ETAS
Hardware Description
ES411.1 - User Guide
22
5.3
Sensor Channels
All sensor channels of the ES411.1 are identical. Every sensor channel consists
of the function groups Signal Processing and Filter as well as Sensor Power
Supply.
5.3.1
Signal Processing and Filters
Fig. 5
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3
Signal Processing and Filters of a Sensor Channel
The level of the input signal is limited in every sensor channel after the overvolt
-
age protection by a capacitively compensated voltage divider. An amplifier
adjusts the input signal to the following analog anti-aliasing filter according to
the selection of the input voltage range. This 4th order analog filter with Butter
-
worth characteristics and a cutoff frequency of 10 kHz can be bridged with a
bypass switch.
An A/D converter digitizes the output signal of the analog filter. The individual
A/D converter available in every sensor channel guarantees synchronous sam
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pling of the measure signals.
A digital filter then processes the digital signal. The digital filter can be config
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ured in the application program. The data is written to a data buffer at the out
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put of the digital filter. It can be queried there by the application program.
Compensating Group Delay
The group delay is the time it takes the input signal of an analog or digital filter
to pass the filter. In the application program (e.g. INCA MDA), the signal must
be delayed to compensate for the group delay.
A special feature of the ES411.1 is the compensation of the group delay within
the module. The group delays of the analog anti-aliasing filter and the configu
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rable digital filter are taken into consideration in this process. The signal in the
application program (e.g. in MDA) no longer has to be delayed to compensate
for the group delay.
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