POU Verification
The verification of the safety-related application code, i.e., of each user POU, is a mandatory part of the acceptance procedure. The implemented POU verification feature helps you with this by providing the possibility to set a special verification flag for each user POU. This is particularly useful in projects with a large number of user POUs.
After verifying the code of a POU, the verification flag can be set for this particular POU by selecting the 'Set verification' item from the context menu of the POU icon.
The verification flag must not be set until the particular POU has been verified without any complaints. Setting the verification flag for an incomplete or incorrect POU results in a gap in the overall safety validation process.
A verified POU cannot be edited. The write-protection is indicated in the tree by a different POU icon (
left: verified FB POU, right: verified program POU 'Main') and by the 'Read-only' text added to the POU node. Furthermore, the CRC checksum of the POU calculated at the moment of verification is shown besides the tree icon.
When opening a worksheet of a verified POU, the editor appears in read-only mode.
To edit a verified POU again, the verification flag must be reset by selecting the 'Withdraw verification' item from the context menu of the icon.
CRC of verified POUs is printed: If the verification flag is set for a POU, the checksum (CRC) that has been calculated by Machine Expert – Safety on verification is not only visible in the tree but also printed below the POU name in the footer of each code worksheet and local variables worksheet of the verified POU (see section "CRC of verified POUs is printed").
If activated for your Machine Expert – Safety version, the CRCs are additionally written to a text file which Machine Expert – Safety stores in the project directory. The file with the name VerifiedPouChecksums.csv lists each POU contained in the project with its checksum or the entry "Not verified" if the flag has not yet been set for a POU.
After having detected a changed CRC (by manually comparing it with the relating CRC in the printed project documentation of an older, archived project version), you can use the project comparison tool for locating project modifications.
Observe the section "Finding project modifications reliably in terms of safety" for information how you have to use the CRC checksums for comparing projects.