Vibration sensors are a widely used type of alarm detection sensor. They use an internal piezoelectric ceramic plate and spring-loaded weight structure to sense parameters of mechanical vibration (such as vibration velocity, frequency, acceleration, etc.) and convert them into usable output signals. These signals are then amplified by operational amplifiers such as LM358 and output as control signals. Sensors used to detect impact or acceleration typically use piezoelectric devices that generate an electric charge when stress is applied. However, sensors using other materials and methods can also be used for detection.
The receiving principle of vibration sensors
Vibration sensors are a key component in testing technology. Their main function is to receive mechanical quantities and convert them into proportional electrical quantities. Because they are also electromechanical conversion devices, they are sometimes called transducers, vibration pickups, etc.
Vibration sensors do not directly convert the original mechanical quantity to be measured into an electrical quantity. Instead, they use the original mechanical quantity as the input to the vibration sensor, which is then received by the mechanical receiving section to form another mechanical quantity suitable for conversion. Finally, the electromechanical conversion section converts this mechanical quantity back into an electrical quantity. Therefore, the performance of a sensor is determined by the performance of its mechanical receiving section and electromechanical conversion section.
1. Relative mechanical receiving principle
Since mechanical motion is the simplest form of material motion, people first thought of using mechanical methods to measure vibration, thus creating mechanical vibration meters (such as Geiger vibration meters). The mechanical receiving principle of sensors is based on this. The working principle of a relative vibration meter is that during measurement, the instrument is fixed on a stationary support, the contact rod is aligned with the vibration direction of the object being measured, and the contact rod contacts the surface of the object using the elastic force of a spring. When the object vibrates, the contact rod moves with it, pushing the recording pen to trace the displacement of the vibrating object over time on a moving paper tape. Based on this recorded curve, parameters such as the magnitude of the displacement and frequency can be calculated.
Therefore, it can be seen that the result measured by the relative mechanical receiving part is the relative vibration of the measured object relative to the reference body. Only when the reference body is absolutely stationary can the absolute vibration of the measured object be measured. This raises a problem: when the required vibration is absolute, but a stationary reference point cannot be found, this type of instrument becomes useless. For example, measuring the vibration of a moving diesel locomotive, or measuring the vibration of the ground and buildings during an earthquake… in these situations, there is no stationary reference point. In such cases, we must use a vibration meter with a different measurement method, namely, an inertial vibration meter.
2. Inertial Mechanical Receiving Principle
When measuring vibration with an inertial mechanical vibration meter, the meter is directly fixed to the measuring point of the vibrating object being measured. When the sensor housing moves with the vibrating object, the inertial mass block, which is elastically supported, will move relative to the housing. The recording pen mounted on the mass block can then record the relative vibration displacement amplitude between the mass element and the housing. Then, using the relationship between the relative vibration displacement between the inertial mass block and the housing, the absolute vibration displacement waveform of the object being measured can be calculated.
