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354 Properties of the Modules

6.16.6 Sampling intervals, filters and anti-aliasing

For each of the 8 fast pressure channels, the sampling time can be freely set to between 1 ms and 60s.

The pressure module comes with a fixed frequency hardware anti-aliasing filter, an analog-digital

converter (ADC) according to the Sigma-Delta method and a digital low-pass filter adapted to the

sampling rate.

On: Additional digital low-pass filter.

Off: Switch off the digital low-pass filter. The analog anti-aliasing filter takes always effect.

Mean value: The output value is averaged by (Sampling interval[ms] / 1 ms) samples.

The following table shows which resulting filter is to be used:

sampling rate

filter

1 ms

Critical damping, 4th order, cutoff frequency 250 Hz

2 ms

Critical damping, 4th order, cutoff frequency 120 Hz

5 ms

Critical damping, 4th order, cutoff frequency 50 Hz

10 ms

Critical damping, 4th order, cutoff frequency 25 Hz

20 ms

Critical damping, 4th order, cutoff frequency 12 Hz

50 ms

Critical damping, 4th order, cutoff frequency 5 Hz

100 ms

Critical damping, 4th order, cutoff frequency 2 Hz

200 ms

Critical damping, 4th order, cutoff frequency 1 Hz

500 ms

Critical damping, 4th order, cutoff frequency 0,5 Hz

Critical damping, 4th order, cutoff frequency 0,2 Hz

2s ..60s

arithmetic mean over the duration of the sampling interval of values sampled at 1 kHz

The filters are optimized to provide good suppression of interference while causing only insubstantial

signal surges in the time domain and only minor delay times. Note that the filters selected are not perfect

anti- aliasing filters (e.g. with damping of 96dB at one-half of the sampling frequency).

If you use a sampling interval other than 1 ms and the default filter is not suited to your measurement

requirements, simply select 1 ms as the sampling interval and then arrange the appropriate low-pass

filtering or averaging by means of a virtual channel.

The frequency response only pertains to the device's electrical portion. The frequency response of the

sensors themselves and of their leadwires is not accounted for.

IMC CANSAS User Manual

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