Software filter

The EL9576 is equipped with a digital software filter which, depending on its settings, can adopt the characteristics of a Finite Impulse Response filter (FIR filter), or an Infinite Impulse Response filter (IIR filter). The filter is activated by default as 50Hz-FIR. If a filter is activated, it is active for the supply voltage and at the same time for the current through the external resistor.

In the respective measuring mode the filter can be activated (0x8000:02) and parameterized (0x8000:1A).

• FIR 50/60 Hz
  The filter 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 operates as a non-recursive filter.
  



• IIR-Filter 1 to 8
  The filter with IIR characteristics is a discrete time, linear, time invariant filter that can be set to eight levels (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.
  

Overview of conversion times

IIR filter Differential equation: Yn = Xn * a0 + Yn-1 * b1 with a0 + b1 = 1 a0 = (see table) b1= 1 - a0