X90 mobile modules
X90 mobile system User's manual V 1.20 - Translation of the original manual
175
5.4.1.5.7.3 Crest factor
The crest factor is defined as a the quotient derived from the peak value and the RMS value. In a sinusoidal
oscillation, this factor amounts to
√
2. This value is also known in electrical engineering as the crest factor.
In a bearing that is operating normally, the crest factor is also approximately the value
√
2. If the condition of the
bearing deteriorates, individual impacts affect the peak value and consequently raise the crest factor. If pronounced
defects are then compounded by overall wear, the RMS value in increased further. In the worst case, the crest
factor can remained unchanged or even sink again, even despite increasing damage.
1.4
Crest factor
RMS value
Peak value
Crest factor
Progressing damage/time
Figure 38: Relationship between the RMS value and peak value
Information:
When a recording of the crest factor is made, the peak and RMS values should also be recorded.
CrestFactorHighFrequency
Name:
CrestFactorHighFrequency01 to CrestFactorHighFrequency04
Registers for reading the raw value ratio of the absolute maximum (
"PeakHighFrequency" on page 171
) to the
RMS value (
"RmsHighFrequency" on page 173
) of the respective channel.
CrestFactorHighFrequency is formed from the high-pass filtered input signal of the oscillation acceleration in the
frequency domain between the value set in register
"HighFrequencyConfig" on page 185
and 10 kHz.
Format
Unit
REAL
1
CrestFactorRaw
Name:
CrestFactorRaw01 to CrestFactorRaw04
Registers for reading the raw value ratio of the absolute maximum to the RMS value of the respective channel.
CrestFactorRaw is formed from the raw signal of the oscillation acceleration up to the maximum frequency config-
ured in register
"MaxFrequencyRaw" on page 186
.
Since this register value is divided by the RMS value in the module (
"RmsRaw" on page 174
), there may be an
overflow if the RMS value is very small. To prevent this, the module has an internal lower limit of 1 mg for the
RMS value.
Format
Unit
REAL
1