In a respiratory air flow measuring monitor, a tubing connector for connecting lumen tubing to the analyzer module includes a connector housing for attaching the tubing connector to the analyzer module, and a female socket in the connector housing for receiving the lumen tubing therein. A light-emitting diode and corresponding light detector detects the presence of the lumen tubing within the female socket. A second pair of light emitters and diodes discriminates different types of respiratory air flow sensors attached to the analyzer module. The female socket is configured to receive multiple lumen tubes, and to maintain polarity by discriminating different diameters of the lumen tubes.