Averaging
Averaging is another feature provided in analyzers/data collectors. The purpose is to obtain more repeatable results, and it also makes interpretation of complex and noisy signals significantly easier. There are various types of averaging:
• Linear averaging
• Peak hold
• Exponential
• Synchronous time averaging.
Linear averaging
Each FFT spectrum collected during a measurement is added to one another and then divided by the number of additions. This helps in obtaining repeatable data and tends to average out random noise. This is the most commonly used averaging technique. The spectra are typically averaged 2, 4, 8, 16 or 32 times, but any number could be used.
Peak hold
With this method, the peak value in each analysis cell is registered and then displayed. In other words, it develops an envelope of the highest spectral line amplitude measured for any average. This technique is used for viewing transients, such as coastdowns or random excitations that may be required during stress analysis studies.
Exponential
In this method, the most recent spectra taken are considered to be more important than older ones, and thus given more mathematical weight when adding and averaging them. This is used for observing conditions that change very slowly with respect to sampling time.
Synchronous time
This method uses a synchronising signal from the machine under investigation, and is used for averaging in the time domain. The synchronising signal is usually in the form of a pulse generated by a photocell or an electromagnetic pickup at a reference position on the shaft circumference. The vibration samples can in this way be taken at the same instant with respect to shaft rotation during averaging.
Non-synchronous vibrations in the system are effectively nullified by this method. The method is generally used if a machine has many rotational components rotating at different speeds. Thus, the vibrations synchronous with the synchronising signal are emphasized while others are averaged out.
Averaging is another feature provided in analyzers/data collectors. The purpose is to obtain more repeatable results, and it also makes interpretation of complex and noisy signals significantly easier. There are various types of averaging:
• Linear averaging
• Peak hold
• Exponential
• Synchronous time averaging.
Each FFT spectrum collected during a measurement is added to one another and then divided by the number of additions. This helps in obtaining repeatable data and tends to average out random noise. This is the most commonly used averaging technique. The spectra are typically averaged 2, 4, 8, 16 or 32 times, but any number could be used.
Peak hold
With this method, the peak value in each analysis cell is registered and then displayed. In other words, it develops an envelope of the highest spectral line amplitude measured for any average. This technique is used for viewing transients, such as coastdowns or random excitations that may be required during stress analysis studies.
Exponential
In this method, the most recent spectra taken are considered to be more important than older ones, and thus given more mathematical weight when adding and averaging them. This is used for observing conditions that change very slowly with respect to sampling time.
Synchronous time
This method uses a synchronising signal from the machine under investigation, and is used for averaging in the time domain. The synchronising signal is usually in the form of a pulse generated by a photocell or an electromagnetic pickup at a reference position on the shaft circumference. The vibration samples can in this way be taken at the same instant with respect to shaft rotation during averaging.
Non-synchronous vibrations in the system are effectively nullified by this method. The method is generally used if a machine has many rotational components rotating at different speeds. Thus, the vibrations synchronous with the synchronising signal are emphasized while others are averaged out.
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