What Is a Seismic Sensor?
A seismic sensor is a device designed to detect and respond to seismic motion.
The measurement unit is the gal (Gal), representing acceleration. One Gal equals 0.01 m/s^2. When seismic motion is detected and the acceleration surpasses a predefined threshold, the device generates a contact signal.
Uses of Seismic Sensors
Seismic sensors are crucial for preventing secondary disasters during earthquakes. Their applications include:
- General industrial facilities
- Power transmission and generation equipment
- Fire safety systems
- Hazardous material-related facilities
These sensors are predominantly used in large-scale settings like power and chemical plants. They play a vital role in disaster prevention, mitigating the risks of fire spreading to hazardous materials and controlling the malfunction of machinery. Thus, they safeguard the lives and properties of people both within and around these facilities.
Principle of Seismic Sensors
Seismic sensors incorporate mechanisms like accelerometers and displacement transducers to detect vibrations from external forces, such as earthquakes. Upon detecting vibrations exceeding a certain threshold, they emit a contact output.
Moreover, by adjusting their sensitivity, seismic sensors can tailor their activation threshold to the intensity of the building’s vibrations, preventing false alarms from minor tremors.
Types of Seismic Sensors
There are various seismic sensor types, including drop-ball, pendulum, and electric models.
1. Drop-Ball Type
This mechanical sensor uses a ball placed on an indented base, emitting a signal when the ball drops. The sensitivity is adjustable by altering the ratio between the ball’s size and the indentation. However, it has limited sensitivity to vertical movements.
2. Pendulum Type
Featuring a pendulum with a contact or detector at its end, this sensor detects the pendulum’s swing speed. Its sensitivity is adjustable by changing the pendulum-to-contact distance. Like the drop-ball type, it is less responsive to vertical movements.
3. Electric Type
Electric seismic sensors use accelerometers on the X, Y, and Z axes. A spring-held pendulum moves with the vibration, and the pendulum position detector generates a current proportional to the pendulum’s acceleration. This type can detect both vertical and horizontal movements.
How to Select a Seismic Sensor
Key factors in selecting a seismic sensor include sensitivity, reliability, and cost. More sensitive sensors can detect finer vibrations. Reliability is crucial, as these sensors must function flawlessly in emergencies. Finally, consider the cost-effectiveness of the sensor for your specific needs.
Seismic Sensors and Other Information
1. Earthquakes and Electrical Fires
During the Great Hanshin-Awaji Earthquake, approximately 60% of building fires were caused by electrical issues. Seismic breakers can significantly reduce the risk of electrical fires by sounding alarms or cutting off power during earthquakes.
2. Mechanism and Features of Gas Seismic Sensors
Gas seismic sensors, designed to meet earthquake-proof standards, automatically shut off the gas supply if earthquake-induced accelerations exceed certain limits. However, they may struggle with long-period seismic motions due to the low rate of change in velocity and displacement. Recent advancements in acceleration sensors have led to the development of more sensitive gas seismic sensors for these motions.