How To Select A Vibration Meter

What Is a Vibration Meter?

Vibration is the mechanical acceleration of an object, stimulated by various forces. A vibration meter analyzes those vibrations and a vital factor called ‘trending’ on the shafts, bearings, or any rotating component. This motion can have a single element at a single frequency, like the one obtained using tuning fork, or several elements co-occurring. This measurement helps to spot the device before depreciation. This meter is used to measure the vibration level of bearings, centrifuges, blowers, motors, fans, pumps, grinders, cooling towers, conveyors, and similar devices.

Applications of a Vibration Meter

  • Pinpoint vibration problems
  • Measure periodic motions
  • Detect imbalance and deflection of any non-stationary machines
  • Recognize mechanical looseness
  • Identify bearing wear
  • Spot bent shafts
  • Condition monitoring imminent and preventive maintenance
  • Troubleshoot machinery

Important Parameters of Vibration Meters

The vibration of an object could be either segmental (impulsive), or whole-body (continuous). In any vibration meter, the three main characteristics measured are the amplitude, frequency, and acceleration.

 

  1. A vibrating body travels, on either side of its stationary position, to a specific maximum distance. Amplitude is the distance to the extreme position on either side from the fixed position and is measured in meters (m). Vibration intensity is dependent upon this amplitude.
  2. A vibrating object that shifts back and forth from its usual stationary location produces a complete vibration cycle on moving from one extreme to another extreme and then back again. This count of the cycles completed by the vibrating object is measured as frequency, measured in hertz (Hz).
  3. During each vibration cycle, the velocity of this object varies from zero to the maximum. It moves most rapidly as it passes to an extreme position through its natural stationary position. The vibrating body slows down as it reaches the extreme, where it stops and then travels across the stationary position towards the other extreme in the opposite direction. During each vibration period, the magnitude of the acceleration varies from zero to the maximum, measured in meters per second square (m/s2) when the vibrating body shifts farther away from its usual stationary location, the velocity increases.

The parameters used for measuring vibration are universally in metric units. The acceptable range of both the types of vibration is between 1-80 Hz, and in cases where the value exceeds creates annoyance and discomfort.

Instrumentation and measurement Techniques

It is unlikely to find a single instrumentation system to meet all the frequency requirements and dynamic selection where this guideline applies. The signals obtained through vibration have many frequencies that make it difficult to differentiate the amplitude-time pattern and the varying frequencies. These properties can be exposed by plotting the amplitude of vibrations against frequency on a graph, also known as frequency analysis.

 

Overall, the measurement of vibration usually includes the following instruments:

  • Transducers, most commonly geophones or piezoelectric accelerometers
  • Signal-conditioning unit
  • System for data recording and analysis

Since the accelerometer is a significant component, it must be chosen carefully, depending upon the requirements. Most manufacturers use the ‘general purpose’ model that satisfies almost all needs. Though 80Hz frequency is the tolerable level, the commonly used frequency level is 50Hz, which is suitable for all purposes. With regards to the background vibration, the SN (signal to noise) ratio must be higher than 5dB. However, a SN ratio between 5dB to 10dB implies that the measured value must be corrected because of the background noise.

Evaluation Principles

To evaluate the vibration meter, the general principles that are used:

  • ISO 2372 (10816) Standard Comparison
  • Trend Comparison
  • Comparison with Other Machinery

Maintenance

To use the device for a longer time,

  • Remove the battery to prevent the erosion over long durations.
  • The condition of the sensor signal line must be checked often to prevent failure of the device display.
  • When trying to dismantle a device, read the user guide carefully to prevent the damage to the device due to erroneous handling

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