The solvent layer on top of the cells / media in the extractor must be maintained. However, in the basic eVOLVER setup, volume in the vial is maintained by setting the efflux straw's height to a certain vial volume and pumping any excess volume away. Therefore in basic eVOLVER, the solvent layer would be the first to go.
Instead, the extractor controls the volume in the vial by using the od90 photodiode - LED pair to monitor fluid levels.
Experiment started
Pump Wait: No pumping until vol_check_wait is exceeded
Blanking: the value where the volume line is below the volume sensor is taken
The raw od90 values just before vol_check_wait are stored and averaged to use as this threshold 'blank'
Continuous Pumping: Cells are pumped from the cell growth bioreactor (chemostat or turbidostat) to the extractor and back from the extractor to the cell growth bioreactor
In cycles based on the eVOLVER broadcast timing
Pump Duration Biasing: Pumping out from the extractor is shorter than pumping in
Extractor Volume Increases: The volume in the extractor steadily rises towards the volume sensor
Volume Threshold Exceeded: When the volume line increases above threshold, the system will only pump OUT one broadcast cycle, decreasing the volume level
Steps repeat