A seismic sensor (also called a “seismometer”, a term coined by Milne-Home in 1841) is an instrument used to measure seismic waves. Now it also covers the movement of the ground when it is shaken by some type of disturbance (which can be caused by explosions, volcanic eruptions and even earthquakes). Today, they are used in different industries. In this article from UAV, We detail what a seismic sensor is and how it works.
A little history
The first precursor of the seismometer was the so-called seismoscope, which detected the origin of earthquakes, but did not measure them. It was created by Zhang Heng, a Chinese polymath who lived during the Han dynasty (2nd century AD). The device consisted of a bronze vessel that carried six small balls, which were balanced in the mouth of six dragons located on the outside of the vessel. In the external-inferior part of these vessels there were some frogs, and if any of the balls fell into them, it was a clear sign that a seismic movement had occurred.
In the mid-19th century, Luigi Palmieri invented an electromagnetic seismograph capable of recording the time and duration of telluric movements. However, it is the Scottish physicist James David Forbes who is credited with creating the seismometer as we know it (1842). T
There are also other versions dating from the 20th century, such as the Japanese Omori (horizontal register pendulum created in 1899) which underwent minimal modifications by the Bosch company and would come to be called the “Bosch-Omori seismometer”. It is also worth mentioning a portable model invented in 1980 (which was called “Wilmore’s” in honor of its creator, the British seismologist Patrick Wilmore), a tubular device that contained a sensitive mass that when vibrating moves according to seismic energy. An electromagnet present was in charge of translating the vibration into electrical signals, which in turn were transmitted to a computer in charge of recording and controlling the information.
In general, there are three terms that we must identify: the seismic sensor or seismometer (which this article deals with), the seismoscope (a device that is limited to indicating that a telluric movement has occurred, but does not give more details) and the seismograph ( It is often used as a synonym for “seismometer”, but this applies more to the primitive versions of this instrument in which both the measurement and recording functions were combined. At present and thanks to the advancement of technology, both functions are specialized and separated.
A seismometer is governed by the principle of inertia and works by measuring the movement of the ground with respect to the same point when there is no disturbance. It comprises two objects: the frame (susceptible to the movements of the ground) and the inertial mass (that which tends not to move, even if the ground and the frame do). In general, the inertial mass is attached to the frame and can move in relation to it: thus, the relation of the movement between both objects makes it possible to calculate the magnitude of the seismic waves. On the other hand, modern seismometers are capable of detecting sound vibrations and oscillations through microphones, various sensors, amplifiers, and electrical recording of output measurements.
Seismic Sensor Types
They can be classified into two types: broadband (extremely flexible and can measure a wide variety of seismic waves; likewise, they have an extensive recording capacity in a wide range of frequencies) and short-long period (limited to measuring waves in a certain range, although they can also be very sensitive).
Seismometers are essential for seismology (the branch of geophysics responsible for the study of earthquakes and the propagation of seismic waves) because they are the central and most important element of seismographs (the other components being timing and recording/recording devices). ) and make it possible to detect the presence of seismic movements, which can alert the population and reduce the number of fatalities.
They are also used in the security industry to identify possible assaults and intrusions to properties and to intercept the actions of diamond cutters, torches, detonators or hammers that try to penetrate walls or security windows. It is worth mentioning that a new technique has emerged involving the use of fiber optic cables as seismometers, which is used to detect earthquakes. In 2016, a group of scientists in England noticed the presence of a noise whose waves had a shape similar to that of seismic waves generated by telluric movements.
Likewise, there was coincidence with a study of an earthquake that occurred in Italy of Mw6.0. As a result of this fact, experiments were carried out in England and Italy with the aim of implementing a global seismic network. What is sought is to apply this new method to the existing submarine fiber optic network, and with this detect earthquakes in real time.