X90 mobile modules
X90 mobile system User's manual V 1.20 - Translation of the original manual
155
5.4.1.5.3.3 Frequency bands
It is possible to individually configure up to 32 frequency bands where the RMS value (RMS) or the noise of a
quadrant is calculated.
Parameter
Settings
Enable
Off | RMS | Noise
Channel
1 | 2 | 3 | 4
Source
Raw acceleration signal | Raw velocity signal | Enveloped acceleration signal | Enveloped velocity signal
Calculation of harmonics
(RMS only)
Yes | No
Rotation-dependent
(RMS only)
Selects the data point for velocity (
see "ActSpeed" on page 156
)
[1/100 Hz]
Standardized damage frequency at 60 rpm
[1/100]
On
± Width of the frequency band (tolerance band)
[1/100 Hz]
Lower frequency
[1/4 Hz]
Off
Upper frequency
[1/4 Hz]
Quadrant (noise only)
1st quadrant | 2nd quadrant | 3rd quadrant | 4th quadrant
5.4.1.5.3.4 Calculating the velocity signal automatically
The module can calculate the velocity signal from the signal provided by the acceleration sensor. This calculation
is disabled by default since it can reduce the accuracy of the acceleration signal.
Reason
When converting from acceleration to velocity, low frequency portions become very large. As a result, the
"autogain"
is decreased by a few levels, which then further degrades accuracy.
If this calculation is not enabled, 0 is output for all characteristic values calculated from the velocity spectrum.
Characteristic value
"Iso10816" on page 172
is not affected by this.
5.4.1.5.3.5 Autogain, AutogainDelay and overflow
The module automatically adjusts the measurement signal dynamically (autogain) to ensure that it is measured
with the highest possible accuracy. This adjustment is made in multiple steps. Each step amplifies the input signal
more than the last. If the signal was very small for a long time and a impact suddenly occurs, an overflow may
occur with some calculated characteristic values. This is indicated by the overflow bit for the respective channel
(Overflow01-04 in register
"Status" on page 159
) being set and the affected module characteristic values being
set to their maximum.
Registers
"OverflowCharacteristicValues" on page 167
and
"OverflowFrequencyBands" on page 168
are auto-
matically generated by Automation Runtime and directly indicate the overflow status of the individual characteristic
values and frequency bands.
If an overflow occurs or if an internal threshold is exceeded, the autogain for the next measurement is reduced by
one level. If no overflow occurs for a certain number of measurements (configurable using register
"AutogainDelay"
on page 156
), or the signal stays below the internal threshold, the autogain is increased by one level again.
If overflows are occurring frequently, increasing AutogainDelay may help.
5.4.1.5.3.6 Term definition: Sampling rate and sampling frequency
The terms sampling rate and sampling frequency are used in this document. The following is a definition of these
terms:
Term
Definition
Sampling rate
Number of times an analog signal is sampled per unit of time. The unit of time is generally 1 second.
Example: 100 samples per second
Sampling frequency
Sampling of an analog signal with respect to 1 second. Specified in Hertz [Hz].
Examples:
•
Sampling an analog signal once per second corresponds to a sampling frequency of 1 Hz.
•
Sampling an analog signal once per millisecond corresponds to a sampling frequency of 1 kHz.
