Gas Chromatograph Integration with ABB Totalflow
Key Takeaway
How to integrate a gas chromatograph with ABB Totalflow via Modbus for live gas composition in AGA flow calculations — improving custody transfer accuracy.
Quick Answer
Gas chromatographs connect to Totalflow via Modbus RTU over RS-485. Totalflow polls the GC for component mole percentages (C1-C10+, CO2, N2) and feeds live composition to AGA-3/7/9 flow calculations, improving measurement accuracy for custody transfer.
Why Live Composition Matters
Gas composition affects compressibility (Z-factor), heating value, and specific gravity — all impacting calculated standard volume and energy content. Fixed composition introduces measurement error when actual composition varies.
Configuration
- Create Modbus master application in PCCU32 for the GC
- Configure GC slave address, register map, and poll interval
- Map component mole percentages to Totalflow composition registers
- Link live composition to AGA flow calculation applications
- Configure quality checks: mole% sum = 100%, heating value plausibility
- Set fallback behavior on GC communication failure (holdover mode)
Quality Checks
- Mole percent sum must equal 100% (±0.1%)
- Heating value within expected range
- GC communication timeout alarm with holdover to last good analysis
See also AGA-3 configuration for linking composition to orifice measurement.
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Frequently Asked Questions
Gas composition varies and directly affects compressibility, heating value, and specific gravity. Live GC data reduces measurement error and improves billing accuracy in custody transfer.
Totalflow continues with the last good composition (holdover) for a configurable period, then generates a GC failure alarm and may revert to backup fixed composition.
Still have questions about your setup? Talk to an engineer or call (210) 405-4248.