Filter

Filter operation (FIR and IIR), index 0x80n0:06, 0x80n0:15

The EP31xx modules incorporate a digital filter which, depending on its settings, can adopt the characteristics of a Finite Impulse Response filter (an FIR filter), or an Infinite Impulse Response filter (an IIR filter). The filter is deactivated by default. Please observe the following note regarding activation with index 0x8000:06.

Activation of the filter (index 0x8000: 06), setting of the filter properties (index 0x8000:15) The filter frequencies are set centrally for all channels of the EP3xxx modules via index 0x8000:15 (channel 1). The corresponding indices 0x80n0:15 of the other channels have no parameterization function.

FIR filter

The filter is a non-recursive notch filter. You can set the filter via the CoE parameter 0x8000:15. The following filter frequencies are available:

• 50 Hz
• 60 Hz

The filter determines the cycle time of the EtherCAT Box in synchronization mode "Free Run":

A notch filter has zeros (notches) in its frequency response at the filter frequency and multiples of the filter frequency. These frequencies are therefore attenuated in amplitude.

Typical attenuation curve of a notch filter with 50 Hz filter frequency

IIR filter

The filter with IIR characteristic is a time-discrete, linear, time invariant filter. It can be adjusted in 8 levels:

• IIR 1 = weak recursive filter
• …
• IIR 8 = strong recursive filter

An IIR filter can be understood to be a sliding mean value calculation after a low pass.

If the IIR filter is activated, the EtherCAT Box runs in synchronization mode "Free Run" with the following cycle time:

The cycle time is independent of the number of activated measuring channels when the IIR filter is activated. You cannot shorten it by disabling channels.

Filter characteristics for IIR filters