Definition
A bidirectional vibration meter is an instrument used to simultaneously measure the vibration parameters of two objects in two mutually perpendicular directions, usually horizontal and vertical. It belongs to the category of general vibration measurement equipment, and by integrating two independent sensing units or a multi-axis sensing unit, it can simultaneously collect and analyze the compound vibration state of objects in the plane, providing key data for evaluating the dynamic properties of structures.
Principle
The core working principle of the instrument is based on vibration sensing technology, commonly the piezoelectric or microelectromechanical system sensing principle. The mass inside the sensor generates an inertial force when subjected to external vibrations, which acts on piezoelectric materials or detectable microstructures, causing it to generate an electric charge or electrical signal proportional to the acceleration. For bidirectional measurements, two sensing channels arranged orthogonally in space work independently, converting the amount of mechanical vibration in the corresponding direction into an electrical signal. Subsequently, the signal conditioning circuit amplifies, filters, and digitizes the original signal, and finally calculates and displays vibration parameters such as displacement, velocity, and acceleration through built-in algorithms.
Its basic relationship can be expressed by the following formula:
The relationship between the acceleration a(t) and the output electrical signal V(t) is: V(t) = S * a(t) + V0, where S is the sensitivity coefficient and V0 is the bias voltage. By integrating the acceleration signal, the vibration velocity and displacement can be further obtained.
Measurement method
When performing bidirectional vibration measurements, a systematic approach needs to be followed to ensure data validity. First, according to the surface characteristics and measurement direction of the measured object, the appropriate installation method should be selected, such as using a magnetic mount, adhesive or bolt to directly fix the sensor at the measurement point, and ensure that the sensor base is in close contact with the measuring surface. Secondly, the measurement parameters need to be set on the instrument, including the measurement range, frequency bandwidth and filter settings, which should refer to the estimated amplitude and main frequency components of the measured vibration. When making formal measurements, ensure that the two measurement axes of the sensor are accurately aligned with the direction to be measured. During the data acquisition process, it is necessary to record the steady-state signal for a sufficient period of time, and the time-domain waveform, spectrogram and characteristic values (such as peak and root mean square value) of vibration in each direction can be obtained through the analysis function of the instrument. For periodic or shock vibrations, multiple measurements may be required to obtain representative data.
Influencing factors
The accuracy of the measurement results is influenced by several factors. Insufficient sensor mounting rigidity or uneven contact surfaces can introduce additional resonance, leading to distortion of the high-frequency response. Changes in ambient temperature can affect the sensitivity and bias of the sensor. Electromagnetic interference at the measurement site may be coupled to the signal line, introducing noise into the data. The transverse sensitivity of the sensor itself, i.e., the response of one axis to the vibration of its spindle perpendicular, can cause crosstalk between channels in bidirectional measurements. In addition, if the selected frequency range does not cover the main energy band of vibration, or if the signal clips due to improper ranging, it can cause measurement errors. Operators need to identify and reasonably evaluate these factors.
Applications
Bidirectional vibration measuring instruments are widely used in industry and scientific research. In mechanical equipment condition monitoring and fault diagnosis, it is used to measure the vibration of rotating mechanical bearing housings such as pumps, fans, and motors in two directions, and analyze faults such as imbalance, misalignment, or looseness. In the field of civil engineering, it is used to monitor the horizontal and vertical vibration response of bridges and building structures under environmental stimuli (e.g., wind load, traffic). In electronics testing, it is used to evaluate the multidirectional vibration resistance of packages or components within products during transportation. In addition, it is also used in scenarios such as automotive parts testing, aerospace component environmental testing, and vibration evaluation of precision machining platforms.
Selection considerations
Choosing the right bidirectional vibration measuring instrument requires comprehensive consideration of technical parameters and application requirements. The core parameters include the measurement range (the maximum acceleration value that can be measured), the frequency range (the frequency interval for flat response), and the sensitivity. The vibration amplitude and main frequency components of the application scenario should fall within the range and frequency of the instrument. Secondly, it is necessary to pay attention to the resolution, noise floor and lateral sensitivity ratio of the sensor, which are related to the detection ability of weak signals and the isolation between multiple channels. The environmental conditions in which it will be used, such as temperature range, humidity, and potential explosion risk, determine the level of protection and safety certifications required for the instrument. In addition, the data output interface, power supply method, supporting analysis software functionality, and compatibility with existing data acquisition systems need to be considered. Ultimately, a trade-off should be made between meeting measurement requirements and long-term reliability.