Signal processing
7.2 Universal input evaluation
SITRANS DA400 for material flow monitoring with protection against explosion
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Operating Instructions, 09/2007, A5E00841152-01
7.2
Universal input evaluation
7.2.1
Universal input evaluation overview
Essentially, the four universal inputs are evaluated according to the same principle, with the
only differences being in the signal names and/or the associated parameters.
The wiring and configuration (P.26 to P.29) should be adapted for the relevant signal type.
7.2.2
Evaluation of analog current signals
Relates to parameters
Parameter no.
Parameter name
Adjustment/display
range
Comment
P.26 to P.29
"INP1" to "INP4"
0-20
4-20
20-0
20-4
Analog signal 0 to 20 mA->0 to 100%
Analog signal 4 to 20 mA->0 to 100%
Analog signal 20 to 0 mA->0 to 100%
Analog signal 20 to 4 mA->0 to 100%
P.30 to P.33
"ALI1" to "ALI4"
-5.0% to 105.0%
Alarm for universal inputs 1 to 4
Procedure
The analog current signal is changed by internal measurement resistance into a voltage that
is strengthened, filtered, and changed via an analog-digital exchanger into a digital signal.
This measured value passes through a low pass filter with a fixed time constant. The
measured value is then monitored for under and overflow, which is used to derive a fault
message if appropriate. The following standardization is performed depending on the setting
for the selected parameter:
P.*
0 %
100%
0 to 20
0 mA
20 mA
4 to 20
4 mA
20 mA
20 to 0
20 mA
0 mA
20 to 4
20 mA
4 mA
The percentage value obtained can then be displayed. It is then monitored to see if it
exceeds the associated alarm "P.30/ALI*" to "P.33/ALI*". The digital signal "dol*" is then
obtained. If the state is "0", the symbol (alarm not received) is displayed, if the state is
"1", the symbol (alarm received).
