Definition
A vibrometer is an instrument used to measure the vibration state of an object (such as displacement, velocity, acceleration). It converts mechanical vibration into electrical signals through sensors, which are processed and presented in numerical or waveform form, providing a quantitative basis for evaluating equipment operating status, structural health, or environmental vibration.
Principle
The core working principle of the vibrometer is based on a vibration sensor. Common sensor types include piezoelectric accelerometers and speed sensors. Piezoelectric accelerometers take advantage of the positive piezoelectric effect of piezoelectric materials: when the sensor is subjected to vibration, the internal mass exerts an alternating force on the piezoelectric element, causing it to generate a charge signal proportional to the acceleration. The signal is amplified and converted by built-in or external circuits to obtain the acceleration value. Speed sensors are typically based on the principle of electromagnetic induction, where the coil moves relative in a magnetic field to generate an induced electromotive force, the magnitude of which is proportional to the vibration velocity. For displacement measurement, it is often achieved by secondary integration of the acceleration signal or primary integration of the velocity signal, and the compensation of low-frequency noise and drift should be paid attention to in the process.
Measurement method
Vibration measurement is usually divided into contact and non-contact types. Contact measurement mounts the sensor directly on the surface of the object being measured, ensuring a secure coupling to accurately transmit vibrations. Mounting options include screw-fixing, mount attachment, or hand-held probes, with screw-fixed frequency response being the best. When measuring, the sensor and instrument settings are selected according to the parameters of interest (acceleration, velocity, or displacement) and frequency range. Non-contact measurements, such as laser vibrometers, use the Doppler effect to measure vibration and are suitable for hot or fragile objects. Regardless of the method, the position, direction and measurement duration of the measurement point should be determined according to relevant standards (such as ISO 10816 series mechanical vibration evaluation standards) before measurement, and the influence of background vibration should be considered.
Influencing factors
Measurement accuracy is influenced by various factors. Insufficient sensor mounting rigidity can lead to reduced resonance frequencies, affecting high-frequency measurements. Temperature changes can change sensor sensitivity and zero drift. The triboelectric effect from cable movement can introduce noise. For integration operations, improper setting of the low-frequency cut-off frequency will amplify the DC offset, resulting in distortion of the displacement results. Ambient electromagnetic interference may be coupled into the signal line. In addition, errors can be introduced by the curvature and material of the measured surface, the angle between the measurement direction and the gravity direction, etc. In practice, these effects need to be reduced through calibration, standardized installation, and reasonable setting of instrument parameters.
Applications
In the industrial field, vibrometers are used for condition monitoring and fault diagnosis of rotating machinery (such as motors, fans, pumps), identifying imbalances, misalignments, or bearing wear through vibration characteristics. In civil engineering, it is used to monitor the structural response of bridges and buildings under earthquake or wind loads. The automotive industry uses it to test the NVH performance of components and vehicles. In electronics testing, the impact of shipping vibrations on packaging integrity is evaluated. In terms of environmental monitoring, measure whether the environmental vibration caused by building construction or traffic meets the limit standards. These applications rely on accurate acquisition and analysis of vibration data.
Selection considerations
The selection of the type should take into account the measurement requirements and technical parameters. First, the main parameter type (acceleration, velocity or displacement) of the measured vibration, as well as the amplitude range and frequency range, are clarified. For example, high-range accelerometers are often used for high-frequency shock measurements, while low-frequency structural vibrations may focus on displacement. Secondly, consider environmental conditions, such as temperature, humidity, and the presence of corrosive media, and choose sensors with corresponding protection levels. In terms of instrument functionality, it is necessary to evaluate whether data storage, real-time spectrum analysis, or multi-channel simultaneous measurements are required. For long-term monitoring, consider a system with integrated wireless transmission. Finally, refer to the requirements of relevant industry standards (such as API, GB/T standards) for instrument accuracy and certification, and ensure that the selected equipment can verify its performance through traceable calibration.