FIG. 1.

Gas flow train and control system. A solenoid control valve allows either gas 1 or gas 2 to enter the fermentor, where oxygen tension is monitored with a polarographic DO sensor; the signal is amplified at the transmitter and sent to a microcomputer with a DAP. The solenoid valve is under computer control and may be programmed for a constant duty cycle, to maintain a particular oxygen concentration, or to shift oxygen concentrations. Gas 1 is usually either the low-oxygen gas or nitrogen, while gas 2 is usually either the high-oxygen gas or air. Gas flow is adjusted with the rotameters and monitored by the mass flow meter. Atm, atmosphere.