Beat the ‘‘Beating Phonemonen’’ with Time Synchronous

Yusuf İHTİYAROĞLU

Özgün YAKAR

Bowl

Scroll Conveyor

•If two vibration components are quite close together in frequency, they will combine in such a way that their sum will vary in level up and down at a rate equal to the difference in frequency between the two components. This phenomenon is known as beating, and its frequency is the beat frequency. Beating phenomenon can be seen on machines working on the same bases and transmitting their vibrations. Pumps and fans working on same base plate can be shown as examples for beating phenomenon. Also, 2X and 2xLF frequencies can be beat on 2 pole asynchronous motors.

•A decanter centrifuge (also known as solid bowl centrifuge) separates continuously solid materials from liquids in the slurry, and therefore plays an important role in the wastewater treatment, chemical, oil and food processing industries. The horizontal decanter centrifuge is a dual rotor system with small rotating speed difference, of which unbalanced vibration is a "beat" signal.

•The balancing job of the decanter parts is generally carried out with balancing machines because of beat signals makes stronger field balancing. This conditions increase the downtime during corrective actions of unbalance conditions.

•Beating phonemenon can be detected two vibration peaks which, frequencies and amiplitudes are quite close on spectrums. The amplitudes are decrease and increase periodically on time wave forms. This is called beat frequency.

•Amplitudes and phase is change dramatically under beating vibration. Therefore field balancing (with influence coeefinicent method) is so hard under beating.

•Linear, exponantial and peak hold averaging methods are calculated from spectrums to smoothing out random noise in a spectrum making discrete frequency componenets easier to see.

•Another type of averaging which is important in machinery monitoring is time synchronous averaging, which requires a tachometer to synchronize each "snapshot" of the signal to the running speed of the machine. Time domain averaging is very useful in reducing the random noise components in a spectrum, or in reducing the effect of other interfering signals such as components from another nearby machine. Asynchronous vibrations like bearing faults, 2xLF or resonance vibrations will not seen on spectrums after time synchronous averaging. Therefore, time synchronous averaging shouldn’t use for route measurements. It’s very useful method for vibration measurements of gearboxes.

•Single plane balancing job has been carried on a horizontal decanter machine with Vibxpert II and time synchronous averaging in this study.

a)Linear Averaging

b)Tme Synchronous Averaging

•Field balancing attempt without using time synchronized averaging; phase and amplitude constantly vary. Therefore, field balancing becomes impossible.

•Field balancing using time synchronized averaging; phase and amplitude stabilize after increasing number of averages and balance job can be completed.

•Velocity Spectrums of decanter for before and after field balancing job.

•Field balancing report;