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Vibration measurement

A preventive approach to greater efficiency and safety

The maintenance of systems and machines is a key factor for greater efficiency and safety. Traditional approaches, which are based on preventive maintenance and often involve the replacement of functional parts, are often very costly. It is therefore no wonder that more and more companies are focussing on condition-based maintenance. One method of condition monitoring is vibration measurement. It makes a significant contribution to identifying faults at an early stage and preventing expensive downtime.

The advantages of vibration measurement, the causes of dangerous vibrations and what correct monitoring in accordance with DIN ISO 10816 looks like - you can read about these in the following article.

The basics of vibration measurement

Generally speaking, vibration measurement is used to record and analyse the mechanical vibration of objects or structures. In order to understand their characteristics, the amplitude, frequency and phase of the vibrations are recorded. The vibrations are measured using vibration sensors. Analysers or software then process the data from the sensors. The aim here is to recognise patterns and identify potential problems such as material fatigue or instabilities.

Vibration measurements are used in numerous areas: In addition to construction monitoring and vehicle technology, it is primarily used in the preventive maintenance of industrial plant and machinery.

The advantages of vibration measurement
as a condition monitoring method

  • Early detection of machine damage: Vibrations can be an early warning sign of various types of machine damage (for examples, see "Causes of dangerous vibrations").
  • Preventive maintenance: Instead of maintenance according to a fixed schedule, vibration analysis enables demand-orientated maintenance. This means that maintenance work is only carried out when there is an actual need based on the vibration measurement data.
  • Extending the service life of machines: Regular vibration monitoring helps to keep machines in optimum condition and extend their service life.
  • Increasing operational safety: By monitoring vibrations, potentially dangerous conditions in a plant can be recognised before they have a negative impact.
  • Increased efficiency: Machines that are correctly aligned and maintained work more efficiently. Vibration measurement helps to identify and maintain these conditions.
  • Cost savings: By preventing major damage and downtime, vibration measurement can save significant costs.

Causes of dangerous vibrations

Whether in engines, steam turbines, generators, gas turbines, fans, pumps or compressors - dangerous vibrations can occur anywhere in machines, components and systems (with moving masses). There are many causes for this:

  • Mechanical imbalance: This is one of the most common causes of vibrations in rotating machinery. It occurs when the centre of gravity of a rotating component is not aligned with its axis of rotation.
  • Misalignment: This refers to the situation when two or more rotating parts are not correctly aligned. Misalignment can lead to uneven torque and increased vibration.
  • Wear and fatigue: Component wear, such as worn bearings, loose bolted connections or material fatigue, can cause increased vibration.
  • Hydraulic and pneumatic forces: Fluctuations in fluid or gas flows often cause vibrations. This occurs particularly in pumps, compressors and pipework systems.

The causes must be identified by means of vibration measurement. Standardised methods and threshold values are used for the analysis, which are laid down, for example, in the standard for machine monitoring DIN ISO 10816 (new: DIN ISO 20816).

This is how vibration measurement works:

  1. Measurement of vibrations: Vibration measurements are usually carried out using vibration sensors. These are attached to various points on the machine or system in order to measure the vibrations in different directions (horizontal, vertical and axial).
  2. Measurement data: The recorded data includes information about the vibration amplitude (the strength of the vibration) and the frequency (how often the vibration occurs per unit of time).
  3. Assessment according to standards: DIN ISO 10816 provides a series of classes and limit values that vary depending on the type and size of the machine or system. These classes indicate whether the measured vibrations are within acceptable limits or indicate anomalies.
  4. Classification: The series of standards categorises machines into different classes based on factors such as size, type of foundation (flexible or rigid) and operating speed. There are specific limit values for each class.
  5. Limit values and condition assessment: The limit values are divided into four zones - A (good, mostly newly commissioned machines are in this zone), B (satisfactory), C (unsatisfactory) and D (unacceptable). A machine whose vibrations fall into zone A is considered to be in good condition, while vibrations in zones C and D indicate possible problems and may require maintenance or repair.
  6. Long-term monitoring and trend analysis: Vibration measurements are often carried out over longer periods of time in order to recognise trends and plan predictive maintenance work.

FAQ about vibration measurement

In order to assess the condition and performance of machines and systems, various parameters are measured, including

  • Amplitude of the vibrations: This refers to the strength or intensity of the vibration. High amplitudes usually mean wear and tear in the machine.
  • Frequency: This measures how often a vibration occurs within a certain period of time. Each machine has its own "normal" operating frequency, and deviations from this can indicate problems.
  • Phase: This indicates at what point in the vibration cycle the vibration is occurring. Phase is often measured in degrees or radians and is important to understand the temporal relationship between different vibrations.
  • Direction of vibration: The direction of vibration can provide information, for example, about an imbalance or misalignment in rotating machinery.
  • Time history pattern: Analysing the time history of the vibrations helps to identify intermittent changes in the operating condition of the machine.
  • Temperature: The temperature is often also monitored, as an increased temperature can be an indicator of increased friction that leads to vibrations.

Where exactly the measurement is taken depends on the purpose of the measurement and the type of component. In the case of motors or pumps, vibrations are often measured at bearings or housings in order to assess the condition of the machine. This can be done with one or more vibration sensors.

The measuring devices record the amplitude, frequency and phase shift of the vibrations. The position of the sensor is crucial here, as it strongly influences the accuracy and relevance of the measurement data.

The correct interpretation of measurement data from vibration measurements is crucial. It determines whether or not preventive measures should be taken.

The following steps must be observed:

  • Selection of measuring points: Firstly, ensure that the measuring points on the machine have been selected correctly.
  • Collecting baseline data: Means collecting data when the machine is in a normal operating condition. This data serves as a reference for future measurements and helps to recognise deviations.
  • Trend analysis: Regular monitoring of vibration data is crucial. By tracking changes over time, deviations can be recognised at an early stage.
  • Diagnosis and measures: In the event of deviations, further investigations should be carried out to determine the exact cause of the vibrations.
  • Documentation: All vibration measurements and analyses should be carefully documented. This helps to track trends and enables effective maintenance planning.

Analysing vibration data can be very complex and require specialist knowledge and experience. It is therefore often advisable to consult an expert in vibration analysis. This ensures that the data is interpreted correctly and appropriate measures are taken.

As a general rule, the limit values of the international standard series DIN ISO 10816 / 20816 are used for this purpose. They depend on various factors, such as the type of machine, its size, speed and intended use. The exact limit values can be found in the respective parts of the standard series.

Here is an example of limit values for fans from DIN ISO 10816-3:

Small fans (e.g. axial or radial fans):

  • Velocity limit value for the effective value of the vibration velocity (rms): 1.0 mm/s
  • Velocity limit value for the peak value of the vibration velocity (peak): 4.0 mm/s

Medium-sized fans:

  • Velocity limit value for the effective value of the vibration velocity (rms): 1.4 mm/s
  • Velocity limit value for the peak value of the vibration velocity (peak): 5.6 mm/s

The frequency of vibration measurements varies. It depends, for example, on the type of system, the operating status, the previous maintenance history, the manufacturer's specifications or legal standards.  

The rule of thumb: preventive maintenance measures such as vibration measurements help to prevent breakdowns and extend the service life of systems. A regular review and adjustment of the maintenance schedule based on the latest operating data and experience is therefore recommended in any case.

A. Hock's services in the field of vibration measurement

Vibration measurement as a method of condition monitoring is essential to ensure reliability, efficiency and safety in industrial plants. A. Hock has products in its portfolio that provide reliable and accurate data especially for systems and motors with rotating masses, e.g. the Honeywell Versatilis™ HVT100 transmitter as a vibration sensor with modern LoRaWAN® protocol.

Finally, the end-to-end complete solution - the LoRaWAN easybox from A. Hock - provides a clear visualisation of the data. It supports advanced, condition-based maintenance.

Would you like to perform permanent vibration measurements on your components?

Do not hesitate to contact us.

Dominic Hock

Dominic Hock

Managing Director

I’m happy to support you with projects and enquiries in the field of valve technology as well as measurement and control technology. My areas of expertise are automation technology and networks.