1. A method of providing self-diagnostic capability for a portable oxygen concentrator using a programmable controller, comprising: triggering the programmable controller to switch from an operational mode to a diagnostic mode; and causing the controller to adjust a process variable of the concentrator to a predetermined level, measure a parameter associated with said process variable, compare measured value of the parameter with a nominal value range, communicate information to a user interface when said measured value deviates from said nominal value range; and display the information on a display screen, wherein communicating information to the user interface when said measured value deviates from said nominal value range comprises translating said information into an abbreviated code, said abbreviated code is configured to indicate to users the nature of the malfunction associated with the deviation of the measured value, wherein causing the controller to measure a parameter associated with said process variable comprises causing the controller to work with one or more sensors to measure the internal pressure drop in the product gas storage device over a period of time, wherein causing the controller to measure a parameter associated with said process variable further comprises causing the controller to work with one or more sensors to measure the time interval for a predetermined pressure change to occur in the product storage device.