YOKOGAWA STARDOM FCN-500, Engineering Manual

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<5. Function Test>
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TI 34P02K35-02E Jun. 6, 2018-00
5.3.3 Unit Test Know-how
This section provides some useful know-how for testing a control application.
● Testing Control Loops
When testing a control loop that makes use of NPAS POUs, besides checking loop
connections such as processing of regulatory data and cascade connection, also
check for correct assignment of engineering parameters.
● Testing Control Logics
When testing control logic, besides checking for true condition, false condition, also
check for concurrent true/false conditions, prevention of chattering and pulse/status
type conditions.
• Concurrent true/false conditions
Consider an example where the open/close state of a valve having both open
and close signals is used as a condition within a control application. At the time
of valve opening or closing, it is possible that open and close signals are both
OFF.
Consider another example where the TRUE/FALSE calculation results of two
control logics are used as conditions of other logics so that processing is
performed when the condition is true. Depending on how the application is
programmed or the requirement specification, it is possible that both calculation
results may be true at the same time.
With these considerations, investigate and debug possible scenarios of
concurrent true results or conditions in control logic and the expected operation
under these scenarios.
• Prevention of chattering
When the PV value or alarm status of an NPAS POU or the state of a digital
input is used within control logic, chattering may occur under actual plant
conditions due to rapid cyclical state changes. However, such chattering may not
be observed in the test environment, which differs from the plant environment.
During debugging, investigate the possibility, suppression and handling of
chattering.
• Pulse-type data versus status-type data
Data used within control logic may be designed as pulse-type or status-type.
For instance, logic for initiating control may make use of a status-type start
condition or a pulse-type start trigger.
If a Start PB is also a status-type, control may be started at the time the start
condition is true.
With these considerations, consider whether data used within control logic is
status type or pulse type and debug accordingly.