In an industrial system, it is vital to regularly monitor machines to avoid any serious injuries and costly downtime. At the same time, monitoring mission-critical machines becomes a priority, as they may include machinery items that need lengthy and costly repairs if they break down.
How Does Vibration Measurement Equipment Work?
Machine vibrations are measured using sensors. You can assess its vibration patterns and behaviors to gauge its efficiency. Though there are many types of vibration sensors available, the accelerometer is the most commonly used device due to its many benefits. And not without many benefits.
First, it creates an electrical signal in proportion to the accelerating component that vibrates. Second, the signal created by the accelerometer transfers to the instrument, which turns it into a velocity waveform, or spectrum. The acceleration created is defined as the speed of velocity made by the component.
Source: Magnetic Bearing
Mounting Techniques for the Accelerometer:
Most industrial equipment works with a rotary mechanism in compressors, motors, gearboxes, pumps, fans, and other machines. Most machines integrate with bearings to support the weight exerted by rotational components. They withstand the pressure associated with vibration and rotation. Bearings are vulnerable to damage due to their constant use. Therefore, vibration measurements required in the rotary fittings of industrial machines need to be robust. For accuracy in measurements, you should mount the accelerometer carefully using the right techniques as detailed below:
|Mount Near the Bearing||Install an accelerometer closely near the bearing. Attach it as close as possible to the bearing’s center to avoid distortions.|
|Ensure Tight Connection||If you want to measure the exact vibration pattern of a component, it is important that an accelerometer follows a similar vibratory motion. It should be attached tightly to the component. Consider mounting with the help of a magnet to ensure proper balance between convenience of usage and reliability of measurement data.|
|Ensure Proper Orientation of Accelerometer||When you need to detect parallel misalignments, this device should be mounted in a radial direction. Typically, the vibration signals depend on orientation of accelerometer because vibratory force may be different in each direction.|
|Maintain Same Device for a Particular Location||To minimize inconsistencies in measurement and errors in results, you should always mount an accelerometer in the same place. It’s best to keep one vibration sensor on the same machine in the same location,|
|Mount on a Firm Structure||Never mount the accelerometer on a flexible location where the spectrum is prone to distortions caused by flapping of the component. Also, avoid mounting it on lightweight structures that can affect the behavior of vibration due to weight of device and magnets used for installation. The weight of the accelerometer should be at least 10% lesser than the weight of the structure on which it is mounted.|
Precautions to Take When Installing an Accelerometer:
If you want to capture accurate, reliable vibration signals, it is important to install the accelerometer at a proper location using the right techniques.
- Device Safety:
The device installed is important because the magnetic mount can largely affect its performance. An installation with a tilted magnetic mounting delivers better results. When detaching the mounting, you should avoid breaking contact by using the accelerometer. The ideal approach is to hold the mounting tightly and tilt it sideways for breaking contact with the device. Do not twist the cable of the accelerometer. A twisted cable may cause distortions in the vibration spectrum measured by the device.
- Personal Safety:
When measuring vibrations, operators are also at a consistent risk due to hazards caused by electric shocks, magnetic force, and moving parts. During installation, prevent entanglement of cables with moving parts. Also, avoid intertwining cables with machinery. Do not wear loose clothes, as it may pose several hazards. An electric shock can happen when the accelerometer is attached to a high voltage surface, so you should avoid this. Finally, do not install the magnetic mounting near objects that are sensitive to magnetic forces.
Setting Measurement Parameters
The process of measuring vibrations in a machine requires accurate and precision driven parameters. These parameters help in collecting relevant data by processing it the right way. Implementation of correct spectrum measurement techniques sets these parameters helps. Here’s an example :
Begin with a simple instrument, like Commtest vb, for monitoring vibration in a system. A default parameter should be taken for measuring the vibrations. This helps in preventing adjustments that may be required for default parametric values. The vb instrument will have these parameters displayed on its screen. Here, consider four main classes used for measuring the spectrum of vibrations. They include:
- Method of Data Collection:
Typically, Trigger Types is a form of parameter determining a data collection method. This device measures continuously if set at Free Run, ensuring a single measurement cycle. Under the Sensor Setup tab, parameters define the type of accelerometer. When using vb kit, you may need an ICP-type accelerometer. In this setup, you should turn on the drive current and match sensitivity of accelerometer with the figures given on Quality Assurance Card of vb kit. Similarly, use default setting time in this device to maintain accuracy of results.
- Speed and Amount of Data Collected:
Measuring speed and amount of data collected involves parameters like Overlap Percentage, F-max, and Spectral Lines. The range of frequency varies with F-max. If it is higher, the instrument will gain more speed. The spectral lines affect amount of information collected by the device. More lines translate into more data that’s required. Ideally, you should use F-max value up to 10 times of operating speed required for collecting the desired information. For spectral lines, 400 is the ideal figure and 50% overlap is sufficient to calculate spectrum accurately.
Source: Acceleration Data
- Method of Data Processing:
Method of data processing depends on parameters such as Window Type, Average Type, and Number of Averages. At the time of measuring the vibration, several spectra calculates their average and takes the average of the entire spectrum. A better measure of vibration behavior reduces random distortions and sound spikes integrally found in vibrating machinery. The average spectra calculates with Average Type. In this calculation, linear averaging uses for most cases. However, if vibratory pattern differs significantly over a set period of time, you can use the exponential averaging method.
The Number of Averages is a parameter to measure the consecutive spectra for calculating averages. When the number of averages is large, more data included may increase the time take to obtain average spectrum. Ideally, stick to the figure of 4 for the number of averages.
Also, use Window-Type parameters to use the right type of window for calculations.
- Display of Data Collected:
First of all, parameters used for displaying spectrum details measures as per a parameter called as the Display Unit. The display of spectrum specifies as per the scale required. This scale of spectrum defines using parameters like log range, velocity max, amplitude scale, and vdB references. If you use linear amplitude scale, you don’t need to factor in log range and vdB reference. Select a proper amplitude scale by using the Velocity max parameter.
Second, data should be clearly specified beforehand. The two main types of amplitudes using these systems are: the rms amplitude and the peak amplitude. When you use peak amplitude, it displays a spectrum that represents maximum speeds gained by a component at varying frequencies while rms amplitude displays indicative energies at varying vibration frequencies.
As a result, to avoid any misinterpretations in vibration measurements, work on the same amplitude type to define measurements points. When you switch over to peak amplitude from rms amplitude, it creates an apparent surge in vibration leading to damages in machines. Alternatively, switching to rms amplitude from peak amplitude may not represent accurate information regarding vibration behavior.
As a matter of practice, clearly define both the units. For frequency and amplitude measure spectrum of vibrations as it may also differ based on the geographical locations. For example, velocity measured in terms of in/s and frequency measured as kilocycles per minute (kcpm) is common in North America. But, they represent as mm/s and Hz respectively in many other parts of the world.
Make Your Vibration Equipment Work With Machine Saver
Let us know about your application by consulting with the Machine Saver team at firstname.lastname@example.org. Our team can provide vibration monitoring solutions and benefits for your present application and extend their vibration expertise and new technology to your entire balance of plant. Call us at +1-832-471-8145 to learn more.
How Is Vibration Measured | Machine Saver