Electric / Electronic Control Systems

It is usual to have three installation wide control systems on a process plant:

- The Process Control System (PCS). This system takes care of running the process and utility systems within normal parameters. Some operators call this system a SCADA system: Supervisory, Control And Data Acquisition.

- The Emergency Shut Down (ESD). This system supervises important /critical parameters in the process and utility system and will shut down the plant if predetermined values are superseded. The ESD system normally has graduated shutdowns with each level given a name e.g. ESD1, ESD2, ESD3 etc. The levels correspond to severity with an ESD 1 shuting down the complete plant, an ESD 2 perhaps closing down a complete system, etc. Some operators call this system a Process Shut Down system (PSD).

- The Fire and Gas system (F&G). This system, unlike a PCS or ESD system, is not process related but facility related. While the first two supervise and control the process, the F&G system supervises and controls hazardous situations i.e. fire or gas release, on the facility.

In addition to the installation wide control systems there are often local control systems:

- High Integrity Process Protection System (HIPPS). Typically a local and normally small control system. In principle this is an ESD system but totally independent to ensure a (high enough) Safety Integrity Level (SIL) according to IEC 61508: Functional safety of electrical/electronic/programmable electronic safety-related systems and IEC 61511: Functional safety - Safety instrumented systems for the process industry sector.

- Local Control System (LCP). Usually housed in a panel close to the piece of machinery that the LCP controls e.g. compressed air unit, water maker unit, HVAC unit. A Local Control System has typically a limited interface to the PCS.

- Unit Control System (UCP). In principle a local control system but has a lot more two way communication with the PSD and ESD. Unit systems are typically turbine control.

- Specialist systems that may feed into LCPs, UCPs or the PCS e.g. anti surge systems on a compressor, or vibration monitoring systems on rotating equipment.