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7.2 Frequency selective characteristic values
For characteristic values designated by the "sel" code, you can define a frequency
band within a range. This is used for the value calculation.
In Trendline the low pass cutoff frequency up to which measurements are to be
taken is defined for each channel. The sampling rate is always 2.56 times the
value of this cutoff frequency. The time signal that is recorded in this way is used
to calculate a frequency spectrum by means of an FFT calculation. This is then
used to recalculate the characteristic values within the defined limits. An a
eff
value of between 2 kHz and 5 kHz is therefore calculated for a low pass filter
setting of 5 kHz, for example.
Characteristic value Analog channel
Frequency range
a
eff
Acceleration
2 kHz - low pass acceleration channel
a
sel
Acceleration
f
min_a
- low pass a (both frequencies adjustable,
see table below )
ISO 10816
Speed
10 Hz - 1 kHz
v
sel
Speed
f
min_v
- low pass v elocity channel (both frequencies
adjustable, see table below )
d
eff
Demodulation
f
min
- low pass demodulation channel
d
sel
Demodulation
f
min
- low pass demodulation channel (both
frequencies adjustable, see table below )
The low pass and FFT length can be adjusted for each channel. Both of these
factors affect the sampling rate, the minimum possible frequency and frequency
resolution.
Lowpass
Sampling
rate
FFT-length
f
min
f
min_v
)
Frequency resolution
200 Hz
512 SPS
1600 lines
0.125 Hz
0.375 Hz
0.125 Hz
200 Hz
512 SPS
3200 lines
0.1 Hz
0.19 Hz
0.0625 Hz
500 Hz
1.28 kSPS
1600 lines
0.3125 Hz
0.94 Hz
0.3125 Hz
500 Hz
1.28 kSPS
3200 lines
0.156 Hz
0.47 Hz
0.156 Hz
1 kHz
2.56 kSPS
1600 lines
0.625 Hz
1.875 Hz
0.625 Hz
1 kHz
2.56 kSPS
3200 lines
0.3125 Hz
0.94 Hz
0.3125 Hz
2 kHz
5.12 kSPS
1600 lines
1.25 Hz
3.75 Hz
1.25 Hz
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