Siemens SIMATIC ET 200AL, System Manual

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High-speed analog modules
8.1 Basics
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
117
Cycle time of an analog output module
The synchronization time for analog output modules refers to the output of the digital-analog
converter
②
. Because the impedance of the connected actuator including connection cable
is unknown in output modules but has a significant impact on the signal run time, the settling
time cannot be added as a fixed value. The respective manuals of the output modules
specify the typical load settling times as reference point. But in practice, a measurement with
an oscilloscope is required for a precise measurement of the settling time. The settling time
may exceed the actual end of the cycle due to very short cycle times and very high
capacitive loads. The cycle time is made up of the following time intervals: t
Z
= t
1
+ t
2
+ t
3
①
Output data is available in digital form in the module
②
Synchronization time for all analog output modules in isochronous mode and simultaneously
output time of data in the digital-analog converter
t
Z
Cycle time
t
1
Transfer time of the backplane bus
t
2
Processing time of data in the module until output at digital-analog converter
t
3
Settling time of hardware until setpoint of output value
t
W
Conversion time of the module
Figure 8-4 Cycle time of the analog output module