METHOD AND APPARATUS FOR MEASURING RATE OF CONSUMPTION OF DISSOLVED GAS IN A LIQUID

1,132,457. Measuring oxygen content of liquids. WALLACE & TIERNAN Inc. Nov.17, 1965 [Nov.17, 1964], No.48902/65. Heading G1N. [Also in Divisions C6 and F1] The rate of consumption of dissolved oxygen in an aerobic biological culture is determined by passing a sample of the culture past a first oxygen detector and then, after a time delay #T during which no oxygen is admitted to the sample, past a second oxygen detector and subtracting the output of the second detector from that of the first. Sufficient oxygen must be present initially for the oxygen consumption to take place at a constant rate. If the concentration of dissolved oxygen at the first detector is changing slowly, the output of the second detector may be directly subtracted from that of the first. However, if the concentration of dissolved oxygen at the first detector is changing rapidly, it is necessary to provide a time delay, equal to #T, between the output of the first detector and the subtracting circuit. The sample may pass first through a mechanical screen (32) and aeration tube (26) and then past a first polarographic oxygen detector (50), a positive displacement pump, and a second polarographic oxygen detector (52). Stirrers (57a), (57b) rotate beneath the detectors and may have flexible bristles (91a), (91b) which brush the bottoms of the detectors. A valve (68) is provided to enable the pump to suck liquid in past both detectors for calibration purposes. The pump comprises two meshing resilient plastics screws and, in effect, pumps discrete packets of fluids. The outputs of the detectors are fed via amplifiers having thermistor feedbacks to correct for the temperature characteristics of the detectors. The time delay #T may be provided by a magnetic tape loop.