Bosch DDU 9 Manual page 90

12 | Analog and Frequency Inputs
12.2.5 Digital filter details
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DDU 9 uses A/D converter oversampling and digital filtering to recording rate.
Digital filters eliminate 'out-of-band' noise
Cut-off frequency automatically adjusted to recording rate
Example:
– 100 Hz recording rate (10 ms)
– <40 Hz pass band (>99 %)
– >50 Hz stop band (<1 %)
Linear phase – no signal distortion
10000Hz Abtastrate
2
1.5
Wert
1
0.5
0
-0.5
-1
-1.5
-2
0 500 1000 1500 2000 2500 3000
Abtastwerte (roh)
Sensor signal with noise
Latency compensation – no filter delay in recorded data
– Filtering is (smart) averaging over several samples
– Filtered signal is delayed with respect to real time signal
DDU 9
100Hz Abtastrate
1.5
1
Wert
0.5
Recorded signal 100Hz
0
(unfiltered)
-0.5
-1
-1.5
0 5 10 15 20 25 30
Abtastwerte (dezimiert)
100Hz Abtastrate
1.5
1
Wert
0.5
Recorded signal 100Hz
0
(filtered)
-0.5
-1
-1.5
0 5 10 15 20 25 30
Abtastwerte (gefiltert)
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