01
Applications & Common Challenges
- For plants relying on manual starts, scattered readings, incomplete alarms, recurring overflow/dry-run events or weak operating records.
- A PLC cannot correct a flawed process or drifting instrument; verify measurements, actuators and logic first.
- Plan around continuous production, availability of the old program/drawings and cutover windows.
02
Information Needed Before Design
- Existing PLC/HMI models, I/O list, program backup, drawings, network and account permissions.
- Level, pumps, valves, mixers, blowers, dosing and pH/ORP/DO/flow instruments with calibration status.
- Normal, manual, maintenance, upset and power-recovery procedures, alarm history and roles.
- Required SCADA, remote support, reporting or facility-system interfaces and cybersecurity requirements.
03
Typical Process Logic
- Field inventory & signal tests → control narrative/I/O review → panel, instrument & software work → offline test → staged cutover → wet/load commissioning → training & handover.
- Select level interlocks, pump rotation, dosing, VFD, HMI, alarm, trend and run-hour functions from risk and operating value.
04
Instrumentation & Control
- Define safe states and manual/auto authority; configure range, filtering, wire-break and out-of-range diagnostics for analogue signals.
- Use alarm priority, delay, acknowledgement and event records while retaining local operation and emergency stop where needed.
- Remote access requires authorisation, least privilege and a secured network; never expose PLC/HMI directly to the public internet.
05
Risks & Project Boundaries
- Define boundaries for legacy code, third-party communications, instruments, electrical work, network and higher-level systems.
- Cutover and load testing may affect production; prepare rollback and temporary-operation procedures.
- Handover includes program backups, drawings, I/O list, control narrative, credentials, training and acceptance records.