Beckhoff ELX3351, Operating Manual

Page: 35 / 71

Parameterization and programming
ELX3351 35 Version: 1.3.1
5.1.2 Block diagram
Fig. 27: ELX3351 - Block diagramm
The ELX3351 processes the data in the following order
1. Hardware low-pass 3.6 KHz
2. 2-channel simultaneous sampling by delta-sigma (ΔΣ) converter and internal prefiltration
3. Software filter (can be deactivated)
4. Calculating the weight
Note
Measurement principle of delta-sigma (ΔΣ) converter
The measurement principle employed in the ELX3351, with real sampling in the MHz
range, shifts aliasing effects into a very high frequency range, so that normally no such ef-
fects are to be expected in the KHz range.
5.1.3 Software filter
The ELX3351 is equipped with a digital software filter which, depending on its settings, can adopt the
characteristics of a
F inite I mpulse R esponse filter ( FIR filter ), or an I nfinite I mpulse R esponse filter ( IIR filter ).
The filter is activated by default as 50Hz-FIR .
In the respective measuring mode the filter can be activated ( 0x8000:01 [
}
60] , 0x8000:02 [
}
60] ) and
parameterized ( 0x8000:11 [
}
60] , 0x8000:12 [
}
60] ) (the ELX3351 supports only mode 0).
• FIR 50/60 Hz
The filter performs a notch filter function and determines the conversion time of the terminal. The
higher the filter frequency, the faster the conversion time. 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.
Fig. 28: Notch characteristic/amplitude curve and step response of the FIR filter