Compare HMI and PLC functions by logic, visualization, data, I/O, networks, cabinet interfaces, operator access, and system boundaries. This guide supports design and procurement discussions; confirm final installation, code, safety, testing, cybersecurity, and qualified engineering requirements.
Define the system boundary
Separate the control cabinet, field devices, PLC, HMI or supervisory software, networks, site conditions, and responsible engineering disciplines before selecting a configuration.
Inputs to document
| Input | Why it matters |
|---|---|
| Equipment and interfaces | Sets layout, entries, clearances, signals, power, network paths, and service access. |
| Process and environment | Guides sensor choice, material, heat, corrosion, moisture, and exposure review. |
| Installation and maintenance | Controls mounting, isolation, access, labels, replacement, and service sequence. |
| Validation and records | Defines drawings, testing, alarm checks, software handover, and supplier documentation. |
Do not transfer a competitor automation performance, cybersecurity, safety, or compliance claim to the complete project without project-specific evidence.
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