Redundant Oxygen-Deficiency Monitoring System

An oxygen-deficiency monitoring system (ODMS) has been developed for a ten-room facility in which the use of large amounts of nitrogen and helium could cause an oxygen deficiency severe enough to be hazardous to personnel. The ODMS comprises three subsystems, of which two monitor three rooms each, and one monitors four rooms. The ODMS generates alarms when the oxygen content of the air in a room falls below 19.5 mole percent. Each subsystem includes transport pumps that draw air continuously from each room through two tubes. Each subsystem includes two oxygen analyzers equipped with sampling pumps, plus two programmable-logic controllers (PLCs) and associated hardware that control electrically actuated valves that admit small fractions of the transport flows to the oxygen analyzers. The PLCs cause the valves to connect the two oxygen analyzers to two different sampling tubes, and then to switch the connections to a different pair of sampling tubes after an interval of about 10 seconds, and so forth until the air from all sampling points has been monitored, and then the sequence repeats. If one sampling tube, oxygen analyzer, pump, or PLC fails, it can be repaired while the system continues to operate, albeit at a reduced rate.