Threshold Value Trigger - Siemens SIMATIC NET S7-1200 Operating Instructions Manual

Configuration and operation
5.8 Notes on configuring individual functions
Note
Evaluation of the value even when the option is disabled
If you enable one or both options and configure a value and then disable the option later, the
grayed out value is nevertheless evaluated.
To disable the two options, delete the previously configured values "Start of measuring
range" or "End of measuring range" from the input boxes and then disable the relevant
option.
Recommendation for quickly fluctuating analog values:
If the analog value fluctuates quickly, it may be useful to smooth the analog value first if the
"Set start of measuring range" and "Set end of measuring range" parameters are enabled.
This avoids a frame being sent every time a limit value is violated if the analog value
fluctuates close to one of the two limit values for a longer period of time.
5.8.6.5

Threshold value trigger

The CP calculates the value for the threshold value trigger after the analog value
preprocessing, refer to the section Threshold value trigger and Analog value preprocessing
(Page 50).
Threshold value trigger: How the integrattion calculation works
To calculate the threshold value trigger, the integration method is used.
In the integration threshold value calculation, it is not the absolute value of the deviation of
the process value from the last stored value that is evaluated but rather the integrated
deviation.
The calculation cycle
The integration threshold value calculation works with a cyclic comparison of the integrated
current value with the last stored value. The calculation cycle in which the two values are
compared is 500 milliseconds.
(Note: The calculation cycle must not be confused with the scan cycle of the CPU memory
areas).
The deviations of the current process value are totaled in each calculation cycle. The trigger
is set only when the totaled value reaches the configured value of the threshold value trigger
and a new process value is entered in the send buffer.
The method is explained based on the following example in which a threshold value of 2.0 is
configured.
54
CP 1243-1 DNP3, CP 1243-1 IEC
Operating Instructions, 02/2014, C79000-G8976-C312-02