Overall Measurement - Adash 4400 VA4 Pro User Manual

ADASH Ltd. Adash 4400 – VA4Pro

Overall measurement

This is typical example of overall measurement. The RMS value of vibration velocity in frequency range 10-1000
Hz is measured.
The first row contains used parameters. The 25.1Hz on the right is the speed, because the tacho sensor was
used.
Change the Detect Type to 0-P.
Note, that the 1.98 is not 1.414 times bigger then 0.570. Some of users mistakenly think, that the formula 0-
P=1.414*RMS is valid for every signal. It is not true. That formula is valid only for pure sine wave ! The true
RMS and true peak measurement are generally independent. The only rule is that the peak value is always
bigger then RMS value.
Let's change the Avg to 8. The eight individual values (1 sec length) will be taken and the result will be the linear
average of them ( RV = (V1+V2+...+V8)/8). The indication 8/8 is on the right top.
Let's change the Avg back to off and change the samples number to 32768. The measurement will be 8 sec
long.
You see that the result is different from the previous value. It is clear, the max 0-P value in 8 sec signal is not
equal the average of 8 0-P values ( which takes 1 sec each).
Let's change the type back to RMS.
Now change the length to 1 sec (4096 samples) and Avg=8.
You see the same result. Both values are equal. The meaning of RMS differs from peak values. The RMS value
depends only of total time of measurement. It does not care if one long signal was taken or several shorter
signals were averaged.
You can define the signal length also in revolutions, not only in samples (=time). The tacho signal must be
available in that case.
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