Beckhoff EP3356-0022, Documentation

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Commissioning/Configuration
EP3356-0022 32 Version: 1.4
Measurement principle of delta-sigma (ΔΣ) converter
The measurement principle employed in the EP3356, with real sampling in MHz range, shifts alias-
ing effects into a very high frequency range, so that normally no such effects are to be expected in
the KHz range.
Averager
In order to make use of the high data rates of the Analog-to-Digital converter (ADC) even with slow cycle
times, a mean value filter is connected after the ADC. This determines the sliding mean value of the last 4
measured values. This function can be deactivated for each mode via the CoE object "Mode X enable
averager".
Software filter
The EP3356 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 50 Hz-FIR.
In the respective measuring mode the filter can be activated (0x8000:01, 0x8000:02) [
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66] and
parameterized (0x8000:11, 0x8000:12) [
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FIR 50/60 Hz
• The filter performs a notch filter function and determines the conversion time of the box. 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.
PDO filter
• The filter behaves like the 50/60 Hz FIR filter described above. However, the filter frequency can be
adjusted here in 0.1 Hz steps by means of an output data object. The filter frequency range extends
from 0.1 Hz to 200 Hz and can be reparameterised during operation. To do this the PDO 0x1601
(“RMB filter frequency”) must be displayed in the process data and the entry “PDO filter frequency”
must be selected in the object 0x8000:11. This function allows the EP3356 to suppress interference of
a known frequency in the measuring signal. A typical application, for example, is a silo that is filled and
weighed by a driven screw conveyor. The rotary speed of the screw conveyor is known and can be
adopted into the object as a frequency. Thus mechanical oscillations can be removed from the
measuring signal.
Fig. 22: Notch characteristic/amplitude curve and step response of the FIR 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.