BPC instruments AMPTS III Operation And Maintenance Manual page 13

The FCU has 2 possible resolutions, 9 mL and 2 mL for low and ultra-low gas measurements.
The operational principle is based on liquid displacement and buoyance. When a certain gas
volume enters the flow cell unit, the force of buoyancy leads the flow cell to open and releases
the entrapped gas (Figure 9). The system counts each flow cell opening and registers the
temperature and pressure for automatic compensation to normalise the flow rate and
volume to standard conditions.
Figure 9. 2 and 9 mL FCUs and working principle.
The entire process involving the different components of the system is summarized in the
illustration below (Figure 10):
Figure 10. Illustration of the process from biogas production to methane measurement.
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