Copyright © Sigicom AB 2019
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3.2.3.
Frequency Detection, Weighting and Trigger filter
Certain standards have a second channel of interval data containing the
frequency of the maximal vibration level
during the interval time. See
Appendix G for a list of standards with this second channel.
These standards may also include a number of frequency weighting
models. A frequency weighting model affects the transient triggering
system, and also implies a recalculation of the interval data according to
the corresponding weighting algorithm. Standards with this functionality
are listed in Appendix H. Tables of Weighted Standards.
A frequency weighting model is selected using the last two characters in
the Node ID Text, see section 4.1.6 and Appendix H for possible
selections.
Note! If the last two characters of the Node ID Text are set to something
else, no weighting is performed. (The first two characters are free to use
as you wish; marked with ** in the tables).
Description of the detection algorithms:
1.
Detect all zero crossings in the vibration level signal.
2.
For each zero crossing, calculate the frequency based on the
number of samples since last zero crossing.
3.
Depending on weighting model, recalculate the maximum
vibration level value within the half period.
4.
Check if the new weighted value is larger than last saved
maximum in the interval.
More facts about standards with weighting model:
•
Transient files are not affected by the weighting.
•
The trigger system uses weighted data, see a descriptive example
in Appendix I.
Note! The trigger event is delayed until the zero crossing after
the signal maximum.
•
Direct SMS messages or INFRA Server messages sends
weighted vibration level values.
•
The log file still contains the unweighted vibration level, and
considers only post-trig data.
