Configuration
4.18 Data points
CP 1243-8 IRC
Operating Instructions, 02/2018, C79000-G8976-C385-03
151
●
Absolute method
With binary and counter values as well as with analog values with configured mean value
generation, the absolute method is used to calculate the threshold value deviation.
●
Integrative method
With analog values without configured mean value generation, the integrating method is
used to calculate the threshold value deviation.
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.
Absolute method
For each binary value a check is made to determine whether the current (possibly smoothed)
value is outside the threshold value band. The current threshold value band results from the
last saved value and the amount of the configured threshold value:
●
Upper limit of the threshold value band: Last saved value + threshold value
●
Lower limit of the threshold value band: Last saved value - threshold value
As soon as the process value reaches the upper or lower limit of the threshold value band,
the value is saved. The newly saved value serves as the basis for calculating the new
threshold value band.
Integrative method
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.
Table 4- 9
Example of the integration calculation of a threshold value configured with 2.0
Time [s]
(calculation cycle)
Process value
stored in the
send buffer
Current process
value
Absolute deviation
from the stored
value
Integrated devia-
tion
0
20.0
20.0
0
0
0.5
20.3
+0.3
0.3
1.0
19.8
-0.2
0.1
1.5
20.2
+0.2
0.3
2.0
20.5
+0.5
0.8
2.5
20.3
+0.3
1.1
3.0
20.4
+0.4
1.5
3.5
20.5
20.5
+0.5
2.0
