/en/shop/part-information/MS3106E14S5S/CAN/EACH/211529.html#layout
- http://penyeara.blogspot.com/2013/08/seismograf.html
- http://media.npr.org/assets/img/2009/10/17/lp_seismogram_custom-4e8ca438cdfac79e9202a9b9866a16600776e166-s800-c15.jpg
