After debugging each control loops and conditional logics, combine and debug them
together. In combined debug, start by debugging the two normal paths: from starting
to ending heating and from stopping to restarting heating.
After debugging the normal paths, debug the exception paths. Exception paths
involve failure of equipment during heating. Assume failure of the temperature
detector or control valve, generate IOP or OOP in the analog I/O, and check
whether the control application operates correctly.
Besides checking for correct operation, also check whether the operation is correct
within the plant environment. For instance, when a failure occurs, consider whether
the valve controlling the temperature should be fully-open, fully-closed or maintained
at its current state, and whether the operation of the control application is correct
within the plant environment. Moreover, if the requirement specification is
inconsistent with correct operation within the plant environment, check with the user.
After the first heating application has been successfully debugged, copy it to the
other locations where the same application is used. As each destination uses the
same logic, provided the copying is done correctly, it should operate the same way
as the first debugged location. Hence, when debugging each destination, it is
sufficient to check for correct operation of the normal paths.
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