Evaluating And Processing Signals; Evaluation Of Acoustic Channels - Siemens SITRANS DA400 Operating Instructions Manual

Evaluating and processing signals

7.1

Evaluation of acoustic channels

Essentially, the four sensor inputs are evaluated according to the same principle, with the
only differences being in the signal names and/or the associated parameters. If a channel is
disconnected due to its configuration (P.1, P.2, P.3 or P.4 set to "oFF"), the measured value
is set to "0" and no alarm is generated.
The electrical signals from the sensors are amplified, filtered and converted into a digital
signal by an analog-digital converter.
This signal is used to determine the sound level. At the same time, the sensors are
monitored for faults.
In case of a sensor fault, a substitute value of 0 ("on L") or 10000 ("on H") is set, depending
on the configuration. If 10000 is selected, this also generates the alarm for the channel with
the fault in addition to the buzzer fault signal. The measured value is then monitored by a
limit sensor with hysteresis against a pre-alarm "PrAL*" and a main alarm "AL*".
The result signals "PrAL*" and "AL*" are used for evaluation by various trace timers. The
final alarms "PrAL*" and "AL*" are generated only when the signals "PrAL*" and "AL*" are
present for the configurable time "P.13/Time". The same delay time also applies it the value
is below the alarm values. When the main alarm responds, the pre-alarm is also activated.
SITRANS DA400 with protection against explosion
Operating Instructions, 02/2006, A5E00684661-01
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7-1