● Testing User Function Blocks
A function block created as a POU behaves the same way in every location where it
is used.
Therefore, when debugging a user function block, thorough testing is only required
in any one location. Once debugged, it can be expected to operate correctly in every
other location, and thus requires only simple verification of correct operation.
● Testing Exception Paths of Control Logic
When debugging control logic, in addition to checking normal execution paths, it is
important to also check exception paths.
For exception paths, consider the following events:
- IOP or OOP event due to equipment failure, etc.
- Indefinite state of digital input due to equipment failure, etc.
- No response to output signal in input signal
- Time lag in response to output signal
- Disconnection or no response during communication with other equipment
In addition to the above, consider other kinds of exception conditions.
Besides exception handling described in the function specification, investigate and
debug other possible errors and exceptions due to equipment failure, etc.
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