Definition
A bidirectional vibrometer is an instrument used to simultaneously measure the vibration parameters of two objects in two directions perpendicular to each other. It is usually used to evaluate the compound vibration state of mechanical structures or equipment in a plane, and can simultaneously obtain vibration displacement, velocity, or acceleration data in two orthogonal directions, providing key information for analyzing vibration patterns and directional characteristics.
Principle
The core of a bidirectional vibrometer typically consists of two vibration sensors arranged perpendicular to each other, such as piezoelectric accelerometers or velocity sensors. Each sensor independently senses vibrations in the direction of its sensitive axis and converts mechanical vibrations into electrical signals. The signal is amplified, filtered and processed by a built-in or external conditioning circuit, and finally the time-domain waveform of the two channels is recorded simultaneously through the data acquisition system. Its basic sensing principle can be expressed as:
a = k · V
where a represents vibration acceleration, k is the sensor sensitivity coefficient, and V is the output voltage signal. For bidirectional measurements, the relationship is established simultaneously in both orthogonal directions and reflects the plane vibration vector through coordinate system synthesis.
Measurement method
In the actual measurement, the instrument should be fixed and installed at the measurement point according to the geometric characteristics of the measured object and the estimated vibration direction to ensure that the axial direction of the two sensors is aligned with the direction to be measured. The measurement process typically involves the following steps: installing the instrument and connecting the data acquisition equipment; Set the sampling frequency and range to ensure that the frequency and amplitude to be measured are covered; Background noise measurements are taken as a reference; Start the test object and collect dual-channel data synchronously; Finally, time-frequency analysis, vector synthesis or directional spectrum analysis are performed by software. Measurements are subject to relevant standards, such as the ISO 10816 series of general guidance on mechanical vibration evaluation.
Influencing factors
The accuracy of the measurement results is influenced by several factors. Instrument mounting, such as bolted, magnetic, or handheld, can affect coupling stiffness and high-frequency response. The transverse sensitivity ratio of the sensor itself, i.e., its sensitivity to non-axial vibrations, can introduce cross-interference. Changes in ambient temperature can affect sensor sensitivity and zero drift. Measurement cable movement and electromagnetic interference can contaminate the signal. In addition, the choice of measurement point position is representative, as well as the curvature and material of the measured surface, also affect the authenticity of the vibration transmission.
Applications
Bidirectional vibrometers are widely used in many industrial and scientific research fields. In rotating machinery condition monitoring, it is used to analyze the plane vibration of pumps, fans, or motors to identify misalignment or loose faults. In civil engineering, it is used to monitor the dynamic response of a bridge or building structure in a two-dimensional plane. In precision manufacturing, it is used to evaluate the smoothness of operation at the end of a CNC machine or robot. In electronics testing, it is used to analyze the reliability of circuit boards or components in complex vibration environments. In the automotive industry, it can be used to study the vibration characteristics of engines or suspension systems.
Selection considerations
When choosing a bidirectional vibrometer, it is necessary to comprehensively consider a number of technical parameters and application requirements. The measurement range, including the amplitude and frequency range, should cover the expected value of the measured vibration. Sensitivity and resolution need to meet the detection requirements of weak signals. The weight and size of the sensor should be small enough to avoid load effects on lightweight structures. The compatibility of the instrument's output interface with the data acquisition system needs to be confirmed. The environmental conditions of use, such as temperature, humidity, and potential explosion risks, determine the protection level and material requirements of the instrument. In addition, the traceability of the calibration certificate, long-term stability, and the functionality of the subsequent data analysis software are also important considerations.