In a communication system including plural communication apparatuses that communicate each other using a single communication path, the state of the communication path is detected for communication. A vibration-sensing unit sensitive to vibrations applied to the detector is provided to produce a vibration output signal representative of a detected parameter of the vibrations. An air cleaner housing is positioned between the speaker housing and the engine for filtering out contaminants from the air before the air is drawn into the engine. Carbon dioxide is removed from the converted gas flow by gas washing, and the washed hydrogen-rich gas flow is subsequently divided in a pressure-swing adsorption system into a product gas flow made of hydrogen and a waste gas flow. The cover has two rows of apertures for engagement with the pins of the support member is attracted by the magnetic inserts forcing the outer periphery of the cover against the top surface of the substrate.