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Why during initialization of Signals with the type REAL and LREAL in XPSMFWIN (ELOP II Factory) there is deviation of 0.2% into the controller?

In rare cases after the compilation of the user program with XPSMFWIN Software, the initial value of a signal will be loaded with a maximum deviation of 0.2% into the controller.
 
Nota:
If the initial value of the signal is used for a safety related function and has any deviation, it may have an impact on the safety of your process.
 
 
 Concerned product:
All Preventa XPSMF products which are programmed with the XPSMFWIN Software package (all versions).
 
Description:
During the project compilation with XPSMFWIN Software the initial values of 32/64bit REAL signals are changed to Big Endian for further use in the controller. This is done by changing the sequence of bytes. For certain rare byte combinations the processor of the engineering station detects an invalid value (not a number/NaN). The processer will then change a single bit of the byte combination (9.th bit of the mantissa). This will change the value in a range of 1/1023ths to 1/512ths.
 
How to manually detect the deviation:
Compare the defined initial values and the values in the force editor to detect the deviation. It is required for the system to be verified with a complete functional test, during which, a safety relevant deviation should have been detected.
 
Workaround:
We recommend using the initial values of local variables or value field instead of the initial values for the signals.
The alternative for detected deviations is a slight change of the initial value. For REAL signals that would be a change on the 7-8th digit in decimal representation and the 15-16th digit for LREAL, respectively.
 
Also we would like to remind you that it is part of the Functional Safety Management to review the check points described in the safety manual XPSMF60/XPSMF40 (33003792.04), including the verification of the initial values of signals.
 
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