Time Required For Reading And Accuracy Of The Analog Value Read In - Siemens SIMATIC S5-90U System Manual

S5-90U/S5-95U
Note
The cyclically read onboard analog inputs of the S5-95U (must be parameterized in DB1)
can be read in directly by means of the integrated FB250 (Reading in analog value).
If you still wish to use the integrated FB250 for reading in analog values although the
analog inputs are not read cyclically, you have to set the bit "Single scan" for FB250.
12.1.3 Time Required for Reading and Accuracy of the Analog Value
Read in
The Table below shows the various possibilities for calculating the time that elapses between the
point of reading in the analog value and the access of the user program to the converted value.
In order to determine how old an analog value is, you need to know how long it takes to read in an
analog value.
Table 12-10. Maximum Duration for Reading in an Analog Value
Possibilities for Reading in
Analog Values
Read analog values from the
process image
Read analog values via direct
I/O access
The time values for the runtimes specified in Table 12-10 are given in the Operations List
(see Appendix A) and Chapter 6.
EWA 4NEB 812 6115-02b
Maximum Duration
of Input from
Onboard I/Os
• Using the L IW ...
operation:
Scan time up to and
including the L IW
operation.
• Using FB250:
Scan time up to and
including FB250
• Using L PW ...:
Execution time for this
operation
• Using FB250:
Exec. time for FB250
Analog Value Processing
Maximum Duration
of Input from
External I/Os
• Using the L IW ...
operation:
No. of channels on module
x Coding time per input
+ Scan time up to and
including the L IW
operation
+ Operating system
runtime
+ PI transfer time
• Using FB 250:
No. of channels on module
x Coding time per input
+ Scan time including
runtime of FB250
+ Operating system
runtime
+ PI transfer time
Not possible
12-7