An oxygen concentrator is a device that concentrates the oxygen from a gas supply (typically ambient air) by selectively removing nitrogen to supply an oxygen-enriched product gas stream. Two methods in common use are pressure swing adsorption and membrane gas separation. High oxygen purity 93%+-3% from 1Liter to 5 liter. Comes with overload protection system, which can protect machine if meet high voltage. Timing function, can setting up working. Time: 30mins, 60mins, 90mins, 120mins. Automatic Alarm Function: Power failure alarm, low voltage alarm, low purity alarm (Optional). Available comes with nebulizer function. Use France imported CECA molecular sieve. Long life time, more than 16000 hours. TUV CE, ISO approved and got free sale certificate. Available use at high altitude place.