Siemens SITRANS P320, Руководство по эксплуатации, Страница: 151 / 260

B:Lower limit with hysteresis
An underrun event is counted when the process value falls below the lower limit (1). The next
underrun event is counted when the process value first rises above the lower limit plus
hysteresis (2), and then falls below the lower limit (3).
C:Lower limit without hysteresis
An underrun event is counted when the process value falls below the lower limit (1). The next
underrun event is counted when the process value rises above the lower limit (2) by a given
value (since the hysteresis is set to zero), and then falls below the lower limit (2).
When hysteresis is disabled (no value entered), three events are counted within the period
specified by 'C'.
D:Upper limit without hysteresis
An overrun event is counted when the process value rises above the upper limit (1). The next
overrun event is counted when the process value falls below the lower limit (2) by a given value
(since the hysteresis is set to zero), and then rises above the upper limit (2).
Limit monitoring not requiring acknowledgment
If limit monitoring display is enabled, a "process value alarm" is set for each limit violation (high
or low violation).
This process value alarm is reset when the monitored process value is again within the limits.
It is not necessary to acknowledge the process value alarm.
Limit monitoring requiring acknowledgment with event counter
With this type of monitoring, the configured diagnostics is only triggered after the specified
number of limit violations has been reached (e.g. maintenance required).
This diagnostic message must be acknowledged. During acknowledgment, the event counters
of the monitored process value and the diagnostic messages are reset.
Events and actions
If the process value rises above the upper limit (overrun) or falls below the lower limit
(underrun), an event is counted with an adjustment by any hysteresis.
Process alarms and warnings are displayed as symbols for the status in the device status
dialog in the engineering system and on the device screen.
All alarms and warnings that have been triggered remain pending until the event counter is
reset. Disabling the action means that no new alarms or warnings are triggered for the
configured limits although the counter remains in operation.
Actions and fail-safe mode
Process alarms can trigger fail-safe behavior at the signal output, while process warnings only
serve as information available via local operation and the engineering system. Process values
set the signal output to fail-safe mode if:
– Specific errors occur (the mA output is set to fail-safe mode). (See Diagnostic messages
(Page 184).)
– A maintenance alarm occurs at a process value selected at the output.
Parameter assignment
9.3 Parameter assignment over remote operation
SITRANS P320/P420 (mA/HART)
Operating Instructions, 06/2018, A5E44852162-AA
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