IMC CANSAS - Sampling Intervals, Filters and Anti-Aliasing

UNI8: universal 425
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
6.20.11 Sampling intervals, filters and anti-aliasing
For each of the 8 channels, the sampling interval can be freely set to between 1 ms an 60 s. UNI8 come
with a hardware-based, permanent anti-aliasing filter (AAF), an analog-digital-converter (ADC) using the
sigma-delta method, and finally a digital low-pass filter adapted to the sampling rate.
The hardware-based AAF is suitable for the 1 ms input frequency. The digital low-pass filter is set to the
sampling rate and can be switched off on the card General of the UNI8. Alternatively to the digital AAF it
is possible to avoid noise simply by averaging through processing arithmetic mean function.
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 table below shows which resulting filter is used. For temperature measurement (Pt100 and
thermocouples):
Sampling rate
Filter
1 ms
Critical damping, 4th order, cutoff frequency 120 Hz
2 ms
Critical damping, 4th order, cutoff frequency 60 Hz
5 ms
Critical damping, 4th order, cutoff frequency 25 Hz
10 ms
Critical damping, 4th order, cutoff frequency 12 Hz
20 ms
Critical damping, 4th order, cutoff frequency 6 Hz
50 ms
Critical damping, 4th order, cutoff frequency 2 Hz
100 ms
Critical damping, 4th order, cutoff frequency 1 Hz
200 ms
Critical damping, 4th order, cutoff frequency 0.5 Hz
500 ms
Critical damping, 4th order, cutoff frequency 0.2 Hz
1 s
Critical damping, 4th order, cutoff frequency 0.1 Hz
2 s to 60 s
Arithmet. mean over the duration of the sampling interval of values sampled at 1 kHz