Configuration and operation
4.7 Configuration in STEP 7 Basic
CP 1243-8 IRC
Operating Instructions, 06/2015, C79000-G8976-C385-01
77
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- 3
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
4.0
20.4
-0.1
-0.1
4.5
20.1
-0.4
-0.5
5.0
19.9
-0.6
-1.1
5.5
20.1
-0.4
-1.5
6.0
19.9
19.9
-0.6
-2.1
In this example, a value of 2.0 was configured for the threshold value trigger.
With the changes in the process value shown in the example, the threshold value trigger
fires twice:
●
At the time 3.5 s: The value of the integrated deviation is at 2.0. The new process value
stored in the send buffer is 20.5.
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