FOUNDATION Fieldbus H1 and HSE

FOUNDATION Fieldbus (FF) is a digital fieldbus for process instrumentation managed by the FieldComm Group and standardised in the IEC 61158/61784 series. It is mainly used with DCS systems in oil & gas, chemicals and refining.

Two levels

H1 segment rules of thumb

• Shielded twisted pair, terminators at both ends of the trunk (100 Ω + 1 µF), bus powered via a power conditioner (not a plain 24 V supply).
• Total cable length up to 1900 m including spurs (type A cable); fewer devices per segment in hazardous areas (FISCO / Entity / high-power trunk concepts).
• Typical design: 8–12 devices per segment, grouped so that one segment failure does not stop a whole unit.

Function blocks and scheduling

• Devices contain standard function blocks (AI, AO, PID, DI, DO…). Control can run in the field (e.g. the PID block in the valve positioner).
• The Link Active Scheduler (LAS) publishes the schedule: cyclic (scheduled) traffic for control, unscheduled traffic for configuration and diagnostics. A backup LAS takes over on failure.
• Device descriptions (DD/EDDL, and FDI packages) let the host configure and diagnose devices.

Commissioning and maintenance tips

1. Check segment physics first: voltage at the furthest device, signal level, noise, jitter (a fieldbus diagnostic module or handheld tester helps).
2. Commission device tags and addresses before downloading the control strategy.
3. Watch for intermittent spurs — water in junction boxes is a classic cause.