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USU ECE 5320 - Seismometer

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ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Seismometer (Sensor)OutlineWhat is it?!Lehman SchematicHow Does a Seismometer Work?Basic PrincipleOperating PrinciplesFirst ever SiesmoscopeModern day InstrumentsClassificationsUsual Types of SeismometersTelesiesmometerAccelerographStrong Motion seismometer that measures acceleration.GeophonesSensitivitiesRichter Scale TableApplicationsDevelopments and trendsWhere to Buy?Reference ListECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Assignment#01: Literature Survey on Sensors and Actuators Topic: Seismometer (Sensor)Prepared by:Vijay C. [email protected]/06/200901/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-2Outline –What is it?!–Lehman Schematic–How it works?–Operating Principle–History–Classification–Types of Seismometers–Applications–Trends–Where to buy?!–Reference List01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-3What is it?!•A seismometer is a measuring device which translates slightest movements of the earth into (preferably) an electrical signal which can be recorded and processed for example. •A Lehman type seismometer consists basically of a horizontally mounted, weighed boom which can swing freely on one end. This motion is usually detected by a coil mounted on the free end of the boom which is seated above a quite strong magnet. Each movement of the boom is translated into an induced voltage in the coil which can be amplified, filtered and recorded or online processed after passing a suitable A/D converter.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-4Lehman Schematic01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-5How Does a Seismometer Work?•A seismograph is a device for measuring the movement of the earth, and consists of a ground motion detection sensor, called a seismometer, coupled with a recording system. •A simple seismometer that is sensitive to up-down motions of the earth can be understood by visualizing a weight hanging on a spring. The spring and weight are suspended from a frame that moves along with the earth’s surface. •As the earth moves, the relative motion between the weight and the earth provides a measure of the vertical ground motion. If a recording system is installed, such as a rotating drum attached to the frame, and a pen attached to the mass, this relative motion between the weight and earth can be recorded to produce a history of ground motion, called a seismogram.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-6Basic Principle•A mass, usually called the inertial mass, that can move relative to the instrument frame, but is attached to it by a system (such as a spring) that will hold it fixed relative to the frame if there is no motion, and also damp out any motions once the motion of the frame stops. •A means of recording the motion of the mass relative to the frame, or the force needed to keep it from moving.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-7Operating Principles•Early seismometers used optical levers or mechanical linkages to amplify the small motions involved, recording on soot-covered paper or photographic paper.•Modern instruments use electronics. In some systems, the mass is held nearly motionless relative to the frame by an electronic negative feedback loop. The motion of the mass relative to the frame is measured, and the feedback loop applies a magnetic or electrostatic force to keep the mass nearly motionless. The voltage needed to produce this force is the output of the seismometer, which is recorded digitally.• In other systems the mass is allowed to move, and its motion produces a voltage in a coil attached to the mass and moving through the magnetic field of a magnet attached to the frame. This design is often used in the geophones used in seismic surveys for oil and gas.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-8First ever Siesmoscope•In 132 CE, Chang Heng of China's Han dynasty invented the first seismoscope.•Description: large bronze vessel, about 2 meters in diameter; at eight points around the top were dragon's heads holding bronze balls. •Working: When there was an earthquake, one of the mouths would open and drop its ball into a bronze toad at the base, making a sound and supposedly showing the direction of the earthquake.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-9Modern day Instruments•Modern instruments use electronic sensors, amplifiers, and recording instruments. Most are broadband covering a wide range of frequencies. Some seismometers can measure motions with frequencies from 30 Hz (0.03 seconds per cycle) to 1/850 Hz (850 seconds per cycle). •Some modern instruments use a "triaxial" design in which three identical sensors that measure motion at the same angle to the vertical are 120 degrees apart on the horizontal. Vertical and horizontal motions can be computed from these measurements. •Seismometers unavoidably introduce some distortion into the signals they measure, but professionally-designed systems have carefully-characterized frequency transforms.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-10ClassificationsBased on period: •Short period.•Long period. •Broad-band. Based on type of output: •Analog. •Digital.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-11Usual Types of Seismometers•Telesiesmometers•Accerlerographs•Geophones01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-12Telesiesmometer•The modern broad-band seismograph can record a very broad range of frequencies. It consists of a small 'proof mass', confined by electrical forces, driven by sophisticated electronics . As the earth moves, the electronics attempt to hold the mass steady through a feedback circuit. The amount of force necessary to achieve this is then recorded.•In most designs the electronics holds a mass motionless relative to the frame. This device is called a "Force Balance Accelerometer". It measures acceleration instead of velocity of ground movement. Basically, the distance between the mass and some part of the frame is measured very precisely, by


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USU ECE 5320 - Seismometer

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