# Standard filters

Up to 3 axis filters can be connected in series and parameterised for each axis. A filter is active when the filter[i].enable parameter is set to 1 and the value of the filter[i].order parameter is > 0. In addition, 1 filter for each filter can be parameterised for the additional interface.

The operating principle of standard filters can be controlled by using the following CNC objects in the GEO task:

Name | Index-Group | Index-Offset | Data type | Description
Active position | 0x121300 +<ch_id> Example Channel 1: 0x121301 | 0x61 +0x10000*<ax_idx> Example 1 Axis: 0x10061 | SGN32 | ACS command position unfiltered [unit 0.1µm or 10^-4°]
Ft_sollwert_gestern | 0x121300 +<ch_id> Example Channel 1 0x121301 | 0x1C +0x10000*<ax_idx> Example 1 Axis 0x1001C | SGN64 | ACS command position after filter cascade [unit 0.1µm or 10^-4°]

<ch_id> channel ID, <ax_idx> Axis index in the NC channel

The following standard filters are available:

- Low-pass filter
  All frequencies below a certain cut-off frequency are passed through the filter. Higher frequencies above this cut-off frequency are attenuated or are not passed through at all. High frequencies are filtered out.
- High-pass filters
  Lower signal frequencies are attenuated or are not passed through at all. Only frequencies above a cut-off frequency are transmitted unchanged.
- Band-stop filters
  One frequency range out of the transmit frequency range is filtered out. All other frequencies are transmitted almost without attenuation. The characteristic frequency is called the centre frequency.
- Band-pass filters
  All frequencies except for the chosen frequency band are filtered out. All other frequencies are attenuated.
- All-pass filters
  These filters have constant gain but generate a frequency-dependent phase shift. They are used for phase correction and to delay signals.
- PT1 filters
  A PT1 filter is a first-order delay element that has a transmission response similar to that of a first-order low-pass filter. The filter transmits frequencies under the cut-off frequency fg = 1 / (2 * Pi * filter[i].time_constant). Frequencies > the cut-off frequency are attenuated at –20 dB/decade.
- PT2 filters
  A PT2 filter is a 2nd order delay element whose transmit function G(s)=1/(1+Ts)2 corresponds to two first order delay elements switched in series. The transmission response is similar to a second-order low-pass filter. Frequencies up to a cut-off frequency of fg = 1 / (2 * Pi * filter[i].time_constant) are transmitted by the filter but higher frequencies are attenuated at –40dB/decade.
- Time delay filters (as of CNC Build 2013, 2803 or 3013)
  A time delay filter can delay the signal time signature. This does not change the signal profile.

## Additional information

- Low-pass filters
- High-pass filters
- Band-pass filters
- Band-stop filters
- All-pass filters
- PT1-filter
- PT2-filter
- Time delay filter