The present invention provides a base with improved internal structure for impact absorption and deflection. Subsequent to the preconditioning, an airfuel excursion is introduced into the exhaust gas feedstream and a signal output from a sensor monitoring the exhaust gas feedstream in the selective catalytic reduction system during the airfuel excursion is monitored. On the other hand, an alternating current power supply that provides the excitation pad with an alternating voltage through a wiring is provided on a sensor IC side of the signal processing device of touch panel.