ETAS
Hardware Description
ES413.1 - User’s Guide
22
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.
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
-
pling of the measure signals.
A digital filter then processes the digital signal. The digital filter can be config
-
ured in the application program. The data is written to a data buffer at the out
-
put of the digital filter. It can be queried there by the application program.
4.3.1.1
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 ES413.1 is the compensation of the group delay within
the module. The group delays of the analog anti-aliasing filter and the configu
-
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.
4.3.1.2
Setting the Filter
For an overview of the possible settings and details of the technical data of the
digital filter, please refer to section 7.8.5 on page 66.
4.3.1.3
Digital Filter Configuration Recommendations
The -3 dB cutoff frequency of the digital filter system of the ES413.1 can be
configured in the application program.
To avoid aliasing effects, be sure to observe recommendations for the configu
-
ration of the filter depending on the selected INCA sampling rate. The following
table contains the relevant notes.
4.3.2
Galvanically Isolation
The sensor channels are galvanically isolated from each other and from the
power supply. The digitized transfer of the measurements on an Ethernet con
-
nection implicitly results in a separation of the sensor channels from the supply
voltage.
Symbol
Meaning
Setting
f
C,AAF
-3 dB cutoff frequency HW anti-
aliasing filter
10 kHz (fixed)
f
S,AD
Sampling rate of the A/D con
-
verter
40 kHz
f
C,FIR
-3 dB cutoff frequency FIR filter
(settable)
Recommendation:
f
C,FIR
0.4 * f
S,INCA
f
S,INCA
INCA sampling rate
Configuration in the application
program