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number of analysis lines. If the generated frequency cannot be predicted, measure the frequency roughly with
high frequency span at first, then set the frequency span and the number of analysis lines so that the
frequency resolution becomes narrower than 1 Hz.
⑥
Setting the Operation type
In the Instantaneous measurement, it is not necessary to set the operation type. In the measurement with
operation function, it is necessary to select the operation type. Then press the INST/AVE key, and press the
START/STOP key.
In order to select the operation type, presses the MENU key, then go into the submenu [FFT] from the Menu
List, and set the Operation type and the Average number.
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Instantaneous measurement
FFT spectra are continuously displayed without averaging. It is used when grasping the characteristics of
phenomenon by observing the time variation of the spectrum, or when the average is not necessary since
the vibration is steady.
The operation type is chosen as follows according to the measurement purpose.
◆
Linear average
It is a popular averaging type, and is used to obtain the arithmetic averaged result. The operation stops
when the number of measured data reaches to the Average number set in the submenu [FFT].
◆
Exponential average
FFT spectra are continuously displayed with a time constant. When amplitude of vibration changes
violently, the averaged amplitude becomes smooth. It is used when grasping the characteristics of
phenomenon by observing the time variation of the spectrum. If an impulsive vibration occurs, you may
miss it in Instantaneous measurement. However you will not miss it in exponential average, since the time
constant keeps the influence of the impulsive vibration for a while.
◆
Maximum hold
It is used when obtaining the maximum value of each frequency component. The operation stops when the
number of measured data reaches to the Average number set in the submenu [FFT].
Setting the Operation type
Setting the Average number