01
Trace the scan
Inputs are sampled, logic is executed and outputs are refreshed. Scan time, task priorities, event handling and the I/O update model affect what the controller can observe and command.
02
Keep interface and control distinct
An HMI presents process context, alarms and operator commands. It should reflect the control model clearly, while interlocks and safety functions stay in the appropriate control layers.
03
Validate at the boundaries
Check signal type, scaling, quality, fail states, mode handling and alarm response. A documented test from sensor through displayed value to output provides a useful commissioning baseline.