Filter 1 (low-pass filter)
A digital filter with predefined properties is available in the analog channel. Depending on the setting, it can take on the characteristics of a filter with finite impulse response (FIR filter) or with infinite impulse response (IIR filter).
This filter works on the integer values and is therefore independent of the interface.
In CoE 0x90n0:1B Sampling Rate the current conversion rate is displayed in [Hz], depending on the filter setting.
The filter can be set per channel via CoE object 0x80n0:15 Filter 1 Settings. The filter is disabled via the selectable value "None".
Filter type | Name | 0x80n0:15 (Dec) |
|---|---|---|
FIR | 50 Hz FIR | 0 (default value) |
FIR | 60 Hz FIR | 1 |
IIR | IIR 1 | 2 |
IIR | IIR 2 | 3 |
IIR | IIR 3 | 4 |
IIR | IIR 4 | 5 |
IIR | IIR 5 | 6 |
IIR | IIR 6 | 7 |
IIR | IIR 7 | 8 |
IIR | IIR 8 | 9 |
- | None | 65535 |
FIR filter
The filter with FIR characteristics operates as a notch filter. A 50 Hz and a 60 Hz filter are available. Notch filter means that the filter has zeros (notches) in the frequency response at the filter frequency and multiples thereof, i.e. it attenuates the amplitude at these frequencies. The FIR filter works as a non-recursive filter.
Fig.21: FIR 50 Hz filterIIR filter
The filter with IIR characteristic is a time-discrete, linear, time-invariant 1st order low-pass filter (-20 dB/decade), which can be set in 8 levels, i.e. cut-off frequencies (level 1 = weak recursive filter, up to level 8 = strong recursive filter). The IIR can be understood to be a moving average value calculation after a low-pass filter.
IIR filter | Cut-off frequency (-3 dB) |
|---|---|
IIR 1 | 1 kHz |
IIR 2 | 500 Hz |
IIR 3 | 285 Hz |
IIR 4 | 142 Hz |
IIR 5 | 66 Hz |
IIR 6 | 33 Hz |
IIR 7 | 17 Hz |
IIR 8 | 8.2 Hz |
Fig.22: Comparison of square wave signal 0.2 Hz/4.5 V, EtherCAT cycle time 100 µs, left filter disabled, right IIR8